Ultrathin carbon nitride nanosheet coated titanium dioxide microsphere catalyst and photocatalytic PET plastic reforming hydrogen production

Abstract

The invention discloses an ultrathin carbon nitride nanosheet coated titanium dioxide microsphere catalyst and hydrogen production by photocatalytic PET (polyethylene terephthalate) plastic reforming. The preparation method comprises the following steps: preparing ultrathin g-C3N4 nanosheets by combining two-step heat treatment of urea with mixed acid etching; tiO2 microspheres are prepared through combination of a glucose template-assisted hydrothermal method and calcination; finally, the composite catalyst is obtained through solvent mixing and self-assembly. The catalyst disclosed by the invention has a core-shell heterojunction structure that TiO2 microspheres are tightly coated with g-C3N4 nanosheets, and photo-generated charges can be efficiently separated. The invention also provides an application method of the catalyst in hydrogen production by photocatalytic PET plastic reforming: after PET is hydrolyzed under an alkaline condition, the catalyst is used for photocatalytic reaction, and hydrogen and high value-added chemicals such as glycollic acid and formic acid can be synchronously produced. The catalyst is high in activity, good in stability and low in cost, and an efficient solution is provided for waste plastic recycling and clean energy production.

Description

Technical Field

[0001] This invention relates to an ultrathin carbon nitride nanosheet-coated titanium dioxide microsphere catalyst and a photocatalytic reforming process for hydrogen production from PET plastic, belonging to the field of chemical technology. Background Technology

[0002] With energy resources becoming increasingly scarce, there is an urgent need to develop new energy sources, and solar energy is one of the most widely available energy sources on Earth. Utilizing photocatalysis to convert waste resources into usable chemicals and fuels is an economically valuable and environmentally friendly approach. Compared to homogeneous photocatalysis, heterogeneous photocatalytic systems offer advantages such as easy catalyst recovery and easy separation of the substrate and catalyst, leading to their widespread development. In heterogeneous photocatalytic systems, under illumination, photogenerated electron-hole pairs are generated within the catalyst. After absorbing photons and undergoing a transition, the photogenerated electrons separate from the holes. Oxidation reactions can occur at the hole end, while reduction reactions can occur at the electron-rich end. Therefore, photocatalytic reactions are essentially redox reactions.

[0003] Plastic materials play an irreplaceable role in modern production and daily life, but they have also caused serious environmental consequences. Recycling and reusing plastics is the best way to solve environmental problems and alleviate resource and energy shortages. Polyethylene terephthalate (PET), due to its low price, non-toxicity, low permeability, light weight, and strong resistance to pollution, has become one of the most widely used polyester plastics in the world, especially in the packaging and textile industries. Annual PET production exceeds 30 million tons, but less than 10% of it is recyclable. The accumulation of waste PET has caused serious environmental problems, urgently requiring the development of new recycling methods to increase PET recovery.

[0004] Photocatalytic water splitting for hydrogen production is considered an effective way to efficiently utilize solar energy. PET photoreforming is a new technology that combines photocatalytic water splitting for hydrogen production with PET recycling. In this strategy, ethylene glycol from PET hydrolysis can provide electrons to promote photocatalytic water splitting to generate hydrogen, while simultaneously converting the treated PET into other high-value-added small-molecule organic compounds. According to Reference 1 (ACS Mater. Lett., 2023, 5, 3032-3041), photocatalytic reforming of PET plastic to produce hydrogen was successfully achieved using a composite of molybdenum sulfide and carbon nitride. Reference 2 (Appl. Catal. B-Environ., 2022, 307, 121143) also achieved photocatalytic reforming of PET plastic to produce hydrogen using nickel-molybdenum attached carbon nanotubes. However, the hydrogen yield in these reactions is very low, and the choice of active metal is also very limited. To improve hydrogen yield and expand the catalyst selection for this reaction, this invention aims to prepare an ultrathin carbon nitride nanosheet-coated titanium dioxide microsphere catalyst to achieve efficient photocatalytic reforming of PET plastics for hydrogen production. Summary of the Invention

[0005] The purpose of this invention is to provide a catalyst for the photocatalytic reforming of PET plastics using ultrathin carbon nitride nanosheets coated with titanium dioxide microspheres (g-C3N4 / TiO2). This invention achieves uniform and stable coating of ultrathin carbon nitride nanosheets on the surface of titanium dioxide microspheres through a specific "two-step annealing-acid etching-hydrothermal synthesis-composite" process, thereby constructing a heterojunction structure with efficient charge separation capability, providing a material basis for improving photocatalytic performance.

