Thermodynamics and kinetics of ion-exchange in perchlorate-selective poly(vinylbenzyltrialkylammonium chloride) matrices

Ion-exchange;perchlorate;anion-exchange;polyelectrolyte;water absorption;polymer;mechanical stress

Langer, James L.

关键词: Ion-exchange;    perchlorate;    anion-exchange;    polyelectrolyte;    water absorption;    polymer;    mechanical stress;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42481/James_Langer.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Perchlorate-selective ion-exchange fiber composites (IXFCs) based on an active resin-on-fiber architecture exhibit rapid exchange kinetics. Coatings consist of hydrophobic poly(vinylbenzyltrialkylammonium chloride) (PVBTC) matrices prepared by quaternization of a poly(vinylbenzyl chloride) precursor using an array of tertiary amines. Bulkier, more hydrophobic amines, such as tributylamine (TBA) or trihexylamine (THxA), yield IXFCs with higher selectivity for perchlorate but slower exchange kinetics. IXFCs based on hydrophilic amines, such as trimethylamine (TMA) and triethanolamine (TEOA), exhibit relatively low selectivity but faster exchange kinetics. An IXFC based on the asymmetric hexadecyldimethylamine (HDMA) displays high effective capacity for perchlorate and relatively fast exchange kinetics, and outperforms the best available technology, Purolite A-532E ion-exchange beads, in a column flow-through test by removing perchlorate from 700 ppb (7 µM) to below 4 ppb (0.04 µM).Immobilized PVBTC thin films are independently studied for their response to environmental stimuli including variable relative humidity and ion-exchange from chloride to perchlorate form. Mass uptake and mechanical stress in the films are investigated using a quartz crystal microbalance and a scanning optical laser apparatus, respectively. Water absorption in these films is strongly correlated to both the amine modifier and counterion present in the matrix.Mass uptake is lowest in a TBA-modified film in perchlorate form and highest in a TMA-modified film in fluoride form. Water uptake results in a maximum relative compressive biaxial stress of -33 MPa and -113 MPa for these two films, respectively. All of the PVBTC films appear to yield upon hydration and dehydration, which is attributed to elasto-viscoplastic deformation and influenced by a depression of the glass transition temperature via plasticizing. These results suggest the mechanical properties of hydrophobic polycations may be effectively controlled through judicious selection of fixed ion and counterion.The exchange of one counterion with another--perchlorate with chloride--induces mechanical stress in polycation matrices. The magnitude of the stress decreases with increasing hydrophobicity of the matrix. Each material exhibits tension upon exchange from chloride to perchlorate form, consistent with matrix dehydration. Data are fit to a chemical equilibrium model assuming proportionality between stress and conversion to perchlorate form. Selectivity coefficients range from 43 for the TMA-modified film to 370 and 450 for the TBA- and tripropylamine (TPrA)-modified films, respectively, again indicating greater selectivity for perchlorate in more hydrophobic matrices. Collectively, these results help clarify the physical origins of perchlorate selectivity in anion-exchange resins, supporting the prevailing theory relating selectivity and diffusion in perchlorate-selective anion-exchange resins to hydrophilicity and water content.