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The toxicity of heavy metals motivated the synthesis of coconut shell‐based activated carbon (CSAC) through single‐stage microwave irradiation technique to scavenge cadmium ions (Cd(II)). Response surface methodology revealed the optimum radiation power and radiation time which translated into 85.45 % of Cd(II) removal and 41.78 % of CSAC's yield. Isotherm and kinetic data were best described by Freundlich and pseudo‐first‐order (PFO) models, respectively. The changes of enthalpy, entropy, and activation energy were determined as well as the reduction of CSAC yield and Cd(II) removal after six regeneration cycles.

The focal point of this study is to synthesis Alpinia galanga Stem-based activated carbon (AGSAC) by using single-step microwave irradiation and testing it for the removal of cationic dye, methylene blue (MB) from aqueous solution. AGSAC was prepared under the flow of carbon dioxide (CO2) for the gasification effect. The factors of contact time (from 0 to 24 h) and initial concentration (25-300 mg/L) on the adsorption performance of AGSAC were studied. With the aid of response surface methodology (RSM) via face-centered composite design (FCD), optimum preparation conditions for AGSAC were found to be 400 W for radiation power and 4 min for activation time, respectively, which resulted in 95.67% of MB dye removal. The optimized AGSAC has a Bruneaur-Emmet-Teller (BET) surface area of 172.19 m2/g, mesopore surface area of 103.32 m2/g, a total pore volume of 0.1077 cm3/g, and fixed carbon content of 47.63%. The pore diameter of AGSAC was found to be a mesoporous type with a pore diameter of 2.50 nm. Freundlich isotherm and pseudo-second-order were found as the best-fitted model for MB adsorption equilibrium and kinetic respectively onto prepared AGSAC. Intraparticle diffusion was found to be the rate-limiting step.

This research aims to optimize preparation conditions of coconut-shell-based activated carbon (CSAC) and to evaluate its adsorption performance in removing POP of dichlorodiphenyltrichloroethane (DDT). The CSAC was prepared by activating the coconut shell via single-stage microwave heating under carbon dioxide, CO2 flow. The total pore volume, BET surface area, and average pore diameter of CSAC were 0.420 cm3/g, 625.61 m2/g, and 4.55 nm, respectively. The surface of CSAC was negatively charged shown by the zeta potential study. Response surface methodology (RSM) revealed that the optimum preparation conditions in preparing CSAC were 502 W and 6 min for radiation power and radiation time, respectively, which corresponded to 84.83% of DDT removal and 37.91% of CSAC’s yield. Adsorption uptakes of DDT were found to increase with an increase in their initial concentration. Isotherm study revealed that DDT-CSAC adsorption system was best described by the Langmuir model with monolayer adsorption capacity, Qm of 14.51 mg/g. The kinetic study confirmed that the pseudo-second-order model fitted well with this adsorption system. In regeneration studies, the adsorption efficiency had slightly dropped from 100% to 83% after 5 cycles. CSAC was found to be economically feasible for commercialization owing to its low production cost and high adsorption capacity.

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