Sulfhydryl and amino group simultaneously functionalized silica for selective removal of Hg(II) from water under neutral conditions and its application by packing into the column

Many adsorbents have been designed to remove Hg(II) contaminated water, however, the challenges of separation, long synthetic route, and high cost limited their application. In this study, sulfhydryl and amino group simultaneously modified silica (SiO2@Glycidoxy@Cys) were prepared by first silylanization of 3-glycidoxypropyltrimethoxysilane on silica, then the ring opening reaction of the epoxy group was carried out by reacting with l-cysteine. SiO2@Glycidoxy@Cys exhibited a prominent performance for the removal of Hg(II). The maximum removal efficiency and adsorption capacity of Hg(II) were 95% at pH 6-8 and 93.55 mg/g, respectively. The adsorption of Hg(II) by SiO2@Glycidoxy@Cys followed the Langmuir isothermal adsorption model, and the adsorption equilibrium can be reached within 5 min. Thermodynamic studies showed the adsorption was spontaneous and endothermic. Moreover, SiO2@Glycidoxy@Cys selectively removed 91% of Hg(II) in the presence of coexisting cations, such as Mn2+, Cu2+, Zn2+, Cd2+, Ni2+, and Co2+. Hg(II) loaded SiO2@Glycidoxy@Cys can be easily regenerated and reused after 5 consecutive cycles without apparent loss of removal efficiency. The theoretical maximum adsorption capacity of Hg(II) in the breakthrough experiments was calculated to be 79.51 mg/g via the Thomas model fitting. Especially, SiO2@Glycidoxy@Cys reduced the low concentration of Hg(II) (1 mg/L) contaminated source water to 22 mu g/L, which meets the discharge standard for pollutants from mercury (<50 mu g/L) industry (GB30770-2014). More importantly, the removal efficiency of Hg(II) from 1 mL of Hg(II)-contaminated lithium battery wastewater (100 mg/L) by 5 mg of SiO2@Glycidoxy@Cys can be as high as 74.2%. The adsorption mechanism showed the complex formed among the -NH-, -SH, and Hg(II) dominated the adsorption process. These results demonstrated that SiO2@Glycidoxy@Cys will be a promising adsorbent for the removal of Hg(II) from wastewater.