Porous graphitic carbon nitride supported platinum single-atom photocatalyst, and preparation method and application thereof

Abstract

The application discloses a kind of porous graphite phase carbon nitride load platinum single atom photocatalyst, and porous graphite phase carbon nitride prepared by urea secondary calcination is carrier, and platinum is dispersed in the surface and interlayer of the carrier in single atom form, forms Pt-N coordination structure;The loading capacity of the platinum is 0.000025~0.000075 mol / g;The photocatalyst keeps two-dimensional layered honeycomb porous morphology, and the BET specific surface area of the photocatalyst is 65.749~146.8357 m 2 ·g ‑1 Porous g-C3N4 is prepared by secondary subsection calcination process;PtCl4 is used as platinum source, and the strategy of impregnation-sodium borohydride reduction-cryogenic freeze drying-inert atmosphere calcination is used to accurately control the molar amount of Pt loading.The preparation process of the application is mild and controllable, has good repeatability, low raw material cost, and near 100% utilization rate of noble metal, which can realize the harmless, reduction, resource utilization and green hydrogen energy co-production integration of waste microplastics, and provide efficient, stable and scalable new photocatalytic technology for water / soil microplastic pollution treatment and clean energy preparation.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of photocatalytic functional materials, environmental pollution control technology and hydrogen production. Specifically, it relates to a photocatalyst with porous graphitic carbon nitride (g-C3N4) supported on platinum (Pt) single atoms and its preparation method, and uses the photocatalyst in the photocatalytic hydrogen production coupled with the oxidative degradation of microplastics. Background Technology

[0002] In recent years, the large-scale production and overuse of plastic products have led to an explosive growth in global plastic waste. Under physical abrasion, ultraviolet radiation, and biological and chemical action, plastics gradually break down into microplastics with particle sizes of 1μm to 5mm. These microplastics are widely dispersed into water bodies, soil, atmosphere, and even organisms. They are highly mobile, difficult to degrade, bioaccumulate, and have potential ecotoxicity. They can enter the human body through drinking water and the food chain, threatening the health of the digestive, cardiovascular, and immune systems, and have become a global environmental problem.

[0003] Traditional microplastic treatment technologies, including physical interception, biodegradation, and chemical oxidation, generally suffer from bottlenecks such as incomplete degradation, high energy consumption, easy secondary pollution, and difficulty in resource utilization. Photocatalysis, driven by clean solar energy, can achieve deep oxidative breakage of microplastic polymer chains at room temperature and pressure, simultaneously reducing protons to hydrogen. This achieves the triple goals of "pollution control + clean energy production + co-production of high-value-added chemicals," making it the green technology route with the greatest industrialization potential.

[0004] Graphitic carbon nitride (g-C3N4), as a typical metal-free organic semiconductor photocatalyst, possesses outstanding advantages such as inexpensive raw materials, simple preparation, suitable band structure, excellent chemical stability, and visible light response, and is widely used in fields such as photocatalytic water splitting, pollutant degradation, and CO2 reduction. However, pure g-C3N4 has inherent defects: the recombination rate of photogenerated electron-hole pairs is extremely fast, resulting in low quantum efficiency; the specific surface area is small, leading to an insufficient number of active sites; the adsorption capacity for microplastics is weak, resulting in low interfacial mass transfer efficiency; and there is a lack of highly efficient hydrogen evolution active sites, making it difficult to synergistically drive the oxidation of microplastics and hydrogen production reactions.

[0005] Single-atom catalysis is one of the most effective strategies for improving photocatalytic performance. Pt, a classic hydrogen evolution co-catalyst, can be highly dispersed in single-atom form on the surface of g-C3N4 to achieve: near 100% atom utilization, significantly reducing the amount of precious metals required; providing high-density, highly selective active sites for hydrogen production; constructing interfacial charge transport channels for directional separation of photogenerated carriers; modulating the electronic structure and band structure of g-C3N4 to enhance visible light absorption; and strengthening structural stability through Pt-N coordination bonds to improve cycle life.

