Preparation method of axial chlorine-coordinated cobalt-based photocatalyst and application thereof in degradation of pet microplastics

Abstract

The application relates to a preparation method of an axial chlorine-coordinated cobalt-based photocatalyst and PET micro-plastic degradation application thereof. In view of the problems of difficult control of the electronic structure of a traditional M-N4 catalyst, easy recombination of photo-generated carriers and poor controllability of an axial coordination process, an equatorial pre-anchoring combined axial chlorine coordination strategy is innovatively adopted: thiourea, melamine and cobalt nitrate hexahydrate are used as raw materials to form Co-N and Co-S equatorial coordination structures through high-temperature pyrolysis, the coordination direction is anchored and a side reaction path is closed; then a chloride is used as a chlorine source to realize axial chlorine modification of a Co center through gas phase directional coordination. The method is simple in process, low in cost and free of secondary pollution. The prepared catalyst has a unique asymmetric coordination structure, the electronic structure is optimized, the carrier separation efficiency is improved, the photocatalytic degradation effect on PET micro-plastics is excellent, the catalyst has good stability and circulation, and has great application potential in micro-plastic pollutant treatment.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and catalytic materials technology, specifically to the preparation of a cobalt-based photocatalyst controlled by axial chlorine coordination engineering and its application in the degradation of PET microplastics. Background Technology

[0002] Microplastics (plastic particles with a diameter of less than 5 mm) are known as "PM2.5 in the ocean" and have become a serious global environmental pollutant. They can accumulate through the food chain and cause multiple harms to ecosystems and human health.

[0003] Currently, mainstream technologies for treating microplastics mainly include pyrolysis, bioenzymatic degradation, biochar adsorption, chemical oxidation, and membrane separation. However, these methods generally suffer from high processing costs, long cycles, cumbersome operations, and high risks of secondary pollution, severely restricting their large-scale application in practical engineering. Photocatalysis, with its advantages of being green, efficient, and having mild reaction conditions, has shown great application potential in the field of microplastic pollution control and has become a current research hotspot. Traditional photocatalysts suffer from bottlenecks such as easy recombination of photogenerated carriers and insufficient active sites (Gao Q, Zheng X, Lin J, et al. Nano-Micro Lett., 2026, 18: 266), which greatly limits their actual degradation efficiency and application scenarios for recalcitrant pollutants like microplastics. Therefore, developing novel photocatalytic materials with both high catalytic activity and high structural stability is the core direction for breaking through existing technological barriers and achieving efficient degradation of microplastics. Single-atom catalysts, as a novel class of atomically dispersed catalytic materials, possess unique advantages such as 100% atomic utilization, uniform active sites, and tunable electronic structure, showing broad application prospects in energy conversion and environmental catalysis (Li X, Xue W, Li P, et al. Nano Energy, 2026, 150: 11769). Among them, the M−N4 structure is a key configuration for improving the catalytic performance of single-atom photocatalysts: M is a central metal element such as Fe, Co, Ni, Cu, or Mn, and N4 represents a planar four-coordinate environment formed by four nitrogen atoms. The metal element is precisely anchored by nitrogen atoms in single-atom form, constituting a highly symmetrical M−N4 coordination active center (Zhao S, Ma C, Yu Y, et al. Coordin. Chem. Rev., 2026, 556: 217664). This structure can significantly accelerate the separation and migration of photogenerated carriers and reduce the energy barrier of interfacial catalytic reactions. During photocatalysis, the M−N4 site can simultaneously and efficiently activate oxygen and water molecules, continuously generating strong oxidizing species such as ·OH and ·O2−, thereby achieving efficient cleavage and deep mineralization of microplastic macromolecular chains, significantly improving photocatalytic degradation efficiency and operational stability.

[0004] However, the high symmetry of the M-N4 structure restricts the formation of localized electron-rich or deficient regions in the central metal, and its localized electronic structure is difficult to precisely control, thus adversely affecting the selective adsorption and activation of reaction intermediates. (Wei S, Zhu J, Chen X, et al. Nat. Commun., 2025, 16: 1652; Li Y, Wei Z, Sun Z, et al. Small, 2024, 20(38): 2401900; Xiong M, Li S, Bi Z, et al. Appl.Catal. B: Environ. Energy, 2026, 385: 126320).

