Description of the Technology: SAMMS™ Assembly
How SAMMS™ works
Self-Assembled Monolayers on Mesoporous Supports (SAMMS™) is an award-winning technology with broad applications in the remediation, water treatment, catalyst, sensor, and controlled release markets. The technology has received awards from R&D Magazine, Environmental Business Journal and the Federal Laboratory Consortium. The Pacific Northwest National Laboratory has teamed with an industrial partner for the development and manufacture of this exciting material, which should soon be available for testing in limited quantities.
SAMMS™ is a hybrid of two frontiers of materials science: self-assembly techniques and mesoporous materials. SAMMS™ are created by attaching a monolayer of molecules to mesoporous ceramic supports (see graphic). The larger pore size offered by the mesoporous materials (20-200 Ã...) enables attachment of the monolayer as well as access to the binding sites within the pores. The high surface area of the materials (~1000 m2/g) also allows an extremely high density of binding sites. Five grams of SAMMS™ powder have the surface area equivalent to a football field, and the binding molecules fully cover the available surface. Together, these properties produce a material with fast kinetics, high material loading, and excellent selectivity.
Both the monolayer and the mesoporous support can be tailored for a specific application. For example, the functional group at the free end of the monolayer can be designed to selectively bind targeted molecules while the pore size, monolayer length, and density can be adjusted to give the material specific diffusive and kinetic properties.
SAMMS™ is being developed in several engineered forms, such as beads, membranes, and membrane cartridges, and can be delivered with a variety of chemically active substances. Samples of the powdered form are currently available.
SAMMS™ Removes...
Heavy metals
The SAMMS™ technology was originally developed for the U.S. Department of Energy, which has identified the separation and removal of mercury from the environment as a key technology need at its Oak Ridge Site. Mercury releases are also a significant environmental concern for the coal and petroleum industries. Mercury contamination of water produced from petroleum production is a significant environmental concern. Globally, the regulations addressing mercury discharge in produced water are getting more and more stringent. In addition, mercury emissions from coal-fired power plants are a significant concern worldwide, with hundreds of tons of mercury being released each year into the air we breathe. In the mining industry, there are problems with mercury (and other heavy metals like Cd and Pb) contaminating impoundments, run-off and streams. SAMMS™ can help to control all of these heavy metal releases. SAMMS™ has proven effective at removing Hg from contaminated oils, and is the only sorbent technology to have proven this capability. SAMMS™ has even been shown to be effective for removing mercury from contaminated chemical warfare agents (e.g. mustards).
Precious metals
Preliminary screening tests for the adsorption of gold and silver show SAMMS can load more than 100 mg gold and 20 mg silver per gram of thiol-SAMMS™ under mild conditions. The gold-loading values are significantly greater than - activated carbon, a widely used adsorbent for the gold mining industry.
Research has shown that this type of sorbent is very effective for recovering expensive catalyst metals, like Pt and Pd (Ind. Eng. Chem.. Res. 2004, 43, 1478-1484). The kinetics of Pd sorption are rapid, while Pt recovery is significantly slower (but nonetheless goes to completion).
Further testing on the performance of thiol-SAMMS™ for precious metals is continuing. Additional data on selectivity, loadings, kinetics, and regeneration will be compared with ion exchange and activated carbon results.
Anions
Pacific Northwest National Laboratory has synthesized and demonstrated the use of metal-chelated ligands immobilized on mesoporous silica as a novel anion-binding materials for toxic anions such as chromate, arsenate, pertechnetate, and selenite. Novel chemical interfaces with chelate-SAMMS™ have shown selective removal of toxic metal oxoanions by a ligand exchange mechanism. This approach allows construction of binding sites that satisfy the stereoelectronic requirements of tetrahedral anions.
Anion-SAMMS™ can remove chromate and arsenate to low levels with competing sulfate ion present. Nearly complete removal of arsenate and chromate is achieved in the presence of interfering anions for solutions containing up to 100 ppm toxic metal anions under a variety of conditions. The material remains effective for even higher concentration solutions (>1000-ppm anions). Anion loading of >130 mg/g (1.12 mmol/g) of SAMMS™ and distribution coefficients of >100,000 have been observed. These properties are comparable to the performance of thiol-SAMMS™.
Our anion removal tests were performed in water containing 1-, 10-, and 100-ppm arsenate and chromate with a water-to-silica (SAMMS™) ratio of 100. In all tests, virtually all of the chromate was removed in a single treatment. Addition of 150-ppm-sulfate-competing anions had little effect on the adsorbing behavior. At the same solution-to-silica ratio (100 mL/g), chromate concentrations higher than 1000 ppm began to produce saturation of the binding sites. The maximum adsorbing capacity is about 130 mg/g or 1.12 mmol/g. For a much higher solution-to-silica ratio (500 mL/g), 100% removal of the chromate is observed for chromate concentrations up to 100 ppm. Higher concentration of chromate under these conditions results in saturation of the binding sites.
Similar results were also obtained for arsenate removal. The maximum loading capacity is 140 mg/g or 1.00 mmol/g. Under the same conditions, the residual concentrations of arsenate are all slightly higher than chromate at low anion concentrations. This suggests the binding chemistry has higher affinity for chromate than arsenate.
The test results can be summarized as follows:
- The SAMMS™ anion materials are very efficient oxoanion binding materials. Efficient anion removal can be achieved over a wide concentration range.
- Oxometallate anions (chromate and arsenate) are preferred over sulfates.
- Low concentrations of chromate and arsenate can be removed from high concentrations of sulfates.
- The binding chemistry is more sensitive for chromate than arsenate at low concentrations.