CATALYST FOR DECOMPOSING NON-DEGRADABLE POLLUTANTS AND NON-DEGRADABLE POLLUTANT DECOMPOSITION SYSTEM INCLUDING THE CATALYST

Abstract

An embodiment relates to a catalyst for decomposing non-degradable pollutants and a non-degradable pollutant decomposition system including the same, and more specifically, to a catalyst for an electro-/nonelectro-Fenton reaction system, the catalyst including at least one of 1) non-reducible transition metal oxide particles having a reduced surface, or 2) non-reducible transition metal oxide particles functionalized with H.sub.3ZPO.sub.4.sup.Z (Z=1 to 3) and having a reduced surface; an electrode including the catalyst for the electro-/nonelectro-Fenton reaction system; and an electro-/nonelectro-Fenton reaction system using the electrode, for efficient decomposition of non-degradable organic matter.

Claims

1. A catalyst for an electro- or nonelectro-Fenton reaction system, comprising surface-reduced catalyst particles; or surface-reduced catalyst particles including a nitrate group or a phosphate group.

2. The catalyst for the electro- or nonelectro-Fenton reaction system according to claim 1, wherein the catalyst particles have a porous structure.

3. The catalyst for the electro- or nonelectro-Fenton reaction system according to claim 1, wherein the catalyst particles have a diameter of 0.1 nm to 500 m.

4. The catalyst for the electro- or nonelectro-Fenton reaction system according to claim 1, wherein the catalyst particles include TiO.sub.2, ZrO.sub.2, Nb.sub.2O.sub.5, or Ta.sub.2O.sub.5 as non-reducible transition metal oxides.

5. The catalyst for the electro- or nonelectro-Fenton reaction system according to claim 1, wherein the nitrate group is NO.sub.3.sup. and the phosphate group is one of H.sub.2PO.sub.4.sup., HPO.sub.4.sup.2, and PO.sub.4.sup.3.

6. A preparation method of a catalyst for an electro- or nonelectro-Fenton reaction system, comprising: preparing catalyst particles having a reduced surface by hydrogen treatment.

7. The preparation method of the catalyst for the electro- or nonelectro-Fenton reaction system according to claim 6, wherein the hydrogen treatment is performed by a reaction gas including H.sub.2.

8. The preparation method of the catalyst for the electro- or nonelectro-Fenton reaction system according to claim 6, further comprising: performing nitrification or phosphorylation treatment of the reduced catalyst particle surface.

9. The preparation method of the catalyst for the electro- or nonelectro-Fenton reaction system according to claim 8, the nitrification treatment is performed by a reaction gas including NO and O.sub.2.

10. The preparation method of the catalyst for the electro- or nonelectro-Fenton reaction system according to claim 8, the phosphorylation treatment is performed by a reaction solution including a phosphorylation precursor.

11. An electrode for an electro- or nonelectro-Fenton reaction system, comprising: a catalyst for an electro- or nonelectro-Fenton reaction system of claim 1; a carrier on which the catalyst is supported; a substrate coated with the carrier; and a binder interposed between the carrier and the substrate to increase coating adhesion.

12. The electrode for the electro- or nonelectro-Fenton reaction system according to claim 11, wherein the catalyst particles have a porous structure.

13. The electrode for the electro- or nonelectro-Fenton reaction system according to claim 11, wherein the catalyst particles have a diameter of 0.1 nm to 500 m.

14. The electrode for the electro- or nonelectro-Fenton reaction system according to claim 11, wherein the carrier is one of carbon (C), Al.sub.2O.sub.3, MgO, ZrO.sub.2, CeO.sub.2, and SiO.sub.2.

15. The electrode for the electro- or nonelectro-Fenton reaction system according to claim 11, comprising the catalyst in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of the carrier.

16. The electrode for the electro- or nonelectro-Fenton reaction system according to claim 11, wherein the binder is an insoluble polymer.

17. An electro- or nonelectro-Fenton reaction system comprising one or more of the electrode of claim 11 and an aqueous electrolyte solution.

18. The electro- or nonelectro-Fenton reaction system according to claim 17, wherein the pH of the electrolyte solution is 2 to 10, and the electrode is input with a power of 2 W or less to cause a Fenton reaction.

