Enhanced photocatalytic reduction of Cr(VI) by combined magnetic TiO₂-based NFs and ammonium oxalate hole scavengers

Heavy metal pollution of wastewater with coexisting organic contaminants has become a serious threat to human survival and development. In particular, hexavalent chromium, which is released into industrial wastewater, is both toxic and carcinogenic. TiO₂ photocatalysts have attracted much attention due to their potential photodegradation and photoreduction abilities. Though TiO₂ demonstrates high photocatalytic performance, it is a difficult material to recycle after the photocatalytic reaction. Considering the secondary pollution caused by the photocatalysts, in this study we prepared Ag/Fe₃ O₄/TiO₂ nanofibers (NFs) that could be magnetically separated using hydrothermal synthesis, which was considered a benign and effective resolution. For the photocatalytic test, the removal of Cr(VI) was carried out by Ag/Fe₃ O₄/TiO₂ nanofibers combined with ammonium oxalate (AO). AO acted as a hole scavenger to enhance the electron-hole separation ability, thereby dramatically enhancing the photoreduction efficiency of Cr(VI). The reaction rate constant for Ag/Fe₃ O₄/TiO₂ NFs in the binary system reached 0.260 min⁻¹, 6.95 times of that of Ag/Fe₃ O₄/TiO₂ NFs in a single system (0.038 min⁻¹). The optimized Ag/Fe₃ O₄/TiO₂ NFs exhibited high efficiency and maintained their photoreduction efficiency at 90% with a recyclability of 87% after five cycles. Hence, taking into account the high magnetic separation behavior, Ag/Fe₃ O₄/TiO₂ NFs with a high recycling capability are a potential photocatalyst for wastewater treatment.