Rapid preparation of binary mixtures of sodium carboxylates as anodes in sodium-ion batteries.

Sodium-ion batteries are emerging as a sustainable solution to tackle the growing global energy demands. In this context, organic electrode materials complement such technologies as they are composed of earth-abundant elements. As organic anodes, sodium carboxylates exhibit promising applicability in a wide range of molecules. To harness the advantages of individual systems and to minimise their limitations, in this work, an approach to form binary mixtures of sodium carboxylates using one-pot, microwave-assisted synthesis is presented. The target mixtures were synthesised in 30 min with disodium naphthalene-2,6-dicarboxylate (Na-NDC) as a common constituent in all. Both components in all mixtures were shown to participate in the charge storage and had a considerable effect on the performance characteristics, such as specific capacity and working voltage, in half and full cell formats. This approach opens a new avenue for enabling organic materials to be considered as more competitive candidates in sodium-ion batteries and promote their use in other material classes to overcome their limitations.

Peptide hydrogen-bonded organic frameworks.

Hydrogen-bonded porous frameworks (HPFs) are versatile porous crystalline frameworks with diverse applications. However, designing chiral assemblies or biocompatible materials poses significant challenges. Peptide-based hydrogen-bonded porous frameworks (P-HPFs) are an exciting alternative to conventional HPFs due to their intrinsic chirality, tunability, biocompatibility, and structural diversity. Flexible, ultra-short peptide-based P-HPFs (composed of 3 or fewer amino acids) exhibit adaptable porous topologies that can accommodate a variety of guest molecules and capture hazardous greenhouse gases. Longer, folded peptides present challenges and opportunities in designing P-HPFs. This review highlights recent developments in P-HPFs using ultra-short peptides, folded peptides, and foldamers, showcasing their utility for gas storage, chiral recognition, chiral separation, and medical applications. It also addresses design challenges and future directions in the field.

Metal-driven folding and assembly of a minimal ß-sheet into a 3D-porous honeycomb framework.

In contrast to short helical peptides, constrained peptides, and foldamers, the design and fabrication of crystalline 3D frameworks from the ß-sheet peptides are rare because of their high self-aggregation propensity to form 1D architectures. Herein, we demonstrate the formation of a 3D porous honeycomb framework through the silver coordination of a minimal ß-sheet forming a peptide having terminal metal coordinated 4- and 3-pyridyl ligands.

Surface-Functionalized Metal-Organic Frameworks for Binding Coronavirus Proteins.

Since the outbreak of SARS-CoV-2, a multitude of strategies have been explored for the means of protection and shielding against virus particles: filtration equipment (PPE) has been widely used in daily life. In this work, we explore another approach in the form of deactivating coronavirus particles through selective binding onto the surface of metal-organic frameworks (MOFs) to further the fight against the transmission of respiratory viruses. MOFs are attractive materials in this regard, as their rich pore and surface chemistry can easily be modified on demand. The surfaces of three MOFs, UiO-66(Zr), UiO-66-NH2(Zr), and UiO-66-NO2(Zr), have been functionalized with repurposed antiviral agents, namely, folic acid, nystatin, and tenofovir, to enable specific interactions with the external spike protein of the SARS virus. Protein binding studies revealed that this surface modification significantly improved the binding affinity toward glycosylated and non-glycosylated proteins for all three MOFs. Additionally, the pores for the surface-functionalized MOFs can adsorb water, making them suitable for locally dehydrating microbial aerosols. Our findings highlight the immense potential of MOFs in deactivating respiratory coronaviruses to be better equipped to fight future pandemics.

Azo-functionalised metal-organic framework for charge storage in sodium-ion batteries.

