Adsorption of carbon dioxide on hydroxylated and dehydroxylated silicas

Surface OH group governing wettability of commercial glasses

Role of surface OH groups in surface chemical properties of metal oxide films

The surface and pore structures of the materials resulting on outgassing the colloidal δ-FeOOH particles at different temperatures in the range 50–300 °C have been investigated by a variety of techniques. The FTIR spectrum of the particles outgassed at 100 °C has a weak broad band at 3650 cm–1 and a strong band at 3150 cm–1 which are assigned to the surface and bulk OH groups of δ-FeOOH, respectively. When outgassed above 150 °C three bands appear at 3665, 3635 and 3400 cm–1. The former two bands and the latter one can be assigned to the surface OH groups and the H2O molecules adsorbed in the micropores, respectively. Increasing the outgassing temperature develops the microporosity of the products. The t-plots of the samples treated above 150 °C indicate the formation of micropores with a 0.8 nm width as confirmed by transmission electron microscopy (TEM).

Surface OH group governing adsorption properties of metal oxide films

Determination of surface OH acidity from the formation of acid/base complexes on ultrathin films of γ-Al 2O 3 on NiAl(100)

Kinetics of low-temperature methane activation on IrO2(1 1 0): Role of local surface hydroxide species

In this study, the effect of UV treatment on the physicochemical properties and structural variation of metal oxide-silica nanocomposites (Mn2O3-Fe2O3@SiO2) has been investigated. Based on the results, UV irradiation significantly affects the nanocomposite structure, where SiO2 network reconfiguration, change in surface OH group density, and surface area were observed. Erythromycin (ERY) has been chosen as a module pollutant to compare the performance of the pristine and UV-treated nanocomposites. The pristine nanocomposite had a high adsorption efficiency (99.47%) and photocatalytic activity (99.57%) at neutral pH for ERY in the first cycle, and this efficiency decreased significantly for the multiple cycles. However, different results have been observed for the UV-treated nanocomposite, where it retained its performance for ten consecutive cycles. This enhanced performance is attributed to the structural modifications after UV exposure, where increased surface area, pore volume, and OH group density resulted in an increased number of the possible mechanisms responsible for the adsorption/oxidation of ERY. Moreover, oxidation of adsorbed molecules by UV light after each cycle can also be another reason for enhanced removal. For the first time, the fate of ERY is studied using regenerated nanocomposites after the last cycle. LC/MS/MS results showed that ERY degraded in 20 min, and the produced reaction by-products were adsorbed by nanocomposites. This study could be a foundation research for the practical approaches for the regeneration of nanomaterials and the successful removal of organic pollutants from aquatic environments.

The surface hydroxyl groups on porous glasses pretreated at various temperatures was determined by the successive-ignition-loss method and by means of active hydrogen analyses, and their hydroxyl groups have been classified into two types (isolated and gem type OH groups). The surface of the porous glass consists of three types of OH groups, isolated, gem type and H-bond OH groups. The isolated OH groups were stable up to 500°C, but the elimination of these groups took place gradually above 500°C. On the other hand, the gem type and H-bond OH groups were removed rapidly below 600°C and disappeared above 800°C. The surface of porous glass pretreated at 800°C for 4h contained only isolated OH groups, and the concentration of the isolated OH groups was found to be about 0.7OH's/100Å2. For water vapor adsorption, the surface OH groups play an important role as adsorption sites, and water molecules are adsorbed more strongly on gem type or H-bond OH groups than on isolated OH groups. In porous glass, the ignition-loss method was inadequate to determine the amount of surface OH groups, since water molecules diffused from inside the glass to its surface during heat treatment.

Adsorption property and surface reactivity on the top and the bottom faces of float glass were compared, and factors governing these properties were investigated. It was found that both the adsorption property with organic substances and the reactivity with silane coupling reagents were higher on the bottom face compared with the top face. It was also revealed by time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements that the difference in these properties was attributed to the density of surface OH group as adsorptive and reactive sites. The high density of surface OH group on the bottom face was explained in terms of the large surface concentration of tin penetrated into the glass during float process. The reason for the surface OH group density dependence on the tin concentration can be explained by X-ray photoelectron spectroscopy (XPS) O1s peak analysis: the SnOH group easily forms as compared with the SiOH group because of the high reactivity with water due to high Lewis basicity. Furthermore, it was found that the surface reactivity of various metal oxide materials was also explainable on the basis of Lewis basicity governing the formation of surface OH group. The analytical results leading to the successful control of the adsorption property and surface reactivity were discussed in detail.

