Bonded OH Groups Research Articles

Role of stacking faults and hydroxyl groups on the lithium adsorption/desorption properties of layered H2TiO3

Layered H2TiO3 ion sieve materials have shown promising selective lithium adsorption properties from brine solutions. Chemical delithiation of Li2TiO3 results in an increase of stacking faults and formation of isolated and hydrogen bonded OH groups. There is a critical knowledge gap in understanding the role of these stacking faults in lithium adsorption/desorption kinetics. Moreover, there is a lack of understanding in manipulation of surface hydroxyl groups to improve the lithium adsorption properties. In this work, layered Li2TiO3 (LTO) was synthesized using two different techniques, i.e., solid-state (ss-LTO) and hydrothermal (HT-LTO) methods to introduce varying concentrations of stacking faults. It was observed that HT-LTO synthesis method has a higher concentration of stacking faults, which results in slower elution of lithium from the precursor compared to ss-LTO. Interestingly, after complete lithium elution, both ss-H2TiO3 and HT-H2TiO3 ion sieves showed similar lithium adsorption properties. We also show that the lithium adsorption properties of layered H2TiO3 can be increased by oxygen annealing of the Li2TiO3 ion sieve precursor. Oxygen annealing improved the maximum lithium adsorption capacity by over 7% in a buffered solution (pH = 9.50) due to the increase in the relative amount of lattice oxygen and isolated surface hydroxyl groups. Spectroscopic studies (XPS, FTIR, and Raman) were used to further investigate and corroborate role of stacking faults and surface hydroxyl groups in the lithium adsorption/desorption process.

Octodecane-cellulose nanofiber flexible composites for latent heat storage

While phase change material (PCM)-encapsulated, emulsion-templated monolithic composites are promising for latent heat storage, they are usually rigid, which hinders their wide applications. Here, we report the fabrication of PCM (octodecane, OD)-encapsulated, emulsion-templated monolithic composites with wide-temperature-range flexibility for latent heat storage. The composites were prepared from OD-in-cellulose nanofiber (CNF) suspension emulsions through interfacial reaction and subsequent drying. Composites from freeze drying showed flexibility at temperature over the melting point of the encapsulated OD (30 °C), while composites from heat drying were flexible at temperatures even below the melting point of the encapsulated OD (such as at 20 °C). The wide-temperature-range flexibility could result from the reduced bonded OH groups within CNFs and the presence of voids with nanofibrous walls. The two types of the composites showed controllable external shapes, robust compression and good encapsulation, without fracture at a high compressive strain of 70% and without leakage at a compressive strain below 30%. Moreover, the composites possessed high reproducibility, extremely high heat capacity (up to 250 J.g−1, even slightly higher than that of bulk OD), high reusability and stability, without obvious deterioration in heat capacity after 100 heating–cooling cycles. The feature that combines wide-temperature-range flexibility, mechanical robustness, high heat capacity and good reusability/stability enabled the OD-encapsulated monolithic composites to be excellent candidates for latent heat storage.

The role of functional groups in the understanding of secondary organic aerosol formation mechanism from α-pinene

The infrared spectra (IR) analysis in combination with electrospray ionization high-resolution orbitrap mass spectra (ESI-HRMS) can provide new insight into the overall structural feature and specific molecules of secondary organic aerosol (SOA). In this study, the functional group signature of SOA produced from OH and O3 channel oxidation of α-pinene is characterized based on the IR and ESI-HRMS. The IR spectra of SOA from the OH channel show strong absorptions of hydrogen bonded OH groups and weak absorptions of CO groups, while the absorptions of CO are more abundant than OH in the O3 channel. A linear relationship between the ratio of functional group absorption area (SO−H/SC=O) and the group number ratio of nO−H/nC=O is obtained. The ratios of nO−H/nC=O in the O3 and H2O2 systems of SOA are estimated to be 0.60 and 3.91, respectively. The ESI-HRMS results show that organic acids are the major products in both the O3 and NO2 systems. In contrast to the O3 channel, alcohols are more abundant from the OH channel. The major compounds of SOA from the H2O2 system are confirmed to be formed by autoxidation of first generation RO2 radicals. The nO−H/nC=O ratio obtained by IR is in good agreement with that by MS. Thus, the ratio of nO−H/nC=O can be used to characterize SOA formation from different oxidation channels. In α-pinene-NO2 irradiations, the ratio of nO−H/nC=O is 0.83, which is quite close to that from the O3 system, but totally different from that in the H2O2 system. This strongly supports that the O3 channel plays a key role in the formation of SOA from the α-pinene-NO2 system. The similarity of both products and the nO−H/nC=O ratios between the α-pinene-O3 and α-pinene-NO2 systems strongly states that a stabilized Criegee intermediate (SCI) is a key factor controlling SOA formation.