[0005] To address this bottleneck, heteroatom doping strategies have been widely used by researchers to modulate the electronic structure of metal active centers, thereby significantly enhancing the catalytic activity of catalysts. In representative studies, Ren et al. successfully constructed a novel Fe−N3P1 coordination structure by partially substituting N atoms in Fe-based catalysts with P atoms, achieving efficient control of the electronic state of the Fe center (Ren T, Lu K, Tao F, et al. Nat. Commun., 2025, 16: 9037). Zeng et al. constructed the S-MnN4 active site by introducing S atom doping into the second coordination shell of a Mn-based catalyst, achieving precise fine-tuning of the d-band energy level of the Mn center (Zeng Y, Yu J, Qi B, et al. Appl. Catal. B: Environ. Energy, 2026, 386: 126433). However, current research mainly focuses on regulating the electronic structure of the central metal through modification of the equatorial coordination environment. Systematic research on regulating the catalytic performance of metal-based catalysts based on axial coordination engineering is still lacking, and the relevant regulatory mechanisms and structure-activity relationships need to be further elucidated. Compared to traditional equatorial plane coordination modulation, axial coordination engineering exhibits irreplaceable advantages in optimizing the performance of metal-based catalysts. Its core regulatory role can be summarized in three dimensions: First, precise and targeted regulation of intrinsic activity. Axial ligands can directly modulate the electronic distribution and orbital energy levels of the central metal through strong orbital coupling, breaking the inherent constraints of equatorial plane coordination modulation and achieving targeted optimization of the intrinsic catalytic activity of active sites. Second, synergistic improvement of reaction selectivity and kinetics. Axial coordination can achieve targeted screening of catalytic reaction pathways and precise optimization of reaction barriers through fine regulation of the electronic microenvironment of active sites, thereby simultaneously improving the selectivity of target products and the intrinsic reaction kinetic rate. Third, significant enhancement of long-term catalytic stability. Axial coordination can effectively inhibit the aggregation, dissolution, and demetallization deactivation of metal active centers by constructing saturated and rigid coordination configurations, significantly improving the structural stability and performance durability of catalysts during long-term applications. In recent years, related work has systematically confirmed the advantages of axial coordination modulation strategies in optimizing the performance of metal-based catalysts through experimental and theoretical calculations.(Zhu G, Zhao S, Yu Y, et al, Adv. Funct. Mater., 2026, Early View: e28316; Fang W, Xu K, Wang X, et al, Nano-Micro Lett., 2026, 18:96; Li F, Wang J, Lv Y, et al, Appl. Catal. B: Environ. Energy, 2026, 386:126391). Among the existing Chinese patent literature, the relevant patents that disclose axial coordination-regulated metal-based catalysts are as follows: CN120797036A "A functionalized carbon nanotube-supported cobalt molecular complex composite and its preparation method and application" discloses a Co composite catalyst with axial coordination bonding prepared by in-situ mixing process using functionalized multi-walled carbon nanotubes (MWCNTs) as conductive carriers and cobalt tetrapyridine molecular complexes (Coqpy) with external modification as catalytic active components.

[0006] CN119707074A, entitled "A fluorine-doped Fe−N−C composite material and its preparation method, application and regeneration", discloses a method for synthesizing Fe-doped metal-organic framework Fe@ZIF-8 material using iron precursor, zinc salt, organic ligand and organic solvent as raw materials, and then carbonizing it into Fe−N−C material; then Fe−N−C is mixed with fluorine source and subjected to secondary carbonization, and fluorine atoms are axially coordinated with Fe at the center of FeN4 to obtain an axially fluorine-coordinated composite material.

[0007] CN120132909A, entitled "A cyanamide-based axially coordinated cobalt single-atom catalyst for persulfate activation, its preparation method and application", discloses a catalyst CoN4(NCN) synthesized by a one-step precipitation method using CoCl2, NH2CN and NaOH, which has isolated Co sites and an axial cyanamide ([NCN]2-) coordination structure.

[0008] Analysis reveals certain shortcomings in the aforementioned patents: they lack effective mechanisms for directional constraint and anchoring of active sites, cannot precisely control the structure and electronic state of active centers, frequently exhibit non-targeted side reactions, and cannot effectively guarantee batch-to-batch consistency of product performance. Furthermore, they are susceptible to factors such as uncontrollable active center configuration and uncontrolled metal species aggregation. In addition, their preparation processes suffer from high raw material costs, lengthy processes, and high energy consumption. Moreover, due to the lack of synthetic control mechanisms, they exhibit low metal atom utilization, numerous byproducts, and poor efficiency and stability.

