Characterization of the porous structure of different humic fractions

Humic substances (HS) are the most important source of organic carbon in the environment. Their colloidal character and high surface functionality make them excellent adsorbents, possessing a superior capacity for the retention of ionic and molecular pollutants, and for facilitating the processes of mobilization/immobilization of these in the environment. However, the characterization of their microstructural properties is essential to the understanding of these processes. In this work, the porous texture of two humic substances, and their fractions (fulvic acid, FA; brown and grey humic acids, BHA and GHA; and humin, HU), have been studied using both experimental and computational methods. It has been determined that the fulvic acids have the largest apparent surface area, and the most narrow microporosity distribution. The coincidence of the maxima in the micro, meso and macropore distributions, among the different humic fractions, points toward a textural similarity between them, independent of their origin. The results obtained from the application of quantum computational methods corroborate the experimental findings, and thus show potential for even greater application towards this type of surface chemistry. (c) 2004 Elsevier B.V. All rights reserved.