Enhanced photocatalytic activity of wool fibers having titanium dioxide nanoparticles formed inside their cortex

A wool-TiO₂ nanoparticle composite material having TiO₂ nanoparticles both infiltrated in the matrix between macrofibrils inside cortical cells of wool fibers and grafted on the fiber surface is obtained in this study, and the wool-nanoparticle composite material is found to have highly photocatalytic activities with an extremely narrow band gap of 2.8 eV. The wool fibers are obtained using three successive technical steps: wool fibers are swollen by using lithium bromide, then saturated with tetrabutyl titanate ethanol solution and subsequently treated in boiling water. It was demonstrated that the chemical bonds formed between the as-synthesized TiO₂ nanoparticles and the wool fibers swollen by lithium bromide include C-Ti⁴⁺(Ti³⁺), N-Ti⁴⁺(Ti³⁺), O-Ti³⁺, and S-Ti⁴⁺(Ti³⁺) bonds. The modified wool fibers have shown markedly improved photocatalytic efficiency due to their enhanced visible light absorption capability, which is much better than the (N-doped) TiO₂ coated wool fibers. In contrast, TiO₂ modified wool fibers swollen by using formic acid have poorer photoactivity, this might be due to the elimination of trivalent titanium between TiO₂ nanoparticles and the wool fibers.