Number Of Adsorbed Layers Research Articles

Porous Carbon Nanofibers with Heteroatoms Doped by Electrospinning Exhibit Excellent Acetone and Carbon Dioxide Adsorption Performance: The Contributions of Pore Structure and Functional Groups.

Rich chemical properties and a well-developed pore structure are the key factors of porous materials for gas storage. Herein, rich heteroatom-doped porous carbon nanofibers (U1K2-X) with a large surface area were prepared by electrospinning followed by potassium hydroxide (KOH) activation. Low-cost urea was chosen as the nitrogen source and structural guiding agent. U1K2-X have a high specific surface area (628–2688 m2 g–1), excellent pore volume (0.468–1.571 cm3 g–1), and abundant nitrogen (2.5–12.8 atom %) and oxygen (4.5–12.5 atom %) contents. Acetone and carbon dioxide were used as target adsorbents to evaluate the adsorption properties of U1K2-X by experiments. These U1K2-X exhibit excellent adsorption performance (260.03–955.74 mg g–1, 25 °C, 18 kPa) and multilayer adsorption (the adsorption layer number n > 2) for acetone, which is mainly attributed to the large specific surface area and pore volume. Besides this, the carbon dioxide uptake reached 2.73–3.34 mmol g–1 at 25 °C. This was attributed to the combination of high nitrogen–oxygen contents and microporous structure. Furthermore, U1K2-X show the desirable repeatability. This study provides a new direction for the preparation of heteroatom-doped porous carbon nanofibers, which will be a promising material for gas adsorption.

Modeling Adsorption in Silica Pores via Minkowski Functionals and Molecular Electrostatic Moments

Capillary condensation phenomena are important in various technological and environmental processes. Using molecular simulations, we study the confined phase behavior of fluids relevant to carbon sequestration and shale gas production. As a first step toward translating information from the molecular to the pore scale, we express the thermodynamic potential and excess adsorption of methane, nitrogen, carbon dioxide, and water in terms of the pore’s geometric properties via Minkowski functionals. This mathematical reconstruction agrees very well with molecular simulations data. Our results show that the fluid molecular electrostatic moments are positively correlated with the number of adsorption layers in the pore. Moreover, stronger electrostatic moments lead to adsorption at lower pressures. These findings can be applied to improve pore-scale thermodynamic and transport models.

Molecular simulations of oil adsorption and transport behavior in inorganic shale

Oil production from shale has grown dramatically in North America, and has the potential to do so globally. Understanding the adsorption and transport of liquid hydrocarbon through nanopores of inorganic minerals is crucial not only to develop liquid-rich shale reservoirs, but also to grasp oil migration from deeply buried extremely low permeability source rocks. In this work, the adsorption and transport behavior of n-octane (pentane, dodecane) confined in nanoscale dolomite slit pores have been investigated by grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The adsorbed phase density, molecular-scale structures at the interface, self-diffusion are then calculated and analyzed by equilibrium molecular dynamics (EMD). The number of adsorption layers is related to the size of pore. Increasing temperature will decrease the amount adsorbed, while pressures have little effect on amount adsorbed. Near the dolomite surface, the n-octane molecules adopt a preferential alignment parallel to the substrate, better packed and diffuse more slowly. Consider three alkanes, the long alkanes (octane, dodecane) are more easily to be adsorbed on dolomite surface. Lastly, the nonequilibrium molecular dynamics (NEMD) have been used to study the pressure-driven flow of n-octane in dolomite slits, flow characterization, viscosity, and slip length are analyzed. A larger driving force will increase slip length, while having only a negligible impact on the effective viscosity of the n-octane.

