scholarly journals The Mo-Co-Al2O3 System. II) Model of Adsorption of Molybdenum on Al2O3 and on Co-Al2O3

1988 ◽  
Vol 5 (1) ◽  
pp. 57-64 ◽  
Author(s):  
M.I. Morales ◽  
M.N. Blanco ◽  
H.J. Thomas
Keyword(s):  
Adsorption Isotherms ◽  
Adsorption Mechanism ◽  
Equilibrium Constants ◽  
Spectroscopic Studies ◽  
Experimental Results ◽  
Equilibrium Adsorption ◽  
Adsorption Model ◽  
Adsorption Sites ◽  
Polymeric Species ◽  
Two Systems

A model which interprets the equilibrium adsorption of molybdenum on Al2O3 and on Co-Al2O3 is presented. This model assumes the adsorption of monomelic and polymeric species of molybdenum on two different adsorption sites of the support. It is proposed a) that the adsorption mechanism can be represented by two independent adsorption reactions; b) that each species is adsorbed only on one type of site, and c) that the adsorption isotherms can be represented by the sum of a Langmuir type expression for the monomer and a sigmoidal one for the polymer. By applying this model to the experimental isotherms obtained for the two systems under study (Mo/Al2O3 and Mo/Co-Al2O3), the equilibrium constants for adsorption on site 1 (K,) and on site 2 (K2) and the numbers of adsorption sites S1 and S2 have been estimated. This adsorption model was confirmed by experimental results data and by spectroscopic studies.

Competitive transport of cadmium and lead through a natural porous medium: influence of the solid/liquid interface processes

2003 ◽  
Vol 48 (3) ◽  
pp. 9-16 ◽  
Author(s):  
A. Bianchi ◽  
M. Petrangeli Papini ◽  
A. Corsi ◽  
P. Behra ◽  
M. Beccari
Keyword(s):  
Liquid Interface ◽  
Equilibrium Adsorption ◽  
Adsorption Model ◽  
Adsorption Sites ◽  
Advection Dispersion ◽  
Transport Behaviour ◽  
Cadmium And Lead ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Medium Influence

Contaminated groundwater typically contains different metal contaminants which may compete with each other for the same adsorption sites. Understanding the fate of these micro-pollutants is of primary importance for the assessment of the risk associated with their dispersion in the environment and for the evaluation of the most appropriate remediation technology. In this regard, column techniques can be considered as useful tools both to perform transport experiments and to obtain equilibrium adsorption data without any perturbation of the actual solid/liquid interface. Cd and Pb monocomponent step column experiments were used to obtain adsorption isotherms on a natural aquifer material. A General Composite approach was used to define the equilibrium adsorption model characterized by two types of sites (ion-exchange and surface complexation sites). Coupling the adsorption model with the Advection-Dispersion equation (by IMPACT code) allowed us to well represent the monocomponent step experiments. The model was successfully used to predict the competitive Cd and Pb transport behaviour. Cd peaks of concentration due to Pb competition were experimentally observed and simulated by the model. This behaviour can be described only by an accurate modelling of the interaction and cannot be predicted by simple isotherms (such as Langmuir or Freundlich type).

scholarly journals Adsorption of tetracyclines on marine sediment during organic matter diagenesis

2013 ◽  
Vol 67 (11) ◽  
pp. 2616-2621 ◽  
Author(s):  
Ying-Heng Fei ◽  
Xiao-Yan Li
Keyword(s):  
Experimental Study ◽  
Organic Matter ◽  
Marine Sediment ◽  
Dynamic Process ◽  
Emerging Pollutants ◽  
Experimental Results ◽  
Sediment Organic Matter ◽  
Artificial Sediment ◽  
Adsorption Sites ◽  
Organic Products

The effect of decomposition and diagenesis of sediment organic matter (SOM) on the adsorption of emerging pollutants by the sediment has been seldom addressed. In the present experimental study, artificial sediment was incubated to simulate the natural organic diagenesis process and hence investigate the influence of organic diagenesis on the adsorption of tetracyclines (TCs) by marine sediment. During a period of 4 months of incubation, SOM initially added into the sediment underwent biodegradation and diagenesis. The results showed an early decrease in TC adsorption by the sediment, which was likely caused by the competition between the microbial organic products and TC molecules for the adsorption sites. Afterward, TC adsorption by the sediment increased significantly, which was mainly due to the accumulation of condensed SOM. The experimental results indicate the interactions between TCs and the sediment during the dynamic process of SOM diagenesis. Moreover, the remaining SOM is shown to have an increasing affinity with the antibiotics.

scholarly journals Water and Carbon Dioxide Adsorption on CaO(001) Studied via Single Crystal Adsorption Calorimetry

2021 ◽  
Author(s):  
J. Seifert ◽  
S. J. Carey ◽  
S. Schauermann ◽  
S. Shaikhutdinov ◽  
H.-J. Freund
Keyword(s):  
Adsorption Energy ◽  
Adsorbed Water ◽  
Spectroscopic Studies ◽  
Detector Response ◽  
Adsorption Calorimetry ◽  
Instrument Response Function ◽  
Line Shapes ◽  
Adsorption Sites ◽  
Saturation Coverage ◽  
Initial Adsorption

