Small Gas Molecules Research Articles

Promoting gas hydrate formation with ice-nucleating additives for hydrate-based applications

Gas hydrates are crystalline icy compounds capturing small gas molecules in the cavities made of hydrogen-bonded water molecules. Hydrates can store a large amount of gas and selectively capture certain gas species depending on thermodynamic conditions and formation pathways. In addition, any impurities that are not stabilized in hydrates are excluded upon hydrate formation. Such interesting properties have allowed the proposal of a variety of hydrate-based applications, including energy storage, CO2 capture, gas separation, and desalination. However, they are not yet utilized as viable technologies, mainly because of the low process efficiency. The major challenges here are to improve the formation kinetics and to enable hydrates to be properly managed in industrial processes. Here, inspired by the similarities in crystallization processes of ice and gas hydrates, we identified the capabilities of two ice-nucleating additives, Icemax® (protein) and Drift® (surfactant), as kinetic promoters for hydrate-based applications. Our experimental results demonstrate that both additives increase the formation kinetics of CH4 (structure I) and CH4/C2H6 (structure II) hydrates under high and low shear. Drift® enlarges the interfacial area at the gas-liquid interface, enhancing the mass transfer, and thus increases the hydrate conversion 18 times under non-stirred cases. Icemax® can better accelerate the initiation of hydrate formation by providing additional nuclei for heterogeneous nucleation. According to visual observations, both additives form porous and soft hydrates, which can be easily handled in industrial scale processes. Major findings confirm the potential of ice-nucleating additives to facilitate hydrate-based applications by improving the production rate and process efficiency.

Magnetite nanoparticles coat around activated γ-alumina spheres: A case of novel protection of moisture-sensitive materials against hydration

Protection of various materials against hydration is of continuing interest to chemists and material scientists. We report on stabilization of porous surface of activated γ-alumina spheres (AAS) against hydration by an adhesive coat of nano-magnetite particles. The nano-Fe3O4-coated AAS were prepared in the ultrasound-agitated suspension of magnetite nanoparticles in heptane and were characterized by using X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area analysis and X-ray photoelectron spectroscopy (XPS). It is deduced that nanoparticle-alumina bonding interaction in non-polar organic solvent is enhanced by van der Waals attractive forces and that sonication induces changes in alumina morphology only in regions of contact between alumina and magnetite nanoparticles. The coated AAS submerged in still water avoid hydration and remain permeable by small gaseous (N2) molecules, while those soaked in moving water lose part of their coat and undergo hydration. The pristine and the coated AAS were briefly compared for their ability to degrade model antibiotics by using LC-MS analysis. It is confirmed that the degradation of trimethoprim is more efficient on the coated AAS. Our results are challenging for further research of Coulombic interactions between nano-particles and appropriate solid supports.

Enhanced activity and sulfur resistance for soot combustion on three-dimensionally ordered macroporous-mesoporous MnxCe1-xOδ/SiO2 catalysts

A series of MnxCe1-xOδ/3DOM-m SiO2 catalysts with different Mn0.5Ce0.5Oδ loadings and different x values were designed and successfully prepared by a very simple method. The as-prepared catalysts, which contain three-dimensionally ordered macroporous (3DOM) structure embedded with ordered mesoporous structure, exhibit high catalytic activity and good stability for soot combustion. The good catalytic performances of as-prepared catalysts are owing to facilitated soot transport through the macroporous structure and synergistic effect between Mn and Ce for the activation of gas molecules (NO and O2) within the mesoporous structure. In addition, the sulfur and water tolerance of as-prepared catalysts were tested and the reasons for sulfur and water tolerance also well illustrated. The probable soot combustion mechanisms are proposed based on the characterization results and DFT calculation. More importantly, this work demonstrates the rational design and facile preparation of highly efficient catalysts for reactions between large solid particles and small gas molecules.

Salt- and gas-filled ices under planetary conditions.

In recent years, evidence has emerged that solid water can contain substantial amounts of guest species, such as small gas molecules-in gas hydrate structures-or ions-in salty ice structures-and that these 'filled' ice structures can be stable under pressures of tens of Gigapascals and temperatures of hundreds of Kelvins. The inclusion of guest species can strongly modify the density, vibrational, diffusive and conductivity properties of ice under high pressure, and promote novel exotic properties. In this review, we discuss our experimental findings and molecular dynamics simulation results on the structures formed by salt- and gas-filled ices, their unusual properties, and the unexpected dynamical phenomena observed under pressure and temperature conditions relevant for planetary interiors modelling. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.

