Xuelian Xin

Metal–organic frameworks based luminescent materials for nitroaromatics sensing

Metal–organic frameworks (MOFs), composed of organic ligands and metal nodes, are well known for their high and permanent porosity, crystalline nature and versatile potential applications, which promoted them to be one of the most rapidly developing research focuses in chemical and materials science. During the various applications of MOFs, the photoluminescence properties of MOFs have received growing attention, especially for nitroaromatics (NACs) sensing, due to the consideration of homeland security, environmental cleaning and military issues. In this highlight, we summarize the progress in recent research in NACs sensing based on LMOFs cataloged by sensing techniques in the past three years, and then we describe the sensing applications for nano-MOF type materials and MOF film, together with MOF film applications.

A multifunctional Eu MOF as a fluorescent pH sensor and exhibiting highly solvent-dependent adsorption and degradation of rhodamine B

Due to their tunable structure and porosity, metal–organic frameworks have provided a new platform for fluorescence sensing and adsorption/separation of gas or organic molecules. Many studies have focused on sensing metal ions, anions, or organic molecules through fluorescence quenching or enhancement of MOFs, but studies on pH-fluorescence sensors are seldom reported. Furthermore, highly solvent-dependent adsorption and degradation of dye molecules based on functional MOFs has not been explored to date. In this study, we describe a multifunctional Eu MOF, [H3O][Eu3(HBPTC)2(BPTC)(H2O)2]·4DMA (UPC-5, UPC = China University of Petroleum [East China]) based on a tetracarboxylate ligand. The luminescence intensity of UPC-5 is strongly correlated with the pH value in the pH range from 7.5 to 10.0, and a linear relationship between pH value and fluorescent intensity is observed. Another attractive property of UPC-5 is that its Li-exchanged form, Li-UPC-5, possesses solvent-dependent adsorption and degradation of rhodamine B. The highly efficient degradation or decolorization of rhodamine B with long-term stability and activity gives Li-UPC-5 a potential advantage in treating rhodamine B pollution.

A multi-aromatic hydrocarbon unit induced hydrophobic metal–organic framework for efficient C2/C1 hydrocarbon and oil/water separation

Oil spills have led to more and more energy waste and economic losses all over the world. Developing highly hydrophobic materials for efficient oil/water separation has become key in solving this global issue. Here we report a highly hydrophobic porous metal–organic framework, named UPC-21, constructed from a pentiptycene-based organic ligand, for efficient oil/water separation. Large and pure crystals of UPC-21 could be obtained with high yield through a developed “diauxic growth” strategy. Due to the existence of multi-aromatic hydrocarbon units in the central pentiptycene core of the ligand, UPC-21 exhibits high hydrophobicity with a water contact angle of 145 ± 1° and superoleophilicity with an oil contact angle of 0°. Strikingly, oil/water separation measurements reveal that UPC-21 can efficiently separate toluene/water, hexane/water, gasoline/water, naphtha/water, and crude oil/water with a separation efficiency being above 99.0% except for crude oil/water due to its high viscosity and complex composition. Our work presented here may open a new avenue for the application of porous MOF materials.

Cyclodextrin-Based Metal-Organic Nanotube as Fluorescent Probe for Selective Turn-On Detection of Hydrogen Sulfide in Living Cells Based on H2S-Involved Coordination Mechanism.

Hydrogen sulfide (H2S) has been considered as the third biologically gaseous messenger (gasotransmitter) after nitric oxide (NO) and carbon monoxide (CO). Fluorescent detection of H2S in living cells is very important to human health because it has been found that the abnormal levels of H2S in human body can cause Alzheimer’s disease, cancers and diabetes. Herein, we develop a cyclodextrin-based metal-organic nanotube, CD-MONT-2, possessing a {Pb14} metallamacrocycle for efficient detection of H2S. CD-MONT-2′ (the guest-free form of CD-MONT-2) exhibits turn-on detection of H2S with high selectivity and moderate sensitivity when the material was dissolved in DMSO solution. Significantly, CD-MONT-2′ can act as a fluorescent turn-on probe for highly selective detection of H2S in living cells. The sensing mechanism in the present work is based on the coordination of H2S as the auxochromic group to the central Pb(II) ion to enhance the fluorescence intensity, which is studied for the first time.

Fluorescence turn-on detection of uric acid by a water-stable metal–organic nanotube with high selectivity and sensitivity

Herein we provide a new strategy for fluorescence detection of uric acid (UA) using a metal–organic nanotube of CD-MONT-2 for the first time. This novel fluorescent probe exhibits high selectivity and sensitivity for UA with a very good detection limit of 4.3 μM. The results of density functional theory calculations and 1H NMR spectra show that the turn-on sensing mechanism arises from the host–guest interactions of capsule-like CD-MONT-2 with UA to result in electron transfer between UA and CD-MONT-2′. Furthermore, CD-MONT-2′ exhibits very fast adsorption of UA molecules in aqueous solution as confirmed by UV-Vis spectra and HPLC analysis, making it a potential candidate for application in the removal of UA from the human blood.

A visual test paper based on Pb(II) metal–organic nanotubes utilized as a H2S sensor with high selectivity and sensitivity

The fluorescent Pb(II)–metal–organic nanotube, CD-MONT-2, which possesses a large {Pb14} metallamacrocycle, is synthesized by a modified biphasic liquid–solid–liquid (BLSL) strategy. This strategy takes advantage of solid cyclohexanol to avoid generation of by-products, and is suitable for producing CD-MONT-2 on a large scale. Importantly, water-stable CD-MONT-2 can be easily made into H2S test papers by coating a solution mixture of sodium carboxymethyl cellulose and CD-MONT-2′ on glass plates, which have the characteristics of high efficiency, rapidity, and visualization based on its fluorescence “turn-off” response. The CD-MONT-2 based visual test papers can be used without pretreatment and possess excellent sensitivity and stability.