Fractal bet and FHH theories of adsorption: a comparative study

1989 ◽  
Vol 423 (1864) ◽  
pp. 169-188 ◽  
Keyword(s):  
Critical Evaluation ◽  
Power Laws ◽  
Wall Effects ◽  
Topological Dimension ◽  
Multilayer Adsorption ◽  
High Coverage ◽  
Adsorbed Phase ◽  
Bet Isotherm ◽  
Adsorption Of Gases ◽  
Bet Theory

Two theories of multilayer adsorption of gases, namely the BrunauerEmmett-Teller (bet) theory and the Frenkel-Halsey-Hill (fhh) theory, have recently been extended to the case of fractal substrates in a number of different ways. We present a critical evaluation of the various predictions. The principal results are the following. At high coverage, the fractal bet and fhh isotherms apply to mass and surface fractals, respectively. Both give characteristic power laws with D -dependent exponents ( D = fractal dimension of the substrate). The bet isotherm additionally depends on the topological dimension D top of the substrate. For fractal aggregates ( D top = 1) with D < 2, the adsorbed phase exists only in a highly disordered state. The bet theory is sensitive to multiple-wall effects (they affect prefactors); the fhh theory is not. For the fhh theory, detailed assessments of the approximations in the model are available. The predictions of the fhh theory have been observed on fractal silver surfaces.

scholarly journals Pickett Equation for the Description of Adsorption on Arbitrary Surfaces

2020 ◽  
Vol 4 (2) ◽  
pp. 17
Author(s):  
Volodymyr V. Kutarov ◽  
Eva Schieferstein ◽  
Shanath A. A. Jayaweera
Keyword(s):  
Fractal Dimension ◽  
Water Vapor ◽  
Coal Sample ◽  
Lunar Regolith ◽  
Theoretical Models ◽  
Multilayer Adsorption ◽  
Topological Approach ◽  
Adsorption Of Water ◽  
Adsorption Of Gases ◽  
Adsorption Of Water Vapor

The theory of multilayer adsorption of gases, namely the Pickett equation, has been developed to the case of adsorption on arbitrary surfaces in a molecular and a topological approach. We present the prediction of the fractal dimension for the surface of an adsorbent and for the set of interfaces generated by the growing of layers. The theoretical models correctly predict quantities and qualitative features of the experiment for two systems: adsorption of water vapor (T = 298 K) on the sample of lunar regolith and of nitrogen (T = 77 K) on a coal sample.

REVERSIBILITY IN PHYSICAL ADSORPTION

1955 ◽  
Vol 33 (2) ◽  
pp. 245-250 ◽  
Author(s):  
E. L. Pace ◽  
K. S. Dennis ◽  
S. A. Greene ◽  
E. L. Heric
Keyword(s):  
Heat Capacity ◽  
Adsorption Isotherms ◽  
Physical Adsorption ◽  
Zero Point ◽  
Solid Surfaces ◽  
Heats Of Adsorption ◽  
Calorimetric Measurements ◽  
Adsorbed Phase ◽  
Adsorption Of Gases ◽  
Calorimetric Studies

The question of reversibility and equilibrium is considered in relation to the physical adsorption of gases on finely divided solid surfaces. Conclusions are drawn from calorimetric measurements of (1) adsorption isotherms, (2) integral, differential, and isosteric heats of adsorption, and (3) heat capacity of the adsorbed phase for surface coverages of the order of a monolayer or less. In line with the preceding, results are presented and discussed for calorimetric studies involving (1) heats of adsorption and heat capacities of methane adsorbed on rutile between 80 and 140°K., (2) heats of adsorption of argon on rutile between 60 and 90°K., and (3) the zero point entropy of krypton adsorbed on rutile at a coverage of about 0.57 of the monolayer capacity.

scholarly journals Beyond Langmuir: surface-bound macromolecule condensates

2020 ◽  
Vol 31 (23) ◽  
pp. 2502-2508
Author(s):  
T. J. Mitchison
Keyword(s):  
Phase Separation ◽  
Lipid Bilayers ◽  
Cell Biology ◽  
Test Case ◽  
Surface Binding ◽  
Multilayer Adsorption ◽  
Low Concentrations ◽  
Binding Surface ◽  
Bet Theory ◽  
Physical Biochemistry

Macromolecule condensates, phase separation, and membraneless compartments have become an important area of cell biology research where new biophysical concepts are emerging. This article discusses the possibility that condensates assemble on multivalent surfaces such as DNA, microtubules, or lipid bilayers by multilayer adsorption. Langmuir isotherm theory conceptualized saturable surface binding and deeply influenced physical biochemistry. Brunauer-Emmett-Teller (BET) theory extended Langmuir’s ideas to multilayer adsorption. A BET-inspired biochemical model predicts that surface-binding proteins with a tendency to self-associate will form multilayered condensates on binding surfaces. These “bound condensates” are expected to assemble well below the saturation concentration for liquid–liquid phase separation, so they can compete subunits away from phase-separated droplets and are thermodynamically pinned to the binding surface. Tau binding to microtubules is an interesting test case. The nonsaturable binding isotherm is reminiscent of BET predictions, but assembly of Tau-rich domains at low concentrations requires a different model. Surface-bound condensates may find multiple biological uses, particularly in situations where it is important that condensate assembly is spatially constrained, such as gene regulation.

