Adsorption isotherms Langmuir-Freundlich isotherm

Fe Oj, FejO, nanocomposites, oxidation polymerization, Langmuir adsorption isotherm, Freundlich adsorption isotherm, Dubinin-Radushkevich adsorption isotherm, Tempkin adsorption isotherm, pseudo-first-order kinetic. Pseudo-second-order kinetic, removal efficiency, adsorption capacity... 

Adsorption Isotherms of Langmuir Type and Freundlich Type... 

Classical Adsorption Isotherms of Langmuir, Freundlich and Tfimkin. 107... 

The adsorption capacity of activated carbon may be determined by the use of an adsorption isotherm. The adsorption isotherm is an equation relating the amount of solute adsorbed onto the solid and the equilibrium concentration of the solute in solution at a given temperature. The following are isotherms that have been developed Freundlich Langmuir and Brunauer, Emmet, and Teller (BET). The most commonly used isotherm for the application of activated carbon in water and wastewater treatment are the Ereundlich and Langmuir isotherms. The Freundlich isotherm is an empirical equation the Langmuir isotherm has a rational basis as will be shown below. The respective isotherms are ... 

Adsorption isotherm of Langmuir-Freundlich for multi-component is defined by... 

Mathematical analysis of adsorption is beyond the scope of this entry, but it is important to point out that the equilibria used are often based on adsorption isotherms. The three isotherms shown in Fig. 3 occur in practice, although linear isotherms are very rare. The nonlinearity of the Langmuir and Freundlich isotherms makes scale-up and analysis tedious. The Freundlich isotherm is based on empirical data analysis and occurs more commonly in practice than the Langmuir isotherm, which has a theoretical basis. 

Equation 2.66 shows that the velocity of a chemical solute concentration Vq is slower than the solution (water) velocity v by a retardation factor Rq. The retardation is caused by the adsorption of the chemical on the solid. Adsorption can be defined using the Freundlich isotherm or Langmuir isotherm. The general form of the Freundlich isotherm is... 

Tables VI to VIII show the summary of the linear regression equations and values of correlation coefficient R, determined firom the adsorption isotherms of Langmuir, Freimdlich and BET m the treatment of resorcmol 100 mg/1,300 mg/l and 500 mg/l respectively. The average values of the correlation coefficient at the three resorcinol concentrations were 0.987,0.966 and 0.939 respectively for the Langmuir, Freundlich and the BET equations.

Among the isotherms that portray the adsorptive equilibrium, the Langmuir isotherm, Freundlich and Dubinin-Raduskevich were cited. For the adsorptive kinetic models, stand out the Lagergren, in models of pseudo-first order and pseudo-second order. 

Figure 5.5. Variation of the heat of adsorption q (Qad in the text) with coverage for various isotherms I - Langmuir isotherm, II - Temkin isotherm. III - Freundlich isotherm. (Reprinted from ref. 1, copyright 1964, with permission from Elsevier)...

Langmuir and Freundlich adsorption isotherms for toluene and MEK are shown in Figs. 2... 

Sorption and desorption are usually modeled as one fully reversible process, although hystersis is sometimes observed. Four types of equations are commonly used to describe sorption/desorption processes Langmuir, Freundlich, overall and ion or cation exchange. The Langmuir isotherm model was developed for single layer adsorption and is based on the assumption that maximum adsorption corresponds to a saturated monolayer of solute molecules on the adsorbent surface, that the energy of adsorption is constant, and that there is no transmigration of adsorbate on the surface phase. 

Predominantly, Freundlich s fitted adsorption isotherms computed by means of simple linear regression were proposed for the mathematical description of the process studied. Unlike the Langmuir equation, the Freundlich model did not reduce to a linear adsorption expression at very low nor very high solute concentrations, as above resulted. 

Plot of adsorption data in a double logarithmic plot. In a Langmuir isotherm the initial slope is unity. A Freundlich isotherm shows in a double log plot a slope of n < 1. Such a Freundlich isotherm is obtained if the adsorbent is heterogeneous (decreasing tendency for adsorption with increasing 6). (Modified from Morel, 1983)... 

Of the various equilibrium and non-equilibrium sorption isotherms or sorption characteristics models, the most popular are the Langmuir and Freundlich models. The correct modeling of an adsorbate undergoing both transport and adsorption through a clay soil-solid system necessitates the selection of an adsorption isotherm or characteristic model which best suits the given system. The use of an improper or inappropriate adsorption model will greatly affect the... 

Abstract Removal of the pesticide metobromuron from aqueous solutions by adsorption at the high area activated carbon cloth was investigated. Kinetics of adsorption was followed and adsorption isotherms of the pesticide was also be determined. In kinetic studies a special V-shaped cell with an UV cuvette attached to it was used for adsorption processes. With this cell it was possible to follow the concentration of pesticide molecule by in situ UV spectroscopy as it is adsorbed at the activated carbon cloth. The obtained absorbance vs time data were converted into concentration vs time data and these data were treated according to pseudo-first-order and psendo-second-order kinetic models. Adsorption of that pesticide was fonnd to follow second-order kinetic model with k 87.35 g mol min. Adsorption isotherms were derived at 25°C on the basis of batch analysis. Isotherm data were treated according to Langmuir and Freundlich models. The fits of experimental data to these equations were examined and founded that the adsorption isotherm was well represented by Frenndlich model. 

Table 22.3 The parameters of Langmuir and Freundlich isotherm equations for the adsorption of metobromuron Langmuir parameters...

When measured adsorption data are plotted against the concentration value of the adsorbate at equilibrium, the resulting graph is called an adsorption isotherm. The mathematical description of isotherms invariably involves adsorption models described by Langmuir, Freundlich, or Brauner, Emmet and Teller (known as the BET-model). Discussion of these models is given in Part 111, as conditions relevant to chemical-subsurface interactions are examined. 

Fig. 5.2 Typical adsorption isotherms described by (a) Langmuir, (b) Freundlich and (c) BET equations (Yaron et al. 1996)...

The adsorption data is often fitted to an adsorption isotherm equation. Two of the most widely used are the Langmuir and the Freundlich equations. These are useful for summarizing adsorption data and for comparison purposes. They may enable limited predictions of adsorption behaviour under conditions other than those of the actual experiment to be made, but they provide no information about the mechanism of adsorption nor the speciation of the surface complexes. More information is available from the various surface complexation models that have been developed in recent years. These models represent adsorption in terms of interaction of the adsorbate with the surface OH groups of the adsorbent oxide (see Chap. 10) and can describe the location of the adsorbed species in the electrical double layer. 

---