[0009] To address the aforementioned issues, this patent employs a core design concept of "equatorial plane pre-anchoring and locking of coordination direction + precise control of electronic structure through axial chlorine coordination." This leads to the development of a low-cost, high-precision, high-catalytic-activity, and high-stability axially chlorine-coordinated cobalt-based photocatalyst, overcoming the shortcomings of existing technologies. It constructs a two-step hierarchical coordination atomic-level precise control system, specifically as follows: First, using low-cost and readily available thiourea, melamine, and cobalt nitrate hexahydrate (Co(NO3)2·6H2O) as raw materials, these materials are uniformly dispersed in boiling water. After drying, each component is simultaneously and uniformly precipitated from the solution, obtaining a uniformly dispersed precursor. The precursor is then calcined in a muffle furnace to obtain the cobalt-based photocatalyst. Because in the prepared cobalt-based photocatalyst, cobalt (Co) forms stable Co−N and Co−S coordination bonds with sulfur (S) and nitrogen (N) atoms in the equatorial plane, pre-occupying Co... In the first step, the X and Y directions of the 3d orbital completely seal off the side reaction pathways such as coordination substitution and interstitial doping of heteroatoms in the equatorial plane. In the second step, during the axial coordination control process, ammonium chloride is used as the axial coordination agent and placed upstream of the tube furnace, while the cobalt-based photocatalyst is placed downstream of the tube furnace. The catalyst is then subjected to high-temperature treatment in a nitrogen (N2) atmosphere. Since the coordination sites in the X and Y directions are completely anchored, leaving only the Z-axis direction as an empty coordination orbital, the HCl molecules generated by the high-temperature decomposition of ammonium chloride can undergo directional and singular axial coordination with the downstream Co-based catalyst, thus eliminating side reactions at the source. By precisely controlling the upstream and downstream spacing of the tube furnace (10 ~ 16 cm), the heating rate (2.5 ~ 7.5 ℃ / min), the calcination temperature (350 ~ 550 ℃), and the holding time (1 ~ 3 h), the rate, concentration, and gas phase transport path of HCl generated by the decomposition of NH4Cl are quantitatively controlled. This allows for atomic-level precise control of the degree of axial Cl coordination at the Co center, and directional optimization of the electronic structure and catalytic performance of the catalyst. Chlorine (Cl) has ideal comprehensive properties in terms of electronegativity, ionic radius, orbital matching degree and reactivity. Its coordination with Co can effectively regulate the local electronic structure of Co, promote the separation and transport of photogenerated carriers, and induce the system to generate active species such as superoxide radicals and singlet oxygen, which significantly improves the photocatalytic degradation efficiency of PET by the catalyst.

[0010] To date, no patents or related literature have reported the preparation of axially chlorine-coordinated catalysts with high photocatalytic efficiency using thiourea, melamine, and Co(NO3)2·6H2O as raw materials and ammonium chloride as an axial coordinating agent, with the calcination temperature adjusted. Summary of the Invention

[0011] To address the shortcomings of existing M-N4 catalysts, this invention provides a method for preparing an axially chlorine-coordinated metal-based photocatalyst and its application in the degradation of PET microplastics. This axially chlorine-coordinated metal-based photocatalyst exhibits good catalytic activity, excellent stability, outstanding practical environmental applicability, and good recyclability, thus overcoming the limitations of catalytic applications caused by the symmetry of M-N4.

[0012] The technical problem to be solved by the present invention is to provide a method for preparing a cobalt-based photocatalyst with axial chlorine coordination that has high efficiency in photocatalytic degradation of microplastics.

