Synthesis of chitosan-magnetite gel microparticles with improved stability and magnetic properties: A study on their adsorption, recoverability, and reusability in the removal of monovalent and multivalent azo dyes

摘要

Here, the membrane emulsification technique was employed to synthesise novel size-controlled chito-san-magnetite emulsion droplets (diameter: 10-35 mu m), which were subsequently converted into hydrogels via alkaline gelation and crosslinking with ethylene glycol diglycidyl ether (EGDE). The microscopy images revealed the efficient trapping of the magnetite nanoparticles within the chitosan emulsion droplets and crosslinked gel matrices. The microparticles exhibited an ideal surface morphology, which yielded a dye-removal percentage of 97 (pH 4), as well as a quick magnetic response. The adsorption reaction employing the chitosan-magnetite gel microparticles correlated with the Langmuir adsorption isotherm, exhibiting remarkable adsorptions towards Acid Orange 7 (AO7, monovalent), Acid Red 13 (AR13, divalent), and Acid Red 27 (AR27, trivalent) dyes with maximum adsorption capacities, Q(max), of 1.71, 1.55, and 1.13 g-dye/g-dry adsorbent, respectively, in a pH 5 buffer. The calculated molar ratio of the adsorbed dyes revealed the contributions of almost all the amino groups of the chitosan gel microparticles to the adsorption of AO7 dye. The fast and efficient recovery of the adsorbent microparticles by magnets, as well as their reusability for over 10 adsorption-desorption cycles without any particle loss or significant decrease in adsorption capacities, were demonstrated. The synthesised chitosan-magnetite gel microparticles could be a "green " state-of-the-art adsorbent exhibiting excellent properties for applications in wastewater treatment.