Abstract
The degradation of phenol, as an organic pollutant model, in water was systematically assessed under solar TiO2-photocatalysis in forced circulation loop reactor. The degradation rate was evaluated at various amounts of TiO2 and different initial concentrations of phenol. Additionally, the influence of coupling heterogeneous photocatalysis with high frequency ultrasonic irradiation (600 kHz) was investigated at various initial substrate concentrations. For both processes, (OH)-O-center dot radical was the main species responsible for the oxidation of phenol. The photocatalytic degradation rate of phenol increased with increasing TiO2 concentration up to 1 g L-1 and decreased afterward. The solar photocatalytic process is efficient even if the pollutant exists at high concentration levels. The initial degradation rate increased with increasing initial substrate concentration, following a complex kinetics that was found to be perfectly described by the Langmuir-Hinshelwood model. The combination of ultrasound and photocatalysis exhibited synergistic effect, which was found strongly dependent on the initial substrate concentration. A synergy factor of 1.15 was obtained for an initial substrate concentration of 10 mg L-1 but for 50 and 100 mg L-1, the synergy factor increased significantly to 1.82 and 1.95, respectively. The synergy was mainly attributed to the advantages of ultrasound on the heterogeneous photocatalytic process.