Sorption Of O2 Research Articles

Fine-tuning metal nodes accessibility of metal-organic frameworks for boosting net photocatalytic H2O2 production

Coordination unsaturated metal nodes in metal-organic frameworks (MOFs) work as photocatalytic active sites in H2O2 production, but over-exposed metal nodes also act as decomposing sites towards the photogenerated H2O2, resulting in low net yield. Herein, fine-tuning of metal nodes accessibility in MOFs was applied for boosting net photocatalytic H2O2 production. The accessibility of the nodes was fine-tuning through varying the feeding amount of benzoic acid (BA) during synthesis, treated MOFs with HCl, re-installed with variable BA, etc. The correlation between nodes accessibility and H2O2 production was systematically investigated, which demonstrates that the NH2-UiO-66-XBA with higher compensated BA possessing large steric effect at nodes would hinder the decomposition of photogenerated H2O2, thus promoting the net H2O2 yield. As a contrary, NH2-UiO-66-HCl without BA showed a distinctive decomposition rate of H2O2, resulting in a low net H2O2 production yield. The re-installed NH2-UiO-66-ReBA10 with compensated BA showed a recovered H2O2 production yield. A combination of O2 sorption isothermals, PL spectra, ESR spin-trap plots, and Koutecky-Levich plots disclosed that O2 was enriched by the framework and then reduced at the metal nodes mainly through two-electron pathway, especially for highly compensated MOFs. This strategy had been applied to other MOFs for boosting the H2O2 production like NU-1401 and PCN-222. This work reveals the fine-tuning of metal nodes accessibility in MOFs is an effective way for boosting H2O2 production.

Resonance and relaxation effects governing the sorption of O2 and CO2 in deionized water under dynamic conditions at 21 ± 1 °C

The behavior of water samples (deionized, deaerated and washed with He) was investigated in dynamics by physicochemical and electrochemical methods. The susceptibility of water samples to sorption of O2 and CO2 from air depends on their pretreatment. Sorption of O2 and CO2 accompanied by the desorption of dissolved helium is a multivariable nonlinear process, presumably, based on resonance and relaxation phenomena within the surface layer. Sorption of O2 and CO2 in water is considered as an interaction between gas molecules and ensembles of H2O molecules, which is assumed to be based on resonance effects. Sorption of gases leads to a, decrease in the surface tension at the water/gas interface. The effect is most pronounced in case of He-washed samples. The decrease in the surface energy upon CO2 absorption and the increase in the relaxation properties of the water surface are probably factors that facilitate sorption of gases, including O2. A fraction of sorbed O2 are contained in nanobubbles formed via water surface relaxation. A change in the viscosity of water samples during the sorption of gases may serve as a relaxation factor favorably affecting the formation and stability of nanobubbles in the surface layer and in bulk water. Irradiation of water with a laser light at λ = 633 nm can generate nano-cavities in the laser beam. In case of very low dissolved O2 concentrations, nanobubbles have no noticeable effect on the oxygen reduction reaction. Water samples washed with helium demonstrate a higher physical and chemical activity compared to other water samples, the activity being manifested in sorption properties. Electrochemical properties of water samples - deionized, deaerated and washed with He - are somewhat different. This is primarily due to the different content of dissolved O2 in the samples. Nonempirical simulations helped in clarifying the experimental data. The key factor that predetermines stability and/or collapse of nanobubbles is the organization of the hydrogen-bond network of water that strongly depends on the presence of water ions and foreign particles. In the case of both deionized water and water washed with He, HCO3-anion cannot participate in stabilization of nanobubbles. On the other hand, OH– anions can stabilize nanobubbles.

