Bismuth impregnated biochar for efficient estrone degradation: The synergistic effect between biochar and Bi/BiO for a high photocatalytic performance.

An innovative advanced oxidation process was successfully developed to photocatalytic-degradation of estrone through the synergistic effect of biochar and Bi/BiO in bismuth-containing photocatalytic biochar (BiPB). The highest reaction rate constant (k) of estrone degradation by BiPB was 0.045 min under the conditions of initial concentration of estrone =10.4 μmol L, [BiPB] =1 g L, pH = 7.0. The k was almost tenfold and more than 20 times than that of biochar without bismuth impregnation and pristine Bi/BiO, respectively. The best photocatalytic performance of BiPB composites for the degradation of estrone was primarily attributed to generation of OH radicals. Impregnation of bismuth helped control the concentration of persistent free radicals (PFRs) and develop a hierarchical porous structure of biochar. The presence of biochar facilitated pre-concentration estrone on BiPB and improved the separation and transfer efficiency of charge carriers. The synergistic effect between biochar and Bi/BiO contributed to the generation of OH radicals for estrone degradation under neutral pH conditions. The transformation pathway of estrone was also proposed based on the measured transformation products in the presence of BiPB. The high efficiency of BiPB composites indicated that this easily-obtained material was promising for estrone-wastewater treatment applications as a low-cost composite photocatalyst.