Eco-Friendly Synthesis and Application of ZnO Nanoparticles for Azo Dye Degradation

Abstract

This research challenges the pressing environmental challenges of water lack and textile industry pollution, specifically focusing on the issue of azo dye contamination. Given the limitations of conventional wastewater treatment methods, this study investigates a novel and sustainable strategy: the synthesis of zinc oxide nanoparticles (ZnO NPs) using Foeniculum vulgare (FV) extract for the degradation of azo dyes. To characterize the synthesized ZnO NPs, a range of techniques are employed. X-ray diffraction (XRD) analysis confirmed the formation of pure ZnO NPs with an average crystallite size of approximately 22.4 nm. UV–vis spectroscopy is used to ascertain the band gap energy of the NPs, determined to be 3.12 eV, which is essential for their photocatalytic activity in dye degradation. Fourier-transform infrared spectroscopy (FT-IR) identified functional groups in both the FV extract and the ZnO NPs, indicating the successful integration of biomolecules from the extract into the ZnO NPs, potentially enhancing their photocatalytic properties. Field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX) provided insights into the physical morphology and elemental composition of the NPs, with elemental mapping revealing the distribution of zinc and oxygen. High-resolution transmission electron microscopy (HR-TEM) confirmed the multi-structured formation of ZnO. The catalytic efficiency is assessed by testing the degradation of commercial methyl orange. At a concentration of 120 mg L⁻¹ and a ZnO dosage of 250 mg L⁻¹, the FV:ZnO catalyst demonstrated a removal efficiency of approximately 89.13%. The photodegradation process adhered to a pseudo-first-order kinetics model.