TiO2 Photocatalysis of the Organophosphorus Fenamiphos: Insight into the Degradation Mechanism

H Mountacer,S M Nemmaoui,S Rafqah,M Sarakha,G Voyard

doi:10.1155/2013/319178

Abstract

The photocatalytic degradation of the organophosphorus fenamiphos (FN) was studied using titanium dioxide as a photocatalyst and 365 nm as an excitation wavelength. Under our experimental conditions and in aerated solutions, the irradiation in the presence of TiO2 P25 (1.0 g L−1) permitted the evaluation of the half lifetime to 9.5 minutes. Laser flash photolysis experiments showed the formation of an initial species owing to the attack of the hydroxyl radical on FN. It was identified as the adduct OH•-FN. The second order rate constant for its formation was evaluated to 7.3×109 moL−1 L s−1. All the products are formed via the formation of such transient intermediate. They were identified by means of HPLC/MS using electrospray in positive mode (ESI+). Two main processes are responsible for FN photocatalytic transformation: (i) hydroxylation on the aromatic structure and (ii) the scission of the C–O bond. A mechanistic scheme was proposed for the photocatalytic process of FN using titanium dioxide. An efficient mineralization was observed within 24 hours by using a suntest setup.

Highlights

Owing to the intensive agriculture within the last three decades, the varieties of employed pesticides have increased considerably
They were identified by means of HPLC/MS using electrospray in positive mode (ESI+)
No significant degradation of fenamiphos was observed within several days when the aqueous solution was kept in the dark and at room temperature, namely, 21∘C

Summary

Introduction

Owing to the intensive agriculture within the last three decades, the varieties of employed pesticides have increased considerably. A considerable number of these pesticides in aqueous solutions may absorb in the actinic portion of the solar spectrum leading to photochemical processes with solar light through direct as well as indirect photoreactions (λ > 295 nm) [1,2,3,4,5]. Within the former process, photochemical reactions such as dissociations, oxidation, and hydrolysis are observed and may lead to the generation of various byproducts that, in some cases, may be more harmful than the parent compound. Singlet oxygen 1O2, superoxide anion O2∙−, and hydroxyl radical ∙OH represent the main reactive ones [6, 9]

Methods

Results

Conclusion