Treatment method of high-salt dye wastewater

Abstract

The invention discloses a high-salt dye wastewater treatment method which comprises the following steps: a, mixing a cerium oxide loaded transition metal monatomic catalyst M-CeO2 with high-salt dye wastewater, and stirring in a dark place until adsorption equilibrium to obtain a mixed solution; and b, adding an oxidizing agent persulfate into the mixed solution, and reacting to obtain the treated wastewater. According to the treatment method of the high-salt dye wastewater, the high-salt dye wastewater is activated and degraded by catalyzing the persulfate through the cerium oxide loaded transition metal monatomic active site, the degradation efficiency is high, the tolerance to inorganic salt is good, the pH application range is wide, the equipment corrosion is small, the process is simple, and the cost is low; the method is a rapid, efficient, simple and convenient method for treating the high-salt dye wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to a method for treating high-salt dye wastewater. Background Art

[0002] Wastewater with a total dissolved inorganic salt content (TDS) greater than 1% is collectively referred to as high-salt organic wastewater, and its generation methods are very broad. The wastewater not only contains a large amount of high-concentration organic pollutants, but also a large amount of Na + , K + , Ca 2+ , SO4 2- , Cl - and the presence of other ions. As a product of modern industry, high-salt organic wastewater mostly comes from oil exploitation, food processing, printing and dyeing, pharmaceutical, chemical and other industries. Among them, the printing and dyeing industry discharges the most high-salt wastewater. With the development of the dye production and printing and dyeing industries, the discharge of dye industrial wastewater has also increased sharply. In China, about 160 million cubic meters of dye wastewater is discharged into the water environment every year, accounting for 35% of the total industrial wastewater discharge. Dye wastewater has the characteristics of high salinity, high chroma, high content of organic pollutants, complex components, large changes in water quality, high biological toxicity, and difficult biodegradation, and it is developing in the direction of anti-photolysis and anti-oxidation, which further increases the difficulty of treating dye wastewater. Dye wastewater contains a large amount of organic pollutants. Discharging it into water bodies will consume dissolved oxygen, destroy the water ecological balance, and endanger the survival of fish and other aquatic organisms. The organic matter sinking to the bottom will produce harmful gases such as hydrogen sulfide due to anaerobic decomposition, deteriorating the environment. High-salt dye wastewater has become one of the difficult-to-treat industrial wastewaters at home and abroad.

[0003] At present, the treatment technologies for high-salt dye wastewater mainly include adsorption, membrane separation, flocculation, advanced oxidation technology and biodegradation and other methods. However, the adsorption method has a high cost and it is difficult to reuse the adsorbent; the membrane separation technology has high investment and operating costs, and the membrane needs to be cleaned and replaced regularly; the Fenton oxidation method has a high operating cost and may require subsequent treatment to remove the generated intermediate products; the biological method has limited removal effect on high-salt dye wastewater, and it is easy to produce malodor and the treatment cycle is long. Compared with the above methods, the sulfate radical generated by the persulfate (PMS or PDS) oxidation method has the advantages of high oxidation potential, strong oxidation ability, long half-life, wide pH application range, good tolerance to coexisting inorganic salts, etc. At the same time, persulfate also has the advantages of safe and convenient storage and transportation and low price. Therefore, the oxidation technology based on the catalytic activation of persulfate is particularly suitable for the treatment of high-salt dye wastewater.

[0004] At present, the catalytic materials for activating catalytic persulfate are mainly supported transition metal catalysts. By loading transition metal or transition metal oxide nanoparticles onto a high specific surface area support, active sites are generated at the edges, corners, surfaces, steps, defects, etc. of the transition metal nanoparticles to catalyze the activation of persulfate. However, only a few special sites in the transition metal nanoparticles loaded on the support surface have catalytic activity, resulting in a large amount of transition metal loading and low utilization rate; in addition, it is difficult to control the size and morphology of the nanoparticles during the synthesis of the catalyst, resulting in poor selectivity of the catalyst. Therefore, the development of efficient and low-cost persulfate catalytic materials is of great significance for the treatment of high-salt dye wastewater. Summary of the Invention

[0005] The present invention is based on the inventor's discovery and recognition of the following facts and problems: At present, transition metal catalysts have the disadvantages of large transition metal loading, low utilization rate, easy loss of transition metals, and poor reaction selectivity during the process of catalytically activating persulfate to degrade high-salt dye wastewater. Therefore, it is necessary to conduct in-depth research on the activation of persulfate by catalysts to degrade high-salt dye wastewater.

[0006] The present invention aims to solve at least one of the technical problems in the related art to some extent. To this end, an embodiment of the present invention provides a method for treating high-salt dye wastewater, which uses a transition metal single-atom active site supported on cerium oxide to catalyze the activation of persulfate to degrade high-salt dye wastewater. It has high degradation efficiency, good tolerance to inorganic salts, a wide pH application range, small equipment corrosion, a simple process, and low cost. It is a fast, efficient, and simple method for treating high-salt dye wastewater.

[0007] The method for treating high-salt dye wastewater according to the embodiment of the present invention includes the following steps:

[0008] a. Mix the cerium oxide-supported transition metal single-atom catalyst M-CeO2 with high-salt dye wastewater, and stir in the dark until adsorption equilibrium is reached to obtain a mixed solution;

[0009] b. Add the oxidant persulfate to the mixed solution and react to obtain the treated wastewater.

