A TiO2 / g-C3N4 S-type heterojunction photocatalyst for antibiotic degradation, its preparation method and application

Abstract

The application provides a TiO2 / g-C3N4 S-type heterojunction photocatalyst with a close interface, which is constructed based on a one-step in-situ thermal polymerization strategy and is used for deep purification of antibiotic wastewater under visible light driving. In the application, anatase TiO2 nanoparticles and melamine precursors are ground and uniformly mixed at a mass ratio of 4:9, calcined at 550 DEG C for 2h for in-situ thermal polymerization, a chemical bonding close heterojunction interface is constructed, and the defects of a large charge transfer resistance of a traditional physical mixing interface are solved. The composite material has a developed mesoporous structure, and the internal strong electric field and S-type charge transfer mechanism significantly improve the photocatalytic performance. Tetracycline hydrochloride can be completely degraded within 70 min under visible light, the environmental interference resistance is strong, the cycle stability is excellent, and the degradation rate is still more than 83% after 4 cycles. The method is simple in process, conforms to atomic economy, and provides a new scheme for the development of efficient heterojunction photocatalytic materials.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photocatalysis and environmental remediation technology, specifically relating to a TiO2 / g-C3N4 S-type heterojunction composite material with a tight interface constructed by a one-step in-situ thermal polymerization strategy, and the application of this material in the deep purification of antibiotic wastewater under visible light driving. Background Technology

[0002] With the acceleration of global industrialization, the residues of antibiotics (such as tetracycline hydrochloride TC-HCl) in water bodies have led to serious problems of antibiotic resistance and persistent toxicity. Developing efficient and green photocatalytic degradation technologies is therefore crucial.

[0003] Titanium dioxide (TiO2) possesses advantages such as high stability, non-toxicity, and low cost; however, its inherent 3.2 eV wide bandgap limits its absorption of visible light, and photogenerated carrier recombination is extremely rapid. While graphitic carbon nitride (g-C3N4) exhibits visible light response, it is limited by its small specific surface area and slow carrier migration rate. Constructing s-type heterojunctions is considered an effective solution to overcome the trade-off between charge separation efficiency and redox capability.

[0004] However, existing heterojunctions obtained through physical mixing exhibit loose interfacial contacts (point contacts), resulting in significant obstacles to interfacial charge transfer. Methods aiming for chemically bonded interfaces often rely on complex multi-step hydrothermal synthesis, high-temperature calcification, or noble metal deposition, which are energy-intensive and difficult to scale up. Therefore, developing a highly efficient S-type heterojunction that conforms to the principle of "atom economy," is simple to synthesize, and exhibits tight interfacial coupling is of great significance. Summary of the Invention

[0005] This invention provides a highly efficient TiO2 / g-C3N4 photocatalyst based on a "one-step in-situ thermal polymerization self-assembly" strategy.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a TiO2 / g-C3N4 S-type heterojunction photocatalyst includes the following steps:

[0008] (1) Premixing and grinding: The melamine precursor and anatase TiO2 nanoparticles were mixed at a mass ratio of 4:9 and then ground thoroughly to ensure uniform component distribution;

[0009] (2) In-situ growth: The mixed powder is placed in a crucible and calcined in an air atmosphere to allow g-C3N4 molecules to condense in situ on the surface of the TiO2 lattice;

[0010] (3) Obtaining the finished product: After the reaction is completed, the product is naturally cooled to obtain a TiO2 / g-C3N4 composite material with a tight heterojunction interface.

[0011] The calcination temperature in step (2) is 550 degrees Celsius, and the calcination time is 2 hours.

[0012] The present invention describes the application of the photocatalyst for the degradation of organic pollutants under visible light irradiation, with the target pollutants being methylene blue (MB) or tetracycline hydrochloride (TC-HCl).

[0013] The beneficial effects of this invention are:

[0014] Interface charge transfer channel optimization: Compared with physical stacking, the in-situ growth strategy constructs a low-resistance charge transfer path.

[0015] Significantly enhanced photoactivity: The rate constant for the degradation of TC-HCl by the optimized composite material is 21 times that of pure TiO2.

