A photocatalyst system for volatile organic compounds with two parts that include a photocatalyst layer on a substrate and a porous overlayer. The photocatalyst layer is reactive with volatile organic compounds when UV light is projected on it. The overlayer is situated on the photocatalyst layer. The overlayer is UV transparent and has an interconnected pore network that allows contaminated air to pass through the overlayer. The size and the shape of the interconnected pores acts to selectively exclude certain contaminants that can deactivate the photocatalyst.