LIST OF FIGURES


Figure page

2-1 Schematic of oxidation and reduction occurring on the semiconductor surface. ....5

2-2 Example of hydroxyl radical attack a) on tetrachloroethylene by self-addition b)
 on 1,1,1-trichloroethane by hydrogen abstraction (notice chlorine shift in the
 ra d ic al) .............................................................................. 8

2-3 Diagram of anatase and rutile crystal structures..............................................10

2-4 Simplified diagram of a catalyst support. .................................... ...............13

2-5 Linkages of SiO 2 tetrahedras........................................................................ .... 17

2-6 Structural changes during the sol-gel process............................................ 20

2-7 Silanol groups on the silica surface ............................................ ............... 23

2-8 Representation of dehydroxylation............................................................23

3-1 C olum n setup. .......................................................................29

4-1 Photolysis of dyes as a function of UV flux for 2 hours of exposure .................31

4-2 Photolysis of MB and MG (2 hours UV exposure at 0.45 mW/cm2) as a function
 of initial dye concentration. ....................................................................... ......... 32

4-3 Photolysis of RR (2 hours UV exposure) as a function of initial dye concentration
 an d flu x ......................................................... ................ 3 2

4-4 Change in absorbance of RR at 538 nm as a function of pH .............................33

4-5 Spectrophotometer scan of 10 mg/L RR as a function of pH, before and after UV
 exposure. ............................................................................34

4-6 Destruction ofRR (pH 7.6) after 2 hours UV exposure versus TiO2 loading as a
 function of flux. ........... .. ............... .... .......... ................. ...... .....35

4-7 Destruction of RR (10 mg/L) after 2 hours UV exposure (0.45 mW/cm2) versus
 TiO2 loading as a function of pH ................. ....... ....................................... 36