Preparation of core/shell-structured ZnFe2O4@ZnIn2S4 catalysts and its ultrafast microwave catalytic reduction performance for aqueous Cr(VI)

Irresponsible discharge of hexavalent chromium (Cr(VI)) containing industrial wastewater is a serious envi-ronmental issue, and a great risk to human health. In this work, a novel class of microwave (MW) responsive core/shell-structured ZnFe2O4@ZnIn2S4 (ZFO@ZIS) catalysts were prepared for aqueous Cr(VI) reduction. These catalysts exhibited "unexpectedly " high MW catalytic activity. The one with the ZFO:ZIS molar ratio = 1:3 led to 100 % Cr(VI) reduction within 15 min in a solution with the Cr(VI) concentration as high as 100 mg/L, which is superior to in the cases of using other photocatalysts previously reported. More significantly, the ZFO@ZIS catalysts exhibited an excellent Cr(VI) reduction ability even at a pH value as high as 6, close to that of industrial wastewater, demonstrating additionally their great feasibility. The excellent MW catalytic activity of the com-posite catalysts can be attributed to the MW induced "hot spots " effect. The MW responsive ZFO@ZIS core/shell-structured catalysts developed in this work can be a promising candidate for high efficiency catalytic reduction of Cr(VI) in wastewater.