Hysteresis in the physical adsorption of nitrogen on bone char and other adsorbents

Gleysteen, L.F.; Deitz, Victor R.

doi:10.6028/jres.035.013

Cited by 18 publications

(13 citation statements)

References 6 publications

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“…All PNDCs show similar shaped curves, with a similar contribution of hysteresis. A hysteresis loop refers to the space in each isotherm where the adsorption and desorption curves do not overlap . From IUPAC standards of sorption isotherms, all PNDCs display a type 4 isotherm.…”

Section: Data Analysis/resultsmentioning

confidence: 99%

“…A hysteresis loop refers to the space in each isotherm where the adsorption and desorption curves do not overlap. [49] From IUPAC standards of sorption isotherms, all PNDCs display a type 4 isotherm. These isotherms are characterized by a distinct hysteresis loop that is indicative of mesopores on the carbon-based surface.…”

Section: Brunauer-emmet-teller Analysismentioning

confidence: 99%

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Renewable‐Resource‐Based Waste Materials for Supercapacitor Application

et al. 2019

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Herein, renewable resource‐based waste materials (used tea leaves and molasses) were utilized as inexpensive and renewable carbon sources to develop Phosphorus and Nitrogen co‐doped Carbon (PNDC) materials for supercapacitor application. A prompt, low cost, single step, green and facile microwave assisted process was utilized to prepare PNDC materials using the aforementioned biomass. Concentration of the doping elements (P and N) was altered in the resulting PNDC materials by varying the mole ratio of used tea/molasses and ammonium polyphosphate (APP) in the reaction mixture. APP served as the Phosphorus and Nitrogen source as well as the microwave absorber. Detailed characterization of all four PNDCs ‐ two derived from molasses (MOLPNDCs) and two from used tea leaves (TEAPNDCs), were performed to investigate their supercapacitor performance. These materials were characterized both physically via BET, XPS, and SEM analysis and electrochemically via cyclic voltammetry, in both 1 M H2SO4 and 6 M KOH. Pore size, surface area, and elemental compositions of each PNDC was analyzed to investigate the critical parameter for supercapacitor performance of the materials. Among all PNDCs, MOLPNDC‐1 exhibited exceptionally high specific capacitance values of 160 Fg−1 in 6 M KOH electrolyte due to highly mesoporous structure and appropriate Nitrogen content. MOLPNDC‐1 was also found to be stable under continuous cycling for 1500 cycles in both acidic and alkaline conditions.

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Section: Data Analysis/resultsmentioning

confidence: 99%

Section: Brunauer-emmet-teller Analysismentioning

confidence: 99%

Renewable‐Resource‐Based Waste Materials for Supercapacitor Application

et al. 2019

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“…As time-dependent results presented in this article are expressed in terms of dimensionless time, it is useful to have an order of magnitude for t r . According to an article by Gleysteen and Deitz 22 published in 1945 on the sorption of nitrogen on carbon adsorbents, steady state is attained in about 20 min, meaning that sorption does not (1984), in Ruthven's book on adsorption, 23,24 sorption experiments of ethane on Linde 4A zeolite are cited, showing about the same time to steady state. Somewhat more extensive measurements were reported in 2010 by Battistutta et al 8 on the sorption of methane, nitrogen, and carbon dioxide on dry coal.…”

Section: Background Materialsmentioning

confidence: 99%

Dynamics of Monolayer Physisorption in Homogeneous Mesoporous Media

Papatzacos

2019

ACS Omega

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A model for monolayer physisorption of a onecomponent gas on the pore surface of a homogeneous macroporous or mesoporous porous medium is presented. It originates from an averaging over many pores of a macroporous medium filled with a onecomponent fluid. The resulting model does not assume anything about pore shape, but assumes that the pores are so large that capillary condensation does not occur. Mathematically, the model gives coverage as the solution of an ordinary, first-order, differential equation, where the time derivative of coverage is proportional to the difference between the chemical potential of the adsorbate and the chemical potential of the ambient gas. Coverage is determined by the ambient gas density, with temperature, adsorbate critical temperature, and the Henry adsorption constant as parameters. The rest of this abstract describes what is deduced from the equations of the model. Adsorbate phase transitions are built into the model by the use of van der Waals equations of state. Equilibrium isotherms are derived from the equality of the chemical potentials. The differential equation for coverage makes it possible to determine the mathematical stability of the equilibrium isotherms, and a number of properties of the isotherms are derived, the most important being as follows: (i) an adsorbate phase transition is always accompanied by a well-defined hysteresis loop, although "loop" is somewhat misleading as its vertical boundaries do not consist of equilibrium states; (ii) the vertical boundaries are exactly located; (iii) the upper and lower boundaries consist of states that are mathematically stable, while being either physically stable or metastable, and if physical metastability is the case, then the actual state of the adsorbate (mono-or bi-phasic) will not be visible on the equilibrium isotherm. The shapes of the equilibrium isotherms are largely determined by the value of the Henry constant, whether the isotherms are subcritical or supercritical. Expressions for the location of an equilibrium isotherm's region of fastest variation and for the locations of the vertical boundaries of its hysteresis loop are found that also show the importance of Henry's constant. Dynamical, that is, time-dependent isotherms are presented for the case describing the variation of coverage resulting from forcing the ambient gas to undergo a compression− decompression loop. Two subcases are considered: the subcritical and the supercritical adsorbate. It is shown that coverage in terms of ambient pressure exhibits closed loops, even in supercritical isotherms. However, supercritical loops shrink when the cycle time increases, reminiscent of rate-dependent hysteresis observed in piezoelectricity. The model is used to interpret two experiments on the sorption of CO 2 and CH 4 on coal that showed hysteresis loops in isotherms of supercritical adsorbates and that were originally interpreted as leading to different Henry constants for adsorption and for desorption. The interpretation set forth here uses the inherent d...

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“…The evidence for interpreting the isotherms as an indication of water being held on the charcoal by capillary condensation is also strong: (1) No satisfactory explanation of hysteresis in desorption has so far been advanced for any process other than capillary condensation. A recent paper by Gleysteen and Deitz (72) suggested that if one applies the multilayer theory of Brunauer, Emmett, and Teller to the adsorption isotherms at high relative pressures in place of the capillary condensation theory and then assumes that desorption involves a larger heat than adsorption, hysteresis can be accounted for. It remains to be explained why the heat of desorption should be larger than the heat of adsorption.…”

Section: B Rate Of Adsorption Of Watermentioning

confidence: 99%