Synthesis Design of Electronegativity Dependent WO3 and WO3∙0.33H2O Materials for a Better Understanding of TiO2/WO3 Composites’ Photocatalytic Activity

• Published in: Catalysts Vol. 11; no. 7; p. 779
• Main Authors: Székely, István, Kedves, Endre-Zsolt, Pap, Zsolt, Baia, Monica
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.07.2021
• Subjects: Acids; Blue shift; Catalysts; Catalytic activity; Chemical reactions; Composite materials; Crystallization; Electronegativity; Hydrothermal treatment; Materials science; morpho-structural properties; Morphology; Nanocrystals; Nanowires; Optical properties; oxygen vacancies; Parameters; Photocatalysis; photocatalytic activity; Photoelectrons; Precursors; Red shift; Semiconductors; surface defects; Synthesis; Titanium dioxide; Tungsten oxides; tungsten trioxide
• ISSN: 2073-4344; 2073-4344
• DOI: 10.3390/catal11070779

The design of a semiconductor or a composite semiconductor system—with applications in materials science—is complex because its morphology and structure depend on several parameters. These parameters are the precursor type, solvent, pH of the solution, synthesis approach, or shaping agents. This study gives meaningful insight regarding the synthesis design of such WO3 materials. By systematically alternating the precursor (sodium tungstate dihydrate—NWH, or ammonium tungstate hydrate—AMT), subsequently shaping the agents (halide salts—NaX, KX, or hydrohalic acids—HX; X = F−, Cl−, Br−, I−), we have obtained WO3 semiconductors by hydrothermal treatment, which in composite systems can enhance the commercial TiO2 photocatalytic activity. We investigated three sample series: WO3-NWH-NaX/WO3-NWH-KX and, subsequently, WO3-AMT-HX. The presence of W+5 centers was evidenced by Raman and X-ray photoelectron spectroscopy. W+5 and W+6 species affected the band gap values of the NaX and KX series; a higher percentage of W+5 and, subsequently, W+6 caused a redshift, while, regarding the HX series, it led to a blue shift. Increased electronegativity of the halide anions has an unfavorable effect on the composites’ photoactivity. In contrast, in the case of hydrohalic acids, it had a positive impact.