Cobalt tungstate catalyst with defects, and preparation method and application thereof

Abstract

The application discloses a kind of cobalt tungstate catalysts with defects and its preparation method and application, belong to water pollution control technical field.It is specific that: the application is synthesized by hydrothermal method using cobalt source and tungsten source to synthesize cobalt tungstate, mixed with sodium borohydride or directly place cobalt tungstate in (H2 / Ar=10% / 90%) protective atmosphere, by controlling different holding time to prepare a series of cobalt tungstate materials with defects.The cobalt tungstate with defects prepared by the application can activate peroxymonosulfate (PMS) to degrade sulfamethoxazole (SMTZ), the material can efficiently remove SMTZ within 5min under the condition of pH=7, and the removal rate can reach 100%.In addition, the synthesis process of the application is green and environmentally friendly, and the prepared catalyst provides reference for the design of subsequent advanced oxidation technology catalysts applied in wastewater treatment field.

Description

Technical Field

[0001] This invention relates to the field of water pollution control technology, and more specifically to a defective cobalt tungstate catalyst, its preparation method, and its application. Background Technology

[0002] In recent years, emerging organic pollutants have caused serious harm to aquatic environments and human health. These mainly include endocrine disruptors (EDCs), pharmaceuticals and personal care products (PPCPs), carcinogenic polycyclic aromatic hydrocarbons (PAHs), brominated flame retardants, and perfluorooctanoic acid (PFOA), and have become international research hotspots and urgent problems to be solved. Among these, sulfonamides (SAs) are among the most widely used antibiotics, primarily for the prevention and treatment of bacterial infectious diseases. They are extensively used in medical treatment, aquaculture, and animal husbandry, leading to the continuous entry of drug residues and their metabolites into environmental water bodies. The detected concentrations of sulfonamides in wastewater effluent from many wastewater treatment plants range from ng / L to μg / L. Traditional wastewater treatment processes have limited effectiveness in removing these trace levels of active drugs, necessitating the development of advanced treatment processes to achieve efficient removal.

[0003] This study used defective cobalt tungstate-activated PMS to degrade sulfonamide antibiotics in water, which showed better degradation performance than the Co(OH)2 and CoO systems. The specific reasons are as follows:

[0004] 1. W in defective cobalt tungstate 6+ With the same coordination structure and similar ionic radius as iron, cobalt, manganese, and nickel ions, W 6+ It can effectively substitute iron, cobalt, and nickel in situ and influence the electronic states of surrounding atoms; the highly electronegative W 6+ The recombination can cause the center of the metal d-band to shift, changing the electronic state density and energy of the surrounding atoms, which is beneficial to the adsorption and desorption of reaction intermediates.

[0005] Jin, M. et al. (J. Colloid Interface Sci. 2021, 587: 581-589.) reported a method for adding W to cobalt hydroxide (CCH) 6+ Atomic doping enhances the oxygen evolution reaction (OER) activity of CCH. 5 at% W doping improves the OER of CCH to 15 mA / cm². 2 The overpotential was reduced by 95.3 mV. Furthermore, the current density was increased by 2.8 times at 1.65 V. A 5% W-PCCH||5% W-CCH based electrolyzer only requires a potential of 1.65 V to provide 10 mA / cm². 2 Used for complete water splitting.

[0006] 2. The binding energy between high-valence W and O is higher than that between 3d metals and oxygen. Furthermore, the high valence difference between them leads to a high Madelung energy, resulting in a more robust overall structure and effectively ensuring the material's stability during catalysis. Low-spin d... 0 W 6+ Atoms have more empty outermost orbitals, which can provide more abundant and efficient adsorption sites without increasing the dissociation energy of the product.

[0007] Yan, J. et al. (Nat. Commun. 2019, 10: 2149.) reported a single-atom W 6+ The doped Ni(OH)₂ nanosheet sample W-Ni(OH)₂ exhibits excellent oxygen evolution reaction (OER) performance. Compared to Ni, the outermost electron orbitals of W are less occupied. In the layered Ni(OH)₂ structure, one Ni is replaced by one W, which is expected to generate some additional adsorption sites on W.

[0008] 3. Oxygen vacancies in defective cobalt tungstate are common anion defects, usually generated by lattice oxygen breaks under specific conditions. They tend to capture relatively unrestricted O atoms from the surrounding environment to achieve efficient electron capture. - Targeted transfer, OV in heterogeneous PMS activation systems s Designed to capture HSO5 - One O atom is used to achieve enhanced interfacial reactions; in addition, OV s It can serve as a strong surface Lewis acid site, promoting chemical bonding between the catalyst and PMS, thereby promoting e - Transferring and improving redox cycle capacity.

