Biotemplated Hierarchical TiO2 Derived from Banana Leaf and Its Adsorption-Photocatalytic Performance

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 degrees C to remove the organic templates and 500 degrees C 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 m(2).g(-1). The adsorption and photocatalysis performance were evaluated using aqueous solutions of methylene blue (MB, C16H18ClN3S center dot 3H(2)O) 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.