Hidden Isolated OH at the Charged Hydrophobic Interface Revealed by Two-Dimensional Heterodyne-Detected VSFG Spectroscopy.

Water around hydrophobic groups mediates hydrophobic interactions that play key roles in many chemical and biological processes. Thus, the molecular-level elucidation of the properties of water in the vicinity of hydrophobic groups is important. We report on the structure and dynamics of water at two oppositely charged hydrophobic ion/water interfaces, that is, the tetraphenylborate-ion (TPB- )/water and tetraphenylarsonium-ion (TPA+ )/water interfaces, which are clarified by two-dimensional heterodyne-detected vibrational sum-frequency generation (2D HD-VSFG) spectroscopy. The obtained 2D HD-VSFG spectra of the anionic TPB- interface reveal the existence of distinct π-hydrogen bonded OH groups in addition to the usual hydrogen-bonded OH groups, which are hidden in the steady-state spectrum. In contrast, 2D HD-VSFG spectra of the cationic TPA+ interface only show the presence of usual hydrogen-bonded OH groups. The present study demonstrates that the sign of the interfacial charge governs the structure and dynamics of water molecules that face the hydrophobic region.

Hidden Isolated OH at the Charged Hydrophobic Interface Revealed by Two‐Dimensional Heterodyne‐Detected VSFG Spectroscopy

AbstractWater around hydrophobic groups mediates hydrophobic interactions that play key roles in many chemical and biological processes. Thus, the molecular‐level elucidation of the properties of water in the vicinity of hydrophobic groups is important. We report on the structure and dynamics of water at two oppositely charged hydrophobic ion/water interfaces, that is, the tetraphenylborate‐ion (TPB−)/water and tetraphenylarsonium‐ion (TPA+)/water interfaces, which are clarified by two‐dimensional heterodyne‐detected vibrational sum‐frequency generation (2D HD‐VSFG) spectroscopy. The obtained 2D HD‐VSFG spectra of the anionic TPB− interface reveal the existence of distinct π‐hydrogen bonded OH groups in addition to the usual hydrogen‐bonded OH groups, which are hidden in the steady‐state spectrum. In contrast, 2D HD‐VSFG spectra of the cationic TPA+ interface only show the presence of usual hydrogen‐bonded OH groups. The present study demonstrates that the sign of the interfacial charge governs the structure and dynamics of water molecules that face the hydrophobic region.

Theoretical modeling of the hydrated serotonin in solution: Insight into intermolecular hydrogen bonding dynamics and spectral shift in the electronic excited states

In this work, the intermolecular hydrogen bonding interaction in both the ground state and electronic excited states of the hydrogen bonded compounds Serotonin–(H2O)nn = 1,2 were investigated by the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) method. By monitoring the structures in different electronic states, it has been demonstrated that the hydrogen bonds in Serotonin–(H2O)nn = 1, 2 are strengthened upon excitation. And the hydrogen bond site of 5-OH of the ring is always strengthened, more significantly. The simulated infrared (IR) spectrum demonstrated that the red-shifts of the stretching vibration frequencies of hydrogen bonded OH groups were consistent with the change trend of hydrogen bonds. Furthermore, the interaction among the hydrogen bonds caused by the bridged-water structure should be considered while making analysis of the calculated results such as the structure information and the IR spectrum.

