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1.
We report a molecular simulation study for gas permeation in two membranes constructed from polymers of intrinsic microporosity (PIM-1 and PIM-7). With rigid ladder polymer chains, the membranes posses approximately 47.7 and 46.6% fractional free volumes (FFVs) in PIM-1 and PIM-7, respectively. The voids in the membranes have a diameter up to 9 Å and are largely interconnected. The sorption and diffusion of four gases (H2, O2, CH4 and CO2) were calculated by Monte Carlo and molecular dynamics simulations. The solubility coefficients increase in the order of H2 < O2 < CH4 < CO2, while the diffusion coefficients increase in the following order: CH4 < CO2 < O2 < H2. The simulation results agree well with experimental data, particularly for the solubility coefficients. The solubility and diffusion coefficients correlate well separately with the critical temperatures and effective diameters of gases. These molecular-based correlations can be used in the prediction for other gases. As attributed to the microporous structure, PIM-1 and PIM-7 outperform most glassy polymeric membranes in sorption and diffusion. PIM-1 has larger solubility and diffusion coefficients than PIM-7 because the cyano groups in PIM-1 lead to a stronger affinity and a larger FFV. The simulated solubility, diffusivity and permeation selectivities of CO2/H2, CO2/O2 and CO2/CH4 are consistent with experimental data. The quantitative microscopic understanding of gas permeation in the PIM membranes is useful for the new development of high-performance membranes. 相似文献
2.
Ane Etxebarria Stephan L. Koch Oleksandr Bondarchuk Stefano Passerini Gilberto Teobaldi Miguel ngel Muoz‐Mrquez 《Liver Transplantation》2020,10(24)
Toward improved understanding and control of the interactions of Li metal anodes with their processing environments, a combined X‐ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) characterization of the effects that O2, CO2, and N2, the main gases in dry‐atmosphere battery production lines, induced on a reproducibly clean Li surface at room temperature is presented here. XPS measurements demonstrate that O2 is ten times more effective than CO2 at oxidizing metal Li. Notably, pure N2 is shown to not dissociate on clean metal Li. UPS results indicate that decomposition of O2 (CO2) reduces the work function of the Li surface by almost 1 eV, therefore increasing the reduction energy drive for the treated substrate by comparison to bare metallic Li. DFT simulations semiquantitatively account for these results on the basis of the effects of dissociative gas adsorption on the surface dipole density of the Li surface. 相似文献
3.
Gas adsorption and separation performance of COF-108 framework impregnated by C60 clusters were simulated. The adsorption properties of pure CO2, the mixtures of CO2/CH4, CO2/N2 and N2/O2 were investigated. The simulated results of the adsorption isotherms, the adsorption quantity, the density fields, the isosteric heats and the selectivity in COF-108s were obtained. It is shown that the impregnation of C60 can enhance the adsorption capacity of CO2, N2 and O2, and the selectivity of CO2/CH4, CO2/N2 and N2/O2 in COF-108. The impregnation of C60 can increase the surface area COF-108 but decrease its free volume and the pore diameter. At low adsorption pressures, the monolayer surface adsorption is dominant. With the increase in adsorption pressure, the dominant factor is changed into the free volume of COF-108 by the multilayer adsorption. The impregnation of C60 plays different roles for the polar or non-polar gases at different pressures. 相似文献
4.
陆地生态系统承载的温室气体对全球碳循环及气候调节服务意义重大,森林生态系统是陆地生态系统的重要组成部分,量化森林对温室气体的储量有利于从生物地球化学角度研究全球变化问题。针对中国森林生态系统承载的温室气体在大尺度上无法有效量化的问题,基于2000与2010年两期土地利用数据和前人的相关研究,通过一个生态系统温室气体值模型,模拟得到中国森林生态系统承载的三大主要温室气体(CO2,CH4,N2O)的量。结果表明:(1)中国森林生态系统的面积从2000年的224.3×106 hm2略增到2010的224.6×106 hm2;其中落叶阔叶林、常绿阔叶林和针叶林的面积减少,而混交林与灌木林的面积增加;(2)对应地,2000和2010年中国森林的温室气体储量分别为154.03和154.37 Pg CO2当量,10年间增加了0.34 Pg CO2当量。其中,常绿针叶林、常绿阔叶林、落叶阔叶林在研究时段内的... 相似文献
5.
