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

Ruey An Doong, Chih Hua Chen, R. A. Maithreepala, Su-Min Chang

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164 Scopus citations

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 0.036min -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 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.

Original languageEnglish
Pages (from-to)2873-2880
Number of pages8
JournalWater Research
Volume35
Issue number12
DOIs
StatePublished - 16 Jul 2001

Keywords

  • 2-chlorophenol
  • Apparent first-order rate constant
  • Coupled semiconductor system
  • Photodegradation

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