Modification of silicalite-1 with ammonium compounds aimed at preparation of acidic catalyst for acetalization of glycerol with acetone

Post-synthesis modification of silicalite-1 (MFI) with solutions of ammonium compounds (NH4F, NH4Cl, NH4NO3, NH4OH) without any additional alkaline agent followed by further thermal treatment appeared a new, facile, and cheap method to generate the acidic sites in starting material. The number and strength of resulting acid sites depend on the nature of anion in the applied ammonium salt. Used procedure resulted in partial removal of external silanol groups and in the formation of acidic internal isolated as well as hydrogen bonded OH groups (e.g. silanol nests). The novel acidic sites show a high catalytic activity for acetalization of glycerol with acetone and high selectivity towards 2,2-dimethyl-1,3-dioxolane-4-methanol (solketal). The modified silicalite-1 indicates also high stability with time on stream. The proposed reaction mechanism considers a combined contribution of both Lewis and very weak Brønsted acid sites.

Complex between Formic Acid and Nitrous Oxide: A Matrix-Isolation and Computational Study.

The complex of formic acid (FA, HCOOH) with nitrous oxide (N2O) was studied experimentally and computationally. Eight structures of the trans-FA···N2O complex and nine structures of the cis-FA···N2O complex were found at the density functional theory (M06-2X and wB97XD), MP2(full), and CCSD(T)-F12a levels. Two structures of the trans-FA···N2O complex (1t and 3t) and two structures of the cis-FA···N2O complex (1c and 3c) were identified by infrared spectroscopy in an argon matrix. Structure 1t with the bonded OH group appears in the matrices after deposition. Structures 3t and 3c with the free OH groups were prepared by vibrational excitation of the trans-FA conformer in structures 1t and 3t, respectively. Structure 3t is thermally unstable and relaxes to structure 1t at ∼15 K. Structure 1c with the bonded OH group is made by vibrational excitation of trans-FA monomer combined with thermal annealing. The lifetimes of the cis-FA···N2O complex structures 1c (81.5 min) and 3c (18.7 min) in an argon matrix at 4.3 K are longer than that of cis-FA monomer (6.3 min). This difference agrees with the calculated stabilization barriers of these species.

Aromatic Alcohols as Model Molecules for Studying Hydrogenolysis Reactions Promoted by Palladium Catalysts

The hydrogenolysis reaction of aromatic alcohols (benzyl alcohol, 1-phenylethanol and diphenylmethanol), promoted by supported palladium catalysts, such as Pd/TiO2, Pd/SiO2 and Pd/Co3O4, has been investigated at 0.1 MPa H2 and 323 K. The catalysts have been characterized by BET, TPR, XRD, TEM and XPS. A different kinetic behaviour was observed: in presence of Pd/TiO2 and Pd/SiO2 catalysts, prepared by impregnation, the hydrogenolysis activity follows the order benzyl alcohol > 1-phenylethanol ≥ diphenylmethanol, whereas it is totally reversed on Pd/Co3O4, prepared by co-precipitation. All results indicate that the reactivity of supported Pd catalysts, in the hydrogenolysis reaction, depends on the support nature, the preparation method of catalysts and the aromatic alcohols structure. Kinetic experiments carried out at different partial hydrogen pressure allow to elucidate the pathway of the C–OH bond scission, involving a radical substitution of the carbon bonded OH group by a hydrogen atom coming from the metal surface “via” associative and dissociative paths.

Further Search for Hydroxyl Nests in Acid Dealuminated Zeolite Y

The removal of Al with acid solution from a zeolite framework is customarily associated with formation of framework defects known as hydroxyl nests, but their existence has not been unambiguously confirmed thus far. In a recent study on acid dealuminated Y zeolite, pre-exchanged predominantly with Cs in order to ensure maximized elimination of molecular water that can conceal hydrogen bonded OH groups, no indication has been found for the presence of hydroxyl nests.9 We present here temperature-programmed desorption (TPD) and Fourier transform infra-red (FTIR) evidence that such hydroxyl nests cannot be identified in an approximately 20% acid dealuminated and solely sodium re-exchanged zeolite NaY(-Al) that has not been exposed to temperatures above 25 °C during and after dealumination. These experimental conclusions were matched by results of combined density functional theory (DFT)-based spectroscopic study and reactive-force field molecular dynamics calculations on full periodic model zeolites. They sh...