[0009] Zhang, H. et al. (Appl Catal B:Environmental.2020.118874.) reported that PMS is activated by surface oxygen vacancies during the reaction process. I -Vo or O II Adsorption and capture in the form of -Vo. Based on PMS reduction. . OH, SO 4. - or H2, enables different electron transfer pathways from Vo to different O sites in PMS at the solid-liquid interface.

[0010] Furthermore, the defective cobalt tungstate catalyst synthesized in this invention has the following advantages and differences compared to existing cobalt tungstate catalysts:

[0011] 1. Faster degradation rate: The degradation rate of cobalt tungstate catalyst is less than 50% within 5 minutes, while the defective cobalt tungstate catalyst synthesized in this patent can completely degrade sulfonamide pollutants within 5 minutes.

[0012] 2, more advantageous morphology: the existing cobalt tungstate catalysts are mostly nanoparticles, He Xiujuan reported that the current driving liquid pH is 6-8, which will synthesize fine particle-shaped, uniform micro-morphology, and regular structure of cobalt tungstate crystal. The morphology of the defect cobalt tungstate catalyst synthesized in this patent is nanorod structure, Zhang Yufang, Zhang Zhenguo and Fang Xiaoming reported that compared with nanoparticles, nanorod structure material has larger specific surface area, unique optical and electrical properties and the advantages of easy electron transmission. It means that the defect cobalt tungstate has more adsorption sites and higher degradation efficiency.

[0013] 3, the synthesis method is more simple: Somchai Thongtem et al. (Ceramics International, 2009, 35(5): 2087-2091.) reported that CoCl2·6H2O and Na2WO4·2H2O solution were sprayed and pyrolyzed on a glass substrate at 250-450℃ to synthesize CoWO4nanopowder. In this study, the defect cobalt tungstate was synthesized by hydrothermal method, ammonium metatungstate was used as tungsten source, cobalt nitrate hexahydrate was used as cobalt source, mixed solution with different mass ratio of cobalt and tungsten was prepared, the pH of the solution was adjusted, the solution was put into a stainless steel autoclave lined with Teflon and hydrothermal reaction was carried out. The preparation steps are simple. SUMMARY

[0014] In view of the problems and deficiencies of the prior art, the present application provides a defect cobalt tungstate catalyst and its preparation method and application. By improving the structure of cobalt tungstate, the degradation rate of peroxymonosulfate (PMS) to sulfamethoxazole (SMTZ) is improved, and the excellent catalytic performance of this material also has reference significance for the preparation of other defect materials and the activation of PMS. And the preparation method defined in the present application is simple, green and environmentally friendly, and is suitable for popularization and application.

[0015] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0016] A preparation method of a defect cobalt tungstate catalyst, comprising the following steps:

[0017] Method (a) under the condition of not adjusting the pH of the system, the aqueous solution of cobalt salt and tungsten salt with different mass ratios is prepared into defect cobalt tungstate by one-step hydrothermal method, the prepared defect cobalt tungstate is mixed with NaBH4, and is ground in a dry environment for 10 min to obtain a black mixture, and the black mixture is placed in a H2 / Ar (10% / 90%) atmosphere;

[0018] or method (b) directly placing the cobalt tungstate hydrate in a tube furnace with hydrogen / argon = 10% / 90%;

[0019] Then, the temperature is raised to 300℃ at a temperature rising rate of 4℃·min -1 and kept at this temperature for 60 or 120 min, to obtain the cobalt tungstate hydrate catalyst with defects.

[0020] The above technical solution achieves the beneficial effects that: through the calcination at a certain rate defined by the present application, a new cobalt tungstate hydrate material catalyst with defects is prepared, which has a significantly improved rate of degrading water pollutants by persulfate compared with the existing cobalt tungstate hydrate catalyst; specifically, the cobalt tungstate hydrate with defects presents a rod-like morphology, which is consistent with the scanning electron microscope (SEM, Figure 1 (d)) figure. In addition, through high-resolution transmission electron microscopy (HR-TEM, Figure 2 (c)), clear crystal lattice fringes of the catalyst can be observed, and by measuring the corresponding fringe spacing, it is known that the lattice spacing is 0.370 nm, which corresponds to the crystal card of JCPDS 15-0867, and it is known that it corresponds to the (-110) crystal face of cobalt tungstate hydrate.

