Ionic Liquid Functionalized Tragacanth Gum Hydrogel for Methyl Orange: Radiation Synthesis, Structure–Properties, and Selective Adsorption

Abstract

The selective adsorption of purely targeted dye from mixed dye solutions draws significant attention for potential recovery and reuse. In this work, a series of alkyl substituted ionic liquids (1-alkyl -3-vinyl- imidazolium bromide [C_nVIm]Br, n = 4, 6, 8, 10, and 12) modified tragacanth gum (TG-C_nBr) was synthesized by radiation technique. The prepared TG based hydrogel was used to separate the molecules of methyl orange (MO) from the mixed anionic dyes. The correlation between the length of alkyl chain and the adsorption performance was investigated. TG-C₁₂Br demonstrated the highest adsorption performance to MO among all the tested anionic dyes. The selectivity coefficient for MO versus indigo carmine (IC) and acid fuchsin (AF) are 5.856 and 107.5, respectively. The optimal conditions for the adsorption of MO were pH of 6.0, adsorbent dose of 0.6 mg/L, and contact time of 420 min. The maximum adsorption capacity of MO on TG-C₁₂Br at 25, 35 and 50 °C are 389.11, 400.00, and 414.94 mg/g, respectively. The MO removal was enhanced under high salinity condition. The adsorption of MO probably through hydrophobic adsorption, hydrogen bond, electrostatic attraction, and π−π interactions. Therefore, TG-C₁₂Br prepared by radiation technique exhibited a promising application prospect for selective adsorption of MO dye.