Preparation method and application of zinc-titanium hydrotalcite anchored heterogeneous single-atom catalyst

Abstract

The application discloses a preparation method and application of a zinc-titanium hydrotalcite anchored heteroatomic single-atom catalyst, and belongs to the field of advanced oxidation in water pollution control. The catalyst is composed of Ti-LDH as a carrier, Co with a loading amount of 0-2.0 wt%, and I with a loading amount of 0-0.6 wt%. The ZnTi-LDH is synthesized by a solvothermal method, Zn element is etched by NaOH to generate metal Zn vacancies, then abundant oxygen vacancies are generated in a methanol system, and a cobalt nitrate or / and ammonium iodide single-atom precursor is selectively anchored to different sites of the vacancy hydrotalcite. The catalyst has the advantages of high selectivity, simple preparation process, low cost and the like, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of advanced oxidation for water pollution control, and relates to a method for preparing and applying a zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst. Background Technology

[0002] Novel organic pollutants (antibiotics, dyes, etc.) have become a bottleneck in traditional water treatment processes due to their low concentration, high toxicity, and recalcitrant degradation characteristics. Persulfate (PMS) can generate strong oxidizing free radicals and non-free radicals under specific catalytic activation conditions, enabling rapid ring-opening removal of novel pollutants and mineralization into carbon dioxide and water. However, traditional PMS catalysts suffer from problems such as low active sites, low dispersion, insufficient metal utilization, and ambiguous structure-activity relationships. Therefore, catalyst selection is crucial for PMS advanced oxidation systems.

[0003] Single-atom catalysts (SACs) possess the unique advantages of atomically dispersed active sites and 100% metal utilization. Luo et al. (Luo H, Zheng J, Liu J, et al. Nanoconfinement-enhanced peroxymonosulfate activation by Co single atoms in hollow mesoporous carbon: Roles of active-site chemistry and mesoscale confinement[J]. Water Research, 2026, 302(3): 126-136.) utilized hollow mesoporous carbon to confine and regulate Co-N coordination, thereby enhancing the activation ability of PMS. Similarly, Yang et al. (Yang Qun, Li Hongyan, Zhang Feng, et al. Cobalt-nitrogen co-doped waste biochar activation of PMS for the removal of gatifloxacin from water[J]. Chemical Industry and Engineering Progress, 2025, 44(2): (1088-1099.) Co-nitrogen co-doped waste biochar (Co-N@MSBC) material was prepared. The Co-N@MSBC / PMS system achieved a removal rate of up to 96.5% for gatifloxacin within 60 min, demonstrating excellent catalytic performance. Therefore, regulating the N coordination environment of the Co single-atom site can effectively induce the breaking of OO bonds in PMS, generating sulfate radicals (SO4· ... -The use of radicals (·OH) to rapidly remove organic pollutants largely solves the problem of dispersibility of active sites in catalysts, reducing metal leaching and thus avoiding secondary pollution. However, single-atom active sites are currently supported on carbon-based supports, which typically involves complex steps such as high-temperature pyrolysis and acid washing to remove metal clusters, resulting in high costs. Furthermore, current single-atom catalysts cannot effectively control the activation pathway of PMS. Although radicals can rapidly remove pollutants, the intermediate products generated during pollutant degradation are more toxic, susceptible to environmental interference, and exhibit low selectivity. High-valence metal oxygen generated through non-radical pathways possesses mild oxidizing power and a relatively long half-life, exhibiting high selectivity and resistance to interference with wastewater matrices. Therefore, catalysts that are simple to prepare, low-cost, and can precisely control the activation selectivity of PMS to generate high-valence metal oxygen are of great significance. Summary of the Invention

[0004] To address the challenges of complex loading processes, ineffective control of PMS activation pathways, and high costs associated with single-atom catalysts, one objective of this invention is to develop a low-cost, simple catalyst capable of selectively controlling the directional generation of high-valence metals from PMS. Based on the solvothermal synthesis of zinc-titanium layered double hydroxides (LDHs), this catalyst utilizes a LDH-like structure. Metal Zn vacancies are formed on the LDH surface through alkaline etching, while oxygen vacancies are generated under UV reduction conditions. Under a reducing atmosphere, Co and I single-atom precursor ions occupy the Zn and oxygen vacancies, respectively, thus synthesizing a zinc-titanium LDH-anchored heterogeneous single-atom catalyst. Co+I / Ti-LDH utilizes the proton-coupled electron transfer effect, with Co providing two electrons to the OO bond on the PMS to form a stable high-valence cobalt metal oxygen structure (CoIV=O). Simultaneously, I accepts protons to accelerate cycling, and the abundant CoIV=O can oxidize pollutants in wastewater.

[0005] This invention provides a zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst. The catalyst of this invention has advantages such as high selectivity, simple preparation process, and low cost, and has broad application prospects.

[0006] This invention provides a zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst with the following composition: Ti-LDH as the support, Co loading of 0-2.0 wt%, and I loading of 0-0.6 wt%.

[0007] Among the catalysts mentioned above, Ti-LDH can be used as a support to support Co alone, I alone, or both Co and I simultaneously.

[0008] Preferably, the catalyst has the following composition: Ti-LDH as support, Co loading of 1.0-2.0 wt%, and I loading of 0.2-0.6 wt%.

[0009] This invention provides a method for preparing the above-mentioned zinc-titanium hydrotalcite anchored heterogeneous single-atom catalyst. ZnTi-LDH was synthesized by a solvothermal method, and on this basis, Zn elements were etched with NaOH to generate metallic Zn vacancies. Then, abundant oxygen vacancies were generated in a methanol system to selectively anchor cobalt nitrate and ammonium iodide single-atom precursors to different sites of the vacancy hydrotalcite.

