N2 Gas Molecules Research Articles

Simulation of O2/N2 behaviors on multi-component polymeric membranes in oxy-fuel combustion system

As a viable way to separate O2 from air, multi-component polymeric membranes exhibit excellent O2/N2 separation capability and can be considered as a potential alternative to an air separation unit (ASU) for oxy-fuel combustion. In this study, the microscopic diffusion and separation behaviors of O2 and N2 gas molecules on the blending azo-bridged porous organic polymers (AZOPOP) and poly(phthalazinone ether sulfone ketone) (PPESK) membranes were simulated and calculated using Universal Force Field (UFF) and Perdew-Burke-Ernzerhof exchange-correlation functional (PBE) for the first time. The results showed that the mean square displacement (MSD) versus simulation time is linear, and the curve at higher temperatures exhibits more fluctuation. The adsorption energy for N2 and O2 on the polymeric membrane was first calculated, and their appreciable disparity (Ead,N2 = −0.247 eV, Ead,O2 = −0.569 eV) proves that O2 is prone to being adsorbed by the AZOPOP/PPESK composite membrane This phenomenon signifies that O2 molecules have more opportunities to transverse the abundant pores in the membrane, which can be attributed to the existence of the nitrogen-phobic azo functional groups. Furthermore, reaction temperature shows a negative correction with the diffusion selectivity (αD): α323K (1.05) < α298K (1.06) < α273K (1.07).

Butadiyne-linked porphyrin nanoring as a highly selective O2 gas sensor: A fast response hybrid sensor

The butadiyne-linked six-metalloporphyrin nanoring (Mg6-P6) and it's complex with a hexapyridyl template, Mg6-P6·T6 have a great potential for employment in future nanoelectronic applications such as a nanosensor for small gas molecules.The goal of this study is to scrutinize and improvement of the CO, N2, and O2 gas sensing capacity of Mg6-P6 and Mg6-P6·T6 using DFT calculations at CAM-B3LYP/6-31G (d,p) level of theory.The geometrical structures, binding energies, band gaps, the density of states (DOS), adsorption energies, HOMO and LUMO energies, Fermi level energies (EFL), NBO, FMO and TD-DFT spectrum were calculated to predict gas adsorption properties of Mg6-P6 and Mg6-P6·T6 systems. Based on the calculated adsorption energies and remarkable decrease in the Eg, it is expected that the Mg6-P6 and Mg6-P6·T6 are sensitive to O2 molecule. Surprisingly, the Mg6-P6-O2 and specially the Mg6-P6.T6-O2 record promising values of recovery times for different attempt frequencies. Therefore, the results open a way for the development of a new and selective O2 nanosensor in the presence of CO and N2 gas molecules.

Magnetic properties of FePc sheet modified by the adsorption of gas molecules

A first-principles study is performed to explore the magnetic properties of the H2, H2O, O2, CO and N2 gas molecules adsorbed on the FePc sheet. The pure FePc sheet has the magnetic moment of 2.00 μB per unit cell. The H2 and H2O molecules can keep the magnetic moment of 2.00 μB. For the O2, CO and N2 molecules, the magnetic moments become 0 μB. The O2 molecule and the Fe atom can form an antiferromagnetic coupling, leading to the zero pure magnetic moment. While for the CO and N2 molecules, the strong interaction can push the z2 orbital to higher level and the low spin configuration will cancel the spin magnetic moments. When the Ag (111) surface as the substrate is considered, the strong interaction can stable the magnetic moments. While for the NaCl/Ag(100) and NaCl substrates, due to the weak interaction, the magnetism can be controlled more easily.

Harnessing Greenhouse Gases Absorption by Doped Fullerenes with Externally Oriented Electric Field.

In this work, a theoretical investigation of the effects caused by the doping of C20 with silicon (Si) atom as well as the adsorption of CO, CO2 and N2 gases to C20 and C19Si fullerenes was carried out. In concordance with previous studies, it was found that the choice of the doping site can control the structural, electronic, and energetic characteristics of the C19Si system. The ability of C20 and C19Si to adsorb CO, CO2 and N2 gas molecules was evaluated. In order to modulate the process of adsorption of these chemical species to C19Si, an externally oriented electric field was included in the theoretical calculations. It was observed that C19Si is highly selective with respect to CO adsorption. Upon the increase of the electric field intensity the adsorption energy was magnified correspondingly and that the interaction between CO and C19Si changes in nature from a physical adsorption to a partial covalent character interaction.

