Surface characterization of some selected zinc oxide samples I: Analytical reagent (Merck) zinc oxide

Abstract

Zinc oxide was thermally dehydrated in vacuo at different temperatures in the range 100 – 530 °C. Specific surface areas, total pore volumes and other surface parameters were estimated from nitrogen adsorption measurements at liquid nitrogen temperature (-195.8 °C). From the adsorption isotherms obtained below 300 °C, an increase in the area of the hysteresis loop was found to result when the dehydration temperature was raised. This was interpreted on the basis of gradual loss of physisorbed water until 300 °C, where the surface areas possess the highest available value. Contrary to the predicted behaviour, the nitrogen Brunauer-Emmett-Teller (BET) surface area increases with an increase in average pore radius; this is tentatively attributed to the development of some narrower (or micro) pores. An increase in the magnitude of the BET C constant was found to be partially responsible for the increase in the nitrogen BET surface area. From two different methods of analysis, the V 1- t method and the n S- n R method, wide pore analysis and size distribution curves have already led to the conclusion that some narrower (or micro) pores develop. The presence of these narrow pores was found to enhance the heat of adsorption (as a measure of the magnitude of the BET C constant), as well as the extent of adsorption (as a measure of the specific surface area). The subject will be presented and discussed briefly.