A traditional semiconductor (WO₃) was synthesized from different precursors via hydrothermal crystallization targeting the achievement of three different crystal shapes (nanoplates, nanorods and nanostars). The obtained WO₃ microcrystals were analyzed by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). These methods contributed to the detailed analysis of the crystal morphology and structural features. The synthesized bare WO₃ photocatalysts were totally inactive, while the P25/WO₃ composites were efficient under UV light radiation. Furthermore, the maximum achieved activity was even higher than the bare P25’s photocatalytic performance. A correlation was established between the shape of the WO₃ crystallites and the observed photocatalytic activity registered during the degradation of different substrates by using P25/WO₃ composites.

WO₃-TiO₂ composite materials were obtained using commercial titania (Evonik Aeroxide P25) and hydrothermally crystallized WO₃. Different ratios of TiO₂/WO₃ were investigated, starting at 1 wt.% of WO₃ to 50 wt.%. The morphology of WO₃ was of the star-like type, and its structure is basically composed of monoclinic crystalline phase. All spectroscopic characteristics of the composites and their derived data (band-gap energy value, light absorption threshold, and IR specific bands) directly varied with the increase of the WO₃ content. However, the oxalic acid photodegradation achieved under UV light reached the highest yield for 24 wt.% WO₃ content, a result that was attributed to the charge separation efficiency and the surface hydrophilicity. The latter mentioned reason points out the crucial importance of the surface quality of the investigated structure in photocatalytic tests.

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.