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 method^2–4,10. 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 water^5,6. 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.