Selective sorption of oxygen and nitrous oxide by an electron donor-incorporated flexible coordination network

Incorporating strong electron donor functionality into flexible coordination networks is intriguing for sorption applications due to a built-in mechanism for electron-withdrawing guests. Here we report a 2D flexible porous coordination network, [Ni2(4,4′-bipyridine)(VTTF)2]n(1) (where H2VTTF = 2,2′-[1,2-bis(4-benzoic acid)-1,2ethanediylidene]bis-1,3-benzodithiole), which exhibits large structural deformation from the as-synthesized or open phase (1α) into the closed phase (1β) after guest removal, as demonstrated by X-ray and electron diffraction. Interestingly, upon exposure to electron-withdrawing species, 1β reversibly undergoes guest accommodation transitions; 1α⊃O2 (90 K) and 1α⊃N2O (185 K). Moreover, the 1β phase showed exclusive O2 sorption over other gases (N2, Ar, and CO) at 120 K. The phase transformations between the 1α and 1β phases under these gases were carefully investigated by in-situ X-ray diffraction, in-situ spectroscopic studies, and DFT calculations, validating that the unusual sorption was attributed to the combination of flexible frameworks and VTTF (electron-donor) that induces strong interactions with electron-withdrawing species.

Molecular dynamics simulation of polypropylene: diffusion and sorption of H2O, H2O2, H2, O2 and determination of the glass transition temperature

Molecular dynamics (MD) simulations in the canonical (NVT) and the isothermal-isobaric (NPT) ensemble using COMPASS III molecular force fields were performed to study the penetrant diffusion of water (H2O), hydrogen peroxide (H2O2) and oxygen (O2) in isotactic polypropylene (iPP) and hydrogen (H2) in iPP and atactic polypropylene (aPP) for time intervals up to 11 ns and in the case of H2O2 up to 22 ns. We found robust cluster formation in the case of H2O and H2O2. Further, the diffusion coefficients for all these systems were estimated by mean-square displacement analysis. Our results are consistent with previously published experimental and computational data except for the diffusion of H2 in polypropylene where our results are one and two orders of magnitude higher, respectively. Grand Canonical Monte Carlo (GCMC) simulations were used to determine the sorption loading and saturation concentration of H2O, O2 and H2 in iPP, where we find good agreement for H2O with experimental results. By means of MD simulation the glass transition temperature (Tg) of iPP was estimated to 273.66 ± 4.21 K which is consistent with previously published experimental results.

Gas barrier properties of polylactide/cellulose nanocrystals nanocomposites

The development of polylactide (PLA)/cellulose nanocrystals (CNC) nanocomposites in the aim to increase gas barrier properties has been widely studied, but gave rise to conflicting results. To better understand the underlying gas transport mechanisms, PLA/CNC nanocomposites were produced at concentrations between 5 and 50 wt%. The role of the PLA/CNC interface for the permeability was investigated using three different CNC surface grafts, namely lauric acid (slightly interacting with PLA), stearic acid (non-interacting with PLA), and poly glycidyl methacrylate bearing a reactive epoxy end-group (crosslinking with PLA). While PLA/CNC composites contained a large number of aggregates, homogenously dispersed nanocomposites were obtained with surface modified CNCs even at high concentration of CNC (up to 30 wt%). All nanocomposites had better O2 and CO2 barrier properties than PLA. Surprisingly, the nanocomposites prepared with surface grafted CNC did not perform better than the ones prepared with neat CNC. The diffusion coefficient was successfully modeled with Nielsen's law, showing the importance of the shape factor and resulting tortuosity for the barrier performance notwithstanding PLA/CNC surface compatibility. The analysis of the dual-mode O2 sorption isotherm showed the creation of a similar quantity of supplementary sorption sites in nanocomposites prepared with neat or lauric acid grafted CNC. PGMA grafts induced a higher number of sorption sites. The most important advantage of CNC surface grafts was the shielding of CNC against water vapor uptake. As a result, the O2 barrier properties could be maintained constant up to 90% relative humidity.