scholarly journals Isolation of Silica-Lignin Composites from Rice Husk and Their Adsorption to Cr(VI)

2018 ◽  
Vol 14 (2) ◽  
pp. 267 ◽  
Author(s):  
Yati B. Yuliyati ◽  
Seli Listiani ◽  
Solihudin Solihudin ◽  
Atiek Rostika Noviyanti
Keyword(s):  
Hexavalent Chromium ◽  
Rice Husk ◽  
Extraction Method ◽  
Metal Content ◽  
Adsorption Process ◽  
Agricultural Waste ◽  
Multilayer Adsorption ◽  
Sem Image ◽  
Bet Isotherm ◽  
Chromium Adsorption

<p>Rice husk is the most abundant agricultural waste in Indonesia. It can be used as a precursor for multifunctional materials such as silica-lignin composite for adsorbents. Silica-lignin can reduce heavy metal content in an industrial waste, such as the content of Cr(VI). This study aims to isolate and characterize silica-lignin composite, and determines the isotherm type of silica-lignin for hexavalent chromium adsorption. The isolation from rice husk used an alkali extraction method. Confirmation of typical functional groups in the silica-lignin composite was characterized by FTIR, while the morphology was characterized by SEM, respectively. The results reveal that the silica-lignin isolation was successfully performed.  FTIR spectra indicate a typical wavenumber of the silica-lignin.  The SEM image of the composite showed homogeneous morphology. The silica-lignin adsorption process on hexavalent chromium followed a Brunauer–Emmett–Teller (BET) isotherm type indicated by multilayer adsorption with a surface area of 948.8421 mg. g<sup>-1</sup><em>.</em></p>

Multilayer Adsorption of Gases on Heterogeneous Solid Surfaces

1975 ◽  
Vol 256O (1) ◽  
Author(s):  
W. Rudziński ◽  
S. Sokolowski ◽  
M. Jaroniec ◽  
J. Tóth
Keyword(s):  
Solid Surfaces ◽  
Multilayer Adsorption ◽  
Adsorption Of Gases ◽  
Heterogeneous Solid

Multilayer adsorption of gases in solids

2003 ◽  
Vol 219 (1-3) ◽  
pp. 187-192 ◽  
Author(s):  
Abderrahim Saber ◽  
S. Dal Toè ◽  
S. Lo Russo ◽  
G. Mattei
Keyword(s):  
Multilayer Adsorption ◽  
Adsorption Of Gases

THE DISCONTINUITY IN THE ADSORPTION OF GASES, VAPORS, AND LIQUIDS ON SOLID SURFACES AT THE CRITICAL TEMPERATURE UNDER CRITICAL PRESSURE: SYSTEM PROPYLENE-ALUMINA

1933 ◽  
Vol 9 (3) ◽  
pp. 240-251 ◽  
Author(s):  
H. E. Morris ◽  
O. Maass
Keyword(s):  
Critical Temperature ◽  
Liquid State ◽  
Critical Pressure ◽  
Solid Surfaces ◽  
Pressure System ◽  
Gaseous State ◽  
Adsorbed Phase ◽  
Adsorption Processes ◽  
Adsorption Of Gases ◽  
Adsorption Curve

An apparatus and a technique for studying the adsorption of gases, vapors and liquids on solid surfaces are described. The arrangement permits investigations in the region of the critical temperature and the critical pressure. Results with the system propylene and alumina are given. Adsorption from the gas and vapor phases indicates the formation of a surface complex which is unstable at low pressure and high temperature. The density of the adsorbed phase is greater than that of the bulk phase. There is no discontinuity in adsorption processes with a change from vapor state to gaseous state. No evidence was obtained of an increase in critical temperature on the surface of the solid. Adsorption does not occur from the liquid state, and there is a marked discontinuity in the adsorption curve with a change from liquid state to gaseous state. This is probably due to a change in the forces of attraction between liquid molecules and the solid as compared with the attraction between gaseous or vapor molecules and the solid surface. If this is the case it is further evidence for the discontinuity in the region of the critical temperature, which has been previously observed in other experiments in this laboratory.

Electron Microscopy of Metal-Matrix Composites

1970 ◽  
Vol 28 ◽  
pp. 404-405
Author(s):  
A. Lawley ◽  
M. R. Pinnel ◽  
A. Pattnaik
Keyword(s):  
Electron Microscopy ◽  
Metal Matrix Composites ◽  
Metal Matrix ◽  
Critical Evaluation ◽  
Elastic Behavior ◽  
Matrix Composites ◽  
Directionally Solidified ◽  
Fracture Characteristics ◽  
Broad Program

As part of a broad program on composite materials, the role of the interface on the micromechanics of deformation of metal-matrix composites is being studied. The approach is to correlate elastic behavior, micro and macroyielding, flow, and fracture behavior with associated structural detail (dislocation substructure, fracture characteristics) and stress-state. This provides an understanding of the mode of deformation from an atomistic viewpoint; a critical evaluation can then be made of existing models of composite behavior based on continuum mechanics. This paper covers the electron microscopy (transmission, fractography, scanning microscopy) of two distinct forms of composite material: conventional fiber-reinforced (aluminum-stainless steel) and directionally solidified eutectic alloys (aluminum-copper). In the former, the interface is in the form of a compound and/or solid solution whereas in directionally solidified alloys, the interface consists of a precise crystallographic boundary between the two constituents of the eutectic.

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