Abstract
The adsorption isotherm of water on most metal oxides gives the II type of isotherm according to Brunauer's classification, but on ZnO a jump appears on the adsorption isotherm of water just before the completion of monolayer coverage. This phenomenon has been explained in terms of the two-dimensional condensation of water which appears on surface hydroxyls having a special structure, i. e., closed hydrogen bonding, on well-developed (1010) plane of ZnO.
The measurement of differential heat of formation of surface hydroxyls shows that it exhibits a distinct maximum near the completion of monolayer coverage due to the additional heat by hydrogen bonding between surface hydroxyls formed; this supports the closed hydrogen bonding structure of surface hydroxyls on ZnO.
