Photocatalytic degradation of chlorophenols in soil washing wastes containing Brij 35. Correlation between the degradation kinetics and the pollutants-micelle binding.

The photocatalytic degradations of 4-chlorophenol (CP), 4-chloro-2-methylphenol (CMP), 4-chloro-3,5-dimethylphenol (CDMP) and 4-chloro-2-isopropyl-5-methylphenol (CIMP) were investigated in water and in simulated soil washing wastes containing Brij 35 (polyoxyethylene(23)dodecyl ether) in the presence of TiO2 dispersions. A neat inhibition of substrate decomposition proportional to their growing hydrophobicity was observed in the washing wastes for CP, CMP and CDMP, whereas CIMP showed a different behaviour. The mineralization of the organic chlorine of CP and CIMP was relatively fast and complete, whereas it was much slower for CMP and CDMP. Micellar solubilization and substrate adsorption onto the semiconductor play opposite roles on the degradation kinetics, and a breakpoint between the corresponding induced effects was evidenced when the pollutants become completely bound to the micellar aggregates.

Photocatalytic degradation of bentazone in soil washing wastes containing alkylpolyoxyethylene surfactants.

Three alkylpolyoxyethylene surfactants bearing the same hydrophobic chain and a different number of oxyethylene groups were investigated as suitable candidates for the soil washing treatment of contaminated soil samples containing bentazone. Comparable good recoveries of the pesticide were obtained working with these surfactants. The photocatalytic treatment of the collected washing wastes, performed in the presence of suspended TiO(2) particles under irradiation with simulated sunlight, leads to the effective degradation of bentazone residues after a time depending on the nature and concentration of the chosen amphiphile. Brij 35 was found to be the best surfactant candidate, giving the faster abatement of the pesticide in the collected wastes. The overall treatment time depends on the bentazone mineralization kinetics, markedly slow in the presence of surfactants. Useful information about the photocatalytic degradation route was obtained from the HPLC-MS analysis of transient intermediates formed in water.