Iron-Based Metal–Organic Frameworks and Their Polymer Composites for Sustainable Delivery of Herbicides

Sustainable agriculture will play a key role in ensuring food security for the rising global population. Controlled and precision delivery of agrochemicals, such as herbicides and pesticides, plays a critical role in sustainable agriculture. Recently, porous metal–organic frameworks (MOFs) have shown promising results for controlled agrochemical delivery. Because of their low toxicity and biocompatibility, iron-based metal–organic frameworks (Fe-MOFs) are highly suitable for applications in agriculture over many other MOFs. In this study, two iron-based MOFs, MIL-101(Fe) and NH₂-MIL-101(Fe), and their biodegradable polymer composites were studied for controlled herbicide delivery. Two herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), were postsynthetically loaded into these two Fe-MOFs and incorporated into a biodegradable polycaprolactone (PCL) matrix to form composite membranes for ease of handling and delivery. MIL-101(Fe) showed loading capacities of 18.06 and 21.51 wt %, respectively, for 2,4-D and MCPA, while for NH₂-MIL-101(Fe), the loading capacities for the same herbicides were 26.61 and 23.32 wt %. Despite high loading capacity, both MOFs showed a certain degree of degradation during herbicide loading. The release of 2,4-D and MCPA from MIL-101(Fe) and NH₂-MIL-101(Fe) and their PCL composites were studied using UV–visible spectroscopy over a nine-day period. NH₂-MIL-101(Fe) and its PCL composite demonstrated slower and more controlled release profiles of the herbicides compared to MIL-101(Fe) and its composites. The results were also corroborated by computational studies, which showed stronger interactions of the herbicides with NH₂-MIL-101(Fe).