Application of platinum monatomic and carbon dot loaded graphitic carbon nitride photocatalyst in hydrogen production from plastics

Abstract

The application provides application of a graphite-phase carbon nitride photocatalyst loaded with platinum monomers and carbon dots in plastic hydrogen production, relates to the fields of material preparation and photocatalysis, and aims to solve the problem of low photocatalytic efficiency of photocatalysts. The preparation method comprises the following steps: taking urea as raw material, and preparing carbon nitride blocks by a modified thermal etching method; taking citric acid and urea as raw material, and preparing carbon dots by a thermal etching method; taking the carbon nitride blocks and the carbon dots as raw materials, and preparing carbon dot-graphite-phase carbon nitride composite materials by a thermal treatment method; and taking the carbon dot-graphite-phase carbon nitride composite materials and chloroplatinic acid as raw materials, and preparing the graphite-phase carbon nitride photocatalyst loaded with platinum monomers and carbon dots by a freeze photoreduction method. The graphite-phase carbon nitride photocatalyst loaded with platinum monomers and carbon dots prepared by the preparation method has high-activity platinum monomer hydrogen production sites and excellent light-generated electron transfer capacity, so that the photocatalytic hydrogen production efficiency is greatly improved.

Description

TECHNICAL FIELD

[0001] The application relates to the field of material preparation and photocatalysis, in particular to application of a graphite phase carbon nitride photocatalyst loaded with platinum monatomic atoms and carbon dots in plastic hydrogen production. BACKGROUND

[0002] Plastics are long-term accumulated in the environment due to their stable polymer chain structure and difficulty in natural degradation, thereby seriously threatening water bodies, soil and biological health. How to realize efficient treatment of waste plastics and further promote their high-value conversion has become a major scientific problem and technical bottleneck to be solved in the world.

[0003] At present, the recycling methods of waste plastics mainly include biological recycling, mechanical recycling and chemical recycling. Among them, the technical path that can realize the conversion of plastics into hydrogen, diesel olefins and other high-value chemicals mainly focuses on chemical recycling methods. Among them, the biological recycling technology is limited by enzymatic efficiency and substrate adaptability, and the overall conversion rate is low; mechanical recycling needs strict classification and cleaning of plastics, and has the problems of complex process and poor economic efficiency; chemical recycling such as plasma pyrolysis, high-temperature cracking and supercritical water technology generally has the problems of high energy consumption, strict equipment requirements and high operation cost. Compared with the above methods, photocatalytic plastic high-value conversion mainly utilizes clean solar energy to drive catalytic reaction, and has the outstanding advantages of green environmental protection, low energy consumption, mild reaction conditions, controllable cost and high product added value, and shows broad application prospect. At present, the core of the research on photocatalytic plastic high-value conversion is to develop photocatalysts with high carrier separation rate and stable hydrogen production.

[0004] Graphite phase carbon nitride (gCN, also known as g-C3N4) as a non-metallic, low-cost and simple-to-prepare visible light responsive photocatalyst has shown application potential in the fields of photocatalytic decomposition of water and removal of organic pollutants. However, gCN is limited by the rapid recombination of photo-generated electron-hole pairs, and lacks sufficient reaction sites on the surface, which makes it difficult to simultaneously efficiently drive the oxidative scission of plastic molecular chains (corresponding to the oxidation half-reaction involving holes) and the proton reduction to generate hydrogen (corresponding to the reduction half-reaction involving electrons), resulting in low overall photocatalytic efficiency. Therefore, how to improve the photo-generated carrier separation efficiency of gCN and increase the reaction active sites is a core scientific and engineering problem for realizing the light-driven high-value conversion of plastics.

[0005] To solve this bottleneck, researchers have tried to improve the photocatalytic performance of gCN by constructing composite structures or introducing atomic-level active sites in recent years. Among them, carbon dots (CDs) can form a close interface interaction or heterojunction structure with gCN due to their excellent electron transfer, band structure regulation and interface electron transfer capacity, which can effectively promote the migration of photo-generated electrons, prolong the carrier lifetime and inhibit the recombination of electron-hole pairs. At the same time, platinum (Pt) is widely used as a cocatalyst due to its high hydrogen production reaction activity, but traditional Pt nanoparticles have high cost and low metal utilization. By anchoring Pt as a single atom dispersed on the surface of gCN, the utilization of Pt can be maximized at the atomic scale, exposing uniform and highly active hydrogen production sites, significantly reducing the hydrogen production reaction energy barrier, and thus improving the overall hydrogen production efficiency. Therefore, the synergistic integration of the electronic regulation advantage of CDs and the high-efficiency catalytic characteristics of Pt single atoms in the gCN matrix is expected to optimize the photo-generated carrier dynamics and surface reaction pathways simultaneously, and to construct a composite photocatalyst with high carrier separation rate and strong hydrogen production site activity. SUMMARY

[0006] The present application aims to at least solve the problem of low photocatalytic efficiency of the photocatalyst in the related art.

