Simulated solar light driven roxarsone degradation and arsenic immobilization with hematite and oxalate

Solar light driven organoarsenicals degradation and simultaneous inorganic arsenic immobilization with naturally abundant hematite is very promising for organoarsenicals remediation, but suffers from the fast electron-hole charge recombination of hematite. Herein, we report that oxalate, widely existed in soil and water environments, can greatly enhance the photocatalytic molecular oxygen activation of hematite to degrade a typical organoarsenical roxarsone and immobilize the resulted inorganic arsenic. It was found that oxalate could chelate with surface Fe(III) of hematite to generate plenty of •OH via a surface Fe(III)/Fe(II) cycle mediated oxygen molecular activation process under a simulated solar light, and thus induced 85.1% of roxarsone transformation into inorganic arsenic species, mainly As(V), within 6 h. The generated As(V) could be further adsorbed on hematite surface with prolonging the reaction time to 24 h in dark, avoiding secondary pollution. More importantly, hematite was reusable for the simulated solar light driven roxarsone degradation and As(V) immobilization in the presence of oxalate. This study offers a green and effective strategy for organoarsenicals remediation, and also sheds light on the environmental effects of iron oxides and oxalate.