Removal of Congo Red and Rhodamine B dyes from aqueous solution using unmodified and NH3/HCl-modified wood charcoal: a kinetic and thermodynamic study

Abstract

In recent years, color removal processes from industrial wastewater which contains dyestuffs have gained great importance. Especially, textile industry wastewater with high volume and variable composition comes first among these wastewaters. These waters bring along many ecological and esthetic problems. In this study, unmodified and acid/base-modified wood charcoal derived from oak wood has been utilized as an eco-friendly adsorbent for removal of anionic dye Congo Red (CR) and cationic dye Rhodamine B (RhB) from aqueous solution. The characterization of raw charcoal was performed using FT-IR, BET and SEM/EDS analysis. The optimum conditions were determined by investigating the effect of adsorption parameters (initial dye concentration, temperature, adsorbent amount, pH and contact time) for efficient removal of dye molecules from aqueous solution by batch adsorption experiments carried out under different conditions and the experimental results were investigated in terms of Langmuir and Freundlich isotherm models. Together with the calculated thermodynamic parameters, the experimental data were applied to pseudo first order, pseudo second order, intra-particle diffusion, Boyd kinetic models and the adsorption mechanism was tried to be explained. The highest removal efficienciency of CR and RhB was achieved as 98% and 92%, respectively. As a result of this study, in which the effectiveness of modified and unmodified adsorbents was compared, it was determined that CR dye was removed at higher efficiency with HCl-modified charcoal. On the other hand, the RhB dye was better removed with NH3-modified charcoal.