Applied Catalysis B: Environmental 163 (2015) 404–414 Contents lists available at ScienceDirect Applied Catalysis B: Environmental j ourna l h omepa ge: www.elsevier.com/locate/apcatb Phenol photocatalytic degradation over anisotropic TiO 2 nanomaterials: Kinetic study, adsorption isotherms and formal mechanisms Asma Turki a , Chantal Guillard b , Frédéric Dappozze b , Zouhaier Ksibi a , Gilles Berhault b , Hafedh Kochkar a,c,∗ a Université de Tunis El Manar, Faculté des Sciences de Tunis, Laboratoire de Chimie des Matériaux et Catalyse, 2092 Tunis, Tunisia b Institut de Recherches sur la Catalyse et l’Environnement, IRCELYON, CNRS—University of Lyon, Villeurbanne 69100, France c Laboratoire de Valorisation des Matériaux Utiles, Centre National de Recherches en Sciences des Matériaux (CNRSM), Technopôle Borj-Cédria, 8027 Soliman, Tunisia a r t i c l e i n f o Article history: Received 19 May 2014 Received in revised form 1 August 2014 Accepted 7 August 2014 Available online 15 August 2014 Keywords: Photocatalytic degradation TiO2 nanomaterials Adsorption isotherms Kinetics Formal mechanisms a b s t r a c t Anisotropic TiO 2 nanomaterials (nanotubes, nanorods, nanoplates, nanospheres, and nanoparticles) with controlled structural and textural properties have been evaluated in the photocatalytic degradation of phenol under UV conditions. The kinetic study of phenol adsorption fits well to a quasi-second-order model whereas the adsorption isotherms of phenol over the different TiO 2 nanomaterials follow the Langmuir model and the degradation kinetics the Langmuir–Hinshelwood (L–H) model. TiO 2 nanoma- terials exposing (0 0 1) or (1 0 1) anatase facets are less active than TiO 2 P25 for the phenol degradation. This is related to their tendency to degrade faster intermediates products (organic acids) rather than phenol itself. A good compromise between anatase crystallinity, crystallites sizes, and specific surface area can however improve the photocatalytic activity of the TiO 2 nanomaterials. Results also showed that the degradation mechanism follows pseudo-first order kinetics. Pseudo-rate constants were therefore determined and formal mechanism schemes proposed. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The contamination of natural and drinking water supplies and of the aquatic environment has become nowadays a serious envi- ronmental problem worldwide [1–6]. Wastewater treatment is based upon various mechanical, biological, physical, and chemi- cal processes. In fact, this is a combination of many conventional operations like coagulation, sedimentation, precipitative soften- ing, filtration, and chlorination of effluents polluted by organic pollutants [7,8]. After elimination of the particles in suspension, the biological treatment remains the ideal process for wastewater treatment, particularly at low pollutant concentrations. Neverthe- less, some organic pollutants are not biodegradable and are known ∗ Corresponding author at: Laboratoire de Valorisation des Matériaux Utiles, Centre National de Recherches en Sciences des Matériaux (CNRSM), Technopôle Borj-Cédria, 8027 Soliman, Tunisia. Tel.: +216 79 325 250; fax: +216 79 325 314. E-mail addresses: asmaturki@gmail.com (A. Turki), h kochkar@yahoo.fr (H. Kochkar). as Bio-Recalcitrant Organic Compounds (BROC). Despite their low concentration, these contaminants are a major health concern because of their extremely high endocrine disrupting potency and genotoxicity [9–11]. Therefore, the effective removal of BROC from wastewater effluent is of high interest. Many technologies based on Advanced Oxidation Processes (AOPs) have been used to overcome this critical problem [12–15]. AOPs processes are based on the generation of strongly oxidizing hydroxyl radicals (HO • ), which in turn are able to degrade the most recalcitrant molecules into biodegradable compounds. Heteroge- neous photocatalysis [16–18] was found to be one of the most promising AOPs for wastewater treatment due to the mild operat- ing conditions, the wide spectrum of pollutants able to be degraded and to its high efficiency for complete organic compounds min- eralization to carbon dioxide and water. Using the photocatalysis process, recalcitrant organics are degraded by the combined actions of mainly: (i) a semiconductor photocatalyst, (ii) an energetic radi- ation source (an artificial or natural light) and (iii) an oxidizing agent [19–21]. Metal oxides and sulfide materials represent a large class of semiconductors suitable for photocatalysis. In particular, http://dx.doi.org/10.1016/j.apcatb.2014.08.010 0926-3373/© 2014 Elsevier B.V. All rights reserved.