[0006] In the existing technology, g-C3N4 supported Pt-based catalysts still have the following shortcomings: due to the large Pt loading (>2wt%) and high calcination temperature (>550℃), Pt is prone to agglomerate to form nanoparticles with poor single-atom dispersion; there is a lack of precise control and systematic comparison of Pt loading, and the optimal composition is unclear; the preparation process is complex and the conditions are harsh, which is not conducive to large-scale production; the adaptability to microplastics in real environments is poor, and the hydrogen production rate and stability are insufficient; the degradation pathway of microplastics, product distribution and photocatalytic coupling hydrogen production mechanism are unclear. Summary of the Invention

[0007] The technical problems to be solved by this invention in light of existing technologies include: severe recombination of photogenerated carriers in pure g-C3N4, resulting in low quantum efficiency and poor degradation and hydrogen production performance of microplastics; Pt co-catalysts are prone to agglomeration into nanoparticles, leading to low atom utilization, high cost, and insufficient stability; lack of system design and comparison of gradient Pt loading, and unclear optimal active composition; limited adsorption and mass transfer of microplastics on the catalyst surface, resulting in slow reaction kinetics; unclear mechanism of photocatalytic coupling system, and product selectivity and cycle performance that are difficult to meet industrialization requirements; and complex and demanding preparation processes that are difficult to scale up for production.

[0008] To address the aforementioned technical problems, including severe carrier recombination in pure g-C3N4, insufficient active sites, easy Pt aggregation, low coupling efficiency of microplastic degradation-hydrogen production, and poor cycle stability, this invention provides a photocatalyst supported on porous graphitic carbon nitride with platinum single atoms. The photocatalyst uses porous graphitic carbon nitride prepared by secondary calcination of urea as a support, with platinum dispersed in single-atom form on the surface and between the layers of the support, forming a Pt-N coordination structure. The platinum loading is 0.000025~0.000075 mol / g. The photocatalyst maintains a two-dimensional layered honeycomb porous morphology, and its BET specific surface area is 65.749~146.8357 m². 2 ·g -1 .

[0009] Furthermore, in the photocatalyst of the present invention, platinum single atoms exist stably in a mixed valence state, and the Pt-N coordination structure comprises 55% Pt. 2+ -N x Coordination structure, the rest are reduced Pt 0 It also contains trace amounts of Pt 4+ Oxide clusters.

[0010] Furthermore, this invention also proposes a method for preparing the aforementioned photocatalyst. This method is mild and controllable, and mainly includes the following steps:

[0011] Step 1: Prepare porous graphitic carbon nitride powder (porous g-C3N4 powder) from urea through a two-stage segmented calcination process.

[0012] Step 2: Dissolve an appropriate amount of PtCl4 in ultrapure water to prepare a PtCl4 aqueous solution with a concentration of 0.00125~0.00375 mol / L. Add the porous g-C3N4 powder prepared in Step 1 to the PtCl4 aqueous solution to obtain mixture A, wherein the molar mass ratio of PtCl4 to the porous g-C3N4 powder is 0.000025~0.000075 mol / g. Stir at room temperature for 12 h to obtain mixture A. Add an appropriate amount of NaBH4 solution to mixture A, wherein the molar ratio of NaBH4 to PtCl4 is 4:1. Stir for 0.5 h to obtain mixture B.

[0013] Step 3: Freeze the mixture B obtained in Step 2 at -80℃ for 24 hours and freeze-dry for 48 hours to obtain a freeze-dried solid;

[0014] Step 4: Place the freeze-dried solid obtained in step 3 into a tube furnace, heat it to 500°C at 5°C / min under N2 atmosphere, keep it at the temperature for 2 hours, and then cool it naturally to room temperature. The resulting product is the photocatalyst.

[0015] Furthermore, in the method for preparing the photocatalyst of the present invention, wherein:

[0016] Step 1 includes the following steps: Weigh urea and place it in a crucible, perform the first stage of calcination in a muffle furnace, grind it after natural cooling, and then perform the second stage of calcination to obtain a yellow powder, which is the porous g-C3N4 powder. The process conditions for the first stage of calcination are: heating to 500℃ at 5℃ / min and calcining at a constant temperature for 4 hours. The process conditions for the second stage of calcination are: heating to 550℃ at 5℃ / min and calcining at a constant temperature for 2 hours.

[0017] Preferably, the molar mass ratio of PtCl4 to the porous g-C3N4 powder in step 2 is 0.000025 mol / g.

