Preparation of various thiol-functionalized carbon-based materials for enhanced removal of mercury from aqueous solution

Abstract

In this work, biochar (BC), activated carbon (AC), and graphene oxide (GO) were thiol-functionalized using 3-mercaptopropyltrimethoxysilane (3-MPTS) (named as BCS, ACS, and GOS, respectively). BCS, ACS, and GOS were synthesized mainly via the interaction between hydrolyzed 3-MPTS and surface oxygen-containing functional groups (e.g., –OH, O–C=O, and C=O) and π-π interaction. The materials before and after modification were characterized and tested for mercury removal, including sorption kinetics and isotherms, the effects of adsorbent dosage, initial pH, and ionic strength. Pseudo-second-order sorption kinetic model (R2\xa0=\u20090.992~1.000) and Langmuir sorption isotherm model (R2\u2009=\u20090.964~0.998) fitted well with the sorption data of mercury. GOS had the most –SH groups with the largest adsorption capacity for Hg2+ and CH3Hg+ (449.6 and 127.5\xa0mg/g), followed by ACS (235.7 and 86.7\xa0mg/g) and BCS (175.6 and 30.3\xa0mg/g), which were much larger than GO (96.7 and 4.9\xa0mg/g), AC (81.1 and 24.6\xa0mg/g), and BC (95.6 and 9.4\xa0mg/g). GOS and ACS showed stable mercury adsorption properties at a wide pH range (2~9) and ionic strength (0.01~0.1\xa0mol/L). Mercury maybe removed by ligand exchange, surface complexation, and electrostatic attraction.