Comparing Effects of Silver and Iron Deposition on Dye-Adsorption in Dark Using Anatase-Titania Nanotubes Catalyst

Abstract

Silver (Ag) and iron (Fe) deposited nanotubes of anatase-TiO2 (ATN) have been processed via the combination of hydrothermal and ultraviolet-reduction techniques. The samples have been characterized using the scanning electron microscope, transmission electron microscope, X-ray diffraction, and ultraviolet visible absorption spectrophotometer for determining their morphology, size, structure, and photoabsorption properties. The dye-adsorption from an aqueous solution has been investigated in the dark-condition using the pure and surface-modified ATN. The methylene blue (MB) dye has been used as a model catalytic dye-agent. It has been demonstrated that the Ag and Fe-deposition results in an enhanced dye-adsorption at equilibrium on the surface of ATN with the maximum dye-adsorption obtained for the Ag/Ti ratio of 1.0%. A model has been proposed to explain the observed differences in the variation of the amount of dye-adsorbed at equilibrium as a function of metal/Ti (M/Ti) ratio as observed for the Ag and Fe-deposition. It is concluded that the MB adsorption at equilibrium on the surface of ATN is primarily controlled by the combination of nanoparticle-size and oxygen-spill-over effects at the lowest M/Ti ratio; while for higher M/Ti ratios, it is controlled by the oxygen-spill-over effect for Ag-deposition and by the multiple-oxidation-state effect for Fe-deposition.