Nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst and a preparation method thereof, the catalyst comprises bismuth oxychloride nanoflowers, the surfaces of the bismuth oxychloride nanoflowers are modified with oxygen vacancies, and the surfaces of the bismuth oxychloride nanoflowers are coated with nitrogen-doped carbon layers. The preparation method comprises the following steps: mixing the nitrogen-doped hollow carbon spheres, bismuth salt and ethylene glycol, adding chlorine salt, and carrying out hydrothermal reaction to obtain the nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst. Compared with a conventional bismuth oxychloride-based photocatalyst, the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst has the advantages of high overall photocatalytic activity, strong singlet oxygen generation capability, good selectivity, good stability, strong practicability, high use value and good application prospect, and can be widely applied to synthesis of hydrogen peroxide and degradation of organic pollutants. The preparation method has the advantages of being simple in process, convenient to operate and the like, the structural integrity of bismuth oxychloride cannot be damaged, and in-situ synergistic enhancement between bismuth oxychloride and the nitrogen-doped carbon layer can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, and relates to a nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst, its preparation method, and its application. Background Technology

[0002] In photocatalysis, reactive oxygen species (ROS) are key active substances, including singlet oxygen (ROS). 1 O2), superoxide radicals (•O2) – ), hydroxyl radicals (•OH), and hydrogen peroxide (H2O2). Among various reactive oxygen species, 1 O2, as a long-lived (2 µs in water) and mild oxidant (E° = 2.2 V NHE), shows great potential in selective organic synthesis, wastewater treatment, bacterial inactivation, and photodynamic therapy. It also exhibits potential in other reactive oxygen species such as •OH and •O2. – compared to, 1 O2 exhibits strong adaptability to complex aquatic environments and excellent reactivity to various organic pollutants, especially high selectivity for electron-rich compounds. 1 O2 exhibits high reactivity to a variety of organic pollutants such as sulfamethoxazole (SMX), bisphenol A (BPA), phenol, and tetracycline (TC), and typically plays a dominant role in their degradation. 1 O2 can effectively cleave the piperazine ring of ciprofloxacin (CIP) through electrophilic attack. Notably, this is achieved even at natural organic matter (NOM) concentrations as high as 50 mg / L. –1 In this case, 1 O2 also maintains its degradation rate of 4-chlorophenol (4-CP), while also exhibiting strong tolerance to a wide range of solution pH values.

[0003] Currently, the mainstream 1 O2 generation strategies mainly involve activating persulfate (PDS) or permonosulfate (PMS) with carbon-based materials. Although these methods can achieve high efficiency... 1 O2 production relies on pre-synthesized chemical oxidants like PDS / PMS, which require continuous addition. This can lead to secondary pollution or necessitate subsequent treatment steps, increasing potential safety risks and operating costs. In contrast, enhancing the exciton effect in materials promotes in-situ... 1 Strategies for O2 production are more in line with the principles of green chemistry and sustainable development. Furthermore, this approach, which promotes anionic ROS (such as •O2) by weakening exciton effects, is more effective than... – •O2 – •O2 2– Compared to the generation of excitons, directly enhancing the exciton effect in layered two-dimensional semiconductors can improve... 1O2 yield appears to show greater practical application value in water purification. Therefore, it is necessary to develop a method with high O2 yield. 1 Two-dimensional semiconductor photocatalyst with O2 yield.

[0004] Bismuth oxychloride, a typical two-dimensional layered semiconductor, has wide applications in photocatalysis due to its unique crystal structure and excellent chemical stability. Currently, research and applications of bismuth oxychloride mainly focus on the following technical solutions, each with its own drawbacks and technical bottlenecks, as detailed below: (1) Original bismuth oxychloride photocatalyst.

[0005] (1.1) The photocatalytic activity is limited, the recombination rate of photogenerated electron-hole pairs is high, the adsorption and activation ability of oxygen molecules is weak, and the overall catalytic efficiency is not high.

[0006] (1.2) Singlet oxygen has extremely low yield and poor selectivity. Its degradation process is often dominated by a mixture of various reactive oxygen species such as hydroxyl radicals, resulting in dispersed energy and low efficiency.

[0007] (2) Bismuth oxychloride photocatalyst modified with oxygen vacancy.

[0008] (2.1) Although modifying oxygen vacancies can improve the overall charge separation efficiency and catalytic activity, it cannot significantly change the singlet-triple band gap of the bismuth oxychloride material itself, and thus fails to fundamentally solve the problem of singlet oxygen generation.

[0009] (2.2) The introduction of oxygen vacancies has a negligible effect on improving the singlet oxygen yield. Its performance improvement is mainly contributed by the free radical generation path based on charge transfer process, rather than the optimal energy transfer process.

[0010] (3) Bismuth oxychloride heterojunction composite photocatalyst.

[0011] (3.1) Combining bismuth oxychloride with another semiconductor (such as carbon nitride) to form a heterojunction structure will promote the dissociation of excitons into free charge carriers, thereby inhibiting or destroying the formation of excitons as singlet oxygen precursors, and failing to achieve efficient and selective generation of singlet oxygen.

[0012] (3.2) Existing bismuth oxychloride heterojunction composite photocatalysts generally focus on regulating the behavior of free charges, that is, promoting the separation of charge carriers (charge transfer process) to improve photocatalytic efficiency, but completely ignore the regulation of exciton behavior inside the material.

[0013] Therefore, developing a bismuth oxychloride-based photocatalyst with high singlet oxygen yield and high overall photocatalytic activity is of great significance for promoting the widespread application of singlet oxygen in the field of photocatalysis. Summary of the Invention

[0014] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst with high singlet oxygen production and high overall photocatalytic activity, as well as its preparation method and application.

[0015] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst includes bismuth oxychloride nanoflowers, the surface of which is modified with oxygen vacancies; the surface of the bismuth oxychloride nanoflowers is coated with a nitrogen-doped carbon layer.

[0016] The above-mentioned nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst is further improved in that the bismuth oxychloride nanoflowers are spherical materials self-assembled from bismuth oxychloride nanosheets; the diameter of the bismuth oxychloride nanoflowers is 300 nm to 800 nm.

[0017] In a further improvement of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst described above, the nitrogen-doped carbon layer grows along the edge of the bismuth oxychloride nanosheet, and the thickness of the nitrogen-doped carbon layer is 1 nm to 4 nm.

[0018] As a general technical concept, the present invention also provides a method for preparing the above-mentioned nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst, comprising the following steps: S1. Mix nitrogen-doped hollow carbon spheres, bismuth salt and ethylene glycol, sonicate and stir to obtain mixed solution A; S2. Add the chloride salt to the mixed solution A obtained in step S1, stir, and obtain mixed solution B; S3. The mixed solution B obtained in step S2 is subjected to a solvothermal reaction to obtain a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst.

[0019] In a further improvement to the above preparation method, in step S1, the mass ratio of the nitrogen-doped hollow carbon spheres to the bismuth salt is 0.05–0.2:1.94; and the ratio of the bismuth salt to ethylene glycol is 0.97 g:30 mL.

[0020] In a further improvement to the above preparation method, in step S1, the mass ratio of the nitrogen-doped hollow carbon spheres to the bismuth salt is 0.08–0.15:1.94; and the bismuth salt is bismuth nitrate pentahydrate.

