Photodegradation kinetics of 4-nitrophenol in TiO2 suspension

A new two-phase swirl-flow monolithic type reactor was designed to study the kinetics of heterogeneous photocatalytic processes on semiconductor catalysts. Most of the earlier work investigated the effects of various parameters on the initial degradation rate (or the formation of CO2) of the pollutants. In the present study, photomineralization of 4-nitrophenol (4-NP) sensitized by Degussa P25 TiO2 in aqueous solution has been investigated as a function of the following different experimental parameters: initial concentration of pollutant (CS0), light intensity (Ia), partial pressure of oxygen (pO2), catalyst concentration, pH, chloride ion and temperature. The kinetic expression obtained can be described by the following formula rs=k0 exp (−E/RT)IαβKO2pO2/(1+KO2pO2)KsCs/(1+KsCs0). The apparent overall activation energy for 4-NP obtained was 7.42 kJ mol−1 by fitting the above equation with experimental data and the values for β, KO2 and Ks were 0.84, 9.98 atm−1 and 0.075 ppm−1 respectively. The kinetic equation can predict the concentration of 4-NP during the entire degradation process at pH value of 4.3 and TiO2 concentration of 2 g l−1, and is therefore, more meaningful. It can be used in the development of large-scale photocatalytic reactor and optimization of experimental conditions for any particular studies. Furthermore, the photodegradation of 4-NP on two different catalysts (P25 and UV100) was compared and the photonic efficiency of the process has also been investigated.