The surface structure of mesoporous silica crystals FSM-16 with a narrowly distributed pore size has been studied by FTIR, measurement of SiOH number and adsorption of N, and H,O. IR spectra of FSM-16 outgassed at temperatures above 170°C showed a sharp band at 3740 cm-' due to free SiOH and a broad shoulder at 3600-3500 cm-' due to hydrogen-bonded SiOH. The SiOH number, determined by a weight-loss method, amounted to 3.3 groups nrn-,, which is less than that of mesoporous silica gels. The amount of H,O adsorbed on FSM-16 decreased with calcination above 800"C, owing to the dehydroxylation of SiOH. On treating with alcohol, the number of free SiOH decreased, leading to a decrease in H,O adsorption. The crystallinity of FSM-16 was lowered by pressing. With increasing pressure the specific surface area decreased and the SiOH number increased, up to 9.5 groups nrn-,.

The surfaces of calcium hydroxyapatite (CaHAP) particles with different Ca/P atomic ratios, synthesized by the precipitation method, were characterized and the adsorption mechanism of CO2 on CaHAP at 25 °C was elucidated mainly by FTIR. The number of surface P-OH groups was maximum at Ca/P ) 1.6 while the quantity of irreversibly adsorbed CO2 was minimum at the same Ca/P. This indicates that the surface P-OH groups not only are the reversible adsorption sites for CO2 but also interfere with the irreversible adsorption of CO2. IR bands due to H2O and CO3 2appeared on CO2 adsorption and were intensified by increasing the adsorbed amount. The physisorbed CO2 was converted into CO3 2ions with the course of time. These results demonstrated that the irreversible adsorption of CO2 progresses via the reaction of CO2 with surface OH -: 2OH -+ CO2 f CO3 2-+ H2O.

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