[0006] This invention achieves the high-value transformation of waste PET resources: combining plastic pollution control with clean energy production, and simultaneously realizing the following in the same photocatalytic system: hydrogen production: using ethylene glycol produced by PET hydrolysis as an electron donor to efficiently catalyze water splitting to generate hydrogen; resource utilization: converting waste PET into high-value-added chemicals such as glyoxal, glycolic acid, acetic acid, and formic acid.

[0007] This invention addresses the shortcomings of existing catalysts: existing PET photo-reforming hydrogen production catalysts (such as molybdenum sulfide / carbon nitride, nickel-molybdenum / carbon nanotubes, etc.) suffer from low hydrogen yield and limited selection of active center metals. This invention provides a high-performance, easily prepared composite photocatalyst, which is applied to the photocatalytic reforming process of PET plastic waste to simultaneously achieve the dual goals of high-yield hydrogen production and high-value conversion of plastics, thus combining environmental and economic benefits.

[0008] The preparation method of the ultrathin carbon nitride nanosheet-coated titanium dioxide microsphere catalyst provided by the present invention includes the following steps:

[0009] S1. The urea was subjected to a first annealing treatment, cooled, and then ground to obtain sample A; S2. Perform a second annealing treatment on sample A to obtain sample B; S3. The sample B is treated in a mixed solution of sulfuric acid and nitric acid, and after dilution, centrifugation, washing and drying, ultrathin carbon nitride nanosheet sample C is obtained. S4. Mix glucose aqueous solution and ammonium fluorotitanate aqueous solution for hydrothermal reaction. After centrifugation, washing and drying, the reaction product is used to obtain precursor sample D. S5. The sample D is subjected to a third annealing treatment to obtain titanium dioxide microsphere sample E. S6. Disperse the sample C in a solvent, add the sample E, stir and mix, and remove the solvent to obtain the titanium dioxide microsphere catalyst coated with ultrathin carbon nitride nanosheets.

[0010] In step S1, the conditions for the first annealing treatment are: in an air atmosphere, the temperature is raised to 500-600℃ at a heating rate of 2-10℃ / min, and held for 2-6 hours.

[0011] In step S2, the second annealing process is carried out in a closed or semi-closed container under the following conditions: the temperature is raised to 450-550°C at a heating rate of 1-5°C / min and held for 1-4 hours.

[0012] In step S3, the concentration of sulfuric acid in the sulfuric acid-nitric acid mixed solution is 8-10 mol / L, and the concentration of nitric acid is 3-5 mol / L; the treatment includes soaking and stirring for 1-15 minutes.

[0013] In step S4, the concentration of the glucose aqueous solution is 0.1-0.3 g / mL, and the concentration of the ammonium fluorotitanate aqueous solution is 0.05-0.1 g / mL; the temperature of the hydrothermal reaction is 160-200℃, and the time is 18-30 hours.

[0014] In step S5, the conditions for the third annealing treatment are: in an air atmosphere, the temperature is raised to 500-600℃ at a heating rate of 2-10℃ / min, and held for 2-6 hours. In step S6, the mass ratio of sample C to sample E is 1:1 to 1:5; the solvent is at least one of methanol, ethanol and isopropanol.

[0015] The ultrathin carbon nitride nanosheet-coated titanium dioxide microsphere catalyst prepared by the method of this invention is a heterojunction composite photocatalytic material. Its structural features are: a core layer composed of titanium dioxide (TiO2) microspheres; a shell layer composed of ultrathin graphitic carbon nitride (g-C3N4) nanosheets; and a composite structure in which the g-C3N4 nanosheets are tightly and uniformly attached to or wrapped around the surface of the TiO2 microspheres through physical adsorption and possible interfacial interactions, forming a core-shell or core-shell-like heterojunction structure. The titanium dioxide microspheres have a particle size of 1-2 μm, and the graphitic carbon nitride nanosheets have a thickness of 1-10 nm.