[0007] The first aspect of the present application is to provide a preparation method of a platinum single atom and carbon dot loaded graphitic carbon nitride photocatalyst, comprising: preparing graphitic carbon nitride with urea as raw material; dissolving citric acid and urea in deionized water, and treating the citric acid-urea mixed solution by microwave heating to obtain a crude product containing carbon dots, re-dispersing the crude product in deionized water, collecting the supernatant after centrifugal separation, and treating the supernatant by dialysis to obtain a carbon dot dispersion liquid, and freeze-drying the carbon dot dispersion liquid to obtain a solid carbon dot powder; dispersing the graphitic carbon nitride in deionized water and adding the solid carbon dot powder, stirring and drying to obtain a solid precursor, and heat treating the solid precursor at 450-500°C for 1.5-2.5 hours to obtain a carbon dot-graphitic carbon nitride composite material; dispersing the carbon dot-graphitic carbon nitride composite material in deionized water, adding an aqueous chloroplatinic acid solution and stirring, freezing the mixed solution of chloroplatinic acid and carbon dot-graphitic carbon nitride composite material in liquid nitrogen to obtain ice crystal solid, irradiating the ice crystal solid with ultraviolet light at 0°C to carry out photoreduction reaction, heating the ice crystal solid to liquid state and washing by centrifugation, and vacuum drying to obtain a platinum single atom and carbon dot loaded graphitic carbon nitride photocatalyst.

[0008] In the above technical solution, the step of preparing graphitic carbon nitride with urea as raw material comprises: placing the urea in a muffle furnace, heating to 530-570°C at a heating rate of 2°C / min, heat treating for 3-5 hours, and then cooling to room temperature to obtain graphitic carbon nitride.

[0009] In the above technical solution, the step of dialysis treatment on the supernatant to obtain the carbon dot dispersion liquid comprises: placing the supernatant in a dialysis bag, immersing the dialysis bag in deionized water, and magnetically stirring the deionized water, replacing the deionized water every 4-8 hours, and replacing for 3-5 times, until the dialysate remains colorless and transparent under continuous stirring, to obtain the carbon dot dispersion liquid.

[0010] Understandably, the dialysate refers to the deionized water contained outside the dialysis bag, which is used to receive small molecular impurities diffused from the bag during dialysis. By regularly replacing and observing whether the external liquid returns and remains colorless and transparent, it can be directly judged whether the small molecular impurities in the carbon dot solution in the bag have been sufficiently removed, thereby serving as a basis for determining the completion of dialysis purification.

[0011] In the above technical solution, the step of freeze-drying the carbon dot dispersion liquid to obtain a solid carbon dot powder comprises: after liquid nitrogen freezing of the carbon dot dispersion liquid, placing it in a freeze dryer for drying to obtain a solid carbon dot powder.

[0012] In the above technical solution, the step of dispersing the graphite phase carbon nitride in deionized water and adding solid carbon dot powder, stirring and drying comprises: dispersing 25 mg of graphite phase carbon nitride in 12.5 mL of deionized water, adding 0.5 mg of solid carbon dot powder, stirring for 12-20 h and drying.

[0013] In the above technical solution, the step of dispersing the carbon dot-graphite phase carbon nitride composite material in deionized water, adding an aqueous chloroplatinic acid solution and stirring comprises: dispersing 25 mg of carbon dot-graphite phase carbon nitride composite material in 12.5 mL of deionized water, adding 25 μL of 100 mg·mL -1 of aqueous chloroplatinic acid solution, and stirring for 12 h.

[0014] The second aspect of the present application provides a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is prepared by the method for preparing the graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots according to any one of the first aspect of the present application.

[0015] The third aspect of the present application provides an application of the g-C3N4 photocatalyst loaded with platinum monatomic atoms and carbon dots in plastic hydrogen production, comprising: placing plastic powder in an alkaline solution, stirring in a 40℃ constant temperature box at a speed of 500 rpm for 48h to obtain a hydrolysis solution; adding 10mg of the g-C3N4 photocatalyst loaded with platinum monatomic atoms and carbon dots and 28mL of deionized water to the hydrolysis solution, irradiating the hydrolysis solution by an LED lamp in an oxygen-free environment; using a gas sampling needle to extract the gaseous product, and analyzing the hydrogen production rate by a gas chromatograph equipped with a TCD (Thermal Conductivity Detector) detector; wherein the catalyst is the g-C3N4 photocatalyst loaded with platinum monatomic atoms and carbon dots according to any one of the second aspect of the present application.

[0016] In the above technical solution, optionally, in the step of irradiating the hydrolysis solution by an LED lamp, the light intensity is 100mW×cm -2 (milliwatts per square centimeter), the wavelength is 420nm to 780nm, and the light irradiation time is 15h to 25h.

[0017] In the above technical solution, optionally, the step of placing the plastic powder in the alkaline solution comprises adding 750mg of plastic to 7mL of a 5M (wherein M is a concentration unit, indicating moles per liter, i.e. mol / L) NaOH solution.

[0018] In the above technical solution, optionally, the alkaline solution comprises sodium hydroxide and / or potassium hydroxide.

[0019] The present application prepares a Pt1-CDs / gCN catalyst with high activity and stability by a thermal etching method and a freeze photoreduction method. In the composite structure, photo-generated electrons first migrate to the Pt monatomic atom sites to drive proton reduction to produce hydrogen, while holes are enriched in the carbon dot region to drive plastic molecule oxidation and cracking, thereby realizing efficient spatial separation of photo-generated carriers and synergistic catalysis. Compared with single gCN, the catalyst shows significantly improved hydrogen production rate and plastic conversion efficiency in the plastic photocatalytic reforming reaction. The preparation method of the present application is simple, easy to operate, low in cost and high in repeatability, and has a wide application prospect in the field of photocatalytic plastic high-value conversion. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the following drawings of which:

[0021] Figure 1 A transmission electron microscope (TEM) image of the gCN catalyst provided for Example 1;

[0022] Figure 2TEM image of the Pt1-CDs / gCN catalyst provided in Example 1;

[0023] Figure 3 TEM image of the Pt1-CDs / gCN catalyst provided in Example 1;

