IR studies of long-range surface effects—excess proton mobility in water in quartz pores

Abstract

LONG-RANGE ordered elements of water structure of micrometre dimensions have long been suspected to exist near certain aqueous/solid interfaces. However, the evidence has been inconclusive1 and it has also been argued that such ordered elements of water structure exist near a glass surface from a comparison of the diffusion coefficients of the hydrogen ion from polarography and the sintered glass diaphragm cell method2–4,10. The pore size of the sintered glass varied between 4 and 15µm. The mobility of the hydrogen ion is known to be very sensitive to the structure of water5,6. We present here convincing evidence from an IR spectroscopic study of IM HC1 in porous silica that such long-range ordering effects exist near a quartz surface and that as a consequence the excess proton mobility is reduced. Such long-range effects have not been conclusively demonstrated previously. With acid solutions the interaction between the easily polarisable hydrogen bonds of H5O2+ groupings may favour such a long-range order and as the absorbance of the polarisable hydrogen bonds is sensitively influenced by all interaction effects this order may be indicated by changes of the IR continua.