High photocatalytic activity of star-like PbWO4 microcrystals: Structural analysis and degradation of anionic and cationic dyes

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PbWO 4 microcrystals were synthesized by coprecipitation followed by hydrothermal treatment and characterized by XRD, FT-Raman, FT-IR, XPS, BET, FE-SEM, and HR-TEM. XRD patterns combined with Rietveld refinement confirmed a scheelite-type tetragonal structure, while FT-IR and FT-Raman spectra revealed characteristic vibrational modes of the [WO 4 ] units. FE-SEM analyses revealed star-like microcrystals formed by self-assembly of octahedral subunits, indicating anisotropic growth. HR-TEM images showed clear lattice fringes indexed to the (112) plane, confirming high crystallinity with minor surface disorder. SAED patterns confirmed a single-crystalline tetragonal structure. EDXS analysis demonstrated high chemical purity and near-stoichiometric composition. XPS spectra identified Pb 2+ and W 6+ as the predominant oxidation states, with additional W 5+ contributions indicating the presence of oxygen vacancies. The O 1 s XPS components indicated defect-related surface oxygen species A nonclassical growth mechanism is proposed to explain the star-like morphology. UV–Vis analysis indicated a band gap of 3.80 eV, suggesting intermediate energy levels related to oxygen defects. Strong blue photoluminescence under 350 nm excitation was observed at room temperature and attributed to distorted [WO 4 ] and [PbO 8 ] clusters. The photocatalytic activity was evaluated through the degradation of Rhodamine B and Reactive Red 195 under UV irradiation, achieving high degradation efficiencies, apparent rate constants up to 2.58 × 10 -2 min -1 , and good stability over four reuse cycles. Scavenger experiments confirmed that hydroxyl radicals (•OH) and photogenerated holes ( h + ) are the main active species, while acute toxicity assays using Artemia salina indicated low toxicity of the treated solutions.

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