CoFe.SUB.2.O.SUB.4.-WTRs composite magnetic catalyst, preparation method and application thereof

Abstract

The present invention discloses a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst for efficiently degrading atrazine by activating peroxymonosulfate, preparation method and application thereof. The CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst is prepared by three steps: the first step is acid-leaching of WTRs, using the WTRs as iron source to provide the iron ions required for the synthesis of CoFe.sub.2O.sub.4; the second step is preparing of a precursor, synthesizing CoFe.sub.2O.sub.4 by chemical co-precipitation method and uniformly loading the prepared CoFe.sub.2O.sub.4 on the WTRs; and the third step is calcining the precursor to synthesize the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst. The catalytic performance of the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst prepared by the present invention is evaluated using PMS as an oxidant and atrazine as a target pollutant. The CoFe.sub.2O.sub.4-WTRs can efficiently remove atrazine from the actual water, exhibiting good potential for practical application.

Claims

1. A method for preparing a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst, comprising the following steps: the first step of acid leaching WTRs (drinking water treatment residuals): drying, crushing and sieving WTRs which is a byproduct of a water supply plant to obtain a WTRS raw material; weighing 10 g of the WTRs raw material and evenly dispersing the WTRs in 150 mL of ultrapure water to form a suspension; adjusting a pH of the suspension to 3 by dropwise adding a HCl solution, and magnetically stirring for 24 h to fully leach irons from the suspension into the HCl solution to obtain a first solution; wherein an iron content of the WTRs after acid leaching is 90.52 mg/g, and an iron leached percentage by weight after acid leaching is 95.3%; the second step of preparing a precursor by chemical co-precipitation method: adding a predetermined dose of cobalt nitrate hexahydrate to the first solution to obtain a mixed solution with a predetermined Co/Fe stoichiometric ratio, and adding NaOH solution dropwise to the mixed solution under vigorous stirring to adjust a pH of the mixed solution to 11.5; then, placing the mixed solution with the pH of 11.5 in a water bath to perform a reaction to obtain a solid precipitate, and centrifuging the solid precipitate, then filtrating, and drying at 105° C. to reach a constant weight to obtain the precursor; and the third step of preparing a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst by calcining the precursor: weighing a predetermined amount of the precursor obtained in the second step, and putting the precursor into a ceramic boat, then putting the ceramic boat into a tube furnace, introducing nitrogen gas at a rate of 150 mL.Math.min.sup.−1 to ensure an inert atmosphere; after 30 min, using the tube furnace to perform a calcination; during the calcination, a temperature is raised from room temperature to a target temperature at a heating rate; and cooling the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst obtained by the calcination, then taking out, grinding and passing the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst through a 100-mesh sieve, and bottling for use.

2. The method according to claim 1, wherein in the second step, the predetermined dose of the cobalt nitrate hexahydrate added is 2.24 g, and the predetermined Co/Fe stoichiometric ratio is 1/2.

3. The method according to claim 1, wherein in the second step, the reaction is carried out in a water bath at 65° C. for 30 min.

4. The method according to claim 1, wherein during the calcination of the third step, the heating rate is 10° C..Math.min.sup.−1, the target temperature is 600° C., a retention time is 2 h, and the nitrogen gas is continuously introduced during the calcination to maintain g reducing atmosphere.

5. A method for degrading atrazine in ultrapure water by activating peroxymonosulfate (PMS) using the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst according to claim 1, comprising the following step: using ultrapure water to prepare 200 mL of 10 μM atrazine solution, adding a solution of PMS (peroxymonosulfate) with a set concentration, and adding a H.sub.2SO.sub.4 solution or a NaOH solution to adjust a pH to 3.15-10.15 to obtain a second solution; then, adding the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst with a set dose to the second solution; wherein, a concentration of the solution of the PMS is 0.15-0.30 mM, and an additive amount of the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst is 0.002-0.008 g; subsequently, stirring the second solution using a magnetic stirrer, and during the stirring, a reaction time is 20 min, a reaction temperature is room temperature, and a reaction atmosphere is air.

6. A method for degrading atrazine in actual water by activating peroxymonosulfate (PMS) using the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst according to claim 1, comprising the following step: preparing 200 mL of 10 μM atrazine solution by using actual water, wherein the actual water is selected from the group consisting of ultrapure water, tap-water, surface water and underground water; adding a solution of PMS with a set concentration to the 200 mL of 10 μM atrazine solution to obtain a second solution, and adding H.sub.2SO.sub.4 to adjust a pH value of the second atrazine solution to 4.01: then, adding the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst to the second atrazine solution with the pH value of 4.01 to obtain a third solution; subsequently, stirring the third solution using magnetic stirrers, and during the stirring, a reaction time is 120 min, a reaction temperature is room temperature, and a reaction atmosphere is air.