[0010] Advantages and technical effects brought by the treatment method of high-salt dye wastewater in the embodiments of the present invention: In the method of the embodiments of the present invention, a cerium oxide-supported transition metal single-atom catalyst is used to catalytically activate persulfate. Compared with traditional supported transition metal nanocatalysts, in the single-atom catalyst, transition metal atoms form an atomically dispersed active site structure by coordinating with O atoms on the surface of the catalyst support. Since the surface transition metal single-atom sites are in a coordinatively unsaturated state, they have a strong binding ability to persulfate and dye molecules, showing higher intrinsic activity. At the same time, due to the interaction between transition metal atoms and O atoms on the surface of the support through coordination bonds, the aggregation and loss of transition metal atoms are effectively inhibited, the stability of the transition metal single-atom catalyst is improved, and the stability of the treatment effect on high-salt dye wastewater is improved.

[0011] In some embodiments, in the step a, the cerium oxide-supported transition metal single-atom catalyst M-CeO2 includes at least one of a cerium oxide-supported single-atom Fe catalyst Fe-CeO2, a cerium oxide-supported single-atom Co catalyst Co-CeO2, a cerium oxide-supported single-atom Ni catalyst Ni-CeO2, a cerium oxide-supported single-atom Mn catalyst Mn-CeO2, a cerium oxide-supported single-atom Cu catalyst Cu-CeO2, and a cerium oxide-supported single-atom Zn catalyst Zn-CeO2.

[0012] In some embodiments, in the step a, the transition metal element in the catalyst is 0.2-3% of the mass of the CeO2 support.

[0013] In some embodiments, the preparation method of the cerium oxide-supported transition metal single-atom catalyst M-CeO2 includes the following steps:

[0014] (1). Add the CeO2 support to the transition metal salt solution, mix and then evaporate the solvent to obtain a solid powder;

[0015] (2). Perform a first calcination treatment on the solid powder obtained in the step (1), the temperature of the first calcination treatment is lower than the decomposition temperature of the soluble metal salt, and after washing, filtering, and drying, a first calcination product is obtained;

[0016] (3). Perform a second calcination treatment on the first calcination product obtained in the step (2) to obtain a cerium oxide-supported metal single-atom catalyst.

[0017] In some embodiments, in the step (1), the transition metal salt includes at least one of chlorides, sulfates, nitrates, acetates, and oxalates of Fe, Co, Ni, Mn, Cu, and Zn; and / or, the transition metal salt solution includes at least one of an aqueous solution, a methanol solution, an ethanol solution, an isopropanol solution, an acetone solution, a DMF solution, and a pyrrolidone solution of the transition metal salt.

[0018] In some embodiments, in the step (1), the mass ratio of the metal element in the transition metal salt solution to the CeO2 support is 1:100 to 10:100.

[0019] In some embodiments, in the step (2), the temperature of the first calcination treatment is higher than the melting point of the soluble metal salt.

[0020] In some embodiments, in the step (2), the temperature of the first calcination treatment is 200 - 600 °C, and the calcination time is 1 - 5 h.

[0021] In some embodiments, in the step (2), the washing liquid used for washing includes at least one of water, methanol, ethanol, isopropanol, acetone, DMF, and pyrrolidone.

[0022] In some embodiments, in the step (3), the temperature of the second calcination treatment is 200 - 900 °C, and the calcination time is 2 - 12 h.

[0023] In some embodiments, in the high-salt dye wastewater, the salt includes at least one of sulfates, chlorides, nitrates, carbonates, phosphates, monohydrogen phosphates, and dihydrogen phosphates, and the salt concentration is 10 - 500 mg·L -1 。

[0024] In some embodiments, in the high-salt dye wastewater, the dye includes at least one of rhodamine B, methyl orange, methylene blue, bromocresol purple, and congo red, and the dye concentration is 0.01 - 100 mg·L -1 。

[0025] In some embodiments, the oxidant persulfate includes at least one of monopersulfate and dipersulfate.

[0026] In some embodiments, in the step a, in the mixed solution, the concentration of the cerium oxide-supported transition metal single-atom catalyst M-CeO2 is 0.01 - 500 mg·L -1 。 Description of the Drawings

[0027] Figure 1 is the aberration-corrected transmission electron microscopy image of the catalyst in Example 2.

[0028] Figure 2 It is the energy spectrum surface scan diagram of the catalyst in Example 2.

[0029] Figure 3 It is the change curve of the concentration of Rhodamine B in the high-salt dye wastewater containing sodium sulfate with the reaction time in Example 2. Specific Embodiments

[0030] The embodiments of the present invention will be described in detail below. The examples are shown in the accompanying drawings. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0031] The method for treating high-salt dye wastewater in the embodiments of the present invention includes the following steps:

[0032] a. Mix the cerium oxide supported transition metal single-atom catalyst M-CeO2 with the high-salt dye wastewater, and stir in the dark until adsorption equilibrium to obtain a mixed solution;

[0033] b. Add the oxidant persulfate to the mixed solution and react to obtain the treated wastewater.