[0010] This invention provides a method for preparing the above-mentioned zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst, comprising the following steps: (1) Preparation of a mixed solution of urea, metal salt and ammonium fluoride Dissolve urea in deionized water to prepare a 1.6-1.7 mol / L urea aqueous solution. Stir at 480-520 rpm for 25-35 min in a magnetic water bath at 30°C, then transfer the solution to a 100 mL round-bottom flask for later use. Weigh 4.5-5.5 mmol of zinc nitrate hexahydrate and 25-35 mmol of ammonium fluoride and dissolve them in deionized water. The resulting mixed solution has a zinc nitrate concentration of 0.2-0.3 mol / L and an ammonium fluoride concentration of 1.0-2.0 mol / L. Stir at 480-520 rpm for 10-20 min in a magnetic water bath at 30°C. Using a pipette, add 13-16 mmol of 99% TiCl4 solution dropwise to the above zinc nitrate and ammonium fluoride mixed solution. At this point, the concentration of the TiCl4 solution is 0.5-1.0 mol / L. 2+ With Ti 4+ The molar ratio is 1:2~4; then stir at 480-520 rpm for 10-20 min to obtain a homogeneous mixed solution of metal salt and ammonium fluoride.

[0011] (2) Preparation of zinc-titanium hydrotalcite catalyst (Zn-Ti-LDH) The mixed solution of metal salt and ammonium fluoride prepared in step (1) was gradually added dropwise to the urea solution. The mixture was stirred at 480-520 rpm for 10-20 min under a magnetic water bath at 30°C to ensure thorough mixing. The mixture was then transferred to a 100 mL polytetrafluoroethylene liner and subjected to hydrothermal reaction for 20-36 h at a temperature controlled at 100-150°C. After the reaction was completed, a white product was obtained by high-speed centrifugation at 8000-12000 rpm. The product was then dried at 55-70°C for 8-12 h. The product was ball-milled and passed through a 100-mesh molecular sieve to obtain the zinc-titanium hydrotalcite catalyst.

[0012] (3) Preparation of etching zinc-titanium hydrotalcite catalyst (E-Ti-LDH) Weigh 7-9 g of NaOH and dissolve it in 90-120 mL of deionized water. Stir at 480-520 rpm for 10-20 min in a magnetic water bath at 30℃. Then weigh 0.8-1.2 g of the zinc-titanium hydrotalcite prepared in step (2) and slowly add it to the NaOH solution. Stir magnetically for 1.5-2.5 h. According to the principle of like dissolves like, the Zn metal is etched away at this time, leaving typical cationic metal vacancies. After stirring, age in a water bath at 30℃ for 10-20 min, then centrifuge and dry. Grind the product and pass it through a 100-mesh molecular sieve to obtain the etched zinc-titanium hydrotalcite catalyst (E-Ti-LDH).

[0013] (4) Preparation of cobalt-anchored zinc-titanium hydrotalcite catalyst (Co / Ti-LDH) Measure 50-70 mL of liquid-phase methanol and 20-40 mL of deionized water using a 100 mL graduated cylinder. Stir both in a magnetic water bath at 30°C at 480-520 rpm for 10-20 min. Then add 25-35 mg of cobalt nitrate hexahydrate and stir until completely dissolved. Transfer the solution to a sealed, light-proof 100 mL reactor and purge with argon gas for 25-35 min. Then add 150-250 mg of the catalyst from step (3) and irradiate it under 365 nm LED ultraviolet light for 2-4 h. After aging for 30 min, the product is obtained by high-speed centrifugation at 8000-12000 rpm. The product is then dried at 55-70°C for 8-12 h. After ball milling, the product is passed through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored cobalt single-atom catalyst.

[0014] (5) Preparation of etched zinc-titanium hydrotalcite anchored iodine single-atom catalyst (I / Ti-LDH) Measure 50-70 mL of liquid-phase methanol and 20-40 mL of deionized water using a 100 mL graduated cylinder. Stir both in a magnetic water bath at 30°C for 480-520 rpm for 10-20 min. Add 10-11 mg of ammonium iodide and stir until completely dissolved. Transfer the solution to a sealed, light-proof 100 mL reactor and purge with argon gas for 25-35 min. Then add 250-350 mg of the catalyst from step (3) and irradiate it under 365 nm LED ultraviolet light for 2-4 h. After aging for 30 min, centrifuge at 8000-12000 rpm to obtain a pale yellow product. Dry the product at 55-70°C for 8-12 h. After ball milling, pass the product through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored iodine single-atom catalyst.

[0015] (6) Preparation of etched zinc-titanium hydrotalcite anchored heterogeneous single-atom catalyst (Co+I / Ti-LDH) Measure 50-70 mL of liquid-phase methanol and 20-40 mL of deionized water using a 100 mL graduated cylinder. Stir both in a magnetic water bath at 30°C and 480-520 rpm for 10-20 min. Add 25-35 mg of cobalt nitrate hexahydrate and stir until completely dissolved. Transfer the solution to a sealed, light-proof 100 mL reactor and purge with argon gas for 25-35 min. Then add 150-250 mg of the catalyst from step (5) and irradiate it under 365 nm LED ultraviolet light for 2-4 h. After aging for 30 min, centrifuge at 8000-12000 rpm to obtain an orange-yellow product. Dry the product at 55-70°C for 8-12 h. After ball milling, pass the product through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored cobalt-iodine heterogeneous single-atom catalyst.

[0016] In the above preparation method, in step (2), the molar ratio of the added Zn and Ti monolithic metal salt solution to the ammonium fluoride solution is 1:3-1:1.

