CATALYSTS FOR FENTON SYSTEM CONTAINING METAL OXIDE CONTAINING FUNCTIONAL GROUP ON SURFACE AND FENTON SYSTEM USING THE SAME
20210300801 · 2021-09-30
Assignee
Inventors
Cpc classification
C02F2305/023
CHEMISTRY; METALLURGY
B01J23/00
PERFORMING OPERATIONS; TRANSPORTING
B01J21/066
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
Provided is a catalyst for a Fenton system, and a method of preparing the same. The catalyst includes one or more species of d.sup.0-orbital-based or non-d.sup.0-orbital-based catalyst including NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on the surface thereof. The method includes preparing a d.sup.0-orbital-based or non-d.sup.0-orbital-based transition metal oxide; and preparing a transition metal oxide catalyst comprising a NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional group on the surface of the catalyst via nitrification, sulfation, or phosphorylation of the transition metal oxide.
Claims
1. A catalyst for an Fenton system, the catalyst comprising one or more species of d.sup.0-orbital-based or non-d.sup.0-orbital-based transition metal oxide catalyst grains including a NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional group on the surface thereof.
2. The catalyst of claim 1, wherein the catalyst grains have a porous structure, and optionally, wherein the catalyst grains have a diameter of 0.1 nm to 500 μm.
3. The catalyst of claim 1, wherein a metal of the transition metal oxide catalyst grains comprises at least one selected from a 3d-block metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn), a 4d-block metal (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, or Cd), a 5d-block metal (La, Hf, Ta, W, Re, Os, Ir, Pt, Au, or Hg), and a 6d-block metal (Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn) in the periodic table, or any combination thereof.
4. The catalyst of claim 1, wherein the catalyst is supported by a carrier and coated on a substrate, and a binder is interposed between the carrier and the substrate to increase coating adhesion strength.
5. The catalyst of claim 4, wherein the carrier is carbon (C), Al.sub.2O.sub.3, MgO, ZrO.sub.2, CeO.sub.2, TiO.sub.2, or SiO.sub.2.
6. The catalyst of claim 4, wherein the catalyst is included in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of the carrier.
7. The catalyst of claim 4, wherein the binder is an insoluble polymer or an inorganic binder.
8. The catalyst of claim 4, wherein an electro-Fenton reaction occurs in an aqueous electrolytic solution.
9. The catalyst of claim 8, wherein the aqueous electrolytic solution has a pH of 3 to 10, and electro-Fenton reaction occurs by inputting a power.
10. The catalyst of claim 8, wherein the electro-Fenton reaction comprises: (1) production of .OH species by heterogeneous decomposition of H.sub.2O.sub.2; (2) conversion of the SO.sub.4.sup.2− functional group into SO.sub.4..sup.− species by the .OH species, conversion of the NO.sub.3.sup.− functional group into NO.sub.3. species by the .OH species, or conversion of the H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups into H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− species by the .OH species; and (3) decomposition of a non-degradable organic material by the NO.sub.3., SO.sub.4..sup.−, H.sub.2PO.sub.4. , HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− species.
11. A method of preparing a catalyst for a Fenton system, the method comprising: preparing a d.sup.0-orbital-based or non-d.sup.0-orbital-based transition metal oxide; and preparing a transition metal oxide catalyst comprising a NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional group on the surface of the catalyst via nitrification, sulfation, or phosphorylation of the transition metal oxide.
12. The method of claim 11, wherein the nitrification is performed by a reaction gas comprising NO and O.sub.2, the sulfation is performed by a reaction gas comprising SO.sub.2 and O.sub.2, and the phosphorylation is performed by a reaction solution comprising a phosphorylating precursor.
13. The catalyst of claim 4, wherein hydrogen peroxide is supplied from a hydrogen peroxide supply unit, and a non-electro-Fenton reaction occurs in an aqueous electrolytic solution.
14. The catalyst of claim 13, wherein the aqueous electrolytic solution has a pH of 5 to 10, and the non-electro-Fenton reaction occurs by supplying hydrogen peroxide using a hydrogen peroxide supply unit at a rate of 10.sup.−5 mol/L to 10.sup.5 mol/L.
15. The catalyst of claim 13, wherein the non-electro-Fenton reaction comprises: (1) production of .OH species by heterogeneous decomposition of H.sub.2O.sub.2; (2) conversion of the SO.sub.4.sup.2− functional group into SO.sub.4..sup.− species by the .OH species, conversion of the NO.sub.3.sup.− functional group into NO.sub.3. species by the .OH species, or conversion of the H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups into H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− species by the .OH species; and (3) decomposition of a non-degradable organic material by the NO.sub.3., SO.sub.4..sup.−, H.sub.2PO.sub.4. , HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− species.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which:
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DETAILED DESCRIPTION
[0088] In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein, in connection with one embodiment, may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views and elements may be exaggerated for the convenience of description.
[0089] Hereinafter, embodiments of the present invention will be described in detail with reference to the appended drawings for one of ordinary skill in the art to be able to perform the invention without any difficulty.
[0090] Catalyst for Electro-Fenton System
[0091] Provided is a catalyst for an electro-Fenton system, the catalyst including one or more species of d.sup.0-orbital-based or non-d.sup.0-orbital-based transition metal oxide catalyst grains functionalized with NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2− or PO.sub.4.sup.3− on the surface thereof. In this regard, the d.sup.0-orbital-based transition metal oxide indicates that the d orbital of a transition metal, as a component of the oxide, is not occupied by electrons. For example, ZrO.sub.2/Nb.sub.2O.sub.5/Ta.sub.2O.sub.5 respectively include Zr.sup.4+/Nb.sup.5+/Ta.sup.5+ whose electronic states are [Kr] 4d.sup.0 5s.sup.0/[Kr] 4d.sup.0 5s.sup.0/[Xe] 4f.sup.14 5d.sup.0 6s.sup.0. In the case of Zr.sup.4+/Nb.sup.5+/Ta.sup.5+ surface species, decomposition of hydrogen peroxide and production of .OH proceed by H.sub.2O.sub.2.fwdarw.2.OH, but the oxidation numbers thereof are not changed during the decomposition of hydrogen peroxide.
[0092] In this regard, the non-d.sup.0-orbital-based transition metal oxide indicates that the d orbital of a transition metal, as a component of the oxide, is occupied by electrons. For example, Fe.sub.3O.sub.4/CoO/NiO respectively include Fe.sup.2+/Co.sup.2+/Ni.sup.2+ whose electronic states are [Ar] 3d.sup.6/[Ar] 3d.sup.7/[Ar] 3d.sup.8. In the case of Fe.sup.2+/Co.sup.2+/Ni.sup.2+ surface species, decomposition of hydrogen peroxide and production of .OH proceed by H.sub.2O.sub.2.fwdarw..OH+OH.sup.−, and the oxidation number increases by 1 during the decomposition of the hydrogen peroxide. Thus, the non-d.sup.0-orbital-based transition metal oxide may be reduced by electrons (e.sup.−) generated during the electro-Fenton process, thereby enabling continuous decomposition of hydrogen peroxide.
[0093] A metal of the transition metal oxide catalyst grains functionalized with NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− includes at least one selected from a 3d-block metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn), a 4d-block metal (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, or Cd), a 5d-block metal (La, Hf, Ta, W, Re, Os, Ir, Pt, Au, or Hg), and a 6d-block metal (Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn) in the periodic table, or any combination thereof. The d orbital of the transition metal, as a component of the oxide, may or may not be occupied by electrons in accordance with the oxidation number of the transition metal. Thus, the transition metal may form a d.sup.0-orbital-based transition metal oxide or non-d.sup.0-orbital-based transition metal oxide.
[0094] The catalyst for the electro-Fenton system may be prepared using a method used to form particular transition metal oxide grains and commonly available in the art. For example, the transition metal oxide grains included in the catalyst may be synthesized using one or more methods among hydrothermal synthesis, solvothermal synthesis, mechano-chemical method (ball-milling), non-templated or templated method, impregnation method, dip coating, and calcination or thermal decomposition method using M-including complex.
[0095] The electro-Fenton system may form NO.sub.3., SO.sub.4..sup.−, H.sub.2PO.sub.4., HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− surface species by using the .OH species produced by oxidation of H.sub.2O (H.sub.2O.fwdarw..OH+H.sup.++e.sup.−) in an anode as an activator on NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional group present in the transition metal oxide grains coated on a cathode. Various types of conductive materials may be used as the anode to promote the oxidation of H.sub.2O, for example, graphite may be used as the anode.
[0096] In addition, the catalyst for an electro-Fenton system may include active species on the surface of the catalyst, the active species used to decompose hydrogen peroxide formed as a result of reduction of oxygen (2H.sup.++O.sub.2+2e.sup.−.fwdarw.H.sub.2O.sub.2) on the cathode. Specifically, catalytic decomposition of hydrogen peroxide (H.sub.2O.sub.2.fwdarw.2.OH or H.sub.2O.sub.2.fwdarw..OH+OH.sup.−) is activated by the d.sup.0-orbital-based transition metal oxide active site (Zr.sup.4+/Nb.sup.5+/Ta.sup.5+) or non-d.sup.0-orbital-based transition metal oxide active site (Fe.sup.2+/Co.sup.2+/Ni.sup.2+) based on homogeneous catalysis or heterogeneous catalysis. By using .OH species produced as a result of decomposition, the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups present in the transition metal oxide grains coated on the cathode may be converted into NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− surface species. Thus, a transition metal oxide catalyst, which includes a large quantity of surface active sites and is inexpensive and easily synthesizable, may be used as the catalyst coated on the cathode to promote the catalytic decomposition of hydrogen peroxide.
[0097] In addition, the catalyst for an electro-Fenton system may form the NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− surface species via radical transfer of the above-described .OH species to the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on the surface of the catalyst and promote decomposition of non-degradable organic materials by using the surface species. Therefore, a transition metal oxide catalyst including a large quantity of NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on the surface of the transition metal oxide catalyst may be used as the catalyst coated on the cathode.
[0098] Performance of the catalyst may be improved by realizing a transition metal oxide catalyst surface capable of maximizing synergistic effects of the active species (H.sub.2O.sub.2 activators) and the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on the surface of the transition metal oxide catalyst as described above, and adjusting type of the transition metal, structure/stoichiometry of the transition metal oxide, functionalization (nitrification/sulfation/phosphorylation) conditions of the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3−, and the amount of functional group.
[0099] According to an embodiment of the present invention, the nitrification may be performed by a reaction gas including NO and O.sub.2. A concentration of NO and O.sub.2 may be in the range of 10 ppm to 10.sup.5 ppm, a flow rate of the reaction gas may be in the range of 10.sup.−5 mL min.sup.−1 to 10.sup.5 mL min.sup.−1, and a pressure may be in the range of 10.sup.−5 bar to 10.sup.5 bar. In addition, the nitrification may be performed at a temperature of 50° C. to 500° C. for 0.1 hours to 24 hours.
[0100] According to an embodiment of the present invention, the sulfation may be performed by a reaction gas including SO.sub.2 and O.sub.2. A concentration of SO.sub.2 and O.sub.2 may be in the range of 10 ppm to 10.sup.5 ppm, a flow rate of the reaction gas may be in the range of 10.sup.−5 mLmin.sup.−1 to 10.sup.5 mLmin.sup.−1, and a pressure may be in the range of 10.sup.−5 bar to 10.sup.5 bar. In addition, the sulfation may be performed at a temperature of 200° C. to 800° C. for 0.1 hours to 24 hours.