[0034] In the method for treating high-salt dye wastewater in the embodiments of the present invention, the cerium oxide supported transition metal single-atom catalyst is used to catalytically activate persulfate. Compared with the traditional supported transition metal nanocatalyst, the transition metal atoms in the single-atom catalyst form an atomically dispersed active site structure by coordinating with atoms such as C, N, O, P, S on the surface of the catalyst support. Since the surface transition metal single-atom sites are in a coordinatively unsaturated state, they have a strong binding ability to persulfate and dye molecules, showing higher intrinsic activity. At the same time, due to the interaction of the transition metal atoms with atoms such as C, N, O, P, S on the surface of the support through coordination bonds, the agglomeration and loss of the transition metal atoms are effectively inhibited, the stability of the transition metal single-atom catalyst is improved, and the stability of the treatment effect on high-salt dye wastewater is improved.

[0035] In some embodiments, in the step a, the cerium oxide supported transition metal single-atom catalyst M-CeO2 includes at least one of the cerium oxide supported single-atom Fe catalyst Fe-CeO2, the cerium oxide supported single-atom Co catalyst Co-CeO2, the cerium oxide supported single-atom Ni catalyst Ni-CeO2, the cerium oxide supported single-atom Mn catalyst Mn-CeO2, the cerium oxide supported single-atom Cu catalyst Cu-CeO2, and the cerium oxide supported single-atom Zn catalyst Zn-CeO2.

[0036] In some embodiments, in the step a, the transition metal element in the catalyst is 0.2-3% of the mass of the CeO2 support.

[0037] In some embodiments, the method for preparing the cerium oxide supported transition metal single-atom catalyst M-CeO2 comprises the following steps:

[0038] (1) Adding a CeO2 support to a transition metal salt solution, mixing and then evaporating the solvent to obtain a solid powder;

[0039] (2) Performing a first calcination treatment on the solid powder obtained in step (1), where the temperature of the first calcination treatment is lower than the decomposition temperature of the soluble metal salt, and after washing, filtering, and drying, a first calcination product is obtained;

[0040] (3) Performing a second calcination treatment on the first calcination product obtained in step (2), where the temperature of the second calcination treatment is higher than that of the first calcination treatment, to obtain a cerium oxide supported metal single-atom catalyst.

[0041] In the method for preparing the catalyst according to the embodiments of the present invention, cerium oxide is used as the catalyst support. O vacancies and Ce vacancies are easily formed on the surface of the cerium oxide support. These vacancies can be used as riveting sites for metal ions. After high-temperature calcination, metal ions are firmly adsorbed on the surface of the CeO2 support, playing a role in stabilizing metal atoms and inhibiting the migration and aggregation of metal atoms, and enabling single-atom loading of metal elements on the CeO2 support. In the method of the embodiments of the present invention, a "two-step calcination method" is adopted, that is, first, the metal salt precursor physically adsorbed on the surface of the CeO2 support is subjected to a first calcination treatment at a lower temperature to promote the reaction of metal ions with O on the surface layer of the CeO2 support to form M-O bonds, playing a role in stabilizing metal atoms and inhibiting the migration and aggregation of metal atoms; then, the metal precursor that has not formed stable M-O bonds is removed by washing; finally, the residual coordination atoms in the metal precursor are removed by a second calcination treatment at a higher temperature to obtain a CeO2 supported metal single-atom catalyst. In the embodiments of the present invention, CeO2 is used as the support, which is a relatively stable metal oxide support. Compared with carbon-based supports, it has better tolerance to the attack of highly active oxidation species in-situ generated during the activation process of persulfate, thus avoiding the oxidation and damage of the catalyst support during the reaction process, improving the stability of the catalyst and the selectivity for the degradation of organic pollutants in organic wastewater, and further improving the utilization efficiency of persulfate.

[0042] In some embodiments, in step (1), the transition metal salt includes at least one of chlorides, sulfates, nitrates, acetates, and oxalates of Fe, Co, Ni, Mn, Cu, and Zn; and / or, the transition metal salt solution includes at least one of an aqueous solution, methanol solution, ethanol solution, isopropanol solution, acetone solution, DMF solution, and pyrrolidone solution of the transition metal salt.

[0043] In some embodiments, in the step (1), the mass ratio of the metal element in the transition metal salt solution to the CeO2 support is 1:100 to 10:100. In the embodiments of the present invention, the ratio of the metal element in the transition metal salt solution to the CeO2 support is further preferably selected, which is beneficial to adsorbing a sufficient amount of metal elements on the surface of the support, increasing the loading amount of metal single atoms in the catalyst, and improving the activity of the catalyst.

[0044] In some embodiments, in the step (2), the temperature of the first calcination treatment is higher than the melting point of the soluble metal salt. In the embodiments of the present invention, it is preferred that the temperature of the first calcination treatment is higher than the melting point of the soluble metal salt, which is beneficial to promoting the formation of M-O bonds and reducing the amount of the soluble metal salt used. However, the temperature of the first calcination treatment should be controlled below the decomposition temperature of the soluble metal salt to avoid the decomposition of the metal salt and the generation of nanoparticles. When the melting point of the soluble metal salt used is lower than the decomposition temperature, the preferred temperature of the first calcination treatment is higher than the melting point of the soluble metal salt and lower than the decomposition temperature of the soluble metal salt. When the melting point of the soluble metal salt is higher than the decomposition temperature, the temperature of the first calcination treatment needs to be controlled below the decomposition temperature of the soluble metal salt.

