PHYSICAL-CHEMICAL CHARACTERIZATION OF POROUS AMORPHOUS ALUMINUM OXIDE

Abstract

Appropriate modeling of adsorption reactions with surface coordination models requires detailed physical/chemical characterization of the adsorbent material. Although such characterization requires careful aquisition of considerable experimental data, the ability to represent adsorption reactions in a manner that captures the details of solution speciation has considerable benefits. The work reported here involves the physical-chemical characterization of porous aluminum oxide particles which have extensive internal porosity. Size reduction of the experimental adsorbent was required to reduce internal mass transport limitations during the characterization procedures. The physical characteristics evaluated were specific surface area (N2 BET), pore size distribution (N2 BET), particle size distribution and particle morphology (SEM). The chemical characteristics evaluated include pHpzc (potentiometric titration, salt titration and electrophoretic mobility), site density, surface acidity constants (potentiometric titration), and sodium and chloride surface binding constants. The accuracy and precision of the experimental methods are compared as well as various data reduction methodologies. For instance, the acidity and salt binding constants were estimated by single extrapolation, double extrapolation and by non-linear least square analysis (FITEQL). The estimation of input parameters for surface coordination models is discussed in terms of uncertainty of analytical methodology and model sensitivity.