[0013] To solve this technical problem, the present invention adopts the following technical solution: A method for preparing an axially chlorine-coordinated cobalt-based photocatalyst, comprising the following steps: 1) Dissolve a certain amount of thiourea, melamine and Co(NO3)2·6H2O in 50~200 mL of boiling water and stir for 1~3 h to dissolve them into a uniformly mixed solution. 2) The mixed solution is dried by forced air at 80 ~ 120 ℃, ground, and then placed in a muffle furnace for pyrolysis at 500 ~ 700 ℃ for 2 ~ 6 h at a heating rate of 5 ~ 15 ℃ / min. After natural cooling to room temperature, a cobalt-based photocatalyst is obtained. 3) A certain amount of ammonium chloride (chlorine source) and cobalt-based catalyst without axial chlorine coordination were placed upstream and downstream of a tube furnace, respectively, with a distance of 10-16 cm between them. Under nitrogen protection, the catalyst was calcined at 350-550 °C for 1-3 h at a heating rate of 2.5-7.5 °C / min, and then naturally cooled to room temperature to obtain cobalt-based photocatalyst with axial chlorine coordination.

[0014] In the above preparation process, thiourea, melamine and Co(NO3)2·6H2O are completely dissolved in boiling water to form a homogeneous mixed solution.

[0015] In the above preparation process, the S and N in thiourea and melamine can be anchored to Co, thereby forming Co−N and Co−S equatorial bonds.

[0016] In the above preparation process, the purpose of controlling the amount of ammonium chloride and cobalt-based catalyst is to synthesize an axially chlorine-coordinated cobalt-based photocatalyst with good photocatalytic efficiency.

[0017] In the above preparation process, the purpose of controlling the distance between upstream and downstream, the heating rate, the calcination temperature and time is to rationally regulate the rate at which NH4Cl decomposes to produce HCl, thereby precisely controlling the degree of axial coordination between the Co-based catalyst and Cl, and finally synthesizing a cobalt-based photocatalyst with good photocatalytic efficiency and axial chlorine coordination.

[0018] Compared with the prior art, this invention has the following outstanding features and effects: In this invention, thiourea, melamine, and Co(NO3)2·6H2O can be completely dissolved in boiling water and formed into a uniformly mixed solution after thorough stirring. Therefore, during drying, each component can be simultaneously and uniformly precipitated from the solution to obtain a precursor with a highly uniform dispersion. Furthermore, in the cobalt-based catalyst generated after calcination, the Co center has already formed stable Co−N and Co−S coordination bonds with S and N atoms in the equatorial plane, pre-occupying all coordination sites in the X and Y directions of the Co center's 3d orbital, constructing a rigid planar anchoring structure, and completely sealing off side reaction pathways such as equatorial plane coordination substitution and heteroatom interstitial doping. Only an empty coordination orbital is reserved in the Z-axis direction. Therefore, when it reacts with a chlorine source in a tube furnace, the chlorine converted from the high-temperature decomposition of ammonium chloride... It can only undergo directional, single axial coordination with the Co center to form a Co-Cl axial bond, fundamentally preventing non-target side reactions from occurring. Cl has suitable electronegativity, ionic radius, and orbital matching degree, which can precisely control the local electronic structure and d-band center of the central Co, breaking the high symmetry restriction of the original M-N4 structure, significantly promoting the separation and transport of photogenerated carriers, and at the same time efficiently activating the system to generate strong oxidizing reactive species such as superoxide radicals and singlet oxygen. Compared with existing related technologies, this method does not require expensive raw materials and complex multi-step processes. It is simple to design, easy to operate, has low preparation cost, and no secondary pollution from organic waste liquid. The product batch stability and structural durability are excellent. It has a more efficient photocatalytic degradation effect on PET microplastics and is suitable for the application needs of large-scale industrial production and actual environmental remediation.