[0017] In the above preparation method, in step (3), the molar concentration of NaOH is 1.5-2.5 mol / L.

[0018] In the above preparation method, in steps (4) to (6), the flow rate of argon gas is controlled at 60 mL / min-100 mL / min; and the LED ultraviolet lamp is used for irradiation and reduction at 16-25 W.

[0019] This invention provides the application of the above-mentioned single-atom catalyst in the removal of organic pollutants from water by activating persulfate (PMS).

[0020] The specific application process is as follows: it is carried out in an acrylic reactor; the catalyst particle size is 40-60 mesh, and the dosage is 5-20 mg; the PMS dosage is 0.25-1 mol / L; the organic pollutant concentration is 5-15 mg / L; the reaction system temperature is 25-35℃; the activity data is tested after the reaction reaches equilibrium; the pollutant degradation evaluation shows that the Co+I / Ti-LDH catalyst can rapidly remove pollutants from water within 25 min, and has good versatility and stability.

[0021] The Co+I / Ti-LDH catalyst synthesized in this invention possesses strong electron transfer capabilities. Through proton-coupled electron transfer, it can effectively activate persulfate (PMS) to selectively generate high-valence metal oxygen species for the oxidation of pollutants in wastewater. The Co+I / Ti-LDH+PMS system is suitable for wastewater contaminated with phenols, antibiotics, and dyes, exhibiting excellent catalytic performance within a pH range of 3-9, along with good stability and environmental friendliness. Therefore, this is a highly efficient, low-cost, and recyclable catalyst with promising applications in wastewater treatment.

[0022] The beneficial effects of this invention are: (1) The entire preparation process of the present invention is simple, convenient and easy to operate, and can be applied to industrial mass production.

[0023] (2) The catalyst prepared in this invention uses Zn-Ti-LDH as a precursor. The good layered structure of LDH gives it good adsorption and catalytic performance. A large number of metal Zn vacancies and oxygen vacancies are generated on its surface by alkaline etching and ultraviolet reduction. The generation of a large number of vacancies further enhances the acidic centers on the catalyst surface, which can effectively activate PMS to generate active oxygen species.

[0024] (3) The catalyst prepared in this invention effectively fixes Co and I single atoms by utilizing metal Zn vacancies and oxygen vacancies. At this time, the electron transfer of Co single atoms selectively activates PMS to generate high-valence Co metal, while I single atoms accept protons to accelerate electron transfer. The proton-coupled electron transfer pathway effectively enhances the selective activation of PMS.

[0025] (4) The catalyst prepared by the present invention is applied to heterogeneous persulfate oxidation technology, which has excellent removal effect on pollutants in wastewater and good stability.

[0026] (5) The catalyst prepared by the present invention can still have good removal ability of pollutants in different pH ranges.

[0027] (6) The catalyst prepared by this invention is environmentally friendly, with no secondary pollution such as metal leaching and a small amount of catalyst added. Attached Figure Description

[0028] Figure 1 The X-ray diffraction (XRD) patterns of the intermediate precursor and the final product obtained in Example 1 are shown.

[0029] Figure 2 The images shown are spherical aberration electron microscopy (HAADF-STEM) images and corresponding energy-dispersive X-ray spectroscopy (EDS) images of the Co+I / Ti-LDH catalyst in Example 1.

[0030] Figure 3The images show the electron paramagnetic resonance (EPR) diagrams of Zn-Ti-LDH, E-Ti-LDH, and Co+I / Ti-LDH in Example 1.

[0031] Figure 4 The diagram shows the catalytic performance of different catalysts activating PMS to remove phenol in Example 3, as well as the effect of different catalyst adsorption on the degradation rate.

[0032] Figure 5 The diagram shows the pseudo-first-order degradation kinetics corresponding to the catalytic performance of PMS activated by different catalysts in Example 3 for the removal of phenol.

[0033] Figure 6 The graph shows the catalytic performance of phenol removal with different amounts of PMS and different amounts of Co+I / Ti-LDH in Example 4.

[0034] Figure 7 The graph shows the catalytic performance of phenol removal at different pH values ​​in Example 4.

[0035] Figure 8 The diagrams show the quenching experiment and the heavy water experiment of removing phenol using the Co+I / Ti-LDH catalyst in Example 5.

[0036] Figure 9 This is a leaching diagram of metal ions in the solution after use in Example 6.

[0037] Figure 10 The diagram shows the PMS cyclic experiment activated by the Co+I / Ti-LDH catalyst in Example 6. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention, and the present invention can be embodied in many different forms of embodiments. All other embodiments obtained based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0039] In the following embodiments, phenol wastewater was selected as a typical recalcitrant organic wastewater for simulation experiments. Phenol is not a limitation on recalcitrant organic matter; any pollutant that falls within the scope of recalcitrant organic matter is within the protection scope of this invention. Example 1

[0040] (1) Dissolve urea in 30 mL of deionized water to prepare a 1.6 mol / L urea aqueous solution. Stir at 500 rpm for 30 min in a magnetic water bath at 30°C, then transfer it to a 100 mL round-bottom flask for later use. Weigh 5 mmol of zinc nitrate hexahydrate and 30 mmol of ammonium fluoride and dissolve them in 20 mL of deionized water. The concentrations of the Zn metal solution and the ammonium fluoride solution are 0.25 mol / L and 1.5 mol / L, respectively. Stir at 500 rpm for 15 min in a magnetic water bath at 30°C. Then, use a pipette to measure 15 mmol of TiCl4 liquid with a mass concentration of 99.9% and add it dropwise to the above mixed solution of zinc nitrate and ammonium fluoride. At this time, the concentration of TiCl4 solution is 0.75 mol / L, and the concentration of Zn is 0.75 mol / L. 2+ With Ti 4+ The molar ratio of metal salt and ammonium fluoride was 1:3, and then the mixture was stirred at 500 rpm for 15 min to obtain a homogeneous mixed solution of metal salt and ammonium fluoride.

