Preparation and application of a novel biochar-supported red mud catalyst：Active sites and catalytic mechanism.

A novel catalyst RM-BC(HP) was synthesized by hydrothermal treatment and pyrolysis (800 ℃) using red mud and coconut shells. Influence of different preparation conditions on catalyst performance was explored. SEM showed that RM-BC(HP) was porous and RM was successfully loaded on the outside surface and inside the pores of BC. XRD revealed that Fe2O3 in RM was reduced to Fe0 and Fe3O4 in the pyrolysis process, in which pyrolysis temperature and addition ratio of coconut shells were critical. TGA-MS, FT-IR and XPS were also applied to character the catalyst. 100% of AO7 was removed within 30 min with conditions of 2 mM PS, 50 mg/L AO7 and 0.5 g/L RM-BC(HP), and the Fe leaching was negligible. High removal rate was obtained in tap, river, and lake water. RM-BC(HP)/PS system also exhibited excellent degradation performance for other dyes (MB, MG and RhB) and antibiotics (TC, OTC and CTC). The mechanism studies demonstrated that PS was mainly activated by Fe0 and Fe2+ in RM-BC(HP) to produce different radicals, then 1O2 was generated by the reactions among these radicals to degrade AO7. Finally, nine intermediate products of AO7 were identified by FT-ICR-MS and a probable degradation pathway was proposed.