[0024] Figure 4 EDS map of Pt element of the Pt1-CDs / gCN catalyst provided in Example 1;

[0025] Figure 5 EDS map of each element of the Pt1-CDs / gCN catalyst provided in Example 1;

[0026] Figure 6 XRD pattern of the gCN, CDs / gCN and Pt1-CDs / gCN catalysts provided in Example 1;

[0027] Figure 7 XPS pattern of the Pt1-CDs / gCN catalyst provided in Example 1;

[0028] Figure 8 UV-Vis spectrum of the gCN, CDs / gCN and Pt1-CDs / gCN catalysts provided in Example 1;

[0029] Figure 9 Comparison chart of the effect of plastic additive amount on the hydrogen production activity of the Pt1-CDs / gCN catalyst provided in Example 1 for reforming PET plastic;

[0030] Figure 10 Comparison chart of the hydrogen production activity of the gCN, CDs / gCN and Pt1-CDs / gCN catalysts provided in Example 1 for reforming PET plastic;

[0031] Figure 11 Comparison chart of the hydrogen production rate of the Pt1-CDs / gCN catalyst provided in Example 1 for reforming household plastic;

[0032] Figure 12 Comparison chart of the effect of alkaline hydrolysis concentration on the hydrogen production activity of the Pt1-CDs / gCN catalyst provided in Example 1 for reforming PET plastic;

[0033] Figure 13 Comparison chart of the effect of different alkaline hydrolysis time on the photocatalytic hydrogen production activity of the Pt1-CDs / gCN catalyst provided in Example 1 for reforming PET plastic;

[0034] Figure 14Cycle activity chart of the Pt1-CDs / gCN photocatalyst provided for Example 1 for reforming PET plastic to produce hydrogen activity;

[0035] Figure 15 Flow chart for preparation of the Pt1-CDs / gCN photocatalyst for one embodiment;

[0036] Figure 16 Flow chart for preparation of the Pt1-CDs / gCN photocatalyst for one embodiment. DETAILED DESCRIPTION

[0037] In order to enable every aspect and feature of the present application to be understood more thoroughly, the present application will be further described below with reference to the drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0038] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and therefore the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0039] The preparation method of the Pt1-CDs / gCN photocatalyst (graphitic carbon nitride photocatalyst loaded with platinum monatomic and carbon dots) of the present embodiment, as shown in Figure 15 includes the following steps:

[0040] S1502: Using urea as raw material, graphitic carbon nitride is prepared by a modified thermal etching method.

[0041] Specifically, in this step, urea is placed in a muffle furnace, heated to 550℃ at a heating rate of 2℃ / min under air atmosphere, kept for 4h, and naturally cooled to room temperature to obtain graphitic carbon nitride (gCN bulk).

[0042] S1504: Using citric acid and urea as raw materials, carbon dots are prepared by a thermal etching method.

[0043] Specifically, in this step, 3.0 g of citric acid and 1.0 g of urea are placed in a 50.0 mL centrifuge tube containing 8.0 mL of deionized water, and the mixture is shaken and dissolved in a vortex mixer. After complete dissolution, the mixture is poured into a 250.0 mL beaker, and then heated in a microwave oven at a power of 800 W for 8 min to obtain a crude product containing carbon dots. The crude product generally contains target carbon dots, incompletely reacted citric acid and urea, and by-products such as large-size carbon particles and organic salts formed due to excessive carbonization. After microwave heating, the mixture is placed in an oven and dried at 80°C for 10 h to remove water and obtain a solid; then the dried product is dispersed in 20.0 mL of deionized water and centrifuged, and the solids that are not soluble in water or have a large particle size (such as the aforementioned large-size carbon particles and some polymer by-products) are discarded by centrifugal force. The supernatant containing size-uniform carbon dots is collected and placed in a dialysis bag for dialysis in continuously stirred deionized water until the outside liquid becomes colorless and transparent, thereby removing residual ionic small molecule impurities (such as citrate and urea) and obtaining a high-purity carbon dot dispersion. Finally, the dialyzed carbon dot dispersion is frozen in liquid nitrogen for 3 min, and then dried in a freeze dryer for 48 h to obtain a solid carbon dot powder (CDs).

[0044] The key to this step is the combination of "liquid nitrogen freezing" and "freeze drying". By instantaneously freezing the carbon dot aqueous dispersion at a very low temperature (-196°C) using liquid nitrogen, the water can quickly form tiny amorphous ice crystals, thereby fixing the carbon dot nanoparticles in situ and effectively avoiding the problem of carbon dot compression and aggregation caused by ice crystal growth and phase separation during slow freezing. Subsequent freeze drying (sublimation process) removes the ice crystals in the absence of liquid phase surface tension, thereby finally obtaining a solid carbon dot powder with good dispersion and no aggregation. This series of fine purification and drying processes maximizes the intrinsic properties of carbon dots as zero-dimensional nanomaterials, laying a solid foundation for their full play as electronic mediators and light trapping agents in subsequent composites.

[0045] S1506: CDs / gCN is prepared by using thermal treatment method with gCN yellow solid and CDs as raw materials;

[0046] Specifically, in this step, first, 25 mg of gCN bulk is dispersed in 12.5 mL of deionized water, 0.5 mg of CDs is added, and after stirring for 12-20 h, it is dried. Through this liquid blending process, CDs are uniformly adsorbed on the surface and interlayer of gCN nanosheets through intermolecular forces, forming a physical mixture of CDs and gCN. The physical mixture is dried to obtain a solid precursor; then the solid precursor is placed in a muffle furnace and heated to 500℃ at a heating rate of 5℃ / min in an air atmosphere, and kept for 2 h, and then naturally cooled to room temperature to obtain a CDs / gCN catalyst (i.e. the above-mentioned carbon dot-graphitic carbon nitride composite material).

