Photoelectrocatalytic PNP removal using C3N4 nanosheets/α-Fe2O3 nanoarrays photoanode: Performance, mechanism and degradation pathways

The massive discharge of p-nitrophenol (PNP) has adversely affected ecosystem and human health. In this work, the g-C3N4 nanosheets was integrated with α-Fe2O3 nanorod arrays (C3N4 NSs/Fe2O3 NRAs) through simple in-situ hydrothermal and electrochemical deposition, and applied for the photoelectrocatalytic degradation of PNP. At the optimum experiment conditions at PNP initial concentration of 10 mg/L, pH value of 6.1, electrolyte concentration of 0.2 mol/L, and bias voltage of 1.5 V, the optimized photoanode displayed the highest PNP removal rate. This improvement was attributed to the synergistic effect between photocatalysis and electrocatalysis, a synergy factor of 1.6 was achieved during this C3N4 NSs/Fe2O3 NRAs photoelectrocatalytic system. The C3N4/Fe2O3 heterojunction and bias voltage facilitated the generation, separation and transfer of electron/hole pairs. The electrolysis also provided rich active species, hydroxyl radicals, etc., which cooperated with the reactive oxygen species derived from enhanced photocatalysis to achieve rapid pollutants decomposition. Based on the intermediates detection and analysis, two PNP degradation pathways, namely direct oxidation and reduction–oxidation path, were proposed, that matched well the existence form and transformation rule of inorganic nitrogen. The radical capture experiments demonstrated that electrons, hydroxyl radicals and holes were the main species responsible for PNP photoelectrocatalytic removal.