WNxOy prepared by oxidation of tungsten nitride as alternative for the sputtered N doped WO3 photocatalyst

WNxOy can be regarded as new potential candidates for photocatalysis because of their lower band gaps compared with WO3 photocatalyst. In this study WNxOy with different nitrogen content were prepared via oxidation of dc sputtered tungsten nitride films at 500 degrees C and for various times of 1, 1.5, and 2 h. X-ray diffraction patterns indicated that the prepared films are indexed to mixed phases of hexagonal WN1.8 and monoclinic WO3 and the relative peak integrated intensity of WO3 phase increased with increasing oxidation time. The overall absorption decreased with increasing oxidation time due to the nitrogen loss from the films. The obtained optical band gap values were 1.64, 1.81, and 3.00 +/- 0.04 eV for films oxidized for 1, 1.5, and 2 h, respectively. All the oxidized WNxOy films had semiconductor behavior and thermally activated conduction. The water contact angle measurements showed that all WNxOy films are hydrophilic and the hydrophilicity increased with increasing oxidation time. The photocurrent density (J(Ph)) of WNxOy photoelectrode of film oxidized for 1 h was used as indicator for hydrogen generation from sea water due to its pronounced impact of plasmonic effect well as its higher absorption. J(Ph) had a value of -0.039 mAcm(-2) under the illumination with the metal halide lamp. The WNxOy photoelectrode showed high sensitivity and reasonable J(Ph) values under monochromatic wavelength illuminations with 540, 440, and 340 nm. The WNxOy photoelectrode can be a good candidate for hydrogen generation from sea water.