[0101] According to an embodiment of the present invention, the phosphorylation may be performed by a reaction solution including a phosphorylating precursor (e.g., phosphoric acid (H.sub.3PO.sub.4) or diammonium phosphate ((NH.sub.4).sub.2HPO.sub.4)). A concentration of the phosphorylating precursor may be in the range of 10.sup.−6 mol L.sup.−1 to 10.sup.6 mol L.sup.−1. The phosphorylating precursor-supporting transition metal oxide may be converted into a transition metal oxide catalyst functionalized by phosphorylation using the reaction gas including O.sub.2. A concentration of O.sub.2 included in the reaction gas may be in the range of 10 ppm to 5×10.sup.5 ppm, a flow rate may be in the range of 10.sup.−5 mL min.sup.−1 to 10.sup.5 mL and a pressure may be in the range of 10.sup.−5 bar to 10.sup.5 bar, and the phosphorylation may be performed at a temperature of 100° C. to 800° C. for 0.1 hours to 24 hours.
[0102] When the conditions for the nitrification/sulfation/phosphorylation of the transition metal oxide catalyst are less than the above-described ranges, functionalization effects on the catalyst with NO.sub.3.sup.−/S O.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/P O.sub.4.sup.3− may be insufficient. Also, when the conditions are greater than the above-described ranges, the surface of the transition metal oxide catalyst may be excessively functionalized and thus surface species such as Zr.sup.4+/Nb.sup.5+/Ta.sup.5+ or Fe.sup.2+/Co.sup.2+/Ni.sup.2+, which promote the activity of the catalytic decomposition of hydrogen peroxide (production of .OH) may vanish. Therefore, the nitrification/sulfation/phosphorylation of the catalyst may be performed within the above-described ranges.
[0103] In the catalyst for an electro-Fenton system according to an embodiment of the present invention, as a surface area increases, a production rate of .OH species by the surfaces species and a conversion rate of the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups into the NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4..sup.−/HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− surface species by the .OH species on the surface of the catalyst may increase (Reaction Schemes 1 to 10). As the above-described rates increase, the amounts of the NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− surface species increase in the reaction system, thereby promoting decomposition of harmful materials.
NO.sub.3.sup.−+.OH+H.sup.+.fwdarw.NO.sub.3.+H.sub.2O Reaction Scheme 1:
NO.sub.3.sup.−+.OH.fwdarw.NO.sub.3.+OH.sup.− Reaction Scheme 2:
SO.sub.4.sup.2−+.OH+H.sup.+.fwdarw.SO.sub.4..sup.−+H.sub.2O Reaction Scheme 3:
SO.sub.4.sup.2−+.OH.fwdarw.SO.sub.4..sup.−+OH.sup.− Reaction Scheme 4:
H.sub.2PO.sub.4.sup.−+.OH+H.sup.+.fwdarw.H.sub.2PO.sub.4.+H.sub.2O Reaction Scheme 5:
H.sub.2PO.sub.4.sup.−+.OH.fwdarw.H.sub.2PO.sub.4.+OH.sup.− Reaction Scheme 6:
HPO.sub.4.sup.2−+.OH+H.sup.+.fwdarw.HPO.sub.4..sup.−+H.sub.2O Reaction Scheme 7:
HPO.sub.4.sup.2−+.OH.fwdarw.HPO.sub.4..sup.−+OH.sup.− Reaction Scheme 8:
PO.sub.4.sup.3−+.OH+H.sup.+.fwdarw.PO.sub.4.sup.2..sup.−+H.sub.2O Reaction Scheme 9:
PO.sub.4.sup.3−+.OH.fwdarw.PO.sub.4.sup.2..sup.−+OH.sup.− Reaction Scheme 10:
[0104] According to an embodiment of the present invention, the catalyst grains functionalized with NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− may have a porous structure and a diameter of 0.1 nm to 500 μm.
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[0108] In addition, when the catalyst grains have the two characteristics described above, they may be coated on the cathode with a higher intensity. This indicates that a leaching phenomenon caused by a vortex of an aqueous electrolytic solution in which electro-Fenton reaction is performed and external electric power is reduced, thereby increasing lifespan of an electrode. When the catalyst is leached from the electrode, .OH production or decomposition of non-degradable organic materials by NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− may be performed by the leached catalyst species based on homogeneous catalysis. In this case, the non-degradable organic material decomposition efficiency decreases and the number of use of the electro-Fenton catalyst is limited.
[0109] That is, as the leaching phenomenon decreases, .OH production or decomposition of non-degradable organic materials by NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− are performed based on heterogeneous catalysis by the catalyst grains coated on the cathode, performance of the catalyst may be maintained even after multiple uses in the electro-Fenton reaction. Therefore, the catalyst grains according to an embodiment of the present invention may have rough surface characteristics with pores not to be leached from the electrode.
[0110] Catalyst for Non-Electro-Fenton System
[0111] According to an embodiment of the present invention, a catalyst for a non-electro-Fenton system may include one or more species of d.sup.0-orbital-based or non-d.sup.0-orbital-based transition metal oxide catalyst grains including NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional groups. Specifically, the transition metal oxide catalyst grains of the present invention may include crystal structures of all metal oxides existing in a stable state in a metal-oxygen phase equilibrium, wherein an oxidation number of metal species M varies from 1 to 4. For example, the transition metal oxide catalyst grains may include Mn.sub.2O.sub.3(Mn.sup.3+), Mn.sub.3O.sub.4(Mn.sup.2+ and Mn.sup.3+), Co.sub.3O.sub.4(Co.sup.2+ and Co.sup.3+), Fe.sub.2O.sub.3(Fe.sup.3+), NiO(Ni.sup.2+), CuO(Cu.sup.2+), Cu.sub.2O(Cu.sup.+), or the like.
[0112] More specifically, the transition metal contained in the transition metal oxide catalyst grains may be a transition metal of period 4 to period 6. According to an embodiment of the present invention, the transition metal may include at least one selected from a 3d-block metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn), a 4d-block metal (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, or Cd), a 5d-block metal (La, Hf, Ta, W, Re, Os, Ir, Pt, Au, or Hg), and a 6d-block metal (Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn) in the periodic table, or any combination thereof.
[0113] According to an embodiment of the present invention, the catalyst for a non-electro-Fenton system may be prepared using a method used to form particular transition metal oxide grains and commonly available in the art. For example, the transition metal oxide grains included in the catalyst may be synthesized using one or more methods among hydrothermal synthesis, solvothermal synthesis, mechano-chemical method (ball-milling), non-templated or templated method, impregnation method, dip coating, and calcination or thermal decomposition method using M-including complex.
[0114] According to an embodiment of the present invention, the catalyst supplied to the non-electro-Fenton system may be coated on a support to efficiently use M.sup.δ+ active sites and NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional groups present on the surface of the catalyst. That is, a support capable of promoting catalytic decomposition of hydrogen peroxide (catalytic H.sub.2O.sub.2 scission) and radical transfer of .OH.Math.NO.sub.3., .OH.Math.SO.sub.4..sup.−, .OH.Math.H.sub.2PO.sub.4., .OH.Math.HPO.sub.4*.sup.−, or .OH.Math.PO.sub.4.sup.2..sup.− and having chemical resistance to radicals and hydrogen peroxide may be used. The support may be formed of a carbonaceous material such as graphite, carbon felt, or glassy carbon fiber or a metallic material such as stainless steel or titanium.
[0115] According to an embodiment of the present invention, the catalyst for a non-electro-Fenton system may include M.sup.δ+ (δ≤2) active species used to decompose the supplied hydrogen peroxide on the surface of the catalyst. Specifically, catalytic decomposition of hydrogen peroxide (H.sub.2O.sub.2.fwdarw..OH+OH.sup.−) is activated using the M.sup.δ+ active sites based on homogeneous catalysis or heterogeneous catalysis and NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional group present in the transition metal oxide catalyst grains coated on the support may be converted into NO.sub.3., SO.sub.4..sup.−, H.sub.2PO.sub.4., HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− surface species using the .OH species produced as a result of the reaction. Therefore, a transition metal oxide, which includes a large quantity of M.sup.δ+ active site and is inexpensive and easily synthesizable, may be used as the catalyst coated on the support to promote the catalytic decomposition of hydrogen peroxide.
[0116] In addition, the catalyst for a non-electro-Fenton system may form the NO.sub.3., SO.sub.4..sup.−, H.sub.2PO.sub.4., HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− surface species (.OH.Math.NO.sub.3., .OH.Math.SO.sub.4..sup.−, .OH.Math.H.sub.2PO.sub.4., .OH.Math.HPO.sub.4*.sup.−, or .OH.Math.PO.sub.4.sup.2..sup.−) based on radical transfer of the above-described .OH species to the NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional group on the surface of the catalyst and promote decomposition of non-degradable organic materials by using the same. Therefore, a transition metal oxide catalyst including a large quantity of NO.sub.3.sup.−, SO.sub.4..sup.−, H.sub.2PO.sub.4..sup.−, HPO.sub.4.sup.−, or PO.sub.4.sup.2− functional groups on the surface thereof may be used.
[0117] As described above, performance of the catalyst may be improved by maximizing the M.sup.δ+ and NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional group on the surface of the transition metal oxide catalyst and adjusting functionalization (nitrification/sulfation/phosphorylation) conditions of NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− on the surface of the transition metal catalyst.
[0118] According to an embodiment of the present invention, the nitrification may be performed by a reaction gas including NO and O.sub.2. A concentration of NO and O.sub.2 may be in the range of 10 ppm to 10.sup.5 ppm, a flow rate of the reaction gas may be in the range of 10.sup.−5 mL min.sup.−1 to 10.sup.5 mL min.sup.−1, and a pressure may be in the range of 10.sup.−5 bar to 10.sup.5 bar. In addition, the nitrification may be performed at a temperature of 50° C. to 500° C. for 0.1 hours to 24 hours.
[0119] According to an embodiment of the present invention, the sulfation may be performed by a reaction gas including SO.sub.2 and O.sub.2. A concentration of SO.sub.2 and O.sub.2 may be in the range of 10 ppm to 10.sup.5 ppm, a flow rate of the reaction gas may be in the range of 10.sup.−5 mLmin.sup.−1 to 10.sup.5 mLmin.sup.−1, and a pressure may be in the range of 10.sup.−5 bar to 10.sup.5 bar. In addition, the sulfation may be performed at a temperature of 200° C. to 800° C. for 0.1 hours to 24 hours.
[0120] According to an embodiment of the present invention, the phosphorylation may be performed by a reaction solution including a phosphorylating precursor (e.g., phosphoric acid (H.sub.3PO.sub.4) or diammonium phosphate ((NH.sub.4).sub.2HPO.sub.4)). A concentration of the phosphorylating precursor may be in the range of 10.sup.−6 mol L.sup.−1 to 10.sup.6 mol L.sup.−1. The phosphorylating precursor-supporting transition metal oxide may be converted into a transition metal oxide catalyst functionalized by phosphorylation using the reaction gas including O.sub.2. A concentration of O.sub.2 included in the reaction gas may be in the range of 10 ppm to 5×10.sup.5 ppm, a flow rate may be in the range of 10.sup.−5 mL min.sup.−1 to 10.sup.5 mL and a pressure may be in the range of 10.sup.−5 bar to 10.sup.5 bar, and the phosphorylation may be performed at a temperature of 100° C. to 800° C. for 0.1 hours to 24 hours.
[0121] When the conditions for the nitrification/sulfation/phosphorylation of the transition metal oxide catalyst are less than the above-described ranges, functionalization effects on the catalyst with NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− may be insufficient. Also, when the conditions are greater than the above-described ranges, the surface of the transition metal oxide catalyst may be excessively functionalized and thus surface species such as Zr.sup.4+/Nb.sup.5+/Ta.sup.5+ or Fe.sup.2+/Co.sup.2+/Ni.sup.2+, which promote the activity of the catalytic decomposition of hydrogen peroxide (production of .OH) may vanish. Therefore, the nitrification/sulfation/phosphorylation of the catalyst may be performed within the above-described ranges.
