Different approaches for preparing a novel thiol-functionalized graphene oxide/Fe-Mn and its application for aqueous methylmercury removal

A novel thiol-functionalized graphene oxide/Fe-Mn composite (SGO/Fe-Mn) was synthesized via three different methods, i.e., acetic acid method (SGO/Fe-Mn-ac), neutral method (SGO/Fe-Mn-ne), and ammonium hydroxide method (SGO/Fe-Mn-am). The composites were characterized and tested for aqueous methylmercury removal. SGO/Fe-Mn was prepared using 3-mercaptopropyltrimethoxysilane (3-MPTS) as a silanizing reagent, and hydrolyzed 3-MPTS mainly interacted with GO/Fe-Mn through surface oxygen-containing groups (i.e., OH, C O, epoxy C O C, carboxyl O C O, and C O) and π-π interactions, partially through self-polymerization. SGO/Fe-Mn-am showed the largest hydrodynamic diameter, strongest π-π bond, fewest S oxidation products, most thiol groups, negative charge, sp 3 defects, and FeOOH. Pseudo-second-order kinetic model and Langmuir and Freundlich isotherm models fitted well with methylmercury sorption kinetic and isotherm data, respectively, resulting in a CH 3 Hg + maximum sorption capacity of 43.88 mg/g for SGO/Fe-Mn-am, 36.33 mg/g for SGO/Fe-Mn-ac, and 28.00 mg/g for SGO/Fe-Mn-ne. The removal mechanism was described by electrostatic attraction, ligand exchange, and surface complexation. This study demonstrates potential and viability of SGO/Fe-Mn for enhanced immobilization of CH 3 Hg + in surface water, groundwater, and soil/sediments.