19. The electro- or nonelectro-Fenton reaction system according to claim 17, wherein the catalyst included in the electrode has a powder form.

20. The electro- or nonelectro-Fenton reaction system according to claim 17, wherein the electro- or nonelectro-Fenton reaction includes: (1) forming .Math.OH species formed by a homolysis of H.sub.2O.sub.2; (2) converting NO.sub.3.sup. surface species functionalized by the .Math.OH species or H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3 surface species into NO.sub.3.Math. surface species or converting into H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math..sup. surface species; and (3) decomposing non-degradable organic matter by one or more of the surface species of the NO.sub.3.Math., H.sub.2PO.sub.4.Math., HPO.sub.4.Math..sup., and PO.sub.4.sup.2.Math..sup..

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing exemplary embodiments thereof in detail with reference to the accompanying drawings, in which:

[0034] FIG. 1 shows scanning electron microscopy (SEM) images of catalysts synthesized according to one embodiment of the present invention;

[0035] FIG. 2 shows a graph illustrating the X-ray diffraction (XRD) pattern results of the catalysts synthesized according to one embodiment of the present invention;

[0036] FIG. 3 shows a graph illustrating the X-ray photoelectron spectroscopy (XPS) results in the N 1s and P 2p regions of the catalysts synthesized according to one embodiment of the present invention;

[0037] FIG. 4 shows a graph illustrating the conversion rate and conversion concentration of acetaminophen decomposed over time under electro-Fenton conditions of the catalysts synthesized according to one embodiment of the present invention;

[0038] FIG. 5 shows a graph illustrating the conversion rate and conversion concentration of acetaminophen decomposed over time under electro-Fenton conditions of the catalysts synthesized according to one embodiment of the present invention;

[0039] FIG. 6 shows a graph illustrating the conversion rate and conversion concentration of acetaminophen decomposed over time under electro-Fenton conditions of the catalysts synthesized according to one embodiment of the present invention;

[0040] FIG. 7 shows a graph illustrating the decomposition rates of acetaminophen, aniline, sulfanilamide, and sulfamethoxazole (SMX) under electro-Fenton conditions of the catalysts synthesized according to one embodiment of the present invention; and

[0041] FIG. 8 shows a graph illustrating the decomposition rates of acetaminophen under nonelectro-Fenton conditions of the catalysts synthesized according to one embodiment of the present invention.

[0042] Hereinafter, the present invention will be described in more detail. However, the present invention may be implemented in various different forms, and the present invention is not limited to the embodiments described herein, and the present invention is only defined by the claims set forth below.

[0043] In addition, the terms used herein are only used to describe specific embodiments and are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular expression includes the plural expression. Throughout the specification of the present invention, unless otherwise specified, the term comprising means that other components may be included rather than meaning that other components are excluded.

[0044] Throughout the specification, when a portion is described to be connected (linked, contacted, joined) to another portion, this includes not only cases where it is directly connected but also cases where it is indirectly connected with another member therebetween. Also, when a portion is described to comprise a certain component, unless otherwise specified, this means that other components may be included rather than meaning that other components are excluded.

[0045] The terms used herein are only used to describe specific embodiments and are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular expression includes the plural expression.

[0046] A first aspect of the present invention provides a catalyst for an electro- or nonelectro-Fenton reaction system, including: surface-reduced catalyst particles; or surface-reduced catalyst particles including a nitrate group or a phosphate group.

[0047] Hereinafter, the catalyst for the electro- or nonelectro-Fenton reaction system according to the first aspect of the present invention is described in detail.

[0048] In one embodiment of the present invention, the catalyst particles may have a porous structure.

[0049] In one embodiment of the present invention, the catalyst particles may have a diameter of 0.1 nm to 500 m. When the diameter of the catalyst particles exceeds the above range, the non-degradable organic matter decomposition rate may decrease, thus causing the problem that the decomposition performance is difficult to maintain.

[0050] In one embodiment of the present invention, the catalyst particles may include TiO.sub.2, ZrO.sub.2, Nb.sub.2O.sub.5, or Ta.sub.2O.sub.5 as non-reducible transition metal oxides, and preferably titanium dioxide (TiO.sub.2) may be used.

