Photocatalytic reduction of hexavalent chromium at gold nanoparticles modified titania nanotubes

• Gold modified titania nanotubes are used to design solid-phase photocatalyst.
• Gold nanoparticles deposition increases the surface area of titania nanotubes.
• Gold on titania nanotubes improves the photocatalytic reduction of Cr(VI).
• The holes produced at the titania nanotubes are scavenged by oxalic acid.
• Gold modified titania nanotubes is a potential candidate for treatment of heavy metals.

N-[3-(Trimethoxysilyl)propyl]ethylenediamine (EDAS) silicate supported titanium dioxide nanotubes-gold ((TiO2 NTs-Au)NCM) nanocomposite material (EDAS/(TiO2 NTs-Au)NCM) was prepared by deposition–precipitation method and characterized by diffuse reflectance spectra, X-ray diffraction pattern, Brunauer–Emmett–Teller surface area analysis, transmission electron micrographs, scanning electron micrographs and energy-dispersive X-ray spectra analysis. The photocatalytic activity of the EDAS/(TiO2 NTs-Au)NCM in the film form was investigated towards the reduction of toxic hexavalent chromium (Cr(VI)) into trivalent chromium (Cr(III)) in the presence of oxalic acid as an electron donor. The EDAS/(TiO2 NTs-Au)NCM film exhibited higher photocatalytic activity when compared to the photocatalytic activities of pristine TiO2 nanoparticles and TiO2 nanotubes (TiO2 NTs) which can be attributed to the effective photoinduced interfacial charge transfer from the (TiO2 NTs-Au)NCM to Cr(VI) through Au nanoparticles (Aunps). The Aunps present in the TiO2 NTs act as an electron sink for the photogenerated electrons that minimizes the charge recombination process at the TiO2 NTs. The Aunps on the TiO2 NTs surface facilitates the transfer of photogenerated electrons to the Cr(VI) leading to the formation of Cr(III) ions.