[0047] The key of this step is to adopt the synergistic strategy of "first liquid-phase uniform dispersion and adsorption, and then high-temperature annealing to form chemical bonding". The long-time liquid-phase stirring in the first step aims to use intermolecular forces to drive CDs to achieve uniform, monolayer physical adsorption on the surface of gCN nanosheets, laying a foundation for spatial distribution for subsequent reactions. The high-temperature heat treatment in the second step is decisive, and its purpose is not simply to remove impurities or change the crystal type, but to promote the condensation reaction between the functional groups on the surface of gCN (such as amino groups, C≡N bonds) and the rich functional groups on the surface of CDs (such as carboxyl groups, hydroxyl groups) at a precisely controlled temperature (500℃), thereby forming firm C-N-C, C-O-C, etc. covalent chemical bonds at the interface between the two. This strong chemical bonding successfully constructs a tight, electron-coupled heterojunction interface, rather than a simple physical attachment, which greatly promotes the directional and rapid migration of photo-generated electrons from gCN to CDs, effectively inhibits the recombination of electron-hole pairs, and provides a core guarantee for the final composite material to achieve high-efficiency photocatalytic performance.

[0048] S1508: Pt1-CDs / gCN is prepared by freeze photoreduction method using CDs / gCN and chloroplatinic acid as raw materials.

[0049] Specifically, in this step, first, 25 mg of CDs / gCN catalyst is dispersed in 12.5 mL of deionized water, 25 μL of 100 mg·mL -1aqueous solution of chloroplatinic acid, and stirred for 12 h to ensure that the platinum precursor was fully and uniformly adsorbed on the surface of the CDs / gCN composite carrier. Subsequently, the mixture was frozen in liquid nitrogen for 3 min to instantaneously solidify the whole reaction system to form an ice-crystal solid. In this state, the system was irradiated with ultraviolet light for 11 min in an ice-water bath at 0 °C. During this process, the CDs / gCN composite material generated electrons under ultraviolet excitation, and these electrons were efficiently transferred to the platinum precursor fixed by the ice matrix through the mediation of CDs, thereby reducing the platinum atoms. After the irradiation was completed, the system was melted, and unreacted chloroplatinic acid precursors and byproducts in the solution were removed by three high-speed centrifugations (10000 x g). Here, 10000 x g refers to ten thousand times g, and g is the acceleration of gravity, which is about 9.8 meters per second 2 Finally, the Pt1-CDs / gCN composite catalyst was obtained by vacuum drying at 60 °C for 18 h.

[0050] The key to this step is the innovative use of the "frozen photoreduction method", which combines the physical confinement effect of "liquid nitrogen freezing" with the chemical driving force of "ultraviolet reduction". The ice matrix formed by liquid nitrogen freezing acts as a physical barrier, effectively limiting the migration and diffusion of newly born platinum atoms after reduction, and fundamentally preventing their agglomeration into nanoparticles. Ultraviolet irradiation provides a precise and controllable reduction driving force in a low-temperature (0 °C) solid phase or solid-liquid coexistence system, ensuring that the platinum precursor is reduced to atoms in situ. This unique strategy of "fixing first and then reducing" is fundamentally different from the traditional liquid-phase photoreduction process, thereby successfully anchoring platinum in the form of high-density and highly stable single atoms on the CDs / gCN carrier, creating maximum atomic utilization efficiency and ultra-high activity hydrogen production sites.

[0051] The platinum single atom and carbon dot loaded graphitic carbon nitride photocatalyst prepared in this example creates a "platinum single atom-carbon dot-graphitic carbon nitride nanosheet" ternary composite system that functions in coordination and synergistically. In this system, the two-dimensional graphitic carbon nitride (gCN) nanosheet serves as the main producer of photo-generated electrons and a two-dimensional platform for reactions, the zero-dimensional carbon dot (CDs) serves as a high-efficiency electron mediator and light trapping unit, and the platinum single atom (Pt1) serves as a high-activity hydrogen production reaction site with extremely high atomic utilization. Through meticulous interface design, the three components together build an "electronic highway" from photo-generation, migration to utilization, achieving efficient separation and directional migration of photo-generated electron-hole pairs, thereby greatly converting light energy into chemical energy.

[0052] Compared with conventional single gCN or binary Pt / gCN photocatalysts, the photocatalyst provided by the application is a zero-dimensional and two-dimensional composite material, which is more conducive to the directional transport and migration of photo-generated carriers, and the catalyst has high active Pt1 hydrogen production sites and excellent photo-generated electron transfer capacity, thereby greatly improving the photocatalytic hydrogen production efficiency. Under the optimized conditions, 10 mg of the Pt1-CDs / gCN composite catalyst exhibits the best hydrogen production performance for the photocatalytic reforming of 750 mg of polyethylene terephthalate (PET), and exhibits excellent stability within 20 hours of reaction time, and the maximum hydrogen production rate can reach 2041.6 μmol·g -1 ·h -1 This performance not only highlights the high efficiency of the catalyst, but also verifies the feasibility of the “waste-to-resource” path of converting waste plastics into hydrogen energy. The preparation method of the photocatalyst provided by the application is simple, low in cost and good in repeatability, and has wide application prospects in the field of photocatalytic plastic high-value conversion, and has good industrial application potential.

