Facile synthesis of zinc oxide nanoparticles loaded activated carbon as an eco-friendly adsorbent for ultra-removal of malachite green from water

Green synthesis ultrasonic method is reported for the preparation of zinc oxide nanoparticles loaded on activated carbon (AC) derived from coffee waste. The zinc modified AC was used effectively for the elimination of malachite green (MG) from wastewater. The examined batch adsorption parameters are; initial pH (2–9), adsorbent dose (0.10–0.50 g/100 mL), mixing time (5–120 min), MG concentrations (25–300 mg/L) and temperature (298–318 K). XRD, SEM/EDS, FT-IR and TGA/DTA techniques were used to characterize the developed Zn(OH)₂-AC composite. The results demonstrated that the adsorption capacity of Zn(OH)₂-AC composite was improved with incremental of the initial dye concentration, pH, and temperature, and decreased as the Zn(OH)₂-AC composite dose was increased. The Langmuir isotherm model (R²=0.97) showed better conventionality than the Freundlich model (R²=0.80) with a maximum removal capacity of 303.03 mg/g at 318 K and pH 7.0. The kinetic results revealed that the equilibrium data well follow the pseudo-second-order model. The thermodynamic investigations indicated the spontaneous and endothermic removal of MG. The cycling test exhibited that the developed Zn(OH)₂-AC composite had virtuous repeatable adsorption/desorption performance particularly until the fourth cycle. In addition to comparatively shorter adsorption time, relatively high adsorption capacity, reasonable reuse performance, and being of cost-effective and eco-friendly of the developed Zn(OH)₂-AC composite make it economic, effective and hopeful adsorbent for cleaning MG containing wastewaters.