Method for degrading polystyrene to produce benzoic acid by using a photo-thermal synergistic catalyst and application thereof

Abstract

The application discloses a method for degrading polystyrene to produce benzoic acid by using a photo-thermal synergistic catalyst and application thereof, and belongs to the technical field of waste plastic resource utilization. The method comprises the following steps: constructing a reaction system comprising polystyrene, a photo-thermal synergistic catalyst and a solvent, and performing a depolymerization reaction under the conditions of light and heating to prepare benzoic acid. The photo-thermal synergistic catalyst is sulfur-doped and nitrogen-vacancy-rich graphite-phase carbon nitride, which is prepared by the following method: urea and thiourea are mixed and dissolved according to a mass ratio of 0.5-9:1, a precursor mixture is obtained through evaporation and crystallization, the precursor mixture is heated and calcined under an air atmosphere to obtain sulfur-doped carbon nitride precursors, and the sulfur-doped carbon nitride precursors are heat-treated in an ammonia atmosphere to introduce nitrogen vacancy defects, so that the photo-thermal synergistic catalyst is obtained. The method has mild conditions, high catalytic efficiency of the catalyst, high polystyrene conversion efficiency and environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic resource utilization technology, specifically relating to a method for the degradation of polystyrene to produce benzoic acid by photothermal synergistic catalyst and its application. Background Technology

[0002] Polystyrene (PS) is one of the most widely used plastics, possessing excellent properties such as light weight, heat insulation, electrical insulation, and corrosion resistance. It is mainly used in packaging materials, disposable tableware, electronic product casings, and building materials. However, polystyrene waste is difficult to degrade naturally and can persist in the natural environment for hundreds of years, affecting the ecological balance and posing health risks. Therefore, developing efficient and clean polystyrene waste treatment technologies to achieve its resource utilization is of significant environmental and economic value.

[0003] Currently, the main methods for treating polystyrene waste include landfill, incineration, and mechanical recycling. Landfill disposal consumes a large amount of land resources, and polystyrene, being chemically stable, hardly degrades under natural conditions, causing long-term potential pollution. Incineration, while recovering some heat energy, produces large amounts of carbon dioxide and toxic gases such as polycyclic aromatic hydrocarbons and dioxins, causing serious secondary pollution. Mechanical recycling reprocesses waste plastics into plastic products through melting and regranulation, but this process often leads to a decrease in the molecular weight and deterioration of mechanical properties of polystyrene, requiring downgraded use, and ultimately still necessitating waste disposal after multiple cycles. Therefore, traditional treatment methods are insufficient for achieving green, efficient, and resource-based utilization of polystyrene waste.

[0004] Chemical recycling technology, which depolymerizes waste plastics into monomers or converts them into high-value-added chemicals, is considered an ideal way to achieve the recycling of waste plastics. Polystyrene is a linear polymer formed by the addition polymerization of styrene monomers, with a molecular weight typically ranging from tens of thousands to hundreds of thousands. The polystyrene molecular chain contains a large number of benzene ring side groups, giving it high chemical and thermal stability. Currently, some research has achieved the "resource recovery" and "high-value utilization" of polystyrene. For example, Chinese patent document CN121342644A discloses a method for degrading polystyrene plastics and upgrading them to benzoic acid based on photocatalytic ozone oxidation using nano-MnO2. This method mixes PS plastic fragments with nano-MnO2 and an organic solvent, then simultaneously introduces ozone into the reaction system at room temperature and pressure and irradiates it with light. Through the synergistic catalytic effect of light and ozone, the molecular chains of PS plastics can be efficiently and selectively broken and oxidized, ultimately directionally converted into high-value-added benzoic acid. Chinese patent document CN120208744A discloses a method for solventless hydrogenation degradation of waste polystyrene plastics to prepare monobenzene-ring liquid chemicals based on a bifunctional catalyst. This method uses Nb₂O₅ as a support and loads 1-3 wt% of the precious metal ruthenium to prepare a bifunctional catalyst. Under solventless conditions, hydrogenation reaction efficiently degrades high molecular weight polystyrene into monobenzene-ring liquid chemicals such as benzene, toluene, and ethylbenzene. However, this method suffers from high energy consumption, high costs due to the use of precious metals or ozone, and the conversion efficiency needs further improvement.