[0041] (2) The mixed solution of metal salt and ammonium fluoride prepared in step (1) was gradually added dropwise to the urea solution. The mixture was stirred at 500 rpm for 15 min under a magnetic water bath at 30°C and then transferred to a 100 mL polytetrafluoroethylene liner. The hydrothermal reaction was carried out for 24 h at a temperature of 130°C. After the reaction was completed, a white product was obtained by high-speed centrifugation at 10000 rpm. The product was then dried at 60°C for 10 h. After ball milling, the product was passed through a 100-mesh molecular sieve to obtain zinc-titanium hydrotalcite.

[0042] (3) Weigh 8 g of NaOH and dissolve it in 100 mL of deionized water. Stir at 500 rpm for 15 min in a magnetic water bath at 30°C. Then weigh 1 g of zinc-titanium hydrotalcite prepared in step (2) and slowly add it to the NaOH solution. Stir magnetically for 2 h. According to the principle of like dissolves like, Zn metal is etched away at this time, leaving typical cationic metal vacancies. After stirring, age in a water bath at 30°C for 15 min. Then centrifuge and dry. After grinding the product, pass it through a 100-mesh molecular sieve to obtain etched hydrotalcite (E-Ti-LDH).

[0043] (4) 60 mL of liquid-phase methanol and 30 mL of deionized water were measured using a 100 mL graduated cylinder. The two were stirred at 500 rpm for 15 min in a magnetic water bath at 30 °C. 30 mg of cobalt nitrate hexahydrate was added and stirred until completely dissolved. The solution was transferred to a sealed, light-proof 100 mL reactor and argon gas was introduced for 30 min. Then 200 mg of the catalyst from step (3) was added and the mixture was irradiated under 365 nm LED ultraviolet light for 3 h. After aging for 30 min, a light green product was obtained by high-speed centrifugation at 10000 rpm. The product was then dried at 60 °C for 10 h. After ball milling, the product was passed through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored cobalt single-atom catalyst.

[0044] (5) 60 mL of liquid-phase methanol and 30 mL of deionized water were measured using a 100 mL graduated cylinder. The two were stirred at 500 rpm for 15 min in a magnetic water bath at 30 °C. 10.5 mg of ammonium iodide was added and stirred until completely dissolved. The solution was transferred to a sealed, light-proof 100 mL reactor and argon gas was introduced for 30 min. Then 300 mg of the catalyst from step (3) was added and the mixture was irradiated under 365 nm LED ultraviolet light for 3 h. After aging for 30 min, a pale yellow product was obtained by high-speed centrifugation at 10000 rpm. The product was then dried at 60 °C for 10 h. After ball milling, the product was passed through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored iodine single-atom catalyst.

[0045] (6) 60 mL of liquid-phase methanol and 30 mL of deionized water were measured using a 100 mL graduated cylinder. The two were stirred at 500 rpm for 15 min in a magnetic water bath at 30 °C. 30 mg of cobalt nitrate hexahydrate was added and stirred until completely dissolved. The solution was transferred to a sealed, light-proof 100 mL reactor and argon gas was introduced for 30 min. Then 200 mg of the catalyst from step (5) was added and the mixture was irradiated under 365 nm LED ultraviolet light for 3 h. After aging for 30 min, an orange-yellow product was obtained by high-speed centrifugation at 10,000 rpm. The product was then dried at 60 °C for 10 h. After ball milling, the product was passed through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored cobalt-iodine heterogeneous single-atom catalyst.

[0046] In this embodiment, a hydrotalcite-anchored cobalt single-atom catalyst, a hydrotalcite-anchored iodine single-atom catalyst, and a hydrotalcite-anchored cobalt-iodine heterogeneous single-atom catalyst were prepared.

[0047] Figure 1The X-ray diffraction patterns of different catalysts in Embodiment 1 of the present invention show that the presence of (003), (006), (012), (101), and (009) crystal planes confirms the successful preparation of Zn-Ti-LDH. After etching Zn with NaOH, it can be found that E-Ti-LDH mainly consists of (101), (004), (200), (105), and (211) crystal planes of TiO2 crystal form. In addition, no obvious single-atom peaks were found after photoreduction loading of single atoms, which is attributed to the uniform distribution of cobalt iodine single atoms on E-Ti-LDH.

[0048] Figure 2 The images shown are spherical aberration electron microscopy (SEM) images and corresponding energy-dispersive X-ray diffraction (EDS) images of Co+I / Ti-LDH in Embodiment 1 of this invention. Co+I / Ti-LDH has been successfully prepared. Meanwhile, EDS has confirmed the presence and uniform dispersion of Co and I single atoms on E-Ti-LDH.

[0049] Figure 3 The electron paramagnetic resonance (EPR) images of Zn-Ti-LDH, E-Ti-LDH, and Co+I / Ti-LDH in Example 1 of this invention are shown. Initially, Zn-Ti-LDH has a small number of vacancies. After alkaline etching and ultraviolet light reduction, a large number of metallic Zn vacancies and oxygen vacancies are generated. At this time, the characteristic EPR signal peak is significantly enhanced. The reason why the signal peak intensity of Co+I / Ti-LDH weakens is that the vacancies anchor Co and I single atoms. Example 2

[0050] Two parallel experiments, 2-1 and 2-2, were conducted to prepare the catalyst using the same method as in Example 1, except for the different reaction conditions. The reaction conditions are shown in the table below:

[0051] Tests showed that Example 2 successfully prepared two groups of hydrotalcite-anchored cobalt single-atom catalysts, hydrotalcite-anchored iodine single-atom catalysts, and hydrotalcite-anchored cobalt-iodine heterogeneous single-atom catalysts, and the obtained catalysts had excellent performance.