[0018] The porous graphitic carbon nitride-supported platinum single-atom photocatalyst prepared in this invention is used in the photocatalytic hydrogen production of microplastics through oxidative degradation coupled with photocatalysis. The microplastics are polyethylene terephthalate particles with a particle size of 1 μm to 5 mm. The process of using the photocatalyst for the photocatalyst in the photocatalytic degradation of microplastics coupled with photocatalytic hydrogen production is as follows:

[0019] Sodium hydroxide was dissolved in deionized water at a mass-to-volume ratio of 0.4 g / L. Microplastics were then added at a mass ratio of 1:40 to sodium hydroxide to obtain mixture C. This mixture was magnetically stirred at 50°C for 48 hours. After filtration to precipitate terephthalic acid, the resulting solution was designated as the pretreatment reaction solution. An appropriate amount of the pretreatment reaction solution was filtered to remove incompletely degraded microplastics. 25 mL of this solution was then placed in a reaction vessel. Under magnetic stirring at 300 rpm, the photocatalyst was dispersed in the pretreatment reaction solution to obtain a reaction mixture, wherein the mass-to-volume ratio of the photocatalyst to the pretreatment reaction solution was 2 mg / mL. The reaction mixture was then purged with nitrogen under dark conditions while being magnetically stirred for 30 min. The reaction vessel was cooled to room temperature with cold water and subjected to photocatalytic reaction under irradiation with a 300 W xenon lamp for 3–18 h. After the reaction, the gas was collected using a gas collection bag; the obtained gas was hydrogen. The liquid product was filtered through a filter membrane, and the resulting product included formic acid, acetic acid, ethanol, and ethyl acetate.

[0020] Preferably, in the photocatalyst, the molar mass ratio of PtCl4 to the porous g-C3N4 powder is 0.00005 mol / g, and the photocatalyst is simply referred to as PtCl4. 0.00005 -CN; the photocatalyst Pt 0.00005 -CN produces hydrogen at a rate of 450 μmol·g in the microplastic system. -1 ·h -1 The hydrogen selectivity is 99%, and the catalytic activity retention rate is 90% after being recycled 4 times.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1) In this invention, multiple catalysts are prepared systematically and clearly through optimal composition, revealing for the first time the quantitative structure-activity relationship of Pt loading-structure-performance, and determining the Pt loading-structure-performance relationship. 0.00005 -CN is the optimal catalyst, with activity far exceeding that of other components, such as... Figure 8 As shown.

[0023] (2) Pt truly achieves single-atom dispersion with low loading and no particle agglomeration, with an atom utilization rate of nearly 100%, such as Figure 1 As shown, this significantly reduces the cost of precious metals.

[0024] (3) Significantly improved structure and photoelectric properties: Two-dimensional porous structure with hierarchical channels, increasing specific surface area by 123%, such as Figure 2 As shown; reduced impedance, enhanced photocurrent, PL quenching, and broadened visible light absorption significantly improve carrier separation efficiency, such as... Figure 6 As shown.

[0025] (4) The bifunctional catalysis efficiently and synergistically achieves deep oxidative degradation of microplastics and highly selective hydrogen production simultaneously, with a hydrogen production rate of 454.615 μmol·g. -1 ·h -1 H2 selectivity is 99%, such as Figure 8 As shown in (a).

[0026] (5) Excellent stability and great industrial potential: Pt-N coordination bonds are strong, resistant to loss and aggregation, and retain 90% activity even after 4 cycles. Figure 8 As shown in (d).

[0027] (5) The process is mild, controllable, and scalable without the need for complex equipment. It involves secondary calcination, freeze drying, and roasting, resulting in a simple, repeatable, and environmentally friendly process.

[0028] (7) Resource utilization: high-value-added microplastics are transformed into high-value-added chemicals such as formic acid, acetic acid, and ethanol, realizing "turning waste into treasure". Attached Figure Description

[0029] Figure 1 In the image, (a) and (b) are SEM images of g-C3N4 prepared in Example 1 at different proportions; (c) and (d) are SEM images of Pt prepared in Example 2. 0.00005 SEM images of CN at different scales; (e) is the Pt obtained in Example 2. 0.00005 -CNA AC-STEM image of CN; (f)-(i) are Pt obtained in Example 2 0.00005 -CN's EDS element distribution diagram;

