4.2.2 Curing Temperature

 The effect of curing temperature was investigated on gels doped with 6% TiO2

and those with no TiO2 (all made with the 140 A initial formula). The literature showed

that there can be an increase in adsorption with gels produced at higher curing

temperatures (up to 4000C) due to increasing the ratio of isolated silanols on the surface

versus other types of silanols. Yet, the curing temperature may have detrimental effects

on the photocatalytic ability of the composites. In looking at the destruction of RR (10

mg/L), Figure 4-12 shows that there is a 30% difference between the 180C gel versus the

500C gel at a pH of 7.8. This difference is less pronounced at pH 4. At 800C, there is a

marked decrease in destruction, regardless of pH. This can be explained by both a

decrease in surface area of the gels at 800C (see Figure 4-13) from an average of 275

m2/g to 150 m2/g for the titania loaded gel and a phase change of titania.


 *pH 4 m pH 7.8
 100
 90
 S80o
 S70-
 & 60
 W 50-
 0 ,40
 2 30-
 20
 10 -
 0 -------------------------
 0 100 200 300 400 500 600 700 800
 Curing Temp (oC)

Figure 4-12. Destruction of RR (10 mg/L) after 2 hours UV exposure (0.45 mW/cm2)
 versus curing temperature as a function of pH.