EFFECT OF ADSORBED POLYELECTROLYTES ON TCE DECHLORINATION AND PRODUCT DISTRIBUTION BY Fe(0)/Fe-OXIDE NANOPARTICLES

摘要

Surface modification of reactive Fe0/Fe-oxide nanoparticles by physisorption of polyelectrolytes is needed to enhance colloidal stability and mobility in the subsurface and may also provide DNALP targetability. However, a mechanistic understanding of how surface modification affects the TCE dechlorinate rate and reaction products formed is not available. This insight would be useful for the design of effective surface modifiers. The objective of this study is to gain an understanding of the effect of sorbed polyelectrolytes on the TCE dechlorinate rate and reaction products formed. Three commercially available polyelectrolytes, poly(styrene sulfonate) (PSS), carboxymethyl cellulose (CMC) and polyaspartate (PAP), are used as representative modifiers. The TCE dechlorination rate and reaction products formed are systematically measured as a function of the sorbed mass of polyelectrolytes. The general trend of the train-loop-tail distribution based on the Scheutjens-Fleer theory for polymer adsorption is applied to distinguish between reactive site blocking by trains (adsorbed polymer attached to the surface) and mass transfer resistance due to loops and tails (adsorbed polymer not directly attached to the surface) on the dechlorination rates and products formed. The layer thickness of the sorbed polyelectrolytes as estimated by Ohshima’s soft particle analysis is measured and used to support the importance of the mass transfer limitation due to the diffusion of TCE through the sorbed polyelectrolyte layer.