Entrapment of nano-ZnO into alginate/polyvinyl alcohol beads with different crosslinking ions for fertilizer applications.

Zinc oxide nanoparticles (nano-ZnO) are attractive as fertilizer materials but high concentrations may negatively affect the environment. To reduce their dispersion in the environment we entrapped nano-ZnO in biodegradable polymer beads consisting of alginate and polyvinyl alcohol (PVA). The alginate/PVA/ZnO beads were prepared via ionotropic gelation using two different crosslinking ions (Ca and Zn), and the effect of alginate crosslinking ion and PVA content on bead structure, water absorption, water retention and zinc release was investigated. The pure CaAlg and ZnAlg beads demonstrated a poor water absorption and retention, which were strongly enhanced by the incorporation of PVA into the beads. The continuous Zn release was measured in a sand column, and it was found that the Zn-crosslinked beads rapidly released high concentrations of Zn followed by a more gradual Zn release, whereas Ca alginates showed only a gradual Zn release. The Zn dissolution kinetics could be tuned by the crosslinking ion composition. The prepared nano-ZnO-containing alginate/PVA beads may be attractive for Zn fertilizer applications under water-limited conditions.