Sodium-ion batteries (NIBs) are emerging as promising devices for energy storage applications. Porous solids, such as metal-organic frameworks (MOFs), are well suited as electrode materials for technologies involving bulkier charge carriers. However, only limited progress has been made using pristine MOFs, primarily due to lack of redox-active organic groups in the materials. In this work a azo-functional MOF, namely UiO-abdc, is presented as an electrode compound for sodium-ion insertion. The MOF delivers a stable capacity (∼100 mA h g-1) over 150 cycles, and post-cycling characterisation validates the stability of the MOF and participation of the azo-group in charge storage. This study can accelerate the realisation of pristine solids, such as MOFs and other porous organic compounds, as battery materials.

Exploring Helical Peptides and Foldamers for the Design of Metal Helix Frameworks: Current Trends and Future Perspectives.

Flexible and biocompatible metal peptide frameworks (MPFs) derived from short and ultra-short peptides have been explored for the storage of greenhouse gases, molecular recognition, and chiral transformations. In addition to short flexible peptides, peptides with specifically folded conformations have recently been utilized to fabricate a variety of metal helix frameworks (MHFs). The secondary structures of the peptides govern the structure-assembly relationship and thereby control the formation of three-dimensional (3D)-MHFs. Particularly, the hierarchical structural organization of peptide-based MHFs has not yet been discussed in detail. Here, we describe the recent progress of metal-driven folded peptide assembly to construct 3D porous structures for use in future energy storage, chiral recognition, and biomedical applications, which could be envisioned as an alternative to the conventional metal-organic frameworks (MOFs).

A structural investigation of organic battery anode materials by NMR crystallography.

Conjugated alkali metal dicarboxylates have recently received attention for applications as organic anode materials in lithium- and sodium-ion batteries. In order to understand and optimise these materials, it is important to be able to characterise both the long-range and local aspects of the crystal structure, which may change during battery cycling. Furthermore, some materials can display polymorphism or hydration behaviour. NMR crystallography, which combines long-range crystallographic information from diffraction with local information from solid-state NMR via interpretation aided by DFT calculations, is one such approach, but this has not yet been widely applied to conjugated dicarboxylates. In this work, we evaluate the application of NMR crystallography for a set of model lithium and sodium dicarboxylate salts. We investigate the effect of different DFT geometry optimisation strategies and find that the calculated NMR parameters are not systematically affected by the choice of optimisation method, although the inclusion of dispersion correction schemes is important to accurately reproduce the experimental unit cell parameters. We also observe hydration behaviour for two of the sodium salts and provide insight into the structure of an as-yet uncharacterised structure of sodium naphthalenedicarboxylate. This highlights the importance of sample preparation and characterisation for organic sodium-ion battery anode materials in particular.

Rapid Microwave-Assisted Synthesis and Electrode Optimization of Organic Anode Materials in Sodium-Ion Batteries.

Sodium-ion batteries are commanding increasing attention owing to their promising electrochemical performance and sustainability. Organic electrode materials (OEMs) complement such technologies as they can be sourced from biomass and recycling them is environmentally friendly. Organic anodes based on sodium carboxylates have exhibited immense potential, except the limitation of current synthesis methods concerning upscaling and energy costs. In this work, a rapid and energy efficient microwave-assisted synthesis for organic anodes is presented using sodium naphthalene-2,6-dicarboxylate as a model compound. Optimizing the synthesis and electrode composition enables the compound to deliver a reversible initial capacity of ≈250 mAh g-1 at a current density of 25 mA g-1 with a high initial Coulombic efficiency (≈78%). The capacity is stable over 400 cycles and the compound also exhibits good rate performance. The successful demonstration of this rapid synthesis may facilitate the transition to preparing organic battery materials by scalable, efficient methods.

Solvothermal Synthesis of a Novel Calcium Metal-Organic Framework: High Temperature and Electrochemical Behaviour.

The rapid growth in the field of metal-organic frameworks (MOFs) over recent years has highlighted their high potential in a variety of applications. For biological and environmental applications MOFs with low toxicity are vitally important to avoid any harmful effects. For this reason, Ca-based MOFs are highly desirable owing to their low cost and high biocompatibility. Useful Ca MOFs are still rare owing to the ionic character and large size of the Ca2+ ion tending to produce dense phases. Presented here is a novel Ca-based MOF containing 2,3-dihyrdoxyterephthalate (2,3-dhtp) linkers Ca(2,3-dhtp)(H2O) (SIMOF-4). The material undergoes a phase transformation on heating, which can be followed by variable temperature powder X-ray diffraction. The structure of the high temperature form was obtained using single-crystal X-ray diffraction. The electrochemical properties of SIMOF-4 were also investigated for use in a Na ion battery.