[0021] Preferably, the mass ratio of the cobalt tungstate hydrate to the NaBH4 in method (a) is 1:2.

[0022] Further, after the heat preservation in method (a), the following steps are needed:

[0023] Cooling to room temperature, filtering the obtained product, and drying in a 60℃ oven.

[0024] Preferably, the preparation steps of the cobalt tungstate hydrate are:

[0025] The cobalt salt is added to the tungsten salt solution, stirred, and the pH value of the system is not adjusted, then the mixed solution is transferred to a stainless steel autoclave lined with Teflon, heated in an oven at 200℃ for 300 min; after cooling to room temperature, the obtained sample is filtered to obtain a deep red precipitate, which is washed with deionized water to obtain a deep red precipitate, which is moved into an oven for drying, and the collected product is ground into fine powder to obtain a brick red cobalt tungstate hydrate.

[0026] The above technical solution achieves the beneficial effects that: the brick red cobalt tungstate hydrate generated after the reaction in the stainless steel autoclave lined with Teflon has a better effect than WO3 and Co3O4 in the process of degrading pollutants by PMS.

[0027] Preferably, the preparation steps of the tungsten salt solution are:

[0028] Dissolve the tungsten salt in ultrapure water, and stir the solution to transparency by magnetic stirring;

[0029] The tungsten salt: the ultrapure water = 1g: 25-70mL.

[0030] Further, the tungsten salt: the ultrapure water = 1g: 25mL or 1g: 50mL or 1g: 66mL or 1g: 70mL.

[0031] The above technical solution achieves the beneficial effects that the materials prepared by different proportions of tungsten salt and ultrapure water can finally obtain different morphologies of hydrated cobalt tungstate.

[0032] Preferably, the mass ratio of Co atoms and W atoms in the cobalt salt and the tungsten salt is Co: W = 8%, 11%, 13%, 16%, 19%;

[0033] The tungsten salt is one or more of ammonium metatungstate, ammonium paratungstate, and sodium tungstate;

[0034] The cobalt salt is cobalt nitrate hexahydrate or cobalt chloride hexahydrate.

[0035] The above technical solution achieves the beneficial effects that different cobalt-tungsten ratios can finally obtain different morphologies of hydrated cobalt tungstate.

[0036] Further, the mass ratio of Co atoms and W atoms in the cobalt salt and the tungsten salt is Co: W = 8% or 13% or 19%.

[0037] Preferably, the drying temperature is 60°C, and the drying time is 30min.

[0038] In order to achieve the above purpose, the present application also provides another technical solution:

[0039] A preparation method of a non-hydrated cobalt tungstate catalyst with defects, comprising the following steps:

[0040] Under the condition that the pH of the system is adjusted to 8, a non-hydrated cobalt tungstate is prepared by mixing aqueous solutions of cobalt salt and tungsten salt with different mass ratios by one-step hydrothermal method, grinding the mixture in a dry environment for 10min to obtain a black mixture, and placing the black mixture in a H2 / Ar (10% / 90%) atmosphere.

[0041] Then, the temperature is raised to 300°C at a temperature rising rate of 4°C·min -1 , and the temperature is kept at this temperature for 60 and 120min to obtain a non-hydrated cobalt tungstate catalyst with defects.

[0042] The beneficial effects achieved by the above technical solution are: through the temperature rising calcination at a certain rate defined by the application, a new type of defective non-hydrated cobalt tungstate material catalyst is prepared, which has a significantly improved rate of degrading water pollutants by persulfate compared with existing cobalt tungstate catalysts, wherein the prepared defective non-hydrated cobalt tungstate has a short rod-like and spherical structure stacked together.

[0043] Preferably, the preparation steps of the non-hydrated cobalt tungstate are:

[0044] The cobalt salt is added to the tungsten salt solution, stirred, and the pH value of the system is adjusted, specifically, 0.5 mol / L NaOH is added to pH equal to 8, and then the mixed solution is transferred to a stainless steel autoclave lined with Teflon, heated in an oven at 200℃ for 300 min; after cooling to room temperature, the obtained sample is filtered, washed to neutral to obtain a dark blue precipitate, moved into an oven for drying, the collected product is ground into fine powder to obtain a non-hydrated dark blue cobalt tungstate powder.

