The roles of free carbon over ZnO in enhancing the photocatalytic properties for removal of Cr(VI)

Core-shell structured ZnO@C composites had been successfully fabricated by self-assembled, in which the thickness of carbon layer on the ZnO surface can be precisely controlled. The effects of carbon layer thickness and calcination temperature on photocatalytic removal of Cr(VI) were investigated in detail. The experimental results revealed that a larger carbon layer thickness could only improve the adsorption capacity of the catalyst, but not the photocatalytic reduction ability of the catalyst. A higher calcination temperature could increase the number and content of carbon layer defects, thereby improving the photocatalytic efficiency of the catalyst. The catalyst with around 7 nm thickness of carbon layer and calcined 2 hours at 600 °C exhibited the best photocatalytic activity for Cr(VI) reduction, which is more than four times than that of pure ZnO.