Sorption of Lead(II), Cadmium(II), and Copper(II) Ions from Aqueous Solutions Using Tea Waste

In the present study, the sorption ability of three metal ions, lead, cadmium, copper, from aqueous solution by tea waste was investigated. Sorption of the evaluated toxic metals by tea waste was pH-dependent, and kinetic data for three metal ions not only indicated a quick sorption process but also were excellently represented by the pseudo-second-order model with all correlation coefficients R2 > 0.97. In addition, the sorption processes of three metal ions by tea waste in different temperatures could be described satisfactorily by both Langmuir and Freundlich isotherms. According to calculated results by the Langmuir equation, the maximum removal capacities of Pb(II), Cd(II), and Cu(II) were 33.49, 16.87, and 21.02 mg/g, respectively. Fourier transform infrared (FT-IR) analysis of the tea waste samples laden with different metals indicated that multiple functional groups were involved in the sorption of metal ions, and the carboxyl group (C═O) and bonded–OH group were primary binding sites in lead and cadmium removal, while the −CN stretching and the carboxyl group were primary binding sites in copper removal. All the results reported strongly implied the potential of tea waste as an economic and excellent bioadsorbent for removal of metal ions from contaminated waters.

Cumene cracking over chromium oxide zirconia: Effect of chromium(VI) oxide precursors

Two types of ZrO2 supported with chromium nitrate (CN) and ammonium chromate (AC) for cumene catalytic cracking were studied. The physical properties of the catalysts were characterized with XRD, nitrogen physisorption, IR and TGA–SDTA. The acidic properties of the catalysts were determined by 2,6-lutidine and CO adsorbed IR spectroscopy. The XRD and nitrogen physisorption analyses confirmed higher tetragonal phase of ZrO2 and specific surface area for Cr2O3–ZrO2(AC) showing the ammonium chromate performed better interaction with Zr(OH)4 than chromium nitrate. Besides, some of the chromium nitrate did not interact with Zr(OH)4 and formed bulk crystalline Cr2O3 during the calcination. 2,6-lutidine and CO adsorbed IR spectroscopies distinguished that Cr2O3–ZrO2(CN) possessed a stronger Lewis acid sites, while Cr2O3–ZrO2(AC) possessed a stronger Brønsted acid sites. In situ IR spectroscopy demonstrated that Cr2O3–ZrO2(CN) showed better interaction with a molecular hydrogen than Cr2O3–ZrO2(AC) in the temperature range of 263–473K. In addition, the bulk crystalline Cr2O3 interacted with a molecular hydrogen to form hydrogen bonded OH groups. At 523K, the cumene hydrocracking indicated that the activity of Cr2O3–ZrO2(CN) was about 1.7-fold higher than that of Cr2O3–ZrO2(AC) with the main products of propylene and benzene. The high activity and stability of Cr2O3–ZrO2(CN) were due to the better interaction with hydrogen molecules which generating high number of active protonic acid sites during the reaction. The activity of Cr2O3–ZrO2(CN) is comparable with SO42−–ZrO2 in the temperature range of 323–573K.

Studies on damage of starches in irradiated wheat and white pepper using Rapid Visco-Analyser (RVA)

Effect of 60Co irradiation on wheat and white pepper grains were investigated in this study using Rapid Visco Analyser (RVA), near infrared reflectance spectroscopy and differential scanning calorimetry. Functional properties of wheat and white pepper were affected by irradiation indicated by a decrease in viscosity values. It was caused by changes of starch structure confirmed by the NIR spectra changes between wavelength 1560–1620 nm, which is the vibration of intermolecular hydrogen bonded OH groups in polysaccharides. The radiation used did not cause significant changes in the thermal properties. RVA proved to be useful for screening radiation induced changes in dry commodities of considerable large starch content on the basis of their rheological behaviour.