[0045] In some embodiments, the temperature of the first calcination treatment is 200 - 600 °C, and the calcination time is 1 - 5 h. In the embodiments of the present invention, the process conditions of the first calcination treatment are preferably selected, which is beneficial to promoting the reaction of metal ions with O on the surface layer of the CeO2 support to form M-O bonds, effectively stabilizing metal atoms, and inhibiting the migration and aggregation of metal atoms. If the calcination temperature is too low, it will be unfavorable for the formation of M-O bonds. If the calcination temperature is too high, it will cause the decomposition of the metal salt precursor and the generation of nanoparticles, which is unfavorable for the formation of M-O bonds. If the calcination time is too short, the amount of metal forming M-O bonds is too small, resulting in too low a loading amount. If the calcination time is too long, the already formed M-O bonds will be further oxidized to generate nanoparticles, reducing the loading amount of single-atom sites.

[0046] In some embodiments, in the step (2), the washing liquid used for washing includes at least one of water, methanol, ethanol, isopropanol, acetone, DMF, and pyrrolidone. In the embodiments of the present invention, after the first calcination treatment, the metal precursor that has not formed stable M-O bonds is removed by washing.

[0047] In some embodiments, in the step (3), the temperature of the second calcination treatment is 200 - 900 °C, and the calcination time is 2 - 12 h. In the embodiments of the present invention, the process conditions of the second calcination treatment are optimized, which is beneficial to removing the residual coordination atoms in the metal precursor on the catalyst to obtain a metal single-atom catalyst. If the calcination temperature is too low, it will be unfavorable for the removal of residual coordination atoms, resulting in a decrease in catalyst activity. If the calcination temperature is too high, the formed M - O bonds will break, causing the metal atoms to migrate and agglomerate on the surface of the support to form nanoparticles, destroying the single-atom structure and reducing the single-atom loading. If the calcination time is too short, it is not conducive to the complete removal of the residual coordination atoms of the metal salt precursor, resulting in a decrease in catalyst activity. If the calcination time is too long, the formed M - O bonds will be further oxidized to generate nanoparticles, reducing the single-atom site loading.

[0048] In some embodiments, in the high-salt dye wastewater, the salt includes at least one of sulfates, chlorides, nitrates, carbonates, phosphates, monohydrogen phosphates, and dihydrogen phosphates, and the salt concentration is 10 - 500 mg·L -1 。

[0049] In some embodiments, in the high-salt dye wastewater, the dye includes at least one of rhodamine B, methyl orange, methylene blue, bromocresol purple, and congo red, and the dye concentration is 0.01 - 100 mg·L -1 。

[0050] In some embodiments, the oxidant persulfate includes at least one of monopersulfate and dipersulfate.

[0051] In some embodiments, in the step a, in the mixed solution, the concentration of the cerium oxide-supported transition metal single-atom catalyst M - CeO₂ is 0.01 - 500 mg·L -1 。In the embodiments of the present invention, the catalyst used has high catalytic activity for persulfate, effectively reducing the dosage of the catalyst in the high-salt dye wastewater.

[0052] The present invention will be described in detail below with reference to examples and drawings.

[0053] Example 1

[0054] I. Preparation of Fe - CeO₂ single-atom catalyst

[0055] Mix 0.4 g of ferric chloride with 15 mL of methanol and stir for 30 min. After the ferric chloride is completely dissolved, a methanol solution of ferric chloride is obtained. Add 2 g of CeO₂ support to the solution and ultrasonically disperse for 10 min. Transfer the above suspension into a round-bottom flask, evaporate the methanol solvent using a rotary evaporator, and place the remaining solid powder in an oven at 80 °C for drying for 12 h to obtain a solid powder.

[0056] Put the dried solid powder into a muffle furnace and first heat it at 2 °C / min -1 to 280 °C and maintain for 2 h for the first calcination treatment; after natural cooling to room temperature, a sample is obtained. Transfer the sample into a beaker, add 200 mL of a methanol-water mixed solvent (the volume ratio of methanol to water is 15:1), stir at room temperature for 2 h; perform suction filtration and collect the filter cake; wash the filter cake successively with 200 mL of water, 200 mL of the methanol-water mixed solvent, and 200 mL of methanol; after suction drying, place it in an oven at 60 °C for drying for 12 h to obtain the first calcination product.

[0057] Put the first calcination product into a muffle furnace and heat it at 5 °C / min -1 to 600 °C and maintain for 3 h for the second calcination treatment; after natural cooling to room temperature, an Fe-CeO₂ single-atom catalyst is obtained. Using ICP-MS, it is measured that in the catalyst, the Fe element is 1.77 wt% of the mass of the CeO₂ support.

[0058] II. Treatment of high-salt dye wastewater

[0059] Add 10 mg of the prepared Fe-CeO₂ catalyst to a 250 mL conical flask, and add 200 mL of a high-salt rhodamine B mother liquor, where the concentration of sodium sulfate is 100 mg / L -1 , and the concentration of rhodamine B is 20 mg / L -1 . Stir in the dark for 40 min until adsorption equilibrium is reached; add peroxymonosulfate (PMS) to the above mixed system and start the reaction timing; use ultraviolet-visible absorption spectroscopy to detect the change rate of the rhodamine B concentration. The removal rate of rhodamine B after 10 min of reaction is 53%, as shown in Table 1 for details.

[0060] Example 2

[0061] I. Preparation of Co-CeO₂ single-atom catalyst

[0062] Mix 0.64 g of cobalt chloride with 80 mL of water and stir for 20 min. After the cobalt chloride is completely dissolved, an aqueous solution of cobalt chloride is obtained. Add 1.5 g of CeO₂ support to the solution and ultrasonically disperse for 50 min. Transfer the above suspension into a round-bottom flask, evaporate the solvent using a rotary evaporator, and place the remaining solid powder in an oven at 105 °C for drying for 8 h to obtain a solid powder.