[0051] In one embodiment of the present invention, the nitrate group may be NO.sub.3.sup. and the phosphate group may be one of H.sub.2PO.sub.4.sup., HPO.sub.4.sup.2, PO.sub.4.sup.3.

[0052] A second aspect of the present invention provides a preparation method of a catalyst for an electro- or nonelectro-Fenton reaction system, including: preparing catalyst particles having a reduced surface by hydrogen treatment.

[0053] For portions that overlap the first aspect of the present application, a detailed description has been omitted, but the same contents described about the first aspect of the present application may be applied even when the description has been omitted for the second aspect.

[0054] Hereinafter, the preparation method of the catalyst for the electro- or nonelectro-Fenton reaction system according to the second aspect of the present invention is described in detail.

[0055] In one embodiment of the present invention, the hydrogen treatment may be performed by a reaction gas including H.sub.2.

[0056] In one embodiment of the present invention, the preparation method may further include: performing nitrification or phosphorylation treatment of the reduced catalyst particle surface.

[0057] In one embodiment of the present invention, the nitrification treatment may be performed by a reaction gas including NO and O.sub.2.

[0058] In one embodiment of the present invention, the phosphorylation treatment may be performed by a reaction solution including a phosphorylation precursor.

[0059] A third aspect of the present invention provides an electrode for the electro- or nonelectro-Fenton reaction system, including: the catalyst for the electro- or nonelectro-Fenton reaction system; a carrier on which the catalyst is supported; a substrate coated with the carrier; and a binder interposed between the carrier and the substrate to increase coating adhesion.

[0060] For portions that overlap the first and second aspects of the present application, a detailed description has been omitted, but the same contents described about the first and second aspects of the present application may be applied even when the description has been omitted for the third aspect.

[0061] Hereinafter, the electrode for the electro- or nonelectro-Fenton reaction system according to the third aspect of the present invention is described in detail.

[0062] In one embodiment of the present invention, the catalyst particles may have a porous structure.

[0063] In one embodiment of the present invention, the catalyst particles may have a diameter of 0.1 nm to 500 m. When the diameter of the catalyst particles exceeds the above range, the non-degradable organic matter decomposition rate may decrease, thus causing the problem that the decomposition performance is difficult to maintain.

[0064] In one embodiment of the present invention, the carrier may be one of carbon (C), Al.sub.2O.sub.3, MgO, ZrO.sub.2, CeO.sub.2, and SiO.sub.2.

[0065] In one embodiment of the present invention, the electrode may further include the catalyst in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of the carrier.

[0066] In one embodiment of the present invention, the binder may be an insoluble polymer.

[0067] A fourth aspect of the present invention provides an electro- or nonelectro-Fenton reaction system including: the electrode for the electro- or nonelectro-Fenton reaction system; and an aqueous electrolyte solution.

[0068] For portions that overlap the first to third aspects of the present application, a detailed description has been omitted, but the same contents described about the first to third aspects of the present application may be applied even when the description has been omitted for the fourth aspect.

[0069] Hereinafter, the electro- or nonelectro-Fenton reaction system according to the fourth aspect of the present invention is described in detail.

[0070] In one embodiment of the present invention, the pH of the electrolyte solution may be 2 to 10, and the electrode may be input with a power of 2 W or less to cause a Fenton reaction.

[0071] In one embodiment of the present invention, the electro- or nonelectro-Fenton reaction may include: (1) forming .Math.OH species formed by a homolysis of H.sub.2O.sub.2; (2) converting NO.sub.3.sup. surface species functionalized by the .Math.OH species or H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3 surface species into NO.sub.3.Math. surface species or converting into H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.Math..sup.2 surface species; and (3) decomposing non-degradable organic matter by one or more of the surface species of the NO.sub.3.Math., H.sub.2PO.sub.4.Math., HPO.sub.4.Math..sup., PO.sub.4.Math..sup.2.

[0072] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art may easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Comparative Example 1: Preparation of O300 Catalyst

[0073] 6.9 g of H.sub.2SO.sub.4 and 11.25 g of TiOSO.sub.4 were dissolved in 37.5 mL of distilled water, and the resulting solution was stirred at 50 C. for three hours, mixed with 75 g of urea dissolved in 500 mL of distilled water, and reflux-stirred at 110 C. for 18 hours. The intermediate product was cooled to 25 C., filtered, rinsed with 2 L of distilled water, and dried at room temperature for three hours to obtain TiO(OH).sub.2, which was calcined at 400 C. for three hours to synthesize O300, which was named as Comparative Example 1.

