Preparation of pore-size tunable activated carbon derived from waste coffee grounds for high adsorption capacities of organic dyes

In this study, we report a promising route to prepare pore-size tunable activated carbon (AC) derived from waste coffee grounds (WCGs) using CO2 activation. The as-prepared highly pure AC displays a high specific surface area of 2407 m2/g with a total pore volume of 1.281 cm3/g. The pore-size distribution can be effectively tuned by adjusting the activation temperature from 800 to 950 °C, and the volume ratio of micropores/total pores for the AC can be tuned from 86.4 to 10.3 v/v %. For the adsorption of organic dyes, methylene blue (MB) and methyl orange (MO), the adsorption capacities for MB (qe =678 mg/g) and MO (qe =612 mg/g) are remarkably high compared with that of a commercial AC (qe = 181 mg/g). The kinetic adsorption results were well fitted with the pseudo-second order model, and the equilibrium data were well described according to the Langmuir isotherm behaviour. The high adsorption capacity of organic dyes onto AC can be attributed to a multi-interaction adsorption mechanism including electrostatic interactions and π-π interactions. The present approach offers a simple route for the conversion of biomass wastes into a highly effective adsorbent for water remediation.