N2 Uptake Research Articles

The dynamics of adsorption and dissociation of N2 in a monolayer of iron on W(110).

We study the adsorption dynamics of N2 on an expanded monolayer of Fe grown pseudomorphically on W(110). To this aim we have performed molecular dynamics simulations in a six-dimensional potential energy surface calculated within density functional theory. Our results show that N2 dissociation on this surface is a highly activated process with an energy barrier of around 1.25 eV. Regarding molecular adsorption, we find that the energetically most favorable adsorption well corresponds to a parallel orientation of the molecule with an adsorption energy of around 520 meV. However, at low molecular energies and surface temperatures, the molecules preferentially adsorb vertically to the surface with an adsorption energy of around 480 meV. A comparative analysis with the results previously obtained on a clean Fe(110) surface shows that while surface strain favors molecular adsorption of N2 in this system, it impedes dissociative adsorption. The former is consistent with the experimental observations showing that the inertness of Fe(110) towards N2 uptake is reduced in the strained surface. The latter leads us to suggest that the experimental observation of dissociated atomic N in the strained surface when increasing surface temperature must be related to the presence of step/defects at the surface.

Equilibrium Adsorption Studies of CO2, CH4, and N2 on Amine Functionalized Polystyrene

Adsorption of CO2, CH4, and N2 has been investigated using amine functionalized polymeric resins having diethanolamine, imidazole, dimethylamine, and N-methyl piperazine covalently attached to the styrene-divinyl benzene copolymer (PS) matrix. The equilibrium adsorption of CO2, CH4, and N2 was examined on these functionalized polymers at pressures from atmospheric to 40 atm for CO2 and N2 while up to 10 atm for CH4 at 303 K. PS-Imidazole showed the highest adsorption capacity for CO2 as compared to other functionalized polymers. No significant uptake of CH4 and N2 was observed at low pressures by any of the functionalized polymers. The adsorption isotherms were analyzed using dual mode sorption model and Ideal Adsorbed Solution Theory (IAST).

K+ exchanged zeolite ZK-4 as a highly selective sorbent for CO2.

Adsorbents with high capacity and selectivity for adsorption of CO2 are currently being investigated for applications in adsorption-driven separation of CO2 from flue gas. An adsorbent with a particularly high CO2-over-N2 selectivity and high capacity was tested here. Zeolite ZK-4 (Si:Al ∼ 1.3:1), which had the same structure as zeolite A (LTA), showed a high CO2 capacity of 4.85 mmol/g (273 K, 101 kPa) in its Na(+) form. When approximately 26 at. % of the extraframework cations were exchanged for K(+) (NaK-ZK-4), the material still adsorbed a large amount of CO2 (4.35 mmol/g, 273 K, 101 kPa), but the N2 uptake became negligible (<0.03 mmol/g, 273 K, 101 kPa). The majority of the CO2 was physisorbed on zeolite ZK-4 as quantified by consecutive volumetric adsorption measurements. The rate of physisorption of CO2 was fast, even for the highly selective sample. The molecular details of the sorption of CO2 were revealed as well. Computer modeling (Monte Carlo, molecular dynamics simulations, and quantum chemical calculations) allowed us to partly predict the behavior of fully K(+) exchanged zeolite K-ZK-4 upon adsorption of CO2 and N2 for Si:Al ratios up to 4:1. Zeolite K-ZK-4 with Si:Al ratios below 2.5:1 restricted the diffusion of CO2 and N2 across the cages. These simulations could not probe the delicate details of the molecular sieving of CO2 over N2. Still, this study indicates that zeolites NaK-ZK-4 and K-ZK-4 could be appealing adsorbents with high CO2 uptake (∼4 mmol/g, 101 kPa, 273 K) and a kinetically enhanced CO2-over-N2 selectivity.