[0021] A further improvement to the above preparation method is that, in step S1, the preparation method of the nitrogen-doped hollow carbon spheres includes the following steps: (1) Sodium dodecyl sulfate, glucose, and melamine are dissolved in water and sonicated to obtain a precursor solution; the mass ratio of sodium dodecyl sulfate, glucose, and melamine is 0.03:1.44:0.04; the ratio of melamine to water is 0.04g:15mL; and the sonication time is 1h. (2) The precursor solution obtained in step (1) is subjected to a hydrothermal reaction, washed, and dried to obtain nitrogen-doped hollow carbon spheres; the temperature of the hydrothermal reaction is 160℃; the time of the hydrothermal reaction is 10h.

[0022] In a further improvement to the above preparation method, in step S1, the ultrasonication time is 10 min to 40 min; the stirring time is 10 min to 40 min.

[0023] In a further improvement to the above preparation method, in step S2, the ratio of the chloride salt to the mixed solution A is 0.2982 g: 60 mL; the chloride salt is at least one of potassium chloride and sodium chloride; and the stirring time is 30 min.

[0024] In a further improvement to the above preparation method, in step S3, the temperature of the solvothermal reaction is 160°C; the time of the solvothermal reaction is 10 h; and after the solvothermal reaction is completed, the following treatment is also included: the product of the solvothermal reaction is centrifuged, the solid product is collected, the solid product is washed with deionized water and anhydrous ethanol until the pH of the washing solution is neutral, and then dried under vacuum at 60°C for 12 h to obtain a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst.

[0025] As a general technical concept, the present invention also provides the application of the above-mentioned nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst or the nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst prepared by the above-mentioned preparation method in the synthesis of hydrogen peroxide or the treatment of organic pollutant wastewater.

[0026] The above application is further improved by using a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst to synthesize hydrogen peroxide, which includes the following steps: mixing the nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst with water to carry out a photocatalytic reaction to obtain hydrogen peroxide.

[0027] In a further improvement to the above application, the amount of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst added is 0.3g to 0.8g per liter of water.

[0028] In the above-described application, a further improvement is made, wherein the photocatalytic reaction time is 60 min to 120 min.

[0029] In a further improvement to the above application, the photocatalytic reaction process also includes adding chloride ions to the system to make the concentration of chloride ions in the system ≥5mM.

[0030] The above-mentioned application is further improved by using a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst to treat organic pollutant wastewater, including the following steps: mixing the nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst with the organic pollutant wastewater to carry out a photocatalytic degradation reaction, thereby completing the removal of organic pollutants from the wastewater.

[0031] In a further improvement to the above application, the amount of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst added is 0.3g to 0.8g per liter of pollutant wastewater.

[0032] In a further improvement to the above application, the organic pollutants in the wastewater are electron-rich compounds; the electron-rich compounds include at least one of sulfamethoxazole, bisphenol A, phenol, ciprofloxacin, and tetracycline.

[0033] In the above-described application, a further improvement is made, wherein the initial concentration of organic pollutants in the wastewater is ≤10 mg / L.

[0034] In the above-described application, a further improvement is made, wherein the initial pH value of the organic pollutant wastewater is 4 to 10.

[0035] In the above-described application, a further improvement is made, wherein the photocatalytic degradation reaction time is 60 min.

[0036] In a further improvement to the above application, the photocatalytic degradation reaction process also includes adding chloride ions to the system to make the concentration of chloride ions in the system ≥5mM.

[0037] Compared with the prior art, the advantages of the present invention are as follows: (1) To address the shortcomings of existing bismuth oxychloride-based photocatalysts, such as low singlet oxygen production and poor overall photocatalytic activity, this invention creatively proposes a nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst. This uses bismuth oxychloride nanoflowers modified with oxygen vacancies as a carrier, and a nitrogen-doped carbon layer is coated on the surface of the bismuth oxychloride nanoflowers. Compared with conventional bismuth oxychloride nanoparticles, the bismuth oxychloride nanoflowers used in this invention have a larger specific surface area. Furthermore, the high localization near the chlorine atom band edge in the bismuth oxychloride nanoflower structure is beneficial for the formation of dense excitons. Simultaneously, the oxygen vacancies on the surface of the bismuth oxychloride nanoflowers can serve as adsorption and activation sites for oxygen molecules, providing a prerequisite for the generation of high-concentration singlet oxygen. At the same time, the nitrogen-doped carbon layer possesses unique nonlinear optical properties, exhibiting a many-body effect in electron and exciton generation during optical processes. This can be used to significantly enhance the exciton effect of bismuth oxychloride and promote energy transfer processes. Based on this, coating the surface of the bismuth oxychloride nanoflowers with a nitrogen-doped carbon layer can... The tight synergistic interface formed between the nitrogen-doped carbon layer and bismuth oxychloride not only ensures a large specific surface area of ​​the material, but also forms a unique catalytically active interface with oxygen vacancies on the bismuth oxychloride surface. Simultaneously, under the synergistic effect of the nitrogen-doped carbon layer and oxygen vacancies, the singlet-triple bandgap of bismuth oxychloride can be reduced by about 36% by promoting spin-orbit coupling, which significantly promotes the intersystem crossing process and thus greatly increases the yield of triplet excitons as precursors of singlet oxygen. In addition, this synergistic interface can also enhance the chemisorption capacity of oxygen molecules in water, so that oxygen molecules are in a highly activated state and are very easy to generate singlet oxygen through energy transfer with triplet excitons. In the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst of this invention, by coating the surface of bismuth oxychloride nanoflowers with a nitrogen-doped carbon layer, the oxygen molecule activation pathway of bismuth oxychloride is successfully transformed into a highly efficient energy utilization pathway dominated by energy transfer, selectively generating high concentrations of singlet oxygen. This high concentration of singlet oxygen can then be used to improve degradation selectivity and efficiency, making the catalyst exhibit stronger tolerance and stability to complex water bodies.Compared with conventional bismuth oxychloride-based photocatalysts, the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst of the present invention has the following advantages: (a) High overall photocatalytic activity and high degradation efficiency of pollutants. Taking ciprofloxacin as an example, its rate constant for degrading ciprofloxacin is 6.9 times that of oxygen vacancy-modified bismuth oxychloride photocatalysts, and it can achieve complete degradation within 60 minutes, with a total organic carbon removal rate of up to 75%, showing significant advantages in terms of the depth and speed of organic pollutant removal; (b) Strong singlet oxygen generation capacity and good selectivity. The singlet oxygen yield is 10 times that of oxygen vacancy-modified bismuth oxychloride photocatalysts, and the reaction pathway is transformed into one dominated by singlet oxygen, which can achieve efficient and selective generation of active species, making energy utilization more concentrated and the degradation process more targeted; (c) Good stability and strong practicality. It still maintains high activity after multiple cycles of use and still shows excellent degradation performance (removal rate of over 87%) in real complex water bodies such as tap water, river water, and lake water, showing great potential for practical application. In addition, other nitrogen-containing carbon materials, such as graphene, carbon nanotubes, and nitrogen-doped polymers, are difficult to form a uniform and dense coating layer in situ on the surface of bismuth oxychloride nanoflowers, thus affecting the synergistic effect between the nitrogen-doped carbon layer and oxygen vacancies. Other oxygen vacancy-modified bismuth oxyhalides (such as bismuth oxybromine and bismuth oxyiodide) may suffer from lattice mismatch due to the difference in atomic radii of bromine and iodine, thereby affecting structural integrity and catalytic performance.

