TiO2 porous nanospheres on polypropylene (PP) films (TiO 2/PP composite) are produced at ambient temperature. Particle/pore size match up is the key anchoring point to overcome the low affinity between hydrophilic materials and hydrophobic materials. With the hydrophilic TiO 2 catalyst evenly dispersed on a hydrophobic surface, the aqueous solution will selectively skip the substrate and wet the catalysts. Such a wettability-induced smart system maximizes the degrading activity of the TiO2 catalyst. In photodegrading reactions, the resulting TiO 2/PP composite film exhibits a 10 times higher activity in flow-type setup than the same TiO2 catalyst in a traditional batch-type setup.