Naresh K. Jena

Borophane as a Benchmate of Graphene: A Potential 2D Material for Anode of Li and Na-Ion Batteries

Borophene, single atomic-layer sheet of boron ( Science 2015 , 350 , 1513 ), is a rather new entrant into the burgeoning class of 2D materials. Borophene exhibits anisotropic metallic properties whereas its hydrogenated counterpart borophane is reported to be a gapless Dirac material lying on the same bench with the celebrated graphene. Interestingly, this transition of borophane also rendered stability to it considering the fact that borophene was synthesized under ultrahigh vacuum conditions on a metallic (Ag) substrate. On the basis of first-principles density functional theory computations, we have investigated the possibilities of borophane as a potential Li/Na-ion battery anode material. We obtained a binding energy of -2.58 (-1.08 eV) eV for Li (Na)-adatom on borophane and Bader charge analysis revealed that Li(Na) atom exists in Li+(Na+) state. Further, on binding with Li/Na, borophane exhibited metallic properties as evidenced by the electronic band structure. We found that diffusion pathways for Li/Na on the borophane surface are anisotropic with x direction being the favorable one with a barrier of 0.27 and 0.09 eV, respectively. While assessing the Li-ion anode performance, we estimated that the maximum Li content is Li0.445B2H2, which gives rises to a material with a maximum theoretical specific capacity of 504 mAh/g together with an average voltage of 0.43 V versus Li/Li+. Likewise, for Na-ion the maximum theoretical capacity and average voltage were estimated to be 504 mAh/g and 0.03 V versus Na/Na+, respectively. These findings unambiguously suggest that borophane can be a potential addition to the map of Li and Na-ion anode materials and can rival some of the recently reported 2D materials including graphene.

Stability of Ar(H2)2 to 358 GPa

Significance Pressure-induced metallization of solid hydrogen is a problem of certain prominence in high-pressure physics. However, it is extremely challenging to be achieved experimentally. It was proposed that “chemical precompression” (introducing impurity atoms or molecules into hydrogen) may facilitate metallization under pressure. In this paper, we selected Ar(H2)2 as a model system and explored the intermolecular interactions of H2 molecules and the metallization of hydrogen in the presence of a weakly bound impurity (Ar). Combining our experimental data and theoretical calculations, we found that Ar does not facilitate the molecular dissociation and bandgap closure of H2, moreover it works in the opposite direction. Our work provides a solid basis for future searches of hydrogen-rich materials which facilitate metallization of hydrogen. “Chemical precompression” through introducing impurity atoms into hydrogen has been proposed as a method to facilitate metallization of hydrogen under external pressure. Here we selected Ar(H2)2, a hydrogen-rich compound with molecular hydrogen, to explore the effect of “doping” on the intermolecular interaction of H2 molecules and metallization at ultrahigh pressure. Ar(H2)2 was studied experimentally by synchrotron X-ray diffraction to 265 GPa, by Raman and optical absorption spectroscopy to 358 GPa, and theoretically using the density-functional theory. Our measurements of the optical bandgap and the vibron frequency show that Ar(H2)2 retains 2-eV bandgap and H2 molecular units up to 358 GPa. This is attributed to reduced intermolecular interactions between H2 molecules in Ar(H2)2 compared with that in solid H2. A splitting of the molecular vibron mode above 216 GPa suggests an orientational ordering transition, which is not accompanied by a change in lattice symmetry. The experimental and theoretical equations of state of Ar(H2)2 provide direct insight into the structure and bonding of this hydrogen-rich system, suggesting a negative chemical pressure on H2 molecules brought about by doping of Ar.

Enabling the Electrochemical Activity in Sodium Iron Metaphosphate [NaFe(PO3)3] Sodium Battery Insertion Material: Structural and Electrochemical Insights

Sodium-ion batteries are widely pursued as an economic alternative to lithium-ion battery technology, where Fe- and Mn-based compounds are particularly attractive owing to their elemental abundance. Pursuing phosphate-based polyanionic chemistry, recently solid-state prepared NaFe(PO3)3 metaphosphate was unveiled as a novel potential sodium insertion material, although it was found to be electrochemically inactive. In the current work, employing energy-savvy solution combustion synthesis, NaFe2+(PO3)3 was produced from low-cost Fe3+ precursors. Owing to the formation of nanoscale carbon-coated product, electrochemical activity was enabled in NaFe(PO3)3 for the first time. In congruence with the first principles density functional theory (DFT) calculations, an Fe3+/Fe2+ redox activity centered at 2.8 V (vs Na/Na+) was observed. Further, the solid-solution metaphosphate family Na(Fe1-xMnx)(PO3)3 (x = 0-1) was prepared for the first time. Their structure and distribution of transition metals (TM = Fe/Mn) was analyzed with synchrotron diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy. Synergizing experimental and computational tools, NaFe(PO3)3 metaphosphate is presented as an electrochemically active sodium insertion host material.

Polyaniline-Stabilized Intertwined Network-like Ferrocene/Graphene Nanoarchitecture for Supercapacitor Application

The present work highlights the effective H-π interaction between metallocenes (ferrocene; Fc) and graphene and their stabilization in the presence of polyaniline (PANI) through π-π interactions. The PANI-stabilized Fc@graphene nanocomposite (FcGA) resembled an intertwined network-like morphology with high surface area and porosity, which could make it a potential candidate for energy-storage applications. The relative interactions between the components were assessed through theoretical (DFT) calculations. The specific capacitance calculated from galvanostatic charging/discharging indicated that the PANI-stabilized ternary nanocomposite exhibited a maximum specific capacitance of 960u2005Fu2009g- at an energy density of 85u2005Whu2009Kg-1 and a current density of 1u2005Au2009g- . Furthermore, electrochemical impedance spectroscopy (EIS) analysis confirmed the low internal resistance of the as-prepared nanocomposites, which showed improved charge-transfer properties of graphene after incorporation of Fc and stabilization with PANI. Additionally, all electrodes were found to be stable up to 5000u2005cycles with a specific capacitance retention of 86u2009%, thus demonstrating the good reversibility and durability of the electrode material.

