Effective removal of inorganic mercury and methylmercury from aqueous solution using novel thiol-functionalized graphene oxide/Fe-Mn composite

A novel thiol-functionalized graphene oxide/Fe-Mn (SGO/Fe-Mn) was investigated for aqueous Hg2+ and CH3Hg + removal. Mercury were removed mainly through ligand exchange and surface complexation with surface active sites (i.e., -SH, -OH, O-C=O, C=C, Si-O, and pi-pi bond). SH had the strongest binding ability with mercury, forming sulfur-containing organic matter or polymers with Hg2+, and sulfur-containing organometallic compounds or thiolate-like species with CH3Hg+. The BET sorption isotherm model well simulated the sorption isotherm data of Hg2+ (R-2= 0.995, q(m)=233.17 mg/g) and CH3Hg+ (R-2=0.997, q(m)=36.69 mg/g), indicating a multilayer adsorption process. The mercury uptake was promoted with the increase of 3-MPTS content, adsorbent dosage, and pH (< 5.5), whereas the uptake was inhibited by high pH (> 5.5) and high concentrations of humic acid and electrolytes. SGO/Fe-Mn demonstrated high mercury uptake in simulated surface water/groundwater and in the presence of Pb, Cu, Ni, Sb, Cd and Zn. The mercury-laden SGO/Fe-Mn can be successfully regenerated and reused for three times with 98.1% and 67.0% of original Hg2+ and CH3Hg+ sorption capacity when 5% thiourea + 2 M KI was used as the desorbing agent. This study demonstrates potential and viability of SGO/Fe-Mn for mercury remediation.