[0045] The beneficial effects achieved by the above technical solution are: due to different preparation steps, the structure, morphology, lattice doping, purity and physical and chemical properties of the cobalt tungstate can be affected. Therefore, the application defines a preparation method of non-hydrated cobalt tungstate, which can ensure that the obtained material meets specific requirements and application needs.

[0046] Preferably, the preparation steps of the tungsten salt solution are:

[0047] The tungsten salt is dissolved in ultrapure water, and the solution is stirred with a magnetic stirrer until it is transparent.

[0048] Among them, the tungsten salt: the ultrapure water = 1 / 0.8 / 0.6 / 0.5 / 0.4 / 0.3g: 66ml.

[0049] The beneficial effects achieved by the above technical solution are: the ammonium metatungstate is completely dissolved, and a purer cobalt tungstate is obtained.

[0050] Preferably, the mass ratio or molar mass ratio of Co atoms and W atoms in the cobalt salt and tungsten salt is: Co: W = 11%, 13%, 18%, 21%, 27%, 36%.

[0051] The tungsten salt is one or more of ammonium metatungstate, ammonium paratungstate, and sodium tungstate.

[0052] The cobalt salt is cobalt nitrate hexahydrate or cobalt chloride hexahydrate.

[0053] The beneficial effects achieved by the above technical solution are: when the cobalt tungsten mass ratio is 21%, the effect of degrading SMTZ by the cobalt tungstate using persulfate is more significant.

[0054] The amount of NaOH added is 4.3-5.2 mL, to pH equal to 8.

[0055] Preferably, the drying temperature is 60℃, and the drying time is 30 min.

[0056] Application of the defective cobalt tungstate hydrate or non-hydrate catalyst prepared by the above preparation method in activating persulfate to degrade water pollutants.

[0057] Preferably, the water pollutants are sulfamethoxazole (SMTZ).

[0058] The two defective cobalt tungstates described above are important catalytic materials, and their micro-atomic structure, activation mechanism and catalyst morphology have important influences on their catalytic performance. These aspects will be described in detail below.

[0059] 1. Micro-atomic structure

[0060] The defective cobalt tungstate crystal has a tungstate structure, in which tungsten ions (W 6+ ), cobalt ions (Co 2+ ) and oxygen ions (O 2- ) form the crystal structure. In the crystal, the tungstate forms a three-dimensional network structure, in which the tungsten ions and oxygen ions form tungsten-oxygen octahedra, and the cobalt ions are located in the interstices of the octahedra. The catalytic performance of the defective cobalt tungstate is influenced by the defect sites and surface active sites in the crystal structure.

[0061] 2. Activation mechanism

[0062] The activation process of the defective cobalt tungstate involves complex physical and chemical changes such as ion exchange, surface reconstruction and redox. During the activation process, external excitation energy (such as heat energy, light energy, etc.) or the interaction between the catalyst and the reactants leads to changes in the crystal structure and the formation of surface active sites. The activation process usually involves steps such as diffusion of surface ions, adsorption and desorption of species, formation and repair of lattice defects. These processes work together to form highly reactive sites on the catalyst surface, thereby promoting the progress of the catalytic reaction.

[0063] 3. Advantages of catalyst morphology and defect structure

[0064] The catalytic performance of the defective cobalt tungstate is also influenced by its morphology characteristics. Morphology includes crystal particle size, crystal surface structure, pore structure, etc. The atomic arrangement and surface energy of the catalyst surface with different morphologies may be different, thereby affecting the adsorption of reactants and the formation of reaction intermediates. Common defective cobalt tungstate morphologies include nanoparticles, nanowires, nanosheets, etc. These morphological characteristics can regulate the specific surface area, crystal face exposure degree and crystal defect density of the catalyst, thereby affecting the catalytic activity and selectivity.

[0065] Advantages of defect structure: The introduction of defect structure can positively affect the physical and chemical properties of the material, the electronic structure of the system, the catalytic properties, etc. In this study, the defect cobalt tungstate catalyst in the activation process, OV s As a strong surface Lewis acid site, it promotes the chemical bond between the catalyst and PMS, promotes the e - Transfer, enhance the redox cycle ability, make the catalyst and the reactant interact, so as to change the crystal structure, form active site, promote the progress of catalytic reaction.