[0053] The applicant describes the preparation method of the platinum single atom and carbon dot loaded graphite phase carbon nitride photocatalyst of the application from multiple more specific embodiments as follows:

[0054] Embodiment 1: As shown in Figure 16 , the preparation method comprises the following steps:

[0055] S1602: Put urea into a muffle furnace, heat to 550℃ at an air atmosphere with a heating rate of 2℃ / min, keep for 4h, and naturally cool to room temperature to obtain a gCN block;

[0056] S1604: Prepare CDs;

[0057] Specifically, 3.0g of citric acid and 1.0g of urea are put into a 50.0mL centrifuge tube containing 8.0mL of deionized water, and then put into a vortex shaker for oscillation and dissolution; after complete dissolution, pour it into a 250.0mL beaker, and then put it into a microwave oven and heat at 800W for 8min; after heating, put it into an oven and dry at 80℃ for 10h; then disperse the dried product in 20.0mL of deionized water and centrifuge, discard the solid precipitate, collect the supernatant, and place it in a dialysis bag, dialyze in continuously stirred deionized water until the outside liquid becomes colorless and transparent; freeze the dialyzed liquid in liquid nitrogen for 3min, and then put it into a freeze dryer to dry for 48h to obtain the target product CDs;

[0058] S1606: Prepare CDs / gCN catalyst;

[0059] Specifically, gCN bulk was dispersed in 12.5 mL of deionized water, 2 mg of CDs was added, and the mixture was stirred for 12-20 h and then dried. The resulting solid product was then placed in a muffle furnace and heated to 500 °C at a heating rate of 5 °C / min in air atmosphere, held at that temperature for 2 h, and then naturally cooled to room temperature to obtain the CDs / gCN catalyst.

[0060] S1608: Preparation of Pt1-CDs / gCN composite catalyst;

[0061] Specifically, 25 mg of CDs / gCN catalyst was dispersed in 12.5 mL of deionized water, and 25 μL of 100 mg·mL⁻¹ catalyst was added. -1 The chloroplatinic acid aqueous solution was stirred for 12 h; then the mixture was placed in liquid nitrogen and frozen for 3 min, and then irradiated with ultraviolet light at 0 °C for 11 min; after the irradiation, the unreacted precursors in the solution were removed by washing three times by high-speed centrifugation (10000×g), and finally vacuum dried at 60 °C for 18 h to obtain the Pt1-CDs / gCN composite catalyst.

[0062] Product analysis was performed on the Pt1-CDs / gCN composite catalyst prepared in Example 1.

[0063] from Figure 1 The TEM (Transmission Electron Microscopy) images show that gCN prepared from urea by thermal etching exhibits a typical wrinkled two-dimensional nanosheet structure, which provides it with a huge specific surface area, which is beneficial for the loading of subsequent components and the adsorption of reactants.

[0064] Figure 2 TEM images show that, after thermal bonding, tiny carbon dots (CDs) (the darker areas within the solid and dashed red boxes) successfully adhered to the surface of the gCN nanosheets. The introduction of CDs did not disrupt the main structure of the gCN nanosheets, but they can be expected to act as efficient electron acceptors and transport bridges, optimizing the separation of photogenerated charges.

[0065] Figure 3 No obvious platinum nanoparticles or clusters were observed in the TEM images. Combined with aberration-corrected electron microscopy analysis, it can be confirmed that platinum (Pt) is anchored on the CDs / gCN composite support in the form of highly dispersed single atoms (Pt1).

[0066] Figure 4 and Figure 5The EDS (Energy-Dispersive X-ray Spectroscopy) mapping of the Pt1-CDs / gCN catalyst can clearly show that the Pt element and the basic elements such as C (carbon) and N (nitrogen) are uniformly and consistently distributed on the surface of the catalyst. This further proves from the spatial element distribution that the platinum single atoms have been successfully and uniformly loaded in the entire composite material, rather than being locally aggregated. Among them, it is necessary to understand that, Figure 5 The HAADF (High-Angle Annular Dark-Field) refers to a Z-contrast imaging technique based on scanning transmission electron microscopy.

[0067] Figure 6 The XRD (X-Ray Diffraction) mapping of the Pt1-CDs / gCN catalyst shows that all the photocatalysts prepared in Example 1 have characteristic diffraction peaks at about 13.1° and 27.4°. Among them, the peak at 13.1° corresponds to the (100) crystal plane of gCN, which reflects the in-plane periodic arrangement of the triazine structural unit; and the stronger diffraction peak at 27.4° corresponds to the (002) crystal plane, which represents the interlayer stacking of the gCN layered material.

[0068] Figure 7 The XPS (X-ray Photoelectron Spectroscopy) mapping of the Pt1-CDs / gCN catalyst is used to analyze the elemental composition and chemical state of the surface of the catalyst prepared in Example 1. Specifically:

[0069] In the C1s spectrum, the characteristic peaks at 284.8 eV and 288.0 eV are respectively attributed to the sp 2 -C and C=N bonds in the material, which are typical characteristics of the gCN skeletal structure.

[0070] In the N1s spectrum, the peaks with binding energies at 398.6 eV, 400.6 eV and 403.9 eV can be respectively attributed to C-N-C in the triazine ring, interlayer connected N-(C)3 and amino or charge effect caused species, which together confirm the existence of the gCN structure.

[0071] The O1s spectrum has peaks at 531.9 eV and 533.3 eV, which are usually attributed to hydroxyl / water molecules and C=O adsorbed on the surface of the catalyst, which are mainly derived from the introduction or surface adsorption of CDs, providing evidence for the successful compounding of CDs.

