CHAPTER 4
 RESULTS AND DISCUSSION

 4.1 Dye Comparison

 In order to accurately measure the photocatalytic ability of the silica-titania (Si02

- TiO2) composites, it was important to choose a dye that displayed little or no photolytic

behavior, i.e. change in absorbance as a response to UV light exposure alone. The

following four dyes were examined in order to determine the most suitable dye for the

studies herein: malachite green (MG), methylene blue (MB), crystal violet (CV), and

reactive red (RR). See Appendix B for structures of these dyes.

 Using a spectrophotometer, each dye was scanned at a range of 290 nm to 800 nm

in order to find each dye's peak absorbance wavelength. A summary of the peak

wavelengths is shown in Table 4-1. The absorbance measured at this peak wavelength

was used for comparing initial and final readings.

Table 4-1. Peak absorbance wavelengths.
 Dye Peak Wavelength
 MG 619 nm
 MB 656 nm
 CV 590 nm
 RR 538 nm


 A 100 mL solution of each dye (10 mg/L) was prepared in a 125 mL Erlenmeyer

flask and exposed to three different intensities of UV light for two hours. The findings are

presented in Figure 4-1. Each dye experienced a change in absorbance of less than 5% at

each flux, except for crystal violet, which experienced a 19% change at a flux of 1.1