Sorption comparison of two indium–organic framework isomers with syn–anti configurations

Two indium–organic framework isomers, namely [Me2NH2][In(BPDC)2] (InOF-3) and [MeNH3][In(BPDC)2] (InOF-4), have been solvothermally prepared from a biphenyl-3,3′-dicarboxylate ligand (H2BPDC) with changeable conformation, and feature skeletal frameworks with equivalent chemical formulae. For the 2D close-packing InOF-3, each 3-connected [In(O2CR)4] node connects to 3 others through syn-BPDC2− ligands, leading to a 3-connected uninodal layer with a point symbol of {63}. For the 3D microporous InOF-4, the framework is assembled from [In(O2CR)4] nodes bridged by dicarboxylate ligands in the anti- fashion. Careful examination of the structure shows that InOF-4 is a 4-fold interpenetrating network and topologically adopts a diamond-like 4-connected uninodal net with a point symbol of {66}. More importantly, the theoretical calculations and the experimental single component gas uptake measurements reveal that the 3D porous InOF-4 has a better low pressure gas storage capacity than its 2D framework isomer InOF-3, with a saturated N2 uptake of 168.2 cm3 g−1 at 77 K and H2 uptake capacities of up to 126.5 cm3 g−1 (1.13 wt%) at 77 K and 1.0 bar, and 98.1 cm3 g−1 (0.88 wt%) at 87 K and 1.0 bar. Finally, the IAST calculations show us that both microporous materials have an outstanding low-pressure selectivity between CO2 and N2, probably due to their intrinsic structural characteristics.

Interpenetration Control, Sorption Behavior, and Framework Flexibility in Zn(II) Metal–Organic Frameworks

Three Zn(II) frameworks [Zn(H2L)(bdc)]·1.4DEF·0.6H2O (1; H2L = 1,4-di(1H-imidazol-4-yl)benzene, H2bdc = terephthalic acid), [Zn(H2L)(bdc)]·1.5DMF·1.2H2O (2), and [Zn(H2L)(L)0.5(bdc)0.5]·formamide·H2O (3) were prepared under the solvothermal conditions in DEF/H2O, DMF/H2O, and formamide/H2O solvent pairs, respectively. All compounds are commonly based on the adamantanoid three-dimensional networks that are mutually entangled to form a 3-fold (1) to 4-fold (2) to 5-fold interpenetrating dia structure (3). The solvent pairs used in the reactions are primarily responsible for the variation of such interpenetration degree. It is noted that the reaction time, temperature, and reactant ratio applied in the present system (2) did not lead to the interpenetration change. The activated sample (1a) shows the gas uptake of N2, H2, and CO2, characteristic of permanent porosity in the flexible framework, while the gases of N2 and H2 are not adsorbed on 2 and 3. The porous compound (1) also exhibits the reversible inclu...

Cyclic adsorption/thermal regeneration of activated carbons

In this work, the cyclic thermal regeneration of activated carbons saturated with p-Nitrophenol was analyzed with two complementary views: the examination of the process itself and the porosity modifications found in the adsorbents.The process, which was followed by TG/DTG/TDA analysis, showed that the regeneration process is highly dependent on the number of uses of the carbon. As it is reused, it becomes more and more resistant towards the heat treatment.Regarding the porosity, the fresh adsorbent (Vmi=0.42cm3g−1), underwent a significant porosity decrease after saturation (Vmi=0.04cm3g−1), mainly due to micropore blockage. The subsequent regeneration succeeded to render around 70% of the adsorbent N2 uptake. However, further uses of the carbon resulted in a progressive decay of the adsorbent capacity, with a marked porosity widening. These features were further investigated by means of Scanning Electron Microscopy and Infrared Spectroscopy.

A highly porous three-dimensional aluminum phosphonate with hexagonal channels: synthesis, structure and adsorption properties

A 3D porous aluminum(III) trisphosphonate, constructed from 1D inorganic aluminum phosphate chains and tripodal organic linkers, contains large hexagonal channels (1.24 nm in diameter) and a highly accessible void (50.3%) which allow it to have a fast and relatively high uptake of H2, N2 and CO2.

H2, N2, and CH4 Gas Adsorption in Zeolitic Imidazolate Framework-95 and -100: Ab Initio Based Grand Canonical Monte Carlo Simulations

A multiscale approach based on ab initio and grand canonical Monte Carlo (GCMC) simulations is used to report the H2, N2, and CH4 uptake behaviors of two zeolitic imidazolate frameworks (ZIFs), ZIF-95 and -100, with exceptionally large and complex colossal cages. The force fields describing the weak interactions between the gas molecules and ZIFs in GCMC simulations are based on ab initio MP2 level of theory aimed at accurately describing the London dispersions. We report the total and excess gas uptakes up to 100 bar at 77 and 300 K. Our results unravel the interplay between the uptake amount, pore volume, guest molecule size, temperature, chlorine functional group, and isosteric heat of adsorption in ZIFs. We found that while the uptake capacity of ZIF-100 outperforms ZIF-95 for small molecules (H2), ZIF-95 offers a superior adsorption capacity for large molecules (CH4). Moderately sized molecules (N2) exhibit a more complex uptake behavior depending on the temperature. Furthermore, we show that the ind...

