Novel La3+/Sm3+ co-doped Bi5O7I with efficient visible-light photocatalytic activity for advanced treatment of wastewater: Internal mechanism, TC degradation pathway, and toxicity analysis.

Controlling semiconductor photocatalysts by doping rare-earth ions is an effective strategy to improve photocatalytic performance. Simple solvothermal and calcination methods were used to prepare La3+ and Sm3+ modified Bi5O7I nanomaterials. Some characterizations such as XRD, XPS, SEM, TEM, UV-vis, etc. were carried out to explore its structural composition and photoelectrochemical properties. The photocatalytic activity was investigated by simulating the degradation of TC and RhB under visible-light irradiation. The degradation results showed that the photocatalytic efficiency of 4S4L-Bi5O7I was the best among the samples with the 100% degradation rate of TC (Tetracycline hydrochloride) and 93% of RhB (Rhodamine B). The capture experiment and ESR test proved that the active substances that play a role in the photocatalytic degradation of pollutants were ·O2-, 1O2 and h+, and on this basis, the possible degradation mechanism was proposed. The final results showed that La/Sm co-doping expanded the light absorption range of Bi5O7I and improved the charge separation efficiency and the specific surface area. Besides, the surface defects were formed on the surface of Bi5O7I due to ion-doping, which could catch e- to promote the separation and transfer of carriers and improve the photocatalytic activity. LC-MS was used to analyze the possible degradation pathways of TC. And the toxicity of TC was also analyzed via T.E.S.T and Toxtree. The results showed comprehensive toxicity of TC was decreased by 4S4L-Bi5O7I so that the overall water pollution was reduced. This work can provide a reference for the subsequent development of bismuth-based photocatalysts.

Construction of Z-scheme Ag-AgBr/Bi2O2CO3/CNT heterojunctions with remarkable photocatalytic performance using carbon nanotubes as efficient electronic mediators.

It is a useful strategy to use a solid electronic mediator with good conductivity to assist the separation of semiconductor photo-induced electron-hole pairs and the redox of semiconductor materials. In order to construct a photocatalyst for more efficient photocatalytic degradation of antibiotics, a simple hydrothermal and precipitation method was used to construct the Ag-AgBr/Bi2O2CO3/CNT Z-scheme heterojunction by using carbon nanotubes (CNTs) as electronic mediators. Compared with the pristine AgBr, Bi2O2CO3, Bi2O2CO3/CNT, the 30%Ag-AgBr/Bi2O2CO3/CNT photocatalyst has better photocatalytic activity under visible light irradiation, showing the best degradation ability to tetracycline (TC). Meanwhile, the photocatalytic properties of 30%Ag-AgBr/Bi2O2CO3/CNT in different pH and inorganic ions were studied. Finally, the degradation pathway and catalytic mechanism of 30%Ag-AgBr/Bi2O2CO3/CNT photocatalytic degradation of TC were also argued. The construction of the Z-scheme electron transport pathway, in which CNTs were used as electronic mediators, and the SPR effect of Ag and Bi metal, which enable the effective separation and transfer of photo-generated electron-hole pairs, are responsible for the significant improvement in photocatalytic performance. It opens up new possibilities for designing and developing high-efficiency photocatalysts with CNTs as the electronic mediator.