Studying the mechanisms of natural rubber pyrolysis gas generation using RMD simulations and TG-FTIR experiments

Abstract Based on pyrolysis technology, natural rubber can be converted to gases of high calorific value and then be used as fuels. In order to further explain the generation mechanisms of natural rubber pyrolysis gas, a combination of reaction molecular dynamics (RMD) simulations and thermogravimetry-infrared spectroscopy (TG-FTIR) experiments were used to study the pyrolysis process. The results show that the pyrolysis gases include CH4, C2H4 and a small amount of C3H6 and C4H6. The TG-FTIR also shows the presence of CH4 and functional groups ( C H, CH2, CH3 and C C ) in C2H4, C3H6 and C4H8. The kinetics data of each reaction which obtained based on the chain reaction mechanism and transition state theory, were input into Aspen Plus® process simulations to further get reasonable reaction path. The simulation results show that CH3 separated from the main chain abstracts H from other molecules to generate CH4, while C2H4 is mainly generated by the breaking of C C bonds on long chains. Other small gas molecules are generated by the breaking up of large olefins or free radicals with low activity. This study provides a theoretical basis for the recycling of pyrolysis gas and may ultimately help to increase the energy efficiency of the pyrolysis process.

Adamantane-Based Micro- and Ultra-Microporous Frameworks for Efficient Small Gas and Toxic Organic Vapor Adsorption.

Microporous organic polymers and related porous materials have been applied in a wide range of practical applications such as adsorption, catalysis, adsorption, and sensing fields. However, some limitations, like wide pore size distribution, may limit their further applications, especially for adsorption. Here, micro- and ultra-microporous frameworks (HBPBA-D and TBBPA-D) were designed and synthesized via Sonogashira–Hagihara coupling of six/eight-arm bromophenyl adamantane-based “knots” and alkynes-type “rod” monomers. The BET surface area and pore size distribution of these frameworks were in the region of 395–488 m2 g−1, 0.9–1.1 and 0.42 nm, respectively. The as-made prepared frameworks also showed good chemical ability and high thermal stability up to 350 °C, and at 800 °C only 30% mass loss was observed. Their adsorption capacities for small gas molecules such as CO2 and CH4 was 8.9–9.0 wt % and 1.43–1.63 wt % at 273 K/1 bar, and for the toxic organic vapors n-hexane and benzene, 104–172 mg g−1 and 144–272 mg g−1 at 298 K/0.8 bar, respectively. These are comparable to many porous polymers with higher BET specific surface areas or after functionalization. These properties make the resulting frameworks efficient absorbent alternatives for small gas or toxic vapor capture, especially in harsh environments.

Shock-Driven Decomposition of Polymers and Polymeric Foams.

Polymers and foams are pervasive in everyday life, as well as in specialized contexts such as space exploration, industry, and defense. They are frequently subject to shock loading in the latter cases, and will chemically decompose to small molecule gases and carbon (soot) under loads of sufficient strength. We review a body of work—most of it performed at Los Alamos National Laboratory—on polymers and foams under extreme conditions. To provide some context, we begin with a brief review of basic concepts in shockwave physics, including features particular to transitions (chemical reaction or phase transition) entailing an abrupt reduction in volume. We then discuss chemical formulations and synthesis, as well as experimental platforms used to interrogate polymers under shock loading. A high-level summary of equations of state for polymers and their decomposition products is provided, and their application illustrated. We then present results including temperatures and product compositions, thresholds for reaction, wave profiles, and some peculiarities of traditional modeling approaches. We close with some thoughts regarding future work.

Understanding the effect of host flexibility on the adsorption of CH4, CO2 and SF6 in porous organic cages