[0038] (2) This invention also provides a method for preparing a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst, which is an in-situ growth method based on "template-guided in-situ synchronous crystallization and coating". Specifically, the method is as follows: First, nitrogen-doped hollow carbon spheres, bismuth salt and ethylene glycol are mixed, ultrasonicated and stirred. On the one hand, compared with other organic solvents (such as ethanol, triethylene glycol), ethylene glycol is used as the solvent in this invention, which can achieve uniform dispersion of nitrogen-doped hollow carbon spheres, which is beneficial to the preparation of nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst with excellent performance. On the other hand, since the density of nitrogen-doped hollow carbon spheres is small, they are easy to float on the surface of the solvent. Therefore, ultrasonic treatment can first disperse the nitrogen-doped hollow carbon spheres more uniformly in ethylene glycol, improve the mixing uniformity of raw materials, which is the basis for the effective adsorption of bismuth ions by nitrogen-doped hollow carbon spheres and the key to achieving uniform coating in the subsequent process. Then, using nitrogen-doped hollow carbon spheres as "templates", bismuth ions (Bi) are preferentially adsorbed and enriched through electrostatic and coordination interactions. 3+ Furthermore, through stirring, the adsorption effect of nitrogen-doped hollow carbon spheres on bismuth ions can be effectively improved, allowing more Bi ions to be adsorbed. 3+ On the "template" surface, chloride salts are then added, and under stirring, chloride ions react with Bi enriched on the surface of nitrogen-doped hollow carbon spheres. 3+The reaction enables controllable surface nucleation of bismuth oxychloride, and finally, simultaneous crystallization and in-situ coating are achieved through a solvothermal reaction. Specifically, under solvothermal conditions, bismuth oxychloride crystallizes outward from the surface of nitrogen-doped hollow carbon spheres to form a "core". At the same time, due to the relatively active structure of the nitrogen-doped hollow carbon spheres, their surface functional groups and some structures can decompose, dissolve, or reconstruct. At this time, the nitrogen-containing carbon species in the nitrogen-doped hollow carbon spheres are uniformly deposited in-situ on the surface of the newly formed bismuth oxychloride crystal, forming a dense nitrogen-doped carbon layer "shell". That is, the nitrogen-doped carbon layer effectively coats the surface of the bismuth oxychloride crystal while the bismuth oxychloride crystal is being formed. It can be seen that by optimizing the process of simultaneous "crystallization" and "coating", this invention ensures that an atomically tight synergistic interface is formed between the bismuth oxychloride core and the nitrogen-doped carbon layer shell, thereby constructing a nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst with a unique core-shell structure and excellent photocatalytic performance. In particular, the preparation method of this invention employs a strategy of "first mixing nitrogen-doped hollow carbon spheres, bismuth salt, and ethylene glycol, then adding chloride salt," which brings the following unexpected technical effects: During the pre-mixing process of nitrogen-doped hollow carbon spheres, bismuth salt, and ethylene glycol, the positively charged Bi... 3+ Ions preferentially adsorb onto the surface of nitrogen-doped hollow carbon spheres, becoming enriched Bi. 3+ In areas of high concentration, chloride salts were subsequently added, Cl... - Ions will preferentially react with Bi atoms already adsorbed on the surface of nitrogen-doped hollow carbon spheres. 3+Ionic reactions precisely induce the nucleation process of bismuth oxychloride crystals on the surface of nitrogen-doped hollow carbon spheres, ensuring in-situ synchronous growth and uniform coating of the nitrogen-doped carbon layer. This allows the nitrogen-doped carbon layer to grow more uniformly on the bismuth oxychloride surface. However, directly mixing chloride salts, bismuth salts, and nitrogen-doped hollow carbon spheres can lead to insufficient mixing of the nitrogen-doped hollow carbon spheres due to the rapid "flash-sink" reaction between bismuth and chloride salts, generating bismuth oxychloride suspensions. This results in irregular morphology of the bismuth oxychloride and affects the uniformity and thickness of the nitrogen-doped carbon layer. Furthermore, compared to other conventional methods (such as plasma treatment and reducing atmosphere annealing), the preparation method of this invention has advantages such as simple process and convenient operation, and does not damage the structural integrity of bismuth oxychloride, which is beneficial for achieving in-situ synergistic enhancement between bismuth oxychloride and the nitrogen-doped carbon layer. Furthermore, when carbon nitride is used as a raw material, a nitrogen-doped carbon layer cannot be formed on the surface of bismuth oxychloride nanoflowers. The reason may be that carbon nitride materials are extremely stable in both chemical and thermal properties. They are polymers formed by covalent bonds, and their thermal decomposition temperature is usually above 550-600℃. Therefore, under the temperature conditions of solvothermal reaction (generally 160℃), carbon nitride materials will not decompose or reconstruct at all. Furthermore, structurally stable carbon nitride materials will undergo weak and non-uniform adsorption with bismuth oxychloride during the preparation process through van der Waals forces or electrostatic attraction, rather than growing on the surface of bismuth oxychloride like nitrogen-doped hollow carbon spheres.

[0039] (3) The present invention also provides an application of nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst in the synthesis of hydrogen peroxide. Specifically, the nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst is mixed with water to carry out photocatalytic reaction, and hydrogen peroxide can be obtained. It has the advantages of simple process, convenient operation, high yield and fast production rate, which can promote the widespread use of hydrogen peroxide.

[0040] (4) The present invention also provides an application of a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst in the treatment of organic pollutant wastewater. Specifically, the nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst is mixed with organic pollutant wastewater to carry out photocatalytic degradation reaction. During the photocatalytic degradation reaction, a large amount of high-concentration singlet oxygen is formed rapidly by the photocatalytic effect of the nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst. Then, the high-concentration singlet oxygen can be used to oxidize and degrade the organic pollutants in the wastewater. Thus, the organic pollutants in the wastewater can be efficiently removed. It has the advantages of simple process, convenient operation, high treatment efficiency and good removal effect, which is conducive to the environmental remediation of organic pollutant wastewater. Attached Figure Description

[0041] 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.

[0042] Figure 1 The images show SEM images of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention.

[0043] Figure 2 This is a TEM image of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in Example 1 of the present invention.

[0044] Figure 3 This is an EDS image of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in Example 1 of this invention.

[0045] Figure 4 The images show the XRD patterns of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention.

[0046] Figure 5 The nitrogen adsorption-desorption curves and pore size distribution diagrams of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10) and bismuth oxychloride photocatalyst (BOC) prepared in Example 1 of this invention are shown.

[0047] Figure 6 XPS images of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention.

[0048] Figure 7 The UV-Vis diffuse reflectance spectra of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15), bismuth oxychloride photocatalysts (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention.

[0049] Figure 8 This is a comparison diagram of the VB positions of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15) and bismuth oxychloride photocatalysts (BOC) prepared in Example 1 of this invention.

[0050] Figure 9 This is a comparison chart showing the oxidation effect of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) and bismuth oxychloride photocatalyst (BOC) prepared in Example 1 of this invention on TMB under different conditions.

