Competitive naphthalene adsorption on activated carbons. Effect of porosity and hydrophobicity

Abstract

The goal of this work was to investigate the mechanism of competitive adsorption of naphthalene on activated carbons from diluted solutions. The polarity of the adsorption media was varied, by selecting solvents ranging from high to low dielectric constants (ethanol, cyclohexane and heptane). By altering the hydrophobicity of the adsorption media, the preferential adsorption of the organic probe is changed; therefore the selectivity and efficiency of naphthalene adsorption may be tuned by optimising the features of the adsorbent upon the adsorption media. Liquid phase adsorption using solvent molecules of different sizes and hydrophobicity can be an effective means of characterising the accessibility and mechanism of competitive adsorption. The results show that the surface polarity of the carbons can be modulated to favour the retention of a non-polar adsorbate (i.e., naphthalene), by controlling the competitive adsorption of the solvent. Oxidation of an activated carbon might result in a better adsorbent even of non-polar compounds, when the competitive adsorption of the solvent becomes important. However, one must also take into account the dimensions of the molecules, and therefore the accessibility to the porosity of the adsorbents. These factors would compensate the slight loss in pore structure and gain in polarity of oxidised carbons, when adsorption takes place from organic media.