Adsorption and dehydrogenation of ammonia on Ru55, Cu55 and Ru@Cu54 nanoclusters: role of single atom alloy catalyst

Hydrogen production by the catalytic decomposition of ammonia (NH3) is an important process for several important applications, which include energy production and environment-related issues. The role of single Ru-atom substitution in a Cu55 nanocluster (NC) has been illustrated using the NH3 decomposition reaction as a model system. The structural stability of Ru@Cu54 NC has been evaluated using Ru55 and Cu55 NCs for comparison. Ru@Cu54 prefers an icosahedron structure (Ih), like Ru55 and Cu55 NCs, with almost comparable average binding energies of -5.55 eV per atom. The adsorption of NHx (x = 0-3) on different adsorption sites of the icosahedron Ru@Cu54 NC has also been studied and the corresponding adsorption energies have been estimated. The site-preference investigation suggested that NH3 prefers to adsorb vertically to the Ru@Cu54. The stable geometries of the N and H atoms on the high symmetry adsorption sites of Ru@Cu54 NC have been studied. Although the N atom favours top and hollow sites, the H atom prefers to stay in the Ru-Cu bridge site along with the hollow sites. The adsorption energy of N on the Ru@Cu54 NC fcc site is found to be -5.42 eV, which is very close to the optimal value (-5.81 eV) of the ammonia decomposition volcano curve. The reaction energies for stepwise H atom elimination from an adsorbed NH3 molecule have been estimated. Finally, NH3 adsorption and decomposition on Ru@Cu54 have been illustrated in terms of electronic structure analysis. The energetics calculations for the dehydrogenation of NH3 suggest that Ru@Cu54 NC can be a suitable catalyst.

CO2 hydrogenation to formic acid on Pd-Cu nanoclusters: a DFT study

Carbon dioxide (CO₂) hydrogenation to formic acid is a promising method for the conversion of CO₂ to useful organic products. The interaction of CO₂ with hydrogen (H₂) on Pd_mCu_n (m + n = 4, 8 and 13) clusters to form formic acid (HCOOH) has been explored using density functional theoretical (DFT) calculations. Pd₂Cu₂, Pd₄Cu₄ and 13-atom Pd₁₂Cu clusters are found to be the most stable among all of the Pd_mCu_n (m + n = 4, 8 and 13) clusters with binding energies of -1.75, -2.16 and -2.40 eV per atom, respectively. CO₂ molecules get adsorbed on the Pd₂Cu₂, Pd₄Cu₄ and Pd₁₂Cu clusters in an inverted V-shaped way with adsorption energies of -0.91, -0.96 and -0.44 eV, respectively. The hydrogenation of CO₂ to form formate goes through a unidentate structure that rapidly transforms into the bidentate structure. To determine the transition state structures and minimum energy paths (MEPs) for CO₂ hydrogenation to formic acid, the climbing image nudge elastic band (CI-NEB) method has been adopted. The activation barriers for the formation of formic acid from formate on Pd₂Cu₂ and Pd₄Cu₄ are calculated to be 0.79 and 0.68 eV, respectively whereas that on the Pd₁₂Cu cluster is 1.77 eV. The enthalpy for the overall process of CO₂ hydrogenation to formic acid on the Pd₂Cu₂, Pd₄Cu₄ and Pd₁₂Cu clusters are found to be 0.83, 0.48 and 0.63 eV, respectively. Analysis of the density of states (DOS) spectra show that the 4d orbital of Pd, the 3d orbital of Cu, and the 2p orbitals of C and O atoms are involved in the bonding between CO₂ molecules and the Pd₂Cu₂ clusters. The CO₂ adsorption on the Pd_mCu_n (m + n = 4 and 8) clusters has also been explained in terms of the charge density distribution analysis.

Revealing Eu3+-doped yttrium pyrogermanate as a soft UV excitable phosphor: retaining the pros of the commercial phosphor and compensating for the cons

This article presents the synthesis of a single-phase red emitting Y2Ge2O7:Eu3+ soft-UV excitable phosphor with up to 10% Eu3+ content. Experimental and theoretical exploration has established its relative potential with respect to the commercial Y2O3:Eu3+ phosphor.

Why Do Relative Intensities of Charge Transfer and Intra-4f Transitions of Eu3+ Ion Invert in Yttrium Germanate Hosts? Unravelling the Underlying Intricacies from Experimental and Theoretical Investigations

