Surface Mineralization of Cellulose by Metal Chloride - an Original Pathway for the Synthesis of Hierarchical Urchin and Needle Carpetlike TiO2 Superstructures

A new pathway has been developed for the preparation of hierarchical TiO2 structures obtained with-and-from the surface of cotton. By reaction with TiCl4 under anhydrous conditions, mineralization of the outer part of the cotton fiber produces hierarchical TiO2 superstructures: at the nanoscale, anatase needles are made of nanorod assemblies and these needles are assembled into urchins and carpets at the submicrometer scale. This one-step cotton fiber cellulose mineralization process differs from a simple deposition from inorganic sol; here, cellulose acts as both a reacting oxygen donor and also as a biotemplate. The material has high-temperature crystal stability, and its photocatalytic activity in the UV range, without any doping, is higher than that of titania standard P25. The high photoactivity is ascribed to efficient light harvesting by hierarchical superstructures, efficient charge separation with reduced recombination in the crystalline material, and efficient sorption ability. From a general standpoint, our findings could be adapted to other metal oxides and pave the way to a number of solar-cell, energy-storage, and photonic-sensor applications.