[0016] This invention relates to titanium dioxide microsphere catalysts that can be used for photocatalytic reforming of waste PET plastics, simultaneously producing hydrogen and high-value-added chemicals. It transforms difficult-to-degrade polyethylene terephthalate (PET) plastic waste (such as mineral water bottles and packaging materials) into clean energy hydrogen and useful chemicals such as glycolic acid and formic acid under mild conditions (room temperature, normal pressure, and light), achieving "turning waste into treasure." This is a highly efficient, practical, and green core photocatalytic material for upgrading PET plastic waste into hydrogen energy and chemicals.

[0017] This invention further provides a method for photocatalytic reforming of PET plastic to produce hydrogen, using the aforementioned ultrathin carbon nitride nanosheet-coated titanium dioxide microsphere catalyst, comprising the following steps: SⅠ. Hydrolyze PET plastic (granules or fragments) in an alkaline aqueous solution by heating to obtain a hydrolysate; SⅡ. Under an inert atmosphere, the titanium dioxide microsphere catalyst is added to the hydrolysate, and a photocatalytic reaction is carried out under the irradiation of a light source to generate hydrogen gas, which is detected by gas chromatography online or offline.

[0018] In step SⅠ, the alkaline aqueous solution is a potassium hydroxide aqueous solution with a concentration of 1-10 mol / L, preferably 2-10 mol / L or 5-10 mol / L; the heating hydrolysis temperature is 60-90℃ and the time is 12-72 hours.

[0019] In step SⅡ, the amount of catalyst added is such that the catalyst concentration in the reaction system is 0.5-2 mg / mL; the inert atmosphere is argon or nitrogen; the light source is a xenon lamp with a power of 200-500 W; and the photocatalytic reaction time is 1-12 hours, preferably 2-8 hours, 4-8 hours or 6-8 hours.

[0020] Compared with the prior art, the present invention has the following significant advantages: The catalyst exhibits excellent performance: the g-C3N4 / TiO2 composite catalyst prepared in this invention demonstrates significantly higher activity than the single component (g-C3N4 or TiO2) in the photocatalytic PET reforming hydrogen production reaction. Example data show that its hydrogen production rate can reach 1396.8 μmol g. -1 h -1 It is more than 10 times that of pure TiO2 and more than 2.5 times that of pure g-C3N4.

[0021] High efficiency of heterojunction structure: By first preparing ultrathin g-C3N4 nanosheets and then compositing them with TiO2 microspheres, effective and uniform coating of g-C3N4 on the TiO2 surface was achieved. This close interfacial contact greatly promotes the transfer of photogenerated electrons from g-C3N4 to TiO2, effectively suppresses charge recombination, and improves quantum efficiency.

[0022] The preparation method is simple and controllable: the entire preparation process requires no complex equipment or harsh conditions, and the raw materials used are inexpensive and readily available. By adjusting the annealing temperature, acid etching conditions, hydrothermal parameters, etc., the morphology and structure of the product can be effectively controlled.

[0023] Win-win for both environment and economy: This technology can not only convert PET waste that is difficult to degrade into hydrogen (clean energy) and high-value chemicals (such as glycolic acid and formic acid), realizing the resource utilization of waste, but also the entire reaction is carried out at room temperature and pressure and under light, with low energy consumption and environmental friendliness.

[0024] The catalyst exhibits good versatility: Examples show that the catalyst is effective not only for pure PET particles but also for actual waste PET bottle fragments. Furthermore, it demonstrates some catalytic reforming ability for other hydrolyzable polyesters (such as polylactic acid PLA), exhibiting a certain degree of substrate versatility. Attached Figure Description

[0025] Figure 1 The images show X-ray diffraction (XRD) and scanning electron microscopy (SEM) images of the ultrathin carbon nitride nanosheets coated with titanium dioxide microspheres prepared in this invention and their control samples. Figure a shows the XRD pattern of g-C3N4 / TiO2 and its control samples g-C3N4 (sample C) and TiO2 (sample E). Figure b shows the scanning electron microscopy image of g-C3N4 / TiO2. Figure c shows the transmission electron microscopy image of g-C3N4 / TiO2. Figure d shows the high-resolution transmission electron microscopy image of g-C3N4 / TiO2. Figure e shows the scanning electron microscopy image of TiO2. Figure f shows the scanning electron microscopy image of g-C3N4.

