Applied Catalysis A: General 402 (2011) 201–207 Contents lists available at ScienceDirect Applied Catalysis A: General j ourna l ho me page: www.elsevier.com/locate/apcata Methylamine and dimethylamine photocatalytic degradation—Adsorption isotherms and kinetics Sihem Helali a,b , Eric Puzenat a , Nathalie Perol a , Mohamed-J. Safi b , Chantal Guillard a,∗ a Université Lyon 1, CNRS UMR 5256, IRCELYON, 2 avenue Albert Einstein, F-69626 Villeurbanne, France b Université Tunis El Manar, Ecole Nationale d’Ingénieurs de Tunis, ENIT, BP 37, le Belvédère 1002, Tunis, Tunisia a r t i c l e i n f o Article history: Received 4 January 2011 Received in revised form 2 June 2011 Accepted 5 June 2011 Available online 13 June 2011 Keywords: Adsorption Dimethylamine Methylamine Photocatalytic degradation TiO2 a b s t r a c t The photocatalytic degradation of two nitrogenous organic compounds, methylamine CH 3 NH 2 and dimethylamine (CH 3 ) 2 NH, used in pharmaceutical and chemical industries was investigated in the pres- ence of UV-irradiated TiO 2 aqueous suspensions. Different parameters were studied: adsorption under dark and UV-A conditions, photolysis, kinetics of degradation, and chemical pathway of methylamine (MA) and dimethylamine (DMA) degradation. The percentage of covered OH in the dark was equal for different concentrations of MA and DMA. The adsorption isotherms of these two amine compounds MA and DMA follow the Langmuir model. The photocatalytic oxidation kinetics of MA and DMA are described by the Langmuir–Hinshelwood model with a first order kinetics for concentrations below 0.5 mmol L -1 , and then reach a plateau. For both MA and DMA, the coverage rates of the TiO 2 surface in the dark and under illuminated condi- tions were different. The nitrogen atoms were decomposed mainly to ammonium (NH 4 + ). Nitrite (NO 2 - ) was also formed but was rapidly oxidized to nitrate (NO 3 - ). MA was detected as an intermediate prod- uct during the degradation of DMA. Formic acid (HCOOH), and two other products not identified were detected. These non-identified products do not correspond to formamide. Total Organic Carbon (TOC) analysis shows the presence of final slightly mineralised intermediate compounds. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Photocatalysis involving TiO 2 has proved to be a good alterna- tive for eliminating chemical water contaminants that are hardly degradable by conventional biological treatment even at low concentration making these contaminants hazardous for the envi- ronment and the human health. Photocatalysis is based on the interaction between UV-light and catalyst producing highly reac- tive oxygen species (OH • , O 2 • - , HO 2 • ) that can mineralize dissolved organic pollutants to CO 2 , H 2 O and inorganic constituents. Photocatalysis with TiO 2 is considered as an advanced and green technology [1] for its non-toxic, clean and safe properties. It is widely applied in air [2–4] and water purification systems. In particular, photocatalysis using TiO 2 was successfully used for degradation of nitrogen compounds [5,6], pesticides [7–10], insec- ticides [11], dyes [12,13] which are difficult to be treated by biological methods. Photocatalysis was also promising for microor- ganism elimination [14,15]. Even if presenting a high photocatalytic activity, titanium diox- ide remains difficult to separate from treated water in practical ∗ Corresponding author. Tel.: +33 4 72 44 53 16; fax: +33 4 72 44 53 99. E-mail address: chantal.guillard@ircelyon.univ-lyon1.fr (C. Guillard). applications. This point is however poorly taken into account in the literature. Kagaya et al. [16] reported that a coagulation technique was recommended to separate titanium dioxide from solution after organic contaminant degradation using basic aluminium chloride as a coagulating agent for rapid flocculation and sedimentation of the titanium dioxide. Malato et al. [17] have demonstrated a sed- imentation technique for separating catalyst from treated water using a new granulated version of the well-known P-25 titanium dioxide named Degussa Aeroperl presenting a large particle size which facilitates sedimentation. Ultrafiltration [18] and cross-flow microfiltration [19] were also investigated to explore the separa- tion of titanium dioxide from water. According to the theory of photocatalysis, the efficiency of pho- tocatalysis decreases due to the recombination of photo-generated electron/hole (e - /h + ) pairs. Jiang et al. [20] reported that photo- catalysis can be enhanced by an electric field across a photocatalyst which can promote the electron/hole separation and can prevent the recombination process. Moreover, Wang et al. [21] reported that O 2 can be added to the water solution to capture the excited electrons reaching the semiconductor surface. Two amine compounds, methylamine (MA) and dimethylamine (DMA), were chosen in the present research to be degraded by heterogeneous photocatalysis using TiO 2 Degussa P25 as photo- catalyst. MA and DMA are widely used in the chemical industry to 0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2011.06.004