Surface structure and reactivity study of phosphotungstic acid-nitrogenated ormosils
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Supramolecular interactions between nitrogenated groups in hybrid ormosils bearing phosphotungstate nanocatalyst were used to tune the photocatalytical activity of these class-II hybrid materials obtained through sol–gel chemistry. Surface chemistry and morphology of the materials was studied by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and water contact angle measurements. The photocatalytic efficiency of these hybrid films, measured by the degradation of crystal violet over-layer deposited on ormosils films, is higher for ormosils bearing neutral, more polar and less H-bonding nitrile groups than those bearing alkylamine/alkylammonium functionalities, despite the lower W/Si atomic ratio on the surface and lower tungsten percentage of the pure nitrile bearing ormosils. Such higher surface reactivity of the nitrile bearing ormosils is due to weaker interaction with the phosphotungstate and the lower activity of amine bearing ormosils is attributed to the competition among reversible photochromism and photocatalysis pathways in these materials.
KeywordsOrmosil Hybrid materials Phosphotungstic acid XPS Photocatalysis Supramolecular chemistry
Part of this work was performed within the exchange program of the Instituto de Química de São Carlos, Universidade de São Paulo and the Faculty of Mathematics and Natural Sciences of the University of Groningen. The authors acknowledge the Panalytical Brazil for XRF measurements. We acknowledge the funding by the São Paulo Research Foundation (FAPESP) Grant # 2011/08120-0 and the National Council for Scientific and Technological Development (CNPq) Grant # 479748/2008-0. F.L.S. de Carvalho and E. P. Ferreira Neto thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for Brazilian studentships; L.C. Battirola thanks CAPES Grant # 5321-09-3 for the international exchange fellowship Brazil/The Netherlands. S. Ullah thanks the Third World Academy of Science (TWAS) and the National Council for Scientific and Technological Development (CNPq, Brazil) for Ph.D fellowship.
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