Spatial distribution of nitrogen fixation in methane seep sediment and the role of the ANME archaea

Nitrogen (N2) fixation was investigated at Mound 12, Costa Rica, to determine its spatial distribution and biogeochemical controls in deep-sea methane seep sediment. Using (15)N2 tracer experiments and isotope ratio mass spectrometry analysis, we observed that seep N2 fixation is methane-dependent, and that N2 fixation rates peak in a narrow sediment depth horizon corresponding to increased abundance of aggregates of anaerobic methanotrophic archaea (ANME-2) and sulfate-reducing bacteria (SRB). Using fluorescence in situ hybridization coupled to nanoscale secondary ion mass spectrometry (FISH-NanoSIMS), we directly measured (15)N2 uptake by ANME-2/SRB aggregates (n = 26) and observed maximum (15)N incorporation within ANME-2-dominated areas of the aggregates, consistent with previous analyses. NanoSIMS analysis of single cells (n = 34) from the same microcosm experiment revealed no (15)N2 uptake. Together, these observations suggest that ANME-2, and possibly physically associated SRB, mediate the majority of new nitrogen production within the seep ecosystem. ANME-2 diazotrophy was observed while in association with members of two distinct orders of SRB: Desulfobacteraceae and Desulfobulbaceae. The rate of N2 fixation per unit volume biomass was independent of the identity of the associated SRB, aggregate size and morphology. Our results show that the distribution of seep N2 fixation is heterogeneous, laterally and with depth in the sediment, and is likely influenced by chemical gradients affecting the abundance and activity of ANME-2/SRB aggregates.

Atomic Property Weighted Radial Distribution Functions Descriptors of Metal–Organic Frameworks for the Prediction of Gas Uptake Capacity

Metal–organic frameworks (MOFs) are porous materials with exceptional host–guest properties with huge potential for gas separation. The combinatorial design of MOFs demands the in silico screening of the nearly infinite combinations of structural building blocks using efficient computational tools. We report here a novel atomic property weighted radial distribution function (AP-RDF) descriptor tailored for large-scale Quantitative Structure–Property Relationship (QSPR) predictions of gas adsorption of MOFs. A total of ∼58,000 hypothetical MOF structures were used to calibrate correlation models of the methane, N2, and CO2 uptake capacities from grand-canonical Monte Carlo (GCMC) simulations. The principal component analysis (PCA) transform of the AP-RDF descriptors exhibited good discrimination of MOF inorganic SBUs, geometrical properties, and more surprisingly gas uptake capacities. While the simulated uptake capacities correlated poorly to the void fraction, surface area, and pore size, the newly intro...

Design and Preparation of a Core–Shell Metal–Organic Framework for Selective CO2 Capture

The design of a core-shell metal-organic framework comprising a porous bio-MOF-11/14 mixed core and a less porous bio-MOF-14 shell is reported. The growth of the MOF shell was directly observed and supported by SEM and PXRD. The resulting core-shell material exhibits 30% higher CO2 uptake than bio-MOF-14 and low N2 uptake in comparison to the core. When the core-shell architecture is destroyed by fracturing the crystallites via grinding, the amount of N2 adsorbed doubles but the CO2 adsorption capacity remains the same. Finally, the more water stable bio-MOF-14 shell serves to prevent degradation of the water-sensitive core in aqueous environments, as evidenced by SEM and PXRD.

