CONCENTRATION AND CONTINUOUS PHOTODECOMPO SITION OF DIOXINS USING AN IMMOBILIZED HYDROPHOBIC MONOLAYER

We used a hydrophobic solid support, octadecylsilylated silica gel C-1 8, packed in a quartz column as the reaction medium for the photolysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,and-TCDD) and 1,2,3,4-T CDD. When we exposed the column to a 450 W UV lamp, the adsorbed 1,2,3 ,4-TCDD or 2,3,7,8-TCDD in 10% 2-propanol/water decomposed completely in 20 min and 5 min, respectively. The large estimated partition coeff icient of 1,2,3,4-TCDD in 10% 8-propanol/water (>1000) indicates that on the C-18 stationary phase, both the saturated hydrocarbon chains an d the adsorbed 2-propanol may act as proton donors and accelerate the photolysis. In direct sunlight, the adsorbed 1,2,3,4-TCDD in 10% 2-pro panol/water decomposed much faster than in a nonaqueous solvent (50% 2 -propanol/methanol). This solvent effect is advantageous for the pract ical application of the C-18 photolysis process in aqueous waste treat ment. We have demonstrated that complete C-18 trapping with continuous photodecomposition of TCDD contained in an aqueous alcohol waste is p ossible.