[0122] In the catalyst for a non-electro-Fenton system according to the present invention, as a surface area increases, a production rate of .OH by the M.sup.δ+ species and a conversion rate of NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional groups into NO.sub.3., SO.sub.4..sup.−, H.sub.2PO.sub.4., HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− surface species by the .OH species on the surface of the catalyst may increase. Representatively, Reaction Schemes c and d show conversion of the NO.sub.3.sup.− functional groups. As the above-described reaction rate increases, the amounts of the amount of NO.sub.3. surface species increases in the reaction system, thereby promoting decomposition of harmful materials.
NO.sub.3.sup.−+.OH+H.sup.+.fwdarw.NO.sub.3.+H.sub.2O Reaction Scheme c:
NO.sub.3.sup.−+.OH.fwdarw.NO.sub.3.+OH.sup.− Reaction Scheme d:
[0123] According to an embodiment of the present invention, the transition metal oxide catalyst grains functionalized with NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− may have a porous structure and a diameter of 0.1 nm to 500 μm.
[0124] When the catalyst grains of the transition metal oxide have 1) a small diameter or 2) a rough surface with pores or protrusions, a surface area increases, and thus a catalytic decomposition rate of hydrogen peroxide increases, so that a production rate of .OH species and conversion rates of NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional groups into NO.sub.3., SO.sub.4..sup.−, H.sub.2PO.sub.4., HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− surface species on the surface by the .OH species may increase.
[0125] In addition, when the transition metal oxide catalyst grains have the above two characteristics, they may be coated on the support with a higher intensity. This indicates that a leaching phenomenon of the catalyst, which is caused by a vortex of an aqueous solution in which decomposition of non-degradable organic materials is performed, is reduced, thereby increasing lifespan of the support coated with the catalyst. When the catalyst is leached from the support, .OH production or decomposition of non-degradable organic materials by NO.sub.3. may be performed by the leached catalyst species based on homogeneous catalysis. In this case, non-degradable organic materials decomposition efficiency decreases and the number of use of the catalyst coated on the support is limited.
[0126] That is, as the leaching phenomenon decreases, .OH production or decomposition of non-degradable organic materials by NO.sub.3. are performed based on heterogeneous catalysis by the transition metal oxide grains coated on the support, and thus performance of the catalyst may be maintained even after multiple uses. Therefore, the transition metal oxide catalyst grains according to an embodiment of the present invention may have rough surface characteristics with pores to inhibit the leaching phenomenon from the support.
[0127] Electrode for Electro-Fenton System
[0128] Hereinafter, an electrode including the catalyst for an electro-Fenton system will be described.
[0129] An electrode for an electro-Fenton system according to an embodiment of the present invention is an electrode for an electro-Fenton system including the catalyst for an electro-Fenton system. The electrode includes a carrier supporting the catalyst for an electro-Fenton system, a substrate on which the catalyst-supporting carrier is formed, and a binder interposed between the carrier and the substrate and increasing a coating adhesive strength.
[0130] The catalyst for an electro-Fenton system includes a transition metal oxide functionalized with NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− as described above. The catalyst may be directly coated on the substrate or supported by the carrier for stably and efficiently constructing an electrode. In this regard, the carrier may be formed on at least one surface of the substrate, preferably, on both surfaces of the substrate. The substrate may be formed of a conductive material commonly used in electrochemical reaction. For example, graphite or a metal such as copper and aluminum may be used.
[0131] In addition, according to an embodiment of the present invention, the carrier may be formed of carbon (C), Al.sub.2O.sub.3, MgO, ZrO.sub.2, CeO.sub.2, TiO.sub.2, or SiO.sub.2 and may include 0.01 to 50 parts by weight of the catalyst for an electro-Fenton system based on 100 parts by weight of the carrier.
[0132] The catalyst-supporting carrier may be coated on the substrate using an impregnation method. In this case, the amount of the coated catalyst may be adjusted for increasing efficiency of .OH production or non-degradable organic material decomposition by NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− and smooth transfer of the .OH to the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on the surface of the catalyst.
[0133] When the catalyst is coated on the substrate, the adhesive strength between the catalyst and the substrate may be increased using the binder. In this case, the binder may be an insoluble polymer or an inorganic binder, preferably, polyvinylidene fluoride (PVDF). The binder may increase the coating adhesive strength between the catalyst-supporting carrier and the substrate. When the binder has insolubility, the binder is not dissolved in an aqueous solution even after repeated electro-Fenton reaction, thereby preventing the leaching phenomenon of the catalyst. That is, lifespan characteristics of the electrode for the electro-Fenton system may be improved by inhibiting leaching of the catalyst. The inorganic binder may include at least one of SiO.sub.2, LiO.sub.2, K.sub.2O, ZrO.sub.2, Al.sub.2O.sub.3, and Na.sub.2SiO.sub.3.
[0134] Electro-Fenton System
[0135]
[0136] Referring to
[0137] Referring to
[0138] It is important that as the production rate of the .OH species produced by the above-described H.sub.2O oxidation and catalytic decomposition of hydrogen peroxide increases, 1) transfer speed of .OH species to NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups present on the surface of the catalyst 160 coated on the cathode 140 increases, 2) formation rate of NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− species on the surface of the catalyst increases by radical transfer reaction between .OH and NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3−, and 3) ultimately, highly-efficient decomposition of organic materials by NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− species based on heterogeneous catalysis is possible.
[0139] The first electrode 130 and the second electrode 140 may be formed of a conductive material. For example, graphite may be used. The catalyst 160 may be coated on at least one surface of the second electrode 140 and may be a catalyst including transition metal oxide grains functionalized with NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− according to the above-described embodiments of the present invention.
[0140] The aqueous electrolytic solution 120 is an aqueous solution used in electro-Fenton reaction and may include one of Na.sub.2SO.sub.4, NaNO.sub.3, NH.sub.4F, KF, KCl, KBr, KI, NaF, NaCl, NaBr, NaI, or any combination thereof having a concentration of 10.sup.4 mol/L to 10 mol/L.
[0141] Hereinafter, a process of decomposing an organic material will be described based on catalytic reaction occurring in the electro-Fenton systems 100 and 100′. Reactions occurring in the electro-Fenton systems 100 and 100′ are expressed by Reaction Schemes 11 to 31 below.
2H.sub.2O.fwdarw.O.sub.2+4H.sup.++4e.sup.− Reaction Scheme 11:
O.sub.2+2H.sup.++2e.sup.−.fwdarw.H.sub.2O.sub.2 Reaction Scheme 12:
M.sup.(δ+1)++e.sup.−.fwdarw.M.sup.δ+ Reaction Scheme 13:
M.sup.δ++H.sub.2O.sub.2.fwdarw.M.sup.(δ+1)++OH.sup.−+.OH Reaction Scheme 14:
H.sub.2O.fwdarw..OH+H.sup.++e.sup.− Reaction Scheme 15:
H.sub.2O.sub.2.fwdarw..OH+.OH Reaction Scheme 16:
NO.sub.3.sup.−+.OH+H.sup.+.fwdarw.NO.sub.3.+H.sub.2O Reaction Scheme 17:
NO.sub.3.sup.−+.OH.fwdarw.NO.sub.3.+OH.sup.− Reaction Scheme 18:
SO.sub.4.sup.2−+.OH+H.sup.+.fwdarw.SO.sub.4..sup.−+H.sub.2O Reaction Scheme 19:
SO.sub.4.sup.2−+.OH SO.sub.4..sup.−+OH.sup.− Reaction Scheme 20:
H.sub.2PO.sub.4.sup.−+.OH+H.sup.+.fwdarw.H.sub.2PO.sub.4.+H.sub.2O Reaction Scheme 21:
H.sub.2PO.sub.4.sup.−+.OH.fwdarw.H.sub.2PO.sub.4.+OH.sup.− Reaction Scheme 22:
HPO.sub.4.sup.2−+.OH+H.sup.+.fwdarw.HPO.sub.4..sup.−+H.sub.2O Reaction Scheme 23:
HPO.sub.4.sup.2−+.OH.fwdarw.HPO.sub.4..sup.−+OH.sup.− Reaction Scheme 24:
PO.sub.4.sup.3−+.OH+H.sup.+.fwdarw.PO.sub.4.sup.2..sup.−+H.sub.2O Reaction Scheme 25:
PO.sub.4.sup.3−+.OH.fwdarw.PO.sub.4.sup.2..sup.−+OH.sup.− Reaction Scheme 26:
NO.sub.3.+e.sup.−.fwdarw.NO.sub.3.sup.− Reaction Scheme 27:
SO.sub.4..sup.−+e.sup.−.fwdarw.SO.sub.4.sup.2− Reaction Scheme 28:
H.sub.2PO.sub.4.+e.sup.−.fwdarw.H.sub.2PO.sub.4.sup.− Reaction Scheme 29:
HPO.sub.4..sup.−+e.sup.−.fwdarw.HPO.sub.4.sup.2− Reaction Scheme 30:
PO.sub.4.sup.2..sup.−+e.sup.−.fwdarw.PO.sub.4.sup.3− Reaction Scheme 31:
[0142] First, water is decomposed into oxygen (O.sub.2) and hydrogen ions (H.sup.+) on the anode 130 by oxidation caused by an external power source (Reaction Scheme 11). Then, the produced oxygen (O.sub.2) and hydrogen ions (H.sup.+) are reduced on the second electrode 140 to form hydrogen peroxide (H.sub.2O.sub.2) (Reaction Scheme 12).
[0143] In an embodiment of the present invention, the formed hydrogen peroxide reacts with metal species M.sup.δ+ included in non-d.sup.0-orbital-based transition metal oxide grains and having an oxidation number of 2 or less to form metal species M.sup.(δ+1)+ having an oxidation number of δ+1 and .OH (Reaction Scheme 14). The metal species M.sup.(δ+1)+ having an oxidation number of δ+1 is reduced by electrons (e.sup.−) back to the metal species M.sup.δ+ having an oxidation number of 2 or less (Reaction Scheme 13). This may solve a conventional problem in recovering the metal species M.sup.δ+ having an oxidation number of 2 or less from the metal species M.sup.(δ+1)+ having an oxidation number of δ+1 that is formed by reaction between the metal species M.sup.δ+ having an oxidation number of 2 or less and hydrogen peroxide (H.sub.2O.sub.2), and hydrogen peroxide (H.sub.2O.sub.2) may be continuously supplied by supplying oxygen (O.sub.2) via electrolysis of water. In addition, .OH may also be continuously supplied via oxidation of H.sub.2O in the first electrode 130 (Reaction Scheme 15).
[0144] In addition, according to an embodiment of the present invention, the formed hydrogen peroxide reacts with metal species (e.g., Zr.sup.4+/Nb.sup.5+/Ta.sup.5+) included in the d.sup.0-orbital-based transition metal oxide grains to produce .OH (Reaction Scheme 16). Since the oxidation number of the metal species (e.g., Zr.sup.4+/Nb.sup.5+/Ta.sup.5+) included in the d.sup.0-orbital-based transition metal oxide grains is not changed unlike the metal species (e.g., Fe.sup.2+/Co.sup.2+/Ni.sup.2+) included in the non-d.sup.0-orbital-based transition metal oxide, hydrogen peroxide (H.sub.2O.sub.2) may be continuously decomposed.
[0145] That is, the production rate of .OH is increased by H.sub.2O oxidation occurring in the first electrode 130 and catalytic decomposition of hydrogen peroxide occurring in the second electrode 140, and the produced .OH interacts with NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on the surface of the catalyst 1600 coated on the second electrode 140 to form NO.sub.3. /SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− surface species (Reaction Schemes 17 to 26). As the amount of the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on the surface of the coated catalyst 160 increases, the production rate of the NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− surface species increases, resulting in enhancement of performance of organic material decomposition by the NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4..sup.−/HPO.sub.4./HPO.sub.4.sup.2..sup.− surface species. Residual NO.sub.3./SO.sub.4./H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2− surface species that have not been used in decomposition of the organic material are reduced back to the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups by electrons (e.sup.−) (Reaction Schemes 27 to 31) to be continuously used to form NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− surface species later.