[0066] In general, the microstructure of defect cobalt tungstate, the activation mechanism and the morphology of the catalyst have important influence on its catalytic performance. Understanding and regulating these characteristics can optimize the performance of defect cobalt tungstate catalyst, improve the catalytic activity, selectivity and stability, and thus be widely used in energy conversion, environmental protection and chemical synthesis.

[0067] Through the above technical solution, compared with the prior art, the present application provides a defect cobalt tungstate catalyst and its preparation method and application, which has the following beneficial effects:

[0068] (1) The present application can synthesize two different cobalt tungstates by adjusting the pH of the system using one-step hydrothermal method. Under the condition of not adjusting the pH of the system, hydrated cobalt tungstate is synthesized, and under the condition of adjusting the pH to 8, non-hydrated cobalt tungstate is synthesized.

[0069] (2) The present application prepares a defect cobalt tungstate catalyst activated peroxymonosulfate (PMS) technology to degrade SMTZ. By hydrothermal method, ammonium metatungstate is used as tungsten source to synthesize cobalt tungstate, and after calcination with H2 / Ar (10% / 90%), defect cobalt tungstate is formed. This material can efficiently remove SMTZ within 5 min under the condition of pH=7, and the removal rate can reach 100%. BRIEF DESCRIPTION OF DRAWINGS

[0070] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creating any creative labor.

[0071] Figure 1 SEM images of hydrated cobalt tungstate in Example 2 and defect hydrated cobalt tungstate in Example 3;

[0072] Among them, Figure 1(a), (b) are SEM images of hydrated tungstenic acid cobalt prepared in Example 2 with the volume of ultrapure water: cobalt nitrate hexahydrate (Co / W) = 25 mL: 13%, 70 mL: 13% respectively;

[0073] (c), (d) are SEM images of defective hydrated tungstenic acid cobalt prepared in Example 3 with the volume of ultrapure water: cobalt nitrate hexahydrate (Co / W): holding temperature = 66 mL: 13%: q-60 min respectively;

[0074] Figure 2 are spherical aberration electron microscope images of defective hydrated tungstenic acid cobalt catalyst prepared in Example 4 under the parameters of 66 mL: Co / W = 8%: 60 min at different magnifications;

[0075] Figure 3 are spherical aberration electron microscope images of non-hydrated tungstenic acid cobalt and defective non-hydrated tungstenic acid cobalt catalysts of Example 5 and Example 6 respectively;

[0076] wherein, Figure 3 (a), (b) are spherical aberration electron microscope images of non-hydrated tungstenic acid cobalt prepared in Example 5 under the conditions of ammonium metatungstate mass: cobalt nitrate hexahydrate (Co / W): NaOH volume = 0.5 g: 21%: 4.60 mL at 10 nm and 50 nm respectively;

[0077] (c), (d) are spherical aberration electron microscope images of defective non-hydrated tungstenic acid cobalt catalyst prepared in Example 6 under the conditions of ammonium metatungstate mass: cobalt nitrate hexahydrate (Co / W): holding time = 0.5 g: 21%: 60 min at 10 nm and 50 nm respectively;

[0078] Figure 4 Figures (1)-(3) are respectively: (1) XRD pattern of hydrated tungstenic acid cobalt: 25 mL doped (Co / W) mass ratio of 13% hydrated tungstenic acid cobalt in Example 2; (2) XRD pattern of defective hydrated tungstenic acid cobalt: 66 mL, Co / W = 0.5% mass ratio q-60 min in Example 3; (3) XRD pattern of tri-tungstenic oxide in Comparative Example 1.

[0079] Figure 5 Figures (1)-(3) are respectively: (1) XRD pattern of non-hydrated tungstenic acid cobalt: Co: W = 21% in Example 5; (2) XRD pattern of defective non-hydrated tungstenic acid cobalt: Co: W = 21%, q-60 min in Example 6; (3) XRD pattern of tri-tungstenic oxide in Comparative Example.