Abstract Molecular simulations for gas adsorption in microporous materials with flexible host structures is challenging and, hence, relatively rare. To date, most gas adsorption simulations have been carried out using the grand-canonical Monte Carlo (GCMC) method, which fundamentally does not allow the structural flexibility of the host to be accounted for. As a result, GCMC simulations preclude investigation into the effect of host flexibility on gas adsorption. On the other hand, approaches such as molecular dynamics (MD) that simulate the dynamic evolution of a system almost always require a fixed number of particles in the simulation box. Here we use a hybrid GCMC/MD scheme to include host flexibility in gas adsorption simulations. We study the adsorption of three gases – CH4, CO2 and SF6 – in the crystal of a porous organic cage (POC) molecule, CC3-R, whose structural flexibility is known by experiment to play an important role in adsorption of large guest molecules [L. Chen, P. S. Reiss, S. Y. Chong, D. Holden, K. E. Jelfs, T. Hasell, M. A. Little, A. Kewley, M. E. Briggs, A. Stephenson, K. Mark Thomas, J. A. Armstrong, J. Bell, J. Busto, R. Noel, J. Liu, D. M. Strachan, P. K. Thallapally, A. I. Cooper, Separation of rare gases and chiral molecules by selective binding in porous organic cages. Nat. Mater. 2014, 13, 954, D. Holden, S. Y. Chong, L. Chen, K. E. Jelfs, T. Hasell, A. I. Cooper, Understanding static, dynamic and cooperative porosity in molecular materials. Chem. Sci. 2016, 7, 4875]. The results suggest that hybrid GCMC/MD simulations can reproduce experimental adsorption results, without the need to adjust the host–guest interactions in an ad hoc way. Negligible errors in adsorption capacity and isosteric heat are observed with the rigid-host assumption for small gas molecules such as CH4 and CO2 in CC3-R, but the adsorption capacity of the larger SF6 molecule in CC3-R is hugely underestimated if flexibility is ignored. By contrast, hybrid GCMC/MD adsorption simulations of SF6 in CC3-R can accurately reproduce experiment. This work also provides a molecular level understanding of the cooperative adsorption mechanism of SF6 in the CC3-R molecular crystal.

Comparative transcriptome analysis reveals significant differences in the regulation of gene expression between hydrogen cyanide- and ethylene-treated Arabidopsis thaliana

BackgroundHydrogen cyanide (HCN) is a small gaseous molecule that is predominantly produced as an equimolar co-product of ethylene (ET) biosynthesis in plants. The function of ET is of great concern and is well studied; however, the function of HCN is largely unknown. Similar to ET, HCN is a simple and diffusible molecule that has been shown to play a regulatory role in the control of some metabolic processes in plants. Nevertheless, it is still controversial whether HCN should be regarded as a signalling molecule, and the cross-talk between HCN and ET in gene expression regulation remains unclear. In this study, RNA sequencing (RNA-seq) was performed to compare the differentially expressed genes (DEGs) between HCN and ET in Arabidopsis. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were subsequently performed to investigate the function and pathway enrichment of DEGs. Parts of key genes were confirmed by quantitative real-time PCR.ResultsThe results showed that at least 1305 genes and 918 genes were significantly induced by HCN and ET, respectively. Interestingly, a total of 474 genes (|log2 FC| ≥1) were co-regulated by HCN and ET. GO and KEGG analyses indicated that the co-regulated genes by HCN and ET were enriched in plant responses to stress and plant hormone signal transduction pathways, indicating that HCN may cooperate with ET and participate in plant growth and development and stress responses. However, a total of 831 genes were significantly induced by HCN but not by ET, indicating that in addition to ET, HCN is in essence a key signalling molecule in plants. Importantly, our data showed that the possible regulatory role of a relatively low concentration of HCN does not depend on ET feedback induction, although there are some common downstream components were observed.ConclusionOur findings provide a valuable resource for further exploration and understanding of the molecular regulatory mechanisms of HCN in plants and provide novel insight into HCN cross-talk with ET and other hormones in the regulation of plant growth and plant responses to environmental stresses.

DFT study of small gas molecules adsorbed on undoped and N-, Si-, B-, and Al-doped graphene quantum dots

A theoretical study about the interaction between small gas molecules (H2O, CO, CO2, NH3, and CH4) with graphene quantum dots (GQDs) was performed. To develop gas sensors with ultralow detection levels, the nature of the bonds between the gas molecules and the GQDs should be understood and controlled. It was found that the binding energy (Eb) of the gas molecules with the GQDs can be controlled if the GQDs are doped. In the first part of the investigation, a choice of appropriated exchange/correlation functionals and basis sets was achieved. After this, the pure generalized gradient approximation (GGA) functionals, including the non-local (NL) density-dependent dispersion correction and the atom-pairwise dispersion correction (D3), were employed and found that they described accurately the Eb for the adsorption of water on GQDs. The use of NL and D3 corrected GGA functionals revealed that the Eb for the adsorption of H2O, CO, and NH3 on Si- and Al-doped GQDs can be improved, which indicates that the detection limit for the detection of these gases can be enhanced. To understand the nature of the bonds involved in the adsorption, different approaches were used, such as the quantum theory of atom in molecules and the electron localization function.

