Development of novel bonded-phase ion exchange systems for the preconcentration and recovery of trace metals from aqueous systems.

摘要

This research focuses on two major components of the bonded-phase ion exchange column to produce a successful metal removal system, namely the immobilized metal chelator and the column support material.; Biopolymers and synthetic “plastic” polymeric chelators are compared and evaluated for their metal binding properties. The flexibility of a short chain polymer allows it to “wrap” around a metal as it binds, finally reaching a free energy minimum that results in a near optimal tertiary conformation for binding a particular metal. Metal binding selectivity can be achieved by choosing polymeric chelators possessing specific combinations of metal binding functionalities along the polymer chain.; Various techniques such as FAA and ICPMS have been used to show that both immobilized biopolymers and synthetic polymers exhibit very strong, selective metal binding at physiological pH as well as allow for quantitative, on-demand release of bound metals through acid stripping. However, these analytical techniques do not permit the direct observation of the changes in the polymers' structure that allow for these different metal binding behaviors under different reaction conditions (i.e. changes in pH). Tapping mode AFM used in conjunction with a liquid cell provides a means for in-situ observation of the changes in the immobilized polymer tertiary structure upon exposure to different chemical metal binding environments. Analysis of these images offers insight into the mechanism of immobilized polymer metal binding and release.; Four types of column substrates were examined for their utility as anchoring surfaces for the immobilized chelators; controlled pore glass (CPG), gold grids, gold-coated CPG, and activated porous carbon. CPG allows for effective ligand immobilization through the reactivity of its surface silanol groups, large available surface area, and structural stability in many harsh chemical environments. Enhanced metal binding capacities per unit surface area were observed on the gold surfaces due to the efficient formation of self assembled monolayers of the target ligand. Carbon materials are relatively inexpensive and are available in a variety of shapes, sizes, and pore distributions, allowing for a wide range of chelator coupling. Gold and carbon also offer the advantage of being conductive, thus allowing possible use with electrochemistry to augment ligand metal binding and release.