Two new entangled coordination polymers constructed by flexible coligands: Synthesis, magnetism, and gas absorption

Two isostructural metal–organic polymers, namely {[M(bce)(bib)]·solv}n (M=Co(II) and solv=CH3OH·H2O for 1; M=Ni(II) and solv=0.5CH3OH·0·25H2O for 2) (H2bce=1,2-bis(4-carboxy-phenoxy)ethane and bib=2,3-bis(4-pyridyl)butane), have been synthesized and characterized. The structures of the two compounds show 2D→2D parallel interpenetrated frameworks with polyrotaxane and polycatenane character. The magnetic behaviors of 1 and 2 indicate antiferromagnetic interactions within paddle-wheel units. Furthermore, the compound 1 exhibits relative high N2 uptake adsorption capacity.

Solvent-Induced Structural Dynamics in Noninterpenetrating Porous Coordination Polymeric Networks

Three novel soft porous coordination polymer (PCP) or metal-organic framework (MOF) compounds have been synthesized with a new rigid ligand N-(4-pyridyl)-1,4,5,8-naphathalenetetracarboxymonoimide (PNMI) by partial hydrolysis of N,N'-di-(4-pyridyl)-1,4,5,8-naphthalenete-tracarboxydiimide (DPNI) during solvothermal reactions with Zn(II), Cd(II), and Mn(II) salts, and they are [Zn(PNMI)]·2DMA (1·2DMA, 1a), [Cd(PNMI)]·0.5DMA·5H2O (2·0.5DMA·5H2O), and [Mn(PNMI)]·0.75DMF (3·0.75DMF). The structure of 1 is based on paddle-wheel secondary building unit (SBU) with a 3,6-connected rtl net topology, whereas 2 and 3 are isotypical but the M(O2C-C)2 fragments aggregate in one-dimension and the overall connectivity is the same rtl net topology. All these three MOFs have one-dimensional rhombic channels filled with guest molecules. The guest molecules in 1a can be exchanged with EtOH in a single-crystal to single-crystal (SCSC) manner to 1·1.25EtOH·0.375H2O (1b). Further, the guest molecules in 1b can be replaced with ethylene glycol, triethylene glycol and allyl alcohol without destroying its single crystal nature. These guest exchanges are accompanied by reduction in volume of the unit cell up to 16%, as well as the void volume up to 33.1%. Similarly, triethylene glycol (TEGly) selectively exchanges EtOH in a mixture of the above solvents, which might be the result of correct fit of the hydrogen-bonded TEGly dimer in the channel of 1. While activated 1 and 3 exhibit no uptake of N2 and H2 at 1 bar and 77 K and very low uptake of CO2 gas at 1 bar and 196 K, activated 2 shows selective CO2 uptake, 278 cm(2)·g(-1), over N2 and H2 at 1 bar and 196 K, which corresponds to 5.87 molecules of CO2 per formula unit of 2.

Fuel characterization and co-pyrolysis kinetics of biomass and fossil fuels

It is not well understood how co-feeding of coal and biomass influences the reaction kinetics of gasification and pyrolysis. Co-pyrolysis of biomass and fossil fuels is investigated in this paper. After fuel characterization, the influences of temperature on the physical and chemical properties of char produced from biomass and non-biomass fuels were investigated, and the kinetics of atmospheric-pressure pyrolysis in a nitrogen environment were determined. The results show that product physical properties, such as surface area, depend on the pyrolysis temperature. For individual fuels, pine sawdust char prepared at 750°C had the highest CO2 and N2 uptake, while switchgrass had very low N2 uptake, but high CO2 uptake. The surface area of the fluid coke decreased with increasing temperature, but was almost constant for coal. Co-pyrolysis in a thermogravimetric analyzer exhibited three stages. Devolatilization of the biomass and coal portions of blended samples occurred independently, i.e. without significant synergy. The Coats–Redfern method was used to analyze the kinetics of solid fuel pyrolysis, indicating that it can be described by multi-step reactions. The model was able to identify likely reaction mechanisms and activation energies of each pyrolysis stage, giving predictions consistent with the experimental results.

