Journal of Molecular Catalysis A: Chemical 235 (2005) 194–199 Visible light photodegradation of phenol on MWNT-TiO 2 composite catalysts prepared by a modified sol–gel method Wendong Wang a , Philippe Serp b , Philippe Kalck b , Joaquim Lu´ ıs Faria a,∗ a Laborat´ orio de Cat ´ alise e Materiais, Departamento de Engenharia Qu´ ımica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias s/n 4200-465 Porto, Portugal b Laboratoire de Catalyse, Chimie Fine et Polym` eres, Ecole Nationale Sup´ erieure d’Ing´ enieurs en Arts Chimiques Et Technologiques, 118 Route de Narbonne Toulouse Cedex 31077, France Received 27 December 2004; received in revised form 15 February 2005; accepted 18 February 2005 Available online 12 May 2005 Abstract Multi-walled carbon nanotubes (MWNT) and TiO 2 composite catalysts were prepared by a modified sol–gel method. The nanoscaled composite materials were extensively characterized by TG, N 2 adsorption-desorption isotherm, XRD, SEM, EDX, TEM and UV–vis spectra. The photocatalytic degradation of phenol was performed under visible light irradiation on these catalysts. An optimum of synergetic effect on photocatalytic activity was observed for a weight ratio MWNT/TiO 2 equal to 20% with an increase in the first-order rate constant by a factor of 4.1. The synergetic effect, induced by a strong interphase interaction between MWNT and TiO 2 , was discussed in terms of different roles played by MWNT in the composite catalysts. © 2005 Elsevier B.V. All rights reserved. Keywords: Photocatalysis; Phenol degradation; Titanium dioxide; MWNT; Composite catalysts 1. Introduction Titanium dioxide has been extensively employed as photo- catalytic material for solving environmental problems, espe- cially for eliminating toxic chemicals from waste water [1,2]. TiO 2 /UV system has been widely investigated in the hetero- geneous photocatalytic process, during which UV irradiation upon the semiconductor can photoactivate TiO 2 generating electron/hole couples with strong redox properties [3]. The photocatalytic activitiy of TiO 2 powder greatly depends upon its microstructure and physical properties due to different preparation conditions and methods [4–11]. Additionally, it has been reported that activated carbon (AC) has some bene- ficial effects on the photocatalytic activities of TiO 2 [12–14]. The major drawback in the practical application under ir- radiation of natural solar light (where only approximately 4% of the solar radiation is effective) is the band gap en- ∗ Corresponding author. Tel.: +351 225 081 645; fax: +351 225 081 449. E-mail address: jlfaria@fe.up.pt (J.L. Faria). ergy (3.2 eV) for anatase TiO 2 . Therefore, the development of photocatalysts that can be excited by visible light has re- ceived much attention. Various efforts have been attempted to extend the light absorption of the photocatalysts to the vis- ible region. For example, TiO 2 impregnated with different transition metals shows a slight shift in the band gap transi- tion to longer wavelengths and an extension of the absorption in the visible region, but also a significant reduction in pho- toactivity due to a higher recombination rate [15]. Rare earth cerium [16] and neodymium [17] ion modified TiO 2 sol can effectively photodegrade reactive brilliant red dye (X-3B) or phenol under visible light irradiation. Photodegradation of or- ganic pollutants by using visible light has also been achieved on superficially modified TiO 2 with different dyestuff or com- plexes [18–22]. Photocatalysts based on TiO 2 for visible light degradation of p-chlorophenol (4CP) have been obtained by a sol–gel process using Na 2 [PtCl 6 ] as a dopant [23], calcination of gels prepared by a sol–gel process using various titanium alkoxide precursors [24] and pyrolysis of hydrolyzed TiCl 4 with nitrogen base [25]. 1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molcata.2005.02.027