The first catalytic enantioselective direct aldol reaction of 3‐acetylcoumarins to pyrazole‐4,5‐diones is reported and shown to proceed through noncovalent substrate activation by a quinine‐derived ...bifunctional tertiary amino‐amide as the catalyst. The densely functionalized products, consisting of an oxygen‐containing quaternary stereocenter and bearing two biologically relevant heterocycles, are generally obtained in high yields with moderate to excellent enantioselectivities.
Organocatalysis: Enantioselective direct aldol reaction of 3‐acetyl‐2H‐chromenes with electrophilic pyrazole‐4,5‐diones has been demonstrated by noncovalent catalysis. The products, comprising an oxygen‐containing quaternary stereogenic center and two biologically important heterocyclic frameworks, were obtained in high yields with moderate to excellent enantioselectivities using a bifunctional tertiary amino‐amide as catalyst.
A rapid and effective strategy has been devised for the swift development of a Zn(II)-ion-based supramolecular metallohydrogel, termed Zn@PEH, using pentaethylenehexamine as a low molecular weight ...gelator. This process occurs in an aqueous medium at room temperature and atmospheric pressure. The mechanical strength of the synthesized Zn@PEH metallohydrogel has been assessed through rheological analysis, considering angular frequency and oscillator stress dependencies. Notably, the Zn@PEH metallohydrogel exhibits exceptional self-healing abilities and can bear substantial loads, which have been characterized through thixotropic analysis. Additionally, this metallohydrogel displays injectable properties. The structural arrangement resembling pebbles within the hierarchical network of the supramolecular Zn@PEH metallohydrogel has been explored using FESEM and TEM measurements. EDX elemental mapping has confirmed the primary chemical constituents of the metallohydrogel. The formation mechanism of the metallohydrogel has been analyzed via FT-IR spectroscopy. Furthermore, zinc(II) metallohydrogel (Zn@PEH)-based Schottky diode structure has been fabricated in a lateral metal–semiconductor-metal configuration and it’s charge transport behavior has also been studied. Notably, the zinc(II) metallohydrogel-based resistive random access memory (RRAM) device (Zn@PEH) demonstrates bipolar resistive switching behavior at room temperature. This RRAM device showcases remarkable switching endurance over 1000 consecutive cycles and a high ON/OFF ratio of approximately 270. Further, 2 × 2 crossbar array of the RRAM devices were designed to demonstrate OR and NOT logic circuit operations, which can be extended for performing higher order computing operations. These structures hold promise for applications in non-volatile memory design, neuromorphic and in-memory computing, flexible electronics, and optoelectronic devices due to their straightforward fabrication process, robust resistive switching behavior, and overall system stability.
A rapid metallohydrogelation strategy has been developed of magnesium(II)-ion using trimethylamine as a low molecular weight gelator in water medium at room temperature. The mechanical property of ...the synthesized metallohydrogel material is established through the rheological analysis. The nano-rose like morphological patterns of Mg(II)-metallohydrogel are characterized through field emission scanning electron microscopic study. The energy dispersive X-ray elemental mapping analysis confirms the primary gel forming elements of Mg(II)-metallohydrogel. The possible metallohydrogel formation strategy has been analyzed through FT-IR spectroscopic study. In this work, magnesium(II) metallohydrogel (Mg@TMA) based metal-semiconductor-metal structures have been developed and charge transport behaviour is studied. Here, it is confirmed that the magnesium(II) metallohydrogel (Mg@TMA) based resistive random access memory (RRAM) device is showing bipolar resistive switching behaviour at room temperature. We have also explored the mechanism of resistive switching behaviour using the formation (rupture) of conductive filaments between the metal electrodes. This RRAM devices exhibit excellent switching endurance over 10,000 switching cycles with a large ON/OFF ratio (~ 100). The easy fabrication techniques, robust resistive switching behaviour and stability of the present system makes these structures preferred candidate for applications in non-volatile memory design, neuromorphic computing, flexible electronics and optoelectronics etc.