[0146] The NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− formed by the above-described reaction may decompose non-degradable or toxic organic materials. The organic material may be phenol-based toxic, carcinogenic, and mutagenic materials. Specifically, the organic material may be a monocyclic, polycyclic, or aromatic material having a structure, in which at least one carbon atom is substituted with oxygen (O), nitrogen (N), or sulfur (S), as a backbone and including various functional groups such as alkane, alkene, alkyne, amine, amide, nitro, alcohol, ether, halide, thiol, aldehyde, ketone, ester, or carboxylic acid group or derivatives thereof.
[0147] Meanwhile, according to an embodiment of the present invention, the aqueous electrolytic solution 120 in which reaction of the catalyst occurs may have a pH of 3 to 10, and the electro-Fenton reaction may be performed at a power of 2 W or less.
[0148] Formation of NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− are formed on the surface of the catalyst coated on the second electrode 140 in the aqueous electrolytic solution 120 of the electro-Fenton reaction, and decomposition of organic materials is performed by NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.−. In this regard, when the pH of the aqueous electrolytic solution 120 is in an acidic level (pH<3) or an alkaline level (pH>10) or when the external power exceeds 2 W, the transition metal oxide grains or the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups may be leached from the catalyst 160 coated on the second electrode 140. The leached homogeneous metal ions and the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups may change the pH of the aqueous electrolytic solution and may serve as major activators of production of .OH and NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.−. This leaching phenomenon decreases organic material decomposition efficiency and durability of the electro-Fenton system when the electro-Fenton reaction is performed for a long time. Therefore, for highly-efficient and continuous decomposition of organic materials, the aqueous electrolytic solution 120 may have a pH of 3 to 10 and a power of 2 W or less may be input to the electro-Fenton system, more preferably, the aqueous electrolytic solution 120 may have a pH of 7 and a power of 0.04 W or less may be input thereto.
[0149] Catalyst Structure for Non-Electro-Fenton System and Non-Electro-Fenton System
[0150] Hereinafter, a catalyst structure including a catalyst for a non-electro-Fenton system and a non-electro-Fenton system using the same will be described.
[0151] According to an embodiment of the present invention, a catalyst structure for a non-electro-Fenton system may include a catalyst for a non-electro-Fenton system, a carrier supporting the catalyst, a support coated with the catalyst-supporting carrier, and a binder for increasing a coating adhesive strength between the carrier and the support.
[0152] The catalyst for a non-electro-Fenton system includes transition metal oxide grains functionalized with NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− as described above. The catalyst may be directly coated on the support, but may be supported by the carrier for more stable and efficient configuration of the support. In this case, the carrier may be coated on at least one surface of the support, preferably, on both surfaces of the support. The support may be formed of a material commonly used in decomposition of non-degradable organic materials or having chemical resistance to radicals or hydrogen peroxides, e.g., a carbonaceous material such as graphite, carbon felt, or glassy carbon fiber or a metallic material such as stainless steel or titanium. Preferably, graphite may be used.
[0153] In addition, according to an embodiment of the present invention, the carrier may be formed of carbon (C), Al.sub.2O.sub.3, MgO, ZrO.sub.2, CeO.sub.2, TiO.sub.2, or SiO.sub.2 and may include 0.01 to 50 parts by weight of the catalyst for a non-electro-Fenton system based on 100 parts by weight of the carrier.
[0154] The catalyst-supporting carrier may be coated on the support using an impregnation method. In this regard, the amount of the coated catalyst may be adjusted to increase efficiency of .OH production or non-degradable organic material decomposition by NO.sub.3., SO.sub.4..sup.−, H.sub.2PO.sub.4., HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− and smooth transfer of the .OH to the NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional groups on the surface of the catalyst.
[0155] When the catalyst is coated on the support, the adhesive strength between the catalyst and the support may be increased using the binder. In this case, the binder may be an insoluble polymer or an inorganic binder, preferably, polyvinylidene fluoride (PVDF). The binder may increase the coating adhesive strength between the catalyst-supporting carrier and the support. When the binder has insolubility, the binder is not dissolved in an aqueous solution even after repeated decomposition of non-degradable organic materials, thereby preventing the leaching phenomenon of the catalyst. That is, lifespan characteristics of the support for the non-electro-Fenton system may be improved by inhibiting leaching of the catalyst. The inorganic binder may include at least one of SiO.sub.2, LiO.sub.2, K.sub.2O, ZrO.sub.2, Al.sub.2O.sub.3, and Na.sub.2SiO.sub.3.
[0156]
[0157] Referring to
[0158] The support may be formed of a carbonaceous material such as graphite, carbon felt, or glassy carbon fiber or a metallic material such as stainless steel or titanium. For example, graphite may be used. At least one surface of the support may be coated with the catalyst which may be a catalyst including manganese oxide grains functionalized with the above-described NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− according to an embodiment of the present invention.
[0159] The aqueous electrolytic solution is an aqueous solution used in non-electro-Fenton reaction and may include one of Na.sub.2SO.sub.4, NaNO.sub.3, NH.sub.4F, KF, KCl, KBr, KI, NaF, NaCl, NaBr, NaI, or any combination thereof having a concentration of 10.sup.4 mol/L to 10 mol/L.
[0160] Hereinafter, a process of decomposing an organic material will be described based on catalytic reaction occurring in the non-electro-Fenton system using NO.sub.3.sup.− functional group by way of example. Reactions occurring in the non-electro-Fenton reaction are expressed by Reaction Schemes e to i below.
M.sup.δ++H.sub.2O.sub.2.fwdarw.M.sup.(δ+1)++OH.sup.−+.OH Reaction Scheme e:
M.sup.(δ+1)++e.sup.−.fwdarw.M.sup.δ+ Reaction Scheme f:
NO.sub.3.sup.−+.OH+H.sup.+.fwdarw.NO.sub.3.+H.sub.2O Reaction Scheme g:
NO.sub.3.sup.−+.OH.fwdarw.NO.sub.3.+OH.sup.− Reaction Scheme h:
NO.sub.3.+e.sup.−.fwdarw.NO.sub.3.sup.− Reaction Scheme i:
[0161] First, hydrogen peroxide supplied by a hydrogen peroxide (H.sub.2O.sub.2) supply unit reacts with metal species M.sup.δ+ having an oxidation number of 2 or less included in transition metal oxide grains to form metal species M.sup.(δ+1)+ having an oxidation number of δ+1 and .OH. The metal species M.sup.(δ+1)+ having an oxidation number of δ+1 is reduced by electrons (e.sup.−) present in the aqueous solution back to the metal species M.sup.δ+ having an oxidation number of 2 or less. Subsequently, the produced .OH interacts with the NO.sub.3.sup.− functional group on the surface of the catalyst coated on the support to form NO.sub.3. surface species. As the amount of the NO.sub.3.sup.− functional group on the surface of the coated catalyst increases, the production rate of the NO.sub.3. surface species increases, resulting in enhancement of performance of the organic material decomposition by NO.sub.3. surface species. Residual NO.sub.3. surface species that have not been used in decomposition of organic materials are reduced back to the NO.sub.3.sup.− functional groups by electrons (e.sup.−) and may be continuously used to form NO.sub.3. surface species later.
[0162] The NO.sub.3. formed by the above-described reaction may decompose non-degradable or toxic organic materials. The organic material may be phenol-based toxic, carcinogenic, and mutagenic materials. Specifically, the organic material may be a monocyclic, polycyclic, or aromatic material having a structure, in which at least one carbon atom is substituted with oxygen (O), nitrogen (N), or sulfur (S), as a backbone and including various functional groups such as alkane, alkene, alkyne, amine, amide, nitro, alcohol, ether, halide, thiol, aldehyde, ketone, ester, or carboxylic acid group or derivatives thereof.
[0163] Meanwhile, according to an embodiment of the present invention, an amount of H.sub.2O.sub.2 supplied by the hydrogen peroxide supply unit may be in the range of 10.sup.−5 mol/L to 10.sup.5 mol/L, and the aqueous solution may have a pH of 5 to 10.
[0164] In an embodiment of the present invention, NO.sub.3. formation occurs on the surface of the catalyst coated on the support in the aqueous electrolytic solution and decomposition of the organic material is performed by NO.sub.3. in the non-electro-Fenton reaction. In this regard, when the pH of the aqueous electrolytic solution is in an acidic level (pH<5) or an alkaline level (pH>10) or when the amount of H.sub.2O.sub.2 is less than 10.sup.−5 mol/L or more than 10.sup.5 mol/L, the transition metal oxide catalyst grains or NO.sub.3.sup.− functional group may be leached from the catalyst coated on the support. The leached homogeneous metal ions species M.sup.δ+ having an oxidation number of 2 or less and NO.sub.3.sup.− functional group may change the pH of the aqueous electrolytic solution and may serve as major activators of production of .OH and NO.sub.3.. This leaching phenomenon decreases organic material decomposition efficiency and durability of the non-electro-Fenton system when the non-electro-Fenton reaction is performed for a long time. Therefore, for highly-efficient and continuous decomposition of organic materials, the aqueous electrolytic solution may have a pH of 5 to 10 and 10.sup.−5 mol/L to 10.sup.5 mol/L of H.sub.2O.sub.2 may be supplied to the non-electro-Fenton system, more preferably, the aqueous electrolytic solution may have a pH of 7 to 10 and 10 mmol/L to 500 mmol/L of H.sub.2O.sub.2 may be supplied thereto.
[0165] Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these examples are made only for illustrative purposes, and the present invention is not be construed as being limited to those examples.
EXAMPLES
Examples 1 to 3: Preparation of ZrO.SUB.2., ZrO.SUB.2 .(N), and ZrO.SUB.2 .(S) Catalysts
[0166] Porous and crystalline ZrO.sub.2 catalysts were prepared by hydrothermal synthesis. Specifically, 20 mmol of ZrOCl.sub.2.8H.sub.2O and 40 mmol of oxalic acid (C.sub.2H.sub.2O.sub.4.8H.sub.2O) were dissolved in 100 mL of distilled water, and the solution was stirred at 50° C. for 60 minutes, followed by drying and calcination at 400° C. for 2 hours. A catalyst prepared in Example 1 is referred to as ZrO.sub.2. The ZrO.sub.2 catalyst of Example 1 was placed in a reactor and exposed to nitrogen monoxide (NO) and oxygen (O.sub.2) diluted with N.sub.2 by simultaneously supplying them at a flow rate of 500 mL min.sup.−1 at ambient atmospheric pressure at 100° C. for 60 minutes, and then cooled to room temperature in a N.sub.2 atmosphere. In the exposure process, an amount of nitrogen monoxide was 5000 ppm and a volume of oxygen was 3 vol %. Under the conditions, a NO.sup.3−-functionalized catalyst according to Example 2 was prepared. Hereinafter, the catalyst of Example 2 is referred to as ZrO.sub.2 (N). The ZrO.sub.2 catalyst of Example 1 was placed in a reactor and exposed to sulfur dioxide (SO.sub.2) and oxygen (O.sub.2) diluted with N.sub.2 by simultaneously supplying them at a flow rate of 500 mL min.sup.−1 at ambient atmospheric pressure at 400° C. for 60 minutes, and then cooled to room temperature in a N.sub.2 atmosphere. In the exposure process, an amount of sulfur dioxide was 5000 ppm and a volume of oxygen was 3 vol %. Under the conditions, a SO.sub.4.sup.2−-functionalized catalyst according to Example 3 was prepared. Hereinafter, the catalyst of Example 3 is referred to as ZrO.sub.2 (S).
