Effect Of Gas Adsorption Research Articles

Gas adsorption effect on the graphene nanoribbon band structure and quantum capacitance

Graphene nanoribbons (GNRs) as a quasi-one dimensional (1D) narrow strip of graphene hold great potential for applications in variety of sensors because of π-bonds that can react with chemical elements. Despite outstanding properties, graphene nanoribbons have not fully exploited for variety of application in nanoelectronic and nanosensors due to poor understanding of their physical, electrical properties and basic limitations on the synthesis. Therefore, in order to achieve analytical understanding on the interaction of the gas molecules with GNR surface and gas sensing mechanism, a theoretical method using tight binding model based on nearest neighbour approximation is developed in this study. Additionally, the adsorption effects of NO2 and CO2 gas molecules on the band structure and electrical properties of the GNRFET based gas sensor are investigated. Based on the proposed model numerical simulation is carried out which emphasizes the significant effect of the gas adsorption on the band structure and electrical properties of GNRs. On the other hand, quantum capacitance created between metal gate and channel as a sensing parameter is considered and its variations when GNR exposed to the NO2 and CO2 molecules are analytically modelled. Moreover, the adsorption energy and charge transfer occurred during gas molecules interaction with GNR surface are calculated. Also band structure and I–V characteristics are analysed using first principle calculation based on density functional theory. The current–voltage analysis clearly indicates the changes of the quantum capacitance when exposed to the gas molecules. The results of the proposed model are compared with the available experimental data or data obtained by density functional theory (DFT) calculations and good agreements are observed.

Experimental and analytical investigation of adsorption effects on shale gas transport in organic nanopores

Gas production from shale gas reservoirs is determined by original gas-in-place and gas transport mechanism in shale. Gas storage in shale consists of three different states: first, free gas in pores and natural fractures; second, adsorbed gas on the organic and inorganic pore walls; and third, absorbed or dissolved gas into formation water and organic matter. On the other hand, gas transport in shale may be dominated by noncontinuum flow in nanopores, which depends on gas slippage, bulk diffusion, Knudsen diffusion and adsorbed surface diffusion. In this study, a gas velocity model involving all of these parameters is proposed to describe the gas adsorption and Non-Darcy flow effects on gas transport behavior in shale gas reservoirs. Adsorption capacity of six shale core samples is measured by the gravimetric method using magnetic suspension sorption system. Regression analysis of the measured data has been performed using the Simplified Local-Density model coupled with modified Peng-Robinson Equation of State (SLD-PR). The presence of the moisture content is taken into consideration to distinguish between gas adsorption on the surface of organic matter and clay minerals. The hydrophilic feature of clay minerals and hydrophobic feature of organic matter result in water molecules preferring adsorbing on the surface of clays, while gas molecules preferring adsorbing on the surface of organic matter. In the developed velocity model, adsorbed gas is treated as mobile gas molecules adsorbing on the surface of organic nanopores, which moves by means of adsorbed surface diffusion. The surface diffusion velocity is characterized by adsorbed surface diffusion coefficient. Simultaneously, bulk gas is governed by second-order gas slippage, which is calculated using Navier-Stokes (N-S) equation associated with second-order slip boundary condition. Finally, the adsorbed surface diffusion is incorporated into bulk gas flow using Langmuir slip model to account for the total gas flow in the organic nanopores. The results of this study indicate that adsorbed surface diffusion contributes to the enhancement or impediment of total gas flow velocity in organic nanopores. Therefore, properly handling the adsorption effect on gas transport in organic nanopores is critical to correctly understand gas production from shale gas reservoirs.

Assessing the feasibility and CO2 storage capacity of CO2 enhanced shale gas recovery using Triple-Porosity reservoir model

