Three-in-One C2 H2 -Selectivity-Guided Adsorptive Separation across an Isoreticular Family of Cationic Square-Lattice MOFs.

Energy-efficient selective physisorption driven C2 H2 separation from industrial C2-C1 impurities such as C2 H4 , CO2 and CH4 is of great importance in the purification of downstream commodity chemicals. We address this challenge employing a series of isoreticular cationic metal-organic frameworks, namely iMOF-nC (n=5, 6, 7). All three square lattice topology MOFs registered higher C2 H2 uptakes versus the competing C2-C1 gases (C2 H4 , CO2 and CH4 ). Dynamic column breakthrough experiments on the best-performing iMOF-6C revealed the first three-in-one C2 H2 adsorption selectivity guided separation of C2 H2 from 1:1 C2 H2 /CO2 , C2 H2 /C2 H4 and C2 H2 /CH4 mixtures. Density functional theory calculations critically examined the C2 H2 selective interactions in iMOF-6C. Thanks to the abundance of square lattice topology MOFs, this study introduces a crystal engineering blueprint for designing C2 H2 -selective layered metal-organic physisorbents, previously unreported in cationic frameworks.

Recognition and Sequestration of Toxic Inorganic Water Pollutants with Hydrolytically Stable Metal-Organic Frameworks.

Water pollution and crisis of freshwater is one of the most alarming concern globally, which threatens the development and survival of living beings. Recycling of contaminated water has been the prime demand of 21st century as the area of contamination in natural waterbodies increasing rapidly worldwide. Detoxification and purification of wastewater via adsorptive removal technology has been proven to be more efficient because of it's simplicity, lesser complexity and cost-effectiveness. As the most rapid-growing division of coordination chemistry, porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) with the liberty of crafting tailorable porous architecture and presence of numerous functional sites have become quintessential for recognition and sequestration of water pollutants. This personal account intends to highlight our recent contributions in the field of sensing and sequestration of toxic aquatic inorganic pollutants by functionalized water stable MOFs.

Selective and Sensitive Fluorescence Turn-On Detection of Cyanide Ions in Water by Post Metallization of a MOF.

Owing to detrimental impact of cyanide ion (CN- ) towards the entire living system as well as its availability in drinking water, it has become very important developing potential sensory materials for the selective and sensitive recognition of CN- ions in water. In the domain of sensory materials, luminescent metal-organic frameworks (LMOFs) have been considered as a promising candidate owing to their unique host-guest interaction, where MOFs can serve as an ideal scaffold for encapsulating relevant guest molecules rendering specific functionality. In this study, a post-synthetically modified MOF (viz., CuCl2 @MOF-867) was applied to recognize cyanide (CN- ) ions in water via "turn-on" response. The bipyridyl functionalities in MOF-867 were used to perform post-synthetic metalation to infiltrate CuCl2 inside porous architecture of the MOF. Moreover, a CuCl2 @MOF-867 based probe demonstrated highly selective and sensitive aqueous phase recognition of CN- ions even in the presence of other interfering anions such as Br- , NO3- , I- , SO42- , OAc- , SCN- , NO2- , etc. The selective binding of CN- ions to the copper-metal center has led to the generation of stable Cu(CN)2 species. This phenomenon has further resulted in a fluorescence turn-on response. The aqueous phase cyanide detection by the rationally modified MOF system exhibited very low limit of detection (0.19 µM), which meets the standardized limit stated by World Health Organization (WHO) that is 1.9 µM.

Unveiling the Impact of Diverse Morphology of Ionic Porous Organic Polymers with Mechanistic Insight on the Ultrafast and Selective Removal of Toxic Pollutants from Water.

