Photocatalytic Degradation of Monolinuron and Linuron in an Aqueous Suspension of Titanium Dioxide Under Simulated Solar Irradiation

Abstract

The photocatalytic degradation of two phenylurea herbicides, monolinuron (MLN) and linuron (LN), was investigated in an aqueous suspension of TiO2 using simulated solar irradiation. The objective of the study was to compare their photocatalytic reactivity and to assess the influence of various parameters such as initial pesticide concentration, catalyst concentration and photonic flux on the photocatalytic degradation rate of MLN and LN. A comparative study of the photocatalytic degradation kinetics of both herbicides showed that these two compounds have a comparable reactivity with TiO2/simulated sun light. Under the operating conditions of this study, the photocatalytic degradation of MLN and LN followed pseudo first-order decay kinetics. The kobs values indicated an inverse dependence on the initial herbicide concentration and were fitted to the Langmuir-Hinshelwood equation. Photocatalytic degradation rates increased with TiO2 dosage, but overdoses did not necessarily increase the photocatalytic efficiency. The degradation rate of MLN increased with radiant flux until an optimum at 580 W m‑2 was reached and then decreased. Under these conditions, an electron-hole recombination was favored. Finally, the photocatalytic degradation rate depended on pH, where an optimum was found at a pH value close to the pH of the point of zero charge (pH = 6).La dégradation photocatalytique de deux herbicides, le monolinuron (MLN) et le linuron (LN), a été étudiée dans une suspension de TiO2 au contact de lumière solaire simulée. L’objectif de cette étude est de comparer leur photoréactivité et d’évaluer l’influence de différents paramètres tels que la concentration initiale en pesticide, la concentration en catalyseur et le flux photonique sur la cinétique de dégradation du monolinuron. L’étude comparative de la dégradation des deux herbicides a montré que les deux composés présentent une réactivité comparable avec le système TiO2/lumière simulée. Dans les conditions opératoires de cette étude, la dégradation photocatalytique du LN et du MLN suit une cinétique de pseudo ordre 1. La pseudo-constante kobs est inversement proportionnelle à la concentration initiale en pesticide et peut être décrite par une équation de Langmuir-Hinshelwood. L’étude de l’influence de la concentration en TiO2 a permis de montrer que la cinétique de dégradation du MLN augmente avec la dose de catalyseur, mais un surdosage n’est pas nécessaire pour augmenter l’efficacité du procédé. Cette étude a permis également de montrer que la pseudo‑constante d’ordre 1 de dégradation du MLN augmente linéairement avec le flux lumineux jusqu’à 580 W m-2 puis décroît. Dans ces conditions, la recombinaison des électrons trous est favorisée. Enfin, la cinétique de dégradation du MLN en fonction du pH passe par un optimum de pH proche du pH de point de charge nulle (pH = 6)

Removal of the herbicide monolinuron from waters by the electro-Fenton treatment

“…MLN complete degradation took place after about 10 and 15 min electrolysis with BDD and Pt anodes, respectively. Degradation of MLN was significantly quicker than that obtained by Zouaghi et al using sonocatalysis (over 40 min) [24] and heterogeneous photocatalysis using TiO2 under simulated solar irradiation (kapp = 0.035 min -1 ) [25]. The better performance of BDD anode can be explained by its large O2-evolution potential and physical adsorption inversely to Pt for which M( • OH) are chemisorbed and consequently less available.…”

Preparation, Characterization and Photocatalytic Activity of N doped TiO2

“…Negligible mineralisation was observed when studies were carried out in absence of light. All these results suggest that mineralization of this compound takes place through photocatalytic mechanism [26]. …”

Influence of Operational Parameters on Photocatalytic Degradation of Linuron in Aqueous TiO2 Pillared Montmorillonite Suspension

“…This inhibition increases with Cl − concentration particularly at low pH values. In neutral media Linuron is easily hydrolyzed, the inhibition of Cl − is small hence the maximum number of Linuron molecules are adsorbed on the Mont-TiO2 surface and consequently result in enhanced photodegradation [40,41]. In an alkaline medium, Linuron degradation decreases due to coulombic repulsion between the negatively charged surface of photocatalyst and hydroxide anions.…”