Beyond the Gold–Hydrogen Analogy: Doping Gold Cluster with H-atom–O₂ 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 Au₈ can bind only weakly with an O₂ molecule, its doped counterpart Au₇H 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 O₂ 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 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 <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_0.445B₂H₂, 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

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, NO₂, NH₃, and CO₂ is quite strong on the borophene surface. Interestingly, our computed binding energies are far stronger than several other reported 2D materials like graphene, MoS₂, 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