A luminescent cationic MOF for bimodal recognition of chromium and arsenic based oxo-anions in water.

Water pollution from heavy metals and their toxic oxo-anionic derivatives such as CrO42-, Cr2O72-, HAsO42-, and HAsO32- has become one of the most critical environmental issues. To address this, herein, we report a new hydrolytically stable luminescent Zn(ii) based cationic metal organic framework (MOF), iMOF-4C, which further successfully exhibited a rare dual "turn off/on" fluorescence response toward Cr(vi), As(v) and As(iii) based oxo-anions respectively in water medium. In addition, iMOF-4C was found to maintain its superior selectivity in the presence of other concurrent anions (e.g. SO42-, Cl-, Br-, ClO4-, NO3-, SCN- and CO32-). More importantly, iMOF-4C exhibited an excellent selective and sensitive luminescence "turn-off" response towards CrO42- and Cr2O72- anions in water medium with the quenching constant (Ksv) values as high as 1.31 × 105 M-1 (CrO42-) and 4.85 × 105 M-1 (Cr2O72-), which are found to be the highest among the values reported in the regime of MOFs. Interestingly, iMOF-4C showed fluorescence "turn-on" response toward HAsO42- and HAsO32- with an enhancement coefficient (Kec) of 1.98 × 104 M-1 and 3.56 × 103 M-1 respectively. The high sensitivity and low detection limits make iMOF-4C more feasible for real-time sensing of such toxic oxo-anions in an aqueous medium. Furthermore, the probable sensing mechanism has been investigated by DFT calculation studies and discussed in detail.

Advances in Organic Anode Materials for Na-/K-Ion Rechargeable Batteries.

Electrochemical energy storage (EES) devices are gaining ever greater prominence in the quest for global energy security. With increasing applications and widening scope, rechargeable battery technology is gradually finding avenues for more abundant and sustainable systems such as Na-ion (NIB) and K-ion batteries (KIB). Development of suitable electrode materials lies at the core of this transition. Organic redox-active molecules are attractive candidates as negative electrode materials owing to their low redox potentials and the fact that they can be obtained from biomass. Also, the rich structural diversity allows integration into several solid-state polymeric materials. Research in this domain is increasingly focused on deploying molecular engineering to address specific electrochemical limitations that hamper competition with rival materials. This Minireview aims to summarize the advances in both the electrochemical properties and the materials development of organic anode materials.

A Water-Stable Ionic MOF for the Selective Capture of Toxic Oxoanions of SeVI and AsV and Crystallographic Insight into the Ion-Exchange Mechanism.

Selectively capturing toxic oxoanions of selenium and arsenic is highly desired for the remediation of hazardous waste. Ionic metal-organic frameworks (iMOFs) especially cationic MOFs (iMOF-C) as ion-exchange materials, featuring aqueous phase stability, present a robust pathway for sequestration of the oxoanions owing to their ability to prevent leaching because of their ionic nature. On account of scarcity of water-stable cationic MOFs, the capture of oxoanions of selenium and arsenic has been a major challenge and has not been investigated using iMOFs. Herein, we demonstrate large scale synthesis of cationic MOF, viz. iMOF-1C that exhibits selective capture of oxoanions of SeVI (SeO42- ) and AsV (HAsO42- ) in water with a maximum sorption capacity of 100 and 85 mg g-1 , respectively. This represents among the highest uptake capacities observed for selenate oxoanion in MOFs. Further, the ion-exchange mechanism was directly unveiled by single crystal analysis, which revealed variable modes of host-guest binding.

Conversion of a microwave synthesized alkali-metal MOF to a carbonaceous anode for Li-ion batteries.