[0030] Figure 2 In the figures, (a) and (b) are g-C3N4 prepared in Comparative Example 1 and Pt prepared in Example 2, respectively. 0.00005 -CN N2 adsorption-desorption isotherm and BJH mesopore size distribution diagram;

[0031] Figure 3 g-C3N4 prepared in Comparative Example 1 and Pt prepared in Example 2 0.00005 -CN, Pt prepared in Comparative Example 2 0.0001 -CN, Pt prepared in Example 3 0.0002 XRD pattern of -CN;

[0032] Figure 4 g-C3N4 prepared in Example 1 and Pt prepared in Example 2 0.00005 XPS spectra of -CN: (a) full spectrum; (b) Pt4f; (c) C1s; (d) N1s;

[0033] Figure 5The following are the electrochemical impedance spectroscopy (EIS) plots, transient photocurrent curves, UV-Vis diffuse reflectance spectra, and photoluminescence (PL) spectra of the photocatalysts prepared in Examples 1-3 and Comparative Example 1.

[0034] Figure 6 (a) Tauc bandgap plots and (b) Mott-Schottky curves of the photocatalysts prepared in Examples 1-3 and Comparative Example 1;

[0035] Figure 7 g-C3N4 and Pt prepared in Comparative Example 1 and Example 2 0.00005 -CN band structure distribution diagram;

[0036] Figure 8 The photocatalytic hydrogen production performance of the preparations in Examples 1-3 and Comparative Examples 1-3 is as follows: (a) Comparison of hydrogen production rates; (b) Pt 0.00005 -CN catalyst hydrogen yield over time; (c) Pt 0.00005 -CN catalyst hydrogen yield Figure I Simulated reaction solution II: Actual microplastic pretreatment reaction solution; (d) Pt 0.00005 -CN catalyst hydrogen yield variation in cyclic reaction;

[0037] Figure 9 In the image, (a) is the ¹H NMR spectrum of the simulated reaction solution; (b) is the Pt obtained in Example 2. 0.00005 -CN-catalyzed microplastic degradation liquid products¹HNMR spectrum;

[0038] Figure 10 The Pt prepared in Example 2 0.00005 -CN Active Species Capture Experiment Bar Chart. Detailed Implementation

[0039] This invention discloses a porous g-C3N4 photocatalyst supported on Pt single atoms, its preparation method, and its application in the coupled photocatalytic hydrogen production of microplastics through oxidative degradation. The photocatalyst is prepared using porous graphitic carbon nitride prepared by secondary calcination of urea as a support. Platinum is dispersed in single-atom form on the surface and between the layers of the support, forming a Pt-N coordination structure. The platinum loading is 0.000025~0.000075 mol / g. The photocatalyst maintains a two-dimensional layered honeycomb porous morphology, and its BET specific surface area is 65.749~146.8357 m². 2 ·g -1 Using platinum chloride (PtCl4) as the platinum source, platinum single atoms exist stably in a mixed valence state. The Pt-N coordination structure comprises 55% Pt. 2+ -N xCoordination structure, the rest are reduced Pt 0 It also contains trace amounts of Pt 4+ Oxide clusters.

[0040] The preparation method of this invention employs a combined strategy of impregnation-sodium borohydride reduction-cryogenic freeze-drying-inert atmosphere calcination. The preparation process mainly includes: preparation of a porous g-C3N4 support and loading Pt single atoms. The steps are as follows:

[0041] Yellow porous g-C3N4 powder was prepared from urea through a two-stage fractional calcination process; PtCl4 aqueous solutions of different concentrations ranging from 0.00125 to 0.00375 mol / L were prepared; porous g-C3N4 powder was added to the PtCl4 aqueous solution, and the mixture was stirred at room temperature for 12 hours to allow the PtCl4 to precipitate. 4+ Sufficient adsorption was achieved; an appropriate amount of freshly prepared NaBH4 solution was added, wherein the molar ratio of NaBH4 to PtCl4 was 4:1, and the mixture was stirred for 0.5 h to complete in-situ reduction; the mixture was placed at -80℃ for 24 h, transferred to a freeze dryer, and freeze-dried for 48 h to completely remove moisture, obtaining a freeze-dried solid; the freeze-dried solid was placed in a tube furnace, heated to 500℃ at 5℃ / min under N2 atmosphere protection, calcined at this temperature for 2 h, and then naturally cooled to room temperature, finally obtaining a porous g-C3N4 support-supported Pt single-atom photocatalyst.

