5 research outputs found
Beyond the Gold–Hydrogen Analogy: Doping Gold Cluster with H-atom–O<sub>2</sub> Activation and Reduction of the Reaction Barrier for CO Oxidation
The gold–hydrogen analogy is well established in terms of analogous chemistry exhibited by gold and hydrogen atoms. A step beyond this analogy is demonstrated here by showing that the replacement of a Au atom with a H-atom in a gold cluster can lead to considerable enhancement in its reactivity. The present computational study reveals that while the closed-shell neutral pristine gold cluster Au<sub>8</sub> can bind only weakly with an O<sub>2</sub> molecule, its doped counterpart Au<sub>7</sub>H shows remarkable enhancement in its binding with molecular oxygen. It also shows an increment in O–O bond length and a red shift in vibrational frequency, indicating the activation of the O<sub>2</sub> molecule. Furthermore, the H-doped gold cluster reduces the barrier height for the environmentally important CO oxidation reaction as compared to the pristine cluster. These observations may spur further studies in the design of a cost-effective and efficient catalyst by doping gold clusters with a cheaper element like hydrogen
Scrupulous Probing of Bifunctional Catalytic Activity of Borophene Monolayer: Mapping Reaction Coordinate with Charge Transfer
We have envisaged
the hydrogen evolution and oxygen evolution reactions (HER and OER)
on two-dimensional (2D) noble metal free borophene monolayer based
on first-principles electronic structure calculations. We have investigated
the effect of Ti functionalization on borophene monolayer from the
perspective of HER and OER activities enhancement. We have probed
the activities based on the reaction coordinate, which is conceptually
related to the adsorption free energies of the intermediates of HER
and OER, as well as from the vibrational frequency analysis with the
corresponding charge transfer mechanism between the surface and the
adsorbate. Ti-functionalized borophene has emerged as a promising
material for HER and OER mechanisms. We believe that our probing method,
based on reaction coordinate coupled with vibrational analysis that
has been validated by the charge transfer mechanism, would certainly
become as a robust prediction route for HER and OER mechanisms in
coming days
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 LiÂ(Na) atom exists in Li<sup>+</sup>(Na<sup>+</sup>) 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 <i>x</i> 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 Li<sub>0.445</sub>B<sub>2</sub>H<sub>2</sub>, 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<sup>+</sup>. 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<sup>+</sup>, 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
Investigation into Biological Environments through (Non)linear Optics: A Multiscale Study of Laurdan Derivatives
The fluorescent marker
Laurdan and its new derivative, C-Laurdan,
have been investigated by means of theoretical calculations in a DOPC
lipid bilayer membrane at room temperature, and a comparison is made
with results from fluorescence experiments. Experimentally, the latter
probe is known to have a higher sensitivity to the membrane polarity
at the lipid headgroup region and has higher water solubility. Results
from Molecular Dynamics (MD) simulations show that C-Laurdan is oriented
with the carboxyl group toward the head of the membrane, with an angle
of 50° between the molecular backbone and the normal to the bilayer,
in contrast to the orientation of the Laurdan headgroup whose carbonyl
group is oriented toward the polar regions of the membrane and which
describes an angle of ca. 70–80° with the membrane normal.
This contrast in orientation reflects the differences in transition
dipole moment between the two probes and, in turn, the optical properties.
QM/MM results of the probes show little differences for one- (OPA)
and two-photon absorption (TPA) spectra, while the second harmonic
generation (SHG) beta component is twice as large in Laurdan with
respect to C-Laurdan probe. The fluorescence anisotropy decay analysis
of the first excited state confirms that Laurdan has more rotational
freedom in the DOPC membrane, while C-Laurdan experiences a higher
hindrance, making it a better probe for lipid membrane phase recognition
Toward the Realization of 2D Borophene Based Gas Sensor
To
the league of rapidly expanding 2D materials, borophene is a
recent addition. Herein, a combination of ab initio density functional
theory (DFT) and nonequilibrium Green’s function (NEGF) based
methods is used to estimate the prospects of this promising elemental
2D material for gas sensing applications. We note that the binding
of target gas molecules such as CO, NO, NO<sub>2</sub>, NH<sub>3</sub>, and CO<sub>2</sub> is quite strong on the borophene surface. Interestingly,
our computed binding energies are far stronger than several other
reported 2D materials like graphene, MoS<sub>2</sub>, and phosphorene.
Further rationalization of stronger binding is made with the help
of charge transfer analysis. The sensitivity of the borophene for
these gases is also interpreted in terms of computing the vibrational
spectra of the adsorbed gases on top of borophene, which show dramatic
shift from their gas phase reference values. The metallic nature of
borophene enables us to devise a setup considering the same substrate
as electrodes. From the computation of the transmission function of
system (gas + borophene), appreciable changes in the transmission
functions are noted compared to pristine borophene surface. The measurements
of current–voltage (<i>I</i>–<i>V</i>) characteristics unambiguously demonstrate the presence and absence
of gas molecules (acting as ON and OFF states), strengthening the
plausibility of a borophene based gas sensing device. As we extol
the extraordinary sensitivity of borophene, we assert that this elemental
2D material is likely to attract subsequent interest