Synthesis, charcterization and catalytic evaluation of tungstophosphoric acid immobilized on Y zeolite

CANDELARIA LEAL MARCHENA, SILVINA GOMEZ, LILIANA B. PIERELLA Y LUIS R. PIZZIO.

Sustainable Energy Developments series

ENGINEERING, WATER & EARTH SCIENCES

Año: 2013; p. 43 - 57

The degradation of chemicals present in wastes by heterogeneous photocatalysis is an importantissue and its study is a constantly growing field. An increasing number of papers deal with TiO2(titania) as one of the most appropriate semiconductor materials to be employed as a photocatalyst,due to its high activity in the photodegradation of organic compounds, low cost, low toxicity, andchemical stability (Antonelli et al., 1995; Herrann, 2010; Sakthivel et al., 2004; Sclafani et al.,1991; Van Grieken et al., 2002;Wang et al., 1998;Yeung et al., 2003;Yu et al., 2000).It is generally reported that titania performance in the photodegradation of contaminants containedin wastes is influenced by the crystal structure, crystallinity, surface area, porosity, andband gap energy (Kyoko et al., 1997; Li et al., 1999; Sakulkhaemaruethai et al., 2005), amongother factors.The fast recombination of the photoinduced electrons and holes can lead to a lowphotocatalyticactivity. Transition metals or metal oxides were used to avoid the recombination of the electron?hole pairs of TiO2-based catalysts (Ikeda et al., 2001; Lee et al., 1992; 1993; Sclafani et al.,1991), improving the photocatalytic activity.Additionally, different heteropolyoxometalates (POM) have been added to TiO2 suspensions(Ozer and Ferry, 2001) or anchored to TiO2 by chemical interactions (Yang et al., 2004), incorporatedeither into TiO2 colloids (Yoon et al., 2001) or into the titania matrix during the TiO2 gelsynthesis (Blanco and Pizzio, 2010; Fuchs et al., 2008; 2009) with the purpose of reducing thecharge recombination in UV-illuminatedTiO2. The capacity of POM as acceptors of the electronsof UV-irradiated TiO2 suspensions, generated in the conduction band (e−cb) together with holes inthe valence band (h+vb), was demonstrated by Park and Choi (2003) using a photoelectrochemicalmethod.Heteropolyoxometalates are widely used as oxidation as well as acid catalysts (Fuchs et al.,2008; Okuhara et al., 1996; Pizzio et al., 1998). They are also employed as effective homogeneousphotocatalysts in the degradation of organic pollutants in water (Hu et al., 2000; Mylonas andPapaconstantinou, 1996; Mylonas et al., 1996; Ozer and Ferry, 2000).POMabsorb strongly in the near visible andUVregion of the light spectrum (λ