Examples 4 to 7: Preparation ZrO.SUB.2 .(P)-0.5, ZrO.SUB.2 .(P)-1.5, and ZrO.SUB.2 .(P)-2.0 Catalysts
[0167] 1 g of the ZrO.sub.2 catalyst of Example 1 was added to 100 mL of an aqueous solution in which a phosphorylating precursor (85 wt %, H.sub.3PO.sub.4) shown in Table 1 below was dissolved, and the solution was stirred/dried at 25° C. for 24 hours, followed by calcination at 350° C. for 3 hours. In the ZrO.sub.2 catalysts including different amounts of the phosphorylating precursor, distribution of H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, and PO.sub.4.sup.3− ions immobilized on the catalyst surface after calcination may vary. The catalysts prepared as described above according to Examples 4 to 7 are respectively referred to as ZrO.sub.2 (P)—Y (where Y is content (wt %) of P contained in the catalyst).
TABLE-US-00001 TABLE 1 Example 4 Example 5 Example 6 Example 7 Catalyst ZrO.sub.2 (P)-0.5 ZrO.sub.2 (P)-1.0 ZrO.sub.2 (P)-1.5 ZrO.sub.2 (P)-2.0 85 wt % 0.037 0.056 0.074 0.093 H.sub.3PO.sub.4(g)
Examples 8 to 19: Preparation of Non-d.SUP.0.-Orbital-Based Transition Metal Oxide Catalysts
[0168] Porous and crystalline transition metal oxide catalysts were prepared by templated synthesis. Manganese oxide was prepared by hydrothermal synthesis. Specifically, 200 mL of an aqueous solution including 20 mmol of MnSO.sub.4.H.sub.2O and 20 mmol of KMnO.sub.4 was stirred for 30 minutes at 25° C. and exposed to hydrothermal reaction conditions in an autoclave reactor at 160° C. for 6 hours to obtain a solid. The obtained solid was filtered/washed with distilled water and ethanol and dried at 70° C. and then further dried at 100° C. for 1 hour. Hereinafter, a manganese oxide (MnO.sub.2) catalyst prepared in Example 8 is referred to as Mn catalyst.
[0169] The Mn catalyst prepared in Example 8 was exposed to an atmosphere including 5000 ppm of NO and 3 vol % of O.sub.2 diluted with N.sub.2 at a flow rate of 500 mL min.sup.−1 at 150° C. for 1 hour, and then cooled to room temperature in a N.sub.2 atmosphere. A NO.sub.3.sup.−-functionalized manganese oxide catalyst prepared under the conditions of Example 9 is referred to as Mn (N).
[0170] The Mn catalyst prepared in Example 8 was exposed to an atmosphere including 5000 ppm of NO and 3 vol % of O.sub.2 diluted with N.sub.2 at a flow rate of 500 mL min.sup.−1 at 100° C. for 1 hour, and then cooled to room temperature in a N.sub.2 atmosphere. A catalyst prepared under the conditions of Example 10 is referred to as Mn (N′).
[0171] In addition, 100 mL of an aqueous solution including 20 mmol of oxalic acid (C.sub.2H.sub.2O.sub.4.2H.sub.2O) and 20 mmol of a metal precursor (FeSO.sub.4.7H.sub.2O for Fe; CoSO.sub.4.7H.sub.2O for Co; NiSO.sub.4.7H.sub.2O for Ni; and CuSO.sub.4.5H.sub.2O for Cu) was stirred for 30 minutes at 50° C. The resultant was filtered/washed using distilled water and ethanol and dried at 70° C., followed by calcination at 300° C. for 1 hour to prepare transition metal oxides (Hereinafter, the prepared materials are referred to as Fe, Co, Ni, and Cu catalysts, respectively).
[0172] The prepared Fe, Co, Ni, or Cu catalyst was exposed to an atmosphere including 5000 ppm of NO and 3 vol % of O.sub.2 diluted with N.sub.2 at a flow rate of 500 mL min.sup.−1 at 100° C. for 1 hour, and then cooled to room temperature in a N.sub.2 atmosphere. The catalysts prepared under the conditions according to Examples 11 to 14 are referred to as Fe(N′), Co(N′), Ni(N′), and Cu(N′), respectively.
[0173] 1 g of the prepared Mn, Fe, Co, Ni, or Cu catalyst was added to 100 mL of an aqueous solution in which 0.087 g of a phosphorylating precursor (98.5 wt % (NR.sub.4).sub.2HPO.sub.4) was dissolved and the solution was stirred and dried at 25° C. for 24 hours, followed by calcination at 350° C. for 3 hours. In the transition metal oxide catalysts including the same amount of the phosphorylating precursor (i.e., Mn, Fe, Co, and Ni), distribution of H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, and PO.sub.4.sup.3− ions immobilized on the catalyst surface may be changed after calcination. The catalysts prepared as described above according to Examples 15 to 19 are respectively referred to Mn (P)-1.5, Fe (P)-1.5, Co (P)-1.5, Ni (P)-1.5, and Cu (P)-1.5 (where 1.5 refers to the content (wt %) of P contained in the catalyst). The catalysts prepared according to Examples 1 to 7 and Examples 15 to 19 were analyzed using an X-ray diffractometer (XRD), and XRD patterns obtained therefrom are shown in
[0174] In order to observe physical properties of the catalyst that is not functionalized and the catalysts functionalized with NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− according to Examples 2 to 4, various analysis methods were used, and the analysis results are shown in Table 2 below. The catalyst of Examples 1 to 4 shows porous morphology which is proved by BET surface area values (S.sub.BET) and BJH pore volume values (V.sub.BJH) of the catalysts.
TABLE-US-00002 TABLE 2 Example Example Example Example 1 2 ZrO.sub.2 3 ZrO.sub.2 4 ZrO.sub.2 Catalyst ZrO.sub.2 (N) (S) (P)-0.5.sup.f S.sub.BET.sup.a (m.sup.2 g.sub.CAT.sup.−1) 117.3 105.8 93.9 77.2 V.sub.BJH.sup.b (cm.sup.3 g.sub.CAT.sup.−1) 0.08 0.03 0.05 0.03 N/Zr, S/Zr, or bulk.sup.c — 0.01 0.02 0.02 P/Zr (≤ ±0.01) (≤ ±0.01) (≤ ±0.01) surface.sup.d — 0.1 0.1 0.09 (≤ ±0.01) (≤ ±0.01) (±0.01) -Q.sub.ST.sup.e (kJ mol.sub.CO.sup.−1) 48.2 43.2 37.4 31.2 (±9.9) (±9.5) (±1.3) (±1.2) N.sub.CO.sup.e 9.1 5.8 3.7 3.4 (μmol.sub.CO g.sub.CAT.sup.−1) (±0.4) (±0.9) (±0.6) (±0.4) (.sup.avia BET. .sup.bvia BJH. .sup.cvia XRF. .sup.dvia XPS. .sup.evia CO isotherm. .sup.fP content of 0.5 wt %.)
[0175] in addition, as a result of quantitative analysis of the catalysts of Examples 2 to 4 using XRF and XPS, it is confirmed that similar amounts of N, S and P are included in the bulk and on the surface (N/Zr, S/Zr and P/Zr molar ratio). For analysis of metal active species (H.sub.2O.sub.2 activator) on the surface of the catalysts of Examples 2 to 4, CO adsorption isotherms of the catalysts were obtained at −20° C., 0° C., and 20° C. After Toth fitting, binding energies (−Q.sub.ST) between the metal surface species and CO when the same moles of CO are adsorbed were calculated using the Clausius-Clapeyron equation and are shown in Table 2. In comparison with the non-functionalized ZrO.sub.2 catalyst of Example 1, it was confirmed that NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3−-functionalized catalysts of Examples 2 to 4 had lower binding force with CO. This indicates that introduction of the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups onto the surface of the ZrO.sub.2 catalyst weakens the binding force between the metal active species and .OH, thereby facilitating leaching of .OH that is a rate-determining step of decomposition of H.sub.2O.sub.2 catalyst. Importantly, it was confirmed that the H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3−-functionalized catalyst of Example 4 had the smallest binding force between the metal surface species and CO. This indicates that introduction of the H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups onto the surface of the ZrO.sub.2 catalyst significantly weakens the binding force between the metal active species and .OH, thereby more easily facilitating leaching of .OH that is a rate-determining step of decomposition of H.sub.2O.sub.2 catalyst. Also, this indicates that introduction of the H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups onto the surface of the ZrO.sub.2 catalyst increases efficiency of catalytic decomposition of hydrogen peroxide, thereby increasing productivity of .OH compared to other catalysts.
[0176] In order to observe physical properties of the catalysts functionalized with different amounts of H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− according to Examples 5 to 7, the catalysts were analyzed using various methods, and the results are shown in Table 3. The catalysts of Examples 5 to 7 show various morphology which is proved by BET surface area values (S.sub.BET) and BJH pore volume values (V.sub.BJH) of the catalyst. Also, as a result of quantitative analysis of the catalysts of Examples 2 to 4 using XRF, it is confirmed that various amounts of P are included in the bulk (P/Zr molar ratio).
TABLE-US-00003 TABLE 3 Example 5 Example 6 Example 7 catalyst ZrO.sub.2 (P)-1.0.sup.d ZrO.sub.2 (P)-1.5.sup.e ZrO.sub.2 (P)-2.0.sup.f S.sub.BET.sup.a (m.sup.2 g.sub.CAT.sup.−1) 46.7 18.1 19.7 V.sub.BJH.sup.b (cm.sup.3 g.sub.CAT.sup.−1) 0.02 0.02 0.01 P/Zr.sup.c (bulk) 0.04 (±0.01) 0.05 (±0.01) 0.06 (±0.01) (.sup.avia BET. .sup.bvia BJH. .sup.cvia XRF. .sup.dP content of 1.0 wt %. .sup.eP content of 1.5 wt %. .sup.fP content of 2.0 wt %.)
[0177] The catalysts prepared according to Examples 8, 9, and 11 to 14 were analyzed using an X-ray diffractometer (XRD), and XRD patterns obtained therefrom are shown in
[0178] It is confirmed that the Mn and Mn(N) catalysts of Examples 8 and 9 have a tetragonal α-MnO.sub.2 phase referring to
[0179] In order to observe changes in physical properties of manganese oxide catalysts by surface functionalization by NO.sub.3.sup.−, the catalysts of Examples 8 and 9 were analyzed using various methods. For quantitative analysis of CO-accessible Mn.sup.δ+ surface species (N.sub.CO) having Lewis acid properties, the catalysts of Examples 8 and 9 were analyzed using CO-pulsed chemisorption, and it was confirmed that the catalysts of Examples 8 and 9 had similar N.sub.CO values (˜0.5 μmol.sub.CO g.sub.CAT.sup.−1). As described above, when the Mn.sup.δ+ species included on the surfaces of the catalysts have similar Lewis acid intensities, adsorption and interaction between Mn.sup.δ+ and H.sub.2O.sub.2 may be similar. That is, when the Mn.sup.δ+ species included on the surfaces of the Mn and Mn (N) catalysts of Examples 8 and 9 have similar Lewis acid intensities, the similar N.sub.co values indicate similar efficiencies of catalytic decomposition of hydrogen peroxide (*OH productivity). For further analysis of Mn.sup.δ+ surface species of the catalysts of Examples 8 and 9, CO.sub.2 adsorption isotherms of the Mn and Mn (N) catalysts were obtained at −20° C., 0° C., and 20° C. After Toth fitting, binding energies (−Q.sub.ST) between the Mn.sup.δ+ surface species and CO.sub.2 in the case that the same moles of CO.sub.2 are adsorbed were calculated, using the Clausius-Clapeyron equation and are shown in
[0180] For further surface analysis of the Mn (N) catalyst of Example 9, in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used and in order to realize an atmosphere similar to nitrification conditions used to prepare the catalyst of Example 2, the surface of the Mn catalyst of Example 8 was saturated with NO/O.sub.2 at 150° C. and the results are shown in
[0181]
[0182] Meanwhile, NO.sub.2.sup.− and SO.sub.3.sup.2− functional groups, which have significantly shorter lifespans and lower oxidizing power than NO.sub.3.sup.− and SO.sub.4.sup.2− functional groups, are not effective on increasing rates of decomposing non-degradable organic material.
