Abstract
In adsorption study, isotherms and kinetics of adsorption process provide pieces of information underlying the mechanisms and dynamics of the process. Several equilibrium and kinetic models are usually employed for performing the experimental design of an adsorption system. In this chapter, the Langmuir, Freundlich, Sips, Liu, Redlich–Peterson nonlinear equations, as well as other unusual isotherm models (Hill, Khan, Radke–Prausnitz, Toth) are discussed. For the kinetics of adsorption, the pseudo-first-order, pseudo-second-order, general-order, Avrami fractionary order, and Elovich chemisorption models are explained. The importance of statistical parameters such as coefficient of determination (\(R^{2}\)), adjusted coefficient of determination (\(R_{\text{adj}}^{2}\)), and standard deviation (root of mean square error) are highlighted. The usage of linearized and nonlinearized equations are illustrated and explained. Some common mistakes commonly committed in the literature using linearized equilibrium and kinetic adsorption models as well as other polemic points in adsorption research are pointed out. Analytical techniques together with thermodynamical data of enthalpy and entropy changes are needed to ascertain if an adsorption process is a chemical or a physical process.
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Abbreviations
- DB-53:
-
Direct Blue 53
- DOF:
-
Degree of freedom
- FTIR:
-
Fourier transform infrared
- MWCNT:
-
Multi-walled carbon nanotube
- SWCNT:
-
Single-walled carbon nanotube
- RB-4:
-
Reactive Blue 4
- RO-16:
-
Reactive Orange-16
- R :
-
Correlation coefficient
- \(R^{2}\) :
-
Coefficient of determination
- \(R_{\text{adj}}^{2}\) :
-
Adjusted coefficient of determination
- SD:
-
Standard deviation (root of mean square error)
- TGA:
-
Thermogravimetric analysis
- q e :
-
Adsorption capacity at the equilibrium (mg g−1) or amount adsorbed by the adsorbent at the equilibrium
- q t :
-
Amount adsorbed by the adsorbent at any time (mg g−1)
- C e :
-
Concentration of the adsorbate at the equilibrium (mg L−1)
- C o :
-
Initial adsorbate concentration (mg L−1)
- Q max :
-
Maximum amount adsorbed (mg g−1)
- K L :
-
Langmuir equilibrium constant (L mg−1)
- K F :
-
The Freundlich equilibrium constant (mg g−1(mg L−1)−1/n)
- n F :
-
The Freundlich exponent (dimensionless)
- K S :
-
The Sips equilibrium constant (mg L−1)−1/ns
- n S :
-
The Sips exponent (dimensionless)
- K g :
-
The Liu equilibrium constant (L mg−1)
- n L :
-
Dimensionless exponent of the Liu equation
- K RP :
-
Redlich–Peterson constants (L g−1)
- a RP :
-
Redlich–Peterson constant (mg L−1)−g
- g :
-
The Redlich–Peterson exponent (dimensionless)
- K H :
-
The Hill equilibrium isotherm constant [(mg L−1)nH]
- n H :
-
The Hill exponent (dimensionless)
- K K :
-
The Khan equilibrium isotherm constant (L mg−1)
- n K :
-
The Khan exponent (dimensionless)
- K RAP :
-
The Radke–Prausnitz equilibrium isotherm constant (L mg−1)
- n RP :
-
The Radke–Prausnitz exponent (dimensionless)
- K T :
-
The Toth equilibrium isotherm constant (L mg−1)
- n T :
-
The Toth exponent (dimensionless)
- dq :
-
Differential of q (adsorption capacity)
- dt :
-
Differential of time
- k f :
-
The pseudo-first-order rate constant (min−1)
- t :
-
Contact time (min)
- k s :
-
The pseudo-second-order rate constant (g mg−1 min−1)
- h o :
-
Initial sorption rate (mg g−1 min−1)
- k N :
-
The rate constant for the order N
- n :
-
The order of adsorption with respect to the effective concentration of the adsorption active sites present on the surface of adsorbent
- θ t :
-
Number of the active sites available on the surface of adsorbent for adsorption
- α :
-
The initial adsorption rate (mg g−1 min−1)
- β :
-
Related to the extent of surface coverage and the activation energy involved in chemisorption (g mg−1)
- k AV :
-
The Avrami kinetic constant (min−1)
- n AV :
-
Is a fractional adsorption order
- k id :
-
The intraparticle diffusion rate constant (mg g−1 min−0.5)
- C :
-
A constant related to the thickness of boundary layer (mg g−1)
- A :
-
The Arrhenius constant
- E a :
-
Is the activation energy (kJ mol−1)
- R :
-
The universal gas constant (8.314 J K−1 mol−1)
- T :
-
The absolute temperature (K)
- K D :
-
The distribution equilibrium constant (dimensionless)
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Acknowledgments
The authors acknowledge funding from Brazilian agencies CNPq, CAPES, and TWAS.
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Lima, É.C., Adebayo, M.A., Machado, F.M. (2015). Kinetic and Equilibrium Models of Adsorption. In: Bergmann, C., Machado, F. (eds) Carbon Nanomaterials as Adsorbents for Environmental and Biological Applications. Carbon Nanostructures. Springer, Cham. https://doi.org/10.1007/978-3-319-18875-1_3
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DOI: https://doi.org/10.1007/978-3-319-18875-1_3
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