[0051] Figure 10The figure shows the effect of nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst (BNC10) and bismuth oxychloride photocatalyst (BOC) on hydrogen peroxide production in Example 2 of the present invention.

[0052] Figure 11 The image shows the removal efficiency of ciprofloxacin by nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) in Example 3 of this invention.

[0053] Figure 12 This is a comparison chart showing the degradation rates of ciprofloxacin by nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) in Example 3 of the present invention. Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0055] In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0056] Example 1 A nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst includes bismuth oxychloride nanoflowers, on which oxygen vacancies are modified; and a nitrogen-doped carbon layer is coated on the surface of the bismuth oxychloride nanoflowers.

[0057] In this embodiment, the bismuth oxychloride nanoflower is a spherical material formed by the self-assembly of bismuth oxychloride nanosheets, and the diameter of the bismuth oxychloride nanoflower is 300nm to 800nm.

[0058] In this embodiment, the nitrogen-doped carbon layer grows along the edge of the bismuth oxychloride nanosheet, and the thickness of the nitrogen-doped carbon layer is 2 nm. In other embodiments, the thickness of the nitrogen-doped carbon layer can also be 1 nm, 1.5 nm, 1.8 nm, 2.2 nm, 2.5 nm, 2.7 nm, 3 nm, 3.2 nm, 3.5 nm, 3.8 nm, or 4 nm.

[0059] In this invention, optimizing the thickness of the nitrogen-doped carbon layer is more conducive to improving the selectivity of the catalyst for singlet oxygen, enabling the more rapid generation of high concentrations of singlet oxygen, and simultaneously improving the overall photocatalytic performance of the catalyst. However, if the thickness of the nitrogen-doped carbon layer is too high, it will affect the full exposure of surface active sites and the photoresponse capability, leading to a decrease in photocatalytic degradation activity; while if the thickness of the nitrogen-doped carbon layer is too low, it will weaken the exciton effect, resulting in a decrease in singlet oxygen yield.

[0060] A method for preparing a nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst includes the following steps: (1) Synthesis of nitrogen-doped hollow carbon spheres: (1.1) Dissolve 0.06 g sodium dodecyl sulfate, 2.88 g glucose and 0.08 g melamine together in 30 mL distilled water and sonicate for 1 hour to dissolve the raw materials in water to obtain a precursor solution.

[0061] (1.2) The precursor solution was transferred to an autoclave and reacted at 160°C for 10 hours. The resulting solid precipitate was washed repeatedly with deionized water and anhydrous ethanol and dried under vacuum at 60°C for 12 hours to obtain nitrogen-doped hollow carbon spheres, denoted as NHCS.

[0062] (2) Synthesis of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst: (2.1) Add 1.94 g of bismuth nitrate pentahydrate and 0.1 g of nitrogen-doped hollow carbon spheres prepared in step (1) to a beaker containing 60 mL of ethylene glycol, sonicate for 30 minutes, and then stir magnetically for 30 minutes to obtain mixed solution A.

[0063] (2.2) Add 0.2982 g of potassium chloride to the above mixed solution A and continue stirring for 30 minutes to form mixed solution B.

[0064] (2.3) The above mixed solution B was transferred to a 100 mL polytetrafluoroethylene-lined autoclave and reacted at 160 °C for 12 hours. The product was centrifuged, the solid product was collected, and washed three times with deionized water and anhydrous ethanol until neutral pH. The product was then dried under vacuum at 60 °C for 12 hours to obtain a yellowish-brown nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst, denoted as BNC10.

[0065] In this embodiment, the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalysts prepared under different nitrogen-doped hollow carbon sphere dosages are prepared using the same method as the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10) in Example 1, with the only difference being the dosage of the nitrogen-doped hollow carbon spheres: 0g, 0.05g, 0.15g, and 0.2g. When the dosage of the nitrogen-doped hollow carbon spheres is 0g, the prepared bismuth oxychloride photocatalyst is denoted as BOC; when the dosage of the nitrogen-doped hollow carbon spheres is 0.05g, 0.15g, and 0.2g, the prepared nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalysts are denoted as BNC5, BNC15, and BNC20, respectively.

[0066] Figure 1 The images show SEM images of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention. Figure 1 In the diagram, a represents NHCS, b represents BOC, and c represents BNC10. (From...) Figure 1 It is known that the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in this invention is flower-shaped and composed of multiple bismuth oxychloride nanosheets. Compared with the bismuth oxychloride photocatalyst (BOC), the nanosheets in the BNC10 microspheres of this invention are thinner and have a tighter self-assembly. This is because NHCS can prevent the nanosheets from growing in the direction perpendicular to the [Bi2O2] and [Cl] plates by forming a passivation layer around the BOC core.

[0067] Figure 2 This is a TEM image of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in Example 1 of this invention. Figure 2 It is known that the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in this invention has a carbon coating on its surface. Specifically, the nitrogen-doped carbon layer grows along the edge of the bismuth oxychloride nanosheets, and the thickness of this carbon coating is 2 nm. Meanwhile, from... Figure 2 It is known that the bismuth oxychloride nanoflowers in the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in this invention are self-assembled from thinner and denser bismuth oxychloride nanosheets with a diameter of 300 nm to 800 nm.

[0068] Figure 3 This is an EDS image of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in Example 1 of this invention. Figure 3 It is known that the elements Bi, O, Cl, C and N are uniformly distributed in the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10) prepared by the present invention.

[0069] Figure 4The images show the XRD patterns of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention. Figure 4 It is known that the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20) prepared in this invention possess a good tetragonal BOC structure with lattice parameters a = b = 3.887 Å and c = 7.354 Å (JCPDS No. 06-0249). The nitrogen-doped hollow carbon spheres (NHCS) exhibit a broad peak at 23.3°, indicating an amorphous structure. However, no diffraction peaks of NHCS were observed in the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20), which may be due to the low loading of NHCS or variations in its crystal structure. With increasing amounts of nitrogen-doped hollow carbon spheres, the (110) and (211) diffraction peaks shifted slightly to a lower 2θ angle by about 0.1°, while the (102) peak shifted to a higher angle by about 0.1°. These subtle changes indicate that the introduction of NHCS produced a small interfacial effect. Meanwhile, XRD patterns showed that the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20) retained the distinct tetragonal main structure of the original BiOCl, indicating that the nitrogen-doped carbon layer modification did not significantly alter the bulk BiOCl lattice. The integrity of this main structure is crucial for studying its exciton properties.

[0070] Figure 5 The nitrogen adsorption-desorption curves and pore size distribution diagrams of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10) and bismuth oxychloride photocatalyst (BOC) prepared in Example 1 of this invention are shown. Figure 5 In the diagram, a represents the nitrogen adsorption-desorption curve, and b represents the pore size distribution. Figure 5 It is known that the BET specific surface area of ​​the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in this invention is 33.6090 m². 2 g -1 The specific surface area of ​​bismuth oxychloride photocatalyst (BOC) is 19.5 × 10⁵ m². 2 g -1 In conjunction with Table 1 and Figure 2The results are consistent with those in the previous studies, indicating that coating the surface of bismuth oxychloride nanoflowers with a nitrogen-doped carbon layer can form micropores or slit-like pores. This carbon-coated material with narrow slit pores brings the following advantages to the photocatalytic O2 activation energy: 1) It provides a low-resistance channel to achieve rapid diffusion and ensure rapid and continuous O2 activation; 2) It provides more opportunities for sufficient contact between the catalyst active site and the reactant O2; 3) It promotes the generation of ROS.