[0026] Figure 2The figures show the catalytic results of applying the ultrathin carbon nitride nanosheets coated with titanium dioxide microspheres prepared in this invention to the photocatalytic reforming reaction of PET plastic to produce hydrogen. Figure a shows the hydrogen yield results obtained by adjusting the concentration of potassium hydroxide (KOH), Figure b shows the hydrogen yield results obtained by adjusting different reaction times, Figure c shows the hydrogen yield results obtained by adjusting different reaction substrates, and Figure d shows the hydrogen yield results obtained by adjusting different catalysts. Detailed Implementation

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0028] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0029] This invention belongs to the field of environmental catalysis and new energy materials, specifically relating to a highly efficient photocatalyst for the resource utilization of plastic waste and its applications. This invention provides a heterojunction composite photocatalyst (g-C3N4 / TiO2) of ultrathin graphitic carbon nitride (g-C3N4) nanosheets coated with titanium dioxide (TiO2) microspheres. This catalyst is obtained through a unique preparation method, characterized by ultrathin, porous g-C3N4 nanosheets tightly and uniformly attached to the surface of TiO2 microspheres, forming a core-shell structure with highly efficient interfacial charge transfer capabilities.

[0030] The catalyst preparation method provided by this invention includes the following key steps: Two-step thermal polymerization and acid etching of urea: Urea was annealed by two programmed temperature rises and then etched by a mixture of concentrated sulfuric acid and nitric acid to prepare ultrathin g-C3N4 nanosheets rich in active sites. Glucose template hydrothermal method: using glucose as a soft template, it reacts with ammonium fluorotitanate through hydrothermal reaction and subsequent calcination to prepare anatase phase TiO2 microspheres with regular morphology. Ultrasonic-assisted self-assembly: The two materials mentioned above are ultrasonically dispersed and stirred and evaporated in a solvent to obtain the final heterojunction catalyst.

[0031] The core application of this invention is the use of this catalyst in the photocatalytic reforming reaction of polyethylene terephthalate (PET) plastics. Under simulated sunlight irradiation, this catalytic system can efficiently catalyze water splitting to produce hydrogen gas using PET hydrolysis products (mainly ethylene glycol) as electron donors, while simultaneously converting the plastic into high-value chemicals such as glycolic acid and formic acid.

[0032] The data from the examples show that this catalyst exhibits unprecedented efficiency: its hydrogen production rate reaches 1396.8 μmol g. -1 h -1The hydrogen production rates were 10.5 times and 2.6 times that of pure TiO2 and pure g-C3N4, respectively, demonstrating a highly significant heterojunction synergistic effect. It exhibits the same high efficiency in processing actual waste PET bottles, with a hydrogen production rate of 1427.9 μmol g. -1 h -1 It possesses strong potential for practical applications. The catalyst exhibits structural stability and good activity durability in a strongly alkaline reaction environment.

[0033] This invention successfully combines the two major challenges of solving "white pollution" and developing "green hydrogen energy," providing a new, low-cost, high-efficiency, and environmentally friendly pathway for upgrading and recycling plastic waste and converting it into solar energy. The catalyst's superior performance stems from its ingenious heterojunction structure design, offering an innovative material solution to address the charge separation efficiency bottleneck in similar photocatalytic systems.

[0034] In the following examples, the gas chromatography detection conditions are as follows: The initial temperature of the injection port was 60℃. A TCD detector was used with a detector temperature of 250℃. Argon was used as the carrier gas with a gas flow rate of 1.314 mL / min and a constant pressure of 6.551 psi.

[0035] In the following examples, the conditions for liquid chromatography detection are as follows: An amino column was used, with a mobile phase of 0.5 g / L H2SO4 aqueous solution, a column temperature of 50℃, a UV detector wavelength of 254 nm, and a flow rate of 0.6 mL / min.