7. The method according to claim 5, wherein a 0.25 mM solution of the PMS and 0.006 g of the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst are added to the 200 mL of 10 μM atrazine solution prepared by using the ultrapure water.

8. The method according to claim 5, wherein 10-40 mg.Math.L.sup.−1 chloride ions exist in the 200 mL of 10 μM atrazine solution.

9. The method according to claim 6, wherein a 0.25 mM solution of the PMS is added to the 200 mL 10 μM atrazine solutions prepared using the actual water, and then 0.006 g of the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst is added.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an x-ray diffraction (XRD) spectrum of a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst.

(2) FIG. 2A is a scanning electron microscope spectrum of a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst at magnification of 100 k.

(3) FIG. 2B is a scanning electron microscope spectrum of a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst at magnification of 200 k.

(4) FIG. 2C is a transmission electron microscope spectrum of a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst at magnification of 10000×.

(5) FIG. 2D is a transmission electron microscope spectrum of a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst at magnification of 25000×.

(6) FIG. 3 is a diagram showing a magnetization curve of a CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst.

(7) FIG. 4 is a diagram showing degradation curves of atrazine by activating PMS using composite magnetic catalysts with different Co/Fe stoichiometric ratios.

(8) FIG. 5 is a diagram showing degradation curves of atrazine in a CoFe.sub.2O.sub.4-WTRs/PMS system under different initial pH values.

(9) FIG. 6 is a diagram showing degradation curves of atrazine in a CoFe.sub.2O.sub.4-WTRs/PMS system under different concentrations of chlorine ions.

(10) FIG. 7 is a diagram showing degradation efficiency of atrazine in real water in a CoFe.sub.2O.sub.4-WTRs/PMS system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) The following Embodiments are intended to further illustrate the present invention, but shall not be construed as limitations to the present invention. Modifications and substitutions of the methods, steps or conditions of the present invention without departing from the spirit and essence of the present invention should be considered as falling within the scope of the present invention. The technical means used in the embodiments are conventional means well known to those skilled in the art unless otherwise specified.

(12) Preparation and Characterization of CoFe.sub.2O.sub.4-WTRs Composite Magnetic Catalyst

(13) The first step: acid leaching of WTRs: WTRs, a by-product from a water supply plant in Beijing, is naturally dried, crushed, sieved and then used as a raw material. 10 g of WTRs is weighed and evenly dispersed in 150 mL of ultrapure water. The pH of the suspension is adjusted to 3 by dropwise adding HCl solution, and magnetically stirring is performed for 24 h to fully leach the iron from WTRs into the HC solution (The iron leaching percentage is 95.3%, that is, the iron content in the leachate is 0.863 g).

(14) The second step: preparation of the precursor by chemical co-precipitation method: 2.24 g of cobalt nitrate hexahydrate is added to the above HCl solution to obtain a mixed solution with a Co/Fe stoichiometric ratio of 1/2, and NaOH solution is added dropwise to the above mixed solution under vigorous stirring until a pH of 11.5 is achieved. Then, the above mixed solution is placed in a water bath to react at 65° C. for 30 min, and the obtained solid precipitate is centrifuged, filtrated, and then dried at 105° C. to reach a constant weight.

(15) The third step: preparation of CoFe.sub.2O.sub.4-WTRs composite material by calcining the precursor: an appropriate amount of the precursor obtained in the second step is weighed, and put into a ceramic boat, then the ceramic boat is put into a tube furnace, nitrogen gas (150 mL.Math.min.sup.−1) is introduced to ensure the inert atmosphere. After 30 min, the tube furnace is started, and the temperature is raised from room temperature to a target temperature of 600° C. at a heating rate of 10° C. min.sup.−1. The retention time is 2 h, and a continuous introduction of nitrogen gas is ensured during the calcination process. The CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst obtained by calcination is taken out after being cooled, then ground, and passed through a 100-mesh sieve to be bottled for use. The characterization results of the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst are shown in FIGS. 1, 2 and 3.

(16) As shown in FIG. 1, the CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst synthesized by method of acid leaching, chemical co-precipitation combined with calcination has distinct characteristic peaks of spinel cobalt ferrite, with high peak intensity and sharp peak shape, indicating the synthesized CoFe.sub.2O.sub.4 has a high crystallinity. In addition, the characteristic peak of graphite carbon is also observed in the XRD spectrum of CoFe.sub.2O.sub.4-WTRs, indicating that the organic matters contained in WTRs are carbonized during the calcination process. FIGS. 2A-2D show that the spinel cobalt ferrite has an irregular cubic structure and well distributed on WTRs without obvious aggregation. FIG. 3 shows that the saturation magnetization of the composite material is 36.4 emu.Math.g.sup.−1, and the inset shows that the CoFe.sub.2O.sub.4-WTRs composite material is easily separated from the aqueous solution by an external magnetic field, exhibiting excellent magnetic separation characteristics.

