Core/shell FeVO₄@BiOCl heterojunction as a durable heterogeneous Fenton catalyst for the efficient sonophotocatalytic degradation of p-nitrophenol

In this study, a FeVO₄@BiOCl p–n heterojunction with n-type porous FeVO₄ nanorods as the core and p-type flower-like BiOCl nanostructures as the shell was successfully prepared by a facile hydrothermal method. The novel heterostructure was investigated as a durable heterogeneous Fenton catalyst for ultrasonic irradiation (US), ultraviolet irradiation (UV) and coupling irradiation systems (US/UV). Characterization of FeVO₄@BiOCl core shell heterojunction was conducted by XRD, SEM, EDS elemental mapping, TEM, HRTEM, SAED, FTIR, Raman, BET, PZC, XPS and DRS. Several different experimental parameters, including irradiation time, H₂O₂ concentration, catalyst amount, initial concentration, and pH value, were optimized. The stability and reusability of the prepared FeVO₄@BiOCl core shell heterojunction were evaluated as well. Mineralization experiments were carried out using the optimized parameters. The results showed that FeVO₄@BiOCl core shell heterojunction exhibits a superior sonophotocatalytic performance compared to either sonocatalysis or photocatalysis. Moreover, the formation of p-n core@shell nanostructures could significantly increase the pH_pzc, and to an excellent stability for the degradation of PNP after six cycles. The remarkable enhancement of the degradation performance of FeVO₄@BiOCl core shell heterojunction can be attributed to the unique structure and morphology with a matched energy band structure owing to the internal electric field induced by the p–n junction, a high transfer efficiency and the efficient separation of e⁻/h⁺ pairs, resulting in a huge number of reactive species for the degradation of PNP. A plausible mechanism over FeVO₄@BiOCl core shell heterojunction for the sonophotocatalytic degradation of PNP is proposed based on a special three-way, i.e. one as a photocatalyst and a two-way Fenton-like mechanism with the dissociation of H₂O₂. Active species trapping and calculated band gap energy were also discussed.