Urea-Loaded Core–Shell MOF/Silica Nanocarriers for Continuous Nitrogen Release to Crops

Nitrogen is currently the most crucial nutrient for crop growth, and the overdose of conventional urea nitrogen fertilizer has resulted in both the waste of fertilizer resource and the eutrophication of water bodies due to low nitrogen use efficiency. Herein, a smart core–shell nanocarrier (MIL-100(Fe)/silica) was fabricated to deliver urea to enhance the use efficiency for sustainable nitrogen management. The results showed that the developed urea/MIL-100(Fe)/silica had a stable core–shell nanostructure with a highly crystallized regular octahedron, which achieved a high nitrogen loading of 25.5%; the duration of the nitrogen release period was up to 56 days in an aqueous solution, which matched well with rice growth. The slow release of urea from the urea/MIL-100(Fe)@silica nanocarrier was ascribed to the silica shell material and hydrogen bonding preventing the premature escape of urea from the MIL-100(Fe) core in the environment. In a pot experiment, the nitrogen use efficiency (NUE) of urea/MIL-100(Fe)/silica treatment (45.5%) was significantly enhanced compared to that of the urea treatment (34.7%) and promoted the grain yield by 13.07%. Therefore, the proposed fertilization strategy based on urea/MIL-100(Fe) significantly benefited both the rice growth and nitrogen use efficiency, providing a promising nanoplatform for precise and efficient nutrient supply.