The depletion of conventional energy sources is leading to increased demand for unconventional energy sources. Shale gas is an important unconventional energy source that has been successfully developed and utilized in the United States. CO2 enhanced shale gas recovery (CO2-ESG) is a promising shale gas extraction technology. Supercritical CO2 injection can enhance the shale gas recovery through competitive absorption between the methane and the CO2 while also providing CO2 geological sequestration. However, assessments of the feasibility of CO2 enhanced shale gas recovery in field scale trials is quite complicated given the complex pore structures in shale reservoirs and the ultralow permeability. This paper describes a triple porosity, dual permeability (TP-DK) model that includes the effects of the shale gas adsorption and desorption, the competitive adsorption and binary gas diffusion. The Sichuan basin in China is selected as the target reservoir. The key parameters in this simulation were determined by experimental measurements of shale samples from the Lower Silurian Longmaxi Formation (LSLF) shale in the Sichuan basin. The results show that the CO2 injection can significantly enhance the shale gas recovery. A 90m thick shale gas reservoir with a 1200m horizontal well absorb injections of CO2 captured from a large 1000 MWe coal-fired power plant for 2years. However, the volume flow rate of the CO2 sequestration decreased with time as the production pressure decreased. Both the production time and the production pressure should be considered on the synergy between the CO2 sequestration and the shale gas recovery.

Effect of Gas Adsorption on Graphene Nanoribbons: A Density Functional Theory

Using first principal calculations we have investigated the change in electronic and structural properties of CO, NO, CO2, and NO2 adsorbed on the ultra thin graphene nanoribbons (GNRs) with armchair and zigzag edges. Gas molecules interacts weakly with GNRs with adsorption energy of -0.07eV, -0.13eV, -0.56eV and -0.32eV for CO, NO, CO2, and NO2 respectively. The charge transfer take place from GNR to CO, CO2 and NO2 molecules while NO act as donor to GNR. Results show that armchair GNR is more sensitive to adsorption of NO2 as compare to CO, NO and CO2.

First-principles theoretical investigation of graphene layers for sensor applications

Graphene is expected to be a potential device material for sensor applications due to its high charge mobility and high sensitivity to adsorbates. This article reviews the first-principles density-functional study that clarifies gas adsorption effects on graphene layers doped with boron and nitrogen atoms. We show adsorption effects of not only common gas molecules but also environmentally polluting or toxic gas molecules on stabilities and structural properties of graphene layers and carbon nanotubes. We also show physical properties induced by the adsorption of the gas molecules and discuss the possibility to detect these gas molecules.

Effectiveness of thin spray-on liners as a gas management tool in underground coal mines

A thin spray-on liner (TSL) is defined as a chemical-based layer or coating (2–5mm) that is sprayed onto the rock surface to support the mining excavations. Besides ground support, TSLs can potentially be used as a gas management tool for underground coal mining. However, the permeability characteristics and effectiveness of TSLs at in-situ gas pressure are the key considerations in application of TSLs for gas management.This paper presents an experimental study to investigate the potential use of TSLs for gas management in underground coal mines. The coal samples were collected from an underground coal mine in New South Wales, Australia. The selected bituminous coal samples were initially characterised using petrographic and uniaxial compression strength (UCS) tests. Single phase gas permeability tests were then conducted on the coal samples. Methane (CH4) and carbon dioxide (CO2) were used for the tests as they are the gases of main concern in underground coal mines, and Helium (He) was used as a control gas to investigate the effect of gas adsorption on the coal permeability. Permeability tests were first conducted on coal samples before the TSL application. The coal samples were then coated with two types of TSL materials with a thickness of 5mm and the permeability tests were repeated. The experimental observations show that both TSLs are very effective in reducing the coal permeability, with the permeability values in the range of nanodarcies.High injection pressure gas flow tests were also conducted to investigate the amount of pressure that the TSLs can resist. The injection pressure was increased until the TSLs failed. The failure of TSLs was demonstrated by a sudden increase in the permeability. The test results show that the failure pressure of the TSLs is directly related to their adhesion strength on coal.

Quantitative determination of abandonment pressure for CO2 storage in depleted shale gas reservoirs by free-simulator approach

