ZnO / Co3O4 composite oxide catalyst as well as preparation method and application thereof

Abstract

The invention is suitable for the technical field of metal oxide catalysts, and provides a ZnO / Co3O4 composite oxide catalyst and a preparation method and application thereof.The preparation method comprises the following steps that zinc nitrate, cobalt nitrate and 2-methylimidazole are subjected to ball milling and mixing and then placed in a crucible, high-temperature calcination is conducted after the temperature is increased, and then the obtained product is ground; wherein the mass ratio of the zinc nitrate to the cobalt nitrate to the 2-methylimidazole is (1.6 to 2.4): (3.12 to 2.32): 2.6. The ZnO / Co3O4 composite oxide catalyst containing a large number of asymmetric oxygen vacancies is prepared, the asymmetry of oxygen vacancies on the surface of a material is increased due to introduction of Zn, the oxygen vacancies on the surface of the material are transited from Co-Ov-Co to Co-Ov-Zn, the local electronic environment is changed, the activation efficiency of persulfate is improved, and therefore the ZnO / Co3O4 composite oxide catalyst can be applied to bisphenol A removal.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal oxide catalysts, and particularly relates to a ZnO / Co3O4 composite oxide catalyst, a preparation method and application thereof. BACKGROUND

[0002] Bisphenol A (BPA) is an organic chemical widely used in the production of plastics and resins in modern industry, but its potential harm to health and the environment has attracted public attention. Numerous studies have shown that long-term exposure to low doses of bisphenol A may be associated with a variety of health problems, including but not limited to reproductive abnormalities, metabolic disorders, obesity, diabetes, cardiovascular disease, and cancer; in addition, BPA has estrogen-like activity, which can interfere with the endocrine system in the human body, and can also affect the development of fetuses and infants, thereby causing damage to the nervous and immune systems; high concentrations of bisphenol A in the environment have also been confirmed to contaminate water sources and have a negative impact on aquatic organisms.

[0003] Advanced oxidation processes (AOPs) are a class of technologies that generate strong oxidizing free radicals and other active species through reaction systems to gradually degrade organic pollutants in water into small molecular organic compounds, and ultimately mineralize them into water and carbon dioxide. AOPs are considered to have good practical application prospects in removing refractory pollutants in wastewater due to their high efficiency and wide applicability, including ozone oxidation, Fenton oxidation, photocatalytic oxidation, and electrochemical oxidation. In recent years, the application of persulfate-based advanced oxidation technology in wastewater treatment has gradually gained widespread attention. Compared with persulfate (PMS), peroxymonosulfate (PDS) has lower cost, higher stability, and better water solubility. Studies have shown that the activation mechanism of PDS is divided into free radical-related processes, which are mainly based on sulfate radicals (SO4· 2- ) and hydroxyl radicals (HO·), and non-free radical-related processes, which depend on surface-activated complexes, electron transfer, and singlet oxygen ( 1 O2). Compared with the free radical pathway, the non-free radical pathway has the following advantages in wastewater treatment: resistance to free radical scavengers (various inorganic ions and natural organic matter), adaptation to a wide pH range, reduction of secondary pollution, and higher selectivity for electron-rich organic pollutants.

[0004] Homogeneous catalytic activation of persulfate generates free radicals with high reaction rates, but this process has many drawbacks such as high cost, difficult to control, and difficult to recycle. In contrast, heterogeneous catalytic systems can overcome the problems of homogeneous catalytic systems because they have the advantages of reusability, milder reaction conditions, and the ability to work in a wider pH range.

[0005] Metal oxides can exist in various oxidation states and crystal structures, which endow them with excellent catalytic performance in various catalytic reaction systems. The multiple oxidation states of metal oxides allow for highly adjustable electronic structures, which can effectively regulate the adsorption and transformation pathways of reactants during the reaction. Meanwhile, the multiple crystal structures of these catalysts provide different reaction environments, further enhancing the diversity and flexibility of catalytic reactions. Compared with homogeneous catalysts such as iron and cobalt ions, heterogeneous catalysts such as cobalt oxides, iron oxides, and manganese oxides have enhanced active site dispersion. Among these transition metal oxides, cobalt oxides and their composites are widely used to activate PDS for the degradation of BPA.

