Absorbance pH 7 ------.Absorbance pH 9.5
 -- Absorbance ph 9.5 after UV

 0.3

 0.25 ,

 o 0.2

 0.15
 0
 0 0.1

 0.05 -Z


 400 450 500 550 600
 Wavelength (nm)

Figure 4-5. Spectrophotometer scan of 10 mg/L RR as a function of pH, before and after
 UV exposure.

 4.2 Optimization of Gels

4.2.1 Titania Loading

 In order to determine the optimal titania loading, 14 gels (140 A) of varied TiO2

loadings (from 0.77% to 40%) were created. The desired optimal loading would be found

as the composite having the highest rate of destruction for RR. These gels were

performance tested at three UV intensities for the destruction of RR (10 mg/L) and the

results are displayed in Figure 4-6. There is a definite plateau where the percent

destruction remains constant, even with the addition of more TiO2. It appears that this

plateau occurs at lower TiO2 percentages with higher UV intensities. For 1.1 mW/cm2,

the plateau occurs at 5% TiO2 and it occurs at 10% for 0.75 mW/cm2. At the lowest UV

intensity, the destruction levels off at 12%. These results were triplicated and the error

bars are included in the figure.