Permeable barriers polymer substrates

Organic contaminants in ground water are an ubiquitous problem in all Department of Energy complexes, including Brookhaven National Laboratory. Across these complexes there are 600 billion gallons of contaminated groundwater from 5700 waste water plumes resulting in 50 million cubic meters of contaminated ground soil. Present treatments such as: ex-situ pump and treat, and in-situ bioremediation are expensive and inefficient. There is growing interest in the use of permeable barriers to manage plumes.

BNL is synthesizing and characterizing polymers for use as permeable barriers. These polymers have hydrophobic cavities similar to molecules which has been shown to sequester the organic molecules that constitute ground water contaminants. We will test these polymers for their efficiency in sequestering organic compounds from ground water.

The removal of hazardous industrial waste from ground water is a challenging environmental problem. Many of these contaminants (aromatic hydrocarbons and halogenated hydrocarbons) are toxic, as well as highly persistent in the ground water environment. As a result, the Environmental Protection Agency (EPA) has severely regulated their presence in ground water.[1] Contaminated groundwater can be found at all of the DOE sites, including Brookhaven National Laboratory, which is a Superfund cleanup site. Conventional ex-situ techniques for treating the contaminated ground water (such as air sparging) are expensive and ineffective.[2] The use of permeable barriers is an attractive alternative technology for in-situ removal of ground water contaminants.

Recently, in-situ barriers have shown potential for contaminated ground water remediation. These "permeable barriers" use sorbants to immobilize contaminants in the waste water and allow purified water to pass through the barrier. Materials used previously (zeolites, metal oxides and oxyhydrides)[2] have all shown promise as sorbants for permeable barriers. These inorganic sorbants are ordered materials with cavities that bind the desired molecule. However, organic systems are better materials for designing sorbants than their inorganic counterparts because one can adjust qualities selectively, such as cavity size, shape and polarity within the sorbant. Therefore, the design of organic systems capable of selectively adsorbing organic contaminants for the use in permeable barriers is both feasible and desirable.

The design and syntheses of organic molecules that bind organic substrates have been enormously fruitful, as seen in the wide variety of molecules which bind neutral molecules in aqueous and non-aqueous environments.[3] An example of such a molecule is the cyclophane I (Figure 1) which binds neutral, planer organic molecules such as nitrobenzene.[4] This molecule's binding behavior makes it ideal for binding such ground water contaminants as benzene, xylenes, and toluene.

Although cyclophane I can bind planer aromatic molecules, such as benzene, it cannot efficiently bind tetrahedral halogenated hydrocarbons such as chloroform. This is because the shape and the polarity of the binding cavity do not permit easy binding of bulkier, electron deficient molecules, such as halogenated hydrocarbons. However, this can easily be overcome by designing a cyclophane with the appropriate cavity. Cyclophane II (Figure 2) has been shown to bind a number of halogenated hydrocarbons.[5] This molecule's binding behavior makes it ideal for binding such ground water contaminants as chloroform, methylene chloride, and trichloroethane. BNL is attempting to synthesize engineered polymers that incorporate the cyclophanes shown above that can bind specific organic molecules commonly found commonly in contaminated ground water.

We will determine the efficiency of these polymers in removing organic waste by circulating water contaminated with a variety of organic pollutants such as xylenes, benzene, trichloroethane and trichloroethylene through a column packed with a specific polymer. We can determine the binding efficiency, as well as its selectivity for each polymer.

References

Drinking Water Detoxification.; Gillies, M. T. Ed.; Noyes Data Corp.; New Jersey, 1978.
EM-54 Technology Development In-Situ Remdiation Integrated Program. August 1993.
Izatt, R. M.; Bradshaw, J. S.; Pawlak, K.; Bruening, R. L.; Tarbot, B. J. Chem Rev. 1992, 92, 1261 and references cited therein.
Jazwinki, J.; Blacker, A. J.; Lehn, J. M.; Cesario, M.; Guilhem, J.; Pascard, C. Tetrahedron Letters, 1987, 28, 6057.
Callot, A. Tetrahedron , 1987, 43, 5725.

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Last Modified: November 12, 2009
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