[0052] Example 3: The effects of different catalysts (Zn-Ti-LDH, E-Ti-LDH, Co / Ti-LDH, I / Ti-LDH, Co+I / Ti-LDH, and blank) in Example 1 of this invention on the removal of phenol from water by PMS were tested.

[0053] Different types of catalysts were added to phenol wastewater, and the mixture was magnetically stirred for 10 min to ensure thorough particle dispersion. Then, 500 μL of a 0.1 mol / L PMS solution was added, and the reaction system was magnetically stirred for 30 min to conduct a concentration removal experiment. During the advanced oxidation reaction, at regular intervals (reaction times 0, 2.5, 5, 7.5, 10, 15, 20, 25, and 30 min), 1 mL of sample was added to 200 μL (0.5 mmol / L) of sodium thiosulfate solution and filtered through a 0.22 μm nylon membrane. The concentration was then determined by liquid chromatography at a detection wavelength of 273 nm to determine the phenol removal rate, thus obtaining the catalytic effect of different materials on phenol. The optimal concentrations were: phenol 10 mg / L, catalyst 0.1 g / L, and PMS 0.5 mmol / L. Adsorption experiments followed the same steps as above, except that PMS solution was not added.

[0054] Figure 4 The diagrams show the catalytic performance of different catalysts activating PMS for phenol removal in Example 3, as well as the effect of adsorption on the degradation rate. It can be seen that adsorption is ineffective in removing phenol. The catalytic performance of Zn-Ti-LDH and E-Ti-LDH is not significantly different from, or even worse than, PMS alone after being added to PMS, indicating poor catalytic performance. The Co+I / Ti-LDH / PMS system can rapidly remove phenol within 25 min and exhibits higher catalytic performance compared to other catalysts.

[0055] Figure 5 The diagram shows the pseudo-first-order degradation kinetics corresponding to the catalytic performance of PMS activated by different catalysts in Example 3 for phenol removal. Although the Co / Ti-LDH / PMS and I / Ti-LDH / PMS systems showed significant improvements compared to single PMS activation, the pseudo-first-order degradation rates were 0.0537 and 0.00394 min, respectively. -1 However, the rate was increased to 0.1862 min in the Co+I / Ti-LDH / PMS system. -1 It is 3.47 times and 47.26 times that of the two systems mentioned above, far exceeding the sum of the two. This is attributed to the synergistic effect of Co and I single atoms. The proton coupling effect effectively promotes the production of high-valence Co metal and effectively removes phenol from wastewater.

[0056] Example 4: The activation of PMS by the Co+I / Ti-LDH catalyst in Example 1 of this invention for the removal of phenol from water was tested under different conditions.

[0057] Co+I / Ti-LDH catalysts of different concentrations (0.05, 0.10, 0.20 g / L) were added to phenol wastewater and magnetically stirred for 10 min to ensure thorough particle dispersion. Then, 500 μL of 0.1 mol / L PMS solution was added, and the reaction system was magnetically stirred for 30 min to conduct a concentration removal experiment. During the advanced oxidation reaction, at regular intervals (reaction times 0, 2.5, 5, 7.5, 10, 15, 20, 25, 30 min), 1 mL of sample was added to 200 μL (0.5 mmol / L) of sodium thiosulfate solution and filtered through a 0.22 μm nylon membrane. The concentration was then determined by liquid chromatography at a detection wavelength of 273 nm to determine the phenol removal rate, thus obtaining the catalytic effect of different materials on phenol. The phenol concentration was 10 mg / L, and the PMS concentration was 0.5 mmol / L.

[0058] The same experimental steps as above were followed, with the catalyst concentration fixed at 0.10 g / L, and the PMS dosage varied to 0.25 mM, 0.50 mM, and 1.00 mM.

[0059] The experimental procedures were the same as described above, with the experimental conditions fixed at phenol 10 mg / L, catalyst 0.1 g / L, and PMS 0.5 mmol / L. The initial pH of the reaction was adjusted by adding 0.1 M HCl or 0.1 M NaOH dropwise.

[0060] Figure 6 The graph shows the catalytic performance of phenol removal with different amounts of PMS and Co+I / Ti-LDH in Example 4. It can be seen that increasing the amount of catalyst and PMS improves the catalytic efficiency; however, excessive addition does not show a significant positive proportional increase in catalytic efficiency. Therefore, selecting appropriate treatment conditions is necessary. The optimized experimental conditions in this patent are phenol 10 mg / L, catalyst 0.1 g / L, and PMS 0.5 mmol / L.

[0061] Figure 7 The graph shows the catalytic performance of phenol removal at different pH values ​​in Example 4. The Co+I / Ti-LDH catalyst exhibits a slower removal rate at pH 11, but still maintains rapid phenol removal in the pH range of 3-9, indicating that Co+I / Ti-LDH has a wide pH operating range and that the high-valence Co metal can effectively maintain stability.

[0062] Example 5: The contribution of reactive oxygen species in the Co+I / Ti-LDH / PMS system of Example 1 of this invention was investigated. Under fixed reaction conditions of phenol 10 mg / L, catalyst 0.1 g / L, and PMS 0.5 mmol / L, different quenchers were added to investigate the contribution of reactive oxygen species in phenol removal. Subsequently, at regular intervals (reaction times 0, 2.5, 5, 7.5, 10, 15, 20, 25, and 30 min), 1 mL of sample was added to 200 μL (0.5 mmol / L) of sodium thiosulfate solution and filtered through a 0.22 μm nylon membrane. The concentration was then determined by liquid chromatography at a detection wavelength of 273 nm to determine the phenol removal rate.

