Preparing Desirable Activated Carbons from Agricultural Residues for Potential Uses in Water Treatment

Abstract

This research aims to outline a simple but effective way combining orthogonal array design (OAD), experiments and characterization to produce desirable activated carbons (AC) from agricultural wastes. OAD, and experiments including carbonization, KOH impregnation and activation were combined to optimize the preparation of AC derived from coffee residues with high specific surface areas. Results suggest that the optimized parameters are a carbonization temperature (Tc) of 450 °C (30 min), a KOH impregnation ratio (Rkc) of 3:1, and an activation temperature (Ta) of 750 °C (60 min). Extensive experiments further showed that a 100-min (ta) activation with Ta of 900 °C achieved AC with a specific surface area of 2111 m2/g, a high value that has not been reported previously in the production of AC from coffee wastes. Such high specific surface areas are favorable for use in water treatment, but will lead to a reduced yield of AC. N2 adsorption–desorption isotherms, scanning electron microscopy and Fourier transform infrared spectroscopy were shown to be useful tools for investigating the specific surface area, surface functional groups and pore size distribution of AC. Capacitance performance that may indicate the electrosorption capability of AC being used as electrode materials in capacitive deionization was examined by cyclic voltammetry and galvanostatic charge–discharge curves, and the consistency with specific surface areas was confirmed.