[0016] Synergistic retention of strong redox sites: The S-type transfer mechanism retains strong reducing electrons in the g-C3N4 conduction band for the generation of superoxide radicals, while retaining strong oxidizing holes in the TiO2 valence band for pollutant degradation.

[0017] Strong environmental adaptability: The material can maintain high degradation efficiency in a wide pH range (3-11) and in environments with multiple coexisting anions. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation process and degradation mechanism of the present invention.

[0019] Figure 2 The microstructure and physical properties of the material are shown: (a) the elemental distribution map verifies the uniform integration of Ti, O, C and N; (b) the nitrogen adsorption curve shows a typical mesoporous structure; and (c) the thermogravimetric curve analyzes the component ratio and thermal stability of the material.

[0020] Figure 3 The material's phase and chemical state are shown: (a) XRD confirms the retention of the anatase phase; (cf) High-resolution XPS spectra reveal a negative shift in the Ti2p binding energy, confirming the spontaneous transfer of electrons from g-C3N4 to TiO2.

[0021] Figure 4 The photocatalytic degradation performance of TC-HCl was demonstrated: (a) degradation curves at different calcination times; (b) first-order kinetic fitting, showing the rate constant k = 0.04579 min for the 2-hour sample. -1 .

[0022] Figure 5Factors affecting degradation efficiency include: (a) catalyst dosage; (b) initial pollutant concentration; and (c) solution pH.

[0023] Figure 6 The interference resistance and cycling stability were demonstrated: (a) the effect of anions; (b) the performance retention after four cycles.

[0024] Figure 7 The photocatalytic mechanism was revealed: (a) Tauc plots determined the band gap; (b) free radical capture experiments; (c) schematic diagram of the S-type charge transfer path. Detailed Implementation

[0025] Example 1: Optimal Synthesis Route of the Material 1000 mg of anatase TiO2 nanoparticles were mixed with 444 mg of melamine (i.e., a 4:9 mass ratio) and ground in a mortar for 10 minutes. The mixed powder was placed in a covered crucible and placed in a muffle furnace, where the temperature was programmed to rise to 550 degrees Celsius. This temperature was maintained for 2 hours, followed by natural cooling with the furnace.

[0026] Analysis: If the calcination time is insufficient, the polycondensation reaction will be incomplete; if it exceeds 2 hours, according to thermogravimetric analysis (…), the reaction will be incomplete. Figure 2 c) The g-C3N4 skeleton undergoes thermal decomposition, leading to the loss of active substances.

[0027] Example 2: Characterization of physicochemical properties

[0028] Specific surface area: The measured specific surface area of ​​the sample was 82.00 m². 2 / g -1 The total pore volume is 0.328 cm³. 3 / g -1 The characteristic pore size is 20.89 nm. This well-developed mesoporous structure is beneficial for pollutant enrichment and material transport.

[0029] XPS analysis revealed that the binding energy of Ti2p in the composite material decreased by approximately 0.32 eV compared to pure TiO2. This displacement indicates the presence of a strong internal electric field (IEF) at the interface, pointing from g-C3N4 towards TiO2, a typical electron distribution characteristic of the S-mode mechanism.

[0030] Example 3: Degradation Experiment and Kinetics. A 20 mg / L TC-HCl solution was prepared, and the catalyst dosage was set to 400 mg / L. After stirring in the dark for 30 minutes to reach equilibrium, a 500W xenon lamp (visible light band) was turned on.

[0031] Results: TC-HCl achieved 100% degradation within 70 minutes. The fitted kinetic constant was 0.04579 min. -1In contrast, the degradation rate of pure TiO2 is less than 10%.

[0032] Example 4: Environmental Adaptability and Stability Test

[0033] pH effect: The degradation rate reached its highest level of 95.64% at a pH of 9. This is because the alkaline environment deprotonates the catalyst surface, making it negatively charged, which enhances the electrostatic attraction to cationic pollutants.