Microscopic mechanism of methane adsorption in shale: Experimental data analysis and interaction potential simulation

The adsorbed methane in shale determines the geological reserves of shale gas and production of the well. Therefore, it is of great importance to clarify the microscopic mechanism of methane adsorption in shale for evaluating the geological condition and formulating exploitation plan. In this study, the experimental data and the simulation result were combined to research the microscopic mechanism of methane adsorption in shale. The experimental data for 99 groups of low-temperature nitrogen adsorption and methane isothermal adsorption were collected, to calculate the number of adsorption layers of methane in shale at the micro-level. The surface, microfracture and micropore structures of the organic matter in shale were constructed by graphite structure with the hydroxyl group. Thereafter, they were used to simulate the interaction potential of the organic matter on methane molecules and the adsorption layer's number by using the theory of intermolecular interaction potential field. Furthermore, the effects of different fracture widths and pore diameters on methane adsorption were analyzed and verified. The results show that the adsorption capacity of methane in shale is related to shale's structure, and the order of the adsorption capacity is surface < microfracture < micropore. Meanwhile, the multilayer adsorption can occur in microfractures with a width of 1.44–1.59 nm and micropores with a diameter of 1.49–1.83 nm, whereas the surface structure just can be the monolayer adsorption. These quantitatively results establish a foundation for the development of adsorption theory for methane in the shale.

Xylene removal from dilute solution by palm kernel activated charcoal: Kinetics and equilibrium analysis

Xylene is an aromatic hydrocarbon that is a highly toxic compound. Therefore, it is essential to remove this component from wastewater before discharging it to the environment. In this research work, palm kernel biomass was activated chemically by H3PO4 and synthesized activated charcoal was applied to separate xylene from aqueous media. The prepared activated charcoal was characterized using FTIR, BET, SEM, pHzpc measurement, Boehm analysis methods. The characterization tests indicated that the produced activated carbon has acidic character with various functional groups and micropores structure. The values of external mass transfer coefficients ranged from 1.87×10-5 to 1.90×10-5. By increasing the temperature, the pore and surface diffusion coefficients were increased from 1.15×10-9 to 1.91×10-9 and 6.98×10-16 to 7.58×10-16, respectively. Sensitivity analysis indicated which the pore diffusion and film diffusion are the main mass transfer parameters. Equilibrium analysis also revealed that the multilayer model with saturation could well describe the data. The number of adsorbate ions for one site, the number of adsorption layers, density of receptor site, and the energy of adsorption at layers were determined using statistical physics modelling. The maximum capacity of prepared activated charcoal at the experimental condition for xylene adsorption was 23.48 mg g-1.

Kondo screening and spin excitation in few-layer CoPc molecular assembly stacking on Pb(111) surface: A DFT+HEOM study

Transition metal phthalocyanine molecules adsorbed on a metal substrate exhibit rich spin-related phenomena such as magnetic anisotropy, spin excitation, and Kondo effect. In this work, we investigate theoretically few-layer cobalt phthalocyanine (CoPc) molecular assembly stacking on Pb(111) surface with the use of a combined density functional theory (DFT) and hierarchical equations of motion (HEOM) approach. Calculation results indicate that the local spin properties of CoPc/Pb(111) composites depend critically on the number of adsorption layers. The first layer of CoPc on the Pb(111) surface serves as a spin-insulating buffer, while the CoPc molecules in the second layer exhibit spin-1/2 Kondo effect with a Kondo temperature of about 22 K. In a triple-layer CoPc assembly stacking on Pb(111), the antiferromagnetic coupling between the second and third layers leads to local spin-flip excitations under finite bias voltages, which gives rise to characteristic signatures in the differential conductance spectra. The DFT+HEOM approach thus provides a practical means for investigating the local electronic and spin properties of two-dimensional molecular assemblies adsorbed on the metal surface. The insights obtained from the first-principles based simulations could be useful for experimental manipulation or design of magnetic composite systems.

