Abstract: Present study was accomplished to prospect the viability of using the montmorillonite (Mon) nanoparticles as an adsorbent to remove the Ampicillin under various experimental conditions. Physico-chemical features of the Mon-nanoparticles were discovered. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms were applied to portray the data obtained from the adsorption studies. The findings showed that the highest R2 values were related to Langmuir and Dubinin–Radushkevich isotherm models. The greatest adsorption capacity (qe) for Langmuir and Dubinin–Radushkevich isotherm models were recognized to be 134.48 mg/g and 141.22 mg/g, respectively; and the separation factor was calculated to be 0.113 which is indicative of a favourable sorption. Temkin Isotherm model clarified that the heat of sorption process was 34.61 J/mol; and the mean free energy calculated by Dubinin–Radushkevich isotherm model was anticipated to be 2.56 Kj/mol which these undoubtedly demonstrate the physisorption process for Ampicillin adsorption experiments.
Results and discussion
The table 1and 2 represented the chemical composition and physicochemical properties of the Mon-nanoparticles, respectively. As it can be seen in Table 1, Montmorillonite has considerable levels of SiO2 (57.7%) and Al2O3 (18.1%) and the quantity of other metal oxides is observed to be lesser than 20%. The investigation of the surface physical morphology of waste and 71 Montmorillonite were fulfilled using the scanning electron microscopy (SEM) technique. Fig 2 shows the SEM images of the Montmorillonite. Furthermore, it was found that the surface area of Montmorillonite is 245.5 m2/g.
Adsorption isotherms: The adsorption data were analyzed to see whether the isotherm obeyed the Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherm models equations 32-36:Where qmax, the monolayer capacity of the adsorbent (mg/g); KL, the Langmuir constant (L/mg) and related to the free energy of adsorption; qm, the theoretical saturation capacity (mg/g); and ?, the Polanyi potential, which is equal to RT Ln (1 + (1/Ce)), where R (J/mol K) is the gas constant and T (K) is the absolute temperature; ?, a constant related to the mean free energy of adsorption per mole of the adsorbate (mol2/kJ2). For Freundlich isotherm, KF is the adsorption capacity at unit concentration (L/g) and is adsorption intensity. Values specify whether isotherm is irreversible ( = 0), favorable ( ) or unfavorable ( ). For Temkin isotherm, the A, b, R, T are equilibrium binding constant (L/g) Temkin isotherm constant, universal gas constant (8.314 J/mol K) and temperature at 298 K, respectively. B is the constant related to heat of sorption (J/mol).The linear plot of 1/Ce versus 1/qe (Fig. 3 a) is utilized to calculate the qmax and KL in Langmuir equation. The calculation of qm and ? of D-R equation is performed by plotting Ln qe versus ?2 (Fig. 3 b). KF and 1/n of Freundlich equation is achieved from the slope and intercepts of linear plot of log qe versus log Ce (Fig. 3 C).Temkin isotherm contains a factor that is explicitly entered into the adsorbent–adsorbate interactions. By ignoring the extremely low and large value of concentrations, the model assumes that heat of adsorption (function of temperature) of all molecules in the layer would decrease linearly rather than logarithmic with coverage. As implied in the equation, its derivation is characterized by a uniform distribution of binding energies (up to some maximum binding energy) was carried out by plotting the quantity sorbed qe against Ln Ce and the constants were determined from the slope and intercept (Fig. 3 d).The Langmuir, Freundlich, Temkin and D-R parameters for the adsorption of Ampicillin onto Mon-nanoparticles were listed in Table 3. The comparison of R2 represented in table 3 advocates that D-R and Langmuir model have more facility to portray the data compared to Temkin and Freundlich models. The constant ? is related to the mean free energy E (kJ/mol) of adsorption per molecule of the adsorbate when it is moved to the surface of the solid from the solution. It is calculated by following relationship 37-40:Where is represented as the isotherm constant. Based on the linear plot obtained from D-R model, the qm was determined to be 141.22 mg/g; the mean free energy, E, was observed to 2.56 Kj/mol which this values indicates the adsorption of Ampicillin is a physisorption process. The R2 value for this isotherm model was calculated to be 0.991.Also considering the Table 3, the values of 1/n = 0.425 and n=2.35 indicate the favourable sorption of Ampicillin unto Mon-nanoparticles and the R2 value is 0.82.Moreover, Table 3 shows that the values of A and B is 1.85 L/g and 34.61 J/mol, respectively which is an indicative of the adsorption heat and a physical adsorption process; the R2 was found to be 0.84. The critical properties of the Langmuir isotherm may be affirmed in terms of equilibrium parameter RL, which is a dimensionless constant related to separation factor or equilibrium parameter 41-44: KL
is considered as the constant referred to the adsorption energy (Langmuir
Constant). RL is value that reveals the adsorption nature, so that the
adsorption could be unfavorable (RL>1), linear (RL=1),