Energy Storage Applications of Cobalt and Manganese Metal–Organic Frameworks

Self-assembled nickel(II)-centered metal-organic square grid complexes for CO2 sensing

Detection and monitoring of hazardous CO2 gas are essential for ensuring human health and environmental safety, which form part of Goal 13 of the United Nations Sustainable Development Goals (SDGs). Metal-organic square complexes in thin-film forms are explored in this work for the first time as CO2 gas sensors. Two new Ni(II) metal-organic square grid complexes [Ni(HL)]4Cl4·26H2O (1) and [Ni(HL)]4 (BF4)4·20H2O (2) were achieved by self-assembly, utilizing 1,5-bis(2-benzoylpyridine) thiocarbohydrazone (H2L) as building blocks. The formation of a molecular square [NiHL]44+ unit containing four octahedrally coordinated Ni(II) centers in complex 1 was confirmed by single crystal X-ray diffraction (SCXRD). Complex 2, conversely, yielded single crystals of a new complex, [NiL]4 (2a), from its DMF and ethanol mixture. The MALDI mass spectral study indicates that the metallosupramolecular square grid units are stable in solution, while the thermogravimetric study reveals the rigidity of the cationic grid structures in their solid states. The solvent accessible pore volume of 1952 Å3 (≈18.2%) for complex 1 was in accordance with the TG result of 18.1% weight loss up to 272 °C. Hirshfeld surface study was used for void surface analysis. The BET surface areas of complexes 1 and 2 were observed to be 2.390 and 4.803 m2 g-1, respectively. The experimentally observed solid-state band gap energy for complexes 1 and 2 was ∼1.45 eV, revealing semiconductor characteristics. Thin films of both these complexes were then developed using a drop casting process and were employed for CO2 sensing, as these metallosupramolecular hosts consist of many secondary amine groups. Both complexes 1 and 2 demonstrated sensing capability towards hazardous CO2 gas, which was found to improve further under white light illumination. The responses to CO2 gas were found to be 31% and 59% for the sensors engineered using complexes 1 and 2, respectively. The limit of detection for reliable CO2 gas sensing with complex 2 was found to be 500 ppm. The thin film gas sensor working in the chemiresistive mode using complex 2 outperformed its counterpart when operated as a CO2 sensor.

Manganese-Based Metal-Organic Frameworks and Their Derivatives for Electrochemical Water Splitting: Recent Advances and Future Outlook

Metal-organic frameworks (MOFs) and their derivatives have recently attracted significant interest as promising candidates in water splitting due to their well-defined structural and electronic features, three-dimensional architecture, high surface area, abundance of active sites, remarkable stability, and improved capabilities for mass transport and diffusion. Mn-based MOFs and their derivatives have been extensively studied and demonstrated significant potential in water splitting, inspired largely by the natural photosystem-II. Despite the development of numerous Mn-based electrocatalysts, Mn-MOFs stand out due to their strong synergistic interactions, tunable electronic properties, efficient charge and mass transfer, and straightforward synthesis. However, recent reviews on MOFs have largely overlooked the specific advancements in Mn-MOFs and their derivatives for water-splitting applications. By providing an overview of the uses of Mn-MOFs and their materials, this article seeks to close that gap. It looks at their stability, porosity, and structure as well as how they are used in water splitting. This study offers a deeper knowledge of the properties and uses of Mn-MOFs and their related materials by drawing on groundbreaking research. The link between structure, property, and performance is examined, current advancements in the subject are discussed, difficulties faced are addressed, and potential future developments are taken into account.

Multifunctional nanomaterials and nanocomposites for sensing and monitoring of environmentally hazardous heavy metal contaminants

The applications of conventional sensors are limited by the long response time, high cost, large detection limit, low sensitivity, complicated usage and low selectivity. These sensors are nowadays replaced by Nanocomposite-based modalities and nanomaterials which are known for their high selectivity and physical and chemical properties. These nanosensors effectively detect heavy metal contaminants in the environment as the discharge of heavy metals into natural water as a result of human activity has become a global epidemic. Exposure to these toxic metals might induce many health-related complications, including kidney failure, brain injury, immune disorders, muscle paleness, cardiac damage, nervous system impairment and limb paralysis. Therefore, designing and developing novel sensing systems for the detection and recognition of these harmful metals in various environmental matrices, particularly water, is of extremely important. Emerging nanotechnological approaches in the past two decades have played a key role in overcoming environmentally-related problems. Nanomaterial-based fabrication of chemical nanosensors has widely been applied as a powerful analytical tool for sensing heavy metals. Portability, high sensitivity, on-site detection capability, better device performance and selectivity are all advantages of these nanosensors. The detection and selectivity have been improved using molecular recognition probes for selective binding on different nanostructures. This study aims to evaluate the sensing properties of various nanomaterials such as metal-organic frameworks, fluorescent materials, metal-based nanoparticles, carbon-based nanomaterials and quantum dots and graphene-based nanomaterials and quantum dots for heavy metal ions recognition. All these nano-architectures are frequently served as effective fluorescence probes to directly (or by modification with some large or small biomolecules) sense heavy metal ions for improved selectivity. However, efforts are still needed for the simultaneous designing of multiple metal ion-based detection systems, exclusively in colorimetric or optical fluorescence nanosensors for heavy metal cations.