[0005] Photothermal synergistic catalysis combines the advantages of photocatalysis and thermocatalysis, providing a new approach for the efficient conversion of waste plastics. The core of photothermal synergistic catalysis lies in utilizing light energy to convert it into heat energy, achieving localized heating of the catalyst surface, while photogenerated charge carriers directly participate in the reaction. The synergistic effect of these two technologies significantly improves reaction efficiency. However, current research on the degradation of polystyrene using photothermal synergistic catalysts is insufficient, and no relevant reports have been found. Summary of the Invention

[0006] To overcome the problems of harsh conversion conditions and low efficiency in existing technologies for polystyrene, this invention provides a method for the degradation of polystyrene to produce benzoic acid using a photothermal synergistic catalyst. This method is characterized by mild conditions and high conversion efficiency, enabling the resource utilization of waste polystyrene and yielding good economic benefits.

[0007] The specific technical solution adopted is as follows:

[0008] A method for producing benzoic acid by photothermal synergistic catalyst degradation of polystyrene includes the following steps:

[0009] A reaction system comprising polystyrene, a photothermal synergistic catalyst, and a solvent was constructed, and a depolymerization reaction was carried out under light and heating conditions to prepare benzoic acid.

[0010] The photothermal synergistic catalyst is sulfur-doped graphitic carbon nitride rich in nitrogen vacancies, which is prepared by the following method: urea and thiourea are mixed and dissolved in a mass ratio of 0.5~9:1, and then evaporated and crystallized to obtain a precursor mixture. The precursor mixture is heated and calcined in an air atmosphere to obtain a sulfur-doped carbon nitride precursor. The sulfur-doped carbon nitride precursor is heat-treated in an ammonia atmosphere to introduce nitrogen vacancy defects, thereby obtaining the photothermal synergistic catalyst.

[0011] The photothermal synergistic catalyst used in this invention introduces sulfur doping by adjusting the ratio of urea to thiourea, and then introduces nitrogen vacancies through ammonia post-treatment, achieving a synergistic effect between sulfur doping and nitrogen vacancies, thus significantly improving the photothermal catalytic conversion efficiency. This photothermal synergistic catalyst works at light source wavelengths of 280–2500 nm and light intensities of 500–1000 mW / cm². 2 Under the conditions of reaction temperature of 90~210 ℃ and reaction time of 1~24h, photothermal synergistic catalytic conversion of polystyrene can be achieved. It has high catalytic activity and high stability, and at the same time, it can achieve low energy consumption and high selectivity to convert polystyrene into high-value chemicals such as benzoic acid.

[0012] Pure graphitic carbon nitride (g-C3N4) suffers from limitations such as limited visible light utilization, rapid recombination of photogenerated electron-hole pairs, low specific surface area, and insufficient active sites, restricting further improvements in its catalytic efficiency. This invention introduces sulfur doping and nitrogen vacancies into graphitic carbon nitride as a photothermal synergistic catalyst. Sulfur doping effectively modulates the band structure of carbon nitride, extending the light absorption range into the visible light region and enhancing the catalyst's utilization of sunlight. Nitrogen vacancies serve as trapping centers for photogenerated electrons and surface active sites, promoting the separation of photogenerated carriers. More importantly, there is a synergistic effect between sulfur doping and nitrogen vacancies: sulfur doping induces the formation of more nitrogen vacancies, which in turn further enhance the electronic effects of sulfur doping. Together, they significantly improve the photothermal conversion efficiency and surface reactivity of the catalyst.

[0013] The photothermal synergistic catalyst for converting polystyrene provided by this invention has a photothermal effect and exhibits good conversion efficiency for polystyrene under full-spectrum sunlight.

[0014] Preferably, the mass ratio of polystyrene to photothermal synergistic catalyst is 1:0.1~2, and more preferably 1:0.5~2.

[0015] Furthermore, the solvent includes acetonitrile, acetone, or water.

[0016] Furthermore, the illumination conditions are: light source wavelength 280~2500 nm, light intensity 500~1000 mW / cm². 2The heating conditions are: reaction temperature 90~210 ℃, further 150~210 ℃, and reaction time 1~24 h, further 3~18 h.

[0017] Furthermore, the depolymerization reaction is carried out in an oxidizing atmosphere, specifically an oxygen atmosphere or an air atmosphere.

[0018] In the preparation of the photothermal synergistic catalyst, sulfur-doped carbon nitride precursor is first introduced by in-situ one-step thermal shrinkage, and then nitrogen vacancy defects are introduced into the sulfur-doped carbon nitride precursor.

[0019] Preferably, the mass ratio of urea to thiourea is 0.5 to 5:1, more preferably one of 5:1, 2:1, or 0.5:1. Different ratios affect the sulfur doping amount and the microstructure of carbon nitride, thereby regulating catalytic performance and achieving in-situ sulfur doping. Sulfur atoms replace nitrogen atoms in the carbon nitride lattice to form CS bonds. This doping method can finely control the electronic structure of the catalyst, narrow the band gap, and enhance the absorption of visible light. At the same time, the change in local charge density caused by sulfur doping can reduce the formation energy of nitrogen vacancies, promoting the generation of nitrogen vacancies during subsequent ammonia treatment.

