Effective removal of methylene blue dye by a novel 4-vinylpyridine-co-methacrylic acid cryogel: kinetic, isotherm, and breakthrough studies

BACKGROUND: Industrial streams are the source of increasing amounts of textile dye pollution every year. Among the various adsorbents that have been tested for the removal of dyes, synthetic macroporous polymers are a promising choice due to their developed structure, the presence of active functional groups, and the possibility of regeneration and reuse for several cycles. In this work, a 4-vinylpyridine-co-methacrylic acid based cryogel (4-VP-MAAc) was synthesized at -12 °C by the free-radical polymerization technique, it was characterized using a set of complimentary methods, and then applied for the removal of methylene blue (MB) from water solutions. RESULTS: The adsorption of MB was enhanced at pH values higher than 7 due to the presence of anionic functional groups. The maximum equilibrium adsorption capacity achieved by 4-VP-MAAc was 703.6 mg/g at pH 8. Several kinetics, equilibrium, pH studies, and fixed-bed column experiments were completed in ultra-pure water to evaluate the performance and the mechanism of interaction of positively-charged dye with the polymer. Among the kinetic models applied, the pseudo-second order model best fit the experimental observations. The Langmuir model efficiently described the adsorption of MB onto the prepared cryogel, thus indicating monolayer adsorption. The ion exchange of the Na⁺ ions present in the structure of the cryogel with dye was found to be the main removal mechanism accompanied with a complexation reaction. No loss of adsorption capacity was observed in four successive adsorption/desorption cycles of 4-VP-MAAc use. CONCLUSION: This is the first time that a 4-vinylpyridine-co-methacrylic acid based cryogel has been synthesized and successfully applied to remove MB from water.