| Summary: | 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 WO<sub>3</sub> 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<sup>−</sup>, Cl<sup>−</sup>, Br<sup>−</sup>, I<sup>−</sup>), we have obtained WO<sub>3</sub> semiconductors by hydrothermal treatment, which in composite systems can enhance the commercial TiO<sub>2</sub> photocatalytic activity. We investigated three sample series: WO<sub>3</sub>-NWH-NaX/WO<sub>3</sub>-NWH-KX and, subsequently, WO<sub>3</sub>-AMT-HX. The presence of W<sup>+5</sup> centers was evidenced by Raman and X-ray photoelectron spectroscopy. W<sup>+5</sup> and W<sup>+6</sup> species affected the band gap values of the NaX and KX series; a higher percentage of W<sup>+5</sup> and, subsequently, W<sup>+6</sup> 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.
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