Using molecular simulations, we studied a diverse collection of zeolite–imidazolate frameworks (ZIFs) to evaluate their performances in adsorption- and membrane-based gas separations. Molecular simulations were performed for both single-component gases (CH4, CO2, H2 and N2) and binary gas mixtures (CO2/CH4, CO2/N2, CO2/H2 and CH4/H2) to predict the intrinsic and mixture selectivities of ZIFs. These two selectivities were compared to discuss the importance of multi-component mixture effects on making predictions about the separation performance of a material. Gas separation performances of ZIFs were compared with other nanoporous materials and our results showed that several ZIFs can outperform well-known zeolites and metal–organic frameworks in CO2 separations. Several other properties of ZIFs such as gas permeability, working capacity and sorbent selection parameter were computed to identify the most promising materials in adsorption- and membrane-based separation of CO2/CH4, CO2/N2, CO2/H2 and CH4/H2. 相似文献
6.
Increasing reactive nitrogen (N) input has been recognized as one of the important factors influencing climate system through affecting the uptake and emission of greenhouse gases (GHG). However, the magnitude and spatiotemporal variations of N‐induced GHG fluxes at regional and global scales remain far from certain. Here we selected China as an example, and used a coupled biogeochemical model in conjunction with spatially explicit data sets (including climate, atmospheric CO2, O3, N deposition, land use, and land cover changes, and N fertilizer application) to simulate the concurrent impacts of increasing atmospheric and fertilized N inputs on balance of three major GHGs (CO2, CH4, and N2O). Our simulations showed that these two N enrichment sources in China decreased global warming potential (GWP) through stimulating CO2 sink and suppressing CH4 emission. However, direct N2O emission was estimated to offset 39% of N‐induced carbon (C) benefit, with a net GWP of three GHGs averaging ?376.3 ± 146.4 Tg CO2 eq yr?1 (the standard deviation is interannual variability of GWP) during 2000–2008. The chemical N fertilizer uses were estimated to increase GWP by 45.6 ± 34.3 Tg CO2 eq yr?1 in the same period, and C sink was offset by 136%. The largest C sink offset ratio due to increasing N input was found in Southeast and Central mainland of China, where rapid industrial development and intensively managed crop system are located. Although exposed to the rapidly increasing N deposition, most of the natural vegetation covers were still showing decreasing GWP. However, due to extensive overuse of N fertilizer, China's cropland was found to show the least negative GWP, or even positive GWP in recent decade. From both scientific and policy perspectives, it is essential to incorporate multiple GHGs into a coupled biogeochemical framework for fully assessing N impacts on climate changes. 相似文献
7.
The potential use of an ethylene absorbent in controlled atmosphere storage of two varieties of apple has been investigated. With Golden Delicious, the rise in ethylene concentration during controlled atmosphere storage can be delayed for about 40 days but not prevented by inclusion of potassium permanganate in the storage container. But with Bramley's Seedling, potassium permanganate can delay ethylene accumulation for over 200 days. Ethylene treatment of Bramley's Seedling in a flowing stream of 5% CO2:3% O2:92% N2 caused accelerated softening, accumulation of α-farnesene and earlier onset of superficial scald. Use of potassium permanganate to remove ethylene during storage in static controlled atmosphere conditions retarded all three processes in Bramley's Seedling kept in 5% CO2:3% O2 and in 9% CO2:12% O2. However, in one experiment, ethylene removal in 5% CO2:3% O2, led to external and internal symptoms of CO2 damage. A subsequent investigation of the combined effects of harvest date, store temperature and ethylene removal in 5% CO2:3% O2 did not show any damage or accumulation of succinic acid which is known to be involved in CO2 injury. This experiment revealed that ethylene removal could be successfully accomplished on Bramley fruit harvested up to a month after the usual date and little α-farnesene accumulated in this fruit. Nevertheless scald did develop on late picked fruit and this raises doubts about the causal role of farnesene in scald. 相似文献
8.
Tord Magnusson 《Plant and Soil》1989,120(1):39-47
The method includes sampling of gases from an equilibration chamber permanently installed in the soil, transferring the sample to laboratory and subsequent measurement by gas chromatography. The equilibration chamber allows sampling of the gas phase both above and below the groundwater level, which is a major advantage. After significant concentration changes in non-saturated soils, gases in chambers regain equilibrium with the surrounding soils within 1–2 days. In the most unfavourable equilibration situations,i.e. in mineral subsoils with stagnant groundwater and very low biological activity, 90% equilibrium is attained in about 15 days. N2, O2+Ar, CO2, CH4, N2O, H2 and Ne, are measured on a series/bypass multi-column system, followed by a thermal conductivity detector. 相似文献
9.
