Green synthesis of α-V2O5 photocatalyst using Gymnema sylvestre leaf extract and an insight into the mechanism of photocatalytic degradation of methylene blue and congo red under visible light illumination

Semiconductor-mediated photocatalysis plays a vital role in the removal of hazardous organic dyes from wastewater. In the present work, a green and sustainable solution combustion method was employed to synthesize α-vanadium pentoxide (α-V 2 O 5 ) using Gymnema sylvestre leaf extract as a natural fuel and reducing agent, with ammonium metavanadate as the vanadium precursor. Powder X-ray diffraction (PXRD) analysis confirmed the formation of phase-pure orthorhombic α-V₂O₅ with an average crystallite size of ∼17.8 nm. Photoluminescence studies revealed the presence of defect-related emission bands, indicating oxygen vacancies and mixed valence states (V⁵⁺/V⁴⁺), which are favorable for charge carrier trapping. FTIR spectra confirmed the characteristic V–O–V and V O vibrational modes, while SEM analysis showed a flake-like morphology with agglomerated porous structures. Elemental composition and purity were verified by EDX analysis. The photocatalytic performance of the synthesized α-V₂O₅ was evaluated for the degradation of methylene blue (MB) and congo red (CR) dyes under visible light irradiation. The degradation efficiency increased with catalyst dosage, with 50 mg identified as the optimal loading, achieving complete decolorization of both dyes within 50 min. The degradation kinetics followed a pseudo-first-order model with apparent rate constants of 0.12948 min⁻¹ for MB and 0.10360 min⁻¹ for CR. The enhanced photocatalytic activity is attributed to efficient charge carrier dynamics arising from oxygen vacancies, polaronic electron hopping, and multivalent vanadium redox cycling, which collectively suppress electron–hole recombination. LC–MS analysis confirmed the stepwise breakdown of dye molecules into smaller intermediates, supporting the proposed degradation mechanism. Overall, this study demonstrates that green-synthesized α-V 2 O 5 is a structurally stable, defect-rich, and efficient visible-light photocatalyst, offering a sustainable and promising approach for the treatment of dye-contaminated wastewater. • Ecofriendly synthesis of V 2 O 5 nanocomposite. • The TEM and XRD analysis confirmed its nano size. • Photocatalysis and dye degradation is evaluated.