δ‐Manganese dioxide (δ‐MnO2) is a 2D material which possesses distinct properties and features due to its unique atomic structure and has already been utilized in numerous disciplines recently, ...especially in the field of magnetism, energy storage, magnetic resonance imaging, biocatalysts, and fluorescence sensing. Keeping an eye on the huge potential of this 2D material, we report our recent discovery of single‐step synthesis of MnO2 nanosheets via bottom‐up laser crystallization (of aqueous KMnO4 solution) and top‐down sonochemical exfoliation of bulk MnO2 powder. The successful synthesis of δ‐MnO2 nanosheets has been proved through the observation of characteristic Raman peaks at 173 and 634 cm−1 and characteristic X‐ray diffraction peaks. The optical band gap was found to be 1.64 and 1.45 eV for both methods. We also demonstrated that 2D‐MnO2 is a prominent candidate material for ammonia sensing and strain sensing. δ‐MnO2 powder, when employed as cathode material in Li‐ion batteries, results in a stable voltage of ˜0.5 V and in contrast, gives ˜1 V when used in Li‐S batteries and the attained voltage is stable even for >5 h. New methods of synthesis of δ‐MnO2 and its hybrids with graphene will lead to future generation devices, it is expected.
Free‐standing δ‐MnO2 atomic sheets have been attained by laser crystallization and sonochemical exfoliation.
There is a huge demand for storage capabilities in a variety of applications due to the recent explosion of emerging memory technologies. Memory components based on gel materials show promise as ...future non-volatile storage architecture designs. Supramolecular gels represent as a “smart” material which is used in many fields such as sensor, nanoelectronics, logic gate, memory device, cosmetics and environmental remediation. These gels are formed through the combination of hydrogels and supramolecular chemistry. Here, we have successfully synthesized Mg(II)-ion-based supramolecular metallohydrogel using pentaethylenehexamine (i.e.Mg@PEH) as a low molecular weight gelator in aqueous medium under ambient conditions. FESEM and TEM images are used to explore the rectangular pebble-like hierarchical network of Mg@PEH metallohydrogel. From elemental mapping through EDX analysis we can confirm the presence of primary chemical constituents in the metallohydrogel. FT-IR spectroscopy provided insights into the possible formation strategy of the metallohydrogel. In this work, we have fabricated Mg(II)-ion-based supramolecular metallohydrogel (i.e.Mg@PEH)-based planner device in a lateral metal-semiconductor-metal configuration to explore its charge transport behaviour. Furthermore, using this Mg@PEH-based metallogel we created a resistive random access memory (RRAM) device that demonstrated bipolar resistive switching behaviour at room temperature. We have also observed their switching behavior at different low temperatures from 100 to 200K. To learn more about the resistive switching process, we investigated the switching mechanism, which involves formation and rupture of conduction filaments. Mg@PEH-based RRAM device showed an excellent endurance over 1000 switching cycles and good performance with a high ON/OFF ratio of roughly 100. This RRAM device has good endurance, which allows them to withstand a large range of read and write cycles without experiencing a noticeable loss in functionality. Here, we have also prepared 2 × 2 Mg@PEH-based crossbar device and observed how it can perform as a logic gate circuit which can be useful for neuromorphic and in-memory computing etc. The robust switching characteristics suggest the possible use of such devices for the design of eco-friendly bioelectronic memory applications. Therefore, metallogel-based RRAM devices are appropriate for important applications in non-volatile memory device, flexible electronics, and optoelectronics devices that demand trustworthy memory solutions since they have demonstrated promising reliability in terms of long-term performance and stability.