[0006] By controlling the exposed crystal planes, morphology, size, and composite with other metal oxides, the catalytic activity can be effectively improved. Oxygen vacancies are considered to be one of the key factors controlling catalytic activity. As a defect structure of metal oxides, oxygen vacancies can significantly enhance the surface activity of the catalyst, providing more active sites to efficiently activate PDS. Oxygen vacancies can be introduced by doping transition metals into metal oxides. Oxygen vacancies are mainly divided into symmetric oxygen vacancies (S-OVs) and asymmetric oxygen vacancies (As-OVs). Symmetric oxygen vacancies usually occur in structures with relatively symmetric metal coordination, such as M1...OV...M1, while asymmetric oxygen vacancies occur in structures with asymmetric metal coordination, such as M1...OV...M2. This structure often exhibits strong local polarization electron characteristics, which significantly enhances the adsorption and polarization of reactants such as PDS and PMS molecules. The concentration and distribution of oxygen vacancies can be controlled through rational material design and synthesis methods. By adjusting the synthesis conditions of the catalyst, such as temperature, pH, and metal coordination, the number and distribution of oxygen vacancies can be optimized to improve catalytic activity and reaction selectivity. Although oxygen vacancies have shown great potential in catalytic reactions, there are still some challenges in practical applications, such as how to accurately control the concentration and distribution of oxygen vacancies in complex reaction systems, which is the focus and difficulty of current research.

[0007] In summary, the structure and surface defect engineering of metal oxide catalysts is still a difficult problem, and the existing catalysts for the degradation of phenolic pollutants have the disadvantages of low efficiency and high energy consumption. SUMMARY

[0008] The purpose of the embodiments of the present application is to provide a preparation method of ZnO / Co3O4 composite oxide catalyst, which aims to solve the problems raised in the above background art.

[0009] The embodiment of the present application is implemented in the following way: a preparation method of a ZnO / Co3O4 composite oxide catalyst, comprising the following steps: mixing zinc nitrate, cobalt nitrate and 2-methyl imidazole in a ball mill, then putting them into a crucible, performing high-temperature calcination after heating, and then grinding the obtained product; wherein the mass ratio of the zinc nitrate, the cobalt nitrate and the 2-methyl imidazole is 1.6-2.4:3.12-2.32:2.6.

[0010] Another object of the embodiment of the present application is to provide a ZnO / Co3O4 composite oxide catalyst prepared by the above preparation method, wherein ZnO and Co3O4 form a heterostructure in the catalyst, and the catalyst has a Co-Ov-Zn type asymmetric oxygen vacancy.

[0011] Another object of the embodiment of the present application is to provide an application of the ZnO / Co3O4 composite oxide catalyst in removing bisphenol A.

[0012] The embodiment of the present application prepares a ZnO / Co3O4 composite oxide catalyst containing a large number of asymmetric oxygen vacancies, wherein the introduction of Zn increases the asymmetry of the oxygen defects on the surface of the material, the type of the oxygen defects on the surface of the material is changed from Co-Ov-Co to Co-Ov-Zn, the local electronic environment is changed, and the activation efficiency of persulfate is improved, so that the catalyst can be applied in removing bisphenol A. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 XRD patterns of samples 1-3 provided by the embodiment of the present application; Figure 2 A transmission electron microscope photo of sample 1 provided by the embodiment of the present application; Figure 3 A transmission electron microscope photo of sample 2 provided by the embodiment of the present application; Figure 4 XPS O1s patterns of samples 1-3 provided by the embodiment of the present application; Figure 5 、 Figure 6 Application results of samples in removing pollutants bisphenol A by activating PDS (PDS is persulfate) Figure 5 a is the removal rate of samples 1-3, Figure 5 b is the TOC result, Figure 5 d is the removal rate of samples 1-2 under different PDS addition amounts, Figure 5 e is the removal rate of samples 1-2 under different catalyst addition amounts; Figure 6 c is the removal rate of samples 1-2 under different BPA concentrations, Figure 6 f is the removal rate of samples 1-2 under different pH values; Figure 7The rate constant results of samples 1-3 provided by the embodiments of the present application in the catalytic reaction. DETAILED DESCRIPTION

[0014] In order to make the objects, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0015] The specific implementation of the present application is described in detail below with reference to specific embodiments.

[0016] Embodiment 1, a ZnO / Co3O4 composite oxide catalyst, the preparation method comprising the following steps: 1.6 g of zinc nitrate, 3.12 g of cobalt nitrate, and 2.6 g of 2-methylimidazole are ball-mixed and then placed in a crucible, which is placed in a muffle furnace for high-temperature calcination at 400℃, the temperature rising rate is 5℃ / min, and then the sample 1 is obtained after grinding treatment.

