Bentonites impregnated with TiO 2 for photodegradation of methylene blue Enéderson Rossetto b , Diego I. Petkowicz b , João H.Z. dos Santos b , Sibele B.C. Pergher a , Fábio G. Penha a, ⁎ a Departamento de Química, Universidade Regional Integrada do Alto Uruguai e das Missões, Campus Erechim, Av. Sete de Setembro, 1621, 99700-000 Erechim, RS, Brazil b Instituto de Química, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, 91501-970, Porto Alegre, RS, Brazil abstract article info Article history: Received 26 August 2009 Received in revised form 5 March 2010 Accepted 9 March 2010 Available online 19 March 2010 Keywords: Bentonites Diatomites Titanium oxide Photodegradation Four bentonites and one diatomite from Rio Negro (Argentina) were used as supports for titanium oxide (TiO 2 ). The materials were characterized by X-ray diffraction, scanning electron microscopy, infrared spectroscopy, textural analysis by nitrogen adsorption, elemental analysis and diffuse reflectance spectroscopy. The specific surface areas calculated by the BET method were 76, 46, 80, and 31 for the bentonites and 153 m 2 /g for diatomite and were not changed by impregnation with TiO 2 . SEM analysis revealed agglomerates, probably due to titania domains on the surface. The properties of the lamellar materials were maintained after TiO 2 impregnation, and all materials showed methylene blue photodegradation activity. The bentonites showed a higher activity than the commercial catalyst P25, likely due to the TiO 2 distribution and better accessibility. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The treatment of colored wastewaters produced by the textile industry is a problem that has recently been heavily researched (Bergamini et al., 2009; Han et al., 2009; Mahvi et al., 2009). Hetero- geneous photocatalysis is one method for treatment of such wastewa- ter; it is a so-called “Advanced Oxidation Process” (AOP) suitable for the oxidation of dyes. The AOP is based on the formation of hydroxyl radicals (HO • ), a strong oxidizing agent (E° = 2.8 eV) that can promote the total mineralization of organic pollutants. The process begins with the absorption of a photon by a semiconductor such as titanium oxide, equal to or larger than its band gap. An electron may then be promoted from the valence band (VB) to the conduction band (CB). After the electronic transition, the VB is left with an electron deficiency (VB + ) and the CB has an electron excess (CB - ). This process affords a redox reaction of the adsorbed species on the semiconductor with the formation of oxided products. It has been proposed that the adsorbed water molecules react with (VB + ) to form hydroxyl radicals (OH • ) to start the photodegrada- tion of the pollutants (Faisal et al., 2007; Saquib et al., 2008; Singh et al., 2008). Titanium oxide is the most investigated photocatalyst for the degradation of organic pollutants from wastewaters. This catalyst is advantageous over other semiconductors because of its chemical stability, non-toxicity, low cost and commercial availability (Li et al., 2008; Suwanchawalit and Wongnawa, 2008; Wang et al., 2008; Yang et al., 2008). The efficiency of TiO 2 is influenced by its crystal structure, particle size, specific surface area and porosity. Ultrafine powders of TiO 2 show a good catalytic activity. However, agglomeration can take place, engendering the production of larger particles and resulting in the reduction or even complete loss of catalytic efficiency. The dispersion of TiO 2 particles on clay mineral layers is a potential solution to this problem. Clay minerals impregnated with TiO 2 show high thermal stability and larger pore sizes that afford better incorporation of the species without diffusion problems, increased specific surface area or increased acidity (Valverde et al., 2003; Suwanchawalit and Wongnawa, 2008). Photocatalytic degradation of hydrocarbons was studied with Na- bentonite, TiO 2 and H 2 O 2 as oxidant (Dékány and Pernyeszi, 2004). A synergetic effect of the clay minerals on the photocatalytic degrada- tion due the large specific surface area was observed. Dékány et al. (2008) studied the role of the clay minerals as supports of the TiO 2 . The authors examined the catalytic properties of the composites for degradation of phenol in aqueous solution and ethanol and toluene vapor. These pollutants were degraded at higher efficiency than by pure TiO 2 . This paper presents the preparation and characterization of titania supported on bentonite and diatomite and the photodegradation of methylene blue. 2. Experimental 2.1. Materials Four bentonites and a diatomite were obtained from Rio Negro (Argentina). Titanium tetrachloride and cyclohexane were purchased Applied Clay Science 48 (2010) 602–606 ⁎ Corresponding author. Tel.: + 55 543520 9000. E-mail address: fpenha@uri.com.br (F.G. Penha). 0169-1317/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2010.03.010 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay