Sequential photocatalytic degradation of organophosphorus pesticides and recovery of orthophosphate by biochar/α-Fe2O3/MgO composite: A new enhanced strategy for reducing the impacts of organophosphorus from wastewater

Photocatalysis is regarded as one of the most promising techniques for degrading organophosphorus pesticides (OPs) from wastewater given its low-cost and environmental benignity. Yet, photocatalytic degradation of OPs is an incomplete process, since PO43− is produced after photocatalysis. Here, biochar-supported α-Fe2O3/MgO composite (BC-α-Fe2O3/MgO) is developed for sequential photocatalytic degradation of OPs and recovery of the produced PO43−. The degradation efficiency of N-phosphonomethyl iminodiacetic acid (NPA) by BC-α-Fe2O3/MgO based photocatalysis reaches 90.1% within 80 min, and the recovery ratio of the produced PO43− by BC-α-Fe2O3/MgO is as high as 82.3%. Besides, the as-prepared BC-α-Fe2O3/MgO used in this integrated photocatalysis and adsorption process maintain a high stability towards NPA degradation and PO43− recovery during five cycling experiments. The mechanistic study reveals that holes, •OH, and •O2– radicals generated in the photocatalytic process are responsible for NPA degradation. UV light can activate persistent free radicals on BC-α-Fe2O3/MgO surface, which provide O2 with electrons for the generation of •O2– and subsequent yield of •OH. Moreover, the presence of α-Fe2O3 and MgO on the surface of biochar leads to the excellent P adsorption performance of BC-α-Fe2O3/MgO. This study opens new possibilities for the recovery of P resource from organophosphorus polluted wastewater.