[0063] Figure 8 Example 5 shows the quenching experiment diagrams and heavy water experiment diagrams for the removal of phenol using the Co+I / Ti-LDH catalyst. It can be observed that the addition of tert-butanol (TBA, quenching hydroxyl radicals), methanol, and ethanol (MeOH, EtOH, quenching sulfate and hydroxyl radicals), and p-benzoquinone (p-BQ, quenching superoxide radicals), did not significantly affect the phenol removal efficiency, essentially eliminating the effect of these free radicals. However, the addition of L-histidine and furfuryl alcohol (L-his, FFA, quenching singlet oxygen) reduced the phenol removal performance to some extent, and the addition of DMSO (quenching high-valence metals) did not effectively remove phenol. Since singlet oxygen has a longer lifespan in heavy water, theoretically the catalytic efficiency should be improved; however, actual heavy water experiments showed no significant change in phenol removal efficiency. In summary, this confirms that higher metal oxygens dominate the reaction system, consistent with the proton-coupled electron transfer system proposed in this patent for enhancing the production of high-valence Co metals.

[0064] Example 6: The leaching amount of ions after use of the Co+I / Ti-LDH catalyst prepared in Example 1 of this invention was tested, as well as the effect of activated PMS on removing phenol from water after multiple cycles and regeneration treatments.

[0065] Co+I / Ti-LDH catalyst was added to phenol wastewater and magnetically stirred for 10 min to ensure complete particle dispersion. Then, 500 μL of 0.1 mol / L PMS solution was added, and the reaction system was magnetically stirred for 30 min to conduct a concentration removal experiment. During the advanced oxidation reaction, at regular intervals (reaction times 0, 2.5, 5, 7.5, 10, 15, 20, 25, 30 min), 1 mL of sample was added to 200 μL (0.5 mmol / L) of sodium thiosulfate solution and filtered through a 0.22 μm nylon membrane. The concentration was then determined by liquid chromatography at a detection wavelength of 273 nm to determine the phenol removal rate, thus obtaining the catalytic effect of different materials on phenol. The optimal concentrations were: phenol 10 mg / L, catalyst 0.1 g / L, and PMS 0.5 mmol / L. In addition, the reaction solution was filtered through a 0.22 μm nylon membrane and subjected to ICP-MS to test the ion concentration. Finally, the catalyst in the water was collected, dried, and the loss was replenished to repeat the above oxidation experiment steps, and the cycle was repeated five times.

[0066] Figure 9 The image shows the leaching of metal ions in the solution after use in Example 6. The leaching amounts of Co and I ions were 660.01 μg / L and 124.37 μg / L, respectively, which meet the groundwater quality standard (GB / T 14848-2017) and avoid secondary pollution.

[0067] Figure 10 The diagram shows the PMS cyclic experiment of Co+I / Ti-LDH catalyst activation in Example 6. As the reaction time increased, the phenol degradation efficiency decreased, possibly due to the deactivation of active sites on the catalyst surface. Even so, Co+I / Ti-LDH maintained good reusability and stability; after five cycles, the degradation efficiency remained at 89.95%, and it could be regenerated to maintain its catalytic performance. The preferred embodiments of the present invention have been described in detail above, but are not intended to limit the implementation. Furthermore, it should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst, characterized in that, The catalyst composition is as follows: Ti-LDH as support, Co loading is 0-2.0 wt%, and I loading is 0-0.6 wt%.

2. The zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst according to claim 1, characterized in that, The catalyst composition is as follows: Ti-LDH as support, Co loading is 1.0-2.0 wt%, and I loading is 0.2-0.6 wt%.

3. A method for preparing a zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst as described in claim 1 or 2, characterized in that, ZnTi-LDH was synthesized via a solvothermal method. Based on this, metallic Zn vacancies were generated by etching Zn elements with NaOH, and then abundant oxygen vacancies were generated in a methanol system. Cobalt nitrate and / or ammonium iodide single-atom precursors were selectively anchored to different sites of vacancy hydrotalcite.