Transition metal-decorated germanene for NO, N2 and O2 sensing: A DFT study

Detecting hazardous and toxic gasses is important to avoid harmful effects on human health and two-dimensional nanostructures have emerged as candidate materials for sensing or scavenging gasses. The chemical interactions between NO, O2, and N2 gas molecules and Cu-, Ag-, and Au-decorated germanene were investigated by using density functional theory simulations, and the potential applications as gas sensors or scavengers were addressed. Except for O2, the studied molecules were physisorbed on pristine germanene, where the most favorable adsorption site is located at the middle of the lattice hexagon, with adsorption energy values ranging from 0.09 eV for the N2 to 0.49 eV for NO adsorbed through the N atom. The results also show that the studied molecules have larger adsorption energies in Cu-, Ag-, and Au-decorated germanene, with energy values of 0.4 eV for the N2 molecule and 1.04 eV for the NO molecule. Therefore, molecule-metal-germanene complexes are more energetically favorable than the molecule-germanene ones and are thus predicted to have an enhanced sensing capability. The larger NO adsorption energies on Ag- (0.8 eV) and Au- (0.87 eV) decorated germanene, in comparison with those of N2 (around 0.1 eV) and O2 (around 0.37 eV), indicate their good selectivity towards NO. To estimate their potential application as NO sensors in gas-insulated switchgear, we calculated the work function and desorption time of the studied molecules adsorbed on Cu-, Ag-, and Au-decorated germanene, obtaining considerable changes in the work function (around 0.5 eV) between the different molecules adsorbed on Cu-decorated germanene, and recovery times of the order of seconds at a temperature of 400 K. The results suggest that metal-germanene complexes are stable in ambient conditions and they are good candidates for sensing and scavenging nitrogen monoxide.

Nitrogen Rejection from Methane via a "Trapdoor" K-ZSM-25 Zeolite.

Nitrogen (N2) rejection from methane (CH4) is the most challenging step in natural gas processing because of the close similarity of their physical-chemical properties. For decades, efforts to find a functioning material that can selectively discriminate N2 had little outcome. Here, we report a molecular trapdoor zeolite K-ZSM-25 that has the largest unit cell among all zeolites, with the ability to capture N2 in favor of CH4 with a selectivity as high as 34. This zeolite was found to show a temperature-regulated gas adsorption wherein gas molecules' accessibility to the internal pores of the crystal is determined by the effect of the gas-cation interaction on the thermal oscillation of the "door-keeping" cation. N2 and CH4 molecules were differentiated by different admission-trigger temperatures. A mild working temperature range of 240-300 K was determined wherein N2 gas molecules were able to access the internal pores of K-ZSM-25 while CH4 was rejected. As confirmed by experimental, molecular dynamic, and ab initio density functional theory studies, the outstanding N2/CH4 selectivity is achieved within a specific temperature range where the thermal oscillation of door-blocking K+ provides enough space only for the relatively smaller molecule (N2) to diffuse into and through the zeolite supercages. Such temperature-regulated adsorption of the K-ZSM-25 trapdoor zeolite opens up a new approach for rejecting N2 from CH4 in the gas industry without deploying energy-intensive cryogenic distillation around 100 K.

A theoretical study of the global and local electrophilicity, nucleophilicity, polarizability and QTAIM theory for calix[4]arene-gas interaction

The calix[4]arene molecule, abbreviated as CX[4], is known by the four phenolic groups and a hydrophobic cavity able to enclose small molecules. The interactions between CX[4] and NO3, NO2, CO2, and N2 gas molecules have been studied. These guest species are placed inside and outside the cavity of the host molecule CX[4]. The formation of H-bonding has been deeply discussed based on the infrared spectrum and the polarizability analysis. Global and local indices have been calculated for a series of gas (NO3, NO2, CO2 and N2) in interaction with the CX[4] molecule to explain the electrophilic or nucleophilic activations in endo-vs. exo-cavity interaction zone. As expected, there is a correlation between the proposed global electrophilicity and global nucleophilicity together for an explanation of the chemo-selectivity region. Finally, the topological parameter analyses of the host-guests interactions have been estimated by using DFT calculations.

