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 (kobs) 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 kobs
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. H2PO-
4 has little effect on the photodegradation
of 2-CP, while HPO2-
4 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. © 2001 Elsevier Science Ltd. All rights
reserved
