Evaluation of surfactant-modified bentonite for Acid Red 88 dye adsorption in batch mode: kinetic, equilibrium, and thermodynamic studies

Abstract

In this study, hexadecyltrimethylammonium (HDTMA) bentonite was synthesized by placing alkylammonium cation onto bentonite. Acid Red 88 (AR88) removal by hexadecyltrimethylammo-nium (HDTMA) modified bentonite was investigated and the specific surface area obtained using Brunauer-Emmett-Teller analysis was 49.2 m2/g for HDTMA-bentonite. However, for natural bentonite, it was only 17.4 m2/g. The effect of main experimental parameters on the removal of AR88 (i.e., initial AR88 concentration, contact time, and HDTMA-bentonite mass) was investigated. Also, six isotherm models were applied for evaluation of the equilibrium adsorption; among the mentioned models, fitting the adsorption data on Langmuir isotherm was associated with supe-rior results (maximum monolayer capacity (qmax) was 91.7 mg/g). The results gave the green light to the unique usability of the pseudo-second-order kinetics model for the portrayal of adsorption data. Using the intraparticle diffusion model, the identification of the adsorption mechanism pro-cess was done so that the trivial effect of the boundary layer was confirmed. Based on Boyd's kinetic model, the external mass transport was the foremost reason for the adsorption of water from dye- water mixtures. In addition, there is no study in the literature on the removal of Acid Red 88 dye using HDTMA-bentonite. The obtained results indicated that, through using HDTMA-bentonite, the elimination of acid dyes from aqueous solutions can occur simply and in a short time.