4. The preparation method of the zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst according to claim 3, characterized in that... Includes the following steps: (1) Preparation of a mixed solution of urea, metal salt and ammonium fluoride Dissolve urea in deionized water to prepare a 1.6-1.7 mol / L urea aqueous solution. Stir at 480-520 rpm for 25-35 min in a magnetic water bath at 30°C, then transfer the solution to a 100 mL round-bottom flask for later use. Weigh 4.5-5.5 mmol of zinc nitrate hexahydrate and 25-35 mmol of ammonium fluoride and dissolve them in deionized water. The resulting mixed solution should have a zinc nitrate concentration of 0.2-0.3 mol / L and an ammonium fluoride concentration of 1.0-2.0 mol / L. Stir at 480-520 rpm for 10-20 min in a magnetic water bath at 30°C. Using a pipette, add 13-16 mmol of 99% TiCl4 liquid dropwise to the above zinc nitrate and ammonium fluoride mixed solution. At this point, the TiCl4 solution concentration should be 0.5-1.0 mol / L. Then, stir at 480-520 rpm. Stir at rpm for 10-20 min to obtain a homogeneous mixed solution of metal salt and ammonium fluoride; (2) Preparation of zinc-titanium hydrotalcite catalyst; The mixed solution of metal salt and ammonium fluoride prepared in step (1) was gradually added dropwise to the urea solution. The mixture was stirred at 480-520 rpm for 10-20 min under a magnetic water bath at 30°C to ensure thorough mixing. The mixture was then transferred to a 100 mL polytetrafluoroethylene liner and subjected to hydrothermal reaction for 20-36 h at a temperature controlled at 100-150°C. After the reaction was completed, a white product was obtained by high-speed centrifugation at 8000-12000 rpm. The product was then dried at 55-70°C for 8-12 h. The product was ball-milled and passed through a 100-mesh molecular sieve to obtain a zinc-titanium hydrotalcite catalyst. (3) Preparation of etching zinc-titanium hydrotalcite catalyst Weigh 7-9 g of NaOH and dissolve it in 90-120 mL of deionized water. Stir at 480-520 rpm for 10-20 min in a magnetic water bath at 30℃. Then weigh 0.8-1.2 g of zinc-titanium hydrotalcite prepared in step (2) and slowly add it to the NaOH solution. Stir magnetically for 1.5-2.5 h. According to the principle of like dissolves like, Zn metal is etched away at this time, leaving typical cationic metal vacancies. After stirring, age in a water bath at 30℃ for 10-20 min, then centrifuge and dry. Grind the product and pass it through a 100-mesh molecular sieve to obtain the etched zinc-titanium hydrotalcite catalyst. (4) Preparation of cobalt-anchored catalysts for etching zinc-titanium hydrotalcite Measure 50-70 mL of liquid-phase methanol and 20-40 mL of deionized water using a 100 mL graduated cylinder. Stir both in a magnetic water bath at 30°C at 480-520 rpm for 10-20 min. Then add 25-35 mg of cobalt nitrate hexahydrate and stir until completely dissolved. Transfer the solution to a sealed, light-proof 100 mL reactor and purge with argon gas for 25-35 min. Then add 150-250 mg of the catalyst from step (3) and irradiate it under 365 nm LED ultraviolet light for 2-4 h. After aging for 30 min, the product is obtained by high-speed centrifugation at 8000-12000 rpm. The product is then dried at 55-70°C for 8-12 h. After ball milling, the product is passed through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored cobalt single-atom catalyst.

5. The preparation method of the zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst according to claim 3, characterized in that... Includes the following steps: (1) Preparation of a mixed solution of urea, metal salt and ammonium fluoride Dissolve urea in deionized water to prepare a 1.6-1.7 mol / L urea aqueous solution. Stir at 480-520 rpm for 25-35 min in a magnetic water bath at 30°C, then transfer the solution to a 100 mL round-bottom flask for later use. Weigh 4.5-5.5 mmol of zinc nitrate hexahydrate and 25-35 mmol of ammonium fluoride and dissolve them in deionized water. The resulting mixed solution should have a zinc nitrate concentration of 0.2-0.3 mol / L and an ammonium fluoride concentration of 1.0-2.0 mol / L. Stir at 480-520 rpm for 10-20 min in a magnetic water bath at 30°C. Using a pipette, add 13-16 mmol of 99% TiCl4 liquid dropwise to the above zinc nitrate and ammonium fluoride mixed solution. At this point, the TiCl4 solution concentration should be 0.5-1.0 mol / L. Then, stir at 480-520 rpm. Stir at rpm for 10-20 min to obtain a homogeneous mixed solution of metal salt and ammonium fluoride; (2) Preparation of zinc-titanium hydrotalcite catalyst; The mixed solution of metal salt and ammonium fluoride prepared in step (1) was gradually added dropwise to the urea solution. The mixture was stirred at 480-520 rpm for 10-20 min under a magnetic water bath at 30°C to ensure thorough mixing. The mixture was then transferred to a 100 mL polytetrafluoroethylene liner and subjected to hydrothermal reaction for 20-36 h at a temperature controlled at 100-150°C. After the reaction was completed, a white product was obtained by high-speed centrifugation at 8000-12000 rpm. The product was then dried at 55-70°C for 8-12 h. The product was ball-milled and passed through a 100-mesh molecular sieve to obtain a zinc-titanium hydrotalcite catalyst. (3) Preparation of etching zinc-titanium hydrotalcite catalyst Weigh 7-9 g of NaOH and dissolve it in 90-120 mL of deionized water. Stir at 480-520 rpm for 10-20 min in a magnetic water bath at 30℃. Then weigh 0.8-1.2 g of zinc-titanium hydrotalcite prepared in step (2) and slowly add it to the NaOH solution. Stir magnetically for 1.5-2.5 h. According to the principle of like dissolves like, Zn metal is etched away at this time, leaving typical cationic metal vacancies. After stirring, age in a water bath at 30℃ for 10-20 min, then centrifuge and dry. Grind the product and pass it through a 100-mesh molecular sieve to obtain the etched zinc-titanium hydrotalcite catalyst. (4) Preparation of etched zinc-titanium hydrotalcite anchored iodine single-atom catalyst Measure 50-70 mL of liquid-phase methanol and 20-40 mL of deionized water using a 100 mL graduated cylinder. Stir both in a magnetic water bath at 30°C for 480-520 rpm for 10-20 min. Add 10-11 mg of ammonium iodide and stir until completely dissolved. Transfer the solution to a sealed, light-proof 100 mL reactor and purge with argon gas for 25-35 min. Then add 250-350 mg of the catalyst from step (3) and irradiate it under 365 nm LED ultraviolet light for 2-4 h. After aging for 30 min, centrifuge at 8000-12000 rpm to obtain a pale yellow product. Dry the product at 55-70°C for 8-12 h. After ball milling, pass the product through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored iodine single-atom catalyst.