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Hybridized Fe/Ru-SiMWCNT-ionic liquid nanofluid for CO2 conversion into carbamate using superoxide ion

Suppressing the nucleophilic susceptibility of ionic liquids based nanofluid is necessary for energy storage and superoxide ion (O2•−) utilization. This study reports the development of novel pseudocapacitive Fe/Ru-SiMWCNT nanofluid comprising of Fe3O4, RuO2, SiO2, and MWCNT hybridized phases. The Fe/Ru-SiMWCNT nanohybrid possessed CO2 and O2 sorption capability, as confirmed from the temperature-programmed desorption experiments. Detailed spectroscopy techniques characterize the Fe/Ru-SiMWCNT nanohybrid component's physicochemical and morphological properties. The novel ionic liquid (IL) based nanofluid index is Fe/Ru-SiMWCNT/1-(2-methoxyethyl)-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate. Therefore, stable O2•− was generated therein at −0.445 V vs Ag/AgCl and recorded long-term stability for 2 days with 87.31 % efficiency. Moreover, the O2•− mediated CO2 conversion to C2O62− at −0.54 V vs Ag/AgCl with 97.90 % energy efficiency. Also, the normalized exchange current density in the nanofluid was 2.20 mA/cm2, which is higher than 1.94 mA/cm2 observed in the IL counterpart. The high normalized exchange current density is due to Fe/Ru-SiMWCNT nanohybrid phase's pseudocapacitance. Accordingly, this pseudocapacitive capability enables converting O2 and CO2 in the nanofluid with lower activation overpotential of −0.305 and −0.460 V vs Ag/AgCl, respectively. In contrast, the conversion of O2 and CO2 in the IL required higher activation overpotential of −0.826 and −1.013 V vs Ag/AgCl, respectively. The electrolysis of O2/CO2 in the nanofluid containing diethanolamine at −1.564 V vs Ag/AgCl, 60 °C and 1.0 h produced methyl 2-hydroxyethyl (methyl) carbamate as the primary product. The heteronuclear multiple bond correlation spectroscopy analysis finally elucidated the carbamate structure by two strong correlations between the protons and carbons in the vicinity of three and four bonds apart. Therefore, this study highlights the control design of electrochemically stable IL-based nanofluids robust for reactive oxygen species, energy storage and conversion.

Modeling of the adsorption and desorption mechanisms of H2O on Al (1 0 0)

Oxidation of Al (O2 or H2O) is an important chemical interaction in electrochemistry, heterogeneous catalysis and metal corrosion [1,2]. Investigations on chemisorption and sorption of O2 and H2O molecules are of great importance, as these are fundamental steps in the oxidation of Al.We studied the adsorption behavior of H2O and O2 on Al surfaces and estimated adsorption and diffusion of H on the Al surface. The main methods of research are theoretical calculations based on the theory of the functional of electronic density and the theory of pseudopotential. It has been shown that O and H atoms can be adsorbed on surface of Al (1 0 0), where adsorption takes place on three different initial adsorption sites (above the atom, between the atoms and the interatomic void), and their adsorption energy increases with an increasing O. The migration of the H atom is lighter on the surface than in the inner layer, and the H atom must be overcome by a higher energy barrier to pass from the surface to the subsurface layer.

CaCox Zr1-x O3-δ Perovskites as Oxygen-Selective Sorbents for Air Separation.

ABO3-δ perovskites are ideal for high-temperature thermochemical air separation for oxygen production because their oxygen nonstoichiometry δ can be varied in response to changes in temperature and oxygen partial pressure [ ]. Herein, the outstanding oxygen-sorption performance of CaCox Zr1-x O3-δ perovskites and their potential application as oxygen-selective sorbents for air separation is reported. In situ thermal X-ray diffraction was used to study the materials' structural changes in response to temperature variations in air and inert atmosphere. Temperature-programmed reduction was employed to elucidate the relationship between perovskite composition and redox property. O2 sorption performance was evaluated by isothermal analyses at various temperature and along with long-term absorption-desorption cycle tests. The high oxygen-sorption capacity was mainly attributed to Co at B-site, whereas partial substitution of Co by Zr enhanced the structural crystallinity and thermal stability of the perovskite. A stable oxygen production of 2.87 wt % was observed at 900 °C during 5 min-sorption cycles for 100 cycles.