AbstractA new method to analyze microcalorimetry data was employed to study the adsorption energies and sticking probabilities of D2O and CO2 on CaO(001) at several temperatures. This method deconvolutes the line shapes of the heat detector response into an instrument response function and exponential decay functions, which correspond to the desorption of distinct surface species. This allows for a thorough analysis of the adsorption, dissociation, and desorption processes that occur during our microcalorimetry experiments. Our microcalorimetry results, show that D2O adsorbs initially with an adsorption energy of 85–90 kJ/mol at temperatures ranging from 120 to 300 K, consistent with prior spectroscopic studies that indicate dissociation. This adsorption energy decreases with increasing coverage until either D2O multilayers are formed at low temperatures (120 K) or the surface is saturated (> 150 K). Artificially producing defects on the surface by sputtering prior to dosing D2O sharply increases this adsorption energy, but these defects may be healed after annealing the surface to 1300 K. CO2 adsorbs on CaO(001) with an initial adsorption energy of ~ 125 kJ/mol, and decreases until the saturation coverage is reached, which is a function of surface temperature. The results showed that pre-adsorbed water blocks adsorption sites, lowers the saturation coverage, and lowers the measured adsorption energy of CO2. The calorimetry data further adds to our understanding of D2O and CO2 adsorption on oxide surfaces.

scholarly journals Statistical Mechanical Model of Gas Adsorption in a Metal-Organic Framework Harboring a Rotaxane Molecular Shuttle

2020 ◽  
Author(s):  
Jonathan Carney ◽  
David Roundy ◽  
Cory M. Simon
Keyword(s):  
Mechanical Model ◽  
Gas Adsorption ◽  
Adsorption Properties ◽  
Temperature Sensitive ◽  
Adsorption Model ◽  
Adsorption Sites ◽  
Statistical Mechanical Model ◽  
Metal Organic ◽  
Statistical Mechanical ◽  
Molecular Shuttle

Metal-organic frameworks (MOFs) are modular and tunable nano-porous materials with applications in gas storage, separations, and sensing. Flexible/dynamic components that respond to adsorbed gas can give MOFs unique or enhanced adsorption properties. Here, we explore the adsorption properties that could be imparted to a MOF by a rotaxane molecular shuttle (RMS) in its pores. In the unit cell of an RMS-MOF, a macrocyclic wheel is mechanically interlocked with a strut of the MOF scaffold. The wheel shuttles between stations on the strut that are also gas adsorption sites. At a level of abstraction similar to the seminal Langmuir adsorption model, we pose and analyze a simple statistical mechanical model of gas adsorption in an RMS-MOF that accounts for (i) wheel/gas competition for sites on the strut and (ii) gas-induced changes in the configurational entropy of the shuttling wheel. We determine how the amount of gas adsorbed, position of the wheel, and differential energy of adsorption depend on temperature, pressure, and the interactions of the gas/wheel with the stations. Our model reveals that, compared to a rigid, Langmuir material, the chemistry of the RMS-MOF can be tuned to render gas adsorption more or less temperature-sensitive and to release more or less heat upon adsorption. The model also uncovers a non-monotonic relationship between the temperature and the position of the wheel if gas out-competes the wheel for its preferable station.

ADSORPTION SITES OF THE PRODUCTS OF GeH4 ON ASYMMETRIC Si(100)(2×1) SURFACE

2004 ◽  
Vol 18 (08) ◽  
pp. 1191-1202
Author(s):  
ŞENAY KATıRCıOĞLU
Keyword(s):  
Density Functional ◽  
Geometry Optimization ◽  
Density Functional Theory Method ◽  
Adsorption Model ◽  
Functional Theory ◽  
Adsorption Models ◽  
Adsorption Sites ◽  
Asymmetric Dimer ◽  
Adsorption Energies ◽  
Relative Adsorption

The decomposition of GeH 4 on Si (100)(2×1) was investigated on different adsorption models of fragments using density functional theory method. The most probable adsorption model of fragments corresponding to the growth steps of SiGe film has been obtained by geometry optimization and single value total energy calculations. The relative adsorption energies of GeH 3, GeH 2 and GeH have been found to be -5.6, -5.1, and -4.5 eV for their most probable adsorption models respectively. It has been found that, the asymmetric dimer bond rows of Ge on Si (100) surface can be constructed by following the adsorption models corresponding to the relative adsorption energies of GeH 3, GeH 2 and GeH .

scholarly journals Criterion for the Quantitative Assessment of Ideal Conditions in Chromatography

1989 ◽  
Vol 6 (4) ◽  
pp. 212-218 ◽  
Author(s):  
A. V. Larin
Keyword(s):  
Adsorption Isotherms ◽  
Quantitative Assessment ◽  
Plate Theory ◽  
Quantitative Relationship ◽  
Equilibrium Adsorption ◽  
Absolute Length ◽  
Independent Variable ◽  
Practical Recommendations

The quantitative relationship between the plate theory variant model of equilibrium adsorption in which time is the only independent variable and the theory of ideal chromatogaphy has been evaluated. It has been shown that an approach to ideal conditions depends directly on an increase in the relative (or absolute) length of the column. Practical recommendations on the choice and assessment of conditions to verify the measurement of adsorption isotherms and on the calculation of chromatographic processes in accordance with the theory of ideal chromatography are given.

Sign in / Sign up

Export Citation Format

Share Document