Removal of methylene blue from aqueous solution by modified bamboo hydrochar.

Four hydrochars (labeled as HC, AHC, MHC, and MAHC, respectively) were prepared by hydrothermal carbonization of bamboo with and without chlorane or followed by NaOH modification. Various techniques were adopted to characterize the physicochemical properties of hydrochars and the removal of methylene blue (MB) by these hydrochars from aqueous solution was investigated. The MB adsorption isotherm and kinetic onto MAHC and MHC can be preferably interpreted by Langmuir adsorption mode and the pseudo-second-order model, respectively. Thermodynamic parameters implied that adsorption was a spontaneous and exothermic process. The adsorption capacity of MAHC was 655.76 mg g-1, which was 2-3 times compared to that of MHC (268.93 mg g-1) at 303 K. The high adsorption capacity of MAHC for MB suggests that hydrothermal carbonization in acidic medium followed by alkaline treatment has the potential application to produce efficient MB adsorbents used in wastewater treatment.