Biogenesis Synthesis of ZnO NPs: Its adsorption and photocatalytic activity for removal of acid black 210 dye

Abstract This study investigated the treatment of textile wastewater contaminated with Acid Black 210 dye (AB210) using zinc oxide nanoparticles (ZnO NPs) through adsorption and photocatalytic techniques. ZnO NPs were synthesized using a green synthesis process involving eucalyptus leaves as reducing and capping agents. The synthesized ZnO NPs were characterized using UV-Vis spectroscopy, SEM, EDAX, XRD, BET, Zeta potential, and FTIR techniques. The BET analysis revealed a specific surface area and total pore volume of 26.318 m 2 /g. SEM images confirmed the crystalline and spherical nature of the particles, with a particle size of 73.4 nm. A photoreactor was designed to facilitate the photo-degradation process. The study investigated the influence of key variables on the adsorption and photocatalytic break-down of AB210. The results indicated that under optimal conditions (AB210 concentration: 5 mg/L, ZnO NPs dosage: 0.75 g/L, pH: 5, and temperature: 45 °C), the removal efficiency after 180 minutes of adsorption was 62%. However, in the case of photo-degradation, complete removal of 5 mg/L AB210 was achieved within 30 minutes at a pH of 7, UV intensity of 24 W/m 2 , and temperature of 45 °C. The adsorption process exhibited the best fit with the pseudo-second-order kinetic model. Various adsorption isotherms, including Freundlich, Langmuir, Temkin, and Dubinin models, were studied, and the Langmuir isotherm provided the best fit to the experimental data (see Supplementary Materials). Fur-thermore, thermodynamic analysis indicated that the adsorption process was spontaneous, endothermic, and favorable, with Δ G°, Δ H°, and Δ S° values of -0.782 kJ/mol, 26.93 kJ/mol, and 0.086 kJ.mol/K, respectively