The adsorption isotherms of benzene, toluene, and chlorobenzene were measured for titanium dioxide (rutile) samples having a controlled number of surface hydroxyl groups, from which the amount of irreversible adsorption (V|") was obtained for each sample. The Virr values for benzene and toluene were the largest on the dehydroxylated surface, and they decreased linearly with increasing degree of surface hydroxylation of the sample. The value for toluene was larger than that for benzene, probably because of an enhanced electron density of the aromatic ring due to the presence of a methyl group carrying an electron-donating nature. The Vte value for chlorobenzene agreed with that for benzene on the dehydroxylated surface but was greater than those for the other two adsorbates on the surface with a higher concentration of hydroxyl groups. The IR absorption band due to the C-C stretching vibration of the aromatic ring shifted to the lower wavenumber with reference to the case of gaseous state, showing that these molecules are adsorbed through the formation of a Ti4+-ir-electron type complex on the dehydroxylated surface and by the formation of a --electron type complex on the hydroxylated surface. Furthermore, by applying the Mulliken-Puranik charge-transfer theory to the relationship between the shift and intensity of the OH absorption band, we found that toluene can be adsorbed only by the --electron interaction as in the case of benzene adsorption while chlorobenzene can be adsorbed by a different mechanism from the cases of the other two adsorbates. Chlorobenzene is adsorbed on the hydroxylated surface through the interaction between surface OH grovjps and the chlorine atoms of chlorobenzene, in addition to the --electron interaction, with so-called dual-site adsorption.

Valinomycin, unlike most surfactants, is a ring-shaped molecule; its hydrophilic groups are evenly distributed around the ring. By the Langmuir-Blodgett (LB) technique, a single monolayer of valinomycin can be deposited on withdrawing a (hydrophilic) glass or mica substrate from the subphase, but the contact angle is not appreciably changed by the deposition of this flat molecule. The monolayer then peels off as the substrate is reintroduced into the water. However, if a thin film of silver is first evapoated on the substrate or three monolayers of lead stearate deposited on it, multiple layers of valinomycin can be built up. LB multilayers can also be deposited on poly (methyl methacrylate) (PMMA). Monitoring the actual (dynamic) contact angle during the process of deposition suggests that, for successful LB deposition, the contact angle must be greater than 90°on immersion and less than 90°on withdrawal. For valinomycin this sequence occurs only with substrates whose contact angles are hysteretic even in clean water.

A possible model for H20 molecularly adsorbed on the bare surface of Ti02 (rutile) is proposed. An H20 molecule on the (110) surface is adsorbed dissociatively to form surface hydroxyls, while an H20 on the (100) or (101) plane can be adsorbed molecularly, its 0 atom being coordinately bonded to a surface Ti atom. Furthermore, the H atoms in the adsorbed H20 molecule interact with two adjacent surface 0 atoms through hydrogen bonding, so that threefold coordination is established for the 0 atoms in the molecularly adsorbed H20 as well as for those on the rutile surface as in the bulk crystal.

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...

hous, hydrated iron oxide layer. The amount of additional film formation was substantial for borate-formed annealed oxide in borate solution at positive potentials but much less at open-circuit potential or for HC104-formed oxides reimmersed into HC104 or HC1 solutions. The voltammograms in 0.1 M KC1 and 0.1 M HC1 were similar, indicating that pitting and dissolution in chloride media are pH independent, as reported by others.17 The role of Cl" adsorption in the pitting process is not well understood, and many theories have been proposed.13,17,18 Our results show that although significant amounts of Cl (2-8%) were incorporated into the film formed on a clean Fe-Cr-Ni-(111) surface in HC1, only traces of Cl (about 1%) were detected by Auger spectroscopy when breakdown of an annealed oxide film occurred in HC1. Evidently Cl adsorption occurs only at localized sites and at total concentrations too small to be detected by Auger spectroscopy.