Shingo Ueda Chun-Sim U. Go Takahito Yoshioka Naohiro Yoshida ast; Eitaro Wada Toshihiro Miyajima ast ast; Atsuko Sugimoto Narin Boontanon Pisoot Vijarnsorn Suporn Boonprakub 《Biogeochemistry》2000,49(3):191-215
We studied the distribution of dissolved O2, CO2, CH4, and N2O in a coastal swamp system in Thailand with the goal to characterize the dynamics of these gases within the system. The gas concentrations varied spatially and seasonally in both surface and ground waters. The entire system was a strong sourcefor CO2 and CH4, and a possible sink for atmospheric N2O. Seasonal variation in precipitation primarily regulated the redox conditions in the system. However, distributions of CO2, CH4, and N2O in the river that received swamp waters were not always in agreement with redox conditions indicated by dissolvedO2 concentrations. Sulfate production through pyriteoxidation occurred in the swamp with thin peat layerunder aerobic conditions and was reflected by elevatedSO
4
2–
/Cl– in the river water. When SO
4
2–
/Cl– was high, CO2 and CH4 concentrations decreased, whereas the N2O concentration increased. The excess SO
4
2–
in the river water was thus identified as a potential indicator for gas dynamics in this coastal swamp system. 相似文献
10.
Net productions of permanent soil atmosphere gases (N2, CO2, O2) and temporary gases (N2O, NO) were monitored in soil cores using a non-interfering, fully automated measuring technique allowing highly time resolved measurements over prolonged periods. The influence of changes in available organic carbon on CO2, N2O, NO and N2 production was studied by changing the soil carbon content through aerobic preincubations of different length, up to 21 days.The aerobic preincubation caused an increase in NO3
- concentration and a decrease in available carbon content. Available carbon content dominated both CO2 and total N gas (N2+N2O+NO) production during anaerobiosis. Both CO2 and total N gas production rates decreased with increasing length of the previous aerobic preincubation, this in spite of the higher initial NO3
- concentration.Total denitrification rates were closely related to the anaerobic CO2 production rates. No relation was found between water soluble carbon content and total denitrification. The N2O/N2 ratio could be explained by an interaction of carbon availability, NO3
- concentration and enzyme status. Net N2O consumption was monitored. The balance between cumulative total N gas production and NO3
- consumption varied according to the different treatments. Cumulative N2O production exceeded cumulative N2 production for 0 up to 5 days. 相似文献
11.
Debjani Sihi Eric A. Davidson Kathleen E. Savage Dong Liang 《Global Change Biology》2020,26(1):200-218
Production and consumption of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) are affected by complex interactions of temperature, moisture, and substrate supply, which are further complicated by spatial heterogeneity of the soil matrix. This microsite heterogeneity is often invoked to explain non‐normal distributions of greenhouse gas (GHG) fluxes, also known as hot spots and hot moments. To advance numerical simulation of these belowground processes, we expanded the Dual Arrhenius and Michaelis–Menten model, to apply it consistently for all three GHGs with respect to the biophysical processes of production, consumption, and diffusion within the soil, including the contrasting effects of oxygen (O2) as substrate or inhibitor for each process. High‐frequency chamber‐based measurements of all three GHGs at the Howland Forest (ME, USA) were used to parameterize the model using a multiple constraint approach. The area under a soil chamber is partitioned according to a bivariate log‐normal probability distribution function (PDF) of carbon and water content across a range of microsites, which leads to a PDF of heterotrophic respiration and O2 consumption among microsites. Linking microsite consumption of O2 with a diffusion model generates a broad range of microsite concentrations of O2, which then determines the PDF of microsites that produce or consume CH4 and N2O, such that a range of microsites occurs with both positive and negative signs for net CH4 and N2O flux. Results demonstrate that it is numerically feasible for microsites of N2O reduction and CH4 oxidation to co‐occur under a single chamber, thus explaining occasional measurement of simultaneous uptake of both gases. Simultaneous simulation of all three GHGs in a parsimonious modeling framework is challenging, but it increases confidence that agreement between simulations and measurements is based on skillful numerical representation of processes across a heterogeneous environment. 相似文献
12.