Influence of water on the coadsorption of oxidizing and reducing gases on the β-Ga 2O 3 surface

The formation energies of H bonds between ice surface OH groups with H2, N2, and CO were calculated from Iogansen's empirical "rule of intensities". They are in reasonable agreement with other experimental and theoretical estimations and close to those of surface OH groups of silica with the same gases. The latter comparison facilitates a quantitative estimation of the acidity of surface ice OH group relative to that of silica surface OH groups and to that of other H-bonding acids. The acidity of surface ice OH groups is about twice that of the OH group of a free water molecule, as a consequence of the cooperative effect.

Effects of surface hydroxyl groups induced by the co-precipitation temperature on the catalytic performance of direct synthesis of isobutanol from syngas

Reduction of fluorescence from high-area oxides of the silica, γ-alumina, silica-alumina, and Y-zeolite types and Raman spectra for a series of molecules adsorbed on these surfaces

Effects due to hydrogen bonding between physically adsorbed molecules and the hydroxyl groups present on the surface of porous silica glass have been studied. Three methods have been used. As well as the classical isotherms, length changes of the adsorbent have been measured using an interferometer, and infra-red absorption spectra have been obtained both of the surface OH groups and the adsorbed molecules. Contractions of the rigid adsorbent, found under certain conditions at low coverages, are shown to be directly related to the strengths and number of the hydrogen bonds formed between the OH groups and the adsorbed molecules. More than half the surface OH groups were replaced by OCH 3 groups by methylation. Experiments performed on the glass after this treatment showed that the contractions had almost completely disappeared. It has been shown that two types of adsorption sites exist, one being the OH groups and the other the silicon or oxygen atoms. With acetone and ammonia, it has been shown spectroscopically that the energy of adsorption is lower on the OH sites than on the others. Consequently, as the temperature is raised the distribution of the adsorbed molecules between the two sites changes. Thus the marked decrease in the contractions with increase of temperature reported previously (Folman & Yates 1958) is due to the weakening of the hydrogen bonding with increase in temperature and also to a decrease in the relative numbers of the adsorbed molecules which are hydrogen-bonded. On the basis of all the results, a model of the surface conditions is proposed, which may explain the occurrence of the contractions found when hydrogen bonding is operative.

The surface OH groups on ..gamma..-Al/sub 2/O/sub 3/ modified with various concentrations of F/sup /minus//, SO/sub 4//sup 2/minus//, or molybdate anions were studied by use of IR techniques as well as by the adsorption of CO/sub 2/ in order to reveal the interaction chemistry between Al/sub 2/O/sub 3/ and molybdate species. Physicochemical characterizations of the modified Al/sub 2/O/sub 3/ were also conducted by means of LRS, XPS, and TPR techniques. It was revealed that the chemical reactivities and surface concentrations of hydroxyl groups determined the interaction modes between the anion and Al/sub 2/O/sub 3/, that is, the dispersion and distribution of the anion and its configuration. The molybdate anions were found to react with basic OH groups in a stoichiometry of OH/sup /minus///Mo = 1 at a concentration of < 10 /times/ 10/sup 13/ Mo cm/sup /minus/2/. It was shown that nonbasic OH groups were simultaneously consumed for anchoring molybdate species in tetrahedral configurations. In this concentration range, the OH/anion ratio was almost identical for SO/sub 4//sup 2/minus// and molybdate anions. With increasing molybdenum content, the OH/Mo ration decreased markedly, resulting in the formation of polymolybdate species. With SO/sub 4//sup 2/minus///Al/sub 2/O/sub 3/ and F/sup /minus///Al/sub 2/O/sub 3/, similar correlationsmore » were established between the formation of surface of subsurface species and the concentrations of reactive OH groups. On reduction or sulfurization of the MoO/sub 3//Al/sub 2/O/sub 3/ catalysts, a part of the consumed OH groups was restored and the extent of recovery increased as the wavenumber decreased.« less