The photocatalytic performances of the SnS2 and the CdS under the irradiation of visible light were investigated by using different organic dyes as reactants. The photodegradation of organic dyes containing N=N double bond on the SnS2 followed a reduction mechanism with photoelectrons via the Sn-IV/Sn-II transition while the photodegradation of organic dyes containing N=N double bond on the CdS and the photodegradation of organic dyes without N=N double bond on either the SnS2 or the CdS followed an oxidation mechanism with center dot O-2 center dot and center dot OH radicals. The SnS2 exhibited much higher activity than the CdS during the photocatalytic degradation of organic dyes containing N=N double bond, since the reduction of reactant molecules on the SnS2 surface was much faster than the migration of either the center dot O-2(-) or the center dot OH radicals. However, the SnS2 displayed even lower activity than the CdS in the photocatalytic degradation of other organic dyes without N=N double bond, since all these reactions followed the oxidation mechanism and the SnS2 displayed a lower efficiency than the CdS in producing center dot O-2(-) or center dot OH radicals due to the presence of the Sn-IV/Sn-II transition. (C) 2012 Elsevier B.V. All rights reserved.