Synthesis of bio-based MIL-100(Fe)@CNF-SA composite hydrogel and its application in slow-release N-fertilizer

With the severe shortage of water resources and the low utilization efficiency of fertilizer, slow-release fertilizer equipped with water-absorbing and water-retaining capacity has captured much attention. Herein, by integrating metal-organic frameworks (MOFs) with cellulose nanofibres (CNFs) and sodium alginate (SA), a novel cellulose-based hydrogel (MIL-100(Fe)@CNF-SA) was fabricated that acted as a carrier for urea. The resultant hydrogel was not only qualified with a high surface area of 129.17 m2/g but also affluent in the hydrophilic groups. In parallel with the good water-holding capacity of 55% when the loading of the resultant hydrogel was only 0.5 g, the complete loss of the water in the treated soil was successfully slowed down by nearly 20 d compared with the soil without treatment. Urea (1.47 g/g) could be captured in the composite hydrogel, wherein the slow release of urea was achieved due to the synergism of the highly porous structure of the hydrogel and the crystals with a high specific surface area. Moreover, the positive effect of the resultant hydrogel on the growth of wheat was indexed to the germination rate, number of tillers, photosynthetic rate and chlorophyll content of the crop, which verified their further application in irrigating farming.