Adsorption of Gas Phase Organic Compounds by Swellable Organically Modified Silica

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Swellable organically modified silica (SOMS) is a sol–gel derived material that spontaneously expands >2.5× upon contact with organic liquids, absorbing 7.8 mL/g. Adsorption of gas-phase volatile organic compounds by SOMS was measured to examine how the capability to swell affects capacity and rate of organic vapor absorption. Static adsorption capacities of SOMS for organic vapors at saturated vapor pressure ranged from 0.7 to 1.05 g/g, which was higher than values for other sorbents (powdered activated carbon, Amberlite XAD-4, Tenax TA, OptiPore, and organophilic zeolite). Rates of adsorption by SOMS were similar to those of XAD-4, a porous polymer with similar surface chemistry, and slower than that of activated carbon. Sequential coadsorption of multiple compounds by SOMS was measured, yielding enhanced adsorption capacity attributed to adsorption-induced pore expansion. The sequential adsorption of phenol and acetone vapor (p = p0) led to a total capacity of 5.7 g/g. Adsorption of organic vapors was not selective and fully reversible in all cases. The hydrophobicity of SOMS strongly excludes water and water vapor. Fluorescence recovery after photobleaching was used to measure in-particle diffusion constants of fluorescein before and after adsorption for vapor and liquid.

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