There is significant need for technologies to clean water, especially as demand continues to increase while fresh water supplies become increasingly strained. Industrial activity, modern agricultural practices, and widespread use of various chemicals has led to contamination of water by organic pollutants. Organic solvents, pesticides, and other emerging contaminants have infiltrated watersheds making such water unfit for use by humans until the contaminating species are removed.
Recently, we discovered a new class of chemically inert silica-based materials that swell 8 times their dry volume in the presence of organic liquids. The expansion of the material is rapid and highly energetic resulting in forces that exceed 100N/g. Swellable organically modified silica (SOMS) does not swell in water, but has the capability of adsorbing large amounts of dissolved organic species from water or air. Preliminary work has shown that SOMS is effective at removing a wide range of organics from water including polar species such as alcohols and methyl tert-butyl ether to non-polar species such and toluene and perchloroethylene. The swelling process is completely reversible when absorbed species are evaporated by heating the material. For these reasons SOMS-based sorbents appear to be ideal for environmental remediation of water contaminated by organic species.
The goals of the proposed work are to: 1. Develop a fundamental understanding of absorption by these novel silica materials. 2. Create composite materials that target the removal of halogenated organics and pesticides from water. 3. Develop and test deployment mechanisms in collaboration with a local engineering firm.
Based on its unusual properties, SOMS may represent a whole new class of absorbent materials. Incursion of organic species leads to the expansion of the matrix which is under tension in the dry state. Experimental work is proposed that will seek to create a physical and thermodynamic model to explain the absorption process. This will be done through a combination of spectroscopic, calorimetric, and equilibrium absorption measurements. These results will be compared to a theoretical framework developed by extension from the classical Flory-Huggins model and work on polyelectrolyte swellable polymers systems consisting of matrixes tensioned by electrostatic forces.
Beyond laying a theoretical groundwork for absorption by animated materials, SOMS-based sorbents will be designed to remove/degrade various types of contaminants including: pesticides; chlorinated solvents, in particular trichloroethylene (TCE) and fluorinated compounds. Composite materials where nanoparticles of zerovalent iron (nanoZVI) are incorporated into SOMS will be created to absorb TCE and subsequently covert it through reduction to chloride ion and ethylene by iron sequestered within the material. The composite materials will be prepared in slurries for injection into underground aquifers. Soil injection methods and pilot experiments will be conducted in collaboration by an environmental engineering firm (Frontz) located in the immediate area that specializes in the deployment of ZVI and other sub-surface treatment methodologies for aquifer remediation. Frontz owns mobile sonic drilling rigs and GeoProbe injection equipment. Chemically modified materials will be synthesized remove fluorinated compounds from water in a separate line of investigation. The initial target compound for this work is perfluorooctanoate which has proven difficult to remove by other measures and will serve as a model system for investigating whether SOMS-based materials can be molecularly engineered to selectively absorb a particular class of substances.
All the work will be accomplished at a liberal arts college which will provide 10-15 chemistry students with research experiences in applied environmental engineering, an area that would be new to the institution. These students would serve as mentors for the SEER program which was developed at Wooster to recruit pre-college minorities into the sciences. Undergraduate researchers would also lead groups of junior high girls in environmental experiments as part of the B-WISER summer science camp.
Swellable organically modified silica, tradename Osorb, is a silica-based material that is nano-engineered to absorb organic molecules from air and water with high affinity and capacity. This project investigated the use of Osorb as a sorbent media for water treatment. Several goals were accomplished. First, a fundamental understanding of how organic contaminants can be extracted from water by engineered silica was completed. These efforts led to the discovery of nanoscale matrix relaxation as being a new type of driving force to remove organic contaminants from water. Using this understanding, new types of Osorb were synthesized that showed good performance in removing pesticides such as atrazine from water. In addition, modification of the Osorb surface allowed extraction of fluorinated compounds, notably perfluorooctanoic acid. Perfluorooctanoic acid is a breakdown product of Teflon and has been found to be difficult to remove from water by other means. Finally, metal-Osorb composite materials were tested for the in situ and ex situ remediation of chlorinated solvents including trichloroethylene. The culmination was a three phase pilot-scale remediation project completed by the research team in conjunction with the Ohio EPA. The objective was the in situ remediation of trichloroethylene using iron modified Osorb sorbent at a brownfield site in central Ohio. Completion of the project goals was assisted by the efforts of 16 undergraduates and 1 high school student. Undergraduate training was a focus of the project in order to attract and prepare students for STEM fields. Several outreach programs were operated with assistance from project funding including a science camp for junior high girls and visit programs for rural high school students involved in science courses and 4H. These programs featured the use of innovative materials for pesticide remediation and exploration of materials science.
