Visible-light-driven photoelectrocatalytic degradation of p-chloronitrobenzene by BiOBr/TiO2 nanotube arrays photoelectrodes: Mechanisms, degradation pathway and DFT calculation

The BiOBr modified TiO2 nanotube arrays (BiOBr/TNAs) photoelectrodes were prepared for photoelectrocatalytic (PEC) degradation of p-chloronitrobenzene (p-CNB) under visible light irradiation. The surface structure analysis demonstrated that BiOBr nanoflakes were successfully deposited on the TNAs surface to form tight heterojunction. The BiOBr/TNAs photoelectrodes showed higher PEC degradation efficiency for p-CNB (71.96%) than that by bare TNAs (41.52%) owing to the improved visible-light absorption and reduced charges recombination. The hydroxyl radical and photogenerated holes were the main active species responsible for degradation, dechlorination and mineralization of p-CNB. The coexistence of dissolved anions and humic acid could decline p-CNB removal due to the radical scavengers or competition for active sites. The density functional theory (DFT) calculations indicated that the matched energy bands between BiOBr and TiO2 formed an internal electric field at the heterojunction interface, which promoted the charges migration and separation. The degradation mechanism and pathways of p-CNB were proposed based on the radical scavenging experiments, GC MS spectra and theoretical calculations. The toxicity of identified intermediates from p-CNB was declined after PEC degradation.