In recent years, there has been great interest in preparation of photocatalysts with hierarchical architectures and multifunctional characteristics, but it remains a great challenge for conventional synthetic methods. Nature provides an abundance of the biological materials with excellent properties and serves as a source of inspirations. In this work, banana leaves, for the first time, were applied as structure-directors to synthesize biomorphic TiO₂ photocatalyst (banana-leaf TiO₂), in order to improve the adsorption and photocatalytic performance. The biotemplate was pretreated by an effective microwave-assisted HCl pretreatment. Subsequently, the banana leaf-TiO₂ composite formed based on the frameworks of original leaves by a simple in-situ growth using 5 vol% ethanol solution of tetrabutyl titanate as precursor. Finally, the banana-leaf TiO₂, which faithfully inherits the hierarchical architectures of banana leaf, was obtained by calcination process at 350 ℃ to remove the organic templates and 500 ℃ to be crystallized. The as-prepared TiO₂ samples were characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and nitrogen-adsorption measurement. The results show that the banana leaf-TiO₂ prepared possesses both of macropores of vascular bundle with layers about 100 nm wide on the walls and typical mesopore structure with an average pore width of 13.03 nm and a high specific surface area of 66.5 m²·g^-1. The adsorption and photocatalysis performance were evaluated using aqueous solutions of methylene blue (MB, C₁₆H₁₈ClN₃S·3H₂O) under Xe-lamp irradiation. The result indicates that the banana-leaf TiO₂ exhibits much higher adsorption ability and photocatalytic activity than Degussa P25 and the common-TiO₂ without any biotemplate. The adsorption capacity of biotemplated sample is 30%, which is 4.3 times of the P25 and 15 times of the common-TiO₂. The photodecomposition of MB by the banana-leaf TiO₂ reaches 100% over 75 min, comparative to 70% by P25 and 40% by the common-TiO₂, and the photocatalytic rate of biotemplated sample (0.0326 min^-1) is 1.5 times and 4 times the rate of P25 (0.0219 min^-1) and common-TiO₂ (0.0079 min^-1), respectively.

Key words: hierarchical structure, titanium dioxide, banana leaf, biotemplate, adsorption-photocatalysis