Zn S is another good catalyst for hydrogen production by photolysis of water among metal sulfide members. In the presence of sulfide/sulfite (Na2S and Na2SO3) as reducing agents, Zn S exhibited a good photocatalytic effect, with an apparent quantum yield of 90% at 313 nm. However, Zn S has a wide band gap (3.6 e V) and can only use ultraviolet light. Doped modified Zn S has been proved to be one of the effective methods to improve its visible light catalytic efficiency [39].