Efficient removal of methylene blue via two-step modification hazelnut shell biochar: Process intensification, kinetics and thermodynamics

Abstract

Porous carbon materials with ultra-high specific surface area and adjustable pore structure characteristics were prepared from food industry waste hazelnut shells for the adsorption of methylene blue (MB) wastewater by two-step activation by impregnation with ZnCl2 followed by chemical activation with KOH. The Fusso effect, which can reduce the size of MB molecules, was further used to enhance the adsorption of MB on porous carbon. The results show that both HSBC-a and HSBC-a-b have ultra-high specific surface area (2979.59 m2/g for HSBC-a, 2882.73 m2/g for HSBC-a-b). The mesopore ratio of HSBC-a-b (Vmeso/Vtotal % = 14.05%) was doubled compared to HSBC-a. It showed an excellent adsorption performance of 694.03 mg/g for MB. It showed a fast adsorption kinetics and the adsorbed amount increased to 882.46 mg/g at 0.1 M NaCl solution. In addition, adsorption processes were studied using adsorption kinetics and adsorption isotherm model fitting. The results of this research confirm that hazelnut shell is a kind of promising and sustainable porous carbon raw material, and its ultra-high specific surface area and adjustable pore structure characteristics are favorable for the efficient treatment of MB from dyeing wastewater. This work could provide potential guidance for the high-value utilization of waste hazelnut shell biochar.