[0020] Preferably, the conditions for heating and calcining the precursor mixture in an air atmosphere are: temperature 450~550℃, holding time 2~4 h, and heating rate 4~6℃ / min.

[0021] Preferably, the conditions for heat treatment of the sulfur-doped carbon nitride precursor in an ammonia atmosphere are 450-550°C, holding time 1-4 h, and ammonia volume concentration of 10-80 vol%. Ammonia treatment can introduce nitrogen vacancies and may further regulate the sulfur doping state.

[0022] Experiments have shown that the electron paramagnetic resonance (EPR) spectrum of this photothermal synergistic catalyst exhibits a characteristic signal of nitrogen vacancies at g=2.003, and X-ray photoelectron spectroscopy (XPS) shows that the S 2p orbital has a characteristic peak corresponding to CS or OS bonds, confirming that sulfur was successfully doped and nitrogen vacancies were formed.

[0023] The present invention also provides the application of the method for the degradation of polystyrene to produce benzoic acid by the photothermal synergistic catalyst in the treatment of waste polystyrene.

[0024] The method of this invention can achieve efficient conversion of various forms of polystyrene waste, including but not limited to polystyrene particles, polystyrene foam boards, and polystyrene plastic cups.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) In this invention, sulfur doping and nitrogen vacancy are synergistically introduced into graphitic carbon nitride catalyst for photothermal catalytic conversion of polystyrene. Sulfur doping can regulate the electronic structure and enhance visible light absorption; nitrogen vacancy provides active sites and promotes carrier separation. The two work synergistically to significantly improve catalytic efficiency and polystyrene conversion efficiency, thus realizing the high-value utilization of polystyrene.

[0027] (2) The method of the present invention is simple and controllable, the preparation method of photothermal synergistic catalyst is simple, easy to industrial production, low cost, and the photothermal synergistic catalyst has good stability and recycling performance.

[0028] (3) The photothermal synergistic catalyst degradation method for producing benzoic acid from polystyrene provided by the present invention can be carried out at a lower temperature and normal pressure compared with traditional thermal cracking, significantly reducing energy consumption, while the conversion efficiency of polystyrene is high.

[0029] (4) The method of the present invention can achieve efficient conversion of polystyrene under mild conditions, obtain high-value chemicals such as benzoic acid with high selectivity, and is green and environmentally friendly, with good economic benefits. Attached Figure Description

[0030] Figure 1 The graph shows the catalytic conversion effect of different catalysts on polystyrene under the conditions of Example 8.

[0031] Figure 2 For catalyst V N -S-CN-21、g-CN、V N XPS plot of -T-CN.

[0032] Figure 3 For catalyst V N -S-CN-21、g-CN、V N EPR map of -T-CN.

[0033] Figure 4 The graph shows the catalytic conversion effect of different catalysts on polystyrene under the conditions of Example 9.

[0034] Figure 5 The graph shows the catalytic conversion effect of different catalysts on polystyrene under the conditions of Example 10.

[0035] Figure 6 The graph shows the catalytic conversion effect of polystyrene measured under different conditions in Example 11.

[0036] Figure 7 The graph shows the catalytic conversion effect of polystyrene measured under different conditions in Example 12.

[0037] Figure 8The graph shows the catalytic conversion effect of polystyrene measured under different conditions in Example 13.

[0038] Figure 9 The image shows the catalytic conversion effect of polystyrene measured under different conditions in Example 14.

[0039] Figure 10 The image shows the catalytic conversion effect of polystyrene measured under the conditions of Example 15.

[0040] Figure 11 The image shows the catalytic conversion effect of polystyrene measured under the conditions of Example 16. Detailed Implementation

[0041] To make the objectives, features, and advantages of this invention more apparent and understandable, a detailed description is provided below through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the invention can be combined appropriately without mutual conflict.

[0042] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer. Contents not described in detail in this specification are prior art known to those skilled in the art. Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0043] Example 1: Preparation of photothermal synergistic catalyst

[0044] (1) Take 8.33g of urea and 1.67g of thiourea, place them in an agate mortar, grind them thoroughly, add 30mL of deionized water, and after they are fully dissolved, evaporate and crystallize them in a 60℃ water bath to obtain a precursor mixture.

[0045] (2) The precursor mixture was transferred to a covered alumina crucible, placed in a muffle furnace, heated to 500°C at a heating rate of 5°C / min, calcined in air atmosphere for 4 hours, and naturally cooled to room temperature to obtain sulfur-doped carbon nitride precursor, denoted as S-CN-51.

