According to EPA estimates > 30,000 U.S. sites require remediation, due in part to heavy element contaminants. In addition, the EPA, which recently set the MCL for arsenic in drinking water at 10 ppb, estimates that ~ 350,000 people in the US drink water containing > 50 ppb of arsenic and nearly 25 million drink water containing >25 ppb arsenic. In addition to the cost of meeting the needs of industry for waste water management, the drinking water contamination problem alone will generate a $17 billion global market for household tap water filters, according to estimates provided in 1999 by Proctor and Gamble Co. (Marguerite Nugent, Reuters, Cleveland, 1999). These filters rely primarily on the use of activated charcoal for the removal of biological, organic and, to a limited extent, inorganic contaminants. However, charcoal alone is not sufficiently effective in removing toxic cations and anions. A much more efficient trapping agent needs to be incorporated into the charcoal to efficiently remove species such as mercury, lead, arsenite, and arsenate ions. A key part of our near-term business plan is to fill this niche, in part, by providing through basic research studies, low cost, high performance organofunctional mesostructured silica (OMS) and aluminosilicate (OMA) trapping agents. The effects of framework pore structure, pore-size, and organofunctional group on heavy element trapping performance will be elucidated. The results will allow us to identify the compositions that are most effective in lowering contaminant levels to EPA MCL values and below. OBJECTIVES: This SBIR Phase 1 project is aimed at developing efficient chemical approaches to the design of high performance forms of organofunctional silica and aluminosilicate mesostructures for use in water purification applications, more specifically, the removal of heavy elements form drinking water purification and waste water streams. The first of the three major technical objective of this Phase 1 project is to develop efficient, low-cost chemical processes for the production of organofunctional mesostructured silicas (OMS) and aluminosilicates (OMA) with thiol or amine ligand functionality for heavy element binding. This is being accomplished using a one-pot direct assembly pathway to minimize processing steps, sodium silicate as the silica source in order to minimize reagent costs, aluminum salts as the alumina source, and electrically neutral amine and di-and tri-block polyether surfactants. A second major objective is to demonstrate that the proposed direct assembly processes do not compromise the textural properties and structural stability of the OMS and OMA products. This will be accomplished by determining the textural properties (pore size distributions, surface areas, and pore volumes) through standard nitrogen adsorption - desorption methods. The third important objective is to demonstrate that OMS and OMA compositions are effective in trapping mercury, lead, and arsenic from water solutions. Equally important, we are investigating the potential life cycles of the trapping agents by determining if the binding strength of the heavy elements is sufficient to allow disposal of the spent trapping agents in land fills. The possibility of regenerating the trapping agents through proton exchange reactions also is under investigation. APPROACH: The chemical processes to be developed in this SBIR Phase 1 project are aimed at producing OMS and OMA compositions based in part on the direct supramolecular assembly principles that have been demonstrated the Pinnavaia group at Michigan State University through its NSF- and NIEHS-sponsored research on the synthesis of mesostructured silicas and their organofunctionalized derivatives. This group also has demonstrated that thiol-functionalized OMS and OMA compositions are excellent trapping agents for heavy metal cations, particularly mercury (II), lead (II), and arsenic, particularly arsenic(III), which is especially difficult to remove from water by ion-exchange because this form of the element exists as a neutral molecule at near neutral pH values. However, the existing chemical processes for the synthesis of OMS and OMA compositions are not practical from a commercial point of view for reasons already presented. In order to meet the general objective of producing commercially viable, high performance OMS and OMA trapping agents, we are developing a research program with the following general aims: (i) achieve high performance through the use of low-cost sodium silicate silicon esters, fumed silica an other expensive silica sources that normally are used to form OMS and OMA compositions; also, use cost-effective aluminum salts in place of aluminum alkoxides as the alumina source in the synthesis of OMA derivatives; (ii) minimize the processing steps and the environmental impact associated with OMS and OMA production through the use of a one-pot direct assembly reaction and the facile recovery and recycling of the structure-directing surfactant porogen; and (iii) achieve stable framework structures so that the trapping agents can be regenerated over many use cycles or, alternatively, can be disposed of in landfills once the trapping agents are spent. With regard to more specific technical aims, our work plan for the development of OMS OMA materials is addressing the following relevant questions: Which direct assembly pathways (electrostatic or hydrogen-bonding) afford the highest level of organic functionalization? Which framework structures (cubic, hexagonal, foam, wormhole, lamellar) afford the greatest fraction of accessible organofunctional groups for heavy element trapping? Which surfactant porogens (alkyl amines, bola amphiphiles, diblock alkyl-PEO polymers, triblock PEO-PPO-PEO polymers, quaternary ammonium ions, mixed cationic - anionic surfactants) are most effective in forming the desired trapping agents? Which ligand (L) functionality (thiol, polysulfide, amine, polyamine, cyclic ether, carboxylate, phosphate or combination thereof) exhibits the greatest selectivity toward heavy elements Which structures are most for regeneration by proton exchange reaction with strong mineral acids?