Abandonment pressure of shale gas reservoirs has been in the center of attention to evaluate the CO2 storage in such reservoirs. However, the evaluation of abandonment pressure in shale gas reservoirs is not clearly defined. To quantitatively determine the abandonment pressure for CO2 storage in depleted shale gas reservoirs, we introduced two effective and reasonable semi-analytical models, named pressure transient analysis (PTA) and rate transient analysis (RTA), based on a free-simulator approach. Firstly, by line source function, CO2 seepage models for an injection well with constant injection rate or constant injection pressure were simultaneously proposed in consideration of gas adsorption, diffusion flow, stress sensitivity and non-Darcy flow effects. Then, we solved seepage models using Laplace transformation, perturbation method, superposition principle and numerical discretization method, thus obtained transient-pressure and transient-rate solutions of the injection well. Further, we compared the proposed mathematical models with existing models. Furthermore, we systematically examined the sensitivity of the parameters, thereby constraining the intrinsic uncertainty to evaluate the abandonment pressure. Finally, we applied the proposed method to study a real case from Sichuan Basin in China, thus demonstrating the promising prosperity of this new quantitative determination of abandonment pressure for CO2 storage in depleted shale gas reservoirs.Our results showed that the maximum difference between our proposed method and numerical method was lower than 5%, suggesting a good agreement between the two methods. Moreover, our results also showed that free-simulator approach gave much faster calculation speed compared to numerical method. As a result, we provided a framework for the quantitative determination of abandonment pressure, by coupling pressure transient analysis (PTA) and rate transient analysis (RTA) during CO2 injection at constant injection pressure and injection rate. Moreover, our results also showed that the abandonment pressure has power law relationship with the injection pressure using PTA method, and the abandonment pressure has logarithm relationship with CO2 injection volume using RTA method.

Numerical simulation of influence of Langmuir adsorption constant on gas drainage radius of drilling in coal seam

To determine reasonable distance of gas pre-drainage drillings in coal seams, a solid–gas coupling model that takes gas adsorption effect into account was constructed. In view of different adsorption constants, the paper conducted the numerical simulation of pre-drainage gas in drillings along coal seam, studied the relationship of adsorption constants and permeability, gas pressure, and effective drainage radius of coal seams, and applied the approach to the layout of pre-drainage gas drillings in coal seams. The results show that the permeability of coal seams is on the gradual increase with time, which is divided into three sections according to the increase rate: the drainage time 0–30d is the sharp increase section; 30–220d is the gradual increase section; and the time above 200d is the stable section. The permeability of coal seams is in negative linear and positive exponent relation with volume adsorption constant VL and pressure adsorption constant PL, respectively. The effective drainage radius is in negative linear relation with VL and in positive exponent relation with PL. Compared with the former design scheme, the engineering quantity of drilling could be reduced by 25%.

Effects of gas adsorption on mechanical properties and erosion mechanism of coal

In order to study coal deformation and fractured mechanism under pore gas action, we chose gases N2 and CH4 as pore fluids, and carried out triaxial compression test of gas-bearing coal. To further explore the effects of gas erosion on coal deformation and failure, we tested the deformation and rapture process of coal during gas adsorption equilibrium under fixed axial load and confining pressure. The results showed that gas adsorption decreases coal's solid surface energy and lowers coal's compressive strength, leading to larger plastic deformation in coal and final rupture instability. From the physicochemical angle, we quantified the adsorbed gas erosion effects of coal based on both Griffith crack extension theory and Mohr–Columb strength criterion, explored the mechanical characteristics and erosion damage process of gas containing coals and put forwarded their mathematical models. These models can describe the experimental phenomena fairly.

Gas Adsorption Effects on the Electronic Properties of Two-Dimensional Nickel Bis(dithiolene) Complex

Two-dimensional (2D) metal–organic frameworks (MOFs) are functional materials in electronic devices, due to the tunable electronic properties. Here, using first-principles calculations, we demonstrate that the recently synthesized π-conjugated nickel bis(dithiolene) complex with a chemical formula Ni3C12S12 can be used to detect poisonous gases, such as CO and NO molecules. The adsorptions of CO and NO molecules on 2D Ni3C12S12 surface lead to a change of electronic structure from semiconducting to metallic, while O2 cannot. The electronic structure change can be understood from two respects: owing to the strong interaction between Ni atoms and CO or NO molecules, charge transfer from the adsorbed molecules to the nanosheet gives rise to a large upward shift of the Fermi level and the strong orbital hybridization between Ni d orbitals and CO σ or NO π* orbitals provides more electronic states around the Fermi level. These results suggest the potential application of 2D MOFs in sensors and electronic devices.