[0080] Figure 6 is a graph of the catalytic degradation efficiency of SMTZ by different materials in the degradation effect verification;

[0081] Figure 7 is the influence of different materials on the catalytic degradation of sulfamethoxazole by PMS (pseudo-first-order kinetics simulation); DETAILED DESCRIPTION

[0082] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0083] Embodiment 1

[0084] A preparation method of cobalt tungstate hydrate, comprising the following steps:

[0085] 1 g of ammonium metatungstate was dissolved in 25 / 50 / 66 / 70 mL of ultrapure water, respectively, and stirred by a magnetic stirrer until the solution was transparent. After the ammonium metatungstate was completely dissolved, cobalt nitrate hexahydrate was added to the transparent solution, respectively, wherein the mass ratio of Co and W atoms was Co: W = 8%. The pH value of the system was not adjusted, and the stirring was continued for 10 min. Then, the solution was transferred to a stainless steel autoclave lined with Teflon, and heated at 200 DEG C in an oven for 300 min. After cooling to room temperature, the obtained sample was filtered to obtain a dark red precipitate. After washing with deionized water, the dark red precipitate was obtained, and then transferred to an oven at 60 DEG C for drying for 30 min. The dried product was collected, and the collected product was ground into fine powder to obtain four kinds of brick red cobalt tungstate hydrate. Specifically, the volume of ultrapure water: cobalt nitrate hexahydrate (Co / W) = 25 mL: 8%; 50 mL: 8%; 66 mL: 8%; 70 mL: 8%.

[0086] Embodiment 2

[0087] The embodiment is basically the same as embodiment 1, and the difference is that the mass ratio of Co and W in the added cobalt nitrate hexahydrate is Co / W = 13%, and four kinds of brick red cobalt tungstate hydrate are finally obtained. Specifically, the volume of ultrapure water: cobalt nitrate hexahydrate (Co / W) = 25 mL: 13%; 50 mL: 13%; 66 mL: 13%; 70 mL: 13%.

[0088] wherein, Figure 1 (a) is a SEM photo of 25 mL of cobalt tungstate hydrate doped with cobalt with a mass ratio of Co / W of 13%.

[0089] Figure 1 (b) is a SEM photo of 70 mL of cobalt tungstate hydrate doped with cobalt with a mass ratio of Co / W of 13%.

[0090] Embodiment 3

[0091] A preparation method of a defective cobalt tungstate hydrate, specifically comprising the following steps:

[0092] A solution of 1 g of ammonium metatungstate obtained from Example 2 was dissolved in 66 mL of ultrapure water, and 300 mg of cobalt tungstate hydrate prepared by adding cobalt nitrate hexahydrate (Co(NO3)2·6H2O, Co / W = 13% mass ratio) was mixed with 600 mg of Na2BH4 in a dry environment and ground for 10 min to obtain a black mixture. The black mixture was heated to 300°C at a heating rate of 4°C·min -1 -1 in a tube furnace in a H2 / Ar (10% / 90%) atmosphere, and then kept at this temperature for 60 and 120 min. After cooling to room temperature, the resulting product was dissolved in ethanol and filtered through a membrane, first washed several times with ethanol, and then washed several times with ultrapure water. The filtered product was then dried in an oven at 60°C.

[0093] By the above three steps, different types of cobalt tungstate hydrate with oxygen defects were synthesized by setting the holding time of the tube furnace. Thus, by changing the holding time, two types of cobalt tungstate hydrate catalysts with defects, q-60min and q-120min, were obtained. Specifically, ultrapure water volume: cobalt nitrate hexahydrate (Co / W): holding temperature = 66 mL: 13%: q-60min; 66 mL: 13%: q-120min.

[0094] wherein, Figure 1 (c) and (d) are SEM images of the defective cobalt tungstate hydrate with a holding time of q-60min in this example at different magnifications.

[0095] Example 4

[0096] A method for preparing a defective cobalt tungstate hydrate, specifically comprising the following steps:

[0097] A solution of 1 g of ammonium metatungstate obtained from Example 2 was dissolved in 25 mL or 66 mL of ultrapure water, and 100 mg of cobalt tungstate hydrate prepared by adding cobalt nitrate hexahydrate (Co(NO3)2·6H2O, Co / W = 8% / 13% mass ratio) was heated to 300°C at a heating rate of 4°C·min -1 -1 in a tube furnace (hydrogen / argon atmosphere 10% / 90%), and then kept at this temperature for 60 and 120 min to obtain dark red and black powders.

[0098] Figure 2 (a)-(c) show the spherical aberration electron microscope images of the black powder prepared under the parameters of 66 mL: Co / W = 8%: 60min at different magnifications. Specifically, from Figure 2It can be seen that the crystal shape is rod-like staggered cluster together, the length is tens to hundreds of nanometers, and the selected 100 nm and 50 nm are enlarged in size, and clear stripes can be seen. The stripe spacing is 0.37 nm, which corresponds to the crystal card of JCPDS 15-0867. It can be seen that the corresponding crystal face is (-110) crystal face.

