The Preparation And Properties Of Thiol-functionalized Activated Carbon For Selective Removal Of Hg²⁺

The pollution of mercury has been a hot issue in the treatment of heavy metal.For a long time, it is difficult for handing mercury-containing PVC waste water withhigh acid and high concentration of impurity ions. Therefore, it is imperative todevelop a material with high selectivity and acid stability.A novel thiol-functionalized activated carbon material (FMTA) was prepared bymodification with3-mercaptopropyl trimethoxysilane(TMMPS) on the activatedcarbon substrate. Various characterization methods including SEM-EDS, XRD, XRF,BET, FT-IR and Roman were utilized for the microstructural analysis of FMTA.Various characterization methods including SEM-EDS, XRD, XRF, BET, FT-IR andRoman were utilized for the evaluation of FMTA. The analysis of SEM shows that theFMTA is filled with holes of different sizes and covered by a similar organicmembrana on the surface and pores, which is beneficial for the diffusion andadsorption. The FT-IR, Raman, SEM, XRD were used to characterize the composite,which indicated that the organic membrana is thiol-functionalization oraganicmonolayers. The introduction of the functionalized monolayers make the materialspossess more high affinity functional groups-SH to mercury ions. BET analysisshows that the specific surface area of FMTA is911.2m2/g and the average pore sizewas1.231nm, which can give more adsorption sites and higher surface energy. XRFanalysis indicates that the proportion of S content in FMTA accountes for4.73%,which could improve the adsorption capacity and selectivity of the adsorbent.To improve the adsorptive property of FMTA, the impacts of ethanol/water ratioand the concentration of TMMPS were evaluated. Adsorption kinetic experimentsindicated that more than98.9%of the mercury ion was absorbed by the compositewithin the first25min. The study of mass transfer of FMTA found that the diffusionof Hg2+in the adsorbent was determined by internal diffusion and surface diffusion.Thermodynamic properties of adsorption process experiment proved that themaximum adsorption capacity of the materials could reach542.8939mg/g. Combinedwith the adsorption thermodynamic data of20°C-60°C, thermodynamic equationswere fitted, and the fitting results:ΔH=-26.707kJ/mol, andΔS=-35.92J/mol.K, whichindicated that the adsorption process was an exothermic process. The Gibbs freeenergy changes from negative to positive with the increasing temperature, whichindicated the existence of physical adsorption and chemical adsorption.For the condition of mercury-containing PVC waste with high acid and impurity ions, the effects of acidity, coexisting ions on the adsorption process was investigated.The results shown that the adsorptive property of FMTA still kept stable in thehigh-acid(pH＜1) condition and FMTA remained high adsorption selectivity formercury ions when the concentration of Cd2+, Pb2+, Cu2+, Zn2+, Cl-is100times ofmercury ion except Pb2+. Above all, FMTA has the potential to be directly applied forthe removal of mercury ion from PVC high-acid waste water, and it also provide areference for the removal of other heavy metal ions in the highly acidic environment.