Body fat does not affect venous bubble formation after air dives of moderate severity: theory and experiment

For over a century, studies on body fat (BF) in decompression sickness and venous gas embolism of divers have been inconsistent. A major problem is that age, BF, and maximal oxygen consumption (Vo2max) show high multicollinearity. Using the Bühlmann model with eight parallel compartments, preceded by a blood compartment in series, nitrogen tensions and loads were calculated with a 40 min/3.1 bar (absolute) profile. Compared with Haldanian models, the new model showed a substantial delay in N2 uptake and (especially) release. One hour after surfacing, an increase of 14-28% in BF resulted in a whole body increase of the N2 load of 51%, but in only 15% in the blood compartment. This would result in an increase in the bubble grade of only 0.01 Kisman-Masurel (KM) units at the scale near KM = I-. This outcome was tested indirectly by a dry dive simulation (air breathing) with 53 male divers with a small range in age and Vo2max to suppress multicollinearity. BF was determined with the four-skinfold method. Precordial Doppler bubble grades determined at 40, 80, 120, and 160 min after surfacing were used to calculate the Kisman Integrated Severity Score and were also transformed to the logarithm of the number of bubbles/cm(2) (logB). The highest of the four scores yielded logB = -1.78, equivalent to KM = I-. All statistical outcomes of partial correlations with BF were nonsignificant. These results support the model outcomes. Although this and our previous study suggest that BF does not influence venous gas embolism (Schellart NAM, van Rees Vellinga TP, van Dijk FH, Sterk W. Aviat Space Environ Med 83: 951-957, 2012), more studies with different profiles under various conditions are needed to establish whether BF remains (together with age and Vo2max) a basic physical characteristic or will become less important for the medical examination and for risk assessment.

Potential Trace Metal Co-Limitation Controls on N2 Fixation and [Formula: see text] Uptake in Lakes with Varying Trophic Status.

The response of N2 fixation and uptake to environmental conditions and nutrient enrichment experiments in three western U.S. lake systems was studied (eutrophic Clear Lake; mesotrophic Walker Lake; oligotrophic Lake Tahoe). We tested the effect of additions of bioactive trace metals molybdenum as Mo(V) and iron (Fe) as well as phosphate (P), N2 fixation, , carbon (C) fixation, chlorophyll a (Chla), and bacterial cell counts under both natural conditions and in mesocosm experiments. We found distinct background N2 fixation and uptake rates: highest at Clear Lake (N2 fixation: 44.7 ± 1.8 nmol N L−1 h−1), intermediate at Walker Lake (N2 fixation: 1.7 ± 1.1 nmol N L−1 h−1; uptake: 113 ± 37 nmol N L−1 h−1), and lowest at Lake Tahoe (N2 fixation: 0.1 ± 0.07 nmol N L−1 h−1; uptake: 37.2 ± 10.0 nmol N L−1 h−1). N2 fixation was stimulated above control values with the addition of Fe and Pin Clear Lake (up to 50 and 63%, respectively); with Mo(V), Fe, and P in Walker Lake (up to 121, 990, and 85%, respectively); and with Mo(V) and P in Lake Tahoe (up to 475 and 21%, respectively). uptake showed the highest stimulation in Lake Tahoe during September 2010, with the addition of P and Mo(V) (∼84% for both). High responses to Mo(V) additions were also observed at some sites for C fixation (Lake Tahoe: 141%), Chla (Walker Lake: 54% and Clear Lake: 102%), and bacterial cell counts (Lake Tahoe: 61%). Overall our results suggest that co-limitation of nutrients is probably a common feature in lakes, and that some trace metals may play a crucial role in limiting N2 fixation and uptake activity, though primarily in non-eutrophic lakes.

Solvent-modified dynamic porosity in chiral 3D kagome frameworks

Dynamically porous metal-organic frameworks (MOFs) with a chiral quartz-based structure have been synthesized from the multidentate ligand 2,2'-dihydroxybiphenyl-4,4'-dicarboxylate (H2diol). Compounds [Ni(II)(H2diol)(S)2]·xS (where S = DMF or DEF) show marked changes in 77 K N2 uptake between partially desolvated [Ni(II)(H2diol)(S)2] (only the pore solvent is removed) and fully desolvated [Ni(II)(H2diol)] forms. Furthermore, [Ni(II)(H2diol)(DMF)2] displays additional solvent-dependent porosity through the rotation of DMF molecules attached to the axial coordination sites of the Ni(II) centre. A unique feature of the four coordinate Ni(II) centre in [Ni(II)(H2diol)] is the dynamic response to its chemical environment. Exposure of [Ni(II)(H2diol)] to H2O and MeOH vapour leads to coordination of both axial sites of the Ni centres and to the generation of a solvated framework, whereas exposure to EtOH, DMF, acetone, and MeCN does not lead to any change in metal coordination or structure metrics. MeOH vapour adsorption was able to be tracked by time-dependent magnetometry as the solvated and desolvated structures have different magnetic moments. Solvated and desolvated forms of the MOF show remarkable differences in their thermal expansivities; [Ni(II)(H2diol)(DMF)2]·DMF displays marked positive thermal expansion (PTE) in the c-axis, yet near to zero thermal expansion, between 90 and 450 K, is observed for [Ni(II)(H2diol)]. These new MOF architectures demonstrate a dynamic structural and colourimetric response to selected adsorbates via a unique mechanism that involves a reversible change in the coordination environment of the metal centre. These coordination changes are mediated throughout the MOF by rotational mobility about the biaryl bond of the ligand.

