Interaction of benzene, cyclohexene, and cyclohexane with the surface of titanium dioxide (rutile)

Abstract

147sols containing particles with diameters well below 0.01 pm. Very small particle sizes are accessible because these materials have high densities (10.5 and 19.3 g/cm3 for silver and gold), and retention in SFFF depends on particle mass.The high extinction efficiencies of these small particles makes detection by optical means practical, even at sample concentrations as low as the 0.005% of the gold sol described here.The silver and gold sols which we have examined are easily dispersed in dilute aqueous FL-70 surfactant. There seems to be little change in the state of dispersion in the course of the SFFF analysis, as determined spectrophotometrically, which makes it possible to detect particle growth as well as flocculation by this method. This represents an advantage over electron microscopy, where the appearance of aggregation is often the result of the sample preparation method.The presence of gelatin adsorbed to the metal particles has little effect on the SFFF results because the gelatin contributes relatively little to either the mass of the particles or their optical extinction, even at 254 nm. Removal of the stabilizing gelatin, as by enzymatic action, may have little short-term effect on the sols, or may result in flocculation. In either case, SFFF is a convenient method for examining the stability of these materials. Acknowledgment.We thank Raymond C. Schuck of these laboratories for preparing some of the Carey Lea silver sols.The adsorption isotherms of organic cyclic molecules, benzene, cyclohexene, and cyclohexane, were measured at 25 O C on rutile samples covered with a controlled number of surface hydroxyl groups. The amount of irreversible adsorption increased with the number of a-electrons of adsorbate molecule and varied inversely with the surface hydroxyl content of the sample. These results suggest the participation of 7r-electrons of adsorbate molecules in the adsorption and give evidence for stronger interaction of a-electrons with surface Ti4+ ions than with surface OH groups. Infrared spectra of adsorbed species were measured for surfaces of both dehydroxylated and hydroxylated rutiles. When benzene was adsorbed on the dehydroxylated surface, the absorption bands due to the C-C stretching vibration shifted to lower wavenumbers compared with those of the gaseous state, which supports the concept of charge transfer from benzene molecules to the dehydroxylated sites, preferentially surface Ti4+ ions. Reversible adsorption occurring on the hydroxylated rutile surface was ascribed to the interaction between the surface OH groups and ?r-electrons for benzene and cyclohexene and to the contribution of dispersion force for cyclohexane having no a-electrons. IntroductionIt is widely known that the surface hydroxyl groups produced by dissociative adsorption of water molecules have a significant effect on the surface properties of the solid. The characterization of surface hydroxyl groups on the solid, especially on metal oxides, has become a matter of great interest.'S2 A study of the interaction o...

Titania Photocatalysts for Selective Oxidations in Water

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Enhanced performance of surface-modified TiO2 photocatalysts prepared via a visible-light photosynthetic route

“…17 Moreover, it is known that benzene molecules adsorb onto titania through a Ti-OHÁ Á Áp interaction at hydroxylated or a Ti 4+ Á Á Áp interaction at dehydroxylated surfaces. 18,19 Hence, under visible light irradiation, weak sub-bandgap transitions from the surface states to the conduction band of TiO 2 are possible.…”

Effect of Coadsorbed Water on Deep Oxidation Mechanisms: Temperature-Programmed Reactions of Benzene and Hydroxyl on the Pt(111) Surface

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