Single-stage microwave assisted coconut shell based activated carbon for removal of Zn(II) ions from aqueous solution – Optimization and batch studies

Abstract

Health and environmental issues associated with heavy metal ions have received serious attention from communities worldwide. This work explores the potential of coconut shell as activated carbon (CSAC), in adsorbing zinc, Zn(II) ions. This adsorbent was prepared via a single-stage microwave irradiation technique under the flow of carbon dioxide, CO 2 gas. CSAC posed BET surface area of 625.61 m 2 /g, 513.25 m 2 /g of mesopores surface area, total pore volume of 0.42 cm 3 /g, and average pore diameter of 4.55 nm. Zeta potential distribution on CSAC was found to be −21 mV. Response surface methodology (RSM) had suggested that the optimum values of variables were 450 W and 3.17 min for radiation power and radiation time respectively, which resulted in 69.65% of Zn(II) removal and 44.32% of CSAC’s yield. Based on F-value, radiation power (473.62) and radiation time (140.50) posed major and moderate effects on Zn(II) removal, respectively. Meanwhile, CSAC’s removal was significantly affected by radiation power (78.84) and less affected by radiation time (7.06). In a batch study, when the initial concentration of Zn(II) was increased, Zn(II) uptakes increased as well. On contrary, Zn(II) removal percentage decreased with the increase of Zn(II)’s initial concentration. Multilayer adsorption of Zn(II) onto CSAC had occurred since this adsorption system followed Freundlich isotherm the best, and the monolayer adsorption capacity, Q m for Zn(II) was revealed to be 7.87 mg/g. The kinetic data of the Zn(II)-CSAC adsorption system was best described by pseudo-first-order (PFO) which indicated the role of physisorption. In the regeneration study, CSAC’s mass and Zn(II) adsorption uptakes had reduced from 100% to 37% and 77%, respectively, after 6 regeneration cycles.