Formamide-assisted one-step synthesis of BiOCOOH and Bi/BiOCOOH micro-/nanostructures with tunable morphologies, composition and their photocatalytic activities

A series of BiOCOOH and Bi/BiOCOOH heterojunction micro-/nanostructures with various morphologies have been successfully synthesized by one-step hydrothermal process with the assistance of formamide. The morphology, structure and composition of as-obtained samples and the effect of formamide were systematically characterized and investigated. The results reveal that the formamide plays multiple roles in the synthesis of the BiOCOOH and Bi/BiOCOOH heterojunctions, which acts as the carbon and alkali source. Moreover, formic acid abundantly provided by hydrolysis of formamide performs as the reductant and structure-directing agent. Photocatalytic activities of all catalysts were evaluated by the degradation of Rhodamine B (RhB) and reduction of potassium dichromate (K2Cr2O7) under simulated sunlight irradiation. It is found that photocatalytic activity is closely related to the morphology and composition of photocatalyst. The well-defined 3D flower-like BiOCOOH prepared at 20 vol.% formamide shows higher photocatalytic activity than other BiOCOOH samples, which could be attributed to the hierarchical nanostructure, larger specific surface area and stronger adsorption capacity. Meanwhile, Bi/BiOCOOH heterojunction obtained at 60 vol.% formamide shows the best photocatalytic performance due to the increased light absorbance capacity and more efficient separation and transfer of photogenerated carriers with the existence of in situ deposited metallic Bi. Trapping experiments reveal that h+ and •O2− are the main active species in the photodegradation process and the possible photocatalytic mechanism is proposed.