Remediation of Dissolved Organic Pollutants in Water Using Organosilica-Based Materials that Rapidly and Reversibly Swel
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Remediation of Dissolved Organic Pollutants in Water Using Organosilica-Based Materials that Rapidly and Reversibly Swell Paul L. Edmiston1 and Laura A. Underwood1 1
College of Wooster, Department of Chemistry, Wooster, OH 44691
ABSTRACT A sol-gel derived organosilica material that energetically swells when exposed to organic molecules was tested as a means to extract dissolved organic species from water. Swellable organically modified silica (SOMS) was demonstrated to be effective at removing butanol, methyl t-butyl ether (MTBE), tetrachloroethylene, trichloroethylene, ethanol, and toluene from lab grade water, salt water, and natural waters. Partition coefficients for the absorption of organic species from water by SOMS ranged from 2.8×105 – 1.0×102, and vary depending on polarity of the contaminant, concentration, and the total mass of contaminant absorbed. Absorption of organic species to SOMS appears to be enhanced by matrix expansion of nanometer sized pores leading to non-selective capture of organics beyond what could be attributed to physisorption. INTRODUCTION Swellable organically modified silica (SOMS) rapidly swells up to 8 times its dried volume upon exposure to non-polar chemical species whether found as a neat liquid, in gaseous form, or dissolved in water [1]. The animated behavior results from a network of inter-connected nanoparticles formed during a particular set of sol-gel processing conditions. The network is tensioned as a wet gel is dried to a zerogel state. Intermolecular forces between particles in the zerogel hold the elastic matrix in a collapsed state until non-polar absorbates disrupt these interactions triggering the expansion process [2]. SOMS has been shown to possess the following attributes: 1) the rate of swelling is mass transport limited, 2) uptake of absorbates generates forces >100N/g as the material rapidly expands, 3) the swelling is completely reversible if absorbed species are removed by evaporation or rinse/drying, 4) absorption is non-selective and can be induced by organic species ranging from methanol to hexane, 5) the material is hydrophobic and does not swell in the presence of water or water vapor, and 6) swelling and absorption is driven by the release of stored tensile force rather than by chemical reaction [2]. Removal of small molecule organic contaminants from water is an important industrial and environmental problem. There are a limited number of sorbent materials used to extract chemical species from water: notably activated carbon [3] and to a lesser extent molecular sieves [4]. Organosilica-based materials can be used produce new types of absorbents since the chemical structure and nano-to-microscale morphology can be tailored [5,6]. SOMS is an example where the material also possess a mechanical means of absorption. We evaluated SOMS effectiveness to absorb a wide range common organic contaminants from water compared to
commercially available activated carbon and organophilic molecular sieves. Dissolved contaminants included 1-butanol, a
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