Examples 1 and 2: Preparation of R300 and R600 Catalysts

[0074] TiO(OH).sub.2 was reduced at 300 C. for four hours with 10% by volume of H.sub.2/He to synthesize R300, which was named Example 1. In addition, TiO(OH).sub.2 at 600 C. for four hours with 10% by volume of H.sub.2/He to synthesize R600, which was named as Example 2.

Examples 3 and 4: Preparation of R600-N and R600-P Catalysts

[0075] The R600 catalyst of Example 2 was mounted in a reactor, and nitrogen monoxide (NO) and oxygen (O.sub.2) diluted with N.sub.2 were simultaneously introduced at a flow rate of 500 mL min.sup.1 to expose the catalyst at 100 C. under normal pressure for 120 minutes, and then the catalyst was cooled to room temperature under N.sub.2 atmosphere. The content of NO at the exposure stage was 5,000 ppm, and that of oxygen was 3% by volume. An NO.sub.3.sup.-functionalized R600-N catalyst corresponding to Example 3 was prepared according to the above conditions. 2 g of the R600 catalyst of Example 3 was added to 200 mL of an aqueous solution in which 4 mmol of a phosphorylation precursor ((NH.sub.4).sub.2HPO.sub.4) was dissolved, and the resulting mixture was stirred/dried at 25 C. for 24 hours, and then calcined at 250 C. for three hours. According to the above conditions, an H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3-functionalized R600-P catalyst corresponding to Example 4 was prepared according to the above conditions.

[0076] FIG. 1 shows the morphology of the catalyst particles of oxidized TiO.sub.2 (O300), reduced TiO.sub.2 (R300 and R600), NO.sub.3.sup.-functionalized reduced TiO.sub.2 (R600-N), and H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3-functionalized reduced TiO.sub.2 (R600-P) according to one embodiment of the present invention. As shown in FIG. 1, when the catalyst particles have a small size (10 to 30 m) or have a rough surface including protrusions, since the surface area increases and thus the H.sub.2O.sub.2 homolysis (H.sub.2O.sub.2.fwdarw.2.Math.OH) becomes faster, the formation rate of .Math.OH and the conversion rate of NO.sub.3.sup./H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3 functional groups on the catalyst surface into NO.sub.3.Math./H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math..sup. surface species by the .Math.OH species (NO.sub.3.sup.+.Math.OH.fwdarw.NO.sub.3.Math.+OH.sup.; H.sub.2PO.sub.4.sup.+.Math.OH.fwdarw.H.sub.2PO.sub.4.Math.+OH.sup.; HPO.sub.4.sup.2+.Math.OH.fwdarw.HPO.sub.4.Math..sup.+OH.sup.; PO.sub.4.sup.3+.Math.OH.fwdarw.PO.sub.4.sup.2.Math.+OH.sup.) may become faster.

[0077] The catalysts prepared through Comparative Example 1 and Examples 1 to 4 were analyzed using an X-ray diffractometer (XRD), and the resulting XRD patterns are shown in FIG. 2. Referring to FIG. 2, it can be seen that the catalysts of Comparative Example 1 and Examples 1 to 4 have a tetragonal TiO.sub.2 crystal phase. This means that the reduction by hydrogen at 300 to 600 C. or the functionalization with NO.sub.3.sup./H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3 did not affect the bulk phase of TiO.sub.2, but affected only the properties of the Brnsted acid (OH)/Lewis acid (Ti.Math..sup.4+) present on the TiO.sub.2 surface, or only the TiO.sub.2 surface was modified by NO.sub.3.sup./H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3.

[0078] Table 2 below shows the properties of the examples.