D. Damasceno Borges M. Prakash N.A. Ramsahye P.L. Llewellyn S. Surblé P. Horcajada 《Molecular simulation》2015,41(16-17):1357-1370
Density functional theory calculations have been combined with forcefield-based grand canonical Monte Carlo simulations to explore the adsorption of CO2, N2, CH4 and H2 on the small one-dimensional channel MIL-102, a naphthalene tetracarboxylate-based metal-organic framework (MOF) built up from a connection of trimers of trivalent iron. A detailed analysis is provided on the preferential arrangement of the confined adsorbates as well as the energetics of the host/guest interactions. The co-adsorption properties of this solid for the elimination of CO2 from hydrogen, natural and flue gases are then revealed. The so-predicted performances are further compared with those reported so far for a diverse series of MOFs. 相似文献
13.
Atmospheric CO2 and O3 concentrations are increasing due to human activity and both trace gases have the potential to alter C cycling in forest
ecosystems. Because soil microorganisms depend on plant litter as a source of energy for metabolism, changes in the amount
or the biochemistry of plant litter produced under elevated CO2 and O3 could alter microbial community function and composition. Previously, we have observed that elevated CO2 increased the microbial metabolism of cellulose and chitin, whereas elevated O3 dampened this response. We hypothesized that this change in metabolism under CO2 and O3 enrichment would be accompanied by a concomitant change in fungal community composition. We tested our hypothesis at the
free-air CO2 and O3 enrichment (FACE) experiment at Rhinelander, Wisconsin, in which Populus tremuloides, Betula papyrifera, and Acer saccharum were grown under factorial CO2 and O3 treatments. We employed extracellular enzyme analysis to assay microbial metabolism, phospholipid fatty acid (PLFA) analysis
to determine changes in microbial community composition, and polymerase chain reaction–denaturing gradient gel electrophoresis
(PCR–DGGE) to analyze the fungal community composition. The activities of 1,4-β-glucosidase (+37%) and 1,4,-β-N-acetylglucosaminidase (+84%) were significantly increased under elevated CO2, whereas 1,4-β-glucosidase activity (−25%) was significantly suppressed by elevated O3. There was no significant main effect of elevated CO2 or O3 on fungal relative abundance, as measured by PLFA. We identified 39 fungal taxonomic units from soil using DGGE, and found
that O3 enrichment significantly altered fungal community composition. We conclude that fungal metabolism is altered under elevated
CO2 and O3, and that there was a concomitant change in fungal community composition under elevated O3. Thus, changes in plant inputs to soil under elevated CO2 and O3 can propagate through the microbial food web to alter the cycling of C in soil. 相似文献
14.
We have examined characteristics of the photoinhibition of photosynthesis which occur in the unicellular cyanobacterium Microcystis aeruginosa, following exposure to photon fluence rates in excess of those required for growth. Photoinhibition occurs following exposure of cells to a photon fluence rate of 1,000 μmol m-2 s-1, which is manifested as a decrease in either light-limited CO2 fixation or light-saturated CO2-dependent O2 evolution. The extent and rapidity of this photoinhibition is greatly enhanced under CO2-depleted conditions. Experiments in which cultures were sparged with different gases indicate that photoinhibition is not an obvious consequence of elevated O2 tensions, unlike the photooxidative bleaching of photosynthetic pigments. Comparative studies on the photoinactivation of CO2-dependent O2 evolution and of the methyl viologen-dependent Mehler reaction, in whole cells, indicate that a primary site of light damage is within the photosynthetic electron-transport reactions and that carbon fixation is initially unaffected. 相似文献
15.
This paper presents diffusion data of N2, O2, H2S and SO2 in MFI and 4A zeolites obtained by molecular dynamics simulations, especially its dependence on temperature and loading. At high loadings and temperatures, the order of self-diffusivity of guests in two zeolites is O2 > N2 > H2S>SO2. The diffusion behaviour is different in different zeolites at lower loadings, reflecting different influences from straight channels (MFI) and α-cages (4A). Furthermore, with increasing loading, the self-diffusivity of guest molecules decreases in MFI but generally increases in 4A. The centre of mass (COM) probability densities and diffusion trajectories of guests give insight into molecular-level diffusion process. The simulation results reveal that with increasing loading, the diffusion mechanism would change from the inter-pore to intra-pore diffusion in MFI. However, in 4A, the intra-pore diffusion is predominant at low and high loadings, but inter-pore diffusion is more important at moderate loadings. 相似文献
16.
