Dissociation Of OH Groups Research Articles

Adsorption and dissociation of water on halogen pre-adsorbed Ni(111) and Ni–Cr(111) surfaces: A DFT study

Theoretical study of the adsorption and dissociation of water on halogen pre-adsorbed Ni(111) and Ni–Cr(111) surfaces has been investigated systematically. The stable co-adsorption configurations and corresponding adsorption energies for H2O molecule and halogen atom were obtained. It was found that the halogen atom strengthens the interaction of H2O with Ni surfaces. The corresponding activation barriers and reaction energies of complete water dissociation were determined. The results show that the pre-adsorbed halogen changes the rate-determining step from the dissociation of OH group to the first step dissociation of H2O molecule. The activation barrier for H2O dissociation step increases significantly by halogen atom, together with lower exothermicity. These phenomena indicate that pre-adsorbed halogen can hinder the dissociation of H2O further retard the formation of protective oxide film.

Infrared Investigation of Dynamic Behavior of Brønsted Acid Sites on Zeolites at High Temperatures

Temperature-dependent behavior of acidic OH groups on zeolites was observed by infrared (IR) spectroscopy. While the IR band of acidic OH groups appeared the same in frequency and intensity below 300 K, gradual shifts in the peak-top position to lower frequencies and decreases in integrated intensity were recognized when samples were heated at higher temperatures. These changes were completely reversible and only dependent on the temperature. Based on the assumption that there is an equilibrium between undissociated and dissociated states of OH groups, a model is proposed in which the intensity decrease is attributed to the dissociation of OH groups to form IR inactive species at high temperatures. The enthalpy difference between the two states was estimated using the van’t Hoff equation, leading to two different values in two temperature ranges (about 398–548 and 573–773 K) for zeolites with various topologies (MFI, MOR, and CHA). Based on the presence of two different types of enthalpy values, different...

Two-dimensional ultrathin arrays of CoP: Electronic modulation toward high performance overall water splitting

Transition metal phosphides (TMPs) have shown promising performance in electrocatalytic water splitting. However, the sluggish kinetic of oxygen evolution reaction (OER) process deteriorates their activity toward overall water splitting. To overcome this issue, two-dimensional (2D) ultrathin arrays of metal-doped CoP (MCoP; M = Fe, Ni, and Mg) were successfully prepared by using layered double hydroxides (LDHs) as precursors. The as-obtained 2D ultrathin arrays exhibit an outstanding electrocatalytic activity and long-term durability toward both half-reaction in overall water splitting. As a result, the electrolyzer assembled by FeCoP UNSAs consumes a cell potential as low as 1.60V (at 10mAcm−2). An experimental-theoretical combination study reveals that the electronic structure of Co is modulated via the incorporation of Fe, which benefits the adsorption of water molecule and the dissociation of OH group, accounting for the largely enhanced activity toward overall water splitting.

The role of oxygen-containing groups on the adsorption of bisphenol-A on multi-walled carbon nanotube modified by HNO 3 and KOH

Abstract The adsorption of bisphenol-A (BPA) on multi-walled carbon nanotubes (MWCNTs) was investigated in this study. To distinguish the influences of surface area and oxygen-containing functional groups, the as-purchased MWCNTs ( A -MWCNTs) were treated by HNO 3 ( N -MWCNTs) and KOH ( K -MWCNTs). The adsorption capacity of N -MWCNTs was less than that of A -MWCNTs at neutral pH due to the steric obstruction resulted from the oxygen-containing functional groups on the N -MWCNTs. The adsorption capacities of BPA on all three types of MWCNTs decreased when the pH values increase to 10 or 11, at which the electrostatic repulsions between the dissociated surface groups and BPA arose. Also, it was found that although the N -MWCNTs and the K -MWCNTs had about the same amount of the oxygen-containing surface groups, their ratios of the adsorption amount at solution pH 11 to that at pH 5 ( q 11 /q 5 ) were different. This indicated that not only the amount but also the types of the oxygen-containing groups would affect the interaction between aromatic compounds and MWCNTs. The dissociation of OH groups and water-clustering would have more significant hindering effects than the carboxylic groups for the adsorption of BPA by MWCNTs at high pH.

