In this work, hierarchical flower-like BiPO4 microspheres were successfully synthesized by a microwave-assisted hydrothermal reaction of bismuth nitrate with [C4mim][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate) in water at 160 °C, where the ionic liquid could act as a phosphorus source, surface modified agent and template. The photocatalytic activities of the as-prepared BiPO4 samples were evaluated by decolorization of rhodamine B in aqueous solution under UV light irradiation. It was found that the BiPO4 sample modified with ionic liquid (IL-BiPO4) exhibited significantly enhanced photocatalytic activity in comparison with the unmodified one prepared in the absence of [C4mim][PF6]. In addition, the effect of ionic liquid modification on the improved photocatalytic activity was investigated in detail and a possible photocatalytic mechanism was proposed for IL-BiPO4. It is suggested that the significantly improved photocatalytic activity of IL-BiPO4 could be mainly attributed to trapping of the photoinduced electron at the conduction band of IL-BiPO4 and thus effectively improving the separation efficiency of photoinduced electron–hole pairs due to ionic liquid modification.