6. The preparation method of the zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst according to claim 3, characterized in that... Includes the following steps: (1) Preparation of a mixed solution of urea, metal salt and ammonium fluoride Dissolve urea in deionized water to prepare a 1.6-1.7 mol / L urea aqueous solution. Stir at 480-520 rpm for 25-35 min in a magnetic water bath at 30°C, then transfer the solution to a 100 mL round-bottom flask for later use. Weigh 4.5-5.5 mmol of zinc nitrate hexahydrate and 25-35 mmol of ammonium fluoride and dissolve them in deionized water. The resulting mixed solution should have a zinc nitrate concentration of 0.2-0.3 mol / L and an ammonium fluoride concentration of 1.0-2.0 mol / L. Stir at 480-520 rpm for 10-20 min in a magnetic water bath at 30°C. Using a pipette, add 13-16 mmol of 99% TiCl4 liquid dropwise to the above zinc nitrate and ammonium fluoride mixed solution. At this point, the TiCl4 solution concentration should be 0.5-1.0 mol / L. Then, stir at 480-520 rpm. Stir at rpm for 10-20 min to obtain a homogeneous mixed solution of metal salt and ammonium fluoride; (2) Preparation of zinc-titanium hydrotalcite catalyst; The mixed solution of metal salt and ammonium fluoride prepared in step (1) was gradually added dropwise to the urea solution. The mixture was stirred at 480-520 rpm for 10-20 min under a magnetic water bath at 30°C to ensure thorough mixing. The mixture was then transferred to a 100 mL polytetrafluoroethylene liner and subjected to hydrothermal reaction for 20-36 h at a temperature controlled at 100-150°C. After the reaction was completed, a white product was obtained by high-speed centrifugation at 8000-12000 rpm. The product was then dried at 55-70°C for 8-12 h. The product was ball-milled and passed through a 100-mesh molecular sieve to obtain a zinc-titanium hydrotalcite catalyst. (3) Preparation of etching zinc-titanium hydrotalcite catalyst Weigh 7-9 g of NaOH and dissolve it in 90-120 mL of deionized water. Stir at 480-520 rpm for 10-20 min in a magnetic water bath at 30℃. Then weigh 0.8-1.2 g of zinc-titanium hydrotalcite prepared in step (2) and slowly add it to the NaOH solution. Stir magnetically for 1.5-2.5 h. According to the principle of like dissolves like, Zn metal is etched away at this time, leaving typical cationic metal vacancies. After stirring, age in a water bath at 30℃ for 10-20 min, then centrifuge and dry. Grind the product and pass it through a 100-mesh molecular sieve to obtain the etched zinc-titanium hydrotalcite catalyst. (4) Preparation of etched zinc-titanium hydrotalcite anchored iodine single-atom catalyst Measure 50-70 mL of liquid-phase methanol and 20-40 mL of deionized water using a 100 mL graduated cylinder. Stir the two in a magnetic water bath at 30°C for 480-520 rpm for 10-20 min. Then add 10-11 mg of ammonium iodide and stir until completely dissolved. Transfer the solution to a sealed, light-proof 100 mL reactor and purge with argon gas for 25-35 min. Then add 250-350 mg of the catalyst from step (3) and irradiate it under 365 nm LED ultraviolet light for 2-4 h. After aging for 30 min, the product is obtained by high-speed centrifugation at 8000-12000 rpm. The product is then dried at 55-70°C for 8-12 h. After ball milling, the product is passed through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored iodine single-atom catalyst. (5) Preparation of etched zinc-titanium hydrotalcite anchored cobalt-iodine heterogeneous single-atom catalyst Measure 50-70 mL of liquid-phase methanol and 20-40 mL of deionized water using a 100 mL graduated cylinder. Stir both in a magnetic water bath at 30°C at 480-520 rpm for 10-20 min. Then add 25-35 mg of cobalt nitrate hexahydrate and stir until completely dissolved. Transfer the solution to a sealed, light-proof 100 mL reactor and purge with argon gas for 25-35 min. Then add 150-250 mg of the catalyst from step (4) and irradiate it under 365 nm LED ultraviolet light for 2-4 h. After aging for 30 min, centrifuge at 8000-12000 rpm to obtain an orange-yellow product. Then dry at 55-70°C for 8-12 h. After ball milling, pass the product through a 100-mesh molecular sieve to obtain an etched hydrotalcite-anchored cobalt-iodine heterogeneous single-atom catalyst.

7. The method for preparing the zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst according to any one of claims 4 to 6, characterized in that, Zn 2+ With Ti 4+ The molar ratio is 1:2~4; the molar ratio of the added Zn and Ti monolithic metal salt solution to the ammonium fluoride solution is 1:3-1:

1.

8. The method for preparing the zinc-titanium hydrotalcite-anchored heterogeneous single-atom catalyst according to any one of claims 4 to 6, characterized in that, The molar concentration of NaOH is 1.5-2.5 mol / L; the flow rate of argon gas is controlled at 60 mL / min-100 mL / min; and the LED ultraviolet lamp is used for irradiation and reduction at 16-25 W.

9. The application of the zinc-titanium hydrotalcite anchored heterogeneous single-atom catalyst according to claim 1 or 2 in the removal of organic pollutants from water by activating persulfate.

10. The application according to claim 9, characterized in that, The application process is as follows: the catalyst particle size is 40-60 mesh, and the dosage is 5-20 mg; the PMS dosage is 0.25-1 mol / L; the concentration of organic pollutants is 5-15 mg / L; the temperature of the reaction system is 25-35℃; the activity data are tested after the reaction reaches equilibrium; the pollutant degradation evaluation shows that the Co+I / Ti-LDH catalyst can rapidly remove pollutants from water within 25 min. The pollutants include phenols, antibiotics, and dyes that pollute wastewater.

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