Synthesis and characterization of double-network hydrogels based on sodium alginate and halloysite for slow release fertilizers.

In this work, novel sodium alginate-based double-network hydrogel beads were prepared and applied for the water-retention and slow release of fertilizers (WSF). The WSF beads were prepared by ion-crosslinking and the free radical polymerization of acrylic acid, acrylamide, and polymerizable β-cyclodextrin in the presence of urea-loaded halloysites. The WSF beads were characterized using SEM, FTIR, and TGA. Their swelling capacity and water retention were measured by a weighing method and their slow-release behavior was studied by spectrophotometry. The water retention and slow release results showed that the fertilizer displayed improved urea release and water retention properties, indicating that halloysite nanotubes clearly improved the performance of fertilizers. In addition, the experimental data of the slow release of urea in water and soil better fitted the Korsmeyer-Peppas model compared with the Higuchi model, a zero-order model or a first order mode. The release behavior of the fertilizer beads followed a Fickian diffusion mechanism.