Photo - electrically responsive dual - network alginate-based composite hydrogels for the controlled release of plant essential nutrients

Hydrogel materials hold great potential in agriculture. In this study, a photo-electric controlled-release doublenetwork hydrogel carrier was fabricated based on polyacrylamide (PAM) and sodium alginate (SA) with the montmorillonite (MMT). This double-network (DN) structure of Fe3+/SA-PAM-MMT (SPM-Fe3+) gel can efficiently improve stability of the carrier through radical polymerization and ion cross-linking reactions. The physicochemical properties of the composite hydrogels were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, differential scanning calorimeter, rheometer, electronic universal testing machine and scanning electron microscopy. The SPM-Fe3+ gel carriers exhibit excellent mechanical properties and photo-electric responsiveness, attributed to their double-network structure and incorporation of MMT. The pore size of the SPM - Fe3+ gel expands under an electric field due to the Coulomb force of carboxyl group on the SA chain. Additionally, the structure of SPM-Fe3+ was broken under UV-irradiation due to the photochemical reaction of Fe3+-SA. The release of urea is regulated by this photoelectrochemical stimulus responsive mechanism. Therefore, this work provides a promising approach to prepare dual-responsive controlled-release carriers and demonstrates that SPM-Fe3+-5 % double-network hydrogel has potential applications in controlled-release fertilizers.