Adsorption of gas molecules and the induced magnetic properties of metal-decorated graphene

ABSTRACTBased on the first-principles of density-functional theory (DFT), the effects of gas adsorption on the change in adsorptive configurations, electronic structures and magnetic properties of graphene with magnetic metal atoms (MMA = Fe, Co, Ni and Mo) systems were investigated. Four metal atoms are strongly trapped at single vacancy graphene (MMA/SV-graphene) and can effectively regulate the adsorption of CO and O2 molecules. It is found that the positive charged of MMA are more prone to adsorb the O2 than that of CO molecule, and these gas molecules on MMA/SV-graphene induce a different type of magnetic properties of systems. Hence, the differences in electronic and magnetic properties of MMA/SV-graphene with the gas molecules are expected to design graphene-based gas sensors and spintronic device.

Necessity of porosity correction before simulation and re-understanding of the effects of gas adsorption on production in shale gas reservoirs

Shale gas contains free gas and adsorbed gas in matrix pores. The size of matrix pore is on the order of nanometer, large specific surface area makes the adsorbed gas occupy a large part of the total void volume. However, most widely used simulators ignore the volume reduction of free gas due to adsorbed gas, resulting in the OGIP errors. In order to make the simulation results be more reasonable and accurate, firstly, we derived the correction formulas of bulk porosity, free gas saturation and connate water saturation used for converting measured data into simulation model. Then, the matrix porosity, gas saturation and connate water saturation are corrected to match the original gas in place (OGIP) and the production data of Barnett Shale. Finally, the effects of gas adsorption on gas production in Barnett Shale with porosity correction are studied. The results show that porosity correction is significantly necessary before inputting the measured parameters into a simulator. In Barnett Shale, the adsorbed gas takes up 1/4 of the total void volume, if this partial volume is ignored, the free gas storage capacity and OGIP will be overestimated by 52.49% and 25.5%, respectively. The cumulative gas production will be much higher without porosity correction due to the artificial increasing of the free gas volume in the model which should be occupied by adsorbed gas in reality. The adsorption effect of shale gas is adverse to the development of shale gas. Only a little fraction of the adsorbed gas contributes to gas production in the late-stage. For Barnett Shale, the recovery factor of free gas is about three times of adsorbed gas; the gas recovery factor in the near-wellbore region is about two times of the gas recovery factor in the whole reservoir.

Gas adsorption and desorption effects on cylinders and their importance for long-term gas records

Abstract. It is well known that gases adsorb on many surfaces, in particular metal surfaces. There are two main forms responsible for these effects (i) physisorption and (ii) chemisorption. Physisorption is associated with lower binding energies in the order of 1–10 kJ mol−1, compared to chemisorption which ranges from 100 to 1000 kJ mol−1. Furthermore, chemisorption only forms monolayers, contrasting physisorption that can form multilayer adsorption. The reverse process is called desorption and follows similar mathematical laws; however, it can be influenced by hysteresis effects. In the present experiment, we investigated the adsorption/desorption phenomena on three steel and three aluminium cylinders containing compressed air in our laboratory and under controlled conditions in a climate chamber, respectively. Our observations from completely decanting one steel and two aluminium cylinders are in agreement with the pressure dependence of physisorption for CO2, CH4, and H2O. The CO2 results for both cylinder types are in excellent agreement with the pressure dependence of a monolayer adsorption model. However, mole fraction changes due to adsorption on aluminium (< 0.05 and 0 ppm for CO2 and H2O) were significantly lower than on steel (< 0.41 ppm and about < 2.5 ppm, respectively). The CO2 amount adsorbed (5.8 × 1019 CO2 molecules) corresponds to about the fivefold monolayer adsorption, indicating that the effective surface exposed for adsorption is significantly larger than the geometric surface area. Adsorption/desorption effects were minimal for CH4 and for CO but require further attention since they were only studied on one aluminium cylinder with a very low mole fraction. In the climate chamber, the cylinders were exposed to temperatures between −10 and +50 °C to determine the corresponding temperature coefficients of adsorption. Again, we found distinctly different values for CO2, ranging from 0.0014 to 0.0184 ppm °C−1 for steel cylinders and −0.0002 to −0.0003 ppm °C−1 for aluminium cylinders. The reversed temperature dependence for aluminium cylinders points to significantly lower desorption energies than for steel cylinders and due to the small values, they might at least partly be influenced by temperature, permeation from/to sealing materials, and gas-consumption-induced pressure changes. Temperature coefficients for CH4, CO, and H2O adsorption were, within their error bands, insignificant. These results do indicate the need for careful selection and usage of gas cylinders for high-precision calibration purposes such as requested in trace gas applications.