[0036] Example 1: 50 mg of g-C3N4 (sample C), which was synthesized from urea and etched by a mixture of sulfuric acid and nitric acid after high-temperature oxygen stripping, was dispersed in 30 mL of methanol solution and sonicated for 15 min. Then, 100 mg of spherical TiO2 (sample E), which was obtained by hydrothermal calcination of a mixture of glucose and ammonium fluorotitanate, was added and stirred. The solvent was then naturally evaporated at room temperature.

[0037] The specific steps for synthesizing samples C and E are as follows: 8 g of urea was annealed twice in a muffle furnace (the first annealing was performed in a porcelain boat, with a heating rate of 5℃ / min and a holding time of 550℃ for 4 h; the second annealing was performed in a crucible, with a heating rate of 2.5℃ / min and a holding time of 500℃ for 2 h, both of which were naturally cooled to room temperature). The resulting sample was soaked in 5 mL of a sulfuric acid-nitric acid mixed solution (98% concentrated sulfuric acid and 65% concentrated nitric acid mixed in a volume ratio of 1:1) for 5 min, then 30 mL of deionized water was added. After centrifugation, washing twice with deionized water, and vacuum drying for 12 h, sample C was obtained.

[0038] 40 mL of a 0.225 g / mL glucose aqueous solution was mixed with 20 mL of a 0.075 g / mL ammonium fluorotitanate aqueous solution, transferred to a reaction vessel, and placed in an explosion-proof oven. The temperature was set at 180 °C for 24 h. After the reaction, the mixture was cooled to room temperature, centrifuged, washed, and vacuum dried at 60 °C for 12 h. The dried sample was then transferred to a ceramic boat and annealed in a muffle furnace. The annealing program was: heating rate 5 °C / min, held at 550 °C for 4 h, yielding sample E.

[0039] Figure 1 Figure a shows the X-ray diffraction patterns of the catalyst g-C3N4 / TiO2 in this embodiment and its control samples g-C3N4 (sample C) and TiO2 (sample E). θ =25.3°, 2 θ =27.4°, 2 θ =37.8°, 2 θ =48.0°, 2 θ =53.9°, 2 θ =55.1° and 2 θ =62.7° corresponds to the (101), (004), (200), (105), (211) and (204) crystal planes of titanium dioxide, respectively; 2 θ =27.4° corresponds to the (002) crystal plane of the graphitic carbon nitride phase.

[0040] Figure 1 Figures b and c show scanning and transmission electron microscopy images of the catalyst g-C3N4 / TiO2 in this embodiment. It can be observed that g-C3N4 flakes are coated on the surface of TiO2 microspheres.

[0041] Figure 1 Image d is a high-resolution transmission electron microscope image of g-C3N4 / TiO2, showing the lattice fringes corresponding to the (101) crystal plane of titanium dioxide. This demonstrates the successful synthesis of ultrathin carbon nitride nanosheets coated with titanium dioxide microspheres, g-C3N4 / TiO2.

[0042] The g-C3N4 / TiO2 catalyst of this embodiment was applied to the photocatalytic reforming of PET plastic to produce hydrogen, and the steps are as follows: The first step involved dispersing 5 g of PET plastic granules in 100 mL of a 5 mol / L KOH solution and stirring in a 70 ℃ oil bath for 24 h. After cooling to room temperature, the solution was filtered, and the filtrate was used for subsequent reactions. The second step involved adding g-C3N4 / TiO2 catalyst at a concentration of 1 mg / mL to the above solution and irradiating it for 10 h under an argon atmosphere using a 300 W xenon lamp as the light source. The gas chromatography results after the reaction are shown below. Figure 2In the reaction, the H2 generation rate was 1396.8 μmol / g / h; liquid chromatography and nuclear magnetic resonance detection results showed that the reaction converted the ethylene glycol from PET hydrolysis into products such as glyoxal, glycolic acid, acetic acid and formic acid.

[0043] Example 2: The operating steps are the same as above, except that the concentration of the KOH aqueous solution is changed to 1 mol / L. Figure 2 As shown in Figure a, the H2 generation rate is 387 μmol / g / h.

[0044] Example 3: The operating procedure is the same as above, except that the concentration of the KOH aqueous solution is changed to 2 mol / L. Figure 2 As shown in Figure a, the H2 generation rate is 797.6 μmol / g / h.