[0017] Embodiment 2, a ZnO / Co3O4 composite oxide catalyst, the preparation method comprising the following steps: 2.4 g of zinc nitrate, 2.32 g of cobalt nitrate, and 2.6 g of 2-methylimidazole are ball-mixed and then placed in a crucible, which is placed in a muffle furnace for high-temperature calcination at 400℃, the temperature rising rate is 5℃ / min, and then the sample 2 is obtained after grinding treatment.

[0018] Comparative example 1, a Co3O4 composite oxide catalyst, the preparation method comprising the following steps: 4.64 g of cobalt nitrate and 2.6 g of 2-methylimidazole are ball-mixed and then placed in a crucible, which is placed in a muffle furnace for high-temperature calcination at 400℃, the temperature rising rate is 5℃ / min, and then the sample 3 is obtained after grinding treatment.

[0019] The prepared samples 1-3 are analyzed, and the XRD diagram is as shown in Figure 1 It can be seen that the diffraction peak of the sample 3 is completely consistent with the standard peak of Co3O4, showing a typical spinel phase structure, and there is no any impurity peak; compared with Co3O4, the characteristic peak at 36.8° of the sample 1 is shifted to the left, proving that the zinc ions are successfully doped into the Co3O4 crystal lattice, resulting in the shrinkage of the crystal lattice, and there is no other diffraction peak of the sample, proving that no other product is generated; the sample 2 shows a mixed phase of two products; the characteristic peak marked in the figure is attributed to the characteristic peak of Co3O4, and the characteristic peak marked is the characteristic peak of ZnO (JCPDS No. 36-1451), which indicates that when the zinc content increases, a new phase ZnO appears, and the product is a composite of Co3O4 and ZnO two oxides; The transmission electron microscopy diagrams of the sample 1 and the sample 2 are as shown in Figures 2-3As shown, it can be seen that both Sample 1 and Sample 2 are composed of small particles smaller than 10 nm, with average particle sizes of 8.0 nm and 4.3 nm, respectively. XPS O1s spectra of samples 1-3 are as follows Figure 4 As shown in the figure, the main states of oxygen in the sample are adsorbed oxygen, defect oxygen, and lattice oxygen. The proportion of defect oxygen to all oxygen is obtained by peak area integration, as shown in Table 1. Table 1

[0020] It can be seen that sample 3 has the highest content of defect oxygen; The position of the symmetrical defect oxygen Co-Ov-Co in sample 3 is 530.8 eV. The energy spectrum peaks of the defect oxygen in samples 1 and 2 shift towards higher energies, indicating that the asymmetric coordination environment Co-Ov-Zn alters the local electron density.

[0021] Application Example 1: Using bisphenol A as the target pollutant, the ability of samples 1-3 to remove bisphenol A was analyzed, specifically including the following steps: Weigh 25 mg of each sample (samples 1-3) into a 100 mL glass beaker, and add 50 mL of each sample with an initial concentration of 20 mg / L. -1 The BPA solution was ultrasonicated for 10 min to uniformly disperse the sample in the solution. The mixture was then magnetically stirred for 1 h in the dark to reach adsorption-desorption equilibrium. Subsequently, 25 mg of potassium persulfate (PDS) was rapidly added. 1.5 mL samples were taken at fixed time intervals and filtered through a 0.45 μm filter membrane. The BPA concentration was determined by high-performance liquid chromatography (HPLC). The results are shown below. Figure 5 As shown in a and b; Based on Example 1, the initial concentration of the BPA solution was changed, and the effect of removing bisphenol A was analyzed. The results are as follows: Figure 6 As shown in c; Based on Example 1, the amount of PDS added was changed, and the effect of removing bisphenol A was analyzed. The results are as follows: Figure 5 As shown in d; Based on Example 1, the amount of bisphenol A added to samples 1-3 was changed, and the effect of removing bisphenol A was analyzed. The results are as follows: Figure 5 As shown in e; Based on Example 1, the pH value was changed, and the effect of removing bisphenol A was analyzed. The results are as follows: Figure 6 As shown in f; according to Figure 5As shown in Figure a, Sample 2 can completely remove pollutants in 9 minutes, while Sample 1 has a removal rate of 70% after 15 minutes of reaction. Surface defects of the catalyst are important active sites in the catalytic reaction. The XPS results show that Sample 3 has the highest oxygen defect content, but its pollutant removal effect is not optimal, with a removal rate of only 50% after 15 minutes. This is because the coordination environment of oxygen defects in Sample 3 is different from that in Samples 1 and 2. The asymmetric oxygen defects (Zn-Ov-Co) in the latter samples change the local electronic environment and improve the efficiency of the catalyst. Since the defect content in Sample 2 is higher than that in Sample 1, it ultimately shows excellent catalytic effect. Figure 5 The TOC results in sample b showed that after 15 minutes of reaction, the organic carbon removal rates in the solution of sample 2, sample 1, and sample 3 were 0.85, 0.70, and 0.51, respectively, confirming that the catalyst product has excellent water treatment capabilities. The removal efficiency of sample 2 / PDS and sample 1 / PDS was analyzed under different BPA concentrations, such as... Figure 6 As shown in Figure c, the removal efficiency of BPA in the Sample 2 / PDS system was 100% when the BPA concentration was 5-20 mg / L, while the removal rate of BPA in the Sample 1 / PDS system decreased with increasing concentration, which may be due to insufficient reactive species. PDS concentration is an important factor in the removal of organic pollutants by SR-AOPs (sulfate radical advanced oxidation technology). Figure 5 The results show that as the amount of PDS increases, the removal efficiency of BPA gradually increases. When the amount of PDS added is greater than 6 mg, BPA can be completely removed in the sample 2 / PDS system. When using 25 mg of PDS, the removal rate of BPA in the sample 1 / PDS system reaches more than 90%. like Figure 5 As shown in Figure e, when the catalyst dosage is 15 mg, the BPA removal rate of the Sample 2 / PDS system reaches 100% within 6 minutes, while the BPA removal efficiency of the Sample 1 / PDS system gradually increases with the increase of catalyst dosage. like Figure 6 As shown in Figure f, acidic conditions significantly reduce the removal efficiency of sample 1 / PDS, while sample 2 / PDS can effectively remove 70% of BPA under acidic conditions (pH=3). This is because acidic conditions affect the stability of the catalyst, while the addition of zinc plays a role in regulating the surface charge of the catalyst and stabilizing the catalyst. The higher zinc content in sample 2 contributes to the stability of the catalyst.