TABLE-US-00002 TABLE 2 Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Catalyst O300 R300 R600 R600-N R600-P S.sub.BET.sup.a (m.sup.2 245.6 229.5 79.1 70.2 35.4 g.sub.CAT.sup.1) V.sub.BJH.sup.b (cm.sup.3 0.3 0.3 0.3 0.2 0.1 g.sub.CAT.sup.1) N/Ti (bulk).sup.c,d 0.011 (+0.005) N/Ti (surface).sup.e 0.11 (+0.01) P/Ti (bulk).sup.c 0.136 (+0.003) P/Ti (surface).sup.e 0.31 (+0.04) N.sub.CO2.sup.f (mol.sub.CO 1.55 1.60 1.49 g.sub.CAT.sub.1) (+0.16) (+0.07) (+0.12) N.sub.CO2.sup.g 566.9 569.9 147.7 82.3 20.6 (mol.sub.CO2 (+8.9) (+1.0) (+33.3) (+15.0) (+0.7) g.sub.CAT.sup.1) band gap.sup.h 3.3 3.3 3.3 3.2 3.1 (eV) .sup.avia BET. .sup.bvia BJH. .sup.cvia ICP. .sup.dvia EA. .sup.evia XPS. .sup.fvia CO-pulsed chemisorption at 40 C. .sup.gvia CO.sub.2 isotherm at 20 C. .sup.hvia Tauc plot.

[0079] Table 2 shows the results of analyzing the properties of the catalysts of Comparative Example 1 and Examples 1 to 4. The catalysts of Comparative Example 1 and Examples 1 to 4 show porous morphology, which is proven by the Brunauer-Emmett-Teller (BET) surface area values (S.sub.BET) and Barrett-Joyner-Halenda BJH pore volume values (V.sub.BJH) of the catalysts. In addition, according to the results of quantitative analyses using inductively coupled plasma-optical emission spectrometry/elemental analysis (ICP/EA) and X-ray photoelectron spectroscopy (XPS), the catalysts of Examples 3 and 4 contain N and P in the bulk and on the surface (N/Ti and P/Ti molar ratios), which means that the R600 (reduced TiO.sub.2) surface was functionalized with NO.sub.3.sup./H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3.

[0080] FIG. 3 shows a graph illustrating the XPS results of the catalysts of Examples 3 and 4 functionalized with NO.sub.3.sup./H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3 (N 1s for Example 3; P 2p for Example 54). As proven by the XPS results, it was found that the catalysts of Examples 3 and 4 contained NO.sub.3.sup./H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3 functional groups on the surface. Specifically, this means that the catalysts of Examples 3 and 4 contain N/P in the bulk and on the surface (Table 2) and contain NO.sub.3.sup./H.sub.2PO.sub.4.sup./HPO.sub.4.sup.2/PO.sub.4.sup.3 functional groups on the surface, and thus may generate NO.sub.3.Math./H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math..sup. for non-degradable organic matter decomposition based on the radical transfer reaction.

[0081] On the other hand, to quantify the number of Lewis acids (NCO) per unit gram of the catalysts of Comparative Example 1 and Examples 1 to 4, a CO-pulsed chemisorption analysis was performed at 40 C. As a result, the numbers of NCO of the catalysts of Comparative Example 1 and Examples 1 to 4 were similar, which means that the numbers of Lewis acids of all the catalysts of the examples were similar. In addition, to quantify the number of total acid sites (Brnsted acid and Lewis acid) (NCO.sub.2) per unit gram of the catalysts of Comparative Example 1 and Examples 1 to 4, a CO.sub.2 isotherm analysis was performed at 20 C. As a result, the NCO.sub.2 value decreased from Comparative Example 1/Example 1 to Example 4, which means that the number of total acid sites decreased from Comparative Example 1/Example 1 to Example 4. In other words, the results of the CO-pulsed chemisorption and the CO.sub.2 isotherm analysis prove that the main acid sites that determine the H.sub.2O.sub.2 homolysis in the catalysts of Comparative Example 1 and Examples 1 to 4 are the Brnsted acid sites, not the Lewis acid sites. More specifically, the rate-determining step (.Math.OH desorption) of the H.sub.2O.sub.2 homolysis (H.sub.2O.sub.2.fwdarw.2.Math.OH) that occurs in the catalysts of Comparative Example 1 and Examples 1 and 2 is determined by their Brnsted acid sites, and the rate-determining step (.Math.OH desorption) of the radical transfer reactions (NO.sub.3.sup.+.Math.OH.fwdarw.NO.sub.3.Math.+OH.sup.; H.sub.2PO.sub.4.sup.+.Math.OH.fwdarw.H.sub.2PO.sub.4.Math.+OH.sup.; HPO.sub.4.sup.2+.Math.OH.fwdarw.HPO.sub.4.Math..sup.+OH.sup.; PO.sub.4.sup.3+.Math.OH.fwdarw.PO.sub.4.sup.2.Math..sup.+OH.sup.) that occur in the catalysts of Examples 3 and 4 is determined by their Brnsted acid sites.

