Facet-dependent photoactivity of Mn3O4/BiOCl for naproxen detoxication: Strengthening effect of Mn valence cycle

Utilizing photocatalysis to degrade pollution is emerging as a promising way to treat wastewater, but is challenged by low efficiency and scanty toxicity cognition. In this work, Mn3O4/BiOCl based crystal plane engineering systems are applied for naproxen (NPX) degradation, and Mn3O4/BiOCl010 displayed better degradation rate, which is 16 and 8 times than that of the Mn3O4/BiOCl001 and BiOCl010. According to the degradation pathway analysis and biological toxicity experiments, the toxicity of the degradation solution increased first and then decreased, which may be caused by the mineralization of NPX and more toxic intermediates. Affected by the distinct internal charge transfer directions of the two crystal planes of BiOCl, Mn3O4/BiOCl010 heterojunction system has a faster charge transform than that of Mn3O4/BiOCl001. Moreover, the valence cycle of Mn can further accelerate the charge transfer, which can also provide a powerful driving force for NPX elimination.