Adsorption Behavior of Radionuclides Using Novel Tannic Acid-type Resin Embedded in High-porous Silica Beads in Seawater

The adsorption behavior of Cs(I), Sr(II), I(I), and Ln(III) species on the novel synthesized tannic acid-type resin embedded in high-porous silica beads (TA resin) in seawater with initial pH 7.7 has been studied at room temperature, compared with those of typical resins such as bisphenol A-type (BA), DIAION CR10, WK10, and PK228 resins. As a result, it was found that the obtained distribution coefficients (Kd) of these metal ions using the examined resins increase in order of WK10, CR10, BA, and TA resins (≒ PK228 resin) for Cs(I) species, in order of WK10, BA, TA, CR10, and PK228 resins for Sr(II) species while these resins have no adsorption ability of I(I) species. Moreover, it was also revealed that these resins can adsorb stronger trivalent lanthanides from La to Lu except for Pm in order of PK228, WK10, BA, TA, and CR10 resins. These results imply that the adsorption ability of our synthesized TA resin for the metal ions such as Cs(I), Sr(II), and Ln(III) species are much higher than those of commercial resins, that is, we have succeeded in the synthesis of the novel effective resin for removal of Cs(I), Sr(II), and Ln(III) species in seawater. The Kd values of Ln(III) species with TA resin were relatively larger than those of Cs(I) and Sr(II) species. The obtained Kd values of Ln(III) species with TA resin increased sharply with increasing the pH (1.5, 2.8, 6.3, 7.2, 7.4, and 8.1) in seawater due to the dissociation of OH groups in TA resin and decreased gradually with an increase of the dilution factor (1.0, 2.0, 3.0, 5.0, and 10.0) of seawater because the complexation reactions between Ln(III) species and CO32− contained in seawater are depressed. In addition, we have examined the adsorption isotherms and thermodynamics (Temp. = 297 - 330 K) of Ln(III) species on TA adsorbent in seawater. As a result, it was found that the adsorption processes between TA resin and Ln(III) species are strongly influenced by the components contained in seawater. Furthermore, their processes were found to be endothermic and spontaneous reactions in nature. From these results, we concluded that the developed TA resin is suitable for removal of Ln(III) species rather than that of Cs(I) and Sr(II) species in contaminated seawater.

Comparison between the free‐radical‐scavenging activities with vitamin E and ubiquinol in biological systems based on their reaction rates: A research account

Detailed kinetic studies have been performed for the reaction of aroxyl (ArO.) radical with vitamin E (alpha-, beta-, gamma-, delta-tocopherol, TocH), ubiquinol-10, and related antioxidants in micellar solution, using a stopped-flow spectrophotometer. The second-order reaction rates (ks) obtained increased in the order of hydroquinone < tocol<delta-TocH<ubiquinol-0<gamma-TocH-beta-TocH<ubiquinol-10<alpha-TocH at pH 4-8. The antioxidants which have lower oxidation potentials (Ep) showed higher reactivities. The reaction rates obtained in micellar solution were pH dependent because of the dissociation of OH groups in the antioxidants. For instance, by comparing the ks values with the mole fraction of each molecular form of ubiquinol-10, the reaction rate ks1 (1.21 x 10(5) M(-1)s(-1)) for undissociated form, ks2 (1.04 x 10(6) M(-1)s(-1)) for monoanion and ks3 (0 M(-1)s(-1)) for dianion, and the pKa1 and pKa2 values (11.4 and 12.7) were determined. It was found that the relative ratio of ks values (100:21:20:2.9) of alpha-, beta-, gamma-, delta-tocopherols in micellar dispersion has good correlation with the relative biological activities for rat fetal resorption, rat haemolysis, and chicken muscle dystrophy. The relative antioxidant activities of alpha-tocopherol and ubiquinol-10 have been discussed on the basis of the products of the ks values and their concentrations in serum and several tissues (heart, muscle, liver, kidney, and brain).