[0099] Example 5

[0100] A preparation method of non-hydrated cobalt tungstate, comprising the following steps:

[0101] Dissolve 1 / 0.8 / 0.6 / 0.5 / 0.4 / 0.3 g of ammonium metatungstate in 66 mL of ultrapure water, and stir with a magnetic stirrer until the solution is transparent. After the ammonium metatungstate is completely dissolved, 0.4 g of cobalt nitrate hexahydrate is added to the transparent solution, and the mass ratio of Co and W atoms is: Co: W = 11%, 13%, 18%, 21%, 27%, 36%. Continue stirring for 10 min, and then add 5.2, 5.05, 5.00, 4.60, 4.60, 4.30 mL of 0.5 mol / L NaOH to pH equal to 8. After stirring for 10 min, the pH is determined to be 8 again, and then stirred for 1 h. Transfer to a stainless steel autoclave lined with Teflon, and keep heating in an oven at 200℃ for 300 min. After cooling to room temperature, the obtained sample is filtered to obtain a dark blue precipitate, which is washed with deionized water to obtain a dark blue precipitate, and then transferred to an oven at 60℃ for drying for 300 min. The collected product is ground into fine powder to obtain six kinds of dark blue cobalt tungstate, and the specific amounts are: ammonium metatungstate mass: cobalt nitrate hexahydrate (Co / W): NaOH volume = 1 g: 11%: 5.2 mL; 0.8 g: 13%: 5.05 mL; 0.6 g: 18%: 5.00 mL; 0.5 g: 21%: 4.60 mL; 0.4 g: 27%: 4.60 mL; 0.3 g: 36%: 4.60 mL.

[0102] wherein, Figure 3 (a), (b) are the spherical aberration electron microscope images of 0.5 g: 21%: 4.60 mL under the conditions of 10 nm and 50 nm.

[0103] Example 6

[0104] A preparation method of a defective non-hydrated cobalt tungstate, comprising the following steps:

[0105] 0.5 g of ammonium metatungstate obtained in Example 6 was dissolved in 66 mL of ultrapure water. 150 mg of non-hydrated cobalt tungstate prepared by adding 0.4 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O, Co / W = 21% by mass) was mixed with 300 mg of Na2BH4 and ground for 10 min under a dry environment to obtain a black mixture. This black mixture was then heated in a tube furnace at 4 °C / min in an H2 / Ar (10% / 90%) atmosphere. -1 The temperature was increased to 300℃, and then held at this temperature for 60 and 120 minutes. After cooling to room temperature, the product was dissolved in ethanol and filtered through a membrane. The product was first washed multiple times with ethanol, then washed multiple times with ultrapure water, and then dried in an oven at 60℃.

[0106] Through the above three steps, different types of oxygen-deficient cobalt tungstate were synthesized according to the set holding time of the tubular furnace. Thus, by different holding times, two types of defective cobalt tungstate catalysts, q-60min and q-120min, were obtained. Specifically, the mass of ammonium metatungstate: cobalt nitrate hexahydrate (Co / W): holding time = 0.5g: 21%: 60min; 0.5g: 21%: 120min.

[0107] in, Figure 3 (c) and (d) are aberration electron micrographs taken at 10 nm and 50 nm for ammonium metatungstate mass: cobalt nitrate hexahydrate (Co / W): holding time = 0.5 g: 21%: 60 min.

[0108] Comparative Example 1

[0109] Ammonium metatungstate (0.5 g) or ammonia solution was added dropwise to cobalt nitrate hexahydrate (cobalt hydroxide was prepared by adding 0.2 g Co(NO3)2·6H2O + 4 mL ammonia solution) in a muffle furnace at 4 °C·min. -1 The temperature was increased to 500℃ and then held at this temperature for 120 min to obtain separate WO3 and Co3O4.

[0110] in, Figure 4 XRD patterns of hydrated cobalt tungstate, defective hydrated cobalt tungstate, and tungsten trioxide;

[0111] Figure 5 XRD of cobalt tungstate, defective cobalt tungstate, and cobalt tetroxide.

