Green Synthesis and Characterisation of Plant-Extract-Mediated Zinc Oxide Nanoparticles for Environmental Remediation: A Model-Based Framework Linking Structural Descriptors to Photocatalytic Performance

Abstract

Plant-extract-mediated synthesis of metal oxide nanoparticles has become one of the most widely reported routes to photocatalysts for wastewater remediation, yet the literature remains difficult to compare because structural descriptors, optical descriptors and kinetic constants are reported under incompatible conventions and are rarely propagated into a single quantitative statement of performance. This article addresses that gap by constructing an explicit, fully specified evaluation framework for phytochemically synthesised zinc oxide, in which every reported number is computed from a declared generating model rather than measured in the laboratory. A wurtzite diffraction dataset was generated for seven indexed reflections from a stated crystallite size of 22 nm and a lattice microstrain of 1.20 × 10⁻³, and the resulting line widths were analysed by the Scherrer and Williamson–Hall methods. Scherrer analysis returned a mean crystallite size of 16.9 ± 0.9 nm, whereas Williamson–Hall regression recovered 20.9 nm together with a microstrain of 9.95 × 10⁻⁴ at a coefficient of determination of 0.9482, quantifying the systematic underestimate that follows when strain broadening is neglected. Tauc extrapolation of a modelled direct-allowed absorption edge returned a band gap of 3.17 eV against a generating value of 3.18 eV. Photocatalytic decolourisation was modelled by Langmuir–Hinshelwood kinetics; linearisation of initial rates recovered a rate constant of 0.441 mg L⁻¹ min⁻¹ and an adsorption constant of 0.0350 L mg⁻¹ with a coefficient of determination of 0.9987, and apparent first-order constants fell from 0.0116 to 0.0055 min⁻¹ as the initial dye concentration rose from 10 to 50 mg L⁻¹. The framework is offered as a reporting and screening template, not as a substitute for experimental validation.