Determination of surface protonation-deprotonation behavior, surface charge, and total surface site concentration for natural, pillared and porous nano bentonite heterostructure

摘要

In this paper, the physicochemical properties of natural, pillared and porous nano bentonite heterostructure in the points of view of surface protonation-deprotonation behaviors were studied. Moreover, the structural heterogeneity in each sample based on three-dimensional field-emission scanning electron microscopy (FESEM) plots were investigated to obtain its effect on the formation of surface active sites. To better understand the surface protonation properties and adsorptive capability of natural, pillared and porous clays, it is essential to investigate the surface charge, surface active sites, pH at point of zero charge (pH(zpc)), and surface acid-base equilibrium constants. Since the information about amphoteric acid-base groups especially in porous clays is still lacking, our main purpose is to obtain the best estimates to compare the surface properties of natural, pillared and porous clays by means of Gran method and surface complexation model from titration data. The 2 plcdiffusion layer model (DLM) was applied to evaluate the contribution and concentration of the various surface site species (such as SOH, SOH2+ and SO-) in the different pH and ionic strengths. This paper indicates considerable new information about surface acid-base reactions, total surface site concentrations, pH(zpc) measurement, which provides basic knowledge of the underlying adsorption mechanisms. The maximum value of total surface sites concentration (8.84 mmol/L) in ionic strengths of 0.05 M NaCI belonged to porous nano bentonite heterostructure (PBH) with the highest pH(zpc) at 9.73. (C) 2019 Elsevier B.V. All rights reserved.