Three d10 based metal-organic frameworks constructed from 2-(3’,4’-dicarboxylphenoxy) isophthalic acid: Dual-functional luminescent sensors for Cu2+, Fe3+ cations and Aspartic acid

Constructing functional metal-organic frameworks by ligand design for environmental applications

Metal-organic frameworks (MOFs) with unique physical and chemical properties are composed of metal ions/clusters and organic ligands, including high porosity, large specific surface area, tunable structure and functionality, which have been widely used in chemical sensing, environmental remediation, and other fields. Organic ligands have a significant impact on the performance of MOFs. Selecting appropriate types, quantities and properties of ligands can well improve the overall performance of MOFs, which is one of the critical issues in the synthesis of MOFs. This article provides a comprehensive review of ligand design strategies for functional MOFs from the number of different types of organic ligands. Single-, dual- and multi-ligand design strategies are systematically presented. The latest advances of these functional MOFs in environmental applications, including pollutant sensing, pollutant separation, and pollutant degradation are further expounded. Furthermore, an outlook section of providing some insights on the future research problems and prospects of functional MOFs is highlighted with the purpose of conquering current restrictions by exploring more innovative approaches.

pH modulated luminescent switching and discriminative detection of amino acid based on metal-organic framework

The detection of glutamic (Glu) or aspartic (Asp) acids is vital for human nutrition and diagnosis of disease. Herein, the dht ligand containing hydroxy group (-OH) is used to design and synthesize a 2D luminescent [Cd₂(idc)(dht)(H₂O)₄] (1); H₂idc = 4,5-imidazoledicarboxylic acid and H₂dht = 2,5-dihydroxyterephthalic acid for sensing amino acids. The compound 1 can discriminatively detect Asp and Glu among other amino acids through blue-shifted emission (yellow → green). The dual sensing mechanism may be attributed to the intermolecular excited-state proton transfer between MOF and water to produce keto form along with the subsequent switching of keto form to enol form by protonation causing the increased band gap energy. This material can serve several benefits in terms of high selectivity, fast response (30s), good reproducibility and low LOD value of 11.34 μM which is less than the harmful concentration of Glu for human health (>400 μM). In addition, 1 shows the broad range detection of Glu covering in safe and unsafe levels. For on-site detection of Glu, MOF-based paper is devised and can be applied through color-scanning application in smartphone. Besides, this sensor can serve to detect Glu in real samples with good recovery.

Pillared Metal-Organic Framework Initiating Intermolecular Atom-Transfer Radical Addition via Visible-Light-Induced Electron Transfer Activation of Haloalkanes

Herein, a novel metal-organic framework (MOF) with a pillared-layer structure was rationally synthesized to initiate intermolecular atom-transfer radical addition (ATRA) via photoinduced electron transfer activation of haloalkanes. The MOF synthesized via the controllable pillared-layer method is of excellent visible-light absorption and high chemical stability. Photocatalytic experiments show the atom transfer of various alkyl halides (R-X, X = Cl/Br/I) onto diverse olefins was successfully achieved to produce functional ATRA products. The mechanism and experimental investigations reveal the prepared MOF serves as an efficient photocatalyst with strong reduction potential to activate haloalkane substrates via photoinduced electron transfer, generating a highly reactive alkyl radical to trigger the ATRA reaction. Key events in the ATRA reaction, including alkyl radical photogeneration as well as halide transfer, have been further regulated to achieve preferable photocatalytic performance with higher yields, shorter reaction time, and desirable cycling capability. It is notable that the work is the first report on photoinduced electron transfer activation of halides by a MOF photocatalyst for the ATRA reaction, providing a new blueprint for MOFs to develop photoinduced radical reactions.