In recent years, detoxification of contaminated water by different types of materials has received a great deal of attention. However, lack of methodical in-depth understanding of the role of various physical properties of such materials toward improved sorption performance limits their applicable efficiencies. In perspective, decontamination of oxoanion-polluted water by porous materials with different morphologies are unexplored due to a shortfall of proper synthetic strategies. Herein, systematic optimization of sequestration performance toward efficient decontamination of toxic oxoanion-polluted water has been demonstrated by varying the morphologies of an imidazolium-based cationic polymeric network [ionic porous organic polymers (iPOP-5)]. Detailed morphological evolution showed that the chemically stable ionic polymer exhibited several morphologies such as spherical, nanotube, and flakes. Among them, the flakelike material [iPOP-5(F)] showed ultrafast capture efficiency (up to ∼99 and >85% removal within less than 1 min) with high saturation capacities (301 and 610 mg g-1) toward chromate [Cr(VI)] and perrhenate [Re(VII)] oxoanions, respectively, in water. On the other hand, the spherical-shaped polymer [iPOP-5(S)] exhibited relatively slow removal kinetics (>5 min for complete removal) toward both Cr(VI) and Re(VII) oxoanions. Notably, iPOP-5(F) eliminated Cr(VI) and Re(VII) selectively even in the presence of excessive (∼100-fold) competing anions from both high- and low-concentration contaminated water. Further, the compound demonstrated efficient separation of those oxoanions in a wide pH range as well as in various water systems (such as potable, lake, river, sea, and tannery water) with superior regeneration ability. Moreover, as a proof of concept, a column exchange-based water treatment experiment by iPOP-5(F) has been performed to reduce the concentration of Cr(VI) and Re(VII) below the WHO permitted level. Mechanistic investigation suggested that the rare in situ exfoliation of flakes into thin nanosheets helps to achieve ultrafast capture efficiency. In addition, detailed theoretical binding energy calculations were executed in order to understand such rapid, selective binding of chromate and perrhenate oxoanions with iPOP-5(F) over other nonmetal-based anions.

Nanotrap Grafted Anion Exchangeable Hybrid Materials for Efficient Removal of Toxic Oxoanions from Water.

Water pollution has attracted worldwide significant attention ever since the finding of its harmful effects on the whole ecosystem, including human health. Although several materials are known for selective removal of specific contaminants, designing a single material that can adsorb a variety of water contaminants is still a very challenging task due to a lack of proper design strategies. Herein, we have rationally designed a new class of anion exchangeable hybrid material where the nanosized cationic metal-organic polyhedra (MOP) are embedded inside a porous covalent organic framework (COF) with specific binding sites for toxic oxoanions. The resulting hybrid material exhibits very fast and selective sequestration of high as well as trace amount of a wide range of toxic oxoanions (HAsO4 2-, SeO4 2-, CrO4 2-, ReO4 -, and MnO4 -) from the mixture of excessive (∼1000-fold) other interfering anions to well below the permissible drinking water limit. Moreover, the hybrid cationic nanotrap material can reduce the As(V) level from a highly contaminated groundwater sample to below the WHO permitted level.

A Water-Stable Cationic Metal-Organic Framework with Hydrophobic Pore Surfaces as an Efficient Scavenger of Oxo-Anion Pollutants from Water.

Water contamination due to heavy metal-based toxic oxo-anions (such as CrO42- and TcO4-) is a critical environmental concern that demands immediate mitigation. Herein, we present an effort to counter this issue by a novel chemically stable cationic metal-organic framework (iMOF-2C) with strategic utilization of a ligand with hydrophobic core, known to facilitate such oxo-anion capture process. Moreover, the compound exhibited very fast sieving kinetics for such oxo-anions and a very high uptake capacity for CrO42- (476.3 mg g-1) and ReO4- (691 mg g-1), while the latter being employed as a surrogate analogue for radioactive TcO4- anions. Notably, the compound showed excellent selectivity even in the presence of other competing anions such as NO3-, Cl-, SO42-, ClO4-. etc.. Furthermore, the compound possesses excellent reusability (up to 10 cycles) and is also employed to a stationary phase ion column to decontaminate the aforementioned oxo-anions from water.