Effect of Nafion and APTEOS functionalization on mixed gas separation of PEBA-FAU membranes: Experimental study and MD and GCMC simulations

Many of the mixed matrix membranes (MMMs) face the challenge of fillers agglomeration. In this paper, the gas separation performance of MMMs based on poly (ether-block-amide) (PEBA, 60 wt% PEO and 40 wt% PA6) filled with different functionalized zeolite faujasite (FAU, X-type) fillers was investigated. To improve the interfacial adherence of the fillers with PEBA chains, Nafion® and 3-aminopropyl triethoxysilane (APTEOS) were used as sulfonic acid and aminosilane functionalizing agents, respectively. Different physicochemical and morphological characterizations such as XRD, FTIR, SEM, AFM, thermal, and mechanical tests were used to characterize the prepared membranes. The prepared membranes were evaluated for single gas and mixed gas separation performances. The results showed that CO2 permeability reached to 110 and 122 Barrer for sulfonic acid- and amine-FAU (1 wt%) filled PEBA, respectively. In addition, amine-MMM (1 wt%) had better performance for CO2/N2 selectivity (117), while SO3-MMM (1 wt%) showed higher CO2/CH4 selectivity (31) due to their intrinsic properties. Molecular simulation was also carried out to study the structural and transport properties of the fabricated membranes. The solubility and diffusivity of CO2, CH4, and N2 gas molecules were studied by Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods, respectively. The acquired results revealed that experimental and simulation data were consistent in approach.

1s-1s electron transfer in collisions of fast C and O ions with adenine

1s-1s electron transfer and K-shell ionization cross sections of adenine (C5H5N5) molecule have been measured in collisions with C and O ions in the energy range of 2.5–5.3 MeV/u. These cross sections have been measured from the study of KLL Auger electron yields as a function of projectile charge state. The K-ionization cross section data have been compared with the ECUSAR calculations [ECPSSR model with the perturbed stationary state (PSS) effect calculated in a united and separated atom (USA) approximation]. The K-ionization data shows a good agreement with the model whereas the K-K transfer cross section is underestimated by the same model. Energy dependence of the K-K transfer cross section for adenine is found to be flat compared to that for N2 gas molecules. The values of the K-K e− transfer and the K-ionization cross sections are found to be comparable in this energy range.

Dynamics of prompt electrons, ions, and neutrals of nanosecond laser ablation of tungsten investigated using optical emission

A Nd:YAG laser with a power density of 15 GW/cm2, operating at a wavelength of 1064 nm, was used to ablate a tungsten (W) target placed in an ambient atmosphere of air at a pressure of 10 mbar. A systematic study of plasma properties employing fast photography and time and space resolved optical emission spectroscopy was carried out. The results showed that there were continuum, neutral, and singly ionized W atom optical emission in the laser-induced plasma; the spectra of ambient gas N2 and N2+ were aslo observed which appeared at very early times (&amp;lt;30 ns). The spectra of N2+ presented a temporal profile with a narrow width (∼20 ns) and a steep rising edge (∼10 ns) that was very close to the laser pulse duration, which revealed that the prompt electrons ejected from the W target collisionally excited and ionized ambient N2 gas molecules. The approximate timescales from nanoseconds to microseconds of four laser-produced W plasma processes including prompt electrons, continuum radiation, ions, and neutral emission were given according to time-resolved optical emission spectroscopy. Fast imaging showed that the prompt electrons were expanding hemispherically. The optical time of flight dynamics of N2+ corresponding to the prompt electrons at different positions showed that the kinetic energy of prompt electrons was up to 22 eV. These prompt electrons with high energy result in the separation from the core plasma which indicated the existence of the transient dynamic plasma sheath during the laser ablation process and interpreted the acceleration of ions.

