TiO2-Au nanocomposite materials embedded in polymer matrices and their application in the photocatalytic reduction of nitrite to ammonia

Titanium dioxide-gold nanocomposite materials ((TiO2-Au)(nps)) were prepared and embedded in methyl functionalized silicate sol-gel (MTMOS) and Nafion (Nf) matrices. The nanocomposite materials were characterized by UV-vis absorption spectra, scanning electron micrographs (SEM) and high resolution transmission electron micrographs (HRTEM). When gold nanoparticles were deposited on TiO2 ((TiO2-Au)(nps)) and immobilized in MTMOS silicate sol-gel and Nafion matrices, the band-gap (E-bg) of the TiO2 shifted to lower energy. During the photocatalytic experiment, the (TiO2-Au)(nps) incorporated polymer matrices improved the photocatalytic reduction of nitrite ions to ammonia, owing to the effective interfacial charge transfer process in the presence of a hole scavenger, oxalic acid. Further increase in the photocatalytic reduction of nitrite to ammonia was observed by incorporating a [Ni(teta)](2+) complex into the MTMOS/(TiO2-Au)nps or Nf/(TiO2-Au)(nps) film. The immobilization of (TiO2-Au)(nps) in a functionalized silicate sol-gel or Nafion matrix is advantageous for the preparation of solid-phase photocatalyst film and to design a solid-solution system leading to the physical separation of the catalyst from the solution and the products in contrast compared to the colloidal photocatalyst system. The Au-nps deposited on TiO2 act as an e sink which promotes efficient interfacial electron transfer from TiO2 to the substrate upon irradiation. The ultimate contact between (TiO2-Au)(nps) and Ni(II) complex in the film efficiently promotes the electron transfer from Au-nps to Ni(II) complex leading to the formation of an intermediate Ni(I) complex, which facilitates the efficient catalytic reduction of nitrite to ammonia.