TiO_2/WO_3 (Ti-W) photocatalysts were prepared by a simple one-step sol-gel method with 1-butyl-3-methylimidazolium ionic liquids ([Bmim][PF_6] and [Bmim][BF_4]). The mixed sol of WO_3 derived from peroxotungstic acid and TiO_2 containing ionic liquid was dried and followed by calcination at 800℃. The resulting Ti-W composite indicated high crystallinity of WO_3 and no crystalline transformation of TiO_2 from anatase to rutile. WO_3 nanoparticles on Ti-W composites (Ti-W[PF_6]) prepared by using water immiscible [Bmim][PF_6] were highly dispersed due to an emulsification effect. Ti-W[PF_6] indicated the highest reactivity in the photodegradation of methylene blue (MB) under visible light irradiation and the photooxidation of As(Ill) under UV irradiation