[0034] Interference experiment: Adding NO3 - SO4 2- Cl - It has a slight inhibitory effect on efficiency, while HCO3 - The inhibition was most significant (decreased to 55.3%).

[0035] Recycling: After four reuses, the material retained 83.88% of its degradation activity. The performance decline was mainly attributed to mass loss and surface contamination during catalyst recovery.

[0036] Example 5: Mechanism Verification. Free radical capture experiments revealed that the degradation rate significantly decreased to 18.01% after the addition of ascorbic acid, confirming the effect of O2. - It is the main active oxide species. This verifies the S-type transfer pathway: lower-energy electrons in the TiO2 conduction band recombine with lower-energy holes in the g-C3N4 valence band at the interface, thereby allowing the electrons with strong reducing power (potential -1.12 V) in the g-C3N4 conduction band to be retained, thus generating a large amount of O2. - .

Claims

1. A TiO2 / g-C3N4 S-scheme heterojunction photocatalyst for degrading antibiotics, characterized in that: The catalyst is composed of anatase TiO2 nanoparticles and graphitic carbon nitride (g-C3N4); the g-C3N4 is grown in situ on the surface of the TiO2 lattice, and the two form a tight heterojunction interface through chemical bonding; this tight interface constructs an internal electric field (IEF) from TiO2 to g-C3N4, guiding photogenerated carriers to undergo S-mode transfer.

2. The TiO2 / g-C3N4S heterojunction photocatalyst according to claim 1, characterized in that: The composite material has a mesoporous structure and a specific surface area of ​​82.00 m². 2 / g, total pore volume is 0.328 cm³ 3 / g; its pore size distribution curve has a characteristic peak at 20.89 nm.

3. The TiO2 / g-C3N4 S-type heterojunction photocatalyst according to claim 1, characterized in that: In X-ray photoelectron spectroscopy (XPS), the binding energy of Ti2p in this composite material shifts by about 0.32 eV towards a lower binding energy direction compared to pure TiO2; this indicates that electrons spontaneously transfer from g-C3N4 to TiO2, verifying the electron distribution characteristics of the S-type heterojunction.

4. A method for preparing the TiO2 / g-C3N4 S-type heterojunction photocatalyst according to claim 1, characterized in that... Includes the following steps: (1) Mixing and grinding: Melamine precursor and anatase TiO2 nanoparticles were mixed at a mass ratio of 4:9 and then ground thoroughly to achieve uniform distribution. (2) In-situ heat treatment: The ground mixed powder is placed in a crucible and calcined in a muffle furnace under an air atmosphere; (3) Cooling and collection: After the reaction is completed, the mixture is naturally cooled to room temperature and then in-situ polycondensed on the surface of TiO2 by g-C3N4 to obtain a heterojunction composite material with a tight interface.

5. The preparation method according to claim 4, characterized in that: The calcination temperature in step (2) is 550℃ and the calcination time is 2 hours.

6. The preparation method according to claim 4, characterized in that: The formation rate of g-C3N4 and the stability of TiO2 are balanced by a calcination time of 2 hours to prevent the thermal decomposition of g-C3N4 at high temperatures for a long time.

7. The application of the TiO2 / g-C3N4S heterojunction photocatalyst according to claim 1 in environmental remediation, characterized in that: The catalyst is added to a water body containing organic pollutants and photocatalytically degraded under visible light irradiation; the organic pollutants include tetracycline hydrochloride (TC-HCl) or methylene blue (MB).

8. The application according to claim 7, characterized in that: The optimal concentration of the catalyst for degrading TC-HCl is 400 mg / L; under visible light, the catalyst achieves 100% removal of TC-HCl within 70 minutes.

9. The application according to claim 7, characterized in that: When degrading methylene blue (MB), the pH of the water is adjusted to 9, and the negative charge on the catalyst surface is used to enhance the electrostatic attraction to the cationic dye, thereby increasing the degradation rate.

10. The application according to claim 7, characterized in that: The catalyst contains NO3 - SO4 2- Cl - and HCO3 - It exhibits good stability in industrial wastewater; and after four cycles of use, its degradation efficiency can still be maintained at over 83%.

Images