BiOBr_nI_1-n solid solutions as versatile photooxidation catalysts for phenolics and endocrine disrupting chemicals

A novel family of visible-light-sensitive photocatalysts, bismuth oxyhalide solid solutions (BiOBr_nI_1-n, n = 0–1), was synthesized by a nonaqueous solvothermal method. The bismuth oxyhalides crystallized in individually separated platelets which aggregated into microspheres, allowing for efficient light capture. By increasing the Br/I ratio, the band gap of BiOBr_nI_1-n could be tuned from 1.95–2.95 eV. The material with the composition BiOBr_0.75I_0.25 exhibited the best photoactivity. It catalysed the degradation of p-cresol under visible light at a rate 31-times that of pure BiOBr and 1.7-times that of BiOI. BiOBr_0.75I_0.25 proved to be a versatile photocatalyst for the degradation of a wide range of substituted alkyl phenols and endocrine disrupting chemicals (EDCs). Total organic carbon in the water was reduced to 10–33 % at > 99 % degradation efficiency. The excellent performance was attributed to a matching bandgap, balance between light absorption and redox potential, and efficient charge separation. Recyclability testing showed that BiOBr_0.75I_0.25 maintained its high activity even after three cycles of p-cresol photodegradation.