Adsorption of aromatic organic acids onto high area activated carbon cloth in relation to wastewater purification

Adsorption of aromatic organic acids: benzoic acid (BA), salicylic acid (SA), p-aminobenzoic acid (pABA) and nicotinic acid (NA), onto high area activated carbon cloth from solutions in 0.4 M H2SO4, in water at natural pH, in 0.1 M NaOH and also from solutions having pH 7.0 were studied by in situ UV-spectroscopic technique. The first-order rate law was found to be applicable for the kinetic data of adsorption. The rates and extents of adsorption of the organic acids were the highest from water or 0.4 M H2SO4 solutions and the lowest from 0.1 M NaOH solution. The order of rates and extents of adsorption of the four organic acids in each of the four solutions (0.4 M H2SO4, water, solution of pH 7.0 and 0.1 M NaOH) was determined as SA > BA > NA ∼ pABA. These observed orders were explained in terms of electrostatic, dispersion and hydrogen bonding interactions between the surface and the adsorbate species, taking the charge of the carbon surface and the adsorbate in each solution into account. Adsorption of BA in molecular form or in benzoate form was analyzed by treating the solution as a mixture of two components and applying Lambert–Beer law to two-component system. The adsorption isotherm data of the systems studied were derived at 30 °C and fitted to Langmuir and Freundlich equations.