Improving Physical Adsorption of CO2 by Ionic Liquids‐Loaded Mesoporous Silica

AbstractCO2 sorption capacities of the neat and silica‐supported 1‐butyl‐3‐methylimidazolium‐based ionic liquids (ILs) were measured under atmospheric pressure. The silica‐supported ILs were synthesized by the impregnation‐vaporization method and charactrized by N2 adsorption/desorption and thermogravimeteric analysis (TGA). Evaluation of the effects of influential factors on sorption capacity demonstrated that by increase of the temperature, flow rate, and the weight percentage of ILs in sorbents, the sorption capacity decreases. Among the sorbents, [Bmim][TfO] and SiO2‐[Bmim][BF4](50) had the highest capacity. By increasing the IL portion in SiO2‐[Bmim][BF4], the selectivity for CO2 to CH4 could be improved. The CO2‐rich sorbents could be easily recycled.

Selective O2 Sorption at Ambient Temperatures via Node Distortions in Sc-MIL-100

An open pored metal–organic framework (MOF) with oxygen selectivity at exceptionally high temperatures is confirmed by synthesis, sorption, and synchrotron structural analyses. The large-pore MIL-100 framework with access to the metal center (e.g., Sc and Fe) resulted in preferential O2 over N2 gas uptake at temperatures ranging from 77 K to ambient temperatures (258, 298, and 313 K). Most notably, Sc-MIL-100 shows exceptional O2 sorption; pair distribution function analyses indicate that this is due to distortions in the framework owing to the size of Sc atoms, in particular in the trimer metal cluster. Experimental studies also correlate very well with GCMC simulations, confirming more favorable O2-framework interactions at pressures up to 1 bar, due to the close proximity of O2 to the high density of metal centers in the small tetrahedral cages. Both materials maintain their crystallinity upon gas adsorption cycling, are regenerable, and show exceptional promise for use in energy efficient oxygen purif...

Reversible and Selective O2 Binding Using a New Thermoresponsive Cobalt(II)-Based Ionic Liquid

A new cobalt(II)-based metal-containing ionic liquid (MCIL), 1, has been prepared that reversibly and selectively absorbs O2 with an associated colorimetric change. This MCIL was impregnated into a porous PTFE polymer support, and the resulting supported membranes show higher O2 sorption over N2 with increasing loading levels of 1. The O2/N2 selectivity of these 1-impregnated membranes was determined to be as high as 26 ± 8 at 25 °C when ∼0.9 bar of feed gas pressure was applied. The absorbed O2 can be removed by moderate heating of the samples from 25 °C to 60 °C in vacuo. The high level of O2 sorption in these 1-impregnated membranes was maintained for at least five successive sorption/desorption cycles.

Gas transport properties of LiA type zeolite-filled poly(trimethylsilylpropyne) membranes

The influence of the inorganic filler LiA zeolite on the sorption and transport properties of mixed-matrix membranes based on poly(trimethylsilylpropyne) has been investigated. Isotherms of O2 and N2 sorption for the membranes containing up to 30 wt % (16.2 vol %) zeolite are described well in terms of the dual-mode sorption model. It has been found that the solubility of the gases increases with an increase in the filler fraction and nitrogen sorption is preferable in the pressure range of up to 3–5 atm. Gas permeability of the mixed-matrix membranes also increases with increasing filler loading (approximately by 20%) in comparison with the polymer matrix. Membranes selectivity is almost unaffected by zeolite addition. It has been shown that the formation of the mixed-matrix membranes is accompanied by an increase in volume (approximately by 13% at 30 wt % of zeolite loading). The main reason behind the enhancement of O2 and N2 permeability through the mixed-matrix poly(trimethylsilylpropyne)/LiA membranes is associated with an additional mass transfer through nanovoids localized around the filler particles.

BaxSr1−xO/MgO nano-composite sorbents for tuning the transition pressure of oxygen: Application to air separation

BaO is a proven oxygen-selective sorbent for air separation via the BaO–BaO2 oxygen sorption–desorption cycle. However, the low transition O2 pressure necessitates a high vacuum that is required for desorption, hence limiting its application. Here, we report facile synthesis of new oxygen-selective BaxSr1−xO/MgO nano-composite sorbents from which O2 can be desorbed at moderate vacuum pressures. These sorbents are obtained from BaxSr1−xMg(CO3)2 precursors synthesized by co-precipitation followed by calcination. It is shown that the transition O2 pressure for the oxide-peroxide cycle is significantly increased by increasing the Sr2+/Ba2+ ratio. XRD results show that the crystal structures are preserved while the lattice constants are reduced upon substitution of Ba2+ by Sr2+ in both precursor carbonates and peroxides. Transmission electron microscopy/energy dispersive X-ray spectroscopy results show that Ba2+ and Sr2+ are mixed molecularly in BaxSr1−xO/MgO nano-composite. We explain that the uniformly substituted Sr2+ in BaO/BaO2 changes the dissociation energy of peroxide ions and the equilibrium of the reversible reactions, promoting decomposition of BaO2. Cyclic O2 sorption and desorption with BaxSr1−xO/MgO nano-composite is demonstrated.

