Preparation of hollow zeolite NaA/chitosan composite microspheres via in situ hydrolysis-gelation-hydrothermal synthesis of TEOS

In situ hydrolysis-gelation-hydrothermal (HGH) synthesis of tetraethylorthosilicate (TEOS) technique was developed to prepare hollow zeolite NaA/chitosan composite microspheres. The chitosan solution coated calcium alginate microspheres served as template to generate hollow structure, which were pre-modified by oleic acid and coated by TEOS. Furthermore, the calcium alginate microspheres were prepared by a simple homemade double T-junction mixer. During the hydrothermal process, the TEOS hydrolyzed and provided silica source for the zeolite NaA shell, meanwhile the inner calcium alginate microsphere core dissolved by the alkaline synthesis mixture and left the hollow structure. The obtained products were characterized by XRD, FT-IR, SEM, TG et al. techniques. The preparation method for calcium alginate microspheres template was simple and the preparation process had no NaA crystal seeds been involved. The hollow size could be adjusted by controlling the synthesis parameters of calcium alginate/chitosan microspheres. In addition, the functional magnetic γ-Fe₂O₃ nanoparticles could be introduced into the cavity during synthesis of calcium alginate/chitosan microspheres and guest magnetic γ-Fe₂O₃ nanoparticles had no effect on the properties of host zeolite NaA. The obtained functional magnetic hollow NaA/chitosan microspheres had decent adsorption performance for Cu²⁺ ions and were easy to recycle.