Infrared spectroscopy and density functional calculations on titanium-dinitrogen complexes

Titanium-nitrogen complexes were generated by laser ablated titanium (Ti) atoms and N2 gas molecules in this study. These complexes were isolated on the pre-deposited solid Ar matrix on the pre-cooled KBr window (T ∼ 5.4 K), allowing infrared spectra to be measured. Laser ablation experiments with 15N2 isotope provided distinct isotopic shifts in the infrared spectra that strongly implicated the formation of titanium-nitrogen complexes, Ti(NN)x. Density functional theory (DFT) calculations were employed to investigate the molecular structures, electronic ground state, relative energies, and IR frequencies of the anticipated Ti(NN)x complexes. Based on laser ablation experiments and DFT calculations, we were able to assign multiple Ti(NN)x (x = 1–6) species. Particularly, Ti(NN)5 and Ti(NN)6, which have high nitrogen content, may serve as good precursors in preparing polynitrogens.

Free energy barriers for CO2and N2in zeolite NaKA: an ab initio molecular dynamics approach

Ab initio Molecular Dynamics (AIMD) is used with spatial constraints to estimate the free energy barriers of diffusion for CO2 and N2 gas molecules in zeolite NaA and KA. We investigate the extent to which the diffusion of these gas molecules is hindered, in the two separate cases of a smaller Na(+) ion or a larger K(+) ion blocking the 8-ring pore window. In contrast to classical Molecular Dynamics, AIMD performs these computations accurately and unbiased in the absence of empirical parameterization. Our work has resulted in stable and reliable force profiles. The profiles show that the larger K(+) ion effectively blocks the passage of both CO2 and N2 molecules while the smaller Na(+) ion will allow both molecules to pass. These results are a quantitative demonstration of the concept of pore blocking where we compute the effect, which the size of the respective cation occupying the pore window has on diffusive properties of each gas molecule. Hence, this effect can be altered through ion exchange to fine-tune the functionality of a specific zeolite as a molecular sieve.

Directing the Structural Features of N2‐Phobic Nanoporous Covalent Organic Polymers for CO2 Capture and Separation

A family of azo-bridged covalent organic polymers (azo-COPs) was synthesized through a catalyst-free direct coupling of aromatic nitro and amine compounds under basic conditions. The azo-COPs formed 3D nanoporous networks and exhibited surface areas up to 729.6 m(2) g(-1) , with a CO2 -uptake capacity as high as 2.55 mmol g(-1) at 273 K and 1 bar. Azo-COPs showed remarkable CO2 /N2 selectivities (95.6-165.2) at 298 K and 1 bar. Unlike any other porous material, CO2 /N2 selectivities of azo-COPs increase with rising temperature. It was found that azo-COPs show less than expected affinity towards N2 gas, thus making the framework "N2 -phobic", in relative terms. Our theoretical simulations indicate that the origin of this unusual behavior is associated with the larger entropic loss of N2 gas molecules upon their interaction with azo-groups. The effect of fused aromatic rings on the CO2 /N2 selectivity in azo-COPs is also demonstrated. Increasing the π-surface area resulted in an increase in the CO2 -philic nature of the framework, thus allowing us to reach a CO2 /N2 selectivity value of 307.7 at 323 K and 1 bar, which is the highest value reported to date. Hence, it is possible to combine the concepts of "CO2 -philicity" and "N2 -phobicity" for efficient CO2 capture and separation. Isosteric heats of CO2 adsorption for azo-COPs range from 24.8-32.1 kJ mol(-1) at ambient pressure. Azo-COPs are stable up to 350 °C in air and boiling water for a week. A promising cis/trans isomerization of azo-COPs for switchable porosity is also demonstrated, making way for a gated CO2 uptake.

