Systematic Control of Monoclinic CdWO4Nanophase for Optimum Photocatalytic Activity

CdWO 4 nanocrystals with controlled particle size and crystallinity were successfully synthesized via a simple hydrothermal method using citric acid as the capping agent. By systematic sample characterization using X-ray powder diffraction, transmission electron microscope, selected area electron diffraction, Barret−Emmett−Teller technique, Fourier transformed infrared spectra, UV−visible diffuse reflectance spectra, and photoluminescence spectra, all as-prepared CdWO 4 samples were demonstrated to crystallize in a pure-phase of monoclinic wolframite structure. With varying the reaction temperature from 160 to 220 °C, particle size was controlled to grow from 11 to 21 nm. With particle size reduction, CdWO 4 nanostructure showed a lattice expansion, as is followed by a surprisingly lowered lattice symmetry, band gap broadening, and red-shift of A u vibration mode. Photocatalytic activity of CdWO 4 nanocrystals was examined by monitoring the degradation of methyl orange dye in an aqueous solution under UV radiation of 254 nm. High crystallinity CdWO 4 nanostructures with relatively small particle size showed an optimum photocatalytic performance. Consequently, systematic control over semiconductor nanostructures is proved to be useful, in some cases likely general, in achieving the advanced photocatalytic properties for technological uses.