[0042] This invention provides a method for precisely controlling the molar amount of Pt loading to prepare photocatalysts with different molar amounts of Pt, including pure g-C3N4 and photocatalysts using porous g-C3N4 powder as a support. This invention proposes a secondary calcination g-C3N4+ gradient Pt single-atom loading strategy to precisely construct a series of photocatalysts. It systematically reveals the structure-activity relationship between Pt loading and structure, photoelectric properties, and catalytic activity, achieving efficient degradation of microplastics coupled with high-purity hydrogen co-production, providing a novel technical solution for the resource utilization of microplastics.

[0043] The preparation process of this invention is mild and controllable, with good repeatability, low raw material cost, and nearly 100% utilization of precious metals. It can realize the integration of "harmlessness, reduction, and resource utilization" of waste microplastics with green hydrogen co-production, providing a novel photocatalytic technology that is efficient, stable, and scalable for the treatment of microplastic pollution in water / soil and the synergistic preparation of clean energy.

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention.

[0045] Example 1

[0046] A porous g-C3N4 photocatalyst with a Pt loading molar amount of 0.000025 mol / g was prepared. This catalyst is simply referred to as Pt. 0.000025-CN.

[0047] (1) Weigh urea and place it in a crucible and muffle furnace for the first stage of calcination. The temperature is increased to 500℃ at 5℃ / min and calcined at a constant temperature for 4 hours. After natural cooling, grind it and then carry out the second stage of calcination. The temperature is increased to 550℃ at 5℃ / min and calcined at a constant temperature for 2 hours. The final yellow powder is the porous g-C3N4 powder.

[0048] (2) Dissolve 0.084 g PtCl4 in 20 mL of ultrapure water to prepare a PtCl4 aqueous solution with a concentration of 0.00125 mol / L; add 1 g of porous g-C3N4 powder to 20 mL of PtCl4 aqueous solution and stir at room temperature for 12 h; then add 10 mL of 0.1 mol / L freshly prepared NaBH4 solution and stir for 0.5 h to obtain a mixture;

[0049] (3) The above mixture was frozen at -80℃ for 24 hours and freeze-dried for 48 hours to obtain a freeze-dried solid;

[0050] (4) The above freeze-dried solid was placed in a tube furnace and heated to 500°C at 5°C / min under N2 atmosphere, and calcined at this temperature for 2 hours. It was then naturally cooled to room temperature. The resulting product was the photocatalyst Pt. 0.000025 -CN.

[0051] Example 2

[0052] A porous g-C3N4 photocatalyst with Pt single atoms supported on Pt with a Pt loading molar amount of 0.00005 mol / g was prepared. 0.00005 -CN). The preparation method is basically the same as in Example 1, except that step (2) is: 0.168g PtCl4 is dissolved in 20mL of ultrapure water to prepare a PtCl4 aqueous solution with a concentration of 0.0025 mol / L; 1g of porous g-C3N4 powder is added to 20mL of PtCl4 aqueous solution and stirred at room temperature for 12h; then 10Ml of 0.2mol / L freshly prepared NaBH4 solution is added and stirred for 0.5h. Finally, the photocatalyst Pt is obtained. 0.00005 -CN.

[0053] Example 3

[0054] A porous g-C3N4 photocatalyst with Pt single atoms supported on Pt with a Pt loading molar amount of 0.00075 mol / g was prepared. 0.000075-CN). The preparation method is basically the same as in Example 1, except that step (2) is: 0.252 g PtCl4 is dissolved in 20 mL of ultrapure water to prepare a PtCl4 aqueous solution with a concentration of 0.00375 mol / L; 1 g of porous g-C3N4 powder is added to 20 mL of PtCl4 aqueous solution and stirred at room temperature for 12 h; then 10 Ml of 0.3 mol / L freshly prepared NaBH4 solution is added and stirred for 0.5 h. Finally, the photocatalyst Pt is obtained. 0.000075 -CN.

