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. 2018 Apr 26;13(4):e0196428. doi: 10.1371/journal.pone.0196428

Table 1. Different kinetic, isotherm, and thermodynamic models.

Kinetic models
Equation Nomenclature Reference
Pseudo-first-order log(qe1qt)=logqe1k12.303t qe1 and qt: biosorption capacity [mg g-1] at equilibrium and at any time t [h], respectively; k1: rate constant of the model [h-1] [33]
Pseudo-second-order tqt=1k2qe22+1qe2t qe2 and qt: biosorption capacity [mg g-1] at equilibrium and at any time t [h], respectively; k2: rate constant of the model [h-1] [34]
Intraparticle diffusion qt = kidt0.5 + c qt: biosorption capacity [mg g-1] at any time t [h]; kid: intraparticle diffusion rate constant [mg g-1 h-0.5]; c: model intercept [35]
Elovich qt=1BEln(AEBE)+1BElnt AE: initial biosorption rate [mg g-1 h -1]; BE: desorption constant of the model [g mg-1] [16]
Fractional power qt = kfptv v: fractional power rate constant [h-1]; kfp: fractional power model constant [mg g-1] [16]
Isotherm models
Two-parameter models
Langmuir qe=qmKLCe1+KLCe qe and qm: biosorption capacity at equilibrium and maximum biosorption capacity [mg g-1], respectively; Ce: liquid phase concentration of dye at equilibrium [mg L-1]; KL: Langmuir constant [L mg-1] [30]
Freundlich qe=KFCe1nF KF: constant of the Freundlich model [(mg g-1)(mg L-1)-1/nF]; nF: heterogeneity factor. [16]
Temkin qe=RTBTln(ATCE) T: absolute temperature [K]; R: ideal gas constant [8.314 J mol-1 K-1]; BT: constant related to heat of biosorption [J mol-1]; AT: Temkin isotherm constant [L mg-1] [35]
Halsey qe=(KH/Ce)1/nH KH: Halsey isotherm model constant [L g-1]-1/nH; nH: Halsey model exponent [16]
Dubinin-Radushkevich qe=qmexp(BDREDR2) BDR: biosorption energy constant [mol2 J-2]; EDR: Polanyi potential [kJ mol-1] [36]
Three-parameter models
Sips qe=qm(KSCe)1/ns1+(KSCe)1/ns Ks: Sips constant; 1/ns: Sips model exponent [30]
Toth qe=qmbTCe(1+(bTCe)nT1)nT bT: Toth model constant [L mg-1]-1/nT; nT: Toth model exponent [36]
Redlich-Peterson qe=KRPCe1+ARPCeBRP KRP: Redlich-Peterson model isotherm constant [L g-1]; ARP: Redlich-Peterson model constant [L mg-1]BRP; BRP: Redlich-Peterson model exponent [36]
Radke-Prausnitz qe=ARRRCeBRAR+RRCeBR1 AR: [L g-1] and RR [L mg-1]: Radke-Prausnitz model constants; BR: Radke-Prausnitz model exponent [16]
Thermodynamic models
Gibbs free energy change Δ G° = −R T ln Kc
KC=qeCe
T: absolute temperature [K]; R: ideal gas constant [8.314 J mol-1 K-1]; Kc: equilibrium constant [L g-1]; Δ G°: Gibbs free energy change [J mol-1] [37]
Entropy change ∂ΔG° = ∂T ∂ΔS° T: absolute temperature [K]; Δ S°: entropy change [J mol-1 K-1] [37]
Enthalpy change Δ H° = ΔG° − T ΔS° Δ H°: enthalpy change [J mol-1] [16]