Adsorption of lead ions and methylene blue on acrylate-modified hydrochars

Hydrochars are promising sorbents for wastewater treatment. Herein, two acrylate-modified hydrochars (AMHC1 and AMHC2) were obtained by grafting acrylic acid on the surface of two hydrochars (MHC1 and MHC2 hydrothermally carbonized in water and acidic medium respectively) with free radical polymerization. Characterizations show that MHC2 is more prone to free radical polymerization than MHC1 does, and has higher carboxylate content after modification. The adsorption amounts of AMHC2 over methylene blue (MB) and Pb(II) are much higher than those of AMHC1. Pseudo-second-order kinetic and Langmuir isotherm equations well fit the Pb(II) and MB sorption data of AMHC2. The Pb(II) adsorptive mechanism is mainly inner-surface complexation accompanied by ion exchange and cation-π interaction. MB adsorption involves ion exchange, electrostatic interaction, H-bonding and π-π interaction. Hence, the one-step modification method of free radical polymerization under alkaline condition has great potential for preparing carboxylate-modified hydrochars to adsorb cationic pollutants.