Selective adsorption on fibrous activated carbon of organics from aqueous solution: correlation between adsorption and molecular structure

Abstract

In industrial processes, granular activated carbon (GAC) is generally used to remove pollutants from wastewater. Recently, a new adsorbant has been explored, fibrous activated carbon (FAC). Experiments were carried out with two FACs having different specific surface areas (1500 and 1300 m².g⁻¹) and pore-size distributions to study adsorption of various organic compounds from aqueous solution. Results were compared with adsorption onto one GAC with a specific surface area of about 1000 m².g⁻¹. Classic models were applied and kinetic constants were computed. In most cases, FAC with the higher specific surface area (named CS 1501) showed better adsorption capacities and kinetics than the two other FACs. For example, adsorption velocity of benzaldehyde was 7.2 ξ 10⁻⁵ 1.mg⁻¹·min⁻¹ with CS 1501 and about 3 ξ 10⁻⁵ 1.mg⁻¹.min⁻¹ with other FACs. Furthermore, adsorption onto CS 1501 of a great number of organic compounds (aliphatic and aromatic) depended on solute molecular characteristics. For instance, solute molecular size seemed to play an important role: adsorption capacity of high molecular weight compounds (humic substances) was about 3 mg.g⁻¹, a value much lower than those of low molecular weight compounds, which were respectively 200 mg.g⁻¹ and 400 mg.g⁻¹ for phenol and benzoic acid. From experimental results, a correlation of QSAR (Quantitative Structure-Activity Relationship) type has been set up. This relationship predicts the adsorbability of organics compounds onto fibrous activated carbon from the molecular properties of these compounds.