Hydrothermal Synthesis of Ionic Liquid [Bmim]OH-Modified TiO2 Nanoparticles with Enhanced Photocatalytic Activity under Visible Light

TiO2 nanocomposites modified with the ionic liquid [Bmim]OH are synthesized by a hydrothermal procedure. X-ray diffraction, Zeta-potential measurement, TEM, thermogravimetric analysis, photoluminescence, UV/Vis, FTIR, and X-ray photoelectron spectroscopy are used to characterize the TiO2 nanocomposites. The TiO2 nanocomposites consist of pure anatase particles of about 10 nm. The modification of [Bmim]OH on the surface of the TiO2 particles extends the TiO2 absorption edge to the visible-light region. The electrochemical redox potentials indicated that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of [Bmim]OH match well with the valence band (VB) and conduction band (CB) of the TiO2 semiconductor. [Bmim]OH-modified TiO2 is much more active than pristine TiO2 under visible-light irradiation in the photocatalytic degradation of methylene blue in aqueous solution. [Bmim]OH is chemically bonded to the surface Ti-OH of TiO2 particles rather than adsorbed on the surface. A possible mechanism for the photocatalysis is proposed.