Characterizing the surface acidity of bentonite by various methods

Surface acidity of bentonite was investigated by using three methods. The first method was inverse gas chromatography; the acid-base character of bentonite surface was estimated by the retention time with different nonpolar and polar probes at infinite dilution region. The adsorption specific free energy (Delta G(SP)), specific enthalpy (Delta H-SP), and specific entropy (Delta S-SP) of polar probes on bentonite were determined. By correlating Delta H-SP with donor and acceptor numbers of the probes, the acidic (K-A) and the basic (K-D) parameters of the sample were calculated. The second method was recording the spectrums of pyridine by Fourier transform infrared spectroscopy (FTIR); the spectrum of pyridine bonded by Bronsted and Lewis acid sites was obtained. The last method was modified amine titration by using Hammett indicators. Copyright (C) 2010 John Wiley & Sons, Ltd.