(17) Degradation of Atrazine by Activating Peroxymonosulfate (PMS) Using the CoFe.sub.2O.sub.4-WTRs Composite Magnetic Catalyst

Embodiment 1

(18) The first step: acid leaching of WTRs: WTRs, a by-product from a water supply plant in Beijing, is naturally dried, crushed, sieved and then used as a raw material. 10 g of WTRs is weighed and evenly dispersed in 150 mL of ultrapure water. The pH of the suspension is adjusted to 3 by dropwise adding HCl solution, and magnetically stirring is performed for 24 h to fully leach the iron from WTRs into the HCl solution.

(19) The second step: preparation of the precursor by chemical co-precipitation method: 2.24 g of cobalt nitrate hexahydrate is added to the above HCl solution to obtain a mixed solution with a Co/Fe stoichiometric ratio of 1/2, and NaOH solution is added dropwise to the above mixed solution under vigorous stirring until a pH of 11.5 is achieved. Then, the above mixed solution is placed in a water bath to react at 65° C. for 30 min, and the obtained solid precipitate is centrifuged, filtrated, and then dried at 105° C. to reach a constant weight.

(20) The third step: preparation of CoFe.sub.2O.sub.4-WTRs composite material by calcining the precursor: an appropriate amount of the precursor obtained in the second step is weighed, and put into a ceramic boat, then the ceramic boat is put into a tube furnace, nitrogen gas (150 mL.Math.min.sup.−1) is introduced to ensure the inert atmosphere. After 30 min, the tube furnace is started, and the temperature is raised from room temperature to a target temperature of 600° C. at a heating rate of 10° C..Math.min.sup.−1. The retention time is 2 h, and a continuous introduction of nitrogen gas is ensured during the calcination process. The CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst obtained by calcination is taken out after being cooled, then ground, and passed through a 100-mesh sieve to be bottled for use.

(21) The fourth step: 200 mL of 10 μM atrazine solution is prepared by ultrapure water, and 0.25 mM PMS solution is added into a 250 mL conical flask on a magnetic stirrer, and then the initial pH of the solution is adjusted to 4.01. 0.006 g of the composite magnetic catalyst is quickly added to initiate the degradation reaction. The reaction time is 20 min, the reaction temperature is room temperature, and the reaction atmosphere is air. 1.8 mL of atrazine supernatant is withdrawn at 2 min, 4 min, 6 min, 8 min, 10 min, 15 min and 20 min, respectively, filtrated with 0.22 μm syringe filters, and immediately quenched with 50 μL EtOH. Then, the concentration of atrazine is determined by high performance liquid chromatography to calculate the atrazine degradation efficiency. The experimental results are shown in FIG. 4.

Embodiment 2

(22) Except that in the second step, 1.49 g of cobalt nitrate hexahydrate is added to obtain a mixed solution with the Co/Fe stoichiometric ratio of 0.75/2.25, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 4.

Embodiment 3

(23) Except that in the second step, 0.90 g of cobalt nitrate hexahydrate is added to obtain a mixed solution with the Co/Fe stoichiometric ratio of 0.5/2.5, the other steps are the same as in that Embodiment 1. The experimental results are shown in FIG. 4.

Embodiment 4

(24) Except that in the second step, 0.41 g of cobalt nitrate hexahydrate is added to obtain a mixed solution with the Co/Fe stoichiometric ratio to be 0.25/2.75, the other steps are the same as in that Embodiment 1. The experimental results are shown in FIG. 4.

(25) As shown in FIG. 4, the composite magnetic catalysts with different Co/Fe stoichiometric ratios have the potential to activate PMS to degrade atrazine. The degradation efficiency of atrazine gradually increases with the increase of the Co/Fe stoichiometric ratio, among which CoFe.sub.2O.sub.4-WTRs possessed the best catalytic reactivity towards PMS and highest atrazine degradation efficiency.

Embodiment 5

(26) Except that in the fourth step, the initial pH of the solution is adjusted to 3.15, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 5.

Embodiment 6

(27) Except that in the fourth step, the initial pH of the solution is adjusted to 4.76, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 5.

Embodiment 7

(28) Except that in the fourth step, the initial pH of the solution is adjusted to 6.85, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 5.

Embodiment 8

(29) Except that in the fourth step, the initial pH of the solution is adjusted to 10.12, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 5.