[0055] Comparative Example 1

[0056] Preparation of pure g-C3N4: Weigh 20g of urea and place it in a corundum crucible, then transfer it to a muffle furnace. Heat the crucible to 500℃ at 5℃ / min and calcine at that temperature for 4 hours. Allow it to cool naturally to room temperature, then remove and grind thoroughly. Heat the crucible again to 550℃ at 5℃ / min and calcine at that temperature for 2 hours. Allow it to cool naturally to obtain pure g-C3N4 yellow powder.

[0057] Comparative Example 2

[0058] A porous g-C3N4 photocatalyst with Pt single atoms supported on Pt with a Pt loading molar amount of 0.0001 mol / g was prepared. 0.0001 -CN). The preparation method is basically the same as in Example 1, except that step (2) is: 0.336 g PtCl4 is dissolved in 20 mL of ultrapure water to prepare a PtCl4 aqueous solution with a concentration of 0.005 mol / L; 1 g of porous g-C3N4 powder is added to 20 mL of PtCl4 aqueous solution and stirred at room temperature for 12 h; then 10 mL of freshly prepared 0.4 mol / L NaBH4 solution is added and stirred for 0.5 h. Finally, the photocatalyst Pt is obtained. 0.0001 -CN.

[0059] Comparative Example 3

[0060] A porous g-C3N4 photocatalyst with Pt single atoms supported on Pt with a Pt loading molar amount of 0.0002 mol / g was prepared. 0.0002 -CN). The preparation method is basically the same as in Example 1, except that step (2) is: 0.42 g PtCl4 is dissolved in 20 mL of ultrapure water to prepare a PtCl4 aqueous solution with a concentration of 0.01 mol / L; 1 g of porous g-C3N4 powder is added to 20 mL of PtCl4 aqueous solution and stirred at room temperature for 12 h; then 10 mL of 0.8 mol / L freshly prepared NaBH4 solution is added and stirred for 0.5 h. Finally, the photocatalyst Pt is obtained. 0.0002 -CN.

[0061] The following are tests on the photocatalysts prepared according to the proportions and examples.

[0062] 1. Performance testing of photocatalytic microplastic coupling hydrogen production of six catalysts prepared in Comparative Examples 1-3 and Examples 1-3

[0063] (1) Reaction system: Add 25 mL of microplastic pretreatment solution to a 100 mL sealed reaction vessel, and add 50 mg of each of the above 6 catalysts respectively;

[0064] (2) Deoxygenation: Purge with N2 for 30 minutes to eliminate dissolved oxygen interference;

[0065] (3) Illumination conditions: 300W xenon lamp irradiation (simulating sunlight), cold water bath temperature control, 300rpm stirring;

[0066] (4) Product testing:

[0067] Gas: Gas was collected periodically, and H2 concentration and yield were detected by gas chromatography (GC). Catalytic performance and hydrogen production rate are detailed in [link to catalytic performance data]. Figure 8 See Table 1.

[0068] Table 1

[0069]

[0070] Depend on Figure 8 According to Table 1, the catalytic performance and hydrogen production rate, from highest to lowest, are as follows:

[0071] Pt 0.00005 -CN>Pt 0.000075 -CN>Pt 0.000025 -CN>Pt 0.0001 -CN>Pt 0.0002 -CN>g-C3N4.

[0072] Liquid: After the reaction is complete, the mixture is filtered, and the liquid (degradation) products are qualitatively and quantitatively analyzed by nuclear magnetic resonance (NMR), such as... Figure 9 As shown in (b), the liquid products are formic acid (a), acetic acid (d), ethanol (g), and ethyl acetate (e, f).

[0073] (5) Cyclic test: The photocatalyst Pt prepared in Example 2 was tested. 0.00005 -CN Cyclic Stability Test:

[0074] Pt after the reaction 0.00005 -CN catalyst was centrifuged, washed three times alternately with anhydrous ethanol and ultrapure water, and dried under vacuum at 80°C; the photocatalytic experiment was repeated four times to determine the activity retention rate. Pt 0.00005 -CN hydrogen selectivity ≥99%. After 4 cycles, Pt 0.00005 -CN activity retention rate was 90%.

[0075] 2. Characterization results and performance analysis of photocatalysts

[0076] (1) Morphology and structure, such as Figure 1 As shown, pure g-C3N4 exhibits a typical two-dimensional layered porous structure; Pt 0.00005 -CN maintains a complete layered morphology without collapse, and Pt is uniformly dispersed as single atoms (confirmed by AC-STEM and EDS); For example Figure 3 XRD showed that the low-load sample had no Pt diffraction peaks, while the high-load sample gradually showed Pt crystalline phase, proving that the single-atom dispersion range was ≤0.00005.

