Novel tunable composites based on bentonite and modified tragacanth gum for removal of acid dyes from aqueous solutions

Abstract

A series of new adsorbents derived from tragacanth gum-graft-poly(methyl methacrylate) and bentonite (TG-g-PMMA/B) were synthesized. The developed composites were evaluated by removal of congo red (CR), methyl orange (MO), and acid blue 113 (AB-113) as model anionic azo dyes from aqueous solutions followed by UV-Vis spectrophotometric determination. It was revealed that the simultaneous introduction of inorganic bentonite clay into the TG-g-PMMA polymer matrix drastically improved capability of the adsorbent and surface morphology of the composites in comparison with TG, and TG graft copolymer and led to better dispersion in the polymeric matrix without agglomeration. Furthermore, the chemical structures of the adsorbate molecules affect the specific interactions of the adsorbents with adsorbates. The adsorbents were characterized by using FTIR, SEM, and TG/DTA analysis. The effect of various factors influence the dye adsorption including the adsorbent dose, sample pH, contact time, and dye concentration were investigated and optimized by response surface methodology (RSM) using central composite design. Under the optimum conditions, maximum adsorption of the CR, MO, and AB-113 dyes were observed at pH 8.5 with adsorbent dose of 5 mg mL⁻¹, 30 mg mL⁻¹, and 75 mg mL⁻¹, respectively. The dye adsorption process was controlled by pseudo-second order and intraparticle diffusion kinetic models. The adsorption equilibrium data of the studied dyes well fitted with Langmuir isotherm with maximum adsorption capacity of 900, 750, and 8.5 mg g⁻¹ for CR, MO, and AB-113, respectively.