[0046] (3) Take 1.0 g of S-CN-51 and place it in a tube furnace. First, purge the air with nitrogen for 30 minutes, then switch to 80 vol% ammonia (flow rate 100 mL / min), raise the temperature to 500℃ at 5℃ / min, and hold for 1 hour to allow the sulfur-doped carbon nitride precursor to undergo heat treatment in an ammonia atmosphere, introducing nitrogen vacancy defects, and then cool naturally to room temperature.

[0047] (4) Grind the sample after the reaction in step (3) to obtain a sulfur-doped and nitrogen-vacancy-modified carbon nitride photothermal synergistic catalyst, denoted as V. N -S-CN-51.

[0048] Example 2 Preparation of photothermal synergistic catalyst

[0049] (1) Take 6.67g of urea and 3.33g of thiourea, place them in an agate mortar, grind them thoroughly, add 30mL of deionized water, dissolve them thoroughly, and then evaporate and crystallize them in a 60℃ water bath to obtain a precursor mixture.

[0050] (2) The precursor mixture was transferred to a covered alumina crucible, placed in a muffle furnace, heated to 500°C at a heating rate of 5°C / min, calcined in air atmosphere for 4 hours, and then naturally cooled to room temperature to obtain sulfur-doped carbon nitride precursor, denoted as S-CN-21.

[0051] (3) Take 1.0 g of S-CN-21 and place it in a tube furnace. First, purge the air with nitrogen for 30 minutes, then switch to 80 vol% ammonia (flow rate 100 mL / min), raise the temperature to 500℃ at 5℃ / min, and hold for 1 hour to allow the sulfur-doped carbon nitride precursor to undergo heat treatment in an ammonia atmosphere, introducing nitrogen vacancy defects, and then cool naturally to room temperature.

[0052] (4) Grind the sample after the reaction in step (3) to obtain a sulfur-doped and nitrogen-vacancy-modified carbon nitride photothermal synergistic catalyst, denoted as V. N -S-CN-21.

[0053] Example 3 Preparation of photothermal synergistic catalyst

[0054] (1) Take 3.33g of urea and 6.67g of thiourea, place them in an agate mortar, grind them thoroughly, add 30mL of deionized water, and after they are fully dissolved, evaporate and crystallize them in a 60℃ water bath to obtain a precursor mixture.

[0055] (2) The precursor mixture was transferred to a covered alumina crucible, placed in a muffle furnace, heated to 500°C at a heating rate of 5°C / min, calcined in air atmosphere for 4 hours, and naturally cooled to room temperature to obtain sulfur-doped carbon nitride precursor, denoted as S-CN-12.

[0056] (3) Take 1.0 g of S-CN-12 and place it in a tube furnace. First, purge the air with nitrogen for 30 minutes, then switch to 80 vol% ammonia (flow rate 100 mL / min), raise the temperature to 500℃ at 5℃ / min, and hold for 1 hour to allow the sulfur-doped carbon nitride precursor to undergo heat treatment in an ammonia atmosphere, introducing nitrogen vacancy defects, and then cool naturally to room temperature.

[0057] (4) Grind the sample after the reaction in step (3) to obtain a sulfur-doped and nitrogen-vacancy-modified carbon nitride photothermal synergistic catalyst, denoted as V. N -S-CN-12.

[0058] Example 4 Preparation of photothermal synergistic catalyst

[0059] (1) Take 6.67g of urea and 3.33g of thiourea, place them in an agate mortar, grind them thoroughly, add 30mL of deionized water, dissolve them thoroughly, and then evaporate and crystallize them in a 60℃ water bath to obtain a precursor mixture.

[0060] (2) The precursor mixture was transferred to a covered alumina crucible, placed in a muffle furnace, heated to 450°C at a heating rate of 5°C / min, calcined in air atmosphere for 4 hours, and naturally cooled to room temperature to obtain sulfur-doped carbon nitride precursor, denoted as S-CN-21-450.

[0061] (3) Take 1.0 g of S-CN-21-450 and place it in a tube furnace. First, purge the air with nitrogen for 30 minutes, then switch to 80 vol% ammonia (flow rate 100 mL / min), raise the temperature to 500℃ at 5℃ / min, and hold for 1 hour to allow the sulfur-doped carbon nitride precursor to undergo heat treatment in an ammonia atmosphere, introducing nitrogen vacancy defects, and then cool naturally to room temperature.

[0062] (4) Grind the sample after the reaction in step (3) to obtain a sulfur-doped and nitrogen-vacancy-modified carbon nitride photothermal synergistic catalyst, denoted as V. N -S-CN-21-450.