Thermodynamics and kinetics of 1,8-dihydroxy-2-(imidazol-5-ylazo)-naphthalene-3,6-disulphonic acid immobilization on Dowex resin

The sorption of 1,8-dihydroxy-2-(imidazol-5-ylazo)-naphthalene-3,6-disulphonic acid (IACA) onto the anion exchange resins Dowex 1-X8 and Dowex 2-X8 was studied by following the absorption spectra of solid phase, as the function of acidity, dye concentration, temperature and time. The aim of this work was to elucidate the thermodynamics and kinetics of the sorption process and to investigate the influence of the sorption on the ionic forms of the modified dye. The Langmuir model was applied to describe equilibrium isotherms of dye sorption onto Dowex 1-X8, 50–100 mesh at pH 4.5. The values of Gibbs free energy Δ G were between −26.0 kJ/mol and −30.5 kJ/mol, in the temperature range from 0 to 25 °C. The results of the kinetic experiments, performed in batch conditions, showed that sorption was pseudo-first order process. IACA diffusion coefficients from 5.2 × 10 −9 to 8.2 × 10 −9 cm 2/s for Dowex 1-X8 and from 4.5 × 10 −9 to 7.1 × 10 −9 cm 2/s for Dowex 2-X8 were obtained. Activation energy values calculated by using Arrhenius equation, were 25.8 kJ/mol, for Dowex 1-X8, and 25.4 kJ/mol for Dowex 2-X8. The apparent equilibrium constants of protonation of the imidazole moiety (log K p = 2.4) and dissociation of OH group from naphthalene nucleus (p K d = 6.4) of the modified dye were determined from the spectrophotometric data using Donnan model, and compared to the values obtained in the solution.

NMR and crystallographic studies of a p-sulfonatocalix[4]arene-guest complex

The {sup 1}H and {sup 13}C NMR spectra of a complex formed from tetrasodium p-sulfonatocalix(4)arene (1{sub 4}) and trimethylanilinium chloride (2) in D{sub 2}O showed that 2 is bound to the cavity of cone-shaped 1{sub 4}: in the acidic pH region (pD 0.4) the phenyl moiety resides in the cavity, whereas in the neutral pH region (pD 7.3) both the trimethylammonium and the phenyl moiety are included nonspecifically in the cavity. The difference was accounted for by the change in the electron density in the benzene {pi}-systems induced by the dissociation of OH groups. The complex was crystallized from acidic aqueous solution. The solid-state {sup 13}C NMR (CP-MAS) supports the inclusion of the phenyl moiety in the cavity. The X-ray crystallographic studies established that (1) 1{sub 4} adopts a cone conformation, (2) 1{sub 4} and 2 form a host-guest-type complex with the phenyl moiety inserted into the cavity, (3) not only the hydrophobic force but also the electrostatic force operates for guest inclusion, and (4) the overall structure is similar to that of clays, 1{sub 4} molecules being arranged into bilayers. These findings serve as a useful cross-link between solution complexes and solid-state complexes.

DECOLORING OF WATER-SOLUBLE AZO DYES BY OZONE

In recent years, the ozone treatments of waste water has attracted attention because of its extensive uses. In this report, the conditions of decoloring reaction by ozone, mainly for a watersoluble azo dye, C. I. Acid Orange 12 (A. O. 12), have been reported. The results obtained are as follows:1) In the decoloring of A. O. 12 by ozonea) The reaction is of pseudo first order.b) The dissociation of OH group of the dye and the self-decomposition of ozone appear to accelerate the reaction.c) The aromatic rings are cloven to form carboxylic acids.2) Ozone mainly attacks N=N bond in mono azo dyes.3) A. O. 12 is considered to decompose to the final products via intermediates containing active oxygen.