Shale productivity prediction and fracturing optimization based on compositional simulation

The reserves of unconventional gas, such as shale and tight gas, is enormous in China. The exploitation of unconventional gas is of significance to secure our nation’s energy future. Precise simulation and prediction of gas flowing behavior in such formations is the key to economic efficiency of exploitation. Different from conventional formations, in shale exist slip flow and gas adsorption. To accurately simulate gas flow in shale, we developed a compositional model based on the hybrid grid which is mainly composed by unstructured PEBI (Perpendicular Bisection) grids. Upon this model, the effects of gas composition, adsorption and slip flow on gas production are analyzed. Horizontal well fracturing in a shale gas reservoir is optimized with the help of this model. The results show that the production of shale gas increases rapidly with the number and effective half-length of fractures, and reaches a plateau when they get large or long enough. Therefore, in order to achieve the maximum economic efficiency, the fracture quantity and effective half-length should be reasonably designed.

A new analytical method based on pressure transient analysis to estimate carbon storage capacity of depleted shales: A case study

In this paper, based on pressure transient analysis (PTA), a quick and reasonable analytical method for estimating CO2 storage capacity of depleted shales is introduced. Firstly, a CO2 seepage model for an injection well with constant injection rate is proposed in consideration of Knudsen diffusion, gas adsorption, and stress-sensitivity effect of permeability. Then, combined with Laplace transform and Pedrosa's substitution, the seepage model is solved and the transient pressure solutions of the injection well are obtained. At last, with these solutions, CO2 storage capacity can be easily estimated at an arbitrary injection pressure. To verify the proposed approach, a derived case from the New Albany Shale is studied. Furthermore, on the basis of the case, the influences of some critical parameters on CO2 storage capacity are analyzed.The research results demonstrate that there is a good agreement between the proposed method and the numerical method, with the maximum difference smaller than 1.5%. In addition, sensitive analysis shows that CO2 storage capacity increases with the increasing of stress-sensitivity coefficient, adsorption index, Knudsen diffusion coefficient and constrained injection pressure; it decreases with the increasing of storage ratio. It is also found that as constrained injection pressure increases, the effects of the parameters above on the storage capacity become more obvious.

Analytical Modeling and Artificial Neural Network (ANN) Simulation of Current-Voltage Characteristics in Graphene Nanoscroll Based Gas Sensors

Graphene nanoscrolls (GNSs) as a new category of quasi one-dimensional (1D) belong to the carbon-based nanomaterials, which have recently captivated the attention of researchers. The latest discoveries of outstanding characteristics of GNSs in terms of structural and electronic properties such as high mobility, controllable band gap, and tunable core size. Previous studies have shown the fact that graphene different structures such as carbon nanotube (CNT), bilayer graphene (BLG) and GNS experience changes in the electrical conductivity when expose to various gases. Therefore, these materials are proposed as a promising candidate for gas detection sensors. These are typically constructed on a field effect transistor (FET) based structure in which the GNS is employed as the channel between the source and the drain. In this study, an analytical model has been proposed and developed with the initial assumption that the gate voltage is directly proportional to the gas concentration as well as its temperature. The effect of gas adsorption on GNS surface makes the changes in GNS conductance which leads to the changes in the current of sensor consequently. This phenomenon is considered as sensing mechanism with proposed sensing parameters. Using the corresponding formula for GNS conductance, the proposed mathematical model is derived. Also, artificial neural network (ANN) algorithms have also been incorporated to obtain other models for the current-voltage (I-V) characteristic in which the analytical data extracted from current and previous related works has been used as the training data set. The comparative study of the results from ANN and the analytical models with the experimental data in hand shows a satisfactory agreement which validates the proposed models.