[0063] Example 5 Preparation of photothermal synergistic catalyst

[0064] (1) Take 6.67g of urea and 3.33g of thiourea, place them in an agate mortar, grind them thoroughly, add 30mL of deionized water, dissolve them thoroughly, and then evaporate and crystallize them in a 60℃ water bath to obtain a precursor mixture.

[0065] (2) The precursor mixture was transferred to a covered alumina crucible, placed in a muffle furnace, heated to 550°C at a heating rate of 5°C / min, calcined in air atmosphere for 4 hours, and naturally cooled to room temperature to obtain sulfur-doped carbon nitride precursor, denoted as S-CN-21-550.

[0066] (3) Take 1.0 g S-CN-21-550 and place it in a tube furnace. First, purge the air with nitrogen for 30 minutes, then switch to 80 vol% ammonia (flow rate 100 mL / min), raise the temperature to 500℃ at 5℃ / min, and hold for 1 hour to allow the sulfur-doped carbon nitride precursor to undergo heat treatment in an ammonia atmosphere, introducing nitrogen vacancy defects, and then cool naturally to room temperature.

[0067] (4) Grind the sample after the reaction in step (3) to obtain a sulfur-doped and nitrogen-vacancy-modified carbon nitride photothermal synergistic catalyst, denoted as V. N -S-CN-21-550.

[0068] Example 6 Preparation of photothermal synergistic catalyst

[0069] (1) Take 6.67g of urea and 3.33g of thiourea, place them in an agate mortar, grind them thoroughly, add 30mL of deionized water, dissolve them thoroughly, and then evaporate and crystallize them in a 60℃ water bath to obtain a precursor mixture.

[0070] (2) The precursor mixture was transferred to a covered alumina crucible, placed in a muffle furnace, heated to 500°C at a heating rate of 5°C / min, calcined in air atmosphere for 4 hours, and then naturally cooled to room temperature to obtain sulfur-doped carbon nitride precursor, denoted as S-CN-21.

[0071] (3) Take 1.0 g of S-CN-21 and place it in a tube furnace. First, purge the air with nitrogen for 30 minutes, then switch to 40 vol% ammonia (flow rate 100 mL / min), raise the temperature to 500℃ at 5℃ / min, and hold for 1 hour to allow the sulfur-doped carbon nitride precursor to undergo heat treatment in an ammonia atmosphere, introducing nitrogen vacancy defects, and then cool naturally to room temperature.

[0072] (4) Grind the sample after the reaction in step (3) to obtain a carbon nitride photothermal synergistic catalyst co-modified by sulfur doping and nitrogen vacancies, denoted as 40%-V. N -S-CN-21.

[0073] Example 7 Preparation of photothermal synergistic catalyst

[0074] (1) Take 6.67g of urea and 3.33g of thiourea, place them in an agate mortar, grind them thoroughly, add 30mL of deionized water, dissolve them thoroughly, and then evaporate and crystallize them in a 60℃ water bath to obtain a precursor mixture.

[0075] (2) The precursor mixture was transferred to a covered alumina crucible, placed in a muffle furnace, heated to 500°C at a heating rate of 5°C / min, calcined in air atmosphere for 4 hours, and then naturally cooled to room temperature to obtain sulfur-doped carbon nitride precursor, denoted as S-CN-21.

[0076] (3) Take 1.0 g of S-CN-21 and place it in a tube furnace. First, purge the air with nitrogen for 30 minutes, then switch to 10 vol% ammonia (flow rate 100 mL / min), raise the temperature to 500℃ at 5℃ / min, and hold for 1 hour to allow the sulfur-doped carbon nitride precursor to undergo heat treatment in an ammonia atmosphere, introducing nitrogen vacancy defects, and then cool naturally to room temperature.

[0077] (4) Grind the sample after the reaction in step (3) to obtain a carbon nitride photothermal synergistic catalyst co-modified by sulfur doping and nitrogen vacancies, denoted as 10%-V. N -S-CN-21.

[0078] Comparative Example 1

[0079] (1) Take 10g of urea, place it in an agate mortar, grind it thoroughly, add 30mL of deionized water, dissolve it thoroughly, and then evaporate and crystallize it in a 60℃ water bath to obtain a precursor mixture.

[0080] (2) Transfer the precursor mixture to a covered alumina crucible, place it in a muffle furnace, heat it to 500°C at a heating rate of 5°C / min, calcine it in air atmosphere for 4 hours, and cool it naturally to room temperature. The resulting carbon nitride is denoted as g-CN.

[0081] Comparative Example 2

[0082] (1) Take 10g of thiourea, place it in an agate mortar, grind it thoroughly, add 30mL of deionized water, dissolve it thoroughly, and then evaporate and crystallize it in a 60℃ water bath to obtain a precursor mixture.