[0019] From SEM (attached) Figure 1 As can be seen from the XRD (attached), the synthesized product contains C, N, S, Co, and Cl elements. Figure 1As can be seen from hj), the sample exhibits characteristic peaks of g-C3N4 at the (100) and (002) crystal planes, but lacks peaks of Co3S4 and Co3O4. The corresponding peak positions on the crystal planes are consistent with the standard card (JCPDS No. 50-1250), proving that the synthesized product is indeed a cobalt-based catalyst with C3N4 as the substrate. Furthermore, after axial chlorine coordination, the sample shifts to a higher angle by 0.2°. If Cl enters the C−N ring interstices in the CN plane in the form of "interstitial doping," it will squeeze the surrounding C and N atoms, forcing the in-plane lattice to undergo "elastic compression," which will reduce the interlayer spacing of (100) and shift the peak value to a higher angle. However, when Cl and Co are axially coordinated, the interlayer stress increases, leading to a reduction in the interlayer spacing of (002) and an increase in the peak shift angle. The above analysis proves that Cl and Co are combined in the form of axial coordination. The FTIR spectrum shows that the broadband detected in the 3000–3500 cm⁻¹ range is mainly due to the N–H transitions of the terminal primary and secondary amines in the CN ring; multiple irregular absorption peaks in the 1200–1700 cm⁻¹ range are attributed to the C–N / C–NH vibrations in the CN heterocycle (Li L, Zeng H, Tang R, et al., Appl. Catal. B: Environ. Energy, 2024, 345: 123693); while the significant signal near 807 cm⁻¹ indicates the typical triazine unit (−C−N−C−) (Deng Y, Zhou Z, Zeng H, et al., Appl. Catal. B: Environ. Energy, 2023320: 121942). The vibrational peaks of C−N / C−NH after the introduction of chlorine (…) Figure 1 l) and the signal peak of the triazine unit ( Figure 1 The simultaneous enhancement of m) may be due to the introduction of chlorine disrupting the symmetry of the triazine ring, leading to a change in polarizability. Furthermore, the axial bonds can also act as channels for electron transfer (Pan M, Li J, Zhang X, et al., J. Mater. Chem. A, 202310: 5095-5103), transferring electrons to the triazine ring and thus promoting the delocalization of π electrons within the ring. (See XPS diagram attached...) Figure 2As can be seen from the data, the binding energy of the Co 2p3 / 2 orbital is 780.94 eV, indicating that the valence state of Co is between 0 and +2 (Huang G, Niu Q, He Y, et al., Nano Res., 2022, 15(9): 8001). After axial coordination with chlorine, the binding energy of the Co 2p1 / 2 orbital increases due to the electron-withdrawing effect of chlorine. Under illumination, the charge flows from Cl to Co, resulting in a decrease in the binding energy of the Co 2p1 / 2 orbital and an increase in the binding energy of the Cl 2p3 / 2 orbital. The above characterization proves that there is an axial chlorine coordination bond in the material, which is conducive to the separation of photogenerated electrons and holes. Therefore, the fluorescence emission spectrum intensity after axial chlorine coordination is the weakest (see appendix). Figure 3 a) The photocurrent is highest (see appendix) Figure 3 b), minimum impedance (attached) Figure 3 c). Axial chlorine coordination enhances the degradation efficiency of cobalt-based photocatalysts for PET because the formation of axial bonds facilitates the separation of photogenerated electrons and holes; therefore, the synthesized sample exhibits better photocatalytic degradation efficiency for PET microplastics (see appendix for details). Figure 4 ).

[0020] In summary, the cobalt-based catalyst with axial chlorine coordination prepared in this invention has the advantages of high light absorption intensity, regulation of the d-band center of the Co-based catalyst, efficient separation of photogenerated electrons and holes, and efficient degradation of PET microplastics using visible light energy. Therefore, it has potential application value in the photocatalytic degradation of microplastics. Attached Figure Description

[0021] Figure 1 SEM and mapping images of 2Co-SCN-Cl (ag); XRD pattern of the sample (hj); FTIR image of the sample (km); Figure 2 XPS full spectrum of the samples (a); C 1s (b); N 1s (c); S 2p (d); Co 2p (e); Cl 2p (f); Figure 3 Fluorescence spectrum of the sample (a); photocurrent spectrum (b); impedance spectrum (c); Figure 4 Catalytic degradation efficiency of PET by different samples under visible light irradiation (PET mass 40 mg, deionized water volume 100 mL, catalyst mass 60 mg, pH value 7, light source is mercury lamp). Detailed Implementation The preparation method of the present invention will be further illustrated by the following examples, but the present invention is not limited to the following examples. Example 1

[0022] 0.5 g thiourea, 3 g melamine and 0.15 g Co(NO3)2·6H2O were dissolved in 100 mL boiling water and stirred for 1 h to form a homogeneous solution. The solution was dried at 100 ℃ by forced air drying, ground and then pyrolyzed in a muffle furnace at 500 ℃ for 2 h at a heating rate of 5 ℃ / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 0.3 g ammonium chloride (chlorine source) and 0.5 g calcined catalyst were placed upstream and downstream of a tube furnace, respectively, 10 cm apart. Under nitrogen protection, the furnace was calcined at 350 ℃ for 1 h at a heating rate of 2.5 ℃ / min and then naturally cooled to room temperature to obtain an axially chlorine-coordinated cobalt-based photocatalyst. Example 2