[0082] The band gaps of the catalysts of Comparative Example 1 and Examples 1 to 4 were quantified using a Tauc plot, and are shown in Table 2. As a result, the band gaps of the catalysts of Comparative Example 1 and Examples 1 to 4 were found to be 3.1 to 3.3 eV, which means that the catalysts of Comparative Example 1 and Examples 1 to 4 are incapable of activating reactions that generate radicals by the above-described semiconduction mechanism or heterojunction mechanism. In addition, this means that the catalysts of Comparative Example 1 and Examples 1 and 2 generate .Math.OH based on the H.sub.2O.sub.2 homolysis to decompose non-degradable organic matter, and the catalysts of Examples 3 and 4 generate NO.sub.3.Math. surface species or H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.Math..sup.2 surface species based on the radical transfer reaction to decompose non-degradable organic matter.

[0083] Hereinafter, the performance of an electro- or nonelectro-Fenton system using the catalysts of Comparative Example 1 and Examples 1 to 4 will be described with reference to FIGS. 4 to 7.

Experimental Example 1: Acetaminophen Decomposition Based on Heterogeneous Catalysis

[0084] To verify that the decomposition of acetaminophen is carried out by the .Math.OH generated as a result of the H.sub.2O.sub.2 homolysis occurring on the catalyst surface, Experimental Example 1 was performed using Comparative Example 1 and Examples 1 and 2 as catalysts. In addition, to verify that the decomposition of acetaminophen is carried out by NO.sub.3.Math./H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math. on the catalyst surface, Experimental Example 1 was performed using Examples 3 and 4 as catalysts. Specifically, an electro-Fenton reaction experiment was performed using Comparative Example 1 and Examples 1 to 4 as catalysts, a graphite electrode as electrode, acetaminophen as an organic matter, and a Na.sub.2SO.sub.4 electrolyte solution. When coating the electrode with a catalyst, polyvinylidene 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 acetaminophen (N.sub.ACETAMONIPHEN, 0) and 0.14 mmol of Na.sub.2SO.sub.4 were dissolved was used as a reaction solution. The electro-Fenton reaction experiment was performed at 25 C. and pH 7 with 0.04 W of power. At this time, after performing the acetaminophen decomposition experiment for one hour, the cathodes of Comparative Example 1 and Examples 1 to 4 were replaced with catalyst-free cathodes and the aqueous solution for the reaction was filtered, and the experiment was performed again. In addition, the acetaminophen conversion rate (X.sub.ACETAMINOPHEN) versus time (reaction time) or the acetaminophen concentration values decomposed for one to six hours (C.sub.ACETAMINOPHEN) obtained in the present experiment were compared with those (X.sub.ACETAMINOPHEN versus time and C.sub.ACETAMINOPHEN) of the experiment conducted with a catalyst-free under the same conditions. Importantly, the consumption of acetaminophen observed after one hour as due to the oxidation occurring at the anode even in the absence of a catalyst (anodic oxidation) or the H.sub.2O.sub.2 homolysis by the NO.sub.3.Math./H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math. reactive species leached from the catalyst (.Math.OH generation; Comparative Example 1 and Examples 1 and 2) or to the NO.sub.3.Math./H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math. reactive species leached from the catalyst (Examples 3 and 4). The X.sub.ACETAMINOPHEN versus time and C.sub.ACETAMINOPHEN decomposed for one to six hours by the method was monitored and shown in FIGS. 4 and 5.