[0071] Table 1 Performance data of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) and bismuth oxychloride photocatalyst (BOC) prepared in Example 1 of this invention.

[0072] Figure 6 XPS images of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention. Figure 6 In the diagram, a represents the full spectrum, b represents C 1s, c represents Cl 2p, d represents N 1s, e represents Bi 4f, and f represents O 1s. (From...) Figure 6 It is known that the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in this invention contains Bi, O, Cl, N, and C elements, and exhibits high-resolution C 1s spectroscopy (…). Figure 6 In (b), the new peak at 288.2 eV in BNC10 is attributed to the C=O bond, indicating that the nitrogen-doped carbon layer (NCL) can bring more oxygen-containing groups to BOC. Combined with the data in Table 1, this demonstrates that BNC10 provides more potential active sites for catalytic reactions. Figure 6 As shown in c, combined with the data on the change in the proportion of N species after NHCS is converted into a nitrogen-doped carbon layer, it can be seen that the defects and disordered structures on BNC10 are reduced. The Bi4f deconvolution shows two strong peaks, which are attributed to Bi. 3+ state( Figure 6 e). Meanwhile, as shown in Table 2, the proportion of adsorbed oxygen in the BNC10 sample (24.45%) was significantly higher than that in the BOC sample (8.73%), indicating a significant increase in surface oxygen vacancies (OVs), which can enhance oxygen adsorption capacity. Figure 6f). Furthermore, combined with the EPR spectrum results, the BNC10 sample exhibits a stronger EPR signal than BOC near g = 2.003, indicating that the introduction of NCL helps increase the concentration of OVs. In addition, under illumination, the EPR signal intensity associated with oxygen vacancies in BNC10 is further enhanced, indicating that illumination excites electrons within pre-existing oxygen vacancies or causes them to capture photogenerated electrons, thereby altering their electron occupancy state. These findings reveal the enhanced O2 activation mechanism of the BNC10 sample structure. Furthermore, combined with Raman spectroscopy results, at 60, 142, and 198 cm⁻¹... -1 The three typical Raman peaks appearing nearby belong to the Bi-Cl stretching vibration modes of the A1g outer mode, A1g inner mode, and Eg inner mode of the BOC crystal, respectively. It is noteworthy that, due to the introduction of NCL, peaks appear near the 1580 cm⁻¹ in the BNC10 sample. -1 A new graphite band (G band) was observed, indicating the presence of sp. 2 - Hybridized carbon structure. The improved orderliness of the NCL structure is consistent with the increasing trend of graphitic N content observed in high-resolution N 1s XPS spectra. Figure 6 (See Tables c and 3), and indirectly supported by XRD results, which show that the NCL coating did not disrupt the good crystallinity of the BiOCl main lattice, providing an ordered substrate for the composite material. Fourier transform infrared (FTIR) spectroscopy also confirmed that the introduction of NCL did not destroy the integrity of the BOC structure; specifically, in the 1200-1600 cm⁻¹ range... -1 Typical peaks within this range can be attributed to aromatic CN heterocycles; other characteristic peaks appear at 962 cm⁻¹. -1 and 1694 cm -1 The presence of oxygen-rich groups, attributed to the stretching vibrations of COC and C=O respectively, confirms that BNC10 is richer in oxygen-rich groups than BOC. This finding is supported by the observation of a new peak at 288.2 eV in BNC10 (attributed to C=O bonding). Based on the above structural characterization results, no bonding interactions were found between Bi atoms and N / C atoms, which clearly demonstrates the integrity of the nitrogen-doped carbon layer on the BOC surface.

[0073] Table 2. Content data of each element in the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention.

[0074] Table 3. Data on different types of nitrogen and their contents in the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention.

[0075] Figure 7 The UV-Vis diffuse reflectance spectra of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1 of this invention are shown. UV-Vis diffuse reflectance spectroscopy (UV-vis DRS) measurements revealed the light absorption characteristics and band gap energy of the prepared samples. E g Since NHCS does not exhibit a photoresponse, coating it onto BOC can enhance the photoresponse; therefore, this... E g It is an apparent value reflecting the optical response of the entire system, not just a single component. Figure 7 It is evident that the apparent optical band gap of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15) prepared in this invention is not smaller than that of BOC. Notably, the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15) series exhibit significantly enhanced absorption in the visible light region. This may be attributed to NCL and sub-bandgap states formed by defects (such as OVs), thereby enhancing overall light capture and promoting the elucidation of the photocatalytic reaction process and mechanism.

[0076] Figure 8 This is a comparison diagram of the VB positions of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15) and bismuth oxychloride photocatalysts (BOC) prepared in Example 1 of this invention. Figure 8 In the study, the valence band (VB) position of each sample was measured using VB-XPS spectroscopy. Figure 8 The results show that the VB of BOC and BNC10 relative to NHE can be calculated as -1.81 and -1.91 eV, respectively. Then, combined with... E g The values ​​were obtained for the CB positions of BOC and BNC10. Notably, the maximum VB (VBM) position of the prepared sample is approximately 1.90 eV. This is likely because the VBM of BiOCl consists of O 2p and Cl 3p orbitals, whose energy levels are relatively stable and did not change drastically due to NCL surface modification. The introduction of NCL and the formation of OVs primarily modulate the electronic structure and light absorption properties of the material.

[0077] In addition, TMB (3,3',5,5'-tetramethylbenzidine) was used as a probe molecule to study O2 activation. The change in absorbance at 370 nm over time represents the oxidation of TMB by ROS, as shown in the results. Figure 9 As shown.

[0078] Figure 9 This is a comparison chart showing the oxidation effect of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) and bismuth oxychloride photocatalyst (BOC) prepared in Example 1 of this invention on TMB under different conditions. Figure 9 In the diagram, a represents the oxidation effect of different samples on TMB, b represents the oxidation effect of samples on TMB under different atmospheres, and c represents the oxidation effect of samples on TMB under different scavenging agents. Figure 9 As shown in figure a, BNC10 exhibits a superior ability to generate ROS compared to the original BOC. It was subsequently discovered that their oxidation performance is highly dependent on O2 (…). Figure 9 (b) This phenomenon indicates that the prepared sample can utilize O2 to generate ROS. To identify the types of ROS generated during O2 activation, various scavengers, including superoxide dismutase (SOD), mannitol, L-histidine (L-his), and catalase (CAT), were used to inhibit O2 activation. – •OH 1 The oxidative activity of O2 and H2O2 on TMB. For example... Figure 9 As shown in Figure c, the contribution rates of ROS in the BOC system are arranged in descending order as follows: •OH, 1 O2 and •O2 – The coexistence of these multiple ROS indicates that photogenerated carriers can participate in reactions through various pathways within the original BOC. Simultaneously, photogenerated excitons may also partially form triplet excitons and generate... 1 O2, but this pathway is inefficient, leading to... 1 The low selectivity for O2 hinders the optimization of photocatalytic energy utilization. In contrast, the dominant ROS in BNC10 is... 1 O2, along with a small amount of H2O2, is produced, which demonstrates unique exciton behavior and O2 activation pathway.

