Kinetic study of the 4-Nitrophenol photooxidation and photoreduction reactions using CdS

We have investigated the kinetics of the photooxidation or photoreduction of 4-Nitrophenol (4-NP) with CdS as photocatalyst, and UV or visible light irradiation in the presence of Na2SO3. The photocatalytic reaction was performed by varying the Na2SO3 concentration under aerobic or anaerobic conditions, photocatalyst load and 4-Nitrophenol concentration. The 4-NP oxidation was attributed to the formation of the hydroxyl radical at 4 mM Na2SO3 concentration in either aerobic or anaerobic conditions under UV light irradiation. The 4-NPhenolate reduction was related to the sulfite radicals formed with appropriate Na2SO3 concentration (8 mM) in anaerobic conditions under UV or visible light. The 4-NP oxidation and reduction reactions follow a zero order kinetic and can be used as a model reaction to evaluate the active photocatalyst under UV or visible light. (C) 2013 Elsevier B.V. All rights reserved.