title: The influence of pH and cadmium sulfide on the photocatalytic degradation of 2-chlorophenol in titanium dioxide suspensions.
abstract: The influence of pH and cadmium sulfide on the photocatalytic degradation of 2-chlorophenol (2-CP) in titanium dioxide suspensions was investigated to evaluate the feasibility of mixed semiconductors on the photodegradation of chlorinated organics in aqueous solution. Apparent first-order rate constants (k(obs)) and initial rate constants were used to evaluate the degradation efficiency of 2-CP. Higher degradation efficiency of 2-CP was observed at higher pH values. The apparent pseudo-first-order rate constant was 0.036 min(-1) at pH 12.5 in TiO2/UV system, while a 2- to 9-fold decrease in k(obs) was observed over the pH range of 2.5-9.5. The addition of phosphate buffer solutions at different pH values have different effects on the degradation of 2-CP. H2PO4- has little effect on the photodegradation of 2-CP, while HPO4(2-) could inhibit the photodegradation efficiency of 2-CP. Chlorocatechol, hydroquinone, benzoquinone and phenol were identified as the predominant aromatic intermediates for the photocatalytic degradation of 2-CP. Moreover, less aromatic intermediates at higher pH were observed. Direct oxidation contributed significantly to the photodegradation of 2-CP. An addition of a semiconductor decreased the initial and apparent first-order rate constants of 2-CP. The cutoff of wavelength of 320nm could diminish the contribution of direct photolysis of 2-CP. The combination of cadmium sulfide and titanium dioxide can lead to an enhanced rate of disappearance of 2-CP compared to those in single semiconductor system. A 1.2 to 2.5-fold increase in rate constant in coupled semiconductor system relative to the single semiconductor system was obtained.
authors.affiliation: Department of Atomic Science, National Tsing Hua University, Hsinchu, Taiwan. radoong@mx.nthu.edu.tw
authors.forename: R A
authors.initials: RA
authors.lastname: Doong
authors.forename: C H
authors.initials: CH
authors.lastname: Chen
authors.forename: R A
authors.initials: RA
authors.lastname: Maithreepala
authors.forename: S M
authors.initials: SM
authors.lastname: Chang
mesh_terms: D001673:Biodegradation, Environmental; D019187:Cadmium Compounds / Q000494:pharmacology*; D002384:Catalysis / Q000187:drug effects / Q000528:radiation effects; D002713:Chlorine / Q000378:metabolism; D002733:Chlorophenols / Q000378:metabolism* / Q000528:radiation effects; D004785:Environmental Pollutants / Q000378:metabolism* / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D008027:Light; D008956:Models, Chemical; D017319:Photosensitizing Agents / Q000494:pharmacology*; D013440:Sulfides / Q000494:pharmacology*; D013535:Suspensions; D014025:Titanium / Q000494:pharmacology*; D014874:Water Pollutants, Chemical
chemical_list: D019187:Cadmium Compounds; D002733:Chlorophenols; D004785:Environmental Pollutants; D017319:Photosensitizing Agents; D013440:Sulfides; D013535:Suspensions; D014874:Water Pollutants, Chemical; C034939:cadmium sulfide; C009495:titanium dioxide; D002713:Chlorine; D014025:Titanium; C030683:2-chlorophenol