Adsorption behavior of Co anchored on graphene sheets toward NO, SO2, NH3, CO and HCN molecules

Abstract Based on the first-principles of density-functional theory (DFT), the effects of gas adsorption on the change in geometric stability, electronic structure and magnetic properties of graphene with anchored Co (Co–graphene) systems were investigated. A single Co adatom interacts much weaker with pristine graphene (Co/pri–graphene) than with the graphene containing a single vacancy (Co/SV–graphene). The Co dopant provides more electrons to the dangling bonds of carbon atom at defective site and exhibits more positive charges, which makes Co/SV–graphene less prone to be adsorbed by gas molecules in comparison to Co/pri–graphene. It is found that the electronic structure and magnetic properties of Co–graphene systems can be modulated by adsorbing gas molecules. Except the NH 3 molecule, the adsorbed NO, SO 2 , CO or HCN as electron acceptors on the Co/pri–graphene can exhibit semiconducting properties. Among the gas molecules, the strong adsorption of NO molecule can effectively regulate the magnetic properties of Co–graphene systems. Moreover, the stable configuration of Co/SV–graphene is more likely to be the gas sensor for detecting NO and SO 2 . The results validate that the reactivity of atomic-scale catalyst is supported on graphene sheets, which is expected to be potentially efficient in the gas sensors and electronic device.

Sensitivity Modelling of Graphene Nanoscroll-Based NO2 Gas Sensors

Graphene nanoscrolls (GNSs) as a new category of quasi one-dimensional (1D) belong to the carbon-based nanomaterials, which have recently captivated the attention of researchers. The latest discoveries of exceptional structural and electronic properties of GNSs like high mobility, controllable band gap, and tunable core size have become a great stimuli for graphene researchers. Due to the importance and critical role of nanoscale sensors and biosensors in medical facilities and human life, using a promising material like graphene has been widely studied to achieve better accuracy and sensitivity in these devices. Up until now, the majority of surveys conducted previously have focused on experimental studies for sensors family. Therefore, there is lake of analytical models in comparison to experimental surveys. In order to start and understand about the modelling of gas sensors structure, the field effect transistor(FET)-based structure is employed as a basic. In this study, graphene nanoscroll conductivity has been evaluated under the impacts which is induced by the adsorption of different values of NO2 gas concentration on GNS surface. So that, when GNS-gas sensor is exposed to NO2 gas molecules, the carrier concentration of GNS is changed which leads to the changes in the conductance, and consequently, in the current, this phenomenon is considered as sensing mechanism. The I–V characteristic of graphene nanoscroll-based gas sensor has been considered as a criterion to detect the effect of gas adsorption. In order to verify the accuracy of the proposed model, the results have been compared with the existing experimental works.

Effect of the Inert Gas Adsorption on the Bilayer Graphene to the Localized Electron Magnetotransport

Graphene has a fascinating property that the two-dimensional electron gas is easily accessible externally and it is challenging to investigate the effects of the adsorption of inert gases on graphene, which may be the least effective chemically and physically. We carry out the magnetotransport measurements of 4He-adsorbed bilayer graphene at low temperatures and the magnetic field B ranging from 0 to 4 T. The magnetoresistance ΔRxx change from the pristine graphene is measured as a function of gate voltage Vg and B for partial coverage of 1/10 (= 0.1) layers and one layer 4He-adsorbed graphene. The overall magnitudes of ΔRxx for one layer are larger than the one for 1/10 layers. Signs of ΔRxx depend on the Vg for the entire range of B, associated with the magnetoresistance oscillation owing to the weak localization in the pristine graphene.

Effect of gas adsorption on acoustic wave propagation in MFI zeolite membrane materials: experiment and molecular simulation.

The present study reports on the development of a characterization method of porous membrane materials which consists of considering their acoustic properties upon gas adsorption. Using acoustic microscopy experiments and atomistic molecular simulations for helium adsorbed in a silicalite-1 zeolite membrane layer, we showed that acoustic wave propagation could be used, in principle, for controlling the membranes operando. Molecular simulations, which were found to fit experimental data, showed that the compressional modulus of the composite system consisting of silicalite-1 with adsorbed He increases linearly with the He adsorbed amount while its shear modulus remains constant in a large range of applied pressures. These results suggest that the longitudinal and Rayleigh wave velocities (VL and VR) depend on the He adsorbed amount whereas the transverse wave velocity VT remains constant.