The paper emphasizes the effect of electric field on photocatalytic efficiency of nanoparticles of TiO₂ (nano TiO₂). The effect was observed by applying electric field to nano TiO₂ during the photocatalytic degradation process of methylene blue. Porous silicon was used as a template to immobilize the nano TiO₂ and to facilitate the application of electric field. Nano TiO₂, having an average particle size of 15 nm, was synthesized by thermal plasma assisted gas phase condensation. A critically selected negative bias potential, applied on the catalyst with reference to the solution, is shown to enhance the photocatalytic efficiency by 18%. The observed effect is explained on the basis of band movements at the TiO₂/solution interface. Band movement influences the oxidation and reduction reactions at the interface and thus controls the photocatalytic degradation.