Zeolite Crystallization in Crosslinked Chitosan Hydrogels: Crystal Size Control and Chitosan Removal

For the purpose of controlling zeolite crystal size, crystallization of zeolite NaA and NaY in glutaraldehyde -crosslinked chitosan (GA-CS) hydrogels was studied in this work. Zeolite crystals were obtained by penetration of Na₂O-Al₂O₃-H₂O alkaline solution into GA-CS hydrogels containing colloidal silica, followed by hydrothermal treatment and removal of GA-CS hydrogels. The synthesis parameters including the amounts of silica, chitosan, and glutaraldehyde, aging and cooking times were systematically investigated. A hydrogen peroxide treatment method was introduced as an effective way for removing GA-CS hydrogels, and the conventional calcination can be avoided. X-ray diffraction (XRD), light scattering, scanning electron microscopy (SEM), thermogravimetric analysis (TG), and N₂ sorption were used to characterize the zeolite samples. This work showed that GA-CS could be a good alternative space-confinement medium for the synthesis of zeolite nanocrystals with tunable crystal sizes and excellent dispersibility in water.