Synthesis and Surface Modification of Hexagonal Mesoporous Silicate–HMS using Chitosan for the Adsorption of DY86 from Aqueous Solution

Many types of dyes are toxic, carcinogenic, non-biodegradable due to their complex aromatic structures and their water solubility and accordingly, they should be removed from wastewaters. In the present research, hexagonal mesoporous silicate HMS was synthesized by sol-gel method and after modification by natural polymer chitosan (Ch-HMS), it was applied for the removal of direct yellow 86 from aqueous media. The characterization of synthesized HMS and chitosan modified HMS were analyzed by some basic analyses such as SEM, FTIR, XRD and BET. The effects of pH, adsorbent dosage and contact time on the removal of direct yellow 86 were investigated. The results revealed that the maximum adsorption of dye was about 92% which was obtained by 0.075 g of Ch-HMS composite at the pH of 2 and for 60 min contact time. The equilibrium data of experiments were studied by Langmuir, Freundlich, Elovich and Temkin isotherm models using linear regression. The Langmuir model with the maximum adsorption capacity of 71.43 mg/g was the predominant model. Kinetic study was also performed using pseudo first and pseudo second order kinetic models where the second order model had the best agreement with the experimental data. The experimental data showed that surface modification of HMS by chitosan and formation of Ch-HMS nanocomposite enhanced the adsorption capacity of HMS and changed it into a useful and powerful adsorbent for the removal of pollutants from aqueous solutions.