Molecular Simulation of Gas Transport in Hydrated Nafion Membranes: Influence of Aqueous Nanostructure

Molecular simulation was used to investigate the nanoporous structure of hydrated Nafion membrane and its impact on gas transport. The structural changes of Nafion induced by water uptakes were characterized in terms of the density and the pore size distribution. It was found that membrane hydration leads to a growth of separated water domains, which are gradually interconnected via newly formed water channels. The sorption and diffusion of H2 and O2 were studied at different temperatures and water contents of Nafion. Simulation results show that the water loading reduces gas solubilities as the adsorption site of gas molecules transforms from small cavities to large surfaces due to the enlargement of aqueous domains. However, such an opening of Nafion porous nanostructure effectively reduces gas diffusion barriers, and results in a 2-fold increase of O2 diffusivities. Molecular configurations of gases inside Nafion nanoporous frameworks were examined on the basis of calculated radial distribution functions.

A novel multiscale method for the prediction of the volumetric and gas solubility behavior of high-Tg polyimides

A multiscale method for the evaluation of the fluid solubility in glassy polymers with high glass transition temperature Tg is presented and applied to the case of two polyimides, Ultem and Kapton. The method adopts Molecular Dynamics (MD) to simulate the polymer pressure–volume–temperature (pVT) behavior at temperatures above Tg not experimentally accessible. Such values are used to obtain the polymer parameters for the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) Equation of State (EoS) required to calculate the gas solubility in the polymers below Tg with the Non Equilibrium PC-SAFT model. The MD-simulated polymer density values agree with the experimental and simulated data available, and the solubility calculated with the Non Equilibrium model represents correctly the experimental values for CH4, N2, O2 and CO2 sorption in Ultem, and the CO2 and SO2 solubility in Kapton at different temperatures. The approach can be applied to other high-Tg glassy polymers.

Preparation and C3H8/Gas Separation Properties of a Synthesized Single Layer PDMS Membrane

In this paper, a new polydimethylsiloxane (PDMS) membrane was synthesized and its ability for separation of heavier gases from lighter ones was examined. Sorption, diffusion, and permeation of H2, N2, O2, CH4, CO2, and C3H8 in the synthesized membrane were investigated as a function of pressure at 35°C. PDMS was confirmed to be more permeable to more condensable gases such as C3H8. This result was attributed to very high solubility of larger gas molecules in hydrocarbon−based PDMS in spite of their low diffusion coefficients relative to small molecules. The synthesized membrane showed much better gas permeation performance than others reported in the literature. Increasing upstream pressure increased solubility, permeability and diffusion coefficients of C3H8, while these values decreased slightly or stayed constant for other gases. Local effective diffusion coefficient of C3H8 and CO2 increased with increasing penetrant concentration which indicated plasticization effect of these gases over the range of penetrant concentration studied. C3H8/gas solubility, diffusivity and overall selectivities also increased with increasing feed pressure. Ideal selectivity values of 4, 13, 18, 20, and 36 for C3H8 over CO2, CH4, H2, O2, and N2, respectively, at upstream pressure of 7 atm, confirmed the outstanding separation performance of the synthesized mebrane.

