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This work is part of a larger collaborative project of the same title led by Robert Riley at PNNL. Our task goal is to use a state of the art microbalance and well-defined mesoporous silica particles to characterize the effects of pore size distribution on carbon tetrachloride release rate and sequestration. Mesoporous silicon dioxide (SiO2) particles with pore size distribution in the range of 20 to 70 Angstroms were synthesized under acidic conditions using nonionic surfactants as structure directing agents (Zhao et al., 1998). Siliceous particles (primarily silica dioxide) containing the template molecules are precipitated from solution, dried and the template is removed by combustion at 550 C. The particles obtained by this procedure were characterized using standard nitrogen adsorption at 77 K. Surface area and pore size distribution were calculated from the data coming from the nitrogen experiments. The particle size distribution was determined by using a centrifugal automatic particle size distribution analyzer, which employs a non-contact measuring method based on liquid-phase sedimentation and the change in particle concentrations on the basis of light transmission. To examine the effects of the pore size on CCl4 sequestration and release, a state-of-the-art microbalance was used to measure real-time desorption profiles of CCl4 released from these mesoporous materials. In addition, a gas chromatograph with flammable ionization detector (FID) and electron capture detector (ECD) was used to close the mass balances and confirm the observations made with the microbalance. Experiments with the microbalance include helium calibration (critical to the measurement of small amounts of CCl4 release), and CCl4 desorption rate experiments, to quantify release rates and residual sequestration of CCl4 in the mesoporous silica particles. Finally, a fully automated accelerated solvent extraction system was used to determine the actual mass of CT remaining in the samples immediately after finishing the desorption experiments

Mechanisms of CCl4 Retention and Slow Release in Model Porous Solids and Sediments