Highly Efficient Liquid-Phase Photooxidation of an Azo Dye Methyl Orange over Novel Nanostructured Porous Titanate-Based Fiber of Self-Supported Radially Aligned H₂Ti₈O₁₇·1.5H ₂O Nanorods

Novel nanostructured porous fibers of self-supported, radially aligned H₂Ti₈O₁₇·1.5H₂O nanorods were prepared from layered H₂Ti₄O₉· 1.2H₂O tetratitanate fibers by novel solvothermal reaction in glycerine at 150-250 °C. The H₂Ti₈O ₁₇·1.5H₂O fibers with diameters of 0.5-1.5 μm and lengths of 10-20 μm 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 °C. Photocatalytic activity of the H₂Ti₈O₁₇·1.5H₂O fibers was evaluated in aqueous photooxidation of an azo dye methyl orange in the presence of UV irradiation and O₂, using P-25 as the standard sample. Both the photocatalytic activity and the dispersity-agglomeration property of H₂Ti₈O₁₇· 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 H₂Ti₈O ₁₇·1.5H₂O fibers becomes more serious from pH 2.0 to pH 5.0 and from pH 6.0 to pH 11.0. Well-dispersed H₂Ti ₈O₁₇·1.5H₂O fibers occur at pH 6.0. Both the total photodegradation of waste chemicals and the entire sedimentation of H₂Ti₈O₁₇· 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· 1.5H₂O fibers.