SnO2 is a totally inactive photocatalyst for the degradation of 2-chlorophenol (2CP) and textile colorant Mercurochrome (MC) at acidic pH values, but shows feeble photocatalytic activity for the degradation of said pollutants at basic pH values. However, coating of a thin MgO layer on SnO2 nanocrystalline particles transforms photocatalytically inactive SnO2 to an active photocatalyst. A negative shift of the flatband (FB) potential of SnO2 was observed with the increase of pH values and coating of a thin MgO layer on SnO2 particles. Further we noticed the retardation of charge recombination on SnO2 upon MgO coating and increase in pH values. Hence, the promoting effects of MgO layer on SnO2 catalyst for the sensitized degradation of colorants and chlorophenol degradation in aqueous phase were assigned to both slow charge recombination and to the negative shift of FB potential. (c) 2006 Elsevier B.V. All rights reserved.