Solar photocatalytic degradation of chlorophenols mixture (4-CP and 2,4-DCP): Mechanism and kinetic modelling

Abstract

The solar-photocatalytic degradation mechanisms and kinetics of 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) using TiO2 have been investigated both individually and combined. The individual solar-photocatalytic degradation of both phenolic compounds showed that the reaction rates follow pseudo–first-order reaction. During the individual photocatalytic degradation of both 4-CP and 2,4-DCP under the same condition of TiO2 (0.5 g L¡1) and light intensities (1000 mW cm-2) different intermediates were detected, three compounds associated with 4-CP (hydroquinone (HQ), phenol (Ph) and 4-chlorocatechol (4-cCat)) and two compounds associated with 2,4-DCP (4-CP and Ph). The photocatalytic degradation of the combined mixture (4-CP and 2,4-DCP) was also investigated at the same conditions and different 2,4-DCP initial concentrations. The results showed that the degradation rate of 4-CP decreases when the 2,4-DCP concentration increases. Furthermore, the intermediates detected were similar to that found in the individual degradation but with high Ph concentration. Therefore, a possible reaction mechanism for degradation of this combined mixture was proposed. Moreover, a modified Langmuir–Hinshelwood (L-H) kinetic model considering all detected intermediates was developed. A good agreement between experimental and estimated results was achieved. This model can be useful for scaling-up purposes more accurately as its considering the intermediates formed, which has a significant effect on degrading the main pollutants (4-CP and 2,4-DCP).