[0085] Referring to FIGS. 4 and 5, the conversion amounts of acetaminophen (C.sub.ACETAMINOPHEN) after one hour in the cathodes of Comparative Example 1, Example 1, Example 2, Example 3, and Example 4 were found to be 38.9 (2.7) M, 37.5 (5.3) M, 42.0 (1.6) M, 43.3 (1.2) M, and 44.2 (3.3) M. These values are similar to 40.7 (2.6) M, which is C.sub.ACETAMINOPHEN due to anodic oxidation, which was observed in the reaction performed without coating the cathode with the catalysts of Comparative Example 1 and Examples 1 to 4. This means that the acetaminophen decomposition reaction occurs based on heterogeneous catalysis by .Math.OH (Comparative Example 1, Example 1 and Example 2) or NO.sub.3.Math./H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math. reactive species (Examples 3 and 4) generated by H.sub.2O.sub.2 decomposition active species that are firmly coated on the electrode and not leached.

Experimental Example 2: Decomposition of Acetaminophen, Aniline, Sulfanilamide, and Sulfamethoxazole (Electro-Fenton Reaction)

[0086] An electro-Fenton reaction experiment was performed using Comparative Example 1 and Examples 1 to 4 as catalysts, a graphite electrode as an electrode, acetaminophen, aniline, sulfanilamide, and sulfamethoxazole (SMX) as organic substances, and an aqueous Na.sub.2SO.sub.4 electrolyte solution. When coating the electrode with a catalyst, 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 the organic substance (N.sub.ORGANICS, 0) and 0.14 mmol of Na.sub.2SO.sub.4 were dissolved was used as a reaction solution. The electro-Fenton reaction experiment was performed at 25 C. and pH 7 with 0.04 W of power. The slope of the pseudo-1.sup.st-order kinetic fitting graph (ln(C.sub.ORGANIC/C.sub.ORGANIC, 0) VS. time) obtained through the conversion rate of the organic substances obtained in the above experiment is equal to the rate constant (k.sub.APP, min.sup.1) of the reaction in which the organic substances are decomposed. The k.sub.APP of each catalyst was multiplied by N.sub.ORGANICS, 0 (0.1 mmol) and divided by the NCO.sub.2 value (the mole number of total acid sites per gram of catalyst accessible to CO.sub.2 as described above; set forth in Table 2) included in the used amount of the catalyst (0.2 g) to calculate the initial organic substance decomposition reaction rate (r.sub.ORGANICS, 0, min.sup.1), which is shown in

[0087] FIGS. 6 and 7.

[0088] The ionization energy, which is the energy required to remove an electron (e.sup.) from an organic substance, is 715.9 kJmol.sup.1 for acetaminophen, 744.9 kJmol.sup.1 for aniline, 789.2 kJmol.sup.1 for sulfanilamide, and 819.1 kJmol.sup.1 for sulfamethoxazole (SMX). When a radical follows the e.sup. transfer mechanism in which an electron (e.sup.) is removed from an organic substance to initiate decomposition, r.sub.ORGANICS, 0 decreases as the ionization energy of the organic substances increases.

[0089] The r.sub.ORGANICS, 0 values of R600-N of Example 3 and R600-P of Example 4 decrease as the ionization energy of the organic substances increases, which is proved by the high correlation coefficient values (R.sup.20.77; FIG. 6) of r.sub.ORGANICS, 0 versus the ionization energy of R600-N and R600-P, and this is consistent with a previous report that NO.sub.3.Math./H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math. initiate organic matter decomposition by the e.sup. transfer mechanism. On the other hand, the correlation coefficient values (R.sup.2; FIG. 6) of r.sub.ORGANICS, 0 versus the ionization energy of O300 of Comparative Example 1, R300 of Example 1, and R600 of Example 2 are low as 0.57 or less, which is consistent with a previous report that .Math.OH initiates organic matter decomposition by addition or H.Math. abstraction. The r.sub.ORGANICS, 0 values increase in the order of O300 of Comparative Example 1<R300 of Example 1<R600 of Example 2, which means that the preferable properties of a Brnsted acid (OH), which is a major acid site that determines the H.sub.2O.sub.2 homolysis (.Math.OH production), are inherent in the reduced TiO.sub.2 (R300 and R600). In addition, R600-N of Example 3 exhibited a similar or higher r.sub.ORGANICS, 0 value than that of R600 of Example 2, which means that NO.sub.3.Math. surface species are more preferable for increasing the organic matter decomposition efficiency than the traditional .Math.OH under the electro-Fenton conditions. In addition, R600-P of Example 4 exhibited the highest r.sub.ORGANICS, 0 value among Comparative Example 1 and Examples 1 to 4 prepared in the present invention, which means that the H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2.Math. surface species realizes superior organic matter decomposition efficiency compared to the traditional .Math.OH under the electro-Fenton conditions.

