Simultaneous photocatalytic redox removal of chromium(VI) and arsenic(III) by hydrothermal carbon-sphere@nano-Fe3O4

The coexistence of multiple-component contaminants, such as Cr(VI) and As(III) in acid mine drainage, brings more difficulties in the wastewater treatment. This study developed a novel strategy for simultaneous redox conversion and removal of Cr(VI) and As(III) in solution. By employing iron oxide encapsulated in a hydrothermal carbon sphere (HCS@Fe3O4), the synergistic photocatalytic reduction of Cr(VI) and oxidation of As(III) were markedly accelerated under simulated solar light irradiation. The transformed Cr(III) and As(V) were readily removed by forming Cr(OH)3 and FeAsO4 precipitates. The Fe(III)/Fe(II) cycle in the system, which was greatly reinforced by photocatalysis in the presence of HCS@Fe3O4, has been demonstrated to be critical in the redox of Cr(VI) and As(III). It can keep sufficient Fe(II) in solution to both directly reduce Cr(VI) and promote the generation of ˙OH for the oxidation of As(III). These findings provide an effectively synergistic conversion and removal strategy for implications in multiple-contaminated water treatment.