Abstract
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.
Highlights
Scanning electron microscopy was employed to evaluate the morphology of the synthesized semiconductors
Three sample series were synthesized from two precursors by adding sodium/potassium salts or hydrohalic acids to the system being studied
The sodium halide series presented rod and wire-like morphologies—the wires formed bundles, potassium halide series presented wire-like morphology
Summary
Tungsten trioxide (WO3 ) is an extensively studied n-type semiconductor (SC) that has a broad application spectrum, including pigment in paints [1], gas sensors [2,3], and humidity sensors [4], or is an essential component in (photo) electrochromic devices [5,6,7,8]. It can be employed as a photocatalyst on its own or in composites with other metal oxides [9,10,11,12,13,14], or with carbon-based materials [15]. The morphology and structure of the WO3 SCs can be influenced by the precursor’s structure [33,34,35], synthesis method [36,37,38], solvent type [39], annealing time, and temperature [40,41]
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