[0083] (2) Transfer the precursor mixture to a covered alumina crucible, place it in a muffle furnace, heat it to 500°C at a heating rate of 5°C / min, calcine it in air atmosphere for 4 hours, and cool it naturally to room temperature. The resulting carbon nitride is denoted as T-CN.

[0084] Comparative Example 3

[0085] The S-CN-21 prepared in Example 2 was used as the sample for Comparative Example 3, which was not subjected to ammonia post-treatment.

[0086] Comparative Example 4

[0087] Take the pure carbon nitride g-CN prepared in Comparative Example 1 and perform heat treatment (500℃, 1h) in an ammonia atmosphere according to step (3) of Example 1 to obtain carbon nitride doped only by nitrogen vacancies, denoted as V. N -g-CN.

[0088] Comparative Example 5

[0089] The pure carbon nitride T-CN prepared in Comparative Example 2 was heat-treated in an ammonia atmosphere (500℃, 1h) according to step (3) of Example 1 to obtain carbon nitride doped only by nitrogen vacancies, denoted as V. N -T-CN.

[0090] Example 8: Production of benzoic acid from polystyrene degradation

[0091] The catalysts prepared in Examples 1-3 and Comparative Examples 4-5 were used to catalytically convert polystyrene in order to investigate the optimal urea-thiourea ratio. Details are as follows:

[0092] Activity experiments were conducted in a 200 mL reactor. 60 mg of waste polystyrene plastic was crushed and placed in a stainless steel reactor with 30 mg of catalyst (polystyrene to catalyst mass ratio 1:0.5). 10 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280~2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 180℃, and the reaction was carried out for 6 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. x Yield, catalyst and unreacted residue were separated by filtration, and the filtrate was analyzed by high-performance liquid chromatography (HPLC) to calculate benzoic acid selectivity (based on the molar carbon content of the product). Results are shown in Table 1. Figure 1 As shown.

[0093] The results are expressed using the conversion rate of polystyrene and the selectivity of benzoic acid, and the calculation method is shown in the following formula:

[0094]

[0095]

[0096] Catalyst V N -S-CN-21、g-CN、V N The XPS and EPR spectra of -T-CN are as follows: Figure 2 and Figure 3 As shown in the figure, the catalytic conversion effect of different catalysts on polystyrene under the conditions of Example 8 is illustrated in the figure. Figure 1 As shown above, the results indicate that:

[0097] (1) The synergistic effect of sulfur doping and nitrogen vacancies has a significant impact on catalytic performance, but the ratio of urea to thiourea is crucial. When the mass ratio of urea to thiourea is 2:1 (Example 2), the catalyst exhibits the highest polystyrene conversion rate while maintaining high benzoic acid selectivity, indicating that the synergistic effect of sulfur doping and nitrogen vacancies is optimal at this ratio.

[0098] (2) Sulfur doping occupies the N site and forms CS bond.

[0099] Table 1. Comparison of the performance of different catalysts for the photothermal catalytic conversion of polystyrene

[0100]

[0101] Example 9

[0102] The catalysts prepared in Examples 2 and 4-5 were used to catalytically convert polystyrene to explore the optimal calcination temperature, as detailed below:

[0103] Activity experiments were conducted in a 200 mL reactor. 60 mg of waste polystyrene plastic was crushed and placed in a stainless steel reactor with 30 mg of catalyst (polystyrene to catalyst mass ratio 1:0.5). 10 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280~2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 180℃, and the reaction was carried out for 6 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. x Yield, catalyst and unreacted residue were separated by filtration, and the filtrate was analyzed by high-performance liquid chromatography (HPLC) to calculate benzoic acid selectivity (based on the molar carbon content of the product). Results are shown in Table 2 and... Figure 4 As shown.

[0104] Table 2 Comparison of the performance of catalysts for the photothermal catalytic conversion of polystyrene at different calcination temperatures

[0105]

[0106] The specific reasons are analyzed as follows:

[0107] (1) The calcination temperature of 450℃ (Example 4) may be too low, resulting in incomplete thermal polycondensation of the precursor, which fails to form the optimal sulfur-doped carbon nitride structure and has insufficient active sites, thus resulting in a low conversion rate.

[0108] (2) 500℃ (Example 2) is the ideal temperature for forming a highly active sulfur-doped carbon nitride crystal structure. The sulfur element was successfully doped and maintained a good framework structure, which is beneficial for introducing an appropriate amount of nitrogen vacancies during subsequent ammonia treatment, thereby producing the best synergistic catalytic effect.

[0109] (3) The calcination temperature of 550℃ (Example 5) is too high, which may lead to excessive polymerization of carbon nitride materials or even thermal decomposition, destroying their ordered structure, or causing excessive loss of sulfur elements, thereby reducing catalytic activity (conversion rate) and selectivity.

