Highly Efficient Liquid-Phase Photooxidation of an Azo Dye Methyl Orange over Novel Nanostructured Porous Titanate-Based Fiber of Self-Supported Radially Aligned H2Ti8O17·1.5H2O Nanorods

Abstract

Novel nanostructured porous fibers of self-supported, radially aligned H2Ti8O17 x 1.5H2O nanorods were prepared from layered H2Ti4O9 x 1.2H2O tetratitanate fibers by novel solvothermal reaction in glycerine at 150-250 degrees C. The H2Ti8O17 x 1.5H2O fibers with diameters of 0.5-1.5 microm and lengths of 10-20 microm consist of multi-scale nanopores and nanostructures. They also are of high crystallinity, large surface area of 127 m2 g(-1), and stable phase up to 350 degrees C. Photocatalytic activity of the H2Ti8O17 x 1.5H2O fibers was evaluated in aqueous photooxidation of an azo dye methyl orange in the presence of UV irradiation and 02, using P-25 as the standard sample. Both the photocatalytic activity and the dispersity-agglomeration property of H2Ti8O17 x 1.5H2O fibers are pH-controllable. Highly photooxidative activity, superior to that of P-25, occurs at pH 6.0-11.0 due to certain distinguishable material characteristics and to large amounts of adsorbed reactants of surface active OH* free radicals, surface hydroxyl OH, O2*-, O*OH, and methyl orange. The agglomeration of H2Ti8O17 x 1.5H2O fibers becomes more serious from pH 2.0 to pH 5.0 and from pH 6.0 to pH 11.0. Well-dispersed H2Ti8O17 x 1.5H2O fibers occur at pH 6.0. Both the total photodegradation of waste chemicals and the entire sedimentation of H2Ti8O17 x 1.5H2O fibers can be timed to end simultaneously at suitable pH value. The photocatalyst-free reaction solution is then easily removed, and the fresh wastewater is added again. Standard unit operation processes of chemical engineering are used to design a continuous, low-cost, large-scale, liquid-phase photocatalysis technique based on the H2Ti8O17 x 1.5H2O fibers.