[0079] In addition, the fluorescence (PF) and phosphorescence (PH) spectra of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) and bismuth oxychloride photocatalyst (BOC) were measured in this invention to explore the behavior of charge carriers and excitons.

[0080] The results showed that, through multi-peak fitting of the PF spectra, both samples exhibited characteristic emission (around 392 nm) related to intrinsic interband exciton recombination in the ultraviolet region. Notably, BNC10 exhibited a significant in-band emission peak at around 525 nm, attributed to defect-state radiative recombination caused by its abundant OVs, consistent with XPS and EPR results. For the BOC sample, its in-band emission peak in the visible region was centered at around 550 nm. Considering its fewer OVs and higher charge separation / transfer efficiency, this peak is more likely related to intrinsic defects, surface states, or specific exciton recombination processes in other BiOCl materials, rather than being primarily induced by oxygen vacancies. Furthermore, the shoulder peaks at around 418 nm in BNC10 and around 421 nm in BOC may be related to the fine structure of intrinsic exciton emission or different exciton states. PF is typically caused by charge carrier recombination or radiative decay of singlet excitons. Transient photocurrent and electrochemical impedance spectroscopy measurements indicated that BNC10 exhibited lower free charge carrier separation / transfer efficiency compared to BOC. Therefore, it can be inferred that the higher PF intensity in BNC10 may be attributed to the introduction of NCL, which significantly increases the initial yield of photogenerated singlet excitons and / or enhances the relative efficiency of radiative recombination.

[0081] The phosphorescence (PH) induced by exciton radiative decay from a triplet excited state to a singlet ground state can be used to selectively study the behavior of triplet excitons. Results show that BNC10 exhibits a stronger PH intensity, indicating a sharp increase in triplet exciton yield. Therefore, BNC10... 1 The increase in O2 production is attributed to the successful transition of excitons from singlet to triplet states.

[0082] The singlet-triplet band gap (ΔE) was measured by the difference between the intrinsic interband excitation peaks of normalized PF and PH. ST This can reveal the conversion efficiency from singlet to triplet excitons. The results show that the introduction of NCL increases the ΔE of the BOC sample. ST The value decreased by approximately 36%, and the ΔE of BOC and BNC10 decreased. ST The values ​​are 0.176 eV and 0.113 eV, respectively, which clearly demonstrates that the reduction of the ISC barrier significantly promotes the generation of triplet excitons.

[0083] Electronic structures of BOC and BNC (specifically BNC5, BNC10, and BNC15) with and without surface OV were calculated using DFT. The density of states (DOS) calculations show that impurity states composed of Bi 6p orbitals appear between the VB and CB of BOC. Interestingly, the introduction of NCL not only affects the impurity states but also causes a redistribution of electrons near the Fermi level, leading to a more localized DOS in the range of -1.5 to 0.2 eV. Furthermore, the DOS of BNC exhibits nonmetallic properties different from that of the original NC, and the band gap is further reduced, consistent with the DRS results. Based on these results, this invention proposes a reasonable exciton process for BNC, in which the charge generated after photoexcitation is trapped by the defect state, producing a trapped singlet exciton (S1*), thereby reducing ΔE. ST To accelerate the generation and orientation of triplet excitons 1 O2 conversion.

[0084] Subsequently, time-resolved PF and PH spectra were further monitored to reveal exciton dynamics in the system. The results showed that the PF lifetime decay of BNC10 (5.93 ± 0.26 ns) was faster than that of BOC (7.11 ± 0.32 ns). The shortened PF lifetime is generally associated with a faster nonradiative inactivation channel for singlet excitons. In the BNC10 system, this phenomenon is mainly attributed to the significantly enhanced intersystem crossing (ISC) from singlet to triplet states promoted by the introduction of NCL, which reduces the probability and time of singlet / triple exciton decay via fluorescence radiation. Combined with the results of steady-state PL spectroscopy, a more efficient singlet to triplet exciton transition was systematically revealed in BNC10. Conversely, a larger ΔE in the BOC system... ST The suppression of singlet exciton relaxation and the accumulation of a large number of singlet excitons led to a slow ET process. PH kinetics provide strong evidence that activated O2 is generated through a rapid spin-flip process of singlet excitons. 1 O2. Time-resolved pH spectra revealed a rapid decay phase attributed to triplet-triplet annihilation or exciton diffusion, followed by a decrease in triplet exciton concentration. Furthermore, the pH lifetime of BNC10 was 118.07 µs, lower than that of BOC (123.62 µs), suggesting that the introduction of NCL improved spin-orbit coupling (SOC).

[0085] The bonding configuration between O2 molecules and the photocatalyst surface is crucial for evaluating activation efficiency. This invention investigates the adsorption state of O2 at different locations using DFT calculations. Differential charge density visually illustrates the charge transfer and O2 bond length changes with BNC and other catalyst configurations. First, the optimal orientation of the adsorption interface was determined. The adsorption energy (E) of O2 on a BNC with surface OV at the BOC interface is... adThe Bader charge transfer coefficient (Ead) was -4.01 eV, significantly better than that of BNC-OV@C at the nitrogen-doped carbon interface (-0.03 eV), where BNC-OV@C refers to the BNC structure with surface oxygen vacancy modification. The Ead on the BOC surface with surface OV was -3.59 eV, lower than that of BNC-OV@B, where BNC-OV@B refers to the BNC structure with surface oxygen vacancy modification at the BOC interface, indicating that the introduced NCL further promotes O2 adsorption. In contrast, NC (0.01 eV), BOC without surface OV (0.01 eV), and BNC without surface OV (-0.19 eV) showed slight or even suppressed adsorption capacity, confirming the significant promoting effect of surface OV on O2 chemisorption. The results of Bader charge transfer coefficients are consistent with Ead. ad The calculated results are largely consistent. In contrast, BNC-OV@B exhibits the largest O2 electron charge (Δρ = 1.18 e), demonstrating the superior reactivity of BNC with O2. Furthermore, the O2 OO bond length (L...) on BNC-OV@B was found to be... O-O The length of the OO bond is significantly extended to 1.52 Å, which means that the OO bond is more easily broken and activated. In summary, in BNC10 1 The efficient generation of O2 is mainly attributed to the synergistic effect of NCL and OVs, which enhances the triplet exciton yield by promoting the ISC process, and then activates O2 through an energy transfer pathway, rather than through a charge transfer process mediated primarily by free charge carriers.

[0086] Example 2 The application of a nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst in the synthesis of hydrogen peroxide, specifically the synthesis of hydrogen peroxide using a nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst, includes the following steps: 20 mg of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) prepared in Example 1 was mixed with 50 mL of water and subjected to a photocatalytic reaction for 60 min under illumination to complete the synthesis of hydrogen peroxide.

[0087] Control group: The bismuth oxychloride photocatalyst (BOC) prepared in Example 1 was used instead of the nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst (BNC10), and other conditions were the same.

[0088] During the photocatalytic reaction, samples were taken at regular intervals, and 1 mL of 0.1 M C8H5KO4 solution and 1 mL of 0.4 M KI solution were added. The hydrogen peroxide content in the solution was detected using a UV-Vis spectrometer (UV-2700, Shimadzu Corporation, Japan) at 350 nm. The results are as follows: Figure 10 As shown.

