Green synthesis of ZnO nanoparticles using Justicia adhatoda for effective photocatalytic degradation of methylene blue dye

Abstract

The proposed eco-friendly technique for synthesizing zinc oxide nanoparticles (ZnO NPs) shows significant potential due to its sustainability, no detrimental impacts, ecological safety, and non-toxicity. In this study, ZnO NPs were synthesized using Justicia adhatoda leaf extract as a reducing and stabilizing agent, leveraging its phytochemical richness to obtain highly crystalline nanoparticles with diverse morphologies, which are used as a photocatalyst to degrade methylene blue (MB) dye. The characterization of prepared ZnO NPs was conducted using XRD, UV-Vis, FTIR, FESEM, and EDX analysis. Optical characterization indicated strong absorption in the UV region (371 nm) with a suitable band gap (3.04 eV) for photocatalysis. The hexagonal wurtzite crystallite size (18.57 nm) was confirmed through XRD pattern analysis. FESEM investigation revealed a rough flower-like morphology with an average particle size of 75 nm. The FTIR spectrum confirmed the presence of Zn–O stretching vibrations, as confirmed by the characteristic peak observed at 693 cm⁻¹. The biosynthesized ZnO NPs exhibited excellent photocatalytic performance in degrading methylene blue under natural sunlight, achieving nearly complete removal under optimized conditions. The degradation process followed pseudo-first-order kinetics, possessing a rate constant of 0.037 min⁻¹. Overall, this work highlights a sustainable and low-cost method for fabricating ZnO-based photocatalysts, offering significant promise for environmental remediation.