Michael J. Nash1, Raul F. Lobo1, Anne-Marie Zimmerman2, and Douglas Doren3. (1) Chemical Engineering, Univesity of Delaware, 150 Academcy St., Newark, DE 19716, (2) Chemistry, Univesity of Delaware, 150 Academcy St., Newark, DE 19716, (3) Chemistry, University of Delaware, 150 Academcy St., Newark, DE 19716
Semiconductors photocatalysts have become increasingly important due to their ability to promote oxidation reactions at low temperatures. However, many of these semiconductor materials have disadvantages that prevent them for being used widely in industry including a high energy band gap and a structure that prevents a high quantum yield (turn over/number of photons absorbed). We have investigated ETS-10 and the vanadium-incorporated forms of ETS-10 as photocatalysts since their unique structure may help elucidate the material and surface properties needed to overcome some of the disadvantages of traditional semiconductors like anatase TiO2. ETS-10 is a microporous titanosilicate[1] composed of octahedral chains of TiO6 connected to tetrahedral SiO4. These chains then stack perpendicular to each other to form a 7.5 Å, three-dimensional channel structure with an ideal stoichiometry of (Na, K)2TiSi5O13.. Vanadium has been show to substitute for the titanium along the chain forming ETVS-10s and can completely replace titanium forming an analogous structure called AM-6.[2,3] In ETS-10 and AM-6, these TiO6/VO6 chains, which are insulated by the SiO4 groups, form a semiconducting “quantum wire” for the formation of electron-hole pairs upon irradiation with UV photons. ETS-10, ETVS-10, and AM-6 has be studied using experimental and computational methods, such as an in-situ DRIFT cell, Raman, UV/vis diffuse reflectance, XRD, N2 adsorption, NEXAFS, EPR, and DFT calculations. Experimental results show a reduction of the band gap energy along with increased photocatalytic activity for the vanadium-incorporated samples under visible light. Results also confirm the presence of two different oxidation states for vanadium along with considerable disorder along the chains which is believed to explain the trends in the band gap energy. These experimental results have been closely tied to computational models which also predict a lowering of the band gap along with increased disorder along the chains. We will also compare defective versus defect-free samples of ETS-10 and V-ETS-10 that show remarkable different activity.
References 1)Kuznicki, S. M, Pat. #4853202, United States, 1989 2)Rocha, J.; et. al.;Angewandte Chemie-International Edition in English 1997, 36, 100 3)Brandao, P.; et. al.;Impact of Zeolites and Other Porous Materials on the New Technologies at the Beginning of the New Millennium, Pts a and B 2002, 142, 327