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 -FN. The second order rate constant for its formation was evaluated to ？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 ( ). 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. 1. Introduction Owing to the intensive agriculture within the last three decades, the varieties of employed pesticides have increased considerably. The presence of these chemicals in groundwater, streams, rivers lakes, and waste water effluents may present serious problems to the environment, human health, and the equilibrium of ecosystems. A considerable number of these pesticides in aqueous solutions may absorb in the actinic portion of the solar spectrum leading then to photochemical processes with solar light through direct as well as indirect photoreactions ( ？nm) [1–5]. 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. In natural waters, indirect processes may be also observed via the excitation of substances such as Natural Organic Matters (NOM) [6–8]. The solar light excitation of these substances leads to the formation of several reactive species such as triplet excited states or/and reactive oxygen species (ROS). Among these latter species, singlet oxygen , superoxide anion , and hydroxyl radical represent the main reactive ones [6, 9]. When an efficient remediation of the contaminated environmental compartments is concerned, research activities toward the development of new treatment methods are undertaken. Various methods, the so-called advanced oxidation processes (AOPs), have been the subject of
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