Over the last decade, two-dimensional (2D) materials have been of great interest in the energy storage field. Large-scale electrochemical energy storage is based on the intercalation of metal ions in ...layered materials having van der Waals gaps. In this work, by means of first-principles calculations, we explored the use of 2D Janus transition metal dichalcogenides (TMDs) CrSSe, CrSTe and CrSeTe as anode materials for lithium and sodium-ion batteries. To examine the electronic properties and electrochemical performance, density functional theory (DFT) calculation was used. Our research shows that lithium diffuses easily with short diffusion distances and prefers to bind effectively to the monolayer. These structures are metallic in their bare phases. The highest adsorption energy shown by CrSSe, CrSTe, and CrSeTe is −1.86 eV, −1.66 eV, −2.15 eV with a low diffusion barrier of 0.3 eV, 0.6 eV, and 0.1 eV for the Li atoms and 0.54 eV, 0.32 eV and 0.15 eV for the Na atoms, respectively. At different chemical stoichiometries, we discovered negligible average open-circuit voltages of 1.0 V, 0.52 V, 0.6 V for lithium and 0.1 V, 0.49 V, and 0.51 V for sodium atoms respectively. The storage capacities shown by CrSSe, CrSTe, and CrSeTe are 348 mA h g
−1
, 254 mA h g
−1
, 208 mA h g
−1
for the Li atoms and 260 mA h g
−1
, 198 mA h g
−1
, 177 mA h g
−1
for the Na atoms respectively.
Over the last decade, 2D materials have been of great interest in the energy storage field.
We designed and investigated the electronic, mechanical, and thermoelectric properties of Graphene/hexagonal Boron Nitride (Gr/h-BN) heterostructure at various twisting angles based on the Ab-initio ...simulation. The structural stability was studied at optimized rotation angles (ϕ) = 0∘, 16.10∘, 21.79∘, 38.21∘, 43.90∘ and 60∘. The heterostructure shows semiconducting nature at ϕ=0∘, 21.79∘ and 38.21∘. These twisted heterostructures have demonstrated extraordinary mechanical properties such as Young’s modulus and bulk modulus. Using the semiclassical Boltzmann transport theory, it is observed that the Seebeck coefficient, electric conductivity, and power factor at ϕ=0∘, 21.79∘, 38.21∘, and 60∘ are much higher than the values measured at ϕ=16.10∘ and 43.90∘. Moreover, at ϕ=60∘, the Power Factor for the n-type dopants can reach 1.37 × 1011 W/msK2. The lattice thermal conductivity at room temperature is found to be very low for ϕ=16.10∘, 21.79∘, 43.90∘ and 38.21∘ rotation angles. An ultralow lattice thermal conductivity with a value of 0.095 W/mK at 300K has been observed for 21.79∘ rotation angle, which is lower than other rotation angles because of very low group velocity (22.1 km/s) and short phonon lifetime (∼0.12 ps). The high thermoelectric performance results from an ultralow thermal conductivity arising due to the strong lattice anharmonicity. The present observations can offer significant impact on the design of high performance thermoelectric materials based on twisted van der Waals heterostructure (vdWH).
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Microwave doping of graphene by phosphorus and sulphur is demonstrated and their optical, optoelectronic, and magnetic behaviours have been explored.
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•Microwave doping of graphene is ...primarily graphitic.•Microwave doping of graphene by P ∼ 15 % and S ∼ 12.5 % is reported.•Microwave P- or S- doped graphene is magnetic at room temperature.•Ms for P- and S- doped graphene are ∼ 0.13 and 0.15 emu/g respectively.•Spin-polarized DFT establishes spin asymmetry caused by doping.
Graphene, sp2-hybridized miracle material of 21st century possesses extra-ordinary physico-chemical properties and hence inspires several salient frontline applications. Lack of magnetic ordering limits its dream spintronic chips applications. Phosphorus and sulfur being large and electron-rich atoms, if adequately doped to graphene, will enable carrier injection (worth for electronic chips) and net spin-polarized electrons (worth for spintronic chips) in it. However, in-plane (preferentially) ultra-doping of graphene by phosphorus and sulfur is extremely challenging by conventional techniques. We report microwave doping of graphene by phosphorus and sulfur atoms up to record doping level of 15 and 12.5 % respectively which render graphene room temperature ferromagnetism with a saturation magnetization as high as 0.13 emu/g and 0.15 emu/g for phosphorus and sulfur doping “respectively”. Spin-polarized DFT band structure calculations suggest vivid spin asymmetry caused by doping which supports our experimental findings of primarily graphitic doped samples. Microwave doping of graphene by phosphorus and sulfur brings in dramatic changes in its magnetic behaviour and thus the present research establishes it as a novel doping strategy with excellent efficiency, scalability, and reproducibility, and will inspire new generations of graphene-based spintronic chips.
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