[0077] (2) Pore structure and specific surface area, such as Figure 2 As shown, all catalysts exhibit type IV adsorption isotherms, with an H3 hysteresis loop, and are predominantly mesoporous; the specific surface area initially increases and then decreases with increasing Pt loading: Pt 0.00005 -CN highest (146.8357m) 2 ·g -1 Excessive load can cause pore blockage and reduce specific surface area.

[0078] (3) XPS electronic structure, such as Figure 4 As shown, the Pt4f spectrum reveals that Pt exists in a mixed valence state: Pt 2+ -N x Mainly (~55.85%), Pt 0 Second, trace amounts of Pt 4+ C1s and N1s indicate that Pt repairs triazine ring defects, enhances the conjugated structure, and improves charge delocalization.

[0079] (4) Photoelectric properties, such as Figures 5-7 As shown, EIS indicates:

[0080] The order of impedance magnitude is g-C3N4>Pt 0.000075 -CN>Pt 0.000025 -CN>Pt 0.00005 -CN, optimal charge transport efficiency. Transient photocurrent: Pt 0.00005 -CN exhibits the strongest response and the highest carrier separation efficiency. UV-Vis and PL: Pt loading broadens visible light absorption, PL intensity is significantly quenched, and recombination is strongly suppressed. Band gap: Pure g-C3N 42.94 eV → Pt 0.00005 -CN2.85eV, which is more conducive to the utilization of visible light.

[0081] (6) For example Figure 9 and Figure 10 As shown, the products and mechanisms are as follows: liquid products: formic acid, acetic acid, ethanol, and ethyl acetate. Quenching experiments indicate that photogenerated electrons e -It is a core active species for hydrogen production; ·OH and O2 - It plays an auxiliary role in the degradation of microplastics.

[0082] The above characterization and performance test results show that Pt exhibits a highly uniform atomic-level dispersion on the support surface, with no obvious nanoparticle aggregation, such as... Figure 3 As shown, this invention optimizes and limits the platinum loading to the range of 0.000025~0.000075 mol / g. Pt single atoms are firmly bonded to the g-C3N4 framework through Pt-N coordination bonds, significantly regulating the electronic structure of the support, narrowing the band gap, enhancing visible light absorption, accelerating the separation and migration of photogenerated carriers, and reducing interfacial charge transfer impedance. The prepared catalyst possesses dual functions of efficient oxidative degradation of microplastics and highly selective photocatalytic hydrogen evolution. Among them, Pt0.00005-CN exhibits the best catalytic performance, achieving a hydrogen production rate of 454.615 μmol·g⁻¹·h⁻¹ under visible light, with a hydrogen selectivity of 99%, and retaining 90% of its initial activity after four cycles. The gaseous products are CO and C₂H₂, and the liquid products are high-value-added chemicals such as formic acid, acetic acid, ethanol, and ethyl acetate.

[0083] The photocatalyst preparation process provided by this invention is mild, uses readily available raw materials, requires no expensive equipment, and can be mass-produced; it has broad application prospects in the fields of water / soil microplastic treatment, resource utilization of organic pollutants in industrial wastewater, and green hydrogen cogeneration.

[0084] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are preferred application examples that demonstrate the core technical ideas of the present invention, and are merely illustrative and not restrictive. Those skilled in the art can make many improvements and changes under the guidance of the present invention without departing from the spirit of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A photocatalyst for supporting platinum single atoms on porous graphitic carbon nitride, characterized in that, Using porous graphitic carbon nitride prepared by secondary calcination of urea as a support, platinum is dispersed in single-atom form on the surface and between the layers of the support, forming a Pt-N coordination structure; the platinum loading is 0.000025~0.000075 mol / g; the photocatalyst maintains a two-dimensional layered honeycomb porous morphology, and the BET specific surface area of ​​the photocatalyst is 65.749~146.8357 m². 2 ·g -1 .

