(counts]-

 2800 C


 156B


 lees-


 see- ISOC


 ze ......... *2" ......... 4* ..*.. *.... ** *'* ** ... ... ** ^.[' 3 e
 20 22 24 26 28 [201 38

Figure 4-14. XRD analysis of various temperature-cured silica-titania composites.

 In looking at adsorption of CV at various curing temperatures, Figure 4-15 shows

800C with the highest adsorption capacity even though it has the lowest surface area.

This may be explained by the cleaner surface (decrease of silanol sights) at this

temperature, resulting in the gel displaying a more hydrophobic behavior (Holysz, 1998).

This would decrease the competition between water and CV, allowing CV to efficiently

interact with the isolated silanols. However, the clean surface can slowly become

rehydroxylated when it is in contact with water (Davydov, 2000; Unger et al., 2000). The

adsorption ability would then most likely follow the same trend as gels that were treated

at lower curing temperatures. Therefore, based upon this and the destruction studies, the

optimal curing temperature chosen was 180C.