Experimental Example 3: Acetaminophen Decomposition (Nonelectro-Fenton Reaction)

[0090] A reaction experiment was performed using Comparative Example 1 and Examples 1 to 4 as catalysts and H.sub.2O.sub.2 dissolved in an aqueous solution and acetaminophen, which is a non-biodegradable organic substance. 0.2 g of the catalyst was used, and 100 mL of an aqueous solution was used as a reaction solution. The reaction experiment was performed at 25 C. and pH 7, and the amount of H.sub.2O.sub.2 used in the reaction was 30 mmol, and the amount of acetaminophen (N.sub.ACETAMINOPHEN, 0) was 0.1 mmol. The slope of the pseudo-1.sup.st-order kinetic fitting graph (ln(C.sub.ACETAMINOPHEN/C.sub.ACETAMINOPHEN, 0) VS. time) obtained through the conversion rate of acetaminophen obtained in the above experiment is equal to the rate constant (k.sub.APP, min.sup.1) of the reaction in which acetaminophen is decomposed. The k.sub.APP of each catalyst was multiplied by N.sub.ACETAMINOPHEN, 0 (0.1 mmol) and divided by the NCO.sub.2 value (the mole number of total acid sites per gram of catalyst accessible to CO.sub.2 as described above; set forth in Table 2) included in the used amount of the catalyst (0.2 g) to calculate the initial acetaminophen decomposition reaction rate (r.sub.ACETAMINOPHEN, 0, min.sup.1), which is shown in FIG. 8.

[0091] The r.sub.ACETAMINOPHEN, 0 values increase in the order of O300 of Comparative Example 1<R300 of Example 1<R600 of Example 2<R600-N of Example 3<R600-P of Example 4, which means that the preferable properties of a Brnsted acid (OH), which is a major acid site that determines the H.sub.2O.sub.2 homolysis (.Math.OH production), are inherent in the reduced TiO.sub.2 (R300 and R600). In addition, this means that the NO.sub.3.Math./H.sub.2PO.sub.4.Math./HPO.sub.4.Math..sup./PO.sub.4.sup.2 surface species are more preferable for increasing the organic matter decomposition efficiency than the traditional .Math.OH under the nonelectro-Fenton conditions.

[0092] According to embodiments of the present invention, the proposed catalysts can be applied to the oxidative decomposition of wastewater, residual water-soluble pharmaceuticals, water-soluble environmental hormones, and chemical warfare agents.

[0093] In addition, according to one embodiment of the present invention, the reduced TiO.sub.2 can provide improved. .Math..Math.OH productivity in the homogeneous decomposition reaction of hydrogen peroxide compared to oxidized TiO.sub.2, and thus the reduced TiO.sub.2 can dramatically improve the reaction rate of non-degradable organic matter decomposition compared to oxidized TiO.sub.2.

[0094] In addition, according to one embodiment of the present invention, the NO.sub.3.sup., H.sub.2PO.sub.4.sup., HPO.sub.4.sup.2, or PO.sub.4.sup.3-functional group on the reduced TiO.sub.2 catalyst surface can react with .Math.OH to be converted into NO.sub.3.Math., H.sub.2PO.sub.4.Math., HPO.sub.4.Math..sup., or PO.sub.4.sup.2.Math. surface species that 1) have a longer lifetime and similar oxidation power compared to .Math.OH, but 2) are operated under wider pH conditions, thereby dramatically improving the reaction rate of non-degradable organic matter decomposition.

[0095] In addition, according to one embodiment of the present invention, leaching of catalyst particles occurring during non-degradable organic matter decomposition can be almost completely avoided, and thus, the performance of non-degradable organic matter decomposition can be maintained even after multiple uses of the catalyst, and the catalyst lifetime can be improved.

[0096] It should be understood that the effects of the present invention are not limited to the above-described effects and include all effects that may be inferred from the features of the invention described in the detailed description or claims of the present invention.

[0097] The above description of the present invention is for illustrative purposes, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single component may be implemented in a distributed manner, and likewise, components described as distributed may be implemented in a combined form.

[0098] The scope of the present invention is indicated by the claims set forth below, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.