Jonathan A. Foster

Metal–organic nanosheets (MONs) are porous 2D materials ideal for use as membranes in separation applications. Here, an isoreticular series of Zr based MONs prepared on a highly porous substrate are investigated for dye separation applications.

Polyisocyanurate (PIR) foams are widely used as insulation, but their performance reduces over time leading to higher heating costs. The addition of metal–organic frameworks have potential for improvement of PIR foam's lifetime performance.

Strong in‐layer interactions are typically considered a key requirement for exfoliating layered materials to form nanosheets. Here, the formation of free‐standing nanosheets held together by halogen bonding interactions is reported for the first time. Layered co‐crystals are synthesized using either iodo‐ or bromo‐functionalized halogen bond donors with pyridyl functionalized acceptors. Sonication resulted in dissolution in a range of polar organic solvents; however, stable suspensions showing Tyndall scattering are observed for the iodo‐systems after exfoliation in water. Atomic force microscopy confirms the formation of micron‐sized nanosheets approaching monolayer thickness. Powder X‐ray diffraction of the nanosheets shows preferred orientation along the (1 1 0) plane, which confirms that the nanosheets are composed of halogen‐bonded chains in one dimension, and π – π stacking interactions in the second. The iodo‐nanosheets are stable in acidic and alkaline conditions and when heated at 80 °C for 48 h. Comparisons between the iodo‐ and bromo‐ analogues confirm that stronger halogen bonding is likely responsible for the difference in stability. The remarkable stability shown by these nanosheets held together by only supramolecular interactions calls for re‐evaluation of the conventional understanding of the requirements for forming 2D materials and establishes halogen‐bonded nanosheets as an exciting new class of materials.

Polyisocyanurate (PIR) foams are widely used to insulate buildings, but their performance reduces over time leading to wasted energy and higher heating costs. High molecular weight gases used to blow the foams gradually diffuse out and are replaced by air leading to an increase in thermal conductivity. A wide variety of additives have been tested to improve the barrier properties of polymers including metal-organic frameworks (MOFs) which have proved promising candidates thanks to their tunable surface chemistry. In this work, a new and robust method for determining gas loss from rigid PIR foams has been developed, and utilised to determine the effect of different MOF additives on gas loss. An accelerated ageing method was developed, in which the mass of a fixed volume of foam was kept in an oven at 70 °C and weighed at 24 hour time intervals. This was found to provide reproducible measurements of gas loss over a period of 28 days with a variation of 1.1 % by mass for typical samples. Five different MOFs were added to polyisocyanurates, and their effects on cell size, closed cell content, and gas loss over time were measured. Cu(ABDC)(DMF) was found to enhance the gas retention of PIR foams with minimal change to cell size or closed cell content. A modulated (flower-like) NH2-MIL-53 MOF increased the closed cell fraction whilst reducing cell size, with no effect on gas loss, whilst an unmodulated (cube like) NH2-MIL-53 MOF increased the gas loss without affecting cell size or closed cell percentage. Two further MOFs, Cu(BTetC)(DMF) and Cu(BDC)(DMF), were found to have no effect. This work therefore identifies Cu(ABDC)(DMF) as a promising additive for reducing gas-loss and maintaining the long-term performance in PIR foams, with its effectiveness demonstrated via an accelerated ageing technique developed for this study.

The development of materials that mimic the catalytic activity of natural enzymes, so called nanozymes, are of crucial importance in biochemical and biotechnological fields. A Zr‐pyridine tribenzoate metal‐organic framework nanosheet (MON), Zr‐PTB with 6‐connected Zr₆O₈ clusters is synthesized via a formic acid modulated solvothermal synthesis. The catalytic activity of MON, graphene‐like 2D materials which possess large external surface areas and tunable properties, is reported for the first time toward peptide bond hydrolysis of various peptides and proteins. Structure‐reactivity analysis and the comparison with Zr‐BTB (BTB = 1,3,5‐tri(4‐carboxyphenylbenzene)), a structural analogue of Zr‐PTB with a more hydrophobic linker, revealed a delicate interplay between coordination bonds and hydrophobic interactions with the MON's surface as the main driving forces influencing reactivity. Compared to 3D MOFs, Zr‐PTB produced a larger number of peptide fragments, indicating the importance of larger external surface area with easily accessible catalytically active sites for more comprehensive hydrolysis of proteins. The advantage of 2D MONs with respect to 3D MOFs, where pore sizes and diffusion of large substrates is a limiting factor influencing their reactivity, is further reflected by the ability to hydrolyze very large proteins. The exceptional stability of Zr‐PTB allowed for its recyclability for over 5 reaction cycles.

