Formate-Bicarbonate Cycle as a Vehicle for Hydrogen and Energy Storage

In recent years, hydrogen has been considered a promising energy carrier for a sustainable energy economy in the future. An easy solution for the safer storage of hydrogen is challenging and efficient methods are still being explored in this direction. Despite having some progress in this area, no cost-effective and easily applicable solutions that fulfill the requirements of industry are yet to be claimed. Currently, the storage of hydrogen is largely limited to high-pressure compression and liquefaction or in the form of metal hydrides. Formic acid is a good source of hydrogen that also generates CO₂ along with hydrogen on decomposition. Moreover, the hydrogenation of CO₂ is thermodynamically unfavorable and requires high energy input. Alkali metal formates are alternative mild and noncorrosive sources of hydrogen. On decomposition, these metal formates release hydrogen and generate bicarbonates. The generated bicarbonates can be catalytically charged back to alkali formates under optimized hydrogen pressure. Hence, the formate-bicarbonate-based systems being carbon neutral at ambient condition has certain advantages over formic acid. The formate-bicarbonate cycle can be considered as a vehicle for hydrogen and energy storage. The whole process is carbon-neutral, reversible, and sustainable. This Review emphasizes the various catalytic systems employed for reversible formate-bicarbonate conversion. Moreover, a mechanistic investigation, the effect of temperature, pH, kinetics of reversible formate-bicarbonate conversion, and new insights in the field are also discussed in detail.

Functionalized Graphitic Carbon Nitride Decorated with Palladium: an Efficient Heterogeneous Catalyst for Hydrogenation Reactions Using KHCO2 as a Mild and Noncorrosive Source of Hydrogen

Functionalization of the widely known graphitic carbon nitride (GCN) material has been performed, and a novel heterogeneous catalyst is reported by incorporating palladium over the surface of functionalized GCN. GCN was functionalized using an optimized ratio of sulfuric acid, nitric acid, and hydrogen peroxide. The developed catalyst was characterized by powder X-ray diffraction, IR, scanning tunneling microscopy, tunneling electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller, thermogravimetric analysis, and solid-state CP-NMR. The developed material containing ≤1% Pd exhibits superior catalytic activity in comparison to other carbon support materials (such as 5% Pd/C) for various hydrogenation reactions under mild conditions. Potassium formate has been chosen as the best hydrogen source among other alkali metal formates. The developed catalyst was also able to catalyze a one-pot three-step reaction for the synthesis of N-benzylaniline which is a precursor of various antihistamine and anticholargenic drugs. Moreover, the catalyst could be recycled multiple times and consistent activity was reported.

Cascade Reaction-Based Chemiresistive Array for Ethylene Sensing

Chemiresistive sensors, which are based on semiconducting materials, offer real-time monitoring of environment. However, detection of nonpolar chemical substances is often challenging because of the weakness of the doping effect. Herein, we report a concept of combining a cascade reaction (CR) and a chemiresistive sensor array for sensitive and selective detection of a target analyte (herein, ethylene in air). Ethylene was converted to acetaldehyde through a Pd-catalyzed heterogeneous Wacker reaction at 40 °C, followed by condensation with hydroxylamine hydrochloride to emit HCl vapor. HCl works as a strong dopant for single-walled carbon nanotubes (SWCNTs), enabling the main sensor to detect ethylene with excellent sensitivity (10.9% ppm^-1) and limit of detection (0.2 ppm) in 5 min. False responses that occur in the main sensor are easily discriminated by reference sensors that partially employ CR. Moreover, though the sensor monitors the variation of normalized electric resistance (ΔR/R₀) in the SWCNT network, temporary deactivation of CR yields a sensor system that does not require analyte-free air for a baseline correction (i.e., estimation of R₀) and recovery of response. The concept presented here is generally applicable and offers a solution for several issues that are inherently present in chemiresistive sensing systems.

Ammonia-Doped Polyaniline-Graphitic Carbon Nitride Nanocomposite as a Heterogeneous Green Catalyst for Synthesis of Indole-Substituted 4H-Chromenes

A nanocomposite of polyaniline with graphitic carbon nitride (GCN) nanosheets has been synthesized by a facile oxidative polymerization of an aniline monomer and GCN to demonstrate its potential to catalyze the synthesis of various indole-substituted 4H-chromenes. The synthesized nanocomposite was thoroughly characterized using different spectroscopic techniques to confirm the morphology and composition. Subsequently, the fabricated nanocomposite was used as a heterogeneous catalyst to synthesize several bioactive indole-substituted 4H-chromenes in an aqueous medium. Organic transformation under benign and environmentally sustainable conditions is of paramount importance in the view of growing environmental pollution. Water is the universal Green solvent and has been a preferred choice of nature to perform various reactions. The catalyst developed in this work showed very good recyclability and adaptability for the synthesis of various medicinally significant indole-substituted 4H-chromenes. This multicomponent reaction imparts very high atom economy (94%) and low environmental factor (0.13).