[0023] 4 g of thiourea, 5 g of melamine, and 0.25 g of Co(NO3)2·6H2O were dissolved in 100 mL of boiling water and stirred for 1 h to form a homogeneous solution. The solution was dried at 100 °C by forced air, ground, and then pyrolyzed in a muffle furnace at 500 °C for 2 h at a heating rate of 5 °C / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 0.9 g of ammonium chloride (chlorine source) and 1.5 g of calcined catalyst were placed upstream and downstream of a tube furnace, respectively, with a distance of 13 cm between them. Under nitrogen protection, the furnace was calcined at 350 °C for 1 h at a heating rate of 2.5 °C / min, and then naturally cooled to room temperature to obtain an axially chlorine-coordinated cobalt-based photocatalyst. Example 3

[0024] 8 g of thiourea, 8 g of melamine, and 0.35 g of Co(NO3)2·6H2O were dissolved in 100 mL of boiling water and stirred for 1 h to form a homogeneous solution. The solution was dried at 100 °C by forced air, ground, and then pyrolyzed in a muffle furnace at 500 °C for 2 h at a heating rate of 5 °C / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 1.5 g of ammonium chloride (chlorine source) and 2.0 g of calcined catalyst were placed upstream and downstream of a tube furnace, respectively, with a distance of 16 cm between them. Under nitrogen protection, the furnace was calcined at 350 °C for 1 h at a heating rate of 2.5 °C / min, and then naturally cooled to room temperature to obtain an axially chlorine-coordinated cobalt-based photocatalyst. Example 4

[0025] 0.5 g thiourea, 3 g melamine and 0.15 g Co(NO3)2·6H2O were dissolved in 100 mL boiling water and stirred for 2 h to form a homogeneous solution. The solution was dried at 100 ℃ by forced air drying, ground and then pyrolyzed in a muffle furnace at 600 ℃ for 4 h at a heating rate of 10 ℃ / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 0.3 g ammonium chloride (chlorine source) and 0.5 g calcined catalyst were placed upstream and downstream of a tube furnace, 10 cm apart, and calcined at 450 ℃ for 2 h at a heating rate of 5 ℃ / min under nitrogen protection. After natural cooling to room temperature, a cobalt-based photocatalyst with axial chlorine coordination was obtained. Example 5

[0026] 4 g of thiourea, 5 g of melamine, and 0.25 g of Co(NO3)2·6H2O were dissolved in 100 mL of boiling water and stirred for 2 h to form a homogeneous solution. The solution was dried at 100 °C by forced air, ground, and then pyrolyzed in a muffle furnace at 600 °C for 4 h at a heating rate of 10 °C / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 0.9 g of ammonium chloride (chlorine source) and 1.5 g of calcined catalyst were placed upstream and downstream of a tube furnace, respectively, with a distance of 13 cm between them. Under nitrogen protection, the furnace was calcined at 450 °C for 2 h at a heating rate of 5 °C / min, and then naturally cooled to room temperature to obtain an axially chlorine-coordinated cobalt-based photocatalyst. Example 6

[0027] 8 g of thiourea, 8 g of melamine, and 0.35 g of Co(NO3)2·6H2O were dissolved in 100 mL of boiling water and stirred for 2 h to form a homogeneous solution. The solution was dried at 100 °C by forced air, ground, and then pyrolyzed in a muffle furnace at 600 °C for 4 h at a heating rate of 10 °C / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 1.5 g of ammonium chloride (chlorine source) and 2.0 g of calcined catalyst were placed upstream and downstream of a tube furnace, respectively, with a distance of 16 cm between them. Under nitrogen protection, the furnace was calcined at 450 °C for 2 h at a heating rate of 5 °C / min, and then naturally cooled to room temperature to obtain an axially chlorine-coordinated cobalt-based photocatalyst. Example 7

[0028] 0.5 g thiourea, 3 g melamine, and 0.15 g Co(NO3)2·6H2O were dissolved in 100 mL of boiling water and stirred for 3 h to form a homogeneous solution. The solution was dried at 100 ℃ by forced air drying, ground, and then pyrolyzed in a muffle furnace at 700 ℃ for 6 h at a heating rate of 15 ℃ / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 0.3 g ammonium chloride (chlorine source) and 0.5 g calcined catalyst were placed upstream and downstream of a tube furnace, respectively, 10 cm apart. Under nitrogen protection, the furnace was calcined at 550 ℃ for 3 h at a heating rate of 7.5 ℃ / min, and then naturally cooled to room temperature to obtain an axially chlorine-coordinated cobalt-based photocatalyst. Example 8