[0063] Put the dried solid powder into a muffle furnace and heat it at 5 °C / min -1 to 300 °C, hold for 5 h, and conduct the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample to a beaker, add 200 mL of water, and stir at room temperature for 1.5 h; perform suction filtration to collect the filter cake; wash the filter cake successively with 100 mL of water, 100 mL of ethanol-water mixed solvent, and 100 mL of ethanol; after suction drying, place it in an oven at 110 °C and dry for 12 h to obtain the first calcined product.

[0064] Put the first calcined product into a tubular furnace, introduce nitrogen, and heat it at 1 °C / min -1 to 700 °C, hold for 12 h, and conduct the second calcination treatment; after natural cooling to room temperature, obtain the Co-CeO₂ single-atom catalyst. Using ICP-MS, it is measured that the Co element in the catalyst is 2.01 wt% of the mass of the CeO₂ support.

[0065] Figure 1 is the aberration-corrected scanning transmission electron microscopy image of the Co-CeO₂ single-atom catalyst prepared in this example. Figure 1 No nanoparticles or nanocluster structures are seen in it. Since the atomic number of Co is less than that of Ce, dark spots of atomically dispersed Co atoms are seen under the aberration-corrected scanning transmission electron microscope, proving that Co-CeO₂ is a single-atom catalyst.

[0066] Figure 2 is the energy-dispersive X-ray spectroscopy mapping image of the Co-CeO₂ single-atom catalyst prepared in this example. From Figure 2 it can be seen that the Co element is uniformly distributed on the CeO₂ support, and at the same time, no nanoparticles or nanoclusters are observed on the CeO₂ support, further proving that the Co element is atomically dispersed on the CeO₂ support, forming the Co-CeO₂ single-atom catalyst.

[0067] II. Treatment of high-salt dye wastewater

[0068] Add 10 mg of the Co-CeO₂ catalyst to a 250 mL conical flask, add 200 mL of the high-salt rhodamine B mother liquor, in which the concentration of sodium sulfate is 500 mg / L -1 , and the concentration of rhodamine B is 20 mg / L -1 , stir in the dark for 40 min until adsorption equilibrium; add peroxymonosulfate (PMS) to the above mixed system, start timing for the reaction; use ultraviolet-visible absorption spectroscopy to detect the change rate of the rhodamine B concentration. The removal rate of rhodamine B after 10 min of reaction is 96%, as shown in Table 1 for details.

[0069] Figure 3 is the degradation effect diagram of the Co-CeO₂ single-atom catalyst prepared in this example for degrading high-salt rhodamine B dye wastewater containing sodium sulfate. FromFigure 3 It can be seen that the Co-CeO2 / PMS system has significant degradation performance for high-salt dye wastewater. The removal rate of Rhodamine B exceeded 96% after 10 min of reaction.

[0070] Example 3

[0071] I. Preparation of Ni-CeO2 single-atom catalyst

[0072] Mix 0.48 g of nickel oxalate with 20 mL of ethanol and stir for 60 min; after the nickel oxalate is completely dissolved, an ethanol solution of nickel oxalate is obtained. Add 2 g of CeO2 support to the solution and ultrasonically disperse for 80 min. Transfer the above suspension into a round-bottom flask, evaporate the ethanol solvent using a rotary evaporator, and put the remaining solid powder into an oven at 100 °C for drying for 2 h to obtain solid powder.

[0073] Put the dried solid powder into a muffle furnace and heat it to 280 °C at a rate of 2 °C / min -1 and maintain for 2 h for the first calcination treatment; after natural cooling to room temperature, a sample is obtained. Transfer the sample into a beaker, add 150 mL of ethanol-water mixed solvent (the volume ratio of ethanol to water is 10:1), stir at room temperature for 3 h; filter by suction and collect the filter cake; wash the filter cake successively with 200 mL of water, 200 mL of ethanol-water mixed solvent, and 200 mL of ethanol; after suction drying, put it into an oven at 80 °C for drying for 12 h to obtain the first calcination product.

[0074] Put the first calcination product into a muffle furnace and heat it to 650 °C at a rate of 2 °C / min -1 and maintain for 4 h for the second calcination treatment; after natural cooling to room temperature, a Ni-CeO2 single-atom catalyst is obtained. By ICP-MS measurement, the Ni element in the catalyst is 1.56 wt% of the mass of the CeO2 support.

[0075] II. Treatment of high-salt dye wastewater

[0076] Add 10 mg of Ni-CeO2 catalyst to a 250 mL conical flask, add 200 mL of high-salt methyl orange mother liquor, where the concentration of sodium nitrate is 50 mg / L -1 , and the concentration of methyl orange is 20 mg / L -1 , stir in the dark for 40 min until adsorption equilibrium; add persulfate (PDS) to the above mixed system and start the reaction timing; use ultraviolet-visible absorption spectroscopy to detect the change rate of methyl orange concentration. The removal rate of methyl orange after 10 min of reaction is 55%, as shown in Table 1 for details.

[0077] Example 4

[0078] I. Preparation of Mn-CeO2 single-atom catalyst

[0079] Mix 0.5 g of manganese oxalate with 20 mL of DMF and stir for 40 min. After the manganese chloride is completely dissolved, a DMF solution of manganese chloride is obtained. Add 2.4 g of CeO2 support to the solution and ultrasonically disperse for 10 min. Transfer the above suspension into a round-bottom flask, evaporate the DMF solvent using a rotary evaporator, and place the remaining solid powder in an oven at 130 °C for drying for 10 h to obtain a solid powder.