A theoretical investigation on the conformation and the interaction of CHF2OCF2CHF2 (desflurane II) with one water molecule

The conformation and the interaction of CHF₂OCF₂CHF₂ (desflurane II) with one water molecule is investigated theoretically using the ab initio MP2/aug-cc-pvdz and DFT-based M062X/6-311++G(d,p) methods. The calculations include the optimized geometries, the harmonic frequencies of relevant vibrational modes along with a natural bond orbital (NBO) analysis including the NBO charges, the hybridization of the C atom and the intra- and intermolecular hyperconjugation energies. In the two most stable conformers, the CH bond of the F2HCO- group occupies the gauche position. The hyperconjugation energies are about the same for both conformers and the conformational preference depends on the interaction between the non-bonded F and H atoms. The deprotonation enthalpies of the CH bonds are about the same for both conformers, the proton affinity of the less stable conformer being 3 kcal mol−1 higher. Both conformers of desflurane II interact with water forming cyclic complexes characterized by CH…O and OH…F hydrogen bonds. The binding energies are moderate, ranging from −2.4 to −3.2 kcal mol−1 at the MP2 level. The origin of the blue shifts of the ν(CH) vibrations is analyzed. In three of the complexes, the water molecule acts as an electron donor. Interestingly, in these cases a charge transfer is also directed to the non bonded OH group of the water molecule. This effect seems to be a property of polyfluorinated ethers.

Statics and Dynamics of Free and Hydrogen-Bonded OH Groups at the Air/Water Interface

We use classical atomistic molecular dynamics simulations of two water models (SPC/E and TIP4P/2005) to investigate the orientation and reorientation dynamics of two subpopulations of OH groups belonging to water molecules at the air/water interface at 300 K: those OH groups that donate a hydrogen bond (called "bonded") and those that do not (called "free"). Free interfacial OH groups reorient in two distinct regimes: a fast regime from 0 to 1 ps and a slow regime thereafter. Qualitatively similar behavior was reported by others for free OH groups near extended hydrophobic surfaces. In contrast, the net reorientation of bonded OH groups occurs at a rate similar to that of bulk water. This similarity in reorientation rate results from compensation of two effects: decreasing frequency of hydrogen-bond breaking/formation (i.e., hydrogen-bond exchange) and faster rotation of intact hydrogen bonds. Both changes result from the decrease in density at the air/water interface relative to the bulk. Interestingly, because of the presence of capillary waves, the slowdown of hydrogen-bond exchange is significantly smaller than that reported for water near extended hydrophobic surfaces, but it is almost identical to that reported for water near small hydrophobic solutes. In this sense water at the air/water interface has characteristics of water of hydration of both small and extended hydrophobic solutes.

Dehydration kinetics of nano-YSZ ceramics monitored by in-situ infrared spectroscopy

The room-temperature dehydration kinetics of dense nano-crystalline yttria-stabilised zirconia (n-YSZ) ceramics and single crystals (s-YSZ) exposed to liquid H2O has been studied by means of near-infrared (NIR) spectroscopy. Spectra obtained for both samples showed a combination band at 5200cm−1 that was attributed to the fundamental (ν2+ν3) vibration modes of H2O molecules. No evidence was found for the presence of structurally bonded OH groups in the samples. The loss of H2O from n-YSZ exposed to air was observed to be significantly slower than from s-YSZ. Identical loss kinetics were found for n-YSZ (and s-YSZ) samples exposed to liquid CH3OH. Considered together, the results suggest that H2O (and CH3OH) are adsorbed on internal surfaces (pores, microcracks) of n-YSZ.

Effects of substrate temperature on the ion conductivity of hydrated ZrO2 thin films prepared by reactive sputtering in H2O atmosphere

Hydrated ZrO2 thin films were prepared by reactive sputtering in H2O atmosphere at different substrate temperatures. The crystal structure, chemical bonding state, film density, refractive index, surface morphology and ion conductivity of the films were investigated. The intensity of the absorbance peaks due to hydrogen bonded OH groups increased and the film density decreased with decreasing substrate temperature. Correspondingly, the ion conductivity increased with decreasing substrate temperature and a maximum ion conductivity of 6×10−6S/m was obtained for the film deposited at the lowest substrate temperature of −30°C. We considered that the addition of H2O in the reactive gas and substrate cooling were very effective in increasing the H2O content and decreasing film density, which resulted in the high proton conductivity of the films.

