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In previous work [1] we showed an unusual temperature dependence for water adsorption in porous activated carbons, and hypothesized that the pore size plays a critical role in water adsorption in mesopores. In this paper, we shed further light on water adsorption in mesopores by investigating its dependence on temperature for a highly graphitized non-porous carbon black and a highly ordered mesoporous...
We have carried out an extensive computer simulation of argon adsorption on graphite at temperatures in the range 40 K–100 K, using a new molecular model for graphite, and compared our simulation results with new high-resolution experimental data. The new model accounts for: (1) The energetic corrugation of the graphene surface. (2) The smaller collision diameter of the carbon atoms (0.28 nm) in the...
Adsorption of methanol on a carbon black has been studied to investigate the effects of the separation distance and orientation of two functional groups on the adsorption isotherm and the isosteric heat. Monte Carlo simulation was carried out to study methanol adsorption on a graphene surface with two hydroxyl groups arranged in three different orientations: (1) outward, (2) co-directional, and (3)...
Isosteric heats of water and methanol adsorption on highly graphitized thermal carbon black have been studied using grand canonical Monte Carlo simulation to investigate the effects of the concentration of functional groups and temperature on the isosteric heats observed experimentally. The heat at zero loading is associated with the interaction between an adsorbate and the functional group. The variation...
Adsorption isotherms of water on porous carbons generally show large hysteresis loops whose origin is believed to be different from simple gases adsorption in mesoporous solids. In this paper, we discussed in details the behavior of water adsorption isotherms and their descending scanning curves for two carbons of different topologies, a highly graphitized thermal carbon black, Carbopack F, and a...
We propose a new method, using the ambient temperature adsorption of methanol in the Henry law region as a molecular probe, to determine the concentration of surface oxygen functional groups (Cα) on carbon adsorbents. Two adsorbents: porous A5 and non-porous Carbopack F have been chosen here as experimental examples. The theoretical Henry constant (Kα) is the product of the intrinsic interaction between...
A new and simple method, using water as a potential molecular probe, is proposed for the determination of the concentration of surface oxygen groups on carbon adsorbents. The procedure is based on a determination of the Henry constant between a water molecule and a functional group from the volume integration of the Boltzmann factor over the accessible space around the functional group. Three porous...
Adsorption of water on graphitized carbon black at various temperatures has been studied with a new molecular model of graphitized carbon black using Monte Carlo simulation. The model is a collection of graphene layers, modelled by the Steele potential, and a number of phenol groups forming clusters of various sizes which are placed randomly at the graphene edge sites to give an O/C ratio of 0.006...
Experiments at several temperatures were carried out for adsorption of non-polar and polar fluids on a highly graphitized carbon black, Carbopack F, which is composed of a basal plane of graphene and functional groups at the edges of the graphene layers. By comparing the experimental Henry constants with the theoretical Henry constants, calculated for adsorption on an ideal basal plane of graphite,...
Water adsorption isotherms in porous carbons were measured at temperatures in the range 263 and 298K. To investigate the role of porous structure, we used RF-50, RF-100, RF-200, derived from resorcinol–formaldehyde cryogels, and an activated carbon (B-AC) derived from bamboo. RF-50 is microporous while RF-100 and RF-200 are micro- and mesoporous with non-overlapping distributions of micropores and...
Adsorption of nitrogen is commonly used to characterise porous carbon solids, and an important prerequisite for a good characterization is that the molecular model for nitrogen should give the correct description of adsorption on a graphite surface over a range of temperatures. To investigate the role of the molecular shape and quadrupole of nitrogen at temperatures below the boiling point we carried...
Adsorption isotherms and isosteric heats have been studied experimentally and by computer simulation for the krypton-graphitic hexagonal pore and krypton–graphite planar surface systems in the 60–109K temperature range. The existence of a 2D transition in the sub-monolayer film on the basal plane of graphite that is observed experimentally is confirmed by the computer simulation results, but this...
Nitrogen-doped porous carbons (N-RFCC) were prepared by NH 3 N 2 mixture gas treatment at high temperature during the carbonization process on resorcinol–formaldehyde cryogels. To show the role of N-doping on the adsorption behavior we carried out water adsorption, and it was found that the amount of water adsorbed is directly related to the nitrogen content over the low pressure region...
Accessible volume, geometrical area and accessible pore size distribution are the fundamental structural parameters in the characterization of porous solids. We provide a novel “inverse” procedure, which is based on the mass balance and an MC optimization scheme, to determine these parameters from the analysis of experimental adsorption isotherms for a number of commonly used activated carbons: BPL,...
A new model is developed to describe the adsorption and desorption branches of water adsorption in activated carbon. This model is an extension of a previous adsorption model proposed by Do and Do [Do DD, Do HD. A new model for water adsorption in activated carbon. Carbon 2000;38:767–73] to account for desorption. The desorption branch is resulted from the relaxation of water clusters inside the micropore...
A mimetic method based on Monte Carlo simulation is proposed to generate a molecular model of char. This char model consists of crystalline and amorphous phases, which are heated and cooled during the simulation of the carbonization process. Resultant char shows irregular shape and interconnected pores whose properties depend on the percentage of non-organized carbon and the carbonization temperature...
A grand canonical Monte Carlo simulation (GCMC) is used to study the adsorption of argon and nitrogen on non-graphitized carbon black. The surface is assumed to be finite in length and composed of three graphene layers, the top layer of which contains defects. The isotherm obtained for the non-graphitized carbon shows a smooth S-shaped type while that obtained for the perfect graphene layer shows...
Solvation pressure due to adsorption of fluids in porous materials is the cause of elastic deformation of an adsorbent, which is accessible to direct experimental measurements. Such a deformation contributes to the Helmholtz free energy of the whole adsorbent–adsorbate system due to accumulation of compression or tension energy by the solid. It means that in the general case the solid has to be considered...
The application of nonlocal density functional theory (NLDFT) to determine pore size distribution (PSD) of activated carbons using a nongraphitized carbon black, instead of graphitized thermal carbon black, as a reference system is explored. We show that in this case nitrogen and argon adsorption isotherms in activated carbons are precisely correlated by the theory, and such an excellent correlation...
Adsorption of pure nitrogen, argon, acetone, chloroform and acetone–chloroform mixture on graphitized thermal carbon black is considered at sub-critical conditions by means of molecular layer structure theory (MLST). In the present version of the MLST an adsorbed fluid is considered as a sequence of 2D molecular layers, whose Helmholtz free energies are obtained directly from the analysis of experimental...
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