Examples 20 to 23: Preparation of Mn(S), Co(S), Ni(S) and Cu(S) Catalysts
[0183] Porous and crystalline manganese oxide, cobalt oxide, nickel oxide, and copper oxide were prepared by templated synthesis. Specifically, 100 mL of an aqueous solution including 20 mmol of oxalic acid (C.sub.2H.sub.2O.sub.4.2H.sub.2O) and 20 mmol of MnSO.sub.4H.sub.2O/CoSO.sub.4.7H.sub.2O/NiSO.sub.4.7H.sub.2O/CuSO.sub.4.5H.sub.2O was stirred for 30 minutes at 50° C. The resultant was filtered/washed with distilled water and ethanol and dried at 70° C., followed by calcination at 300° C. for 1 hour to prepare manganese oxide, cobalt oxide, nickel oxide, and copper oxide. The prepared metal oxide was exposed to an atmosphere including 500 ppm of SO.sub.2 and 3 vol % of O.sub.2 diluted with N.sub.2 at a flow rate of 500 mL min.sup.−1 at 500° C. for 45 minutes, and then cooled to room temperature in a N.sub.2 atmosphere. A SO.sub.4.sup.2−-functionalized catalysts prepared under the conditions are referred to as Example 20 (Mn(S)), Example 21 (Co(S)), Example 22 (Ni(S)) and Example 23 (Cu(S)), respectively.
[0184] The catalysts prepared in Examples 20 to 23 were analyzed using an X-ray diffractometer (XRD), and XRD patterns obtained therefrom are shown in
Examples 24 to 28: Preparation of Mn.SUB.Z.Catalysts (where Z=3, 2, 1.5, 1, 0)
[0185] As shown in Table 4, porous and crystalline Mn.sub.Z catalysts were prepared by solvothermal synthesis. Specifically, 177.6 g of an ethylene glycol solution including (Z×10) mmol of MnCl.sub.2.4H.sub.2O, ((3−Z)×10) mmol of FeCl.sub.3.6H.sub.2O, 3.6 g of NaNO.sub.3, and 1 g of polyethylene glycol was stirred for 30 minutes at 25° C. and exposed to solvothermal reaction conditions in an autoclave reactor at 200° C. for 12 hours to obtain a solid. The obtained solid was filtered/washed with distilled water and ethanol and dried at 70° C. and then further dried at 100° C. for 1 hour to prepare Mn.sub.Z catalysts. Hereinafter, the M.sub.Z catalysts are referred to as catalysts of Examples 24 to 28. Hereinafter, Mn.sub.3O.sub.4, Mn.sub.2Fe.sub.1O.sub.4, Mn.sub.1.5Fe.sub.1.5O.sub.4, Mn.sub.1Fe.sub.2O.sub.4, and Fe.sub.3O.sub.4 catalysts according to Examples 24 to 28 are referred to as Mn.sub.3, Mn.sub.2, Mn.sub.1.5, Mn.sub.1, and Mn.sub.0, respectively, according to molar ratio of manganese.
TABLE-US-00004 TABLE 4 Example Example Example Example Example 24 25 26 27 28 Precursor MnCl.sub.2•4H.sub.2O 30 20 15 10 0 (mmol) FeCl.sub.3•6H.sub.2O 0 10 15 20 30 (mmol) Product Mn.sub.3(Mn.sub.3O.sub.4) Mn.sub.2(Mn.sub.2Fe.sub.1O.sub.4) Mn.sub.1.5(Mn.sub.1.5Fe.sub.1.5O.sub.4) Mn.sub.1(Mn.sub.1Fe.sub.2O.sub.4) Mn.sub.0(Fe.sub.3O.sub.4)
Examples 29 to 33: Preparation of Mn.SUB.Z.(S) Catalysts (where Z=3, 2, 1.5, 1, 0)
[0186] The Mn.sub.z catalysts prepared in Examples 24 to 28 were exposed to an atmosphere including 500 ppm of SO.sub.2 and 3 vol % of O.sub.2 diluted with N.sub.2 at a flow rate of 500 mL min.sup.−1 at 500° C. for 1 hour, and then cooled to room temperature in a N.sub.2 atmosphere. The Mn.sub.Z(S) catalysts prepared under the above conditions are referred to as catalysts of Examples 29 to 33. The catalysts according to Examples 29 to 33 are referred to Mn.sub.3 (S), Mn.sub.2 (S), Mn.sub.1.5 (S), Mn.sub.1 (S), and Mn.sub.0 (S), respectively, according to molar ratio of manganese.
[0187] The catalysts prepared in Examples 24 to 33 were analyzed using an X-ray diffractometer (XRD), and XRD patterns obtained therefrom are shown in
[0188] It is confirmed that the crystal phases of the SO.sub.4.sup.2−-functionalized catalysts of Examples 30 to 32 are identical to those of the Examples 25 to 27. Since surface functionalization of the catalysts of Examples 29 to 31 by SO.sub.4.sup.2− does not create a new bulk phase such as MnSO.sub.4 and Fe.sub.2(SO.sub.4), it is confirmed that the surface functionalization does not affect the bulk phase. On the contrary, it is confirmed that the catalyst according to Example 29 has an orthorhombic MnSO.sub.4 phase that has not been observed in Example 24, and this indicates the surface functionalization of the catalyst by SO.sub.4.sup.2− partially changes the crystal phase of Mn.sub.3O.sub.4 into MnSO.sub.4. Also, in the case of Example 33, due to a high temperature (500° C.) for surface functionalization of the catalyst by SO.sub.4.sup.2− of Example 29, the metastable cubic Fe.sub.3O.sub.4 phase was converted into the rhombohedral Fe.sub.2O.sub.3 phase. However, since a new bulk phase such as Fe.sub.2(SO.sub.4) was not creased in the case of Example 33, it is confirmed that surface functionalization of the catalyst by SO.sub.4.sup.2− catalyst does not affect the bulk phase.
[0189] In order to observe physical properties of the SO.sub.4.sup.2--functionalized catalysts (Mn.sub.z(S)) of Examples 29 to 33, the catalysts were analyzed using various methods. The Mn.sub.z(S) catalysts exhibit porous morphology which is proved by BET surface area values (5-25 m.sup.2 g.sub.CAT.sup.−1) of the catalysts. In addition, it is confirmed that the Mn.sub.z(S) catalysts have stoichiometrically defined metal (Mn+Fe)/oxygen (O) ratios (molar basis) based on quantitative analysis results using XRF as shown in Table 5. The Mn.sub.3 (S) of Example 29 has a higher sulfur (S)/metal (Mn+Fe) ratio (molar basis) than those of the catalysts of Examples 30 to 33 (Table 5). This is consistent with the result that a new bulk phase MnSO.sub.4 is additionally generated by SO.sub.4.sup.2− functionalization of the Mn.sub.3 catalyst of Example 24 described above.
TABLE-US-00005 TABLE 5 Example Example Example Example Example 29 30 31 32 33 Mn.sub.3 (S) Mn.sub.2 (S) Mn.sub.1.5 (S) Mn.sub.1 (S) Mn.sub.0 (S) Metal (Mn + Fe)/ 0.79 0.77 0.78 0.79 0.78 Oxygen (O) (±0.09) (±0.05) (±0.03) (±0.02) (±0.02) Sulfur (S)/ 0.22 0.04 0.02 0.01 0.01 Metal (Mn + Fe) (±0.03) (<±0.01) (<±0.01) (<±0.01) (<±0.01)
[0190] For quantitative analysis of CO-accessible Mn.sup.δ+ surface species (N.sub.CO) having Lewis acid properties, the catalysts of Examples 29 to 33 were analyzed by CO-pulsed chemisorption. The Mn.sub.3 (S) and Mn.sub.0 (S) catalysts of Examples 29 and 33 provided higher N.sub.CO values than the other catalysts (≥˜0.27 μmol.sub.CO g.sub.CAT.sup.−1 for Mn.sub.3 (S) and Mn.sub.0 (S); ≤˜0.15 μmol.sub.CO g.sub.CAT.sup.−1 for Mn.sub.2 (S), Mn.sub.1.5 (S), and Mn.sub.1 (S)). This indicates that the Mn.sub.3 (S) and Mn.sub.0 (S) catalysts of Examples 29 and 33 increase efficiency of catalytic decomposition of hydrogen peroxide, thereby increasing .OH productivity when compared with the other catalysts.
[0191]
[0192]
[0193]
[0194] Hereinafter, performance of Fenton systems using the catalysts of the above-described examples will be described.
Experimental Example 1: Hydrogen Peroxide (H.SUB.2.O.SUB.2.) Decomposition Test
[0195] A reaction test is performed using the catalysts of Examples 1 to 4, a graphite electrode, hydrogen peroxide (H.sub.2O.sub.2) as a .OH precursor, and a Na.sub.2SO.sub.4 aqueous electrolytic solution in the absence of electricity. When the catalysts are coated on the electrode, poly(vinylidene fluoride) (PVDF) was used as a binder. 0.2 g of the catalyst was used and 100 mL of an aqueous solution in which 0.2 mol of Na.sub.2SO.sub.4 was dissolved was used as a reaction solution. The reaction test was performed at 25° C. at a pH of 7. An amount of H.sub.2O.sub.2 used in the reaction was 0.12 mmol which was observed after 8 hours of reaction in the absence of phenol under the electro-Fenton reaction conditions of Experimental Example 2 below. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.H2O2/C.sub.H2O2,0) VS. time) obtained based on a conversion rate of H.sub.2O.sub.2 in the test is equal to a H.sub.2O.sub.2 decomposition rate constant (k.sub.APP, min.sup.−1).
[0196] An initial H.sub.2O.sub.2 decomposition rate (−r.sub.H2O2,0, min.sup.−1) was calculated by multiplying k.sub.APP of each catalyst by N.sub.H2O2,0, and dividing the result value by N.sub.CO value (number of moles of Lewis acid per gram of the above-described CO-accessible catalyst; shown in Table 2) contained in the amount (0.2 g) of the used catalyst and is shown in
[0197] A reaction test was performed using the catalysts of Examples 8 and 9 and hydrogen peroxide (H.sub.2O.sub.2) dissolved in an aqueous solution as a non-degradable organic material. 0.2 g of the catalyst was used and 100 mL of an aqueous solution was used as a reaction solution, and the reaction test was performed at 25° C. at a pH of 7 using 30 mmol of H.sub.2O.sub.2. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.H2O2/C.sub.H2O2,0) VS. time) obtained based on a conversion rate of H.sub.2O.sub.2 in which measurement values (autolysis of H.sub.2O.sub.2 and adsorption of H.sub.2O.sub.2 by catalyst) of the test were corrected is equal to a H.sub.2O.sub.2 decomposition rate constant (k.sub.APP, min.sup.−1). An initial H.sub.2O.sub.2 decomposition rate (−r.sub.H2O2,0, min.sup.−1) was calculated by multiplying k.sub.APP of each catalyst by N.sub.H2O2,0, and dividing the result value by the amount (0.2 g) of the catalyst and shown in
[0198] A reaction test was performed using the catalysts of Examples 29 to 33, a graphite electrode, hydrogen peroxide (H.sub.2O.sub.2) as a non-degradable organic material, and a Na.sub.2SO.sub.4 aqueous electrolytic solution in the absence of electricity. When the catalysts were coated on the electrode, poly(vinylidene fluoride) (PVDF) was used as a binder. 0.2 g of the catalyst was used and 100 mL of an aqueous solution in which 0.2 mol of Na.sub.2SO.sub.4 was dissolved was used as a reaction solution. The reaction test was performed at 25° C. at a pH of 7. An amount of H.sub.2O.sub.2 used in the reaction was an amount observed after 8 hours of reaction in the absence of phenol under the electro-Fenton reaction conditions of Experimental Example 25 below (N.sub.H2O2,0: 0.13 mmol.sub.H2O2 for Mn.sub.3 (S); 0.18 mmol.sub.H2O2 for Mn.sub.2 (S); 0.26 mmol.sub.H2O2 for Mn.sub.1.5 (S); 0.22 mmol.sub.H2O2 for Mn.sub.1 (S); and 0.23 mmol.sub.H2O2 for Mn.sub.0 (S)). A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.H2O2/C.sub.H2O2,0) VS. time) obtained based on a conversion rate of H.sub.2O.sub.2 in which measurement values of the test were corrected is equal to a H.sub.2O.sub.2 decomposition rate constant (k.sub.APP, min.sup.−1).
