Synthesis of SnO2QDs-g-C3N4/C and Its Photocatalytic Degradation of Tetracycline

Antibiotics have been widely used in clinical medicine，animal husbandry，and aquaculture since antibiotics were discovered. However，the abuse of antibiotics and the incomplete absorption of organisms have brought great harm and potential threat to organisms in the environment. Therefore，the technology of removing residual antibiotics has drawn interesting attention. Among them，Photocatalytic degradation technology based on solar energy was designed to remove residual antibiotics from the environment. Catalyst materials play an important role in photocatalytic degradation technology，such as graphene，nano-diamond，carbon nano tube. Among them，graphite phase carbon nitride（g-C3N4）has attracted extensive attention due to its unique crystal structure，band structure，easy preparation，environmental protection，and low cost. However，the pure phase g-C3N4 has some disadvantages，such as low absorption of visible light，high recombination rate of photo-generated carriers，and low specific surface area reactive active sites，which seriously limited its application. In order to solve the problems，biological stems can be used as templates to adjust the morphology and size of g-C3N4 because biological stems have the advantages of uneven surface structure，high morphology similarity，low cost，and easy access. Meanwhile，metal oxide quantum could be adopted to g-C3N4 to adjust the energy band structure of semiconductors and reduce photo-carrier recombination through the quantum size effect，high surface activity，and special energy band structure. In this work，SnO2QDs/ACN was designed to be synthesized with SnCl2·2H2O as Sn source and g-C3N4/C（ACN）material as a carrier by simple hydrothermal method. X-ray diffraction（XRD）was used to detect the crystal structure and chemical composition of SnO2QDs/ACN composites，and the microscopic morphology of SnO2QDs/ACN composites was observed by scanning electron microscopy（SEM）and transmission electron microscopy（TEM）. The results of XRD，SEM，and TEM showed that SnO2QDs/ACN composites had been successfully synthesized and the biocarbon skeleton structure remained completely，while the lattice of SnO2QDs was anchored evenly on the carbon surface. Fluorescence spectrum test（PL）results showed that the emission peak intensity of 7%SnO2QDs/ACN-2 significantly decreased with the introduction of SnO2QDs，which proved that the carrier separation efficiency of SnO2QDs/ACN-2 further improved. The results of nitrogen adsorption-desorption test（BET）showed that 7%SnO2QDs/ACN-2 had high specific surface area，rich mesoporous structure and large specific surface area，resulting in increasing the contact area between the composites and the degradants to provide more active sites，and improve the photocatalytic activity of the materials. Based on the optical absorption theory，the band gap values of ACN-2（1.27 eV）and 7%SnO2QDs/ACN-2（1.50 eV）could be estimated by using Kubelka-Munk formula，which indicated the band gap of the composites was affected by with the quantum size effect of SnO2QDs. However，the band gap values of 7%SnO2QDs/ACN-2 were still smaller than that of g-C3N4. The results showed that the electron transition of 7%SnO2QDs/ACN-2 required low energy. Therefore，it was easy to produce photogenerated charge carriers under visible light irradiation under the action.，the photogenerated electron-hole pair was not easy to recombine and obtained a longer life to improve efficient photocatalytic ability. To further reveal the mechanism of the photocatalytic reaction，the role of each free radical in the catalytic reaction was studied by adding quenching agent. The results showed that h+ and·OH did not participate in the reaction and·O2- played a decisive role in the reaction. When the semiconductor exposed to visible light irradiation，the electrons were excited from valance band to the conduction band of g-C3N4 and then the electrons of the conduction band of g-C3N4 transferred to the conduction band of SnO2QDs. The conduction potential of SnO2QDs（-0.38 eV）and g-C3N4（-1.37 eV）was higher than that of E（O2/O2-），the resulting electrons could easily move to the surface of the material through highly conductive biological carbon. Where they could react with O2 to form·O2-. Through the analysis of photocatalytic degradation efficiency and reaction kinetics of SnO2QDs/ACN-2 for tetracycline within 30 min，7%SnO2QDs/ACN-2 showed the highest degradation efficiency and could degrade 56.5% tetracycline，which was 2.87 times that of g-C3N4 and 1.78 times that of ACN-2. The results showed that SnO2QDs/ACN-2 with good photocatalytic degradation effect and stability had been successfully constructed，which was a potential candidate material for tetracycline purification. © 2024 Editorial Office of Chinese Journal of Rare Metals. All rights reserved.