A first-principles study: Adsorption of small gas molecules on GeP3 monolayer

Using first-principles calculation, we have studied the adsorption effect of small gas molecules (H2O, CO2, CH4, SO2, H2S, and NH3) on GeP3 monolayer. To determine the most stable adsorption site, five adsorption sites (center, Ge, P, bridge GeP, and bridge PP) were considered in the paper. Through calculations of adsorption energy, adsorption distance, and charge transfer, we preliminarily determined that H2O, CO2, and CH4 were physically adsorbed on GeP3 via weak van der Waals force. However, SO2, H2S, and NH3 were chemically adsorbed on GeP3 with new covalent bonds formed, as concluded by calculations of electron localization function and charge density difference. Gas molecule adsorption can cause significant changes in the band gap of single-layer GeP3, indicating that pristine GeP3 monolayer is sensitive to these gases. In addition, the adsorption energy of the H2O, CO2, and CH4 adsorbed on GeP3 can be tuned effectively by employing an external electric field. Our theoretical studies reveal that GeP3 monolayer is a promising gas-sensitive material used in nanometer devices.

Thermodynamic and kinetic roles of H2 in structure evolution of urchin-like Co: A density functional theory study

Small gas molecules acting as good capping agents play important roles in controlling the morphologies and surface structures of metal nanocrystals. In the present work, the thermodynamic and kinetic roles of H2 molecules in the morphology of Co nanocrystals were systematically studied by density functional theory (DFT). The Gibbs surface free energies of Co(100), Co(110), and Co(111) at different hydrogen surface coverages were determined by ab initio thermodynamics. The phase diagram of stable H coverage on each plane was obtained and morphology evolution of the Co nanocrystals with various surface hydrogen coverages was predicted by the Wulff construction. Addition of H2 changes the facet stability, generating diverse morphological Co nuclei. The kinetic role of H2 in adatom Co surface diffusion at different H coverages was investigated by DFT. The results suggest that surface H hinders Co surface diffusions, except for Co(100) at 0.56 monolayer coverage. The projected density of states gives deeper insight into the electronic structures of Co adatoms with addition of the surface H atoms, which affect its surface diffusion ability.

Co-pyrolysis characteristics and synergistic mechanism of low-rank coal and direct liquefaction residue

ABSTRACTIn this study, the co-pyrolysis of low-rank pulverized coal (SJC) and direct liquefaction residue (DCLR) was comparatively examined. The structure and composition of tar and the evolution characteristics of gas during pyrolysis were analyzed through GC-MS, TG-FTIR, and other analytic techniques. Results showed that SJC+DCLR co-pyrolysis exhibited a significant synergistic effect. SJC and DCLR served as hydrogen donors to facilitate the hydrogenation of small molecular free radical fragments through pyrolysis, which increased the tar yield by 5.55%. Aromatic hydrocarbon and phenol contents in tar decreased by 11.88% and 7.94%, respectively, and alkane content increased by 12.25%. H2 content in gas decreased by 19.05%, and CH4 content increased by 19.60%. Co-pyrolysis could be divided into three stages. In the first stage, adsorbed water and CO2 were removed at room temperature to 344.91°C, and the weak chemical bond between SJC and DCLR began to break. In the second stage, SJC and DCLR became pyrolyzed, small molecular free radical fragments were hydrogenated, large amounts of tar and small-molecule gases were produced at 344.91–643.35°C, and synergistic effect was primarily observed. In the third stage, condensation reaction occurred between small molecular free radical fragments at 643.35–845.75°C, thereby producing solid coke and a small amount of gas.

Adsorption of HCOH and H2S molecules on Al12P12 fullerene: a DFT study

In this study, we have investigated the adsorption and dissociation of four small gas molecules including HCOH, H2S, NH3, and O2 on Al12P12 fullerene using density functional theory (DFT). The computations have been performed with B3LYP-D and M06-2X levels of theory and have been calculated with the 6-311++G** basis set. The adsorption of HCOH, H2S, NH3, and O2 molecules can be attributed to the chemical and physical behavior of these molecules. The computational results show that the dissociation energies of HCOH and H2S on the surface of Al12P12 fullerene were found more negative than those of their adsorption. On the contrary, the adsorption energies of O2 and NH3 on the surface of Al12P12 fullerene were found to be more negative than those of their dissociation. The results also indicate that the differences between calculated energies at both levels are negligible. The complex bonds between all molecules and Al12P12 fullerene have been formed due to the charge transfer that occurred during these interactions. According to the computations and the plots of total density of state (TDOS), the results indicate that Al12P12 fullerene is slightly sensitive toward HCOH and H2S molecules.