[0089] Figure 10This diagram illustrates the effect of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) and bismuth oxychloride photocatalyst (BOC) on hydrogen peroxide production in Example 2 of this invention. Figure 10 It can be seen that the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) produces 73.9 µM h of hydrogen peroxide after 60 min of photocatalytic reaction. –1 The yield of hydrogen peroxide synthesized by the bismuth oxychloride photocatalyst (BOC) was 31.6 µM h. –1 .

[0090] Additionally, 5,5-dimethyl-1-pyrrolidone N-oxide (DMPO) was used as a trapping agent to identify •O2. – Combined with the EPR spectral results, it can be seen that a stronger DMPO-•O2 was observed in the BOC system. – sext signal (α N = 13.5 G, α β H = 10.1 G, g = 2.0070), indicating that the BOC system is more inclined to charge-mediated O2 activation (O2 + e-). – → O2 – Furthermore, a triple signal of TEMPO (1:1:1, α) was detected in the EPR spectrum under dark conditions. N = 17.7 G, g = 2.0067). Interestingly, the reaction rate between photogenerated electrons in the TEMPO and BNC10 system is low, indicating poor charge separation efficiency or low participation in charge carrier-mediated photocatalytic reactions. Most notably, the BNC10 system, compared to the BOC system under illumination, exhibits a more significant triple ERP signal (1:1:1, aN = 16.3 G, g = 2.0068) when using 2,2,6,6-tetramethyl-4-piperidinol-N-oxy (TEMP) as a trapping agent. The BNC10-generated electrons... 1 The steady-state concentration of O2 was further calculated using an FFA probe experiment, and its concentration was higher than that produced by BOC. 1 O2 is an order of magnitude higher. Furthermore, after adding various ROS scavengers to the FFA probe experiments, effects of other ROS on... 1 The effect of O2 generation was negligible. Additional EPR measurements were performed using DMPO as a spin trapping agent to investigate the potential role of •OH. The results showed that its concentration was extremely low, consistent with observations in the probe experiments, where the addition of tert-butanol (TBA, a •OH scavenger) had almost no effect on the FFA degradation rate. These findings allow for the substantial exclusion of the charge transfer pathway as a significant factor in the degradation rate. 1 The formation of O2 is facilitated because such pathways typically involve other ROS intermediates. The above results indicate that...1 O2 is mainly generated through energy transfer mechanisms.

[0091] Example 3 The application of a nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst in the treatment of organic pollutants, specifically the treatment of ciprofloxacin wastewater using the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst, includes the following steps: Weigh 20 mg of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) prepared in Example 1, and mix them with 50 mL of 10 mg / L ciprofloxacin (CIP) wastewater. Stir for 30 min in the dark and carry out photocatalytic degradation reaction for 60 min under light to complete the removal of ciprofloxacin from the wastewater.

[0092] During the photocatalytic degradation reaction, samples were taken at regular intervals to test the residual ciprofloxacin in the solution. The removal rate and degradation rate of ciprofloxacin were calculated, and the results are as follows: Figure 11 and Figure 12 As shown.

[0093] Figure 11 This image shows the removal rate of ciprofloxacin by the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) in Example 3 of this invention. Figure 11 It can be seen that the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20) all achieved a removal rate of over 90% for ciprofloxacin (CIP) within 60 minutes under visible light irradiation. In particular, BNC10 can completely remove CIP, while the removal rate of bismuth oxychloride photocatalyst (BOC) is only 66%, and the removal rate of nitrogen-doped hollow carbon spheres (NHCS) is less than 20%.

[0094] Figure 12 This is a comparison chart showing the degradation rates of ciprofloxacin by nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20), bismuth oxychloride photocatalyst (BOC), and nitrogen-doped hollow carbon spheres (NHCS) in Example 3 of the present invention. Figure 12 In this study, the degradation rate of CIP by nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, BNC20) was calculated using pseudo-first-order kinetics. Figure 12It can be seen that the degradation rate constants of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalysts (BNC5, BNC10, BNC15, and BNC20) are all very high, especially the degradation rate constant (k) of BNC10. app =0.0843 min – ¹) is the original BOC(k) app = 0.0123 min –1 It is 6.9 times more potent than BiOX-based photocatalysts, and also outperforms most reported BiOX-based photocatalysts.

[0095] In this embodiment, the removal efficiency of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) for bisphenol A (BPA), acetaminophen (ACE), and tetracycline (TC) was also investigated, with other conditions being the same as in Example 3. The results showed that under visible light irradiation for 60 min, BNC10 achieved removal rates of 84.2%, 98.6%, and 100% for BPA, acetaminophen (ACE), and tetracycline (TC), respectively, with degradation rates of 0.0306 min for each. -1 0.0669min -1 0.0982min -1 .

[0096] In this embodiment, the cyclic removal efficiency of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) for ciprofloxacin (CIP) was also investigated, with other conditions remaining the same as in Example 3. The results showed that after five cycles, the removal rate of ciprofloxacin (CIP) by BNC10 remained as high as 87%, indicating that the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst of this invention has good stability and practicality. Furthermore, in this embodiment, the XRD patterns of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) before and after use were measured. The results showed that the XRD pattern of BNC10 remained essentially unchanged before and after use, further demonstrating the good stability of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst of this invention.

[0097] In this embodiment, the removal efficiency of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) on ciprofloxacin (CIP) wastewater at different pH values ​​was also investigated. Specifically, ciprofloxacin (CIP) wastewater with pH values ​​of 4, 5, 6.2, 7.5, 8.5, and 10 was treated using nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10), with other conditions being the same as in Example 3. The results showed that the reactivity increased with increasing initial pH value, and the degradation rate increased significantly. In particular, at pH = 10, the degradation rate reached 0.1134 min. –1 .

[0098] In this embodiment, the removal efficiency of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) on ciprofloxacin (CIP) wastewater under different chloride ion concentrations was also investigated. Specifically, sodium chloride was added to the ciprofloxacin (CIP) wastewater at concentrations of 5 mM, 25 mM, 50 mM, and 100 mM, respectively, while other conditions remained the same as in Example 3. The results showed that increasing the chloride ion concentration... – After reaching a certain concentration, the degradation performance showed an enhanced trend. During this process, Cl... – Can be with h + The reaction generates chlorine radicals (•Cl), with a standard reduction potential of 2.4 VNHE. Furthermore, the small amounts of •OH and H₂O₂ produced by BNC₁₀ also promote chlorine activation or generate chlorine radicals through reaction with •Cl. 1 O2. In particular, •Cl exhibits excellent selectivity and oxidation properties for electron-rich organic compounds. Considering that the main ROS in the BNC10 photoexcitation system is ET-mediated. 1 O2, in Cl – In their presence, CIP removal rates can be synergistically enhanced. In contrast, Cl... – The presence of [a substance] hinders the photodegradation process of CIP by the original BOC. It is speculated that this may be due to the insufficient ability of the original BOC to activate chlorine. Excess Cl [is present]. – It will further consume •Cl to generate dichloro radicals (Eº (•Cl2) – / Cl – ) = 2.0 V NHE), which has a low redox potential and usually reacts with organic compounds much slower than •Cl.