[0199] An initial H.sub.2O.sub.2 decomposition rate (−r.sub.H2O2,0, min.sup.−1) was calculated by multiplying k.sub.APP of each catalyst by N.sub.H2O2,0, and dividing the result value by N.sub.co value (number of moles of Lewis acid per gram of the above-described CO-accessible catalyst) included in the amount (0.2 g) of the catalyst and shown in
Experimental Example 2: Phenol Decomposition Test
[0200] (1) Electro-Fenton Reaction
[0201] An electro-Fenton reaction test was performed using the catalysts according to Examples 1 to 4 and Examples 29 to 33, a graphite electrode, phenol (C.sub.6H.sub.5OH) as an organic material, and a Na.sub.2SO.sub.4 aqueous electrolytic solution. When the catalysts were coated on the electrode, poly(vinylidene fluoride) (PVDF) was used as a binder. 0.2 g of the catalyst was used and 100 mL of an aqueous solution in which 0.1 mmol of phenol (N.sub.PHENOL,0) and 0.2 mol of Na.sub.2SO.sub.4 were dissolved was used as a reaction solution. The electro-Fenton reaction test was performed at 25° C. at a pH of 7 with a power of 0.04 W. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.PHENOL/C.sub.PHENOL,0) VS. time) obtained based on a conversion rate of phenol in the test is equal to a phenol decomposition rate constant (k.sub.APP, min.sup.−1). An initial phenol decomposition rate (−r.sub.PHENOL,0, min.sup.−1) was calculated by multiplying k.sub.APP of each catalyst by N.sub.PHENOL,0 (0.1 mmol) and dividing the result value by N.sub.CO value (number of moles of Lewis acid per gram of the above-described CO-accessible catalyst; shown in Table 2) contained in the amount (0.2 g) of the catalyst and shown in
[0202] As predicted in the analysis of physical properties of the catalysts of Examples 29 to 33, it was confirmed that the Mn.sub.1.5 (S) catalyst of Example 31 had higher −r.sub.PHENOL,0 and η.sub.PHENOL values than those of the other catalysts (Mn.sub.3 (S), Mn.sub.2 (S), Mn.sub.1 (S) and Mn.sub.0 (S)). In addition, amounts of Mn and Fe leached from the catalysts during the phenol decomposition reaction were quantified and shown in Table 6. As shown in Table 6, it was confirmed that less amounts of Mn and Fe were leached from the Mn.sub.1.5 (S) catalyst of Example 31 when compared to the other catalysts (Mn.sub.3 (S), Mn.sub.2 (S), Mn.sub.1 (S) and Mn.sub.0 (S)). This results indicate that it is important to select the types and stoichiometry Z of M.sub.A/M.sub.B included in the SO.sub.4.sup.2−-functionalized (M.sub.A).sub.Z(M.sub.B).sub.3-ZO.sub.4 for continuous improvement of the ability to decompose non-degradable organic materials.
TABLE-US-00006 TABLE 6 Example Example Example Example Example 29 30 31 32 33 Mn.sub.3 (S) Mn.sub.2 (S) Mn.sub.1.5 (S) Mn.sub.1 (S) Mn.sub.0 (S) Mn 0.18 0.60 0.03 0.01 — (mol. %) (<±0.01) (±0.01) (±0.01) (<±0.01) Fe — 0.01 0.03 0.07 0.06 (mol. %) (<±0.01) (±0.01) (<±0.01) (<±0.01)
[0203] (2) Non-Electro-Fenton Reaction
[0204] A reaction test is performed using the catalysts of Examples 1 to 4, 8, and 9, and hydrogen peroxide (H.sub.2O.sub.2) dissolved in an aqueous solution as an organic material, and phenol (C.sub.6H.sub.5OH) as a non-degradable organic material. 0.2 g of the catalyst was used and 100 mL of an aqueous solution was used as a reaction solution, and the reaction test was performed at 25° C. at a pH of 7 using 30 mmol of H.sub.2O.sub.2 and 0.1 mmol of phenol. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.PHENOL/C.sub.PHENOL,0) VS. time) obtained based on a conversion rate of phenol in the test is equal to a phenol decomposition rate constant (k.sub.APP, min.sup.−1). An initial phenol decomposition rate (−r.sub.PHENOL,0) was calculated by multiplying k.sub.APP of each catalyst by N.sub.PHENOL,0 (0.1 mmol), and dividing the result value by the amount (0.2 g) of the catalyst and shown in
Experimental Example 3: Phenol Decomposition Test Using Scavenging Agent
[0205] The reaction was performed under the same conditions as those of Experimental Example 2 using the catalysts of Examples 1 to 4, Examples 8 and 9, Example 26 (Mn.sub.1.5) and Example 31 (Mn.sub.1.5 (S)), except that an excess of catechol, hydroquinone, ethanol, tert-butanol, 1,4-dioxane, tetrahydrofuran (THF), or isopropyl alcohol, as a scavenging agent, was added thereto to quench the .OH and NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− formed during the reaction in different quenching rates, and the results are shown in
TABLE-US-00007 TABLE 7 k.sub.*OH k.sub.*OOH k.sub.NO3* k.sub.SO4*− k.sub.H2PO4* (M.sup.−1s.sup.−1) (M.sup.−1s.sup.−1) (M.sup.−1s.sup.−1) (M.sup.−1s.sup.−1) (M.sup.−1s.sup.−1) catechol 1.1 × 10.sup.10 4.7 × 10.sup.4 — — — (C.sub.6H.sub.6O.sub.2) hydroquinone 5.2 × 10.sup.9 1.7 × 10.sup.7 — — — (C.sub.6H.sub.6O.sub.2) ethanol 2.2 × 10.sup.9 — 1.4 × 10.sup.6 4.3 × 10.sup.7 7.7 × 10.sup.7 (C.sub.2H.sub.6O) tert-butanol 5.7 × 10.sup.8 — 5.7 × 10.sup.4 6.5 × 10.sup.5 3.9 × 10.sup.6 (C.sub.4H.sub.10O)
[0206] For amounts of the scavenging agents added to each reaction, refer to Chemical Reaction Scheme 32 that may occur during catalytic decomposition of H.sub.2O.sub.2 using surface active species of the d.sup.0-orbital-based transition metal oxide and the amounts were calculated by adding bulk N/S/P content present in the catalyst to twice the amount of H.sub.2O.sub.2 generated by the catalysts of Examples 1 to 4, Example 26 (Mn.sub.1.5) and Example 31 (Mn.sub.1.5 (S)) in the presence of electricity.
H.sub.2O.sub.2.fwdarw.(½).OH+(½).OOH Reaction Scheme 32:
[0207] It was confirmed that the −r.sub.PHENOL,0 values of all catalysts of Experimental Example 3 performed after adding the scavenging agent thereto were smaller than the −r.sub.PHENOL,0 values obtained in the absence of the scavenging agent. This indicates that decomposition of phenol is performed by .OH or NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2..sup.− generated in the electro-Fenton reaction when the catalysts according to Examples 1 to 4, Examples 8 and 9, Example 26 (Mn1.5) and Example 31 (Mn1.5 (S)) were used. Also, it was confirmed that the −r.sub.PHENOL,0 values of the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3−-functionalized catalysts of Examples 2 to 4 were greater than the −r.sub.PHENOL,0 value of the non-functionalized catalyst Example 1 in the presence of the scavenging agent. Based on the tendency and size of radical quenching rate constants (secondary rate constants) of each scavenging agent, the results of
Experimental Example 4: Phenol Decomposition Based on Heterogeneous Catalysis
[0208] In order to verify that phenol decomposition of Example 1 is performed by .OH generated by H.sub.2O.sub.2 decomposition occurring on the surface of the catalyst, Experimental Example 4 was performed under the same conditions as those of Experimental Example 2 above using the catalyst of Example 1. In addition, in order to verify that phenol decomposition of Examples 2 to 4, Example 8 (Mn), Example 9 (Mn(N)), and Example 31 (Mn.sub.1.5 (S)) was performed by NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2. of the surface of the catalyst, Experimental Example 4 was performed under the same conditions as those of Experimental Example 2 above using the catalyst of Examples 2 to 4, Example 8 (Mn), Example 9 (Mn(N)), and Example 31 (Mn.sub.1.5 (S)). In this regard, a test was performed in the same manner as in Experimental Example 2 for 1 hour, and then was continued after replacing the cathodes of Examples 1 to 4 with cathodes without the catalysts and filtering the aqueous reaction solutions. It is important that consumption of phenol observed after 1 hour is caused by anodic oxidation occurring in the anode even in the absence of the catalyst, H.sub.2O.sub.2 decomposition (.OH production; Example 1) by active species leached from the catalyst, or NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2. active species leached from the catalyst (Examples 2 to 4). Conversion amounts of phenol with time according to the method were monitored and shown in
[0209] Referring to
[0210] Referring to
Experimental Example 5: Electron Paramagnetic Resonance (EPR) Spectroscopy Analysis
[0211] To prove H.sub.2O.sub.2 scission (.OH production) occurring in the Mn catalyst of Example 8 and formation of NO.sub.3. active species on the surface of the Mn (N) catalyst of Example 9, EPR spectroscopy analysis was performed, and the results are shown in
Experimental Example 6: Catalyst Durability Test
[0212] To verify durability of the developed catalysts, Experimental Example 6 was performed under the same conditions as those of Experimental Example 2 using the catalysts of Examples 1 to 4, Examples 8 and 9, and Example 31 (Mn.sub.1.5 (S)). The catalysts after each reaction cycle were washed/dried/accumulated and are used for a subsequent reaction cycle. Results of Experimental Example 6 are shown in
[0213] It was confirmed that −r.sub.PHENOL,0 values gradually decreases as the number reaction cycles increases in the cases of the catalysts of Examples 1 to 4. However, it was confirmed that the tendency of the −r.sub.PHENOL,0 values of the catalysts observed in Experimental Example 2 (1.sup.st cycle) (ZrO.sub.2<ZrO.sub.2 (N)<ZrO.sub.2 (S)<ZrO.sub.2 (P)-0.5) was maintained in the 5.sup.th cycle. This indicates that it is important to select type/stoichiometry/structure of the metal included in the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3−-functionalized d.sup.0-orbital-based transition metal oxide and functionalization conditions thereof for continuous improvement of the ability to decompose non-degradable organic materials as shown in the results of Experimental Examples 1 and 2. Although the −r.sub.PHENOL,0 values of the NO.sub.3.sup.−-functionalized Mn (N) catalyst continuously decreases from −1.2 μmol.sub.PHENOL g.sub.CAT.sup.−1 min.sup.−1 to ˜0.8 μmol.sub.PHENOL g.sub.CAT.sup.−1 min.sup.−1 as the number of reaction cycles increases, considerably high −r.sub.PHENOL,0 values were obtained during a recycle test compared to the non-functionalized Mn catalyst. This indicates that the NO.sub.3.sup.−-functionalized Mn (N) catalyst has excellent recyclability of performance of non-degradable organic material decomposition compared to the non-functionalized Mn catalyst.
