Study On Preparation Of Bi₂O₄-Based Composite Catalysts And Their Photocatalytic Performance For Tetracycline Degradation

Antibiotic contamination has become a serious threat to the ecosystem and human health worldwide,and its effective management has been the focus of much attention by researchers.Advanced oxidation technology mediated by semiconductor photocatalysts is considered one of the most effective methods to address antibiotic contamination because of its high efficiency and energy-saving advantages.In this study,we synthesized direct Z-scheme heterojunction 0D/1D Sn O₂/Bi₂O₄,S-scheme heterojunction 2D/1D Bi₂O₄@Sn S and double S-scheme CeO₂/g-C₃N₄/Bi₂O₄,etc.The fabricated samples were described by SEM,TEM,XRD,XPS,PL,ESR,etc.The photocatalytic properties of the composite photocatalysts were evaluated with tetracycline（TC）as the target contaminant,and the charge transfer mechanism and photocatalytic mechanism of the heterojunction interface were explored.The details,results and conclusions are as follows:（1）Combined zero-dimensional/one-dimensional（0D/1D）Sn O₂/Bi₂O₄photocatalysts were successfully prepared by a simple hydrothermal method.0D Sn O₂nanoparticles were uniformly dispersed and anchored on the surface of 1D Bi₂O₄micrometer rods,and the resulting Sn O₂/Bi₂O₄had a larger specific surface area and more reactive sites,and its photocatalytic activity was greatly improved.Among them,the 30 wt%Sn O₂/Bi₂O₄（30%mass ratio of Sn O₂to Bi₂O₄）composite exhibited the best photocatalytic degradation performance with a removal efficiency of 84.3%for TC（10 mg/L）over 120 min.The photocatalytic reaction rate constant k for 30 wt%Sn O₂/Bi₂O₄was 0.029017 min^-1.ESR tests showed that Superoxide radicals（·O₂^-）and holes（h⁺）were the major reactive radicals in the Sn O2/Bi2O4 photocatalytic reaction.Combining the energy band structures of Sn O₂and Bi₂O₄,it is inferred that the charge transfer between the interfaces of Sn O₂/Bi₂O₄heterojunction photocatalysts follows a Z-scheme mechanism.（2）A novel two-dimensional/one-dimensional（2D/1D）Bi₂O₄@Sn S S-scheme heterojunction composite photocatalyst with a layered core-shell structure was constructed by preparing Bi₂O₄micrometer rods by hydrothermal method and compounding them with Sn S nanosheets at different mass ratios.The results showed that the optimal ratio of 20wt%Bi₂O₄@Sn S（20%mass ratio of Sn S to Bi₂O₄）composite photocatalyst degraded TC with 91%efficiency in 120 min,and its reaction rate constants were 3.3 and 10.6 times higher than those of pure Bi₂O₄and Sn S,respectively.The significant improvement in photocatalytic degradation activity was attributed to two aspects.On the one hand,the formation of S-scheme heterojunctions between Bi₂O₄and Sn S not only significantly improves the separation of photogenerated carriers,but also retains electrons（e^-）with strong reducing ability and h⁺with strong oxidizing ability;on the other hand,the 2D/1D layered core-shell structure effectively expands the spectral area of the photocatalyst and broadens the visible light absorption range.In addition,environmental factors such as p H,typical inorganic cations,anions,and natural organic matter have less influence on TC photocatalytic degradation,indicating the potential application of the fabricated heterojunction photocatalysts in the treatment of antibiotic-contaminated water bodies.Combined with the ESR and in situ XPS characterization results,it was inferred that the charge transfer between the interfaces of this heterojunction catalyst followed an S-scheme pattern.（3）A novel CeO₂/g-C₃N₄/Bi₂O₄ternary heterojunction composite photocatalyst was constructed using a combination of high-temperature calcination and hydrothermal method.The catalyst exhibited higher photocatalytic reaction activity than the single component CeO₂,g-C₃N₄,Bi₂O₄,and the binary composite catalysts of g-C₃N₄/Bi₂O₄and CeO₂/g-C₃N₄.The best composite ratio of 30-CCNB ternary heterojunction photocatalysts showed a degradation efficiency of TC up to 94%within 120 min,and the reaction rate constants were 7.8,12.9,4.3,2.2,and 3.1 times higher than those of CeO₂,g-C₃N₄,Bi₂O₄,g-C₃N₄/Bi₂O₄and CeO₂/g-C₃N₄,respectively.The main reason for their excellent photocatalytic performance is the construction of two different electron transport channels and built-in electric fields,which facilitating the separation of photogenerated carriers effectively.In addition,environmental factors such as p H,typical inorganic cations,anions,and natural organic matter all have a small effect on the photocatalytic degradation of TC by CeO₂/g-C₃N₄/Bi₂O₄,indicating that the produced ternary heterojunction photocatalysts have equally bright application prospects in the treatment of antibiotic-contaminated water bodies.Combined with the in situ XPS and ESR characterization results,it is inferred that the interfacial charge transfer between CeO₂/g-C₃N₄/Bi₂O₄ternary heterojunctions follows the same S-scheme pattern（double S-scheme）.