[0045] Example 4: The operating steps are the same as above, except that the concentration of the KOH aqueous solution is changed to 10 mol / L. Figure 2 As shown in Figure a, the H2 generation rate is 1441.6 umol / g / h.

[0046] Example 5: The operating steps are the same as above, except that the light reaction time is changed to 2 hours. Figure 2 As shown in Figure b, the H2 generation rate is 532 μmol / g / h.

[0047] Example 6: The operating steps are the same as above, except that the light reaction time is changed to 4 hours. Figure 2 As shown in Figure b, the H2 generation rate is 606.4 μmol / g / h.

[0048] Example 7: The operating steps are the same as above, except that the light reaction time is changed to 6 hours. Figure 2 As shown in Figure b, the H2 generation rate is 1039.1 μmol / g / h.

[0049] Example 8: The operating steps are the same as above, except that the light reaction time is changed to 8 hours. Figure 2 As shown in Figure b, the H2 generation rate is 1360.3 μmol / g / h.

[0050] Example 9: The operating steps are the same as above, except that the PET plastic granules are replaced with waste PET plastic bottles, such as... Figure 2 As shown in Figure c, the H2 generation rate is 1427.9 umol / g / h.

[0051] Example 10: The operating steps are the same as above, except that the PET plastic granules are replaced with polylactic acid (PLA) granules, such as... Figure 2 As shown in Figure c, the H2 generation rate is 1036.1 μmol / g / h.

[0052] Comparative Example 1: The operation steps are the same as above, except that the catalyst is replaced with the control sample spherical TiO2 (sample E). Figure 1 Figure a shows the X-ray diffraction pattern of spherical TiO2 (sample E). θ =25.3°, 2 θ =27.4°, 2 θ =37.8°, 2 θ =48.0°, 2 θ =53.9°, 2 θ =55.1° and 2 θ =62.7° corresponds to the (101), (004), (200), (105), (211) and (204) crystal planes of titanium dioxide, respectively. Figure 1 Figure e shows a scanning electron microscope image of spherical TiO2 (sample E), revealing a relatively uniform spherical structure. Figure 2 As shown in Figure d, the H2 generation rate is 132.9 μmol / g / h.

[0053] Comparative Example 2: The operating procedure is the same as above, except that the catalyst is replaced with the control sample g-C3N4 (sample C).

[0054] Figure 1 Figure a shows the X-ray diffraction pattern of g-C3N4 (sample C), 2 θ =13.1° and 2 θ =27.4° corresponds to the (100) and (002) crystal planes of the graphitic carbon nitride phase, respectively.

[0055] Figure 1 Figure f in the middle shows a scanning electron microscope image of g-C3N4 (sample C), which shows that the sample exhibits a nanosheet-like structure.

[0056] like Figure 2 As shown in Figure d, the H2 generation rate is 541.4 μmol / g / h.

[0057] As can be seen from the above embodiments and comparative examples: Alkaline environment optimization: Comparison of Examples 2, 3, 1, and 4 shows that PET hydrolysis requires a sufficient alkaline concentration (≥5 M KOH) to be complete, providing ample electron donors (ethylene glycol) to achieve optimal hydrogen production performance. The catalyst remains stable in strong alkali.

[0058] Reaction kinetics: Examples 5-8 show that the hydrogen production is basically linear with time within 2-8 hours, indicating that the catalyst activity is stable and there is no rapid deactivation.

[0059] Substrate universality and practicality: Example 9 demonstrates that the catalyst exhibits excellent performance comparable to pure PET on real waste PET plastics with complex compositions, highlighting its practical application value. Example 10 shows that the catalytic system is also effective on another type of hydrolyzable polyester, PLA, demonstrating the scalability of the technical route.

[0060] The decisive role of heterojunctions: Comparative Examples 1 and 2 directly demonstrate the enormous advantages of the g-C3N4 / TiO2 heterojunction structure. Its performance far surpasses that of a single component, and is not a simple additive result, confirming that efficient charge separation and transfer at the interface is the fundamental reason for the performance leap.

[0061] The g-C3N4 / TiO2 composite catalyst provided by this invention exhibits high activity, high stability, good practical application potential, and certain substrate universality in the application of photocatalytic PET reforming for hydrogen production, providing an efficient solution for the resource utilization of plastic waste and hydrogen production.