The dominant intensity of parity-forbidden intra-4f transitions of europium(III) over O → Eu charge-transfer band (CTB) intensity is against common perceptions, yet this trend is observed in many germanate hosts and has not been rationalized so far. In search of a plausible explanation for this unusual trend, present work reports an experimental and theoretical investigations in conjunction on two sibling germanate host, namely, Y₂GeO₅ and Y₂Ge₂O₇ having dopant Eu³⁺ in their respective YO₇ polyhedra. Whereas for Y₂GeO₅:Eu³⁺, the CTB is more intense than the intra-4f transitions in the excitation spectrum, in the case of Y₂Ge₂O₇:Eu³⁺, the relative intensities of CTB and intra-4f transitions are reversed. Comparative structural analysis reveals that Eu³⁺ present in YO₇ of Y₂GeO₅ has a greater number of tetra-coordinated oxygen (O_tetra) and yttrium atom as first and second neighbors, respectively (Eu³⁺-O_tetra-Y³⁺ linkages). Conversely, in Y₂Ge₂O₇ host, the Eu³⁺ ion mostly has tricoordinated oxygen (O_tri) as its nearest neighbor and germanium ions next to O_tri (Eu³⁺-O_tri-Ge⁴⁺ linkage). Theoretical calculations reveal that while Y₂GeO₅:Eu has O_tetra(4Y) dominating at the Fermi level and the 4f state of Eu³⁺ remains inert toward mixing, in Y₂Ge₂O₇:Eu, the Fermi level has major contribution from O_tri(2Y + 1Ge) with significant mixing with 4f states of Eu. The dominant control of Eu³⁺-O_tri-Ge⁴⁺ linkages in geometrical and electronic structure of Y₂Ge₂O₇:Eu owing to the GeO₄ surrounding has been attributed to relative poor intensity of O → Eu CTB. Siege of Eu³⁺ by GeO₄ and subsequent occurrence of Eu³⁺-O_tri-Ge⁴⁺ linkages play a dual role: First, it induces electronic rigidity to hinder excitation of electron at bridging (O_tri) oxygen by highly charged small Ge⁴⁺ cation; second, the covalent character in Eu-O bond is achieved by intermixing of Eu's 4f and O_tri 2p orbital which facilitates relaxing of the parity-selection rule thus enhancing the probability of intra-4f transitions. The inferences drawn remain valid when extrapolated to other inorganic oxides having EuO_x polyhedra surrounded by covalent units like PO₄, SiO₄, etc. and have a prevailing number of low-coordinated oxygen atoms and highly charged small cation in the first and second coordination shells, respectively. The optical basicity concept is also found to endorse our explanation. These remarkable generic inferences will pave the rational way for designing efficient phosphors for solid-state lighting.

Does the chromagen blue filter lens affect the reading speed, accuracy and contrast sensitivity

PURPOSE

To determine the effects of ChromaGen blue filter lens in reading speed, accuracy and contrast sensitivity.

METHODS

A cross-over, randomised study was carried out on 40 individuals (11 males and 29 females) aged 21 to 30 years. The rate of reading and reading accuracy was calculated with and without ChromaGen blue filter lens in all subjects. Wilkins Rate of Reading Test was used to measure the rate of reading and reading accuracy. Contrast sensitivity was also evaluated by using with and without the ChromaGen blue filter lens.

RESULTS

The mean rate of reading with and without ChromaGen blue filter lens was 160.58±16.03 words per minute and 150.52±15.66 words per minute respectively, with significant difference of p<0.001. The mean of reading accuracy (words correctly read per minute) in subjects, with ChromaGen blue filter was 149.30±0.79 words and without using filter lens was 148.53±1.11 words and found to be significant (p<0.001). There was no significant difference in the contrast sensitivity between subjects with and without the ChromaGen blue filter lens (p=0.083). No significant correlation was noted between the reading speed with age, spherical equivalent, contrast sensitivity, and reading accuracy.

CONCLUSION

This study concludes that there was an increase of 6.68% in the rate of reading and improvement of 0.52% in accuracy among subjects with ChromaGen blue filter lens.

Modulation of band gap by an applied electric field in silicene-based hetero-bilayers

Electronic properties of the hetero-structures consisting of silicene, graphene and BN monolayers under the influence of an electric field were investigated using density functional theory.

h-BN monolayer on the Ni(111) surface: a potential catalyst for oxidation

The hexagonal boron nitride (h-BN) is traditionally considered to be inert. In sharp contrast to the inert behavior of free-standing hexagonal boron nitride (h-BN), we propose the catalytic property of h-BN monolayer on Ni(111) substrate using first-principles density functional theory investigation. The interaction of O2 molecule with the h-BN/Ni(111) substrate results in nondissociative adsorption of the molecule along with elongation of the O-O bond. This can be considered as the activated state of the O2 molecule. Further interaction of this complex viz O2-h-BN/Ni(111) with an incoming CO molecule leads to the spontaneous formation of CO2. Interestingly, the CO adsorption on the h-BN/Ni(111) substrate was found to be unfavorable, thereby implying the oxidation of CO selectively through Eley-Rideal (ER) mechanism.

Simulation Study on Geometric and Electronic Structure of Photovoltaic Molecules

We investigate the geometric and electronic structure of porphyrin-fullerene based supramolecular system in which have an extremely long-lived charge-separated state have been achieved, using first principle calculations. The results suggest that the LUMO state of this supramolecule is localized on the fullerene and HOMO state is localized on the porphyrin moiety.