| dc.description.abstract | In this investigation, the reaction sequence for the photocatalytic degradation of monochlorobenzene (MCB) in UV/TiO2 process, including substrate adsorption, degradation, and mineralization, was studied. Four commercial powder TiO2 with different characteristics were used as photocatalyst. The gaseous adsorption results illustrated that the adsorption capacity of MCB vapor on the base of the same surface area, was independent of crystalline. Moreover, the adsorption of MCB onto TiO2 surface was suppressed in aqueous solution obviously. For isotherm adsorption in aqueous phase, the theoretical maximum adsorption capacity of MCB onto TiO2 surface was in the range of 0.164 to 2.071 ?mol MCB/m2 of TiO2.
As compared with direct photolysis and H2O2-assisted photocatalysis, UV/TiO2 process was proven to be an effective method for the degradation of MCB. Large surface area and higher surface sites capacity of TiO2 photocatalyst and higher relative surface coverage of MCB were favor for the photocatalytic degradation. In accordance with the experimental results, the degradation of MCB was a function of the initial substrate concentration, incident light intensity, and TiO2 dosage. Langmuir-Hinshelwood kinetic model was applied to simulate the degradation of MCB. In addition, the low dependency of the initial degradation rate on the light intensity revealed the considerable adverse effect of e–-h+ pair recombination. In this study, the optimum photocatalyst dosage was in the range of 1.0 to 2.0 g/L. The influence of the solution pH on the degradation of MCB can be explained by the generation of hydroxyl radicals (•OH) and the potential for the adsorption. Experimental results revealed that the neutral medium was beneficial for the degradation of MCB. In comparison, the mineralization was most improved at acidic condition.
Oxygen was proven to be a determining parameter for improving the photocatalytic degradation. Both degradation and mineralization efficiencies were improved with increasing DO concentration. Owing to H2O2 acted as electron and •OH radicals scavenger, the addition of H2O2 should in a proper dosage range to promote the degradation and mineralization of MCB. A simplified two-step consecutive kinetic model was used to model the mineralization of MCB.
Mineralization and dechlorination were both occurred during the photocatalytic degradation of MCB. Nevertheless, an analysis of Cl– ion concentration in the bulk solution and the characteristics of used TiO2 concluded that the Cl– ions reacted with TiO2 particles. | en_US |