Selective oxidation of benzyl alcohol using a Ni(OH)2-modified CdS-MoS2 composite photocatalyst under ambient conditions

The selective photocatalytic oxidation of alcohols to aldehydes is difficult to accomplish in pure water, which is a substantial obstacle for the practical application of the photocatalytic synthesis of aldehydes. In this work, a composite photocatalyst was constructed by assembling Ni(OH)2 on a CdS-MoS2 heterostructure, which allowed for the effective photocatalytic oxidation of benzyl alcohol to benzaldehyde by photogenerated holes in anaerobic pure water. The conversion of benzyl alcohol was increased from 18.9% to 94.2%. Ni(OH)2 loaded on CdS-MoS2 could serve as a hole-transport layer, enhancing the transport of holes to the catalytic surface to achieve more efficient benzyl alcohol oxidation. A part of Ni2+ was reduced to Ni0 by a small amount of photoinduced electrons. Both Ni2+ and Ni0 adsorbed the α-H of benzyl alcohol, which was the dehydrogenation unit, thus providing more active sites for the conversion of benzyl alcohol to benzaldehyde. The self-reduction of Ni2+ on the surface may be reduced to Ni0 and it may protect the inner Ni2+ from self-reduction due to the fast electron transfer and electron active site, which benefited the photocatalytic stability of the Ni(OH)2-modified CdS-MoS2 heterostructures. The synergistic effect of Ni(OH)2 and metallic Ni significantly improved the photocatalytic oxidation properties.