[0080] Put the dried solid powder into a muffle furnace and raise the temperature to 200 °C at a rate of 1 °C / min -1 and maintain for 2 h for the first calcination treatment. After natural cooling to room temperature, a sample is obtained. Transfer the sample into a beaker, add 200 mL of a DMF-water mixed solvent (the volume ratio of DMF to water is 6:1), stir at room temperature for 12 h, filter by suction, and collect the filter cake. Wash the filter cake successively with 100 mL of DMF, 200 mL of the DMF-water mixed solvent, and 100 mL of water. After suction drying, place it in an oven at 130 °C for drying for 10 h to obtain the first calcination product.

[0081] Put the first calcination product into a muffle furnace and raise the temperature to 650 °C at a rate of 2 °C / min -1 and maintain for 5 h for the second calcination treatment. After natural cooling to room temperature, a Mn-CeO2 single-atom catalyst is obtained. By ICP-MS measurement, the Mn element in the catalyst is 1.93 wt% of the mass of the CeO2 support.

[0082] II. Treatment of high-salt dye wastewater

[0083] Add 10 mg of the Mn-CeO2 catalyst to a 250 mL conical flask, and add 200 mL of a high-salt methylene blue mother liquor, where the potassium nitrate concentration is 300 mg / L -1 and the methylene blue mother liquor concentration is 20 mg / L -1 . Stir in the dark for 40 min until adsorption equilibrium is reached. Add persulfate (PDS) to the above mixed system and start the reaction timing. Use ultraviolet-visible absorption spectroscopy to detect the change rate of the methylene blue concentration. The removal rate of methylene blue after 10 min of reaction is 68%, as shown in Table 1 for details.

[0084] Example 5

[0085] I. Preparation of Cu-CeO2 single-atom catalyst

[0086] Mix 0.3 g of copper acetate with 30 mL of pyrrolidone and stir for 20 min. After the copper acetate is completely dissolved, a pyrrolidone solution of copper acetate is obtained. Add 1.0 g of CeO2 support to the solution and ultrasonically disperse for 15 min. Transfer the above suspension into a round-bottom flask, evaporate the pyrrolidone solvent using a rotary evaporator, and place the remaining solid powder in an oven at 120 °C for drying for 15 h to obtain a solid powder.

[0087] Put the dried solid powder into a muffle furnace and heat it at 10 °C / min -1 to 220 °C and maintain for 8 h for the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 200 mL of pyrrolidone-water mixed solvent (the volume ratio of pyrrolidone to water is 10:1), stir at room temperature for 5 h; filter by suction and collect the filter cake; wash the filter cake successively with 50 mL of pyrrolidone, 200 mL of pyrrolidone-water mixed solvent, and 50 mL of water; after suction drying, put it into an oven at 120 °C and dry for 15 h to obtain the first calcination product.

[0088] Put the first calcination product into a muffle furnace and heat it at 1 °C / min -1 to 750 °C and maintain for 9 h for the second calcination treatment; after natural cooling to room temperature, obtain the Cu-CeO₂ single-atom catalyst. Using ICP-MS, it is measured that in the catalyst, the Cu element is 0.98 wt% of the mass of the CeO₂ support.

[0089] II. Treatment of high-salt dye wastewater

[0090] Add 10 mg of the Cu-CeO₂ catalyst to a 250 mL conical flask, and add 200 mL of the high-salt bromocresol purple mother liquor, where the sodium chloride concentration is 200 mg / L -1 , and the bromocresol purple concentration is 20 mg / L -1 ; stir in the dark for 40 min until adsorption equilibrium; add peroxymonosulfate (PMS) to the above mixed system and start the reaction; use ultraviolet-visible absorption spectroscopy to detect the change rate of the bromocresol purple concentration. The removal rate of bromocresol purple after 10 min of reaction is 82%, as shown in Table 1 for details.

[0091] Example 6

[0092] I. Preparation of Zn-CeO₂ single-atom catalyst

[0093] Mix 0.56 g of zinc sulfate and 20 mL of isopropyl alcohol and stir for 60 min; after the zinc sulfate is completely dissolved, obtain the isopropyl alcohol solution of zinc sulfate. Add 1.6 g of the CeO₂ support to the solution and ultrasonically disperse for 10 min. Transfer the above suspension into a round-bottom flask, use a rotary evaporator to evaporate the isopropyl alcohol solvent, and put the remaining solid powder into an oven at 90 °C and dry for 8 h to obtain the solid powder.

[0094] Put the dried solid powder into a muffle furnace and heat it at 2 °C / min -1Raise the temperature to 450 °C, maintain for 3 h, and perform the first calcination treatment; after natural cooling to room temperature, obtain the sample. Transfer the sample into a beaker, add 200 mL of isopropanol-water mixed solvent (the volume ratio of isopropanol to water is 20:1), stir at room temperature for 4 h; perform suction filtration and collect the filter cake; wash the filter cake successively with 200 mL of water, 100 mL of isopropanol-water mixed solvent, and 50 mL of isopropanol; after suction drying, place it in an oven at 90 °C and dry for 6 h to obtain the first calcination product.