Sorption of Methane, Nitrogen, Oxygen, and Argon in ZSM-5 with different SiO2/Al2O3 Ratios: Grand Canonical Monte Carlo Simulation and Volumetric Measurements

Sorption of CH4, N2, O2, and Ar in ZSM-5 with different SiO2/Al2O3 ratios was studied by volumetric measurements and grand canonical Monte Carlo simulation. Sorption capacity for all the gases studied was observed to decrease with an increase in the SiO2/Al2O3 ratio of ZSM-5. The sorption selectivity of CH4 over N2 increases, whereas sorption selectivities of N2 over O2 and Ar decrease with an increase in the SiO2/Al2O3 ratio of ZSM-5. ZSM-5 with SiO2/Al2O3 of 900 showed higher selectivity for CH4 over N2, whereas the SiO2/Al2O3 ratio of 25 showed higher N2 selectivity over O2 and Ar. The heats of adsorption for CH4 and N2 decrease and that for O2 and Ar remain unaffected with an increase in SiO2/Al2O3 ratio of ZSM-5. The values of Henry’s constant were also calculated for CH4, N2, O2, and Ar for adsorption in ZSM-5 having varied SiO2/Al2O3 ratio. The experimental results were compared with theoretically calculated data using grand canonical Monte Carlo (GCMC) simulation. Simulation studies expectedly showed the proximity of N2 molecules to the sites occupied by extraframework sodium cations.

Oxygen isotope evidence for sorption of molecular oxygen to pyrite surface sites and incorporation into sulfate in oxidation experiments

Abstract Experiments were conducted to investigate (i) the rate of O-isotope exchange between SO4 and water molecules at low pH and surface temperatures typical for conditions of acid mine drainage (AMD) and (ii) the O- and S-isotope composition of sulfates produced by pyrite oxidation under closed and open conditions (limited and free access of atmospheric O2) to identify the O source/s in sulfide oxidation (water or atmospheric molecular O2) and to better understand the pyrite oxidation pathway. An O-isotope exchange between SO4 and water was observed over a pH range of 0–2 only at 50 °C, whereas no exchange occurred at lower temperatures over a period of 8 a. The calculated half-time of the exchange rate for 50 °C (pH = 0 and 1) is in good agreement with former experimental data for higher and lower temperatures and excludes the possibility of isotope exchange for typical AMD conditions (T ⩽ 25 °C, pH ⩾ 3) for decades. Pyrite oxidation experiments revealed two dependencies of the O-isotope composition of dissolved sulfates: O-isotope values decreased with longer duration of experiments and increasing grain size of pyrite. Both changes are interpreted as evidence for chemisorption of molecular O2 to pyrite surface sites. The sorption of molecular O2 is important at initial oxidation stages and more abundant in finer grained pyrite fractions and leads to its incorporation in the produced SO4. The calculated bulk contribution of atmospheric O2 in the dissolved SO4 reached up to 50% during initial oxidation stages (first 5 days, pH 2, fine-grained pyrite fraction) and decreased to less than 20% after about 100 days. Based on the direct incorporation of molecular O2 in the early-formed sulfates, chemisorption and electron transfer of molecular O2 on S sites of the pyrite surface are proposed, in addition to chemisorption on Fe sites. After about 10 days, the O of all newly-formed sulfates originates only from water, indicating direct interaction of hydroxyls from water with S at the anodic S pyrite surface site. Then, the role of molecular O2 is as proposed in previous studies: acting as electron acceptor only at the cathodic Fe pyrite surface site for oxidation of Fe(II) to Fe(III).

The effect of temperature and humidity on the oxygen sorption in Diels–Alder polyphenylenes

The gas transport properties of post-sulfonated Diels–Alder polyphenylene (SDAPP) membranes were measured and compared to poly(perfluoro sulfonic acid) (Nafion 112). The SDAPP materials had ion exchange capacities of 1.6 and 2.2mequiv/g. The O2 gas permeability in the SDAPP 2.2 was about half that observed in Nafion@ 112. The O2 sorption in each membrane was measured in both the non-humidified and humidified state. In the non-humidified state, the O2 sorption followed Henry's Law behavior. The enthalpy of sorption for the SDAPP materials in the dry state was about double that measured for Nafion@ 112. In the presence of moisture, the O2 sorption followed Type IV behavior typically exhibited by hydrophilic polymers. The SDAPP samples had a higher percent wet-O2 mass uptake compared to Nafion@ 112, because of a higher ion exchange capacity.