The influence of pH and cadmium sulfide on the photocatalytic degradation of 2-chlorophenol in titanium dioxide suspensions

• Published in: Water research (Oxford) 2001-08, Vol.35 (12), p.2873-2880
• Main Authors: Doong, Ruey-An, Chen, Chih-Hua, Maithreepala, R.A, Chang, Sue-Min
• Format: Article
• Language: English
• Subjects: 2-chlorophenol; apparent first-order rate constant; Applied sciences; Biodegradation, Environmental; Cadmium Compounds - pharmacology; Catalysis - drug effects; Catalysis - radiation effects; Chlorine - metabolism; Chlorophenols - metabolism; Chlorophenols - radiation effects; coupled semiconductor system; Environmental Pollutants - metabolism; Environmental Pollutants - radiation effects; Exact sciences and technology; Hydrogen-Ion Concentration; Industrial wastewaters; Light; Models, Chemical; photodegradation; Photosensitizing Agents - pharmacology; Pollution; Sulfides - pharmacology; Suspensions; Titanium - pharmacology; Wastewaters; Water Pollutants, Chemical; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/S0043-1354(00)00580-7

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 TiO 2/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. H 2PO 4 − has little effect on the photodegradation of 2-CP, while HPO 4 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 320 nm 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.