Affinity for Anions Developed in Charcoal by Acid Treatment

In this study, we report a two-step method that creates at the surface of charcoal acidic groups that remove nitrate from an aqueous solution. The process used in this work with charcoal includes first an acid treatment followed by a heat treatment in a non-oxidizing atmosphere —a simple method to perform this treatment in a standard laboratory furnace is additionally presented—. As a control group, we use a process that omits the acid treatment and includes only the heat treatment. The precursors and products of the investigated processes were characterized in terms of (a) surface chemistry (zero charge point, Boehm titration), (b) structure (scanning electron microscopy, X-ray diffraction, nitrogen adsorption, Hg porosimetry), and (c) composition (CHN elemental analysis, thermal gravimetric analysis, Energy Dispersive X-ray Fluorescence). Acid-thermal treatment of charcoal creates Lewis acid groups that remove nitrate anions from an aqueous solution. The nitrate-removing Lewis acid groups were absent in the starting material as well as in the material obtained in the control group. The creation of these surface groups occurs without significant damage to the macropore structure of the charcoal particles. A simple process can generate chemical groups with an affinity for anions in an aqueous solution on the charcoal surface.