[0072] In the Pt 4f spectrum, the doublet appearing at 72.8 eV and 76.1 eV is positively shifted by about +1.8 eV compared with the standard binding energy of metallic platinum (about 71.0 eV). The shift is due to the loss of delocalized electron shielding effect in the metal bond when the platinum atom exists in the form of isolated single atom, resulting in the increase of its atomic potential barrier; at the same time, the strong coordination between the platinum single atom and the electronegative atoms such as N and O on the carrier further reduces its electron cloud density. The results strongly prove that platinum does not exist in the form of metal nanoparticles, but is stably anchored on the CDs / gCN carrier in the form of single atom (Pt1).

[0073] Figure 8 The UV-Vis (Ultraviolet-Visible) spectrum (ultraviolet-visible diffuse reflectance spectrum) shows that, compared with gCN and CDs / gCN, Pt1-CDs / gCN exhibits significantly enhanced light absorption intensity, and its absorption band edge is right-shifted. This indicates that the introduction of CDs and Pt single atoms together acts, not only improves the catalyst's ability to capture visible light, but also effectively broadens its light response range, laying a solid foundation for obtaining excellent photocatalytic performance.

[0074] Example 2: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum single atoms and carbon dots, which is different from that in example 1 in that 1.5 μL of 100 mg·mL-1 -1 aqueous chloroplatinic acid solution is added in S1608 instead of 25 μL of 100 mg·mL-1 -1 aqueous chloroplatinic acid solution in example 1, and other steps are the same as in example 1.

[0075] Example 3: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum single atoms and carbon dots, which is different from that in example 1 in that 3.1 μL of 100 mg·mL-1 -1 aqueous chloroplatinic acid solution is added in S1608 instead of 25 μL of 100 mg·mL-1 -1 aqueous chloroplatinic acid solution in example 1, and other steps are the same as in example 1.

[0076] Example 4: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum single atoms and carbon dots, which is different from that in example 1 in that 6.2 μL of 100 mg·mL-1 -1 aqueous chloroplatinic acid solution is added in S1608 instead of 25 μL of 100 mg·mL-1 -1 aqueous chloroplatinic acid solution in example 1, and other steps are the same as in example 1.

[0077] Example 5: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum single atoms and carbon dots, which is different from that in example 1 in that 12.5 μL of 100 mg·mL-1-1 chloroplatinic acid aqueous solution of 100 mg·mL-1 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1. -1 chloroplatinic acid aqueous solution of 100 mg·mL-1 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1.

[0078] Example 6: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is different in that 50 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution is added in S1608 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1. -1 chloroplatinic acid aqueous solution of 100 mg·mL-1 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1. -1 chloroplatinic acid aqueous solution of 100 mg·mL-1 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1.

[0079] Example 7: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is different in that 62.5 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution is added in S1608 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1. -1 chloroplatinic acid aqueous solution of 100 mg·mL-1 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1. -1 chloroplatinic acid aqueous solution of 100 mg·mL-1 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1.

[0080] Example 8: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is different in that 75 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution is added in S1608 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1. -1 chloroplatinic acid aqueous solution of 100 mg·mL-1 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1. -1 chloroplatinic acid aqueous solution of 100 mg·mL-1 instead of 25 μL of 100 mg·mL-1 chloroplatinic acid aqueous solution in Example 1, and other steps are the same as Example 1.

[0081] Example 9: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is different in that 0.5 mg of CDs is added in S1606 instead of 2 mg of CDs in Example 1, and other steps are the same as Example 1.

[0082] Example 10: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is different in that 5 mg of CDs is added in S1606 instead of 2 mg of CDs in Example 1, and other steps are the same as Example 1.

[0083] Example 11: A preparation method of a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is different in that 10 mg of CDs is added in S1606 instead of 2 mg of CDs in Example 1, and other steps are the same as Example 1.

[0084] Example 12: A method for preparing a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is different from example 1 in that 10 mg of CDs is added in S1606 instead of 2 mg of CDs added in example 1, 62.5 μL of 100 mg·mL -1 of chloroplatinic acid aqueous solution is added in S1608 instead of 25 μL of 100 mg·mL -1 of chloroplatinic acid aqueous solution added in example 1, and other steps are the same as example 1.

[0085] Example 13: A method for preparing a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots, which is different from example 1 in that the following step is removed in S1606: the obtained solid product is placed in a muffle furnace, and heated to 500℃ at a heating rate of 5℃ / min in an air atmosphere, and kept for 2h, and naturally cooled to room temperature, and other steps are the same as example 1.

[0086] The parameters of each example are shown in Table 1 below.

[0087] The photocatalysts prepared by examples 1 to 13 are used for photocatalytic reforming of PET plastic.

[0088] The specific test steps are as follows: 450 mg of PET powder is placed in a 5M alkaline solution (KOH or NaOH can be used, and KOH is used in this example), and hydrolysis is carried out in a constant temperature oven at 40℃ with stirring at a speed of 500 rpm for 48h to obtain a pretreated hydrolysate. 7 mL of the pretreated hydrolysate is taken, 10 mg of catalyst and 28 mL of deionized water are added, and nitrogen is blown to ensure an oxygen-free environment. Then, under the irradiation of an LED lamp with a light intensity of 100 mW·cm -2 and a wavelength of 420-780 nm at room temperature 25℃, the reaction is carried out. After 20h of irradiation, the gas product is extracted using a gas sampling needle, and the hydrogen concentration is analyzed by a gas chromatograph equipped with a TCD detector, and the maximum hydrogen production rate is calculated. The chromatographic column type is TDX-01, the carrier gas is argon, the flow rate is 60 mL / min, and the column temperature is constant at 80℃. The quantification of H2 is carried out by external standard method, and a standard hydrogen gas with known concentration is used for calibration.