FRACTAL PORE STRUCTURE MODEL AND MULTILAYER FRACTAL ADSORPTION IN SHALE

The complex structure and surface property of porous media have significant impact on its accumulation and adsorption capacity. Based on the fractal theory, this paper presents a fractal pore structure model for shales. The effect of different pore structures on fractal dimension is discussed, and the influence of fractal dimension and pore size distribution on porosity is also analyzed. It is shown that the fractal dimension D decreases with the increase of structure parameter q/m for a certain pore diameter ratio, and porosity has positive relationship with fractal dimension. This paper also presents a multilayer fractal adsorption model which takes into account the roughness of adsorption surface by using fractal theory. With the introduction of pseudo-saturated vapor pressure in the supercritical temperature condition, the proposed adsorption model can be applied into a wider range of temperature. Based on the low-pressure nitrogen adsorption and methane isothermal adsorption experiments, the effect of fractal dimension on the adsorption behavior of shales is discussed. Fractal dimension has significant impact on the surface adsorption property and adsorption layer number n. The monolayer saturated adsorption volume Vm increases with the increase of D, while parameter C has the opposite variation trend. Finally, the optimal combination of fractal parameters for describing pore structure of shale samples is selected.

Adsorption of a Non-Woven Fabric with Activated Carbon for CO&lt;sub&gt;2&lt;/sub&gt;

The adsorption of CO2 on a non-woven fabric with activated carbon before and after dipping treatment has been studied. It has been found that dipping treatment with Na2CO3 and KOH can improve the adsorption of CO2 on the non-woven fabric. KOH is a better dipping agent than Na2CO3. High temperature is beneficial to the adsorption of CO2 on the fabric dipped with KOH. With increasing relative humidity, the adsorption efficiency is decreased for both original fabric and that dipped with KOH. Increasing adsorption layer number can improve adsorption efficiency. However, when the number of adsorption layers exceeds 3 the increased amplitude of adsorption efficiency is obviously reduced, while the pressure loss of the system is remarkably increased.

Polymolecular adsorption of gases and its relation to gas state parameters

The relationship between processes proceeding in a gas phase and the polymolecular adsorption of gas molecules on a solid surface arranged in the gas volume was studied. The developed description allows for the removal of molecules from the gas phase both through their adsorption and in the course of gas condensation with the formation of liquid microparticles in the gas volume. The description of the latter process was proposed to give physically reasonable results under all representable changes in process conditions. With consideration for the corresponding dependence, a gas state equation was obtained to describe gas compression and condensation in an explicit form. It was demonstrated that the simultaneous occurrence of condensation in a gas phase and adsorption on a solid surface is responsible for obtaining typical polymolecular adsorption isotherms also in the case that surface coverage proceeds according to the Langmuir mechanism. A procedure was developed to calculate, based on a single experimental isotherm, the amount of adsorption sites on a surface (surface area), the number of adsorbed layers on this surface, and the constants responsible for the adsorption of the first and subsequent layers.

Adsorption of Volatile Organic Compounds on Soil and Prediction of Desorption Breakthroughs

Vapor extraction of volatile organic compounds from soil was investigated by performing adsorption and desorption experiments of trichloroethylene, trichloroethane, and chlorobenzene on soil particles. The adsorption breakthrough curves were obtained using a dynamic response technique based on frontal analysis chromatography. The shape of the breakthrough curves indicated that the adsorption process was close to an ideal adsorption system of no mass transfer resistance, no axial dispersion, and infinitesimal width of mass transfer zone. The adsorption isotherms were BET Type I for trichloroethylene and trichloroethane, and BET Type II for chlorobenzene. Two types of desorption profiles were observed depending on the compounds, i.e., the continuously decreasing profiles of trichloroethylene and trichloroethane and the stepwise decreasing profiles of chlorobenzene. The desorption profiles of trichloroethylene and trichloroethane were simulated using a local equilibrium theory which indicated that desorption behavior was independent of the number of adsorption layers on soil. For chlorobenzene, the monolayer desorption was the rate-controlling step of the overall desorption process. The effect of moisture on desorption efficiency was significant for chlorobenzene, which showed more unfavorable desorption behavior than trichloroethylene and trichloroethane.