Impact of Cationic and Neutral Clay Minerals’ Incorporation in Chitosan and Chitosan/PVA Microsphere Properties

Abstract

This study investigates the synthesis of chitosan and chitosan/poly(vinyl alcohol) (PVA) microspheres incorporated with kaolinite and synthetic saponite clays. The microspheres were prepared using a two-step process: (i) reticulation of chitosan and chitosan/PVA with kaolinite or saponite to form a clay-biopolymer matrix and (ii) further reticulation of chitosan/PVA to produce double-layered microspheres. The resulting materials were characterized using FTIR, XRD, thermal analysis and SEM. Their properties were evaluated for water uptake, cation exchange capacity, specific surface area, acid stability, and methylene blue, Cr³⁺, Cr⁶⁺, and Ni²⁺ adsorption. XRD analysis confirmed a successful polymer interaction with both clay structures. Cationic saponite clay favored clay dispersion, resulting in more homogeneous microspheres. Swelling tests revealed that chitosan-kaolinite microspheres exhibited 75% swelling, while chitosan-PVA-kaolinite microspheres showed 70% swelling, attributed to structural changes induced by PVA. Adsorption tests demonstrated that KaolCSL microspheres removed 53% of methylene blue (MB) and 82% of Ni²⁺, while SapCPSL microspheres exhibited superior removal of Cr³⁺ (91%), Cr⁶⁺ (19%), and silver nanoparticles (>90%). Biocompatibility assessments using zebrafish and HaCat cells showed no mortality or genotoxicity, with a 38% increase in cell viability for Cr-loaded microspheres. These results suggest that the use of modified clay-biopolymer microspheres can be an effective, low-cost solution for water purification and wastewater treatment.