Segmented nanoporous WO 3 prepared via anodization and their photocatalytic properties
- PDF / 562,780 Bytes
- 8 Pages / 584.957 x 782.986 pts Page_size
- 29 Downloads / 173 Views
Chai Yan Ng Green Electronics Nanomaterials Group, School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia; and Department of Mechanical and Material Engineering, Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, 43000 Kajang, Selangor, Malaysia
Ehsan Ahmadi, Khairunisak Abdul Razak, and Zainovia Lockmana) Green Electronics Nanomaterials Group, School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia (Received 28 October 2015; accepted 9 February 2016)
Segmented nanoporous WO3 is prepared via anodization with an electrolyte containing 1 M Na2SO4 and 0.07–0.7 g of NH4F. Annealing (500 °C for 1 h) was also performed to induce crystallinity in WO3. More pores (50–80 nm in diameter) and thicker porous layer were formed by increasing the amount of NH4F (400 nm for 0.3 g of NH4F). However, further increase of the NH4F amount to 0.5 and 0.7 g did not increase the porous layer thickness. Segmented nanoporous structure formation was attributed to the dissolution of anodic oxide by H1 and F ions in the electrolyte, as well as the healing process induced by the electric field. The photocatalytic activity of the WO3 samples was evaluated through degradation of methyl orange solution. The asanodized sample showed lower photocatalytic ability in comparison with the annealed sample because of the amorphous behavior of as-anodized WO3.
I. INTRODUCTION
Tungsten oxide (WO3) is an interesting semiconductor oxide with potential applications in photocatalysts, electrochromic devices, and gas sensors. WO3 possesses a small band gap of 2.4–2.8 eV and presents many advantages for visible light-driven photocatalysis, such as a deep valence band (13.1 eV), strong absorption within the solar spectrum, stable physicochemical properties, and resilience to photocorrosion.1 The band gap of a semiconductor increases with decreasing particle size and is indicated by an absorption shift toward shorter wavelengths.2 Nanosized defects may act as electron traps that can lengthen the lifetime of the generated charge carriers and enhance photoactivity. However, if an electron is held within a deep trapping site, it may exhibit a lower redox potential despite having a longer lifetime, thereby decreasing photoreactivity.3 WO3 usually presents lower light energy conversion efficiency than the more widely used titanium oxide (TiO2) because
Contributing Editor: Xiaobo Chen a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.71 J. Mater. Res., Vol. 31, No. 6, Mar 28, 2016
http://journals.cambridge.org
Downloaded: 07 Jun 2016
electrons in WO3 have low conduction band levels and lower reduction potentials. Various methods, including chemical vapor deposition,4 electrochemical deposition,5 sol–gel coating,6 hydrothermal,7 and acid treatment8 have been used to fabricate WO3. The formation of nanostructured WO3 with a large surface area has drawn the interest of m
Data Loading...
