Hydroxyl group surface concentration effect

The effect of drying temperature on the available surface hydroxyl concentration of a silica is shown in Figure 8. A constant slurry concentration of 4% silica/toluene was used in these experiments. These results are comparable with other data (20, 62), and they indicate that the surface hydroxyl group concentration is reduced with increasing drying temperatures. The reaction of metal hydrocarbyl compounds with strained siloxane groups is illustrated in Reaction 4. 

Figure 8.6 shows the effect of water vapor on the formation of C02 and BA for the toluene oxidation. The concentration of C02 increased linearly with the increase in relative humidity. The yield at 60% relative humidity was greater by one order than that in the dry condition. It has been pointed out that the amount of 02 adsorbed under photoillumination is proportional to that of hydroxyl groups (OH-) un the Ti02 surface. The phenomenon has been explained by the following reactions ... 

Gelation is performed by deprotonation of surface hydroxyl groups. NH3 or amines in very low concentration effectively induce the gelation of the nonaqueous suspension. A quaternary ammonium ion is formed. It establishes a link between neighboring negatively charged surface sites. 

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