Molecular design of intercalation based sensors .2. Sensing of carbon dioxide in functionalized thin films of copper octanediylbis(phosphonate)

Self-assembled thin films of layered copper alkanediylbis-(phosphonates) retain the amine-specific intercalation chemistry of the corresponding microcrystalline solids, Aliphatic and aromatic amines bind in a 1:1 ratio to coordinatively unsaturated copper ions in anhydrous Cu-2(O3P(CH2)(8)PO3); and by selecting an amine with an appropriate functional tail group, a chemically and sterically well-defined interlamellar binding site for CO2 is created. powder X-ray diffraction, Fourier transform infrared spectroscopy, and solid-state NMR experiments were used to study the intercalation of 3-aminopropanol, (3-aminopropyl)methyldihydroxysilane, and p-xylylenediamine, and their reversible reaction with CO2 to form carbonates and carbamates, respectively, By growing these films on the electrodes of a quartz crystal microbalance device, a sensor can be fabricated for monitoring CO2 in gas streams at concentrations of 0.5-19% (v/v), A Henrian response (frequency change directly proportional to CO2 partial pressure) was observed, and the time required for equilibration of these devices with CO2, using 5-layer films, was 3-4 min, Effective diffusion coefficients for CO2 in the films were determined using a dual-transport model and were found to be in the range (6-9) x 10(-9) cm(2)/s.