Hierarchical carbon-rich materials have shown immense potential for various electrochemical applications. Metal-organic frameworks (MOFs) are well suited precursors for obtaining such templated carbon matrices. Usually these conversions are carried out by energy intensive processes and lead to the presence of toxic transition metal residues. Herein, we demonstrate the green, scalable, microwave-assisted synthesis of a three-dimensional s-block metal based MOF and its efficient transformation into a carbonaceous material. The MOF-derived solid functions as a negative electrode for lithium-ion batteries having moderate low-rate capacities and cycling stability.

Hydrophobic Shielding of Outer Surface: Enhancing the Chemical Stability of Metal-Organic Polyhedra.

Metal-organic polyhedra (MOP) are a promising class of crystalline porous materials with multifarious potential applications. Although MOPs and metal-organic frameworks (MOFs) have similar potential in terms of their intrinsic porosities and physicochemical properties, the exploitation of carboxylate MOPs is still rudimentary because of the lack of systematic development addressing their chemical stability. Herein we describe the fabrication of chemically robust carboxylate MOPs via outer-surface functionalization as an a priori methodology, to stabilize those MOPs system where metal-ligand bond is not so strong. Fine-tuning of hydrophobic shielding is key to attaining chemical inertness with retention of the framework integrity over a wide range of pH values, in strong acidic conditions, and in oxidizing and reducing media. These results are further corroborated by molecular modelling studies. Owing to the unprecedented transition from instability to a chemically ultra-stable regime using a rapid ambient-temperature gram-scale synthesis (within seconds), a prototype strategy towards chemically stable MOPs is reported.

Chemically stable ionic viologen-organic network: an efficient scavenger of toxic oxo-anions from water.

Detoxification of water has been demonstrated with a viologen-based cationic organic network (compound-1), which was stable not only in water, but also in acidic and basic media. The presence of free exchangeable Cl- ions inside the network of compound-1 and a high physiochemical stability of the materials offered a suitable scope for the capture of hazardous anionic pollutants from water. Rapid removal of the toxic water pollutant and carcinogenic chromate (CrO4 2-) from water was shown with compound-1. Furthermore, the oxo-anion of the radioactive isotope of technetium (99Tc), i.e. the TcO4 - ion, also counts as a toxic water pollutant and by using surrogate anions (MnO4 - and ReO4 -), a model capture study was performed. Notably, compound-1 showed high capacity values for each of the oxo-anions and these were comparable to some of the well-performing compounds reported in the literature. Furthermore, to check the real time aspect, removal of all of the aforementioned anions from water was demonstrated, even in the presence of other concurrent anions.

Base-Resistant Ionic Metal-Organic Framework as a Porous Ion-Exchange Sorbent.

A systematic approach has been employed to obtain a hydrolytically stable cationic metal-organic framework (MOF). The synthesized two-dimensional Ni(II)-centered cationic MOF, having its backbone built from purely neutral N-donor ligand, is found to exhibit uncommon resistance over wide pH range, particularly even under highly alkaline conditions. This report presents a rare case of a porous MOF retaining structural integrity under basic conditions, and an even rarer case of a porous cationic MOF. The features of stability and porosity in this ionic MOF have been harnessed for the function of charge- and size-selective capture of small organic dye through ion-exchange process across a wide pH range.

Multifunctional Behavior of Sulfonate-Based Hydrolytically Stable Microporous Metal-Organic Frameworks.

An isostructural pair of extremely rare, permanently microporous sulfonate-based metal-organic frameworks (MOFs) having a novel topology has been reported here by integration of rationally chosen building units. The compounds bear polar sites in the pore surfaces and exhibit selective adsorption of CO2, which features among the highest reported uptakes in the domain of organosulfonate-based MOFs. The compounds also exhibit multifunctionality for C6-cyclic hydrocarbon separation and selective detection of neurotransmitter nitric oxide. Such multifunctional behavior on the basis of permanent porosity has been rarely observed for sulfonate-based MOFs. The efficacy of the synthesis approach is further highlighted by the resistance over a wide pH range and promising feasibility of reticular chemistry in porous organosulfonate-based systems.