Two-dimensional carbon-based nanocomposites for photocatalytic energy generation and environmental remediation applications

In the pursuit towards the use of sunlight as a sustainable source for energy generation and environmental remediation, photocatalytic water splitting and photocatalytic pollutant degradation have recently gained significant importance. Research in this field is aimed at solving the global energy crisis and environmental issues in an ecologically-friendly way by using two of the most abundant natural resources, namely sunlight and water. Over the past few years, carbon-based nanocomposites, particularly graphene and graphitic carbon nitride, have attracted much attention as interesting materials in this field. Due to their unique chemical and physical properties, carbon-based nanocomposites have made a substantial contribution towards the generation of clean, renewable and viable forms of energy from light-based water splitting and pollutant removal. This review article provides a comprehensive overview of the recent research progress in the field of energy generation and environmental remediation using two-dimensional carbon-based nanocomposites. It begins with a brief introduction to the field, basic principles of photocatalytic water splitting for energy generation and environmental remediation, followed by the properties of carbon-based nanocomposites. Then, the development of various graphene-based nanocomposites for the above-mentioned applications is presented, wherein graphene plays different roles, including electron acceptor/transporter, cocatalyst, photocatalyst and photosensitizer. Subsequently, the development of different graphitic carbon nitride-based nanocomposites as photocatalysts for energy and environmental applications is discussed in detail. This review concludes by highlighting the advantages and challenges involved in the use of two-dimensional carbon-based nanocomposites for photocatalysis. Finally, the future perspectives of research in this field are also briefly mentioned.

Plant leaves as natural green scaffolds for palladium catalyzed Suzuki-Miyaura coupling reactions

This work presents a novel approach of using natural plant leaf surfaces having intricate hierarchical structures as scaffolds for Pd nanoparticles and demonstrated it as a Green dip catalyst for Suzuki-Miyaura coupling reactions in water. The influence of the topographical texture of the plant leaves on the deposition and catalytic properties of Pd nanoparticles are presented and discussed. The catalytic activity can be correlated to the surface texture of the leaves, wherein it has been found that the micro/nanostructures present on the surface strongly influence the assembly and entrapment of the nanoparticles, and thereby control aggregation and leaching of the catalysts. This approach can provide insights for the future design and fabrication of bioinspired supports for catalysis, based on replication of leaf surfaces.

An unusual chemoselective oxidation strategy by an unprecedented exploration of an electrophilic center of DMSO: a new facet to classical DMSO oxidation

A conceptually new dimethyl sulfoxide (DMSO) based oxidation process without the use of any activator has been demonstrated for the oxidation of active methylenes and benzhydrols. The developed protocol utilizes the electrophilic center of DMSO for oxidation, which was unexplored before. Mechanistic investigation has confirmed that the source of oxygen is DMSO.

Hypervalent iodine mediated direct one pot transformation of aldehydes to ketones

An environmentally benign, step economical synthesis of ketones directly from aldehydes has been developed using hypervalent iodine as an oxidant.

Zinc, copper and selenium in reproduction

Of the nine biological trace elements, zinc, copper and selenium are important in reproduction in males and females. Zinc content is high in the adult testis, and the prostate has a higher concentration of zinc than any other organ of the body. Zinc deficiency first impairs angiotensin converting enzyme (ACE) activity, and this in turn leads to depletion of testosterone and inhibition of spermatogenesis. Defects in spermatozoa are frequently observed in the zinc-deficient rat. Zinc is thought to help to extend the functional life span of the ejaculated spermatozoa. Zinc deficiency in the female can lead to such problems as impaired synthesis/secretion of (FSH) and (LH), abnormal ovarian development, disruption of the estrous cycle, frequent abortion, a prolonged gestation period, teratogenicity, stillbirths, difficulty in parturition, pre-eclampsia, toxemia and low birth weights of infants. The level of testosterone in the male has been suggested to play a role in the severity of copper deficiency. Copper-deficient female rats are protected against mortality due to copper deficiency, and the protection has been suggested to be provided by estrogens, since estrogens alter the subcellular distribution of copper in the liver and increase plasma copper levels by inducing ceruloplasmin synthesis. The selenium content of male gonads increases during pubertal maturation. Selenium is localized in the mitochondrial capsule protein (MCP) of the midpiece. Maximal incorporation in MCP occurs at steps 7 and 12 of spermatogenesis and uptake decreases by step 15. Selenium deficiency in females results in infertility, abortions and retention of the placenta. The newborns from a selenium-deficient mother suffer from muscular weakness, but the concentration of selenium during pregnancy does not have any effect on the weight of the baby or length of pregnancy. The selenium requirements of a pregnant and lactating mother are increased as a result of selenium transport to the fetus via the placenta and to the infant via breast milk.

Histological and biochemical changes in testis of zinc deficient BALB/c strain of mice

Zinc, protein, cholesterol, phospholipids, alkaline phosphatase (AlPase), acid phosphatase (AcPase), adenosine-5-triphosphatase(ATPase) and histology were studied in testis of zinc-deficient mice. Zinc and protein decreased in the 3-week experiment whereas they increased in the 6-week experiment. Zinc is involved in several functions of the cell and is regulated by hormones. Inhibition of spermatogenesis indicates for decreased zinc levels in 3-week whereas the increase in 6-week experiment indicates for accumulation of zinc in oedomatous fluid and uncontrolled diffusion of zinc across the blood testis barrier. Glycogen decreased in the 3-week as well as 6-week experiments due to blockage of androgen and spermatogenesis. Cholesterol and phospholipids increased in the 3-week experiment and decreased in 6-week experiment as both the parameters are related to steroidogenesis. Zinc deficiency leads to aspermatogenic condition and comparatively less injury to non-germinal cells. This could have blocked the transport of material across the testis barrier and therefore might have increased AlPase levels. Increased AcPase, probably represents lysosomal enzymes, as the cell debris of disorganised epithelium are to be digested and removed. ATPase increased in 3-week experiment and can be correlated to increased demands of energy of testicular cells to overcome the insults of zinc deficiency whereas the decrease in 6-week experiment could be as a result of inhibition of spermatogenesis.