Aamod V. Desai

Selective and Sensitive Aqueous‐Phase Detection of 2,4,6‐Trinitrophenol (TNP) by an Amine‐Functionalized Metal–Organic Framework

Highly selective and sensitive aqueous-phase detection of nitro explosive 2,4,6-trinitrophenol (TNP) by a hydrolytically stable 3D luminescent metal-organic framework is reported. The compound senses TNP exclusively even in the presence of other nitro-compounds, with an unprecedented sensitivity in the MOF regime by means of strategic deployment of its free amine groups. Such an accurate sensing of TNP, widely recognized as a harmful environmental contaminant in water media, establishes this new strategic approach as one of the frontiers to tackle present-day security and health concerns in a real-time scenario.

A Water‐Stable Cationic Metal–Organic Framework as a Dual Adsorbent of Oxoanion Pollutants

A three-dimensional water-stable cationic metal-organic framework (MOF) pillared by a neutral ligand and with Ni(II)  metal nodes has been synthesized employing a rational design approach. Owing to the ordered arrangement of the uncoordinated tetrahedral sulfate (SO4 (2-) ) ions in the channels, the compound has been employed for aqueous-phase ion-exchange applications. The compound exhibits rapid and colorimetric aqueous-phase capture of environmentally toxic oxoanions (with similar geometries) in a selective manner. This system is the first example of a MOF-based system which absorbs both dichromate (Cr2 O7 (2-) ) and permanganate (MnO4 (-) ) ions, with the latter acting as a model for the radioactive contaminant pertechnetate (TcO4 (-) ).

Engineering metal–organic frameworks for aqueous phase 2,4,6-trinitrophenol (TNP) sensing

2,4,6-Trinitrophenol (TNP) is a highly explosive molecule that is also widely used in industrial processing on a large scale. During synthesis, processing and disposal, TNP is released to the environment especially to water streams, contaminating ground and surface water. TNP and its biologically transformed products like picramic acids have been identified as highly toxic species to biota and may lead to chronic diseases such as sycosis and cancer. Thus, aqueous phase detection of TNP becomes an imperative aspect for the design of any potential sensor. Metal–organic frameworks (MOFs) have emerged as an important class of sensors owing to their permanent porosity, designability and variety of signal transduction pathways. Luminescent MOFs (LMOFs) have shown great potential as sensors for various nitro explosives by modulation of their luminescence behaviour in the presence of nitro explosives. Most of the LMOFs detect nitro explosives in the vapour phase and/or in organic solvents while aqueous phase detection is rarely investigated. Herein we present recent developments in the area of LMOFs for aqueous phase TNP sensing and discuss strategies used to improve the sensing performance. Finally, based on our perspective, important aspects of LMOF performance needing immediate attention for future developments are provided.

Metal-organic framework based highly selective fluorescence turn-on probe for hydrogen sulphide

Hydrogen sulphide (H2S) is known to play a vital role in human physiology and pathology which stimulated interest in understanding complex behaviour of H2S. Discerning the pathways of H2S production and its mode of action is still a challenge owing to its volatile and reactive nature. Herein we report azide functionalized metal-organic framework (MOF) as a selective turn-on fluorescent probe for H2S detection. The MOF shows highly selective and fast response towards H2S even in presence of other relevant biomolecules. Low cytotoxicity and H2S detection in live cells, demonstrate the potential of MOF towards monitoring H2S chemistry in biological system. To the best of our knowledge this is the first example of MOF that exhibit fast and highly selective fluorescence turn-on response towards H2S under physiological conditions.