[0214] In the case of the Mn.sub.1.5 (S) catalyst, the −r.sub.PHENOL,0 values gradually decrease from ˜1.4 μmol.sub.PHENOL g.sub.CAT.sup.−1 min.sup.−1 (1.sup.st cycle) to ˜0.4 μmol.sub.PHENOL g.sub.CAT.sup.−1 min.sup.−1 (5.sup.th cycle) as the number reaction cycles increases. However, it was confirmed that the −r.sub.PHENOL,0 value of the Mn.sub.1.5 (S) catalyst observed at the 5.sup.th cycle is greater than or similar to the −r.sub.PHENOL,0 values of the Mn.sub.3 (S) catalyst of Example 29 (0.1 μmol.sub.PHENOL g.sub.CAT.sup.−1 min.sup.−1) and the Mn.sub.0 (S) catalyst of Example 33 (0.8 μmol.sub.PHENOL g.sub.CAT.sup.−1 min.sup.−1) obtained at the 1.sup.st cycle. This result indicates that it is important to select the type and stoichiometry Z of M.sub.A/M.sub.B included in the SO.sub.4.sup.2−-functionalized (M.sub.A).sub.Z(M.sub.B).sub.3-ZO.sub.4 for continuous improvement of the ability to decompose non-degradable organic materials, as shown in the results of Experimental Examples 24 and 25.
Experimental Example 7: Aniline Decomposition Test
[0215] For application of the developed catalysts, an electro-Fenton reaction test was performed using the catalysts according to Examples 1 to 4 and 29 to 33, a graphite electrode, aniline (C.sub.6H.sub.5NH.sub.2) as an organic material, and a Na.sub.2SO.sub.4 aqueous electrolytic solution. When the catalysts were coated on the electrode, poly(vinylidene fluoride) (PVDF) was used as a binder. 0.2 g of the catalyst was used and 100 mL of an aqueous solution in which 0.1 mmol of aniline (N.sub.ANILINE,0) and 0.2 mol of Na.sub.2SO.sub.4 were dissolved was used as a reaction solution. The electro-Fenton reaction test was performed at 25° C. at a pH of 7 with a power of 0.04 W. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.ANILINE/C.sub.ANILINE,0) VS. time) obtained based on a conversion rate of aniline in the test is equal to an aniline decomposition rate constant (k.sub.APP, min.sup.−1). An initial aniline decomposition rate (−r.sub.ANILINE,0, min.sup.−1) was calculated by multiplying k.sub.APP of each catalyst by N.sub.ANILINE,0, and dividing the result value by N.sub.CO value (number of moles of Lewis acid per gram of the above-described CO-accessible catalyst; shown in Table 2) contained in the amount (0.2 g) of the catalyst used and is shown in
[0216] Also, in the electro-Fenton reaction test, a carbon conversion rate to an aniline conversion rate was quantified as η.sub.ANILINE and shown in
Experimental Example 8: Phenol Decomposition Test
[0217] An electro-Fenton reaction test was performed using the catalyst according to Example 1 and the catalyst having different bulk P contents according to Examples 4 to 7, a graphite electrode, phenol (C.sub.6H.sub.5OH) as an organic material, and a Na.sub.2SO.sub.4 aqueous electrolytic solution. When the catalysts were coated on the electrode, poly(vinylidene fluoride) (PVDF) was used as a binder. 0.2 g of the catalyst was used and 100 mL of an aqueous solution in which 0.1 mmol of phenol (N.sub.PHENOL,0) and 0.2 mol of Na.sub.2SO.sub.4 were dissolved was used as a reaction solution. The electro-Fenton reaction test was performed at 25° C. at a pH of 7 with a power of 0.04 W. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.PHENOL/C.sub.PHENOL,0) VS. time) obtained based on a conversion rate of phenol in the test is equal to a phenol decomposition rate constant (k.sub.APP, min.sup.−1). An initial phenol decomposition rate (−r.sub.PHENOL,0, min.sup.−1) was calculated by multiplying k.sub.APP of each catalyst by N.sub.PHENOL,0 (0.1 mmol), and dividing the result value by the amount (0.2 g) of the catalyst and shown in
Experimental Example 9: Verification of Phenol Decomposition Adaptability of NO.SUB.3..SUP.−.-Functionalized Transition Metal Oxides
[0218] To verify non-degradable organic material decomposition adaptability of transition metal oxide catalysts including the NO.sub.3.sup.− functional group, Experimental Example 7 was performed under the same conditions for the phenol decomposition test of Experimental Example 2 using oxides of Mn, Fe, Co, Ni, and Cu according to Examples 10 to 14 as catalysts, and the results are shown in
Experimental Example 10: Phenol Decomposition Test
[0219] (1) Electro-Fenton Reaction
[0220] To prove decomposition adaptability of non-d.sup.0-orbital-based transition metal oxide catalysts including H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on non-degradable organic materials, Experimental Example 9 was performed under the same conditions as those of Experimental Example 2 using the Mn, Fe, Co, Ni, and Cu oxides of Examples 15 to 19 as catalysts, and the results are shown in
[0221] Therefore, the catalyst for an electro-Fenton system according to an embodiment of the present invention may decompose non-degradable organic material based on heterogeneous catalysis by coating the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3−-functionalized d.sup.0-orbital-based or non-d.sup.0-orbital-based catalysts on the cathode such that the NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2. functional groups formed as a result of radical transfer of .OH are distributed on the surfaces of the catalysts. In addition, the non-degradable organic material decomposition efficiency may be adjusted or increased according to the type/stoichiometry/structure of the metal included in the transition metal oxide or the number/distribution of the NO.sub.3./SO.sub.4..sup.−/H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2. functional groups, and leaching phenomenon of the surface-activating metal species (H.sub.2O.sub.2 activator) or the NO.sub.3.sup.−/SO.sub.4.sup.2−/H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3−-functional groups from the surfaces of the catalysts may be reduced during the decomposition. Therefore, the effects on improving performance and lifespan of the electro-Fenton system that decomposes organic materials may be obtained using the catalysts.
[0222] (2) Non-Electro-Fenton Reaction
[0223] To prove decomposition adaptability of non-d.sup.0-orbital-based transition metal oxide catalysts including H.sub.2PO.sub.4.sup.−/HPO.sub.4.sup.2−/PO.sub.4.sup.3− functional groups on non-degradable organic materials, a reaction test was performed using the Mn, Fe, Co, Ni, and Cu oxides of Examples 15 to 19 as catalysts, hydrogen peroxide (H.sub.2O.sub.2) as an organic material, and phenol (C.sub.6H.sub.5OH) as a non-degradable organic material. 0.2 g of the catalyst was used and 100 mL of an aqueous solution was used as a reaction solution, and the reaction test was performed at 25° C. at a pH of 7 using 30 mmol of H.sub.2O.sub.2 and 0.1 mmol of phenol. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.PHENOL/C.sub.PHENOL,0) VS. time) obtained based on a conversion rate of phenol in the test is equal to a phenol decomposition rate constant (k.sub.APP, min.sup.−1). An initial phenol decomposition rate (−r.sub.PHENOL,0) was calculated by multiplying k.sub.APP of each catalyst by N.sub.PHENOL,0 (0.1 mmol), and dividing the result value by the amount (0.2 g) of the catalyst and shown in
[0224] It was confirmed that the catalysts of Examples 15 to 19 had a significant range of −r.sub.PHENOL,0 values (0.4 to 1.4 μmol.sub.PHENOL g.sub.CAT.sup.−1 min.sup.−1). This indicates that the H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2. surface species present on the surfaces of the catalysts suggested in the present invention are also produced under the non-electro Fenton conditions (using H.sub.2O.sub.2), and the method of decomposing phenol by the H.sub.2PO.sub.4./HPO.sub.4..sup.−/PO.sub.4.sup.2. surface species under non-electro Fenton conditions (using H.sub.2O.sub.2) may be possible using various non-d.sup.0-orbital-based transition metal oxide catalysts.
Experimental Example 11: Phenol Decomposition Test
[0225] To prove decomposition adaptability of non-d.sup.0-orbital-based transition metal oxide catalysts including SO.sub.4.sup.2− functional group on non-degradable organic materials under the non-electro Fenton conditions (using H.sub.2O.sub.2), a reaction test was performed using the Mn, Co, Ni, and Cu oxides of Examples 20 to 23 as catalysts, hydrogen peroxide (H.sub.2O.sub.2) as an organic material, and phenol (C.sub.6H.sub.5OH) as a non-degradable organic material. 0.2 g of the catalyst was used and 100 mL of an aqueous solution was used as a reaction solution, and the reaction test was performed at 25° C. at a pH of 7 using 30 mmol of H.sub.2O.sub.2 and 0.1 mmol of phenol. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.PHENOL/C.sub.PHENOL,0) VS. time) obtained based on a conversion rate of phenol in the test is equal to a phenol decomposition rate constant (k.sub.APP, min.sup.−1). An initial phenol decomposition rate (−r.sub.PHENOL,0) was calculated by multiplying k.sub.APP of each catalyst by N.sub.PHENOL,0 (0.1 mmol), and dividing the result value by the amount (0.2 g) of the catalyst and shown in
[0226] It was confirmed that the catalysts of Examples 20 to 23 had a significant range of −r.sub.PHENOL,0 values (0.3-1.2 μmol.sub.PHENOL g.sub.CAT.sup.−1 min.sup.−1). This indicates that the SO.sub.4..sup.− surface species present on the surfaces of the non-d.sup.0-orbital-based transition metal catalysts suggested in the present invention are also produced under the non-electro Fenton conditions (using H.sub.2O.sub.2), and the method of decomposing phenol by the SO.sub.4..sup.− surface species under non-electro Fenton conditions (using H.sub.2O.sub.2) may be possible using various non-d.sup.0-orbital-based transition metal oxide catalysts.
Experimental Example 12: Calculation of Activation Energy of Phenol (C.SUB.6.H.SUB.5.OH) Decomposition Test
[0227] A reaction test was performed under the same conditions as those of the phenol decomposition test of Experimental Example 8 using the catalysts of Examples 8 and 9, except that reaction temperatures varied to 25° C., 35° C., 45° C., and 55° C. A slope of a pseudo-1.sup.st-order kinetic fitting graph (−ln(C.sub.PHENOL/C.sub.PHENOL,0) VS. time) obtained based on a conversion rate of phenol obtained by correcting measurement values (phenol decomposition by H.sub.2O.sub.2 and phenol adsorption by catalyst) in the test is equal to a phenol decomposition rate constant (k.sub.APP, min.sup.−1). The obtained decomposition rate constants were Arrhenius-plotted (ln (k.sub.APP) versus 1/T; T: reaction temperature), and activation energy of phenol decomposition was calculated using the obtained slope and shown in
[0228] According to an embodiment of the present invention as described above, the NO.sub.3.sup.−, SO.sub.4.sup.2−, H.sub.2PO.sub.4.sup.−, HPO.sub.4.sup.2−, or PO.sub.4.sup.3− functional group on the surface of the catalyst reacts with .OH and is converted into the NO.sub.3. , SO.sub.4..sup.−, H.sub.2PO.sub.4., HPO.sub.4..sup.−, or PO.sub.4.sup.2..sup.− functional group (surface species) which (1) has a longer lifespan than .OH and a similar oxidizing power thereto, and (2) operates in a wider pH range, resulting in an increase in non-degradable organic material decomposition rates.
[0229] In addition, according to an embodiment of the present invention, leaching of grains occurring during decomposition of non-degradable organic materials may be reduced, catalyst performance may be maintained despite repeated use thereof, and lifespan of the catalyst may be increases. However, the scope of the present invention is not limited by these effects.
[0230] While one or more embodiments of the present invention have been described with reference to the drawings, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.