Facile synthesis of pure TiO₂(B) nanofibers doped with gold nanoparticles and solar photocatalytic activities

Pure and highly crystallized gold nanoparticles-doped-TiO₂(B) nanofibers (Au-TBNFs), with thickness of 50–200 ㎚ and length of several microns, were successfully synthesized by combination of lowtemperature (150 ℃) hydrothermal reaction of titanium (Ⅳ) isopropoxide (Ti[OC₃H₇]₄) and sonication of the ensued precipitate with gold nanoparticles followed by post-heat treatment at 300 ℃. Formation of pure TiO₂(B) was confirmed by X-ray diffraction, high resolution transmission electron microscopy and Raman spectroscopy. The UV–vis diffuse reflectance spectra (DRS) of Au–TiO₂(B) nanofibers exhibited surface-state absorption beyond 400 ㎚ with band gap energy at 2.94 eV and broad gold plasma resonance band around 550 ㎚. The photoluminescence (PL) emission spectra of the Au-TBNFs exhibited structural emission band around 410 ㎚ with shoulders around 464 ㎚ and 540 ㎚. Analysis of these optical properties revealed that the surface state absorption is attributed to the indirect transition. These results suggest that coupling of the surface charge carriers with the lattice phonon of Au-TBNFs is so strong that the charge recombination is mostly nonradiative as supported by the significantly quenched emission of Au-TBNFs as compared to that of free TBNFs. These optoelectronic properties were well correlated with highly efficient solar photocatalytic activities of Au-TBNFs for oxidation of methylene blue (MB).