Thiol-SAMMS™
Thiol-SAMMS™ was specifically developed for the removal of mercury from liquid media. It has the unique ability to bind cationic, organic, metallic, and complexed forms of mercury. Because of the high surface area, extensive binding sites, and tailored functional group, results of tests with mercury demonstrate the high loadings (up to 635 mg Hg/g SAMMS™), high affinity (distribution coefficient, or Kd, ~1 x 108) and rapid kinetics (minutes) possible through the use of these molecularly-engineered materials. SAMMS™ has also been shown to be effective for removing mercury from contaminated oils and chemical warfare agents (e.g. mustards) with excellent results.
Selectivity, isotherm, kinetic, stability, and regeneration data on thiol-SAMMS™ are available for multiple metals. The binding affinity of thiol-SAMMS™ for selected metal species is summarized in Table 1. Results show that thiol-SAMMS™ can selectively adsorb, in addition to mercury, other soft acid cations: silver, cadmium, copper, and lead. In all cases, thiol-SAMMS™ show minimal interference from alkali and alkali earth metals, such as Na+, Mg2+, and Ca2+.
| Metal | Initial Concentration (µg/L) | Final Concentration (µg/L) | Metal Loading (mg/g) | Distribution Coefficient (Kd) (mL/g) |
|---|---|---|---|---|
| Ag(I) | 90 | 1 | 0.0089 | 8900 |
| Ca(II) | 2070 | 2070 | 0 | 0 |
| Cd(II) | 4670 | 32 | 0.4638 | 14467 |
| Co(II) | 2810 | 2670 | 0.0140 | 5 |
| Cu(II) | 2240 | <5 | >0.2235 | >44700 |
| Eu(III) | 9010 | 1220 | 0.7790 | 639 |
| Hg(II) | 487 | 0 | 1.0146 | 1 x 108 |
| Mg(II) | 1580 | 1580 | 0 | 0 |
| Pb(II) | 3040 | 300 | 0.2740 | 913 |
| Zn(II) | 2790 | 2410 | 0.0380 | 16 |
Adsorption Isotherms for Hg, Ag, Cd, Cu, and Pb
Isotherms for mercury, silver, cadmium, copper, and lead using thiol-SAMMS™ have been obtained. The most extensive data have been obtained for mercury with equilibrium solution concentrations covering nine orders of magnitude and multiple speciation and chelator effects. Data for silver, cadmium, copper, and lead span a smaller range of equilibrium concentrations, pH, and chelator effects. Maximum metal loadings for thiol-SAMMS™ are summarized in Table 2.
| Metal | Loading (mg/g) | Loading (mmol/g) |
|---|---|---|
| Ag | 440 | 4.08 |
| Cd | 97 | 0.86 |
| Cu | 40 | 0.63 |
| Hg | 635 | 3.17 |
| Pb | 122 | 0.59 |
Kinetics
Kinetic experiments exploring the adsorption of mercury in 10- and 500-parts-per-million (ppm) mercury solutions have demonstrated the rapid binding kinetics of thiol-SAMMS™. As illustrated in the figure below, SAMMS™ rapidly reduced the mercury concentration from 500 ppb to 0.5 ppb within 5 minutes; for the 10-ppm case (not shown), the mercury concentration was reduced to 3.1 ppb within 5 minutes. For comparison purposes, the binding kinetics of a commercial ion exchange resin being evaluated for mercury removal from groundwater at the Oak Ridge National Laboratory are also presented.
Supporting Publications
"A Thiol-Functionalized Nanoporous Silica Sorbent for Removal of Mercury from Actual Industrial Waste" by Shas Mattigod and Glen E. Fryxell, in Environmental Applications of Nanomaterials: Synthesis, Sorbents and Sensors; G. E. Fryxell and G. Cao, eds.; Imperial College Press, 2007; 275-284.
"Separation of Complexed Mercury from Aqueous Wastes Using Self-Assembled Mercaptan on Mesoporous Silica", Shas V. Mattigod, Xiangdong Feng, Glen E. Fryxell, Jun Liu, Meiling Gong, Separation Science and Technology, 1999, 34, 2329-2345.
"Mercury separation and immobilization using self-assembled monolayers on mesoporous supports", Chen, X., X. Feng, J. Liu, G. E. Fryxell & M. Gong, Sep. Sci. & Tech. 1999, 34, 1121-1132.