[0089] The hydrogen production activity results of each example are shown in Table 1:

[0090] Table 1

[0091]

[0092] From the above Table 1, it can be seen that the Pt1-CDs / gCN catalyst prepared in each example has good hydrogen production rate.

[0093] The applicant below explores the effect of different plastic concentrations on the photocatalytic reforming of PET plastic to produce hydrogen activity of the Pt1-CDs / gCN catalyst provided in Example 1: the experimental steps are the same as the photocatalytic plastic PET reforming method, the difference is that the amount of plastic used is 75 mg, 150 mg, 300 mg, 450 mg, 750 mg, and 1000 mg. The results are shown in Figure 9 Overall, the amount of plastic used and the photocatalytic reforming of PET plastic to produce hydrogen activity showed a trend of first increasing and then decreasing, and the optimal amount of plastic added was 750 mg. That is, in this experimental system, the optimal mass ratio of catalyst to PET plastic is 1:75. When the amount of PET is insufficient, it cannot provide enough hole sacrificial agent and proton source, resulting in an increase in the recombination probability of electron-hole pairs; while when the amount of PET is excessive, it may cause the viscosity of the reaction system to be too high, the light transmittance to decrease, and the photocatalytic reaction to be inhibited.

[0094] The applicant below explores the effect of different plastic concentrations on the photocatalytic reforming of PET plastic to produce hydrogen activity of the Pt1-CDs / gCN catalyst provided in Example 1: the experimental steps are the same as the photocatalytic plastic PET reforming method, the difference is that the amount of plastic used is 75 mg, 150 mg, 300 mg, 450 mg, 750 mg, and 1000 mg. The results are shown in

[0095] The preparation of gCN only includes step S1602 in Example 1, without the steps of CDs complexation and Pt loading. The preparation of CDs / gCN includes steps S1602, S1604 and S1606 in Example 1, without the step of Pt monatomic loading in step S1608.

[0096] As shown in Figure 10 , 10 mg of Pt1-CDs / gCN composite catalyst exhibits the best hydrogen production performance for photocatalytic reforming of PET plastic, with a maximum hydrogen production rate of 2040 μmol·g -1 ·h -1 It can be seen that the introduction of CDs as an electronic bridge optimizes the charge separation, and Pt monatomic as a hydrogen production site, both of which synergistically form a high-efficiency photocatalytic hydrogen production system, and are indispensable. The performance of the ternary composite Pt1-CDs / gCN is significantly better than any binary or unary component, fully demonstrating the rationality and superiority of the composite material design of the application.

[0097] The applicant below explores the effect of Pt1-CDs / gCN photocatalyst on the photocatalytic reforming of household plastic polyethylene terephthalate (PET), polybutylene terephthalate (PBAT), polybutylene succinate (PBS), or polylactic acid (PLA) to produce hydrogen activity: the experimental steps are the same as the photocatalytic plastic PET reforming method, the difference is that the amount of plastic added is 750 mg, and the plastic used is PET, PBAT, PBS and PLA plastic powder respectively. As shown in Figure 11As shown, the photocatalytic hydrogen production activity of Pt1-CDs / gCN composite catalyst for PBAT, PET, PLA and PBS living plastics are 1972.3 μmol·g -1 ·h -1 , 2041.6 μmol·g -1 ·h -1 , 2120.1 μmol·g -1 ·h -1 and 2364.4 μmol·g -1 ·h -1 , respectively. It can be seen that the catalyst shows excellent and universal catalytic reforming activity for various common polyester plastics.

[0098] The applicant then explored the effect of different alkaline hydrolysis concentrations on the photocatalytic hydrogen production activity of the Pt1-CDs / gCN catalyst provided in Example 1 for reforming PET plastic: the experimental steps were the same as the photocatalytic plastic reforming method, except that the plastic addition amount was 750 mg and the plastic treatment KOH concentration was 0 M (where M means mol / L), 0.5 M, 1.0 M, 5.0 M and 10.0 M, respectively. As shown in Figure 12 , in general, the concentration of alkali is positively correlated with the photocatalytic hydrogen production activity of plastic reforming.

[0099] The applicant then explored the effect of different alkaline hydrolysis times on the photocatalytic hydrogen production activity of the Pt1-CDs / gCN catalyst provided in Example 1 for reforming PET plastic: the experimental steps were the same as the photocatalytic reforming PET plastic method, except that the plastic addition amount was 750 mg and the plastic pretreatment time was 24 h, 48 h and 72 h, respectively. As shown in Figure 13 , the photocatalytic hydrogen production activity of plastic reforming increases first and then decreases with the extension of alkaline hydrolysis time, because if the hydrolysis time is too short, PET cannot be fully depolymerized and there is not enough sacrificial agent for consumption; if the hydrolysis time is too long, the depolymerization products may be excessively degraded into inert small molecules or generate intermediates that inhibit the catalytic process, thereby reducing the catalytic efficiency.

[0100] Cyclic experiment: the Pt1-CDs / gCN catalyst after the reaction in Example 1 was centrifuged and dried in an oven at 60°C under vacuum, and then used again for photocatalytic reforming of PET plastic to measure the hydrogen production concentration. The experimental steps were the same as the photocatalytic reforming PET plastic method, except that the plastic addition amount was 750 mg. As shown in Figure 14As shown, after the photocatalyst is recycled for 6 times, there is still 90% of catalytic activity, it can be seen that the Pt single atom site constructed by the "frozen photoreduction method" and the firm chemical bond formed between the CDs / gCN carrier give the Pt1-CDs / gCN composite material excellent structural stability and chemical stability, effectively prevent the loss, agglomeration or inactivation of the active component in the recycling process, meet the basic requirement of long-term effectiveness of the catalyst for practical application.

