Efficient removal of methylene blue by activated hydrochar prepared by hydrothermal carbonization and NaOH activation of sugarcane bagasse and phosphoric acid

Activated-hydrochar (AHC) derived from sugarcane bagasse was synthesized by hydrothermal carbonization (HTC) using phosphoric acid and sodium hydroxide (NaOH) as activators. The properties of AHC were systematically characterized by elemental analysis, BET, SEM, FTIR, XPS and zeta potential, and applied to evaluate the adsorption ability of methylene blue (MB) by batch adsorption tests. The MB adsorption isotherm and kinetics of AHC were well described by the Langmuir model and pseudo-second-order kinetic model. Characteristic analysis suggested electrostatic attraction, hydrogen bonding and π–π interactions were the main contributors to MB adsorption. Analysis of mass transfer mechanisms demonstrated the adsorption process towards MB by AHC involved intra-particle diffusion to some extent. Thermodynamic studies indicated MB adsorption was an endothermic, spontaneous process associated with a disorder increase at the solid–liquid interface. The maximum adsorption capacity of AHC for MB was 357.14 mg g(−1) at 303 K. Thus, the combination of HTC in phosphoric acid and NaOH activation offered a facile, green and economical alternative for conversion of sugarcane bagasse into efficient adsorbents used in wastewater treatment.