Photocatalytic WO3/TiO2 nanowires: WO3 polymorphs influencing the atomic layer deposition of TiO2Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra18899k

• Main Authors: Nagy, Dávidné, Firkala, Tamás, Drotár, Eszter, Szegedi, Ágnes, László, Krisztina, Szilágyi, Imre Miklós
• Format: Article
• Language: English
• ISSN: 2046-2069
• DOI: 10.1039/c6ra18899k

50-70 nm hexagonal (h-) and 70-90 nm monoclinic (m-) WO 3 nanoparticles (NPs) were prepared by controlled annealing of (NH 4 ) x WO 3 in air at 470 and 600 °C, respectively. In addition, 5-10 nm thick and several micrometer long h-WO 3 nanowires (NWs) were obtained by microwave hydrothermal synthesis at 160 °C with Na 2 WO 4 , HCl and (NH 4 ) 2 SO 4 as starting materials. TiO 2 was deposited on h-WO 3 NWs by atomic layer deposition (ALD) at 300 °C using Ti( i OPr) 4 and H 2 O as precursors. The as-prepared materials were studied by TG/DTA-MS, XRD, Raman, SEM-EDX, TEM, ellipsometry, UV-Vis, and their photocatalytic activity was also tested by the photodecomposition of aqueous methyl orange. Our study is the first evidence of diverse ALD nucleation on various WO 3 polymorphs, since on h-WO 3 NWs TiO 2 nucleated only as particles, whereas on m-WO 3 conformal TiO 2 film was formed, explained by the different surface OH coverage of h- and m-WO 3 . The h-WO 3 NWs had significantly higher photocatalytic activity compared to h-WO 3 NPs, and similar performance as m-WO 3 NPs. By adding TiO 2 to h-WO 3 NWs by ALD method, the photocatalytic performance increased by 65%, showing clearly the uniqueness of ALD to obtain superior oxide composite photocatalysts. Study on h-WO 3 /TiO 2 nanowires as ALD nucleation of TiO 2 was found to be influenced by the WO 3 polymorphs.