[0095] Put the first calcination product into a muffle furnace, raise the temperature to 600 °C at a rate of 5 °C min-1, maintain for 2 h, and perform the second calcination treatment; after natural cooling to room temperature, obtain the Zn-CeO2 single-atom catalyst. Using ICP-MS, it is measured that in the catalyst, the Zn element is 2.21 wt% of the mass of the CeO2 support.

[0096] II. Treatment of high-salt dye wastewater

[0097] Add 10 mg of Zn-CeO2 catalyst to a 250 mL conical flask, add 200 mL of high-salt Congo red mother liquor, where the sodium sulfate concentration is 300 mg L -1 , and the Congo red concentration is 20 mg L -1 . Stir in the dark for 40 min until adsorption equilibrium; add persulfate (PDS) to the above mixed system, and start the reaction timing; use ultraviolet-visible absorption spectroscopy to detect the change rate of Congo red concentration. The removal rate of Congo red after 10 min of reaction is 51%, as shown in Table 1 for details.

[0098] Comparative Example 1

[0099] Adopt the same high-salt dye wastewater treatment method as in Example 2, except that no catalyst is added during the treatment of high-salt dye wastewater. The removal rate of Rhodamine B after 10 min of reaction is 10%, as shown in Table 1 for details.

[0100] Comparative Example 2

[0101] Adopt the same high-salt dye wastewater treatment method as in Example 2, except that an equal amount of CeO2 is used to replace the Co-CeO2 single-atom catalyst during the treatment of high-salt dye wastewater. The removal rate of Rhodamine B after 10 min of reaction is 12%, as shown in Table 1 for details.

[0102] Comparative Example 3

[0103] Adopt the same high-salt dye wastewater treatment method as in Example 2, except that an equal amount of CoO is used to replace the Co-CeO2 single-atom catalyst during the treatment of high-salt dye wastewater. The removal rate of Rhodamine B after 10 min of reaction is 36%, as shown in Table 1 for details.

[0104] Comparative Example 4

[0105] The same high-salt dye wastewater treatment method as in Example 2 was adopted, except that an equal amount of Co3O4 was used to replace the Co-CeO2 single-atom catalyst in the treatment of high-salt dye wastewater. The removal rate of rhodamine B was 57% after 10 min of reaction. See Table 1 for details.

[0106] Comparative Example 5

[0107] Same as the method of Example 2, except that the first calcination treatment was cancelled during the catalyst preparation process, and only one calcination treatment was carried out. The calcination steps were as follows: The dried solid powder was put into a muffle furnace and heated to 700 °C at a rate of 1 °C / min, and maintained for 12 h; it was naturally cooled to room temperature to obtain the Co3O4 / CeO2 catalyst. By ICP-MS measurement, in the catalyst, the Co element was 6.6 wt% of the mass of the CeO2 support. -1 The obtained Co3O4 / CeO2 catalyst was used to treat high-salt dye wastewater. The treatment method was the same as that in Example 2. The removal rate of rhodamine B was 48% after 10 min of reaction. See Table 1 for details.

[0108] The obtained Co3O4 / CeO2 catalyst was used to treat high-salt dye wastewater. The treatment method was the same as that in Example 2. The removal rate of rhodamine B was 48% after 10 min of reaction. See Table 1 for details.

[0109] Comparative Example 6

[0110] Same as the method of Example 2, except that the second calcination treatment was cancelled during the catalyst preparation process.

[0111] Comparative Example 7

[0112] Same as the method of Example 2, except that the time of the first calcination treatment was 0.5 h.

[0113] Comparative Example 8 was the same as the method of Example 2, except that the temperature of the first calcination treatment was 800 °C.

[0114] Table 1

[0115] Example Catalyst Name Dye Removal Rate at 10 min (%) Example 1 <![CDATA[Fe-CeO2]]> 53 Example 2 <![CDATA[Co-CeO2]]> 96 Example 3 <![CDATA[Ni-CeO2]]> 55 Example 4 <![CDATA[Mn-CeO2]]> 68 Example 5 <![CDATA[Cu-CeO2]]> 82 Example 6 <![CDATA[Zn-CeO2]]> 51 Comparative Example 1 None 10 Comparative Example 2 <![CDATA[CeO2]]> 12 Comparative Example 3 CoO 36 Comparative Example 4 <![CDATA[Co3O4]]> 57 Comparative Example 5 <![CDATA[Co3O4 / CeO2]]> 48 Comparative Example 6 <![CDATA[Co-CeO2]]> 42 Comparative Example 7 <![CDATA[Co-CeO2]]> 53 Comparative Example 8 <![CDATA[Co3O4 / CeO2]]> 43

[0116] As can be seen from Table 1, in the method of the embodiments of the present invention, the transition metal single-atom catalyst supported on cerium oxide was used to catalytically activate persulfate, so that the high-salt dye wastewater could be effectively degraded, and the conversion rate within 10 min could reach more than 50%. In particular, the Co-CeO2 catalyst prepared in Example 2 had a conversion rate of rhodamine B in the high-salt rhodamine B wastewater as high as 96%.

[0117] In Comparative Examples 1, 2, 3, and 4, when no catalyst was added or only the carrier CeO2 or cobalt oxide was added alone, the dye could not be effectively degraded, and the removal rates of the high-salt dye wastewater were far lower than those of Example 2 of this application.

[0118] In Comparative Example 5, during the preparation of the catalyst, the first low-temperature calcination treatment was not carried out. The Co element could not form single-atom loading but was loaded on the cerium oxide support in the form of an oxide, resulting in a removal rate of Rhodamine B in the high-salt Rhodamine B wastewater of only 48%.

