Fabrication Of AgX（X=Br,I）-Modified TiO₂ Supported On Carbon Nanofibers And Their Visible-light Catalytic Performance

The application of titanium dioxide（TiO₂） in photocatalysis is hindered by the weak adsorption ability, easily reunion, reclamation difficulty, and the low light utility efficiency. In order to improve the light utility and photocatalytic efficiency of TiO₂, as well as the stability of TiO₂-based catalyst, research work related to doping modification and immobilized technology of TiO₂ has been done by many researchers. In this paper,carbon nanofibers（CNFs） prepared by the electrospinning followed by calcination treatment were used as carriers and they were coupled with both silver halide（AgX, X= Br, I） and TiO₂. Thus AgX-modified TiO₂ supported on CNFs were obtained. The as-prepared catalysts were applied in degrading different organic pollutants under visible light irradiation to examine their photocatalytic activity. We hope to obtain a novel visible-light responsive catalyst with excellent recyclable and renewable performance. The concrete study contents were shown below:First, Ag nanoparticles, which were prepared by in-situ reduction, were adhered to the surface of P25. Then Ag-P25 composites were absorbed by CNFs. By exposing Ag-P25/CNFs in iodine atmosphere, Ag-AgI-P25/CNFs could be fabricated by oxidizing most of Ag into AgI. The morphology, structure and composition of the as-prepared catalysts were examined by SEM, TEM, XRD and XPS, and so on. The photodegradation experiments showed that Ag-AgI（4 %）-P25/CNFs had higher activity than other catalysts.Secondly, TiO₂ nanoparticles were coated on the surface of CNFs by solvothermal synthesis, which were carbonized at 600 ℃. Ag+ was loaded on the surface of TiO₂/CNFs by physical adsorption. Being exposed in bromine or iodine atmosphere,Ag+-TiO₂/CNFs could be transformed into AgX-TiO₂/CNFs（X = Br, I）. The photocatalytic experiments showed that AgX（10 %）-TiO₂/CNFs had the highest activity among the as-prepared catalysts. However, the cycling performance of the as-prepared composites was very poor.Finally, Ag/PAN NFs were fabricated by electrospinning and in-situ reduction, and then they were carbonized at 350 ℃ to get Ag/CNFs. Similarly, TiO₂ nanoparticles were coated on the surface of Ag/CNFs by solvothermal synthesis. Subsequently,AgX-TiO₂/CNFs（X = Br, I） were fabricated by gas/solid oxidation in bromine or iodine atmosphere. The photocatalytic performance of the as-fabricated composites was evaluated by degrading methyl orange, methylene blue, phenol, acid red 18, and sodiumfluorescein under visible light irradiation. The experimental results showed that AgX-TiO₂/CNFs（X = Br, I） had an excellent photocatalytic performance. The same reduced activity could be observed in the cycling tests of AgX-TiO₂/CNFs. It was astonished to find that the deactivated catalysts could be regenerated by exposing them in bromine or iodine atmosphere for a second time.According to the results of trapping experiments, h+ and ?O₂ˉ were the main active species in degrading organic dyes under visible light irradiation. Xˉ could be oxidized into X0 by h+. Due to the strong oxidbillity of X0 and ?O₂ˉ, MO could be decomposed.Besides, the generated Ag0 could inhibit the further decomposition of AgX.In conclusion, combining doping modification with loading technology, a novel visible-light responsive one-dimensional AgX-TiO₂/CNFs（X = Br, I） composite catalysts could be fabricated. These composites could utilize solar energy effectively and they could be easily separated from reaction system without any losses, which provide a potential application in wastewater treatment and air cleaning.