Solar-driven WO3•H2O/TiO2 heterojunction films immobilized onto bamboo biotemplate: Relationship between physical color, crystal structure, crystal morphology, and energy storage ability

In this study, different morphologies of WO3 center dot H2O/TiO2 (WT) heterojunction films were successfully synthesized on bamboo biotemplate via facile two-step hydrothermal deposition methods. The WO3 center dot H2O self-assembled by nanosheets or nanoplates on anatase TiO2-coated bamboo (TiO2-B) exhibited a distinctive surface color. The addition of WO3 center dot H2O could significantly extend the optical responses of TiO2-B in the ultraviolet to the visible region. Based on the various analysis techniques, the formation mechanisms of the WO3 center dot H2O/TiO2 hierarchical architectures with different crystal structures were also proposed. In addition, the photoactivity and post illumination activity of WT films were examined by constructing center dot O-2(-) and center dot OH in light and in light-off, respectively. The results showed that WT films with different crystal structures exhibited different photoactivity and energy storage abilities, and the photoactivity of WT films was negatively correlated with their energy storage ability. The presence of an anatase TiO2 thin film on the bamboo surface provided abundant active sites for WO3 center dot H2O growth, which formed direct S-scheme heterojunctions for solar energy conversion and storage. Therefore, we anticipate that solar-driven energy storage heterojunctions with accessible and rich crystal morphologies will provide new insights for various applications, such as efficient wastewater treatment, self-cleaning coating, and air purification.