[0062] In summary, the ultrathin carbon nitride nanosheet-coated titanium dioxide microsphere catalyst, its preparation method, and its application provided by this invention successfully solve the problem of poor interfacial contact between g-C3N4 and TiO2, constructing a highly efficient heterojunction photocatalytic system. This system exhibits high activity, high stability, good practical application potential, and controllability in the photocatalytic reforming of PET plastics for hydrogen production, providing an efficient, green, and promising technical solution for the resource utilization of plastic waste and solar energy conversion and storage.

Claims

1. A method for preparing an ultrathin carbon nitride nanosheet-coated titanium dioxide microsphere catalyst, comprising the following steps: S1. The urea was subjected to a first annealing treatment, cooled, and then ground to obtain sample A; S2. Perform a second annealing treatment on sample A to obtain sample B; S3. The sample B is treated in a mixed solution of sulfuric acid and nitric acid, and after dilution, centrifugation, washing and drying, ultrathin carbon nitride nanosheet sample C is obtained. S4. Mix glucose aqueous solution and ammonium fluorotitanate aqueous solution for hydrothermal reaction. After centrifugation, washing and drying, the reaction product is used to obtain precursor sample D. S5. The sample D is subjected to a third annealing treatment to obtain titanium dioxide microsphere sample E. S6. Disperse the sample C in a solvent, add the sample E, stir and mix, and remove the solvent to obtain the titanium dioxide microsphere catalyst coated with ultrathin carbon nitride nanosheets.

2. The preparation method according to claim 1, characterized in that: In step S1, the conditions for the first annealing treatment are: in an air atmosphere, the temperature is raised to 500-600℃ at a heating rate of 2-10℃ / min, and held for 2-6 hours.

3. The preparation method according to claim 1 or 2, characterized in that: In step S2, the second annealing process is carried out in a closed or semi-closed container under the following conditions: the temperature is raised to 450-550°C at a heating rate of 1-5°C / min and held for 1-4 hours.

4. The preparation method according to any one of claims 1-3, characterized in that: In step S3, the concentration of sulfuric acid in the sulfuric acid-nitric acid mixed solution is 8-10 mol / L, and the concentration of nitric acid is 3-5 mol / L; the treatment includes soaking and stirring for 1-15 minutes.

5. The preparation method according to any one of claims 1-4, characterized in that: In step S4, the concentration of the glucose aqueous solution is 0.1-0.3 g / mL, and the concentration of the ammonium fluorotitanate aqueous solution is 0.05-0.1 g / mL; the temperature of the hydrothermal reaction is 160-200℃, and the time is 18-30 hours.

6. The preparation method according to any one of claims 1-5, characterized in that: In step S5, the conditions for the third annealing treatment are: in an air atmosphere, the temperature is raised to 500-600℃ at a heating rate of 2-10℃ / min, and held for 2-6 hours. In step S6, the mass ratio of sample C to sample E is 1:1 to 1:5; the solvent is at least one of methanol, ethanol and isopropanol.

7. The titanium dioxide microsphere catalyst coated with ultrathin carbon nitride nanosheets prepared by the method of any one of claims 1-6.

8. A method for photocatalytic reforming of PET plastic to produce hydrogen, using the titanium dioxide microsphere catalyst coated with ultrathin carbon nitride nanosheets as described in claim 7, comprising the following steps: SⅠ. Hydrolyze PET plastic by heating in an alkaline aqueous solution to obtain a hydrolysate; SⅡ, Under an inert atmosphere, the titanium dioxide microsphere catalyst is added to the hydrolysate, and a photocatalytic reaction is carried out under the irradiation of a light source to generate hydrogen gas.

9. The method according to claim 8, characterized in that: In step SⅠ, the alkaline aqueous solution is a potassium hydroxide aqueous solution with a concentration of 1-10 mol / L; the heating hydrolysis temperature is 60-90℃ and the time is 12-72 hours.

10. The method according to claim 8 or 9, characterized in that: In step SⅡ, the amount of catalyst added is such that the concentration of catalyst in the reaction system is 0.5-2 mg / mL; the inert atmosphere is argon or nitrogen; the light source is a xenon lamp with a power of 200-500 W; and the photocatalytic reaction time is 1-12 hours.

Images