Effects of γ-irradiation on the structural, optical and photocatalytic performance of bismuth vanadate nanoparticles

This paper investigates the effects of γ-irradiation on the physico-chemical properties of monoclinic scheelite-type BiVO₄ nanoparticles synthesized via a microwave (MW)-assisted method. The nanoparticles were exposed to absorbed doses of 20 and 200 kGy, and their structural, optical, defect-related, surface, adsorption, and photocatalytic properties were evaluated. X-ray diffraction (XRD) confirmed retention of the monoclinic scheelite ( ms ) structure, with crystallite sizes of 22–24 nm. The transmission electron microscopy (TEM) and microstructural analyses indicated dose-dependent changes and particle reorganization with minor variations in lattice strain and dislocation density. Diffuse reflectance spectroscopy (DRS) revealed only modest variations in the Tauc-derived band gap. Electron paramagnetic resonance (EPR) showed a broad V⁴⁺-related resonance in all samples and a non-monotonic change in relative signal intensity, without any additional spectrally resolved paramagnetic species. X-ray photoelectron spectroscopy (XPS) showed no measurable changes in the stable dominant Bi³⁺ and V⁵⁺ states but revealed a gradual increase in the high-binding-energy O 1s component, indicating modification of the surface oxygen environment. Zeta potential and dynamic light scattering (DLS) measurements further demonstrated dose-dependent changes in electrokinetic and colloidal behavior. The most pronounced effects were observed for methylene blue (MB) removal. Pristine ms -BiVO₄ achieved 95.63% total removal, comprising 67.97% dark adsorption and a 27.66% photocatalytic removal contribution. After γ-irradiation, dark adsorption decreased to 6.00% and 12.22% at 20 and 200 kGy, respectively, while the corresponding photocatalytic removal contributions were 40.50% and 12.01%. Overall, γ-irradiation preserves bulk monoclinic structure but alters defect-related and surface-associated characteristics, emphasizing the importance of distinguishing adsorption from photocatalysis in performance evaluation.