An entrapped metal-organic framework system for controlled release of ethylene

A novel gas storage and release system was developed for ethylene, an exogenous plant hormone that regulates fruit ripening and senescence. This system consists of a metal organic framework (MOF) core and an alginate-based shell. The MOF comprises a coordination complex of Al and [btc]^3- ligands, which formed hexagonal structure (P6₃/mmc) with unit cell of 14.28 × 14.28 × 31.32 ų, as revealed by the X-ray diffraction analysis. Ethylene absorption isotherm exhibited an absorption capacity of 41.0 cm³/g MOF at 25 °C and 101.3 kPa. After charging with ethylene, the MOFs are further entrapped in a close-knit bead formed with alginate-Fe(III) matrix, observed under a scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The alginate shell is degraded by exposing to 200 mM sodium citrate aqueous solution, triggering a continuous release of ethylene. With 20 mg of MOF, ethylene concentration reached 0.41-0.46 mg/L per mg MOF after 2.5 h. This is the first report regarding a controlled release of ethylene through degrading alginate-Fe(III) matrix rather than by changing the interfacial pore size of MOF under extreme conditions. This technology can enable precisely controlled and targeted applications of ethylene for food processing and agricultural applications.