Selective Recognition of Hg2+ ion in Water by a Functionalized Metal-Organic Framework (MOF) Based Chemodosimeter.

A metal-organic framework (MOF)-based highly selective and sensitive probe (UiO-66@Butyne) for the detection of Hg(II) ion has been developed. To the best our knowledge, this is the foremost example of a chemodosimeter-based approach to sense Hg(II) ion using a MOF-based probe. The chemical stability of UiO-66@Butyne renders the sensitive detection of Hg2+ ion in an aqueous phase. UiO-66@Butyne has been found to be selective for Hg(II) ions even in the presence of other metal ions.

Guest-Responsive Metal-Organic Frameworks as Scaffolds for Separation and Sensing Applications.

Metal-organic frameworks (MOFs) have evolved to be next-generation utility materials because of their serviceability in a wide variety of applications. Built from organic ligands with multiple binding sites in conjunction with metal ions/clusters, these materials have found profound advantages over their other congeners in the domain of porous materials. The plethora of applications that these materials encompass has motivated material chemists to develop such novel materials, and the catalogue of MOFs is thus ever-escalating. One key feature that MOFs possess is their responsiveness toward incoming guest molecules, resulting in changes in their physical and chemical properties. Such uniqueness generally arises owing to the influenceable ligands and/or metal units that govern the formation of these ordered architectures. The suitable host-guest interactions play an important role in determining the specific responses of these materials and thus find important applications in sensing, catalysis, separation, conduction, etc. In this Account, we focus on the two most relevant applications based on the host-guest interactions that are carried out in our lab, viz., separation and sensing of small molecules. Separation of liquid-phase aromatic hydrocarbons by less energy-intensive adsorption processes has gained attention recently. Because of their tailored structures and functionalized pore surfaces, MOFs have become vital candidates in molecular separation. Prefunctionalization of MOFs by astute choice of ligands and/or metal centers results in targeted separation processes in which the molecular sieving effect plays a crucial role. In this view, separation of C6 and C8 liquid aromatic hydrocarbons, which are essential feedstock in various chemical industries, is one area of research that requires significant attention because of the gruesome separation techniques adopted in such industries. Also, from the environmental perspective, separation of oil/water mixtures demands significant attention because of the hazards of marine oil spillage. We have achieved successful separation of such by careful impregnation of hydrophobic moieties inside the nanochannels of MOFs, resulting in unprecedented efficiency in oil/water separation. Also, recognition of small molecules using optical methods (fluorescence, UV, etc.) has been extended to achieve sensing of various neutral species and anions that are important from environmental point of view. Incorporation of secondary functional groups has been utilized to sense nitroaromatic compounds (NACs) and other small molecules such as H2S, NO, and aromatic phenols. We have also utilized the postfunctionalization strategy via ion exchange to fabricate MOFs for sensing of environmentally toxic and perilous anionic species such as CN- and oxoanions. Our current endeavors to explore the applicability of MOFs in these two significant areas have widened the scope of research, and attempts to fabricate MOFs for real-time applications are underway.

Ultrahigh Ionic Conduction in Water-Stable Close-Packed Metal-Carbonate Frameworks.

Utilization of the robust metal-carbonate backbone in a series of water-stable, anionic frameworks has been harnessed for the function of highly efficient solid-state ion-conduction. The compact organization of hydrophilic guest ions facilitates water-assisted ion-conduction in all the compounds. The dense packing of the compounds imparts high ion-conducting ability and minimizes the possibility of fuel crossover, making this approach promising for design and development of compounds as potential components of energy devices. This work presents the first report of evaluating ion-conduction in a purely metal-carbonate framework, which exhibits high ion-conductivity on the order of 10-2 S cm-1 along with very low activation energy, which is comparable to highly conducting well-known crystalline coordination polymers or commercialized organic polymers like Nafion.