Fluence-controlled PLAL synthesis of WO₃ nanoparticles for visible-light dye degradation

Surfactant-free WO₃ colloids were synthesized by nanosecond pulsed laser ablation in water at fluences of 10, 20, 40, 70, and 100 J cm⁻². The study evaluates fluence as a processing parameter for tuning the structure, morphology, optical response, colloidal state, and visible-light dye-degradation performance of pristine WO₃ nanoparticles. XRD confirmed monoclinic WO₃ across the full fluence range, with sharper and more intense diffraction features at higher energy density. UV–Vis analysis showed reduced broadband attenuation, increased transmission, and widening of the Tauc-derived optical band gap from 2.59 to 3.10 eV, mainly reflecting changes in optical-edge sharpness, scattering, and suspension heterogeneity. AFM and FE-SEM revealed fluence-dependent changes in deposited surface features, aggregate texture, and nanoparticle packing. TEM showed particle refinement from 72 nm at 10 J cm⁻² to 36 nm at 70–100 J cm⁻², while DLS indicated nonmonotonic hydrodynamic-size evolution. The smallest hydrodynamic size, 58 nm, was obtained at 40 J cm⁻², followed by renewed aggregation at higher fluence. Visible-light methylene blue degradation followed this intermediate-fluence behavior, with the 40 J cm⁻² condition reaching 76% degradation after 180 min and a pseudo-first-order rate constant of 0.00849 min⁻¹ . These results establish a processing–structure–colloid–performance relationship for PLAL-derived WO₃ and demonstrate fluence selection as an effective route for tuning additive-free oxide colloids.