Solvothermal Synthesis of CeO₂–TiO₂ Nanocomposite for Visible Light Photocatalytic Detoxification of Cyanide

Abstract

A CeO2–TiO2 nanocomposite was synthesized solvothermally using ascorbic acid (A), urea (U), or polyvinylpyrrolidone (PVP). Powder X-ray and selected area electron diffractometries and Raman spectroscopy confirm the anatase phase of TiO2 and face-centered cubic lattice of CeO2. Energy dispersive X-ray spectroscopy confirms the purity of the synthesized composites and provides their compositions. Scanning electron, field emission scanning electron, and transmission electron microscopies give the sizes and shapes of the synthesized nanoparticles. UV–visible diffuse reflectance spectroscopy shows the optical absorption edges of CeO2–TiO2 (A), CeO2–TiO2 (U), and CeO2–TiO2 (PVP) as 510, 441, and 410 nm, respectively. The blue, blue-green, and green emissions shown by the three nanocomposites indicate the existence of defects such as oxygen vacancies in the crystal lattices. All three composites differ in their electrical properties, obtained by solid-state impedance spectroscopy. Furthermore, solid-state impedance spectroscopy shows photoconductance of CeO2–TiO2 confirming the band gap excitation by visible light. Under UV as well as visible light, the nanocomposite synthesized using ascorbic acid is the most efficient photocatalyst to detoxify cyanide in alkaline solution; the composite synthesized with urea is the least active photocatalyst. At neutral pH, CeO2–TiO2 synthesized with ascorbic acid is the most active to photocatalytically degrade dye, and the order of photocatalytic activity remains unaltered. The synthesized nanocomposites are not only photocatalysts but are bactericides as well. Ascorbic acid-assisted solvothermally synthesized CeO2–TiO2 is the most efficient bactericide, tested with S. aureus in the absence of direct light.