CO2 adsorption on zeolite X/activated carbon composites

Two series of zeolite X/activated carbon composites with different ratios of zeolite and activated carbon were prepared through a combination process of CO2 activation of the mixtures of elutrilithe and pitch and subsequent hydrothermal crystallization in alkaline solution. An additional surface modification was achieved in diluted NH4Cl solution. CO2 and N2 uptakes on the composites before and after modification were determined for pressures up to 101 kPa at 273 and 298 K, respectively. Langmuir-Freundlich and Toth adsorption models were used to describe the adsorption isotherms of CO2 and the corresponding heats of adsorption were estimated with the Clausius-Clapeyron equation. Both before and after modification, all composites exhibited a remarkable preferential adsorption of CO2 compared to N2, with the modified composites showing a higher adsorption selectivity to CO2 over N2 than the unmodified composites. With an increasing ratio of zeolite in the composites, adsorption capacity and adsorption heat of CO2 on the composites increased simultaneously. Lower adsorption heat was observed both before and after modification especially at the low-loading region and when there was less energetic heterogeneity on the surface of the modified composites. The results may be attributed to the elimination of strong basic sites on the modified composites, which is favorable for desorption of CO2 on the adsorbents and application in pressure swing adsorption processes.

Accurate Computation of Gas Uptake in Microporous Organic Molecular Crystals

Microporous organic molecular crystals (MOMCs) are materials composed of discrete organic molecules interacting noncovalently. The gas uptake of CO2, CH4, N2, and Xe in one of the most widely investigated MOMCs, trispiro(benzodioxole[2′.2:2″.4:2‴.6]1,3,5,2,4,6-triazatriphosphinine) (1), was computed by grand canonical Monte Carlo (GCMC) simulations based on our lately developed force field method vdW3, which is fitted to accurate ab initio potentials (double hybrid functional B2PLYP with a D3 dispersion correction using def2-TZVPP basis sets). The B2PLYP-D3 results compare very well with CCSD(T)/CBS interaction energies for benzene–gas model complexes. Our multiscale modeling approach to accurate interaction potentials is found to be essential in order to obtain reasonable adsorption isotherms and heats of adsorption. The good agreement between the simulation results and experimental data in all cases gives us the opportunity to design novel complex materials for gas adsorption based solely on first-princ...

Influence of process conditions on chemical composition and electronic properties of AlN thin films prepared by ArF reactive pulsed laser deposition

AbstractAluminium nitride (AlN) thin films were deposited using a reactive ArF excimer pulsed laser ablation (PLD) of a pure Al target in a N2 plasma atmosphere, generated by a RF source, onto p‐Si &lt;100&gt; substrates, at increasing substrate temperatures. A radio‐frequency (13.56 MHz RF) apparatus was introduced with the specific aim of increasing the fraction of excited and/or ionized nitrogen species and, ultimately, to increase its reactivity toward the aluminum atoms, expanding in the plume, and the formation of AlN. We studied the dependence and correlation of structural, compositional and electric properties with the specific experimental conditions. The chemical composition of films, determined by XPS spectroscopy, revealed a trend of increased N2 reactivity, uptake and nitride formation, with deposition temperature. Electrical resistivity, measured by the four‐point‐probe method, has been found to be also strongly dependent on the substrate temperature and nitrogen incorporation. A possible explanation of the correlation of surface conductivity with chemical composition is suggested and discussed. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)