(30) As shown in FIG. 5, the degradation efficiency of atrazine is significantly affected by the initial solution pH. Highest degradation efficiency is achieved when the initial solution pH is 4.01, with atrazine being almost completely degraded within 20 min. However, superacid, neutral and alkaline conditions are not conducive to the degradation of atrazine.

Embodiment 9

(31) Except that in the fourth step, 10 mg.Math.L.sup.−1 of chloride ions are additionally added to the 250 mL conical flask, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 6.

Embodiment 10

(32) Except that in the fourth step, 20 mg.Math.L.sup.−1 of chloride ions are additionally introduced to the 250 mL conical flask, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 6.

Embodiment 11

(33) Except that in the fourth step, 30 mg.Math.L.sup.−1 of chloride ions are additionally introduced to the 250 mL conical flask, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 6.

Embodiment 12

(34) Except that in the fourth step, 40 mg.Math.L.sup.−1 of chloride ions are additionally introduced to the 250 mL conical flask, the other steps are the same as that in Embodiment 1. The experimental results are shown in FIG. 6.

(35) As shown in FIG. 6, chloride ions inhibited the degradation of atrazine, but the negative effect does not obviously increase with the increase of the concentration of the chloride ions, indicating that the CoFe.sub.2O.sub.4-WTRs/PMS system can maintain good catalytic performance even in the presence of high concentration of chloride ions.

Embodiment 13

(36) The first step: acid leaching of WTRs: WTRs, a by-product from a water supply plant in Beijing, is naturally dried, crushed, sieved and then used as a raw material. 10 g of WTRs is weighed and evenly dispersed in 150 mL of ultrapure water. The pH of the suspension is adjusted to 3 by dropwise adding HCl solution, and magnetically stirring is performed for 24 h to fully leach the iron from WTRs into the HC solution.

(37) The second step: preparation of the precursor by chemical co-precipitation method: 2.24 g of cobalt nitrate hexahydrate is added to the above HCl solution to obtain a mixed solution with a Co/Fe stoichiometric ratio of 1/2, and NaOH solution is added dropwise to the above mixed solution under vigorous stirring until a pH of 11.5 is achieved. Then, the above mixed solution is placed in a water bath to react at 65° C. for 30 min, and the obtained solid precipitate is centrifuged, filtrated, and then dried at 105° C. to reach a constant weight.

(38) The third step: preparation of CoFe.sub.2O.sub.4-WTRs composite material by calcining the precursor: an appropriate amount of the precursor obtained in the second step is weighed, and put into a ceramic boat, then the ceramic boat is put into a tube furnace, nitrogen gas (150 mL min.sup.−1) is introduced to ensure the inert atmosphere. After 30 min, the tube furnace is started, and the temperature is raised from room temperature to a target temperature of 600° C. at a heating rate of 10° C..Math.min.sup.−1. The retention time is 2 h, and a continuous introduction of nitrogen gas is ensured during the calcination process. The CoFe.sub.2O.sub.4-WTRs composite magnetic catalyst obtained by calcination is taken out after being cooled, then ground, and passed through a 100-mesh sieve to be bottled for use.

(39) The fourth step: 11 0.006 g of the composite magnetic catalyst is quickly added to initiate the degradation reaction. The reaction time is 20 min, the reaction temperature is room temperature, and the reaction atmosphere is air. 1.8 mL of atrazine supernatant is withdrawn at 2 min, 4 min, 6 min, 8 min, 10 min, 15 min and 20 min, respectively, filtrated with 0.22 μm syringe filters, and immediately quenched with 50 μL EtOH. Then, the concentration of atrazine is determined by high performance liquid chromatography to calculate the atrazine degradation efficiency. The experimental results are shown in FIG. 7.

Embodiment 14

(40) Except that in the fourth step, 200 mL of 10 μM atrazine solution prepared by tap-water is added into a 250 mL conical flask, the other steps are the same as that in Embodiment 13. The experimental results are shown in FIG. 7.

Embodiment 15

(41) Except that in the fourth step, 200 mL of 10 μM atrazine solution prepared by surface water is added into a 250 mL conical flask, the other steps are the same as that in Embodiment 13. The experimental results are shown in FIG. 7.

Embodiment 16

(42) Except that in the fourth step, 200 mL of 10 μM atrazine solution prepared by underground water is added into a 250 mL conical flask, the other steps are the same as that in Embodiment 13. The experimental results are shown in FIG. 7.

(43) As shown in FIG. 7, except that the degradation efficiency of atrazine in the tap-water is 68.7%, the atrazine in ultrapure water, surface water and underground water can be almost completely degraded, indicating that the CoFe.sub.2O.sub.4-WTRs/PMS system has good practical application potential.