Monte Carlo simulation of the static properties of Hg solution in (O2, N2) gassed water

Canonical Monte Carlo (CMC) simulations were carried out to investigate the influence of O2 and N2 gases on elemental mercury (Hg) solution in water. Particle–particle interactions were all modeled using Lennard–Jones potential function. To provide insight into the interaction of O2 and N2 gases with Hg atom in water, two independent mixtures Hg/(O2,H2O) and Hg/(N2,H2O) with the same bulk mole fraction of component (0.9956, 0.0023, 0.0023, 0.0021 for H2O, O2, N2 and Hg, respectively) were simulated at T=298K.The results show that Hg in water interacts favorably with O2 more than with N2. This is consistent with the hypothesis that stronger interaction of O2 gas with the mercury atom leads to a higher adsorption and lower dynamic structure compared with N2 gas. Independent simulation of Hg/(O2,H2O) and Hg/(N2,H2O) mixtures indicates that N2 gas molecules stay off the distance at which O2 interacts with Hg as the nearest neighboring distance. This procedure enables us to describe the structural properties of Hg⋯O2 and Hg⋯N2 in water at molecular scale which hints exploring techniques of the toxicity level of mercury contaminated water. Alternatively, comparison of potential of mean force indicated that Hg⋯O2 interaction exposes the free energy of −2.93kJmol−1 which is more stable pair interaction relative to Hg⋯H2O (−2.50kJmol−1) and Hg⋯N2 (−1.79kJmol−1).

Titanium nitride coatings to inner wall of narrow tube

Titanium nitride (TiN) shows considerable hydrogen impermeability and is expected as a hydrogen-impermeable coating of cladding tubes for metal hydride fission fuel. The TiN coating production by the plasma process is very complicated because the cladding tube is not wide enough to create stable plasma. In this study, a simple reactive evaporation process was employed for the coating process of TiN films on the inner wall of a narrow tube. The films were thermally deposited on stainless steel sheets as the substrate and were coiled around the inner wall of silica glass tubes. A Ti wire twisted with a Mo filament was used for the evaporant. As a result, thin films with gold color were obtained. From the XRD measurement of the films, distinct diffraction patterns of TiN phase were observed. A reactivity of N2 gas molecules with Ti atoms in Ti-N film formation was measured quantitatively. The reaction probability of N2 molecules rN2 is defined as the ratio of the N2 absorption rate AN2 on Ti to the rate of N2 impingement ZN2. Reactive evaporation process showed 013 . 0 2 ≅ N r . It was 1/5

Titanium nitride coatings to inner wall of narrow tube

Titanium nitride TiN has considerable hydrogen impermeability and is expected as a prevention coating of hydrogen gas parmiation for a cladding tube of metal hydride fission fuel. The TiN coating produced with plasma process is very complicated because the cladding tube is not wide enough to create stable plasma. A simple reactive evaporation process was selected for coationg process of TiN films to inner wall of narrow tube or stainless steal tube. The films were thermally deposited on stainless steel sheets coiled around inner wall of silica glass tubes. Nitrogen as a reactive gas was introduced into the vacuum chamber with pressure range of 5.0×10-2 Pa ∼ 3.0×10-1 Pa. Thin films with gold color were obtained. From XRD measurement of films, distinct diffraction patterns of TiN phase were observed. A reactivity of N2 gas molecules with Ti atoms in Ti-N film formation has measured quantitatively. The reaction probability of N2 molecules rN2 is defined as the ratio of the absorbing rate of N2 on Ti surface AN2 to the rate of N2 impingement ZN2. Reactive evaporation process exhibits the highest N2 reaction probability rN2 ≅ 0.05. It was the similar value of rN2 with Ti film prepared by ARE plasma processes.

Characterization and catalytic activity of cobalt containing MCM-41 prepared by direct hydrothermal, grafting and immobilization methods