[0119] In Comparative Example 6, during the preparation of the catalyst, the first calcination product after the first calcination treatment, washing, and drying was not subjected to the second calcination treatment, resulting in a large amount of coordinated anions remaining on the prepared catalyst, and the activity of the catalyst decreased significantly, causing the removal rate of Rhodamine B in the high-salt Rhodamine B wastewater to be only 42%.

[0120] In Comparative Example 7, during the preparation of the catalyst, due to the too short first calcination time, fewer Co-O bonds were formed between the Co salt and the cerium oxide support, and most of the cobalt salt was washed away during the washing process after the first calcination treatment. Although a Co single-atom catalyst was also prepared after the second calcination treatment in Comparative Example 7, the loading amount of Co in the catalyst decreased significantly, resulting in a removal rate of Rhodamine B of only 53%.

[0121] In Comparative Example 8, during the preparation of the catalyst, the temperature of the first calcination treatment was too high, resulting in the decomposition of cobalt chloride. Cobalt chloride formed Co3O4 particles on the surface of the cerium oxide support. Cobalt chloride could not form Co-O bonds with the cerium oxide support, and a single-atom Co catalyst could not be prepared, but a Co3O4 nanoparticle catalyst was formed. The removal rate of Rhodamine B in the high-salt Rhodamine B wastewater was only 43%.

[0122] In the present invention, terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0123] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for treating high-salt dye wastewater, characterized in that It includes the following steps: a. Mix the cerium oxide supported transition metal single-atom catalyst M-CeO2 with the high-salt dye wastewater, and stir in the dark until adsorption equilibrium is reached to obtain a mixed solution; b. Add the oxidant persulfate to the mixed solution and react to obtain the treated wastewater.

2. The treatment method of high-salt dye wastewater according to claim 1, wherein, In the step a, the cerium oxide supported transition metal single-atom catalyst M-CeO2 includes at least one of the cerium oxide supported single-atom Fe catalyst Fe-CeO2, the cerium oxide supported single-atom Co catalyst Co-CeO2, the cerium oxide supported single-atom Ni catalyst Ni-CeO2, the cerium oxide supported single-atom Mn catalyst Mn-CeO2, the cerium oxide supported single-atom Cu catalyst Cu-CeO2, and the cerium oxide supported single-atom Zn catalyst Zn-CeO2; And / or, the transition metal element in the catalyst is 0.2-3% of the mass of the CeO2 support.

3. The treatment method of high-salt dye wastewater according to claim 1 or 2, characterized in that, The preparation method of the cerium oxide supported transition metal single-atom catalyst M-CeO2 includes the following steps: (1). Add the CeO2 support to the transition metal salt solution, mix and then evaporate the solvent to obtain a solid powder; (2). Perform a first calcination treatment on the solid powder obtained in the step (1), the temperature of the first calcination treatment is lower than the decomposition temperature of the soluble metal salt, and after washing, filtering, and drying, a first calcination product is obtained; (3). Perform a second calcination treatment on the first calcination product obtained in the step (2), the temperature of the second calcination treatment is higher than the temperature of the first calcination treatment, and a cerium oxide supported metal single-atom catalyst is obtained.

4. The treatment method of high-salt dye wastewater according to claim 3, characterized in that In the step (1), the transition metal salt includes at least one of chlorides, sulfates, nitrates, acetates, and oxalates of Fe, Co, Ni, Mn, Cu, and Zn; and / or, the transition metal salt solution includes at least one of an aqueous solution, a methanol solution, an ethanol solution, an isopropanol solution, an acetone solution, a DMF solution, and a pyrrolidone solution of the transition metal salt.

5. The treatment method of high-salt dye wastewater according to claim 3, characterized in that, In the step (1), the mass ratio of the metal element in the transition metal salt solution to the CeO2 support is 1:100 to 10:

100.

6. The treatment method of high-salt dye wastewater according to claim 3, wherein, In the step (2), the temperature of the first calcination treatment is higher than the melting point of the soluble metal salt; And / or, the temperature of the first calcination treatment is 200-600°C, and the calcination time is 1-5h; And / or, the washing liquid used for washing includes at least one of water, methanol, ethanol, isopropanol, acetone, DMF, and pyrrolidone.

7. The treatment method of high-salt dye wastewater according to claim 3, characterized in that, In the step (3), the temperature of the second calcination treatment is 200-900°C, and the calcination time is 2-12h.

8. The treatment method of high-salt dye wastewater according to claim 1, characterized in that In the high-salt dye wastewater, the salt includes at least one of sulfate, chloride, nitrate, carbonate, phosphate, monohydrogen phosphate, and dihydrogen phosphate, and the salt concentration is 10-500 mg·L -1 ; And / or, in the high-salt dye wastewater, the dye includes at least one of rhodamine B, methyl orange, methylene blue, bromocresol purple, and congo red, and the dye concentration is 0.01-100 mg·L -1 .

9. The treatment method of high-salt dye wastewater according to claim 1, characterized in that The oxidant persulfate includes at least one of monopersulfate and dipersulfate.

10. The treatment method of high-salt dye wastewater according to claim 1, characterized in that In the step a, in the mixed solution, the concentration of the cerium oxide supported transition metal single atom catalyst M-CeO2 is 0.01-500 mg·L -1 .

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