Hydrogen-Bonded Organic Frameworks (HOFs): A New Class of Porous Crystalline Proton-Conducting Materials

Two porous hydrogen-bonded organic frameworks (HOFs) based on arene sulfonates and guanidinium ions are reported. As a result of the presence of ionic backbones appended with protonic source, the compounds exhibit ultra-high proton conduction values (σ) 0.75× 10(-2)  S cm(-1) and 1.8×10(-2)  S cm(-1) under humidified conditions. Also, they have very low activation energy values and the highest proton conductivity at ambient conditions (low humidity and at moderate temperature) among porous crystalline materials, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). These values are not only comparable to the conventionally used proton exchange membranes, such as Nafion used in fuel cell technologies, but is also the highest value reported in organic-based porous architectures. Notably, this report inaugurates the usage of crystalline hydrogen-bonded porous organic frameworks as solid-state proton conducting materials.

A Nitro-Functionalized Metal–Organic Framework as a Reaction-Based Fluorescence Turn-On Probe for Rapid and Selective H2S Detection

The toxic gas H2 S has recently emerged as one of the important signaling molecules in biological systems. Thus understanding the production, distribution, and mode of action of H2 S in biological system is important, but the fleeting and reactive nature of H2 S makes it a daunting task. Herein we report a biocompatible, nitro-functionalized metal-organic framework as reaction-based fluorescence turn-on probe for fast and selective H2 S detection. The selective turn-on performance of MOF remains unaffected even in presence of competing biomolecules.

Framework-Flexibility Driven Selective Sorption of p -Xylene over Other Isomers by a Dynamic Metal-Organic Framework

Chemical separation has great importance in industrial applications. Separation of xylene isomers still prevails to be one of the most important challenges in chemical industry, due to the large amount of commercial use of p-xylene in the production of beverage bottles, fibers and films. A novel Zn(II)-based dynamic coordination framework based on flexible ether-linkage, exhibiting selective adsorption of p-Xylene over its congener C8-alkyl aromatic isomers at ambient conditions is reported. Notably, no dynamic structure based MOF compound is known in the literature which shows clear preference of p-xylene over other isomers. This type of framework-breathing and guest-induced reversible solid-state structural transformations with unique adsorption selectivity can be exploited purposefully to develop smart functional host materials capable of industrially important chemical separations.

Selective anion exchange and tunable luminescent behaviors of metal-organic framework based supramolecular isomers.

Owing to the conformational (cis or trans) flexibility of a N-donor ligand, the combinations of the same and Cd(ClO4)2 under variable solvent templates afforded two supramolecular isomers based on two-dimensional metal-organic frameworks. Both compounds contain weakly coordinating ClO4(-) anions attached to the metal centers. Both frameworks showed facile anion exchange behaviors with various kinds of foreign anions. Moreover, both frameworks showed anion-driven structural dynamism and exhibited the preferential uptake of strongly coordinating anions over others. Anion-regulated modulation in luminescent behaviors was also observed in both cases.

A Post-Synthetically Modified MOF for Selective and Sensitive Aqueous-Phase Detection of Highly Toxic Cyanide Ions.

Selective and sensitive detection of toxic cyanide (CN(-) ) by a post-synthetically altered metal-organic framework (MOF) has been achieved. A post-synthetic modification was employed in the MOF to incorporate the specific recognition site with the CN(-) ion over all other anions, such as Cl(-) , Br(-) , and SCN(-) . The aqueous-phase sensing and very low detection limit, the essential prerequisites for an effective sensory material, have been fulfilled by the MOF. Moreover, the present detection level meets the standard set by the World Health Organization (WHO) for the permissible limit of cyanide concentration in drinking water. The utilization of MOF-based materials as the fluorometric probes for selective and sensitive detection of CN(-) ions has not been explored till now.

An Amide‐Functionalized Dynamic Metal–Organic Framework Exhibiting Visual Colorimetric Anion Exchange and Selective Uptake of Benzene over Cyclohexane

A novel porous metal-organic framework (MOF) architecture is formed by a neutral amide-functionalized ligand and copper(II). Upon desolvation, this compound undergoes a dynamic structural transformation from a one-dimensional (1D) porous phase to a two-dimensional (2D) non-porous phase that shows selective uptake of benzene over cyclohexane. The as-synthesized compound also acts as a visual colorimetric anion sensor for thiocyanate.