Carbon membranes for bio gas upgrading

Abstract Carbon materials have a lattice plane distance in the range of the kinetic diameter of small gas molecules making them interesting for gas separating membranes. Thin carbon layers ( Because of the mole sieving behavior nearly constant separation performance was found in synthetic CO2/CH4-mixtures over a wide range of variation in pressure (from 0.2 MPa to 1.2 MPa) and gas composition (from 10% to 90% CO2). By only one membrane step a mixture of a typical biogas composition of 0.57 CH4 / 0.43 CO2 was separated in a highly concentrated CH4-stream of 94% at 1.2 MPa and a highly concentrated CO2-stream of 91% at 0.1 MPa. In real biogas treatments on two different biogas plants a robust membrane performance during the testing period of at least one month was observed. CH4 of 94% was produced from the biogas in only one membrane step. Water as well as H2S (up to 180 mg/m³) permeated through the membrane without any damage of the membrane. Both can be also separated from the biogas by the membrane in one single step. Carbon membranes are a robust alternative to polymeric membranes of lower chemical and pressure stability. There are clear advantages in costs, energy consumption, flexibility and convenience of biogas upgrading with carbon membranes in comparison to classical technologies like PSA and scrubbing.

Determination of formaldehyde in single cell by capillary electrophoresis with LIF detection.

As a small molecule gas, formaldehyde (FA) is the simplest carbonyl active material and plays an important role in the carbon cycle of metabolism. However, due to the volatile nature of the gas, it is difficult to accurately quantify its content, which limits the study of the mechanism of action in life activities. Thus, an efficient approach to quantitative detection of FA in cells especially in single cell is urgent needed. Nevertheless, no method for quantifying FA in single cell has been reported to date. In this work, a fluorescent probe N-propyl-4-hydrazino-naphthalimide (NPHNA), which has highly desirable attributes and has been applied to living biological samples, was chosen as labeling reagent to detect endogenous FA at single cell level. After optimization of separation conditions, fast baseline separation of the FA derivative N-propyl-4-hydrazone-naphthalimide product (NPHNA-FA) and NPHNA was achieved in about 5 min by CE with LIF detection. The detection limit for FA was 5 amol (S/N ratio of 3). The developed method was validated by the measurements of intracellular levels of FA in single cell.

Guest encapsulations in non-porous crystals of fully fluorinated dinuclear metal complexes with the M2O2 core (M = Fe3+, Co2+, Ni2+).

Two different coordination types of fully fluorinated dinuclear metal complexes, [Fe2L4(OMe)2] and [M2L4(OH2)2] (M = Co2+, Ni2+ and HL = bis(pentafluorobenzoyl)methane), were obtained. All of the complexes form non-porous crystals, which act as hosts for the adsorption of various benzene derivatives, e.g., benzene, toluene, p-xylene, anisole, and small gas molecules, e.g., CO2, O2, and NO. The complex of iron selectively adsorbs NO in high amounts and the complex of cobalt is found to store adsorbed O2.

Basic Steps in Chemical Dissociation of Gaseous Molecules Using an Even-Odd Rule, a Specifically Adapted Periodic Table and a Covalent Bonding Rule

When writing equations of chemical dissociation, students and scholars are taught two fundamental rules to balance the equation. On both sides of the equation, the types of elements and their quantity are conserved, as well as the global electrical charge. This paper introduces additional methods during dissociation of gaseous compounds, to precisely describe how electrical charges locally move and how bonding structures are modified. Specific rules revolving around electrons pairs displacements are developed and applied to about 150 dissociations of small gaseous molecules using atoms from the three first rows of the periodic table. Results obtained tend to demonstrate the relevance of these tools for chemists.

Graphene oxide membranes with narrow inter-sheet galleries for enhanced hydrogen separation.

This paper reports synthesis of graphene oxide (GO) membranes with narrow interlayer free spacing on scalable polyester substrates using GO sheets prepared by Brodie's method. The GO membranes show interlayer free spacing of ∼3.2 Å with significantly improved hydrogen perm-selectivity than the GO membranes with the large inter-sheet spacing reported in literature.

The role of hydrogen sulfide in gastric mucosal damage

Gastrointestinal disease is a major global threat to public health. In the past few decades, numerous studies have focuses on the application of small molecule gases in the disease treatment. Increasing evidence has shown that hydrogen sulfide (H2S) has anti-inflammatory and anti-oxidative effects, and can regulate gastric mucosal blood flow in the gastric mucosa. After gastric mucosa damage, the level of H2S in the stomach decreases. Administration of H2S can protect and repair the damaged gastric mucosa. Therefore, H2S is a new target for the repair and treatment of gastric mucosa damage. In this review, we introduce the roles of H2S in the treatment of gastric mucosa damage and provide the potential strategies for further clinical treatment.