Saline Accelerates Oxime Reaction with Aldehyde and Keto Substrates at Physiological pH

We have discovered a simple and versatile reaction condition for oxime mediated bioconjugation reaction that could be adapted for both aldehyde and keto substrates. We found that saline accelerated the oxime kinetics in a concentration-dependent manner under physiological conditions. The reaction mechanism is validated by computational studies, and the versatility of the reaction is demonstrated by cell-surface labeling experiments. Saline offers an efficient and non-toxic catalytic option for performing the bioorthogonal-coupling reaction of biomolecules at the physiological pH. This saline mediated bioconjugation reaction represents the most biofriendly, mild and versatile approach for conjugating sensitive biomolecules and does not require any extensive purification step.

Electronic structure, stability and non-linear optical properties of aza-fullerenes C60-2nN2n(n=1–12)

Through ab initio based density functional theory calculations, we have investigated the electronic structure, stability and non-linear optical properties of a series of nitrogen substituted fullerenes (azafullerenes) with the general formula C60-2nN2n (n=1–12). For each system, we have considered different possible isomers and the minimum energy isomer is subjected to further detailed investigations. We have calculated different properties such as HOMO-LUMO gaps, vertical ionization potentials, vertical electron affinities, etc. to verify the stability of the considered fullerenes. From the Hessian calculations, it is observed that all the fullerenes are not only associated with real vibrational frequencies, but the minimum frequencies are also found to be considerably large which further confirms the stability of the considered fullerenes. We find that the presence of unperturbed C6 rings enhances the stability of the fullerene whereas, the -N-C-N- fragments are found to destabilize the structure. At lo...

Prospects of Graphene–hBN Heterostructure Nanogap for DNA Sequencing

Recent advances in solid-state nano-device-based DNA sequencing are at the helm of the development of a new paradigm, commonly referred to as personalized medicines. Paying heed to a timely need for standardizing robust nanodevices for cheap, fast, and scalable DNA detection, in this article, the nanogap formed by the lateral heterostructure of graphene and hexagonal boron nitride (hBN) is explored as a potential architecture. These heterostructures have been realized experimentally, and our study boasts the idea that the passivation of the edge of the graphene electrode with hBN will solve many of practical problems, such as high reactivity of the graphene edge and difficulty in controlled engineering of the graphene edge structure, while retaining the nanogap setup as a useful nanodevice for sensing applications. Employing first-principle density-functional-theory-based nonequilibrium Greens function methods, we identify that the DNA building blocks, nucleobases, uniquely couple with the states of the nanogap, and the resulting induced states can be attributed as leaving a fingerprint of the DNA sequence in the computed current-voltage (I-V) characteristic. Two bias windows are put forward: lower (1-1.2 V) and higher (2.7-3 V), where unique identification of all four bases is possible from the current traces, although higher sensitivity is obtained at the higher voltage window. Our study can be a practical guide for experimentalists toward development of a nanodevice DNA sensor based on graphene-hBN heterostructures.

Strain controlled electronic and transport anisotropies in two-dimensional borophene sheets

Two recent reports on realization of an elemental 2D analogue of graphene:borophene (Science, 2015, 350, 1513-1516; Nat. Chem., 2016, 8, 563-568) focus on the inherent anisotropy and directional dependence of the electronic properties of borophene polymorphs. Achieving stable 2D borophene structures may lead to some degree of strain in the system because of the substrate-lattice mismatch. We use first principles density functional theory (DFT) calculations to study the structural, electronic and transport properties of β12 and χ-borophene polymorphs. We verified the directional dependency and found the tunable anisotropic behavior of the transport properties in these two polymorphs. We find that strain as low as 6% brings remarkable changes in the properties of these two structures. We further investigate current-voltage (I-V) characteristics in the low bias regime after applying a strain to see how the anisotropy of the current is affected. Such observations like the sizeable tuning of transport and I-V characteristics at the expense of minimal strain suggest the suitability of 2D borophene for futuristic device applications.

5-Benzoyl triazole as new structural dimension in glycoconjugates

In recent years, 1,4-triazole rings are being widely used for the synthesis of carbohydrate derived biomimetics, due to their easy synthesis and wide range of functional group compatibility. These triazole rings lead to synthetic molecules with improved enzymatic stability, bioavailability, and structural diversity. In this present work, a benzoyl group has been introduced at the C-5 position of the triazole ring present in the synthetic glycoconjugates providing further structural diversity to the molecule. 5-Benzoyl 1,4-triazole ring containing glycoconjugates were synthesized using Cu(I) catalyzed [3xa0+xa02] cycloaddition reaction of per-O-acetylated glycopyranosyl azide and phenyl acetylene followed by in situ electrophilic addition of benzoyl group to the Cu(I) coordinated triazole intermediate. The X-ray crystal structure of one of the 5-benzoyl 1,4-triazole linked glycoconjugate derived from d-xylose {1-N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)-4-phenyl-5-benzoyl-1,2,3-triazole} showed unique pattern of intermolecular CH…O interactions arranging the molecules in an anti-parallel orientation. The structure and morphology of the compounds were further explored using computational calculation and scanning electron microscopic (SEM) study which firmly established the uniqueness of 5-benzoyl 1,4-triazole linked glycoconjugates compared to that of 5-H 1,4-triazole linked derivative.