Soil redox plays a key role in regulating biogeochemical transformations in terrestrial ecosystems, but the temporal and spatial
patterns in redox and associated controls within and across ecosystems are poorly understood. Upland humid tropical forest
soils may be particularly prone to fluctuating redox as abundant rainfall limits oxygen (O2) diffusion through finely textured soils and high biological activity enhances O2 consumption. We used soil equilibration chambers equipped with automated sensors to determine the temporal variability in
soil oxygen concentrations in two humid tropical forests with different climate regimes. We also measured soil trace gases
(CO2, N2O, and CH4) as indices of redox-sensitive biogeochemistry. On average, the upper elevation cloud forest had significantly lower O2 concentrations (3.0 ± 0.8%) compared to the lower elevation wet tropical forest (7.9 ± 1.1%). Soil O2 was dynamic, especially in the wet tropical forest, where concentrations changed as much as 10% in a single day. The periodicity
in the O2 time series at this site was strongest at 16 day intervals and was associated with the hourly precipitation. Greenhouse gas
concentrations differed significantly between sites, but the relationships with soil O2 were consistent: O2 was negatively related to both CO2 and CH4 and positively related to N2O. These results are among the first to quantify the temporal and spatial scale of variability in soil redox in humid tropical
forests, and show that the timing of precipitation plays a strong role in biogeochemical cycling on the scale of hours to
weeks. 相似文献
17.
All measurements of photorespiration and gross photosynthesis in leaves, whether using isotopes or not, are underestimated because of the recycling of O2 or CO2. On the basis of a simple diffusion model, we propose a method for the calculation of the recycling and the corresponding underestimation of the measurements. This procedure can be applied when the stomatal resistance is known, and allows for a correction of certain results in the literature. It is found that measurements of the photorespiratory CO2 release are usually underestimated by 20 to 100%, which sets the estimated rate of CO2 photorespired at 30 to 50% of the net photosynthesis in C3 plants under normal conditions. In water stress studies, the correction of the photorespiration is still more important (1.5-3.3) because the stomata are closed more. Analysis of the diffusion of O2 shows that its recycling is low and that the underestimation of photorespiration with 18O2 is negligible. 相似文献
18.
不同干扰因素对森林和湿地温室气体通量影响的研究进展 总被引:5,自引:0,他引:5
森林和湿地是CO2、CH4和N2O等温室气体重要的源、汇和转换器,在全球气候变化过程中起着重要作用。森林和湿地温室气体通量受到诸多因子的作用,其中干扰便是一个重要的因素。不同干扰因素对于森林和湿地生态系统温室气体通量的影响,国际上已经开展了相应的研究。基于人为和自然两大类干扰方式,分别从采伐、施肥、垦殖等人为干扰因素和火烧、台风(飓风)等自然干扰因素综述了干扰对于森林和湿地生态系统CO2、CH4和N2O通量的影响。根据目前研究中存在的不足,提出了今后应需加强的领域,以期更好地揭示干扰对于森林和湿地生态系统温室气体通量的影响及作用机制,为今后深入开展相关研究提供一定的参考价值。 相似文献
19.
S. R. Bernard 《Bulletin of mathematical biology》1961,23(1):1-14
Some progress has been made on the problem of the interaction of respiratory gases with whole blood. A working mathematical
model for the O2−CO2 interaction phenomena has been developed from mathematical studies of the data. The Edsall-Wyman (1958) model for CO2 absorption is improved upon in this paper by consolidating it with the O2 absorption model developed in paper I of this set (Bernard, S. R.,Bull. Math. Biophysics,22, 391–415, 1960). This improved model assumed the effect of O2 on CO2 absorption is mediated through the electrical charge possessed by the hemoglobin molecule,i.e., O2 molecules bound to hemoglobin displace protons from the hemoglobin thereby increasing the negative charge on the hemoglobin
and at the same time increasing the acidity of the solution. The model is tested against the data. 相似文献
20.
Seda Keskin 《Molecular simulation》2013,39(1):14-24
Grand canonical Monte Carlo and equilibrium molecular dynamics simulations were used to assess the performance of an rht-type metal–organic framework (MOF), Cu-TDPAT, in adsorption-based and membrane-based separation of CH4/H2, CO2/CH4 and CO2/H2 mixtures. Adsorption isotherms and self-diffusivities of pure gases and binary gas mixtures in Cu-TDPAT were computed using detailed molecular simulations. Several properties of Cu-TDPAT such as adsorption selectivity, working capacity, diffusion selectivity, gas permeability and permeation selectivity were computed and compared with well-known zeolites and MOFs. Results showed that Cu-TDPAT is a very promising adsorbent and membrane material especially for separation of CO2 and it can outperform traditional zeolites and MOFs such as DDR, MFI, CuBTC, IRMOF-1 in adsorption-based CO2/CH4 and CO2/H2 separations. 相似文献