Removal of Selenium by Adsorption onto Granular Activated Carbon (GAC) and Powdered Activated Carbon (PAC)

AbstractThe present work involves the study of Se(IV) adsorption onto granular activated carbon (GAC) and powdered activated carbon (PAC). The adsorbents are coated with ferric chloride solution for the effective removal of selenium. The physico‐chemical characterization of the adsorbents is carried out using standard methods, e. g., proximate analysis, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), thermo‐gravimetric (TGA) and differential thermal analysis (DTA), etc. The FTIR spectra of the GAC and PAC indicate the presence of various types of functional groups, e. g., free and hydrogen bonded OH groups, silanol groups (Si‐OH), alkenes, and CO group stretching from aldehydes and ketones on the surface of adsorbents. Batch experiments are carried out to determine the effect of various factors such as adsorbent dose (w), initial pH, contact time (t), and temperature (T) on the adsorption process. The optimum GAC and PAC dosage is found to be 10 g/L and 8 g/L, respectively, for Se(IV) removal with C0 = 100 mg/L. The percent removal of Se(IV) increases with increasing adsorbent concentration, while removal per unit weight of adsorbent increases with decreasing adsorbent concentration. Se(IV) adsorption onto both the GAC and PAC adsorbents is high at low pH values, and decreases with increased initial pH. The results obtained are analyzed by various kinetic models. The parameters of pseudo‐first order, pseudo‐second order kinetics, and Weber‐Morris intra particle kinetics are determined. It is seen that the sorption kinetics of Se(IV) onto GAC and PAC can be best represented by the pseudo‐second order kinetic model.

Solution mechanisms of silicate in aqueous fluid and H 2O in coexisting silicate melts determined in-situ at high pressure and high temperature

The structure of H 2O-saturated silicate melts, coexisting silicate-saturated aqueous solutions, and supercritical silicate liquids in the system Na 2O·4SiO 2–H 2O has been characterized with the sample at high temperature and pressure in a hydrothermal diamond anvil cell (HDAC). Structural information was obtained with confocal microRaman and with FTIR microscopy. Fluids and melts were examined along pressure-temperature trajectories defined by the isochores of H 2O at nominal densities, ρ fluid, (from EOS of pure H 2O) of 0.90 and 0.78 g/cm 3. With ρ fluid = 0.78 g/cm 3, water-saturated melt and silicate-saturated aqueous fluid coexist to the highest temperature (800 °C) and pressure (677 MPa), whereas with ρ fluid = 0.90 g/cm 3, a homogeneous single-phase liquid phase exists through the temperature and pressure range (25–800 °C, 0.1–1033 MPa). Less than 5 vol% quartz precipitates near 650 °C in both experimental series, thus driving Na/Si-ratios of melt + fluid phase assemblages to higher values than that of the Na 2O·4SiO 2 starting material. Molecular H 2O (H 2O°) and structurally bonded OH groups were observed in coexisting melts and fluids as well as in supercritical liquids. Their OH/(H 2O)-ratio is positively correlated with temperature. The OH/(H 2O)° in melts is greater than in coexisting fluids. Structural units of Q 3, Q 2, Q 1, and Q 0 type are observed in all phases under all conditions. An expression of the form, 12Q 3 + 13H 2O ⇋ 2Q 2 + 6Q 1 + 4Q 0, describes the equilibrium among those structural units. This equilibrium shifts to the right with increasing pressure and temperature with a ΔH of the reaction near 425 kJ/mol.

MoO 3 and Sb 2O 3 effects on bubble formation in silicate glass coatings during sintering

Small additions (0.25–0.5 mol%) of MoO 3 were effective in preventing bubble defects from forming in silicate glass powder coatings during sintering, without changing the glass transition temperature or molten viscosity. Surface tension was reduced to a similar linear degree as predicted by Kucuk's model, by approximately 20 mN/m per mol% MoO 3. MoO 3 increases the temperature where open porosity is sealed in the coating, allowing gas to escape before bubbles form. Sb 2O 3, a common fining agent used in industrial glass melts, does not significantly affect surface tension but produced higher bubble size and volume due to reduction above 1050 °C. Bonded OH groups in the glass frit were identified as a source of gas for bubble growth.