[0029] 4 g of thiourea, 5 g of melamine, and 0.25 g of Co(NO3)2·6H2O were dissolved in 100 mL of boiling water and stirred for 3 h to form a homogeneous solution. The solution was dried at 100 ℃ by forced air drying, ground, and then pyrolyzed in a muffle furnace at 700 ℃ for 6 h at a heating rate of 15 ℃ / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 0.9 g of ammonium chloride (chlorine source) and 1.5 g of calcined catalyst were placed upstream and downstream of a tube furnace, respectively, with a distance of 13 cm between them. Under nitrogen protection, the furnace was calcined at 550 ℃ for 3 h at a heating rate of 7.5 ℃ / min, and then naturally cooled to room temperature to obtain an axially chlorine-coordinated cobalt-based photocatalyst. Example 9

[0030] 8 g of thiourea, 8 g of melamine, and 0.35 g of Co(NO3)2·6H2O were dissolved in 100 mL of boiling water and stirred for 3 h to form a homogeneous solution. The solution was dried at 100 ℃ by forced air drying, ground, and then pyrolyzed in a muffle furnace at 700 ℃ for 6 h at a heating rate of 15 ℃ / min. After natural cooling to room temperature, a cobalt-based photocatalyst was obtained. 1.5 g of ammonium chloride (chlorine source) and 2.0 g of calcined catalyst were placed upstream and downstream of a tube furnace, respectively, with a distance of 16 cm between them. Under nitrogen protection, the furnace was calcined at 550 ℃ for 3 h at a heating rate of 7.5 ℃ / min, and then naturally cooled to room temperature to obtain an axially chlorine-coordinated cobalt-based photocatalyst.

Claims

1. A method for preparing a cobalt-based photocatalyst with axial chlorine coordination, characterized in that... Includes the following steps: 1) Dissolve a certain amount of thiourea, melamine and Co(NO3)2·6H2O in a certain amount of boiling water and stir for 1 to 3 hours to dissolve them into a homogeneous solution; 2) The mixed solution is dried by forced air at 80 ~ 120 ℃, ground, and then placed in a muffle furnace for pyrolysis at a certain temperature and time at a certain heating rate. After natural cooling to room temperature, a cobalt-based photocatalyst is obtained. 3) A certain amount of chlorine source and a certain amount of cobalt-based catalyst were placed upstream and downstream of a tube furnace, respectively. Under nitrogen protection, they were calcined at a certain temperature for a certain time at a certain heating rate, and then naturally cooled to room temperature to obtain a cobalt-based photocatalyst with axial chlorine coordination.

2. The preparation method according to claim 1, characterized in that: In the above preparation process, the amount of thiourea is 0.5~8g, the amount of melamine is 3~8g, and the amount of Co(NO3)2·6H2O is 0.15~0.35g. They are dissolved together in boiling water to form a uniformly dispersed mixed solution.

3. The preparation method according to claim 1, characterized in that: In the above preparation process, the chlorine source in the tube furnace is ammonium chloride, with a content of 0.3 ~ 1.5 g.

4. The preparation method according to claim 1, characterized in that: In the above preparation process, the mass of the cobalt-based catalyst in the tube furnace is 0.5 ~ 2.0 g.

5. The preparation method according to claim 1, characterized in that: In the above preparation process, the cobalt-based catalyst is upstream of the tubular furnace, and the ammonium chloride is downstream of the tubular furnace, with a distance of 10 to 16 cm between the upstream and downstream.

6. The preparation method according to claim 1, characterized in that: In the above preparation process, the heating rate of the muffle furnace is 5 ~ 15 ℃ / min, the calcination temperature is 500 ~ 700 ℃, and the calcination time is 2 ~ 6 h.

7. The preparation method according to claim 1, characterized in that: In the above preparation process, the heating rate of the tube furnace is 2.5 ~ 7.5 ℃ / min, the calcination temperature is 350 ~ 550 ℃, and the calcination time is 1 ~ 3 h.

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