V. J. Surya

Tuning Electronic Structure of Graphene: A First-Principles Study

Based on first-principles study, tuning of electronic structure of graphene is reported. The emergence of band gap in this semimetal can be accomplished through different mechanisms. In this study, we have reported on the band gap modulations in graphene through chemical functionalization with oxygen, under the application of external stress, and through the creation of vacancies. Our study suggests that all these mechanisms alter either electronic properties or both structural and electronic properties of graphene. As a result, these mechanisms completely destroy the nature of massless Dirac fermions of graphene. Also, we report on the effect of static electric field on the band gap in hydrogenated graphene (graphane). The combined action of structural modifications that involves stretching and compression of C-C bonds in the hexagonal network and charge transfer mechanism are responsible for the gap opening in electronic spectrum of graphene, which is essential for the future application of graphene in electronics. The introduction of strain is a nondestructive method when compared to other methods for band gap engineering in graphene.

Investigation of Hydrogen Desorption From Hydrogenated Single-Walled Carbon Nanotubes Functionalized With Borane

The present experimental study reports on hydrogen desorption behavior of hydrogenated single-walled carbon nanotubes (SWCNTs), functionalized with borane (BH3). Desorption is carried out using a thermal annealing technique. The hydrogenated samples are annealed at 200 °C for 30 min and characterized using Fourier transform infrared (FTIR) and Raman spectroscopy studies. The amount of released hydrogen is measured by thermogravimetric/thermal desorption spectroscopy (TG/TDS) studies. FTIR and Raman studies confirm the desorption of hydrogen. The TG/TDS results reveal that 100% of stored hydrogen is released in approximately 1.5 min in the temperature range 100-150°C.

Activation of CO and CO2 on homonuclear boron bonds of fullerene-like BN cages: first principles study.

Using density functional theory we investigate the electronic and atomic structure of fullerene-like boron nitride cage structures. The pentagonal ring leads to the formation of homonuclear bonds. The homonuclear bonds are also found in other BN structures having pentagon line defect. The calculated thermodynamics and vibrational spectra indicated that, among various stable configurations of BN-60 cages, the higher number of homonuclear N-N bonds and lower B:N ratio can result in the more stable structure. The homonuclear bonds bestow the system with salient catalytic properties that can be tuned by modifying the B atom bonding environment. We show that homonuclear B-B (B2) bonds can anchor both oxygen and CO molecules making the cage to be potential candidates as catalyst for CO oxidation via Langmuir–Hinshelwood (LH) mechanism. Moreover, the B-B-B (B3) bonds are reactive enough to capture, activate and hydrogenate CO2 molecules to formic acid. The observed trend in reactivity, viz B3 > B2 > B1 is explained in terms of the position of the boron defect state relative to the Fermi level.

COMPUTATION OF INTERACTION POTENTIAL OF ADSORBATES ON ZIGZAG SWCNTs — APPLICATION TO FUNCTIONALIZATION AND HYDROGEN STORAGE

Nature of the interaction potential of different adsorbates on different zigzag single-walled carbon nanotubes is investigated. The intermolecular potentials for H2 absorbed in carbon nanotubes (5, 0), (6, 0), (7, 0), (8, 0), (9, 0), and (10, 0) are computed and sketched. This study is extended to N2 adsorbed on (4, 0) and BH3 adsorbed on (10, 0) tubes. The equilibrium positions of the adsorbates obtained from the potential model serve as an initial guess in designing the CNT + adsorbate complex in the simulation cell and this process considerably reduces the computation time. Further, the hydrogen storage capacity of CNT(10,0) + BH3 complex is calculated. The estimated storage capacity of this system is in the range 6–12 wt.%.

Ripples in Graphene: A Theoretical Analysis Using Two Dimensional Vibrating Membrane Model

We have investigated the formation of ripples in graphene using two‐dimensional vibrating membrane model. We have chosen both armchair and zigzag graphene sheets with different sizes. The amplitude of vibrational modes of each graphene sheet is determined using this model. We observed that the vertical displacement (amplitude of the ripples) of the graphene sheet reaches a maximum height of about 0.99 nm from the mean plane in certain graphene sheets (nanoribbons) whose lengths are integral multiple of the basic armchair/zigzag units.

Desorption Studies on Hydrogenated Single Walled Carbon Nanotubes Functionalized with Borane (BH3)

In this work, desorption of hydrogen from hydrogenated single walled carbon nanotubes (SWCNTs) functionalized with borane is discussed. A hydrogen storage medium based on SWCNTs functionalized with borane is designed. The SWCNTs are functionalized with borane (BH3) using LiBH4 as the precursor by solution cast method. The functionalized samples are hydrogenated. A storage capacity of 1.5 wt.% is obtained just above room temperature (50°C). The hydrogenated and dehydrogenated samples are characterized using FTIR and Raman studies. The thermogravimetry/differential thermal analysis (TG/DTA) results reveal that the entire amount of (1.5 wt.%) stored hydrogen is released in the temperature range 100 - 150°C. This temperature range is suitable for hydrogen fuel cells used for vehicular applications.

Hydrogenation in SWCNTs Functionalized with Borane

We have done the experimental investigation of hydrogen storage in functionalized single‐walled carbon nanotubes (SWCNTs). The SWCNTs having the average diameter of 22 nm are deposited on alumina substrates by drop casting method. The functionalization of SWCNTs with BH3 using LiBH4 as the precursor, over the surface of SWCNTs is done by the same chemical method. Further, the functionalized samples are hydrogenated in the hydrogenation chamber. The samples are characterized through FTIR, XPS and CHNS studies. A hydrogen storage capacity of 0.87 wt % at 100 °C is observed.

STUDY OF HYDROGEN STORAGE IN ALUMINUM HYDRIDE COATED SINGLE-WALLED CARBON NANOTUBE

In this study, we report the hydrogen storage in aluminum hydride coated single-walled carbon nanotube. All the H2 adsorption is molecular with H–H bond length of 0.756 A. The hydrogen storage capacities with half and full coverages are 6.01 (8.3) wt% and 7.2 (10.3) wt%, respectively, without (with) H3 of AlH3. At high coverage of AlH3 (C10AlH3) interesting clustering/ dimerization of AlH3 is observed. These systems are quite stable and the H2 can be extracted from the system without disturbing the C–Al bonding or detaching the AlH3 from the carbon nanotube. This present study on a full molecular adsorption of hydrogen via light metal-hydride AlH3 is new and it leads to a practically viable hydrogen storage process.