Modelling the photocatalytic degradation kinetics of organochloride chemicals in aqueous solutions

Abstract

Polychlorinated endocrine disrupting chemicals are environmental pollutants that are increasingly found in water sources. As a result of their hydrophobic properties, they generally accumulate in adipocytes of humans and wildlife when ingested. In this study, the feasibility of the advanced oxidation processes (AOPs) such as heterogeneous photocatalysis technology is investigated for the treatment of organochlorides in water systems. Titanium dioxide (TiO2) is the semiconductor catalyst of interest. The literature suggests that the most prominent organochlorides in the region are organochloride pesticides (OCPs). A group of 5 compounds were identified for the investigation; DDT, DDE, heptachlor, chlordane, and a polychlorinated biphenyl compound named 2,3,4-trichlorobiphenyl. Reverse phase solid phase extracted (RP-SPE) surface water organic analytes analysis was conducted using gas chromatography mass spectroscopy (GC-MS). Results from most sampling sites showed high concentration levels of the organochlorides in the environment. Heterogeneous photocatalysed mineralisation processes of organochlorides in aqueous systems were conducted in a batch reactor. Organochloride spiked solutions of differing catalyst concentrations are irradiated using a UV lamp for a period of 30 minutes. The reaction kinetics are determined and weighed against conventional photolysis. Results showed improved photo degradation of organochlorides under photocatalytic imposed conditions in comparison to photolysis. Results also suggest that photocatalytic degradation of organochlorides is less favoured with increased TiO2 catalyst concentrations. Enhanced catalyst performance studies through TiO2 surface property modification were conducted using copper nitrate (CuNO3) as a catalyst dopant. The doped catalyst showed slightly improved degradation of organochlorides at particular catalyst concentrations. Simulated photocatalytic rate of reaction kinetics results are in correlation with the modeled experimental results. They show variability of the degradation constant in the rate of reaction with varied catalyst concentrations. Catalyst concentration efficiency of each compound and the rate of the reactions were determined.