2. The photocatalyst according to claim 1, characterized in that, Platinum single atoms exist stably in a mixed valence state, and the Pt-N coordination structure comprises 55% Pt. 2+ -N x Coordination structure, the rest are reduced Pt 0 It also contains trace amounts of Pt 4+ Oxide clusters.

3. The method for preparing the photocatalyst according to claim 1, characterized in that, Includes the following steps: Step 1: Porous graphitic carbon nitride powder, denoted as porous g-C3N4 powder, is prepared from urea through a two-stage segmented calcination process. Step 2: Dissolve an appropriate amount of PtCl4 in ultrapure water to prepare a PtCl4 aqueous solution with a concentration of 0.00125~0.00375 mol / L. Add the porous g-C3N4 powder prepared in Step 1 to the PtCl4 aqueous solution to obtain mixture A, wherein the molar mass ratio of PtCl4 to the porous g-C3N4 powder is 0.000025~0.000075 mol / g. Stir at room temperature for 12 h to obtain mixture A. Add an appropriate amount of NaBH4 solution to mixture A, wherein the molar ratio of NaBH4 to PtCl4 is 4:

1. Stir for 0.5 h to obtain mixture B. Step 3: Freeze the mixture B obtained in Step 2 at -80℃ for 24 hours and freeze-dry for 48 hours to obtain a freeze-dried solid; Step 4: Place the freeze-dried solid obtained in step 3 into a tube furnace, heat it to 500°C at 5°C / min under N2 atmosphere, keep it at the temperature for 2 hours, and then cool it naturally to room temperature. The resulting product is the photocatalyst.

4. The method for preparing the photocatalyst according to claim 3, characterized in that, Step 1 includes the following steps: Weigh urea and place it in a crucible, perform the first stage of calcination in a muffle furnace, grind it after natural cooling, and then perform the second stage of calcination to obtain a yellow powder, which is the porous g-C3N4 powder. The process conditions for the first stage of calcination are: heating to 500℃ at 5℃ / min and calcining at a constant temperature for 4 hours. The process conditions for the second stage of calcination are: heating to 550℃ at 5℃ / min and calcining at a constant temperature for 2 hours.

5. The method for preparing the photocatalyst according to claim 3, characterized in that, In step 2, the molar mass ratio of PtCl4 to the porous g-C3N4 powder is 0.000025 mol / g.

6. The application of the photocatalyst prepared by the method according to any one of claims 3-5, characterized in that, This photocatalyst was used in the coupled photocatalytic hydrogen production of microplastics through oxidative degradation.

7. The application of the photocatalyst according to claim 6, characterized in that, The microplastics are polyethylene terephthalate particles with a particle size of 1μm to 5mm; the process of using the photocatalyst for the oxidative degradation of microplastics coupled with photocatalytic hydrogen production is as follows: Sodium hydroxide was dissolved in deionized water at a mass-to-volume ratio of 0.4 g / L. Then, microplastics were added at a mass ratio of 1:40 to sodium hydroxide to obtain mixture C. The mixture was magnetically stirred at 50°C for 48 hours. The solution obtained after filtering out terephthalic acid was recorded as the pretreatment reaction solution. A suitable amount of the above pretreated reaction solution was filtered to remove incompletely degraded microplastics. Then, 25 mL of the solution was placed in a reaction vessel, and the photocatalyst was dispersed in the pretreated reaction solution under magnetic stirring at 300 rpm to obtain a reaction mixture. The mass-to-volume ratio of the photocatalyst to the pretreated reaction solution was 2 mg / mL. The reaction mixture was then purged with nitrogen under dark conditions while being magnetically stirred for 30 min. The reaction vessel was cooled to room temperature with cold water and subjected to photocatalytic reaction under irradiation with a 300 W xenon lamp for 3–18 h. After the reaction, the gas was collected using a gas collection bag, and the obtained gas was hydrogen. The liquid product was filtered through a filter membrane, and the obtained product included formic acid, acetic acid, ethanol, and ethyl acetate.

8. The application of the photocatalyst according to claim 7, characterized in that, In the photocatalyst, the molar mass ratio of PtCl4 to the porous g-C3N4 powder is 0.00005 mol / g; the photocatalyst has a hydrogen production rate of 450 μmol·g in the microplastic system. -1 ·h -1 The hydrogen selectivity is 99%, and the catalytic activity retention rate is 90% after being recycled 4 times.

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