Concentration and continuous photodecomposition of dioxins using an immobilized hydrophobic monolayer.

We used a hydrophobic solid support, octadecylsilylated silica gel C18, packed in a quartz column as the reaction medium for the photolysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and 1,2,3,4-TCDD. 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 coefficient of 1,2,3,4-TCDD in 10% 2-propanol/water (>1000) indicates that on the C18 stationary phase, both the saturated hydrocarbon chains and 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-propanol/water decomposed much faster than in a nonaqueous solvent (50% 2-propanol/methanol). This solvent effect is advantageous for the practical application of the C18 photolysis process in aqueous waste treatment. We have demonstrated that complete C18 trapping with continuous photodecomposition of TCDD contained in an aqueous alcohol waste is possible.