Controlling the Uptake and Release of Semiochemicals in Channel-Type Metal-Organic Frameworks Through Pore Expansion.

Semiochemicals can be used to manipulate insect behaviour for sustainable pest management strategies, but their high volatility is a major issue for their practical implementation. Inclusion of these molecules within porous materials is a potential solution to this issue, as it can allow for a slower and more controlled release. In this work, we demonstrate that a series of Zr(IV) and Al(III) metal-organic frameworks (MOFs) with channel-type pores enable controlled release of three semiochemicals over 100 days by pore size design, with the uptake and rate of release highly dependent on the pore size. Insight from grand canonical Monte Carlo simulations indicates that this is due to weaker MOF-guest interactions per guest molecule as the pore size increases. These MOFs are all stable post-release and can be reloaded to show near-identical re-release profiles. These results provide valuable insight on the diffusion behaviour of volatile guests in MOFs, and for the further development of porous materials for sustainable agriculture applications.

Post-exfoliation functionalisation of metal-organic framework nanosheets via click chemistry.

The liquid exfoliation of layered metal-organic frameworks (MOFs) to form nanosheets (MONs) exposes buried functional groups making them useful in a range of sensing and catalytic applications. Here we show how high yielding click reactions can be used post-exfoliation to systematically modify the surface chemistry of MONs allowing for tuning of their surface properties and their use in new applications. A layered amino-functionalised framework is converted through conventional post-synthetic functionalisation of the bulk MOF to form azide functionalised frameworks of up to >99% yield. Ultrasonic liquid exfoliation is then used to form few-layer nanosheets, which are further functionalised through post exfoliation functionalisation using Cu(I)-catalysed azide-alkyne cycloaddition reactions. Here we demonstrate the advantages of post-exfoliation functionalisation in enabling: (1) a range of functional groups to be incorporated in high yields; (2) tuning of nanosheet surface properties without the need for extensive recharacterisation; (3) the addition of fluorescent functional groups to enable their use in the sensing of hazardous nitrobenzene. We anticipate that the versatility of different functional groups that can be introduced through high yielding click reactions will lead to advances in the use of MONs and other 2D materials for a variety of applications.

Monolayer nanosheets formed by liquid exfoliation of charge-assisted hydrogen-bonded frameworks.

Hydrogen-bonded organic frameworks (HOFs) are a diverse and tunable class of materials, but their potential as free-standing two-dimensional nanomaterials has yet to be explored. Here we report the self-assembly of two layered hydrogen-bonded frameworks based on strong, charge-assisted hydrogen-bonding between carboxylate and amidinium groups. Ultrasound-assisted liquid exfoliation of both materials readily produces monolayer hydrogen-bonded organic nanosheets (HONs) with micron-sized lateral dimensions. The HONs show remarkable stability and maintain their extended crystallinity and monolayer structures even after being suspended in water at 80 °C for three days. These systems also exhibit efficient fluorescence quenching of an organic dye in organic solvents, superior to the quenching ability of the bulk frameworks. We anticipate that this approach will provide a route towards a diverse new family of molecular two-dimensional materials.

Tandem catalysis by ultrathin metal-organic nanosheets formed through post-synthetic functionalisation of a layered framework.

Covalent post-synthetic functionalisation of layered metal-organic frameworks is demonstrated as a new approach to forming ultrathin nanosheets for use in catalysis. An aminoterephthalate framework was partially functionalised with sulfonate chains and exfoliated to form predominantly monolayer nanosheets able to catalyse a two-step acid-base reaction in one pot.