Salt-stable ZnO nanoparticles stabilized by citric-acid-crosslinked Canna edulis ker. starch

This study examines how citric acid crosslinking density in Canna edulis ker. starch (CEkS) governs electrosteric stabilization of ZnO nanoparticles under saline stress. Citric acid-modified CEkS polymers spanning degrees of substitution (DS = 0.26-0.67) were synthesized and used to cap ZnO nanoparticles via aqueous co-precipitation. FTIR and XRD confirmed ester formation and ZnO crystallinity, while thermal analysis indicated enhanced thermal resilience of the crosslinked polymer-ZnO system. Colloidal stability was quantified by hydrodynamic diameter (DLS), zeta potential, and UV-Vis turbidity during storage across 0-200 mM NaCl. An intermediate-crosslinked formulation (CA35%) provided the most robust salt tolerance: at 200 mM NaCl, CA35% reached 1271 ± 5 nm after 7 days, whereas the non-modified CEkS control grew to 2633 ± 18 nm. In salt-free dispersions, CA35% remained 301 ± 2 nm at 7 days, while the control reached 2896 ± 6 nm. Higher-crosslinked samples formed stiffer shells that were less tolerant to ionic compression, accelerating aggregation despite more negative surface charge. Overall, the results establish a practical crosslinking-stability design rule for polysaccharide-capped ZnO nanocolloids in ionic media and provide a foundation for subsequent, application-specific validation where safety or regulatory testing is required.