[0099] In this embodiment, the removal efficiency of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10) on ciprofloxacin (CIP) wastewater at different humic acid (HA) concentrations was also investigated. Specifically, humic acid (HA) at concentrations of 1 mg / L, 5 mg / L, and 10 mg / L was added to the ciprofloxacin (CIP) wastewater, with other conditions remaining the same as in Example 3. The results showed that the degradation efficiency slightly increased with increasing HA concentration. Specifically, HA can promote the transformation from excited ³HA to excited triplet CIP (CIP). 3 The ET process of CIP (Chemical Injection Process), where the latter reacts with O2 to generate •O2. – and 1O2 is used for the degradation reaction. Typically, high concentrations of HA significantly inhibit the reactivity of charge transfer-mediated catalytic systems because NOM (nitrogenous organic matter) impedes the mass transfer of free charges on the catalyst surface by capturing photogenerated carriers, thereby inhibiting ROS generation and even acting as a scavenger of photoactive species. Conversely, in this invention, an ET-mediated non-radical (NOM) photocatalyst based on a nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst is used. 1 The O2 oxidation system exhibits strong tolerance to interfering ions and organic matter.

[0100] To evaluate the performance of BNC10 in actual water samples, this embodiment also studied its removal effect on CIP in tap water (TW), river water (RW), and lake water (LW). Specifically, ciprofloxacin (CIP) in tap water, river water, and lake water was treated using a nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst (BNC10). The results showed that despite the high concentrations of coexisting organic and inorganic ions in the three actual water samples, BNC10 could still achieve a removal rate of over 87% for CIP. This indicates that the BNC10 photocatalyst has significant photocatalytic degradation performance in complex water environments and has great potential in practical applications, mainly due to: (1) efficient photocatalytic activation of O2 through ET; (2) the removal of Cl... − Excellent ability to convert to •Cl; (3) Good cycle stability.

[0101] As can be seen from the above results, compared with conventional bismuth oxychloride-based photocatalysts, the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst of the present invention has the following advantages: (a) High overall photocatalytic activity and high degradation efficiency of pollutants. Taking ciprofloxacin as an example, its rate constant for degrading ciprofloxacin is 6.9 times that of oxygen vacancy-modified bismuth oxychloride photocatalysts. Complete degradation can be achieved within 60 minutes, and the total organic carbon removal rate is as high as 75%, which has significant advantages in terms of the depth and speed of organic pollutant removal; (b) Strong singlet oxygen generation capacity and good selectivity. The singlet oxygen yield is 10 times that of oxygen vacancy-modified bismuth oxychloride photocatalysts, and the reaction pathway is transformed into singlet oxygen dominance, which can achieve efficient and selective generation of active species, making energy utilization more concentrated and the degradation process more targeted; (c) Good stability and strong practicality. It still maintains high activity after multiple cycles of use and still shows excellent degradation performance (removal rate of more than 87%) in real complex water bodies such as tap water, river water, and lake water, showing great potential for practical application.

[0102] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst, characterized in that, The invention includes bismuth oxychloride nanoflowers, the surface of which is modified with oxygen vacancies; the surface of which is coated with a nitrogen-doped carbon layer.

2. The nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst according to claim 1, characterized in that, The bismuth oxychloride nanoflowers are spherical materials self-assembled from bismuth oxychloride nanosheets; the diameter of the bismuth oxychloride nanoflowers is 300 nm to 800 nm; the nitrogen-doped carbon layer grows along the edge of the bismuth oxychloride nanosheets, and the thickness of the nitrogen-doped carbon layer is 1 nm to 4 nm.

3. A method for preparing a nitrogen-doped carbon layer-coated bismuth oxychloride composite photocatalyst as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Mix nitrogen-doped hollow carbon spheres, bismuth salt and ethylene glycol, sonicate and stir to obtain mixed solution A; S2. Add the chloride salt to the mixed solution A obtained in step S1, stir, and obtain mixed solution B; S3. The mixed solution B obtained in step S2 is subjected to a solvothermal reaction to obtain a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst.

4. The preparation method according to claim 3, characterized in that, In step S1, the mass ratio of the nitrogen-doped hollow carbon spheres to the bismuth salt is 0.05–0.2:1.94; the ratio of the bismuth salt to ethylene glycol is 0.97 g:30 mL.

5. The preparation method according to claim 4, characterized in that, In step S1, the mass ratio of the nitrogen-doped hollow carbon spheres to the bismuth salt is 0.08 to 0.15:1.94; the bismuth salt is bismuth nitrate pentahydrate.

6. The preparation method according to claim 5, characterized in that, In step S1, the method for preparing the nitrogen-doped hollow carbon spheres includes the following steps: (1) Sodium dodecyl sulfate, glucose, and melamine are dissolved in water and sonicated to obtain a precursor solution; the mass ratio of sodium dodecyl sulfate, glucose, and melamine is 0.03:1.44:0.04; the ratio of melamine to water is 0.04g:15mL; and the sonication time is 1h. (2) The precursor solution obtained in step (1) is subjected to a hydrothermal reaction, washed, and dried to obtain nitrogen-doped hollow carbon spheres; the temperature of the hydrothermal reaction is 160℃; the time of the hydrothermal reaction is 10h.

7. The preparation method according to any one of claims 3 to 6, characterized in that, In step S1, the ultrasound time is 10 min to 40 min; the stirring time is 10 min to 40 min. In step S2, the ratio of the chloride salt to the mixed solution A is 0.2982 g: 60 mL; the chloride salt is at least one of potassium chloride and sodium chloride; the stirring time is 30 min. In step S3, the temperature of the solvothermal reaction is 160°C; the time of the solvothermal reaction is 10 h; after the solvothermal reaction is completed, the following treatment is also included: the product of the solvothermal reaction is centrifuged, the solid product is collected, the solid product is washed with deionized water and anhydrous ethanol until the pH value of the washing liquid is neutral, and dried under vacuum at 60°C for 12 h to obtain a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst.

8. The application of a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst as described in claim 1 or 2, or a nitrogen-doped carbon layer coated bismuth oxychloride composite photocatalyst prepared by any one of claims 3 to 7, in the synthesis of hydrogen peroxide or the treatment of organic pollutant wastewater.

9. The application according to claim 8, characterized in that, The synthesis of hydrogen peroxide using a nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst includes the following steps: mixing the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst with water to carry out a photocatalytic reaction to obtain hydrogen peroxide; the amount of nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst added is 0.3g to 0.8g per liter of water; the photocatalytic reaction time is 60min to 120min; the photocatalytic reaction also includes adding chloride ions to the system to make the chloride ion concentration in the system ≥5mM.

10. The application according to claim 8, characterized in that, The method for treating organic pollutant wastewater using a nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst includes the following steps: mixing the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst with the organic pollutant wastewater to carry out a photocatalytic degradation reaction, thereby removing organic pollutants from the wastewater; the amount of the nitrogen-doped carbon-coated bismuth oxychloride composite photocatalyst added is 0.3g to 0.8g per liter of organic pollutant wastewater; the organic pollutants in the organic pollutant wastewater are electron-rich compounds; the electron-rich compounds include at least one of sulfamethoxazole, bisphenol A, phenol, ciprofloxacin, and tetracycline; the initial concentration of organic pollutants in the organic pollutant wastewater is ≤10mg / L; the initial pH value of the organic pollutant wastewater is 4 to 10; the photocatalytic degradation reaction time is 60min; the photocatalytic degradation reaction also includes adding chloride ions to the system to make the chloride ion concentration in the system ≥5mM.

Images