[0112] Degradation effect verification

[0113] Experiments on the degradation of SMTZ by PMS activated by different materials were conducted in 250 mL beakers, with 1 mL of 1 mmol·L⁻¹ PMS containing SMTZ. - 1SMTZ was added into 100 mL water with stirring, then 100 uL of 100 mmol·L -1 PMS, continuously stirred on a magnetic stirrer, the pH value of the system was adjusted to 7 by 0.1 mol·L -1 of NaOH solution, 1 mL of water sample was taken and immediately filtered through a 0.22 um organic nylon filter into a pre-added 0.1 mL of 100 mmol·L -1 Na2SO3 solution sample bottle. Then 10 mg of different kinds of materials were weighed and added, the reaction was started and timed. At the set time points of 1 min, 2 min, 3 min, 5 min, 7 min, 10 min, 1 mL of water sample was taken and filtered through a 0.22 um organic nylon filter into a pre-added 0.1 mL of 100 mmol·L -1 Na2SO3 solution sample bottle, 0.1 mL of 100 mmol·L -1 Na2SO3 solution was used to quench the residual free radicals generated by PMS. PMS alone was without catalyst material, adsorption was without PMS, and the other experimental steps were the same.

[0114] Summary: using different materials to catalyze the degradation of SMTZ, only PMS and SMTZ pollutants exist, the content of SMTZ is almost unchanged;

[0115] For the synthesized catalyst material of cobalt tungstate hydrate with defects, the catalytic activation efficiency of PMS for degrading SMTZ is very limited, and the degradation rate is less than 1% within 10 min. Non-hydrated tungsten acid and hydrated tungsten acid as cobalt-based materials also have certain ability to activate PMS to degrade SMTZ. The catalytic ability of the prepared defective hydrated tungsten acid (q-60min, q-120min) material to activate PMS to degrade SMTZ is better, and the catalytic activation performance of the defective hydrated tungsten acid q-60min is the strongest, which can efficiently remove SMTZ within 2 min under the condition of pH=7, and the removal rate can reach 100%. Compared with the catalytic ability of the prepared defective non-hydrated tungsten acid (q-60min, q-120min) material to activate PMS to degrade SMTZ, the catalytic activation performance of the defective tungsten acid q-60min is the strongest, which can efficiently remove SMTZ within 5 min under the condition of pH=7, and the removal rate can reach 100%. For details, see Figure 6 and 7 The curve graph and quasi-first-order kinetics simulation graph of different materials catalyzing PMS to degrade sulfamethoxazole.

[0116] The various embodiments described in this specification are implemented in a progressive manner, each embodiment focusing on the differences from other embodiments, and the same or similar parts between embodiments can be mutually referred to. For the apparatus disclosed by the embodiments, since it corresponds to the method disclosed by the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0117] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those of ordinary skill in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Therefore, the application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The application of a defective cobalt tungstate catalyst in the activation of persulfate degradation of water pollutants, characterized in that, The preparation method of the cobalt tungstate catalyst includes the following steps: Method (a) Cobalt hydrate tungstate and NaBH4 are mixed and ground and then placed in an H2 / Ar (10% / 90%) atmosphere, wherein the mass ratio of cobalt hydrate tungstate to NaBH4 is 1:2; Alternatively, method (b) involves directly placing hydrated cobalt tungstate in a tube furnace under an H2 / Ar (10% / 90%) atmosphere; Then at 4℃‧min -1 The temperature was rapidly increased to 300℃ and held at this temperature for 60 or 120 min to obtain a series of defective cobalt tungstate catalysts. The preparation steps of the hydrated cobalt tungstate include: Cobalt salt was uniformly added to the tungsten salt solution and stirred until homogeneous. The pH value of the system was not adjusted. The solution was then heated at 200°C for 300 minutes, cooled to room temperature, and then filtered, washed with water, dried, and ground in sequence to obtain the hydrated cobalt tungstate.

2. The application according to claim 1, characterized in that, The cobalt salt is cobalt nitrate hexahydrate or cobalt chloride hexahydrate; The tungsten salt is one or more of ammonium metatungstate, ammonium paratungstate, and sodium tungstate.

3. The application according to claim 1, characterized in that, The preparation conditions for the hydrated cobalt tungstate are as follows: the mass-to-volume ratio of tungsten salt to ultrapure water in the tungsten salt solution is 1 g: (25-70) mL; When the mass ratio of Co atoms to W atoms in the cobalt salt and the tungsten salt is 8%, 11%, 13%, 16%, or 19%, the hydrated cobalt tungstate prepared by the one-step hydrothermal method without adjusting the pH value of the system is brick-red hydrated cobalt tungstate.

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