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<p>Green synthesis of metal oxide semiconductor-based photocatalysts has emerged as an effective strategy to tailor defect chemistry and enhance sunlight-driven photocatalytic performance. In this work, tungsten oxide (WO<sub>3</sub>) nanoparticles were synthesized via Trachyspermum <i>ammi</i> seed plant extract-assisted green synthesis and conventional chemical route, followed by annealing at different temperatures. X-ray diffraction analysis supported by Rietveld refinement reveals that the green-synthesized unannealed sample consists of a mixed phase of monoclinic WO<sub>3</sub> and tungsten hydrate, whereas progressive thermal annealing improves crystallinity and yields a phase-pure monoclinic WO<sub>3</sub> structure at 400&#xa0;°C. Morphological analysis using Field emission scanning electron microscopy (FESEM) indicated that the unannealed green synthesized sample has an average particle size of ~ 85&#xa0;nm with mixed morphology, primarily consisting of quasi-spherical crystallites along with secondary larger cubical structures, whereas the 400&#xa0;°C annealed sample demonstrated a reduced average particle size of ~ 64.5&#xa0;nm and a more uniform quasi-spherical morphology. Optical studies indicate that the band gap values remain nearly unchanged in the range of ~ 2.4–2.6&#xa0;eV. However, a pronounced Urbach tail and a shift in the absorption edge are observed in green-synthesized samples, attributed to defect-induced localized states within the band gap. Lastly, the photodegradation of methylene blue (MB) dye in sunlight as a function of time is elucidated. The unannealed raw and low-temperature annealed Trachyspermum <i>ammi</i> seed plant extract assisted green synthesized samples exhibit higher photocatalytic performance compared to chemically synthesized WO<sub>3</sub>. The highest degradation efficiency of (70.7 ± 5.7) % and rate constants of (0.00992 ± 0.00079) min<sup>− 1</sup> are obtained for the green-synthesized unannealed raw sample, whereas the chemically synthesized counterpart shows a much lower degradation efficiency of (59.74 ± 4.8) % with a rate constant of (0.00578 ± 0.00046) min<sup>− 1</sup>, following pseudo-first-order kinetics. The enhanced photocatalytic activity observed in the unannealed green-synthesized sample is attributed to the presence of mixed phases and a higher degree of structural disorder, which leads to defect-induced modifications in the optical absorption behavior. With increasing annealing temperature, crystallinity and phase purity increases, however a reduction in defect density leads to comparatively lower photocatalytic activity. This study demonstrates that green synthesis, combined with controlled annealing, provides an effective route for tuning phase composition and defect states to optimize the photocatalytic performance of WO<sub>3</sub> nanoparticles.</p>

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Phytochemical Complex-Driven Green-synthesis of tungsten oxide nanoparticles derived from Trachyspermum ammi seed extract for enhancing solar photocatalysis: performance comparison with conventional chemical route

  • 期刊论文

  • 发表日期：

    2026年5月25日

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  • Shakun Saini,
  • Ishan Choudhary

摘要

Green synthesis of metal oxide semiconductor-based photocatalysts has emerged as an effective strategy to tailor defect chemistry and enhance sunlight-driven photocatalytic performance. In this work, tungsten oxide (WO3) nanoparticles were synthesized via Trachyspermum ammi seed plant extract-assisted green synthesis and conventional chemical route, followed by annealing at different temperatures. X-ray diffraction analysis supported by Rietveld refinement reveals that the green-synthesized unannealed sample consists of a mixed phase of monoclinic WO3 and tungsten hydrate, whereas progressive thermal annealing improves crystallinity and yields a phase-pure monoclinic WO3 structure at 400 °C. Morphological analysis using Field emission scanning electron microscopy (FESEM) indicated that the unannealed green synthesized sample has an average particle size of ~ 85 nm with mixed morphology, primarily consisting of quasi-spherical crystallites along with secondary larger cubical structures, whereas the 400 °C annealed sample demonstrated a reduced average particle size of ~ 64.5 nm and a more uniform quasi-spherical morphology. Optical studies indicate that the band gap values remain nearly unchanged in the range of ~ 2.4–2.6 eV. However, a pronounced Urbach tail and a shift in the absorption edge are observed in green-synthesized samples, attributed to defect-induced localized states within the band gap. Lastly, the photodegradation of methylene blue (MB) dye in sunlight as a function of time is elucidated. The unannealed raw and low-temperature annealed Trachyspermum ammi seed plant extract assisted green synthesized samples exhibit higher photocatalytic performance compared to chemically synthesized WO3. The highest degradation efficiency of (70.7 ± 5.7) % and rate constants of (0.00992 ± 0.00079) min− 1 are obtained for the green-synthesized unannealed raw sample, whereas the chemically synthesized counterpart shows a much lower degradation efficiency of (59.74 ± 4.8) % with a rate constant of (0.00578 ± 0.00046) min− 1, following pseudo-first-order kinetics. The enhanced photocatalytic activity observed in the unannealed green-synthesized sample is attributed to the presence of mixed phases and a higher degree of structural disorder, which leads to defect-induced modifications in the optical absorption behavior. With increasing annealing temperature, crystallinity and phase purity increases, however a reduction in defect density leads to comparatively lower photocatalytic activity. This study demonstrates that green synthesis, combined with controlled annealing, provides an effective route for tuning phase composition and defect states to optimize the photocatalytic performance of WO3 nanoparticles.