[0110] Example 10

[0111] The catalysts prepared in Examples 2 and 6-7 were used to catalyze the conversion of polystyrene to investigate the optimal ammonia concentration, as detailed below:

[0112] Activity experiments were conducted in a 200 mL reactor. 60 mg of waste polystyrene plastic was crushed and placed in a stainless steel reactor with 30 mg of catalyst (polystyrene to catalyst mass ratio 1:0.5). 10 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280~2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 180℃, and the reaction was carried out for 6 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. x Yield, catalyst and unreacted residue were separated by filtration, and the filtrate was analyzed by high-performance liquid chromatography (HPLC) to calculate benzoic acid selectivity (based on the molar carbon content of the product). Results are shown in Table 3 and... Figure 5 As shown.

[0113] Table 3. Comparison of the performance of nitrogen vacancies introduced by different ammonia concentrations on the photothermal catalytic conversion of polystyrene.

[0114]

[0115] The results show that higher ammonia concentrations result in stronger etching effects, introducing more nitrogen vacancy defects. These nitrogen vacancies can serve as active sites, effectively regulating the electronic structure and surface properties of the catalyst, thereby significantly improving catalytic activity (conversion rate).

[0116] Example 11

[0117] The catalyst obtained in Example 2 was used to catalytically convert polystyrene, and the catalytic conversion performance of polystyrene under different temperature conditions was tested, as follows:

[0118] Activity experiments were conducted in a 200 mL reactor. 60 mg of waste polystyrene plastic was crushed and placed in a stainless steel reactor with 30 mg of catalyst (polystyrene to catalyst mass ratio 1:0.5). 10 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280~2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 90~210℃, and the reaction was carried out for 6 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. x Yield, filtration to separate catalyst and unreacted residue, analysis of filtrate by high-performance liquid chromatography (HPLC), and calculation of benzoic acid selectivity (based on product carbon molarity).

[0119] Depend on Figure 6 It is known that the catalyst of the present invention has a good effect on the catalytic conversion of polystyrene at temperatures above 150 degrees Celsius. This is because when the temperature reaches 150 degrees Celsius, polystyrene can fully swell in acetonitrile solvent, which is conducive to the breaking of chemical bonds.

[0120] Example 12

[0121] The catalyst obtained in Example 2 was used to catalytically convert polystyrene, and its catalytic conversion performance on polystyrene at different time points was tested, as follows:

[0122] Activity experiments were conducted in a 200 mL reactor. 60 mg of waste polystyrene plastic was crushed and placed in a stainless steel reactor with 30 mg of catalyst (polystyrene to catalyst mass ratio 1:0.5). 10 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280~2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 180℃, and the reaction was carried out for 1-24 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. x Yield, filtration to separate catalyst and unreacted residue, analysis of filtrate by high-performance liquid chromatography (HPLC), and calculation of benzoic acid selectivity (based on product carbon molarity).

[0123] Depend on Figure 7 It is known that the catalyst of the present invention reaches optimal selectivity at 6 hours. With the extension of reaction time, the active sites of the catalyst are deactivated, and the generated benzoic acid is over-oxidized to CO. x .

[0124] Example 13

[0125] The catalyst prepared in Example 2 was used to catalytically convert polystyrene, and the catalytic conversion performance of polystyrene with different PS:catalyst ratios was tested, as follows:

[0126] Activity experiments were conducted in a 200 mL reactor. 60 mg of waste general-purpose polystyrene plastic was crushed and placed in a stainless steel reactor with 6 mg, 18 mg, 30 mg, 60 mg, and 120 mg of catalyst (catalyst to polystyrene mass ratio 1:0.1~2). 10 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280~2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 180℃, and the reaction was carried out for 6 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. x Yield, filtration to separate catalyst and unreacted residue, analysis of filtrate by high-performance liquid chromatography (HPLC), and calculation of benzoic acid selectivity (based on product carbon molarity).

[0127] Depend on Figure 8 It is known that the optimal polystyrene:catalyst ratio in this invention is 1:0.5.

[0128] Example 14

[0129] The catalyst obtained in Example 2 was used for the catalytic conversion of polystyrene. The catalytic conversion performance of the recycled catalyst for polystyrene was tested, as follows:

[0130] Activity experiments were conducted in a 200 mL reactor. 60 mg of waste general-purpose polystyrene plastic was crushed and placed in a stainless steel reactor along with 30 mg of recycled catalyst (catalyst to polystyrene mass ratio 1:0.5) recycled 1-6 times. 10 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280-2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 180℃, and the reaction was carried out for 6 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. x Yield, filtration to separate catalyst and unreacted residue, analysis of filtrate by high-performance liquid chromatography (HPLC), and calculation of benzoic acid selectivity (based on product carbon molarity).

