Leaves extracts-driven synthesis of ZnO nanoparticles for enhanced adsorption of methyl red dye

Abstract

Textile dye contamination in wastewater poses a significant ecological threat, demanding urgent attention from industrialists and scientists. This study explores an environmentally benign method to manufacture zinc oxide nanoparticles (ZnO-NPs) using a quick, affordable, and sustainable method with aqueous extracts of Mangifera indica and Syzygium cumini leaves (1:1) to remove methyl red dye (MR). Characterization of the synthesized ZnO-NPs was conducted using UV–Vis, FTIR, DLS, zeta potential, SEM, EDX, BET, and X-ray diffraction (XRD). The XRD spectra, aligned with JCPDS card (00-005-0664), confirmed the presence of ZnO-NPs, with average crystallite sizes of 11.83 nm and 19.09 nm determined by the Scherrer formula and W–H technique, respectively. SEM analysis revealed an average size of 41.78 nm. The batch adsorption study revealed that MR removal efficiency using ZnO-NPs depends on pH (1–8), initial dye concentration (5–60 mg/L), contact time (0–30 min), and adsorbent dose (2–20 mg). The highest MR removal rate was 99% after 10 min at pH 4 in 20 mg/L solution. Kinetic analysis aligned with the pseudo-second-order model, supported by four statistical error models, while adsorption isotherm findings fit the Langmuir isotherm, exhibiting an adsorption capacity of 66.4 mg/g. Thermodynamic analysis indicated that MR dye adsorption on ZnO is an endothermic (∆H° > 0) and spontaneous (∆G° < 0) process. The ZnO nanoparticles exhibited promising antibacterial activity, with desorption data and cost analysis confirming their stability, reusability, and feasibility over multiple cycles. This study highlights the intriguing efficacy of green ZnO nanoparticles for effectively removing dyes from textile waste streams.

Graphical abstract