[0101] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0102] Although the embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and purposes of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. Application of a graphite phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots in plastic hydrogen production, characterized in that, The application relates to a method for preparing a g-C3N4 photocatalyst loaded with platinum single atoms and carbon dots. The method comprises the following steps: placing plastic powder in an alkaline solution, stirring the plastic powder in a 40 DEG C constant-temperature box at a speed of 500 rpm for 48 h to obtain a hydrolysis solution; 10 mg of the g-C3N4 photocatalyst loaded with platinum single atoms and carbon dots and 28 mL of deionized water are added to the hydrolysis solution, and the hydrolysis solution is irradiated by an LED lamp in an oxygen-free environment; A gas sampling needle is used to extract the gaseous product, and the hydrogen production rate is analyzed by using a gas chromatograph; The method for preparing the g-C3N4 photocatalyst loaded with platinum single atoms and carbon dots comprises the following steps: The g-C3N4 is prepared by using urea as raw material; Citric acid and urea are dissolved in deionized water, the citric acid-urea mixed solution is subjected to microwave heating treatment to obtain a crude product containing carbon dots, the crude product is dispersed in deionized water again, centrifugal separation is carried out, and the supernatant is collected; the supernatant is subjected to dialysis treatment to obtain a carbon dot dispersion liquid; the carbon dot dispersion liquid is subjected to freeze-drying to obtain solid carbon dot powder. The g-C3N4 is dispersed in deionized water, and the solid carbon dot powder is added; stirring and drying are carried out to obtain a solid precursor; the solid precursor is kept at 450 DEG C to 500 DEG C for 1.5 h to 2.5 h to obtain a carbon dot-g-C3N4 composite material. The carbon dot-g-C3N4 composite material is dispersed in deionized water, an aqueous chloroplatinic acid solution is added, and stirring is carried out; the mixed solution of chloroplatinic acid and the carbon dot-g-C3N4 composite material is frozen in liquid nitrogen to obtain ice crystal solid; the ice crystal solid is irradiated by ultraviolet light at 0 DEG C to carry out photoreduction reaction; the ice crystal solid is heated to a liquid state and subjected to centrifugal washing; vacuum drying is carried out to obtain the g-C3N4 photocatalyst loaded with platinum single atoms and carbon dots.

2. Use of the platinum monatomic and carbon dot loaded graphitic-phase carbon nitride photocatalyst according to claim 1 in hydrogen production from plastics, characterized in that, The step of preparing the g-C3N4 by using urea as raw material comprises the following steps: The urea is placed in a muffle furnace, and the temperature is raised to 530 DEG C to 570 DEG C at a temperature raising rate of 2 DEG C / min; the temperature is kept for 3 h to 5 h; and then the temperature is cooled to room temperature to obtain the g-C3N4.

3. Use of the graphitic-phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots according to claim 1 in the hydrogen production from plastics, characterized in that, The step of subjecting the supernatant to dialysis treatment to obtain the carbon dot dispersion liquid comprises the following steps: The supernatant is placed in a dialysis bag, the dialysis bag is immersed in deionized water, and the deionized water is subjected to magnetic stirring; the deionized water is replaced every 4 h to 8 h; the replacement is carried out for 3 times to 5 times; and the dialysis external liquid remains colorless and transparent under continuous stirring to obtain the carbon dot dispersion liquid.

4. Use of the graphitic-phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots according to claim 1 in the hydrogen production from plastics, characterized in that, The step of subjecting the carbon dot dispersion liquid to freeze-drying to obtain solid carbon dot powder comprises the following steps: The carbon dot dispersion liquid is subjected to liquid nitrogen freezing, and then is placed in a freeze-drying machine to carry out drying to obtain the solid carbon dot powder.

5. Use of the graphitic-phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots according to claim 1 in the hydrogen production from plastics, characterized in that, The step of dispersing the g-C3N4 in deionized water and adding solid carbon dot powder, and then carrying out stirring and drying comprises the following steps: 25 mg of g-C3N4 is dispersed in 12.5 mL of deionized water, 0.5 mg of solid carbon dot powder is added, and stirring is carried out for 12 h to 20 h and then drying is carried out.

6. Use of the graphitic-phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots according to claim 1 in the hydrogen production from plastics, characterized in that, The step of dispersing the carbon dot-g-C3N4 composite material in deionized water, adding an aqueous chloroplatinic acid solution and stirring comprises the following steps: Twenty-five mg of carbon dot-graphitic carbon nitride composite material was dispersed in 12.5 mL of deionized water, 25 μL of 100 mg-mL -1 of aqueous chloroplatinic acid solution was added, and stirred for 12 h.

7. Use of the graphitic-phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots according to claim 1 in the hydrogen production from plastics, characterized in that, The light intensity is 100 mW x cm -2 , the wavelength is 420 nm to 780 nm, and the light irradiation time is 15 h to 25 h.

8. Use of the graphitic-phase carbon nitride photocatalyst loaded with platinum monatomic and carbon dots according to claim 1 in the hydrogen production from plastics, characterized in that, The alkali in the alkaline solution is sodium hydroxide and / or potassium hydroxide.

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