Controlling the Packing of Metal-Organic Layers by Inclusion of Polymer Guests

Interfacing metal organic frameworks with polymers or carbon-based materials: from simple to hierarchical porous and nanostructured composites

In the past few years, metal organic frameworks (MOFs) have been assembled with (bio)polymers and a series of carbon-based materials (graphene, graphene oxide, carbon nanotubes, carbon quantum dots, etc.) leading to a wide range of composites differing in their chemical composition, pore structure and functionality. The objective was mainly to overcome the limitations of MOFs in terms of mechanical properties, chemical stability and processability while imparting novel functionality (electron conductivity, (photo)catalytic activity, etc.) and hierarchical porosity. These composites were considered for numerous applications including gas/liquid adsorption and separation, (photo)catalysis, biomedicine, energy storage, conversion and so on. The performance of such composites depends strongly on their microstructural and physico-chemical properties which are mainly driven by the chemical strategies used to design and process such composites. In this perspective article, we propose to cover this topic and provide a useful survey of recent progress in the synthesis and design of MOFs-carbon material composites. This article will describe the development of composites with increasing complexity in terms of porous architecture, spatial structuration and organisation, and functionality.

Bottom-Up Synthesis of Covalent Organic Frameworks with Quasi-Three-Dimensional Integrated Architecture via Interlayer Cross-Linking

Developing strategies to enhance the structural robustness of covalent organic frameworks (COFs) is of great importance. Here, we rationally design and synthesize a class of cross-linked COFs (^CCOFs), in which the two-dimensional (2D) COF layers are anchored and connected by polyethylene glycol (PEG) or alkyl chains through covalent bonds. The bottom-up fabrication of these ^CCOFs is achieved by the condensation of cross-linked aldehyde monomers and tritopic amino monomers. All the synthesized ^CCOFs possess high crystallinity and porosity, and enhanced structural robustness surpassing the typical 2D COFs, which means that they cannot be exfoliated under ultrasonication and grinding due to the cross-linking effect. Furthermore, the cross-linked patterns of PEG units are uncovered by experimental results and Monte Carlo molecular dynamics simulations. It is found that all ^CCOFs are dominated by vertical cross-layer (interlayer) connections (clearly observed in high-resolution transmission electron microscopy images), allowing them to form quasi-three-dimensional (quasi-3D) structures. This work bridges the gap between 2D COFs and 3D COFs and provides an efficient way to improve the interlayered stability of COFs.

An Efficient, Multiplexed Strategy for Instant Detection of Bacterial Biomarker by a Lanthanide-Organic Material

Water contamination is a highly critical issue owing to its strong relationship to human health. In addition to chemical pollutants, microorganisms such as multiresistant pathogenic bacteria have received significant attention from the World Health Organization. The main problem associated with monitoring pathogenic bacteria in water is the interference from concomitant species and their low concentrations. To address this problem, we synthesized a bilanthanide-organic material as an efficient luminescence sensor for the detection of Pseudomonas aeruginosa, a representative bacterium, via its two unique biomarkers: 1-hydroxyphenazine (1-HX) and 2-aminoacetophenone (2-AA). This multiplexed sensing approach overcomes a common issue encountered by single-marker luminescence sensors that may report false positives due to coexisting species in the complex environment. High sensitivities and low limits of detection for 1-HX and 2-AA were obtained with very fast response time. The key structural factors governing the high-performance sensing function were revealed. This work provides an alternative route for the effortless and instant detection of bacterial biomarkers in water.

PEG-stabilized coaxial stacking of two-dimensional covalent organic frameworks for enhanced photocatalytic hydrogen evolution

Two-dimensional covalent organic frameworks (2D COFs) featuring periodic frameworks, extended π-conjugation and layered stacking structures, have emerged as a promising class of materials for photocatalytic hydrogen evolution. Nevertheless, the layer-by-layer assembly in 2D COFs is not stable during the photocatalytic cycling in water, causing disordered stacking and declined activity. Here, we report an innovative strategy to stabilize the ordered arrangement of layered structures in 2D COFs for hydrogen evolution. Polyethylene glycol is filled up in the mesopore channels of a β-ketoenamine-linked COF containing benzothiadiazole moiety. This unique feature suppresses the dislocation of neighbouring layers and retains the columnar π-orbital arrays to facilitate free charge transport. The hydrogen evolution rate is therefore remarkably promoted under visible irradiation compared with that of the pristine COF. This study provides a general post-functionalization strategy for 2D COFs to enhance photocatalytic performances.