Reduced graphene oxide-Fe3O4-TiO2 nanocomposite catalyst for the mineralization of herbicide dalapon by heterogeneous photoelectro-Fenton process

Fast degradation and complete mineralization of herbicide dalapon (DPN) as the target pollutant has been investigated for the first time by the heterogeneous photoelectro-Fenton (hPEF) process using a nitrogen doped reduced graphene oxide (NrGO) modified carbon felt (CF) cathode (NrGO@CF) and a ternary nanocomposite catalyst (TNC) based on reduced graphene oxide (rGO), Fe3O4, and TiO2 to maintain high yield generation of H2O2 and center dot OH. The effects of main variables, including the catalyst composition and amount, applied current, and initial pH of the solution, were investigated. The as-synthesized nanomaterials exhibit significant improvements thanks to their high specific surface area, increased H2O2 production, catalytic activity, and the possibility to work in a wide pH range. This system also promotes photoreduction and photooxidation reactions by increasing photon absorption. By combining highly conductive carbon materials and the photoexcited electrons from TiO2, redox cycling between - FeII and - FeIII was facilitated, thus improving the process performance. Catalytic stability measurements show that the use of a NrGO@CF cathode, an equimass rGO-Fe3O4-TiO2 TNC and boron doped diamond (BDD) anode trio resulted in the fast degradation and complete mineralization of DPN within 30 and 60 minutes, respectively, after five consecutive cycles under UV light irradiation, 500 mA current intensity, 0.1 g L- 1 catalyst concentration and pH 6 conditions. Moreover, intermediate products of DPN oxidation were identified. Therefore, this study highlights an efficient and stable cathode and catalyst duo for the removal of a short chain halogenated aliphatic herbicide from aqueous media.