Metal–organic framework nanosheets (MONs) have proved themselves to be useful additives for enhancing the performance of a variety of thin film solar cell devices. However, to date only isolated examples have been reported. In this work we take advantage of the modular structure of MONs in order to resolve the effect of their different structural and optoelectronic features on the performance of organic photovoltaic (OPV) devices. Three different MONs were synthesized using different combinations of two porphyrin-based ligands meso-tetracarboxyphenyl porphyrin (TCPP) or tetrapyridyl-porphyrin (TPyP) with either zinc and/or copper ions and the effect of their addition to polythiophene-fullerene (P3HT-PC₇₁BM) OPV devices was investigated. The power conversion efficiency (PCE) of devices was found to approximately double with the addition of MONs of Zn₂(ZnTCPP) -4.7% PCE, 10.45 mA/cm² short-circuit current density (J_SC), 0.69 open-circuit voltage (V_OC), 64.20% fill-factor (FF), but was unchanged with the addition of Cu₂(ZnTPyP) (2.6% PCE, 3.68 mA/cm²J_SC, 0.59 V_OC, 46.27% FF) and halved upon the addition of Cu₂(CuTCPP) (1.24% PCE, 6.72 mA/cm²J_SC, 0.59 V_OC, 56.24% FF) compared to devices without nanosheets (2.6% PCE, 6.61 mA/cm²J_SC, 0.58 V_OC, 56.64% FF). Our analysis indicates that there are three different mechanisms by which MONs can influence the photoactive layer – light absorption, energy level alignment, and morphological changes. Analysis of external quantum efficiency, UV–vis and photoelectron spectroscopy data found that MONs have similar effects on light absorption and energy level alignment. However, atomic force and Raman microscopy studies revealed that the nanosheet thickness and lateral size are crucial parameters in enabling the MONs to act as beneficial additives resulting in an improvement of the OPV device performance. We anticipate this study will aid in the design of MONs and other 2D materials for future use in other light harvesting and emitting devices.

Peptides are important biomarkers for various diseases, however distinguishing specific amino‐acid sequences using artificial receptors remains a major challenge in biomedical sensing. This study introduces a new approach for creating highly selective recognition surfaces using phage display biopanning against metal–organic nanosheets (MONs). Three MONs (ZIF‐7, ZIF‐7‐NH_2, and Hf‐BTB‐NH₂) are added to a solution containing every possible combination of seven‐residue peptides attached to bacteriophage hosts. The highest affinity peptides for each MON are isolated through successive bio‐panning rounds. Comparison of the surface properties of the MONs and high‐affinity peptides provide useful insights into the relative importance of electrostatic, hydrophobic, and co‐ordination bonding interactions in each system, aiding the design of future MONs. Coating of the Hf‐BTB‐NH₂ MONs onto a quartz crystal microbalance (QCM) produced a five‐fold higher signal for phage with the on‐target peptide sequence compared to those with generic sequences. Surface plasmon resonance (SPR) studies produce a 4600‐fold higher equilibrium dissociation constant (K_D) for on‐target sequences and are comparable to those of antibodies (K_D = 4 x 10⁻¹⁰ m). It is anticipated that insights from the biopanning approach, combined with the highly tunable nature of MONs, will lead to a new generation of highly selective recognition surfaces for use in biomedical sensors.

The effects of linker length on nanosheet dimensions and properties are investigated through the ultrasonic liquid exfoliation of an isoreticular series of layered metal–organic frameworks.

Two-dimensional metal-organic nanosheets (MONs) have emerged as attractive alternatives to their three-dimensional metal-organic framework (MOF) counterparts for heterogeneous catalysis due to their greater external surface areas and higher accessibility of catalytically active sites. Zr MONs are particularly prized because of their chemical stability and high Lewis and Brønsted acidities of the Zr clusters. Herein, we show that careful control over modulated self-assembly and exfoliation conditions allows the isolation of the first example of a two-dimensional nanosheet wherein Zr₆ clusters are linked by dicarboxylate ligands. The hxl topology MOF, termed GUF-14 (GUF = Glasgow University Framework), can be exfoliated into monolayer thickness hns topology MONs, and acid-induced removal of capping modulator units yields MONs with enhanced catalytic activity toward the formation of imines and the hydrolysis of an organophosphate nerve agent mimic. The discovery of GUF-14 serves as a valuable example of the undiscovered MOF/MON structural diversity extant in established metal-ligand systems that can be accessed by harnessing the power of modulated self-assembly protocols.