Cobalt containing hexagonal mesoporous molecular sieves (MCM-41) were prepared by different methods viz., direct hydrothermal synthesis, grafting and immobilization. The calcined material was characterized by various spectroscopic tools such as powder X-ray diffraction (XRD), N2 adsorption–desorption isotherms, Fourier transformed infra-red (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV–vis and X-ray photoelectron spectroscopy (XPS). The XRD patterns show the highly intense (100) reflection peak in the range 2–3° (2θ angle), characteristic of mesoporous material. Higher order reflection peaks suggest highly ordered mesoporous structure. N2 adsorption–desorption isotherms are of type IV according to IUPAC classification and the steep rise in the isotherms in the narrow range 3.5–4.5 of relative pressure (P/P0) is due to the condensation of N2 gas molecules in the pores (characteristic of mesoporous structure). In FT-IR increase in the intensity of band at 960cm−1 with the increase of the cobalt content in Co-MCM-41 samples indicate the incorporation of cobalt ions in the framework of MCM-41. SEM and TEM reveal spherical morphology for the cobalt substituted MCM-41. UV–vis spectra demonstrate the characteristic features of framework and extraframework cobalt in MCM-41. Cobalt is in +2 oxidation state as evidenced from UV–vis and XPS. The catalysts were tested for the side chain oxidation of ethylbenzene using 70wt.% tert-butyl hydrogen peroxide as an oxidant with and without the use of solvent. Solvents have effect in the catalytic activity and selectivity. In the absence of solvent, substituted cobalt [Co-MCM-41 (50)] in the framework of MCM-41 gives maximum ethylbenzene conversion while higher selectivity to acetophenone was achieved over immobilized cobalt on the MCM-41. Leaching data shows, immobilized cobalt catalyst is well hetrogenized.

Studies of the plume emission during the femtosecond and nanosecond ablation of graphite in nitrogen

Comparative studies of the pulsed laser ablation of graphite in 20mTorr of N2 using both 15ns and 450fs pulses at a wavelength of 248nm are reported. Emissions from the resulting ablation plumes, and from collisions with ablated material and the background N2 gas molecules, have been investigated by wavelength-, space-, and time-resolved optical emission spectroscopy (OES), and the observations correlated with the results of the analyses of films formed when such material is incident on a silicon substrate. Wavelength-dispersed spectra of the plume arising in nanosecond ablation reveal CI, CII, and C2 emissions—concentrated close to the target—and, at greater distances, strong CN and weak N2+ emissions. N2+(B–X) emission dominates in the case of femtosecond ablation. Time-gated imaging studies have allowed estimation of propagation velocities for these various emissions. Possible production routes for secondary emitters such as CN and N2+ are discussed, and arguments presented to show that measurements of the apparent propagation “velocities” of such emissions are unlikely to provide meaningful measures of the velocities (or energies) with which these carriers impact on a substrate surface. Laser Raman spectroscopy confirms nitrogen incorporation within the films grown by both nanosecond and femtosecond ablations; the former films are deduced to be both thicker and to have higher N content—findings that accord with the OES analyses.

Development of the molecular design rules of ultra-permeable poly[1-(trimethylsilyl)-1-propyne] membranes

Poly[1-(trimethylsilyl)-1-propyne] (PTMSP) is known to have the highest permeability coefficients for glassy polymers. However, unlike other glassy membranes such as polycarbonates or polysulfones, the high permeability of PTMSP decays as a function of time. A series of measurements of the gas permeability coefficients were reported in this work to highlight the effect of the physical ageing on the permeability of N2 gas molecules through PTMSP membranes. In order to develop the molecular design rules for this high permeability, and the molecular structural parameters mostly responsible for the physical ageing, molecular dynamics techniques were used to investigate the effect of the presence of the double bond, the Si-atom, the bulky trimethylsilyl side group, the co-operative effect of the singular methyl and the trimethylsilyl side groups on the diffusion coefficients of nitrogen and argon through the polymer. It was shown that a combination of a high volume fraction, high torsion barriers around the single bonds in the main backbone and high specific electrostatic interactions due to the presence of the Si-atom are all necessary for high diffusion coefficients of gases through PTMSP membranes. This combination was also shown to provide the necessary voids for the diffusion process as well as for characterising the polymer with low cohesive energy densities and extra rigidity resulting in an exceptionally high permeability. Loss in free-volume due to the physical ageing may thus lead to lower permeability coefficients.

Reactivity of nitride thin films deposited by ion-plating process

The reactivity of N2 gas molecules with Ti atoms (neutral and/or ion) in TiN film formation has been measured quantitatively. Increasing the fraction of Ti ions in all the evaporeted Ti from 2.7×10-3 to 0.26 enhances the N2 reaction probability up to 102 times and facilitates the formation of stoichiometric TiN.