[0022] The rate constants of samples 1-3 (samples with different zinc-cobalt ratios) in the catalytic reaction are as follows: Figure 7As shown, it can be seen that the reaction rate of the catalyst for removing BPA increases with the zinc content increasing from 0 to 35%, which indicates that the introduction of zinc increases the asymmetry of the oxygen defect on the surface of the material, the type of the oxygen defect on the surface of the material changes from Co-Ov-Co to Co-Ov-Zn, the local electronic environment is changed, the activation efficiency of the persulfate is improved, and the performance of the catalyst is reduced with the continuous increase of the zinc content, the number of asymmetric oxygen defects is reduced, and the number of low-activity sites of Zn-Ov-Zn is increased.

[0023] The above only describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a ZnO / Co3O4 composite oxide catalyst, characterized in that, The process includes the following steps: mixing zinc nitrate, cobalt nitrate, and 2-methylimidazole by ball milling and placing the mixture in a crucible, heating it up and calcining it at high temperature, and then grinding the resulting product; wherein the mass ratio of zinc nitrate, cobalt nitrate, and 2-methylimidazole is 1.6-2.4:3.12-2.32:2.

6.

2. The method for preparing the ZnO / Co3O4 composite oxide catalyst according to claim 1, characterized in that, The ball milling process involves mixing balls in a 1:1 ratio at a speed of 500 rpm for 30 minutes, with a 1-minute rest period every 10 minutes.

3. The method for preparing the ZnO / Co3O4 composite oxide catalyst according to claim 1, characterized in that, The heating rate is 4.5-5.5℃ / min.

4. The preparation method of the ZnO / Co3O4 composite oxide catalyst according to claim 1, characterized in that, The high-temperature calcination temperature is 380-420℃, and the time is 120 minutes.

5. A ZnO / Co3O4 composite oxide catalyst, characterized in that, It is prepared by any one of the preparation methods described in claims 1-4. In the catalyst, ZnO and Co3O4 form a heterostructure with Co-Ov-Zn type asymmetric oxygen vacancies.

6. The application of the ZnO / Co3O4 composite oxide catalyst as described in claim 5 in the removal of bisphenol A.

7. The application according to claim 6, characterized in that, The ZnO / Co3O4 composite oxide catalyst removes bisphenol A by activating persulfate.

8. The application according to claim 7, characterized in that, The process includes the following steps: adding the ZnO / Co3O4 composite oxide catalyst to a bisphenol A solution, ultrasonically dispersing it uniformly, magnetically stirring it in the dark to reach adsorption-desorption equilibrium, and then rapidly adding persulfate.

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