[0131] Depend on Figure 9It is evident that the catalyst of the present invention retains good catalytic activity after washing and drying, demonstrating high efficiency and versatility for a variety of practical polystyrene wastes.

[0132] Example 15

[0133] The catalyst obtained in Example 2 was used to catalytically convert polystyrene, and the catalytic conversion performance of the catalyst for polystyrene was tested, as follows:

[0134] Activity experiments were conducted in a 200 mL reactor. 600 mg, 900 mg, and 1200 mg of waste polystyrene plastic were pulverized and then mixed with 300 mg, 450 mg, and 600 mg of catalyst (catalyst to polystyrene mass ratio 1:0.5) respectively in a stainless steel reactor. 100 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280~2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 180℃, and the reaction was carried out for 6 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. x Yield, filtration to separate catalyst and unreacted residue, analysis of filtrate by high-performance liquid chromatography (HPLC), and calculation of benzoic acid selectivity (based on product carbon molarity).

[0135] Depend on Figure 10 It is known that the catalyst of the present invention can achieve efficient catalytic conversion of gram-level waste polystyrene.

[0136] Example 16

[0137] The catalyst obtained in Example 2 was used for the catalytic conversion of polystyrene. The catalytic conversion performance of the catalyst on actual polystyrene waste plastic was tested, as follows:

[0138] Activity experiments were conducted in a 200 mL reactor. 60 mg of waste general-purpose polystyrene plastic, polystyrene foam board, and a polystyrene plastic cup lid were crushed and placed in a stainless steel reactor with 30 mg of catalyst (polystyrene to catalyst mass ratio 1:0.5). 10 mL of acetonitrile was added as a solvent. The reaction atmosphere was oxygen. The reactor was equipped with a 300 W xenon lamp (simulating sunlight, light source wavelength 280~2500 nm, light intensity 500 mW / cm²). 2 The reaction was carried out using a heating and temperature control system. The reaction temperature was controlled at 180℃, and the reaction was carried out for 6 hours under normal pressure. After the reaction was completed, the mixture was cooled to room temperature, and the gaseous products of polystyrene oxidation were detected by gas chromatography (GC) to calculate CO. xYield, filtration to separate catalyst and unreacted residue, analysis of filtrate by high-performance liquid chromatography (HPLC), and calculation of benzoic acid selectivity (based on product carbon molarity).

[0139] Depend on Figure 11 It is evident that the catalyst of this invention can maintain good conversion rate and benzoic acid selectivity without significant decrease when facing different polystyrene products, demonstrating its excellent versatility and providing reliable technical support for the resource-based conversion of polystyrene plastics.

[0140] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing benzoic acid by photothermal synergistic catalyst degradation of polystyrene, characterized in that, Includes the following steps: A reaction system comprising polystyrene, a photothermal synergistic catalyst, and a solvent was constructed. A depolymerization reaction was carried out under light and heating conditions at a temperature of 150–210 °C for 1–24 h to prepare benzoic acid. The mass ratio of polystyrene to the photothermal synergistic catalyst was 1:0.5–2. The solvent included acetonitrile, acetone, or water. The photothermal synergistic catalyst is sulfur-doped graphitic carbon nitride rich in nitrogen vacancies, which is prepared by the following method: urea and thiourea are mixed and dissolved in a mass ratio of 0.5~5:1, and then evaporated and crystallized to obtain a precursor mixture. The precursor mixture is heated and calcined in an air atmosphere to obtain a sulfur-doped carbon nitride precursor. The sulfur-doped carbon nitride precursor is heat-treated in an ammonia atmosphere to introduce nitrogen vacancy defects, thereby obtaining the photothermal synergistic catalyst. The precursor mixture was calcined in air at a temperature of 450-550℃ for 2-4 h. The sulfur-doped carbon nitride precursor was heat-treated in an ammonia atmosphere at a temperature of 450-550℃ for 1-4 h with an ammonia volume concentration of 10-80 vol.

2. The method for producing benzoic acid by photothermal synergistic catalyst degradation of polystyrene according to claim 1, characterized in that, The illumination conditions are: light source wavelength 280~2500 nm, light intensity 500~1000 mW / cm². 2 .

3. The method for producing benzoic acid by photothermal synergistic catalyst degradation of polystyrene according to claim 1, characterized in that, The depolymerization reaction is carried out in an oxidizing atmosphere.

4. The application of the photothermal synergistic catalyst degradation method for producing benzoic acid from polystyrene according to any one of claims 1-3 in the treatment of waste polystyrene.

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