Characterization and adsorption properties of tetrabutylammonium montmorillonite (TBAM) clay: Thermodynamic and kinetic calculations

The montmorillonite has been subjected to modification through ion-exchange reaction by tetrabutylammonium bromide (TBAB). The modified sample was studied by X-ray diffraction (XRD) technique, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) methods. The basal spacing of modified montmorillonite was determined as 14.40 Å. The IR spectra of modified montmorillonite showed CH vibrations. The characterization of tetrabutylammonium montmorillonite (TBAM) and the adsorption of p-chlorophenol (p-CP) on organomontmorillonite was studied as a function of the solution concentration and temperature. The observed adsorption rates were found to fit to the pseudo-second-order kinetics. The rate constants were calculated for temperatures ranging between 25.0–35.0 °C at constant concentration. The adsorption energy, E, and adsorption capacity, (qm), for phenolic compounds adsorbing on organomontmorillonite were estimated using the Dubinin–Radushkevich (D–R) equation. Thermodynamic parameters (Δga=−11.063Δga=−11.063 and −11.802 kJ/mol−11.802 kJ/mol, Δha=−30.032Δha=−30.032 and −30.789 kJ/mol−30.789 kJ/mol, Δsa=−0.0636Δsa=−0.0636 and −0.0637 kJ/mol K−0.0637 kJ/mol K for 298 and 308 K, respectively) were calculated by a new approximation from the adsorption isotherms of p  -CP on organomontmorillonite. These isotherms were modeled according to Freundlich and Dubinin–Radushkevich adsorption isotherms, through which the first-order and second-order coefficients (K1ads=0.0152K1ads=0.0152 and 0.0127 μmol/g min, K2ads=0.0130K2ads=0.0130 and 0.0108 L/min μmol, respectively) were obtained at 298 and 308 K.