High-surface area mesoporous activated carbons were prepared from biomass by incorporating H2O2 as an oxidizing agent during hydrothermal pre-treatment of the raw material (coconut shell). Use of H2O2 led to enhanced formation of OFGs in the hydrochar precursor and resulted in activated carbons possessing high mesopore and BET surface areas. A strong interdependence is observed between the extent of formation of oxygenated functional groups (OFGs) in the hydrochars obtained from the hydrothermal pre-treatment and mesopore area in corresponding carbons. The mesoporous carbons showed high adsorption capacity for Rhodamine B up to 714 mg/g. (C) 2015 Elsevier B.V. All rights reserved.