Photocatalytic degradation of p,p′-DDT under UV and visible light using interstitial N-doped TiO2

Abstract

1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (or p,p′-DDT) is one of the most persistent pesticides. It is resistant to breakdown in nature and cause the water contamination problem. In this work, a major objective was to demonstrate the application of N-doped TiO2 in degradation and mineralization of the p,p′-DDT under UV and visible light in aqueous solution. The N-doped TiO2 nanopowders were prepared by a simple modified sol–gel procedure using diethanolamine (DEA) as a nitrogen source. The catalyst characteristics were investigated using XRD, SEM, TEM, and XPS. The adsorption and photocatalytic oxidation of p,p′-DDT using the synthesized N-doped TiO2 under UV and visible light were conducted in a batch photocatalytic experiment. The kinetics and p,p′-DDT degradation performance of the N-doped TiO2 were evaluated. Results show that the N-doped TiO2 can degrade p,p′-DDT effectively under both UV and visible lights. The rate constant of the p,p′-DDT degradation under UV light was only 0.0121 min−1, whereas the rate constant of the p,p′-DDT degradation under visible light was 0.1282 min−1. Under visible light, the 100% degradation of p,p′-DDT were obtained from N-doped TiO2 catalyst. The reaction rate of p,p′-DDT degradation using N-doped TiO2 under visible light was sixfold higher than that under UV light. According to Langmuir-Hinshelwood model, the adsorption equilibrium constant (K) for the N-doped TiO2 under visible light was 0.03078 L mg−1, and the apparent reaction rate constant (k) was 1.3941 mg L−1-min. Major intermediates detected during the p,p′-DDT degradation were p,p′-DDE, o,p′-DDE, p,p′-DDD and p,p′-DDD. Results from this work can be applied further for the breakdown of p,p′-DDT molecule in the real contaminated water using this technology.