Single-and double transition metal atoms anchored C2N as a high-activity catalyst for CO oxidation: A first-principles study.

The oxidation of CO has attracted great interest in recent years due to its important role in enhancing the catalyst durability in fuel cells and solving the growing environmental problems caused by CO emissions. Consequently, the catalytic oxidation of CO at double non-noble metal atoms anchored C2N is investigated using density functional theory (DFT) computations. All the screened Ti@C2N and Ti2@C2N are thermodynamically stable based on their binding energy calculations. The electronic characteristics, the natural bond orbital analyses (NBO), Frontier orbital, statistical thermodynamics, projected densities of states (PDOS) characteristics, non-covalent interactions (NCI), and quantum theory of atoms in molecules (QTAIM) descriptors of these systems have been examined to analyze the interaction process. Our comparative study suggested that the newly predicted double-atom catalyst (Ti2@C2N) is highly active for CO oxidation, which is a useful guideline for further development. The calculated static first-order hyperpolarizability (ßo) illustrated that the double-atom catalyst under investigation can be considered a potential candidate for non-linear optical behavior and could be used for NLO applications. CO oxidation on Ti2@C2N along the Eley-Rideal (ER) mechanism with a low energy barrier of 0.16 eV, which is smaller than the maximum energy barrier (0.73 eV) of CO oxidation along the Langmuir-Hinshelwood (LH) mechanism. Consequently, the ER mechanism is more favorable both thermodynamically and dynamically. This work can provide useful insights and guidelines for future theoretical and experimental investigations to promote the design and development of highly effective and low-cost non-precious-metal Ti2@C2N nanocatalysts towards CO oxidation at ambient temperature.

DFT study of adsorbing SO2, NO2, and NH3 gases based on pristine and carbon-doped Al24N24 nanocages.

The adsorption of SO2, NO2, and NH3 toxic gases on Al24N24 and Al24N23C nanocages was investigated by using density functional theory (DFT) calculations. The adsorption energies, frontier orbitals, charge transfer using natural bonding orbital (NBO) analysis, dipole moment, the partial density of states (PDOS), thermodynamic relationships, non-covalent interaction (NCI), and quantum theory of atoms in molecules (QTAIM) were considered. The results reveal that carbon-doped Al24N24 nanocage increases the adsorption energies for SO2 and NO2 gases while decreasing the adsorption energy of NH3 gas. The ΔG for all configurations were negative except the configurations A1 and G2 confirming the weak adsorption of these two complexes. In conclusion, Al24N24 and Al24N23C nanocages are in general promising adsorbents for the removal of SO2, NO2, and NH3 toxic gases. The Al24N24 and Al24N23C nanocages are ideal electronic materials.

A comparative theoretical study of metal functionalized carbon nanocones and carbon nanocone sheets as potential hydrogen storage materials.

The hydrogen storage of Ti functionalized carbon nanocones and carbon nanocone sheets is investigated by using the state-of-the-art density functional theory calculations. The Ti atom prefers to bind at the hollow site of the hexagonal ring. The average adsorption energies corrected for dispersion forces are -0.54 and -0.39 eV per hydrogen molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 9.31 and 11.01 wt%. The hydrogen storage reactions are characterized in terms of simulated infrared spectra, projected densities of states, kinetics, and statistical thermodynamics. The free energies and enthalpies of the Ti functionalized carbon nanocone meet the ultimate targets of the Department of Energy for all temperatures and pressures. The closest reactions to zero free energy occur at 378.15 K/2.961 atm for carbon nanocones and 233.15 K/2.961 atm for carbon nanocone sheets. The translational component is found to exert a dominant effect on the total entropy change with temperature. More promising thermodynamics are assigned to the hydrogenation of Ti functionalized carbon nanocone sheets at 233.15 K. As the temperature is increased, the lifetimes of the hydrogen molecules adsorbed at the surface drop and the rate constants increase. At fixed pressure, the rate constants of hydrogenation of Ti functionalized carbon nanocones are smaller than those of Ti functionalized carbon nanocone sheets, while the lifetimes are greater.

Role of cationic size in the optical properties of the LiCl crystal surface: theoretical study.

The size of the cations (either Ca(2+), Sr(2+), Ga(+), or Au(+)) at the F(A1)-type color centers on the (100) surface of LiCl crystal plays an important role in the optical properties of this surface. In this work, double-well potentials at this surface were investigated using ab initio quantum mechanical methods. Quantum clusters were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surface, and the ions that were the nearest neighbors to the F(A1) site were allowed to relax to equilibrium. The calculated Stokes-shifted optical transition bands, optical-optical conversion efficiency, and relaxed excited states of the defect-containing surface, as well as the orientational destruction of the color centers, recording sensitivity, exciton (energy) transfer, and the Glasner-Tompkins empirical relation were all found to be sensitive to the size of the dopant cation.

Spectral studies and molecular orbital PPP-calculations of some azo-dyes.

The UV, IR and 1H-NMR spectra of some 4-(R-phenyl azo) 1-hydroxy 2-naphthoic acid derivatives are studied. The effects of substituent groups and the solvent polarity on electronic spectral, IR bands and 1H-NMR proton chemical shifts are considered, the molecular orbital calculations obtained are rationalized quantitatively with that obtained practically using the PPP-model with configuration interaction (CI).

FA(I):A(+) and FA(II):Cu(+) laser activity and photographic sensitization at the low coordinated surfaces of AgBr ab initio calculations.

The twofold potentials of F(A)(I):Au(+) and F(A)(II)Cu(+) color centers at the low coordinated surfaces of AgBr thin films in providing tunable laser activity and photographic sensitization were investigated using ab initio methods of molecular electronic structure calculations. Clusters of variable size were embedded in simulated Coulomb fields that closely approximated the Madelung fields of the host surfaces, and the nearest neighbor ions to the F(A) defect site were allowed to relax to equilibrium in each case. Based on the calculated Stokes shifted optical transition bands and horizontal shifts along the configuration coordinate diagrams, both F(A)(I):Au(+) and F(A)(II):Cu(+) color centers were found to be laser active. The laser activity faded quickly as the bromide ion coordination decreased from 5 (flat) to 4 (edge) to 3 (corner) and as the size of the impurity cation increased from Cu(+) to Au(+). The latter relation was explainable in terms of the axial perturbation of the impurity cation. The smallest calculated Stokes-shift at the corner surface suggested that emission had the same oscillator strength as absorption. All relaxed excited states RESs of the defect containing surfaces were deep below the lower edges of the conduction bands of the defect free ground state surfaces, indicating that F(A)(I):Au(+) and F(A)(II):Cu(+) are suitable laser defects. The probability of orientational destruction of the two centers attributed to the assumed RES saddle point ion configurations along the <110> axis was found to be directly proportional to the size of the impurity cation, with activation energy barriers of about 0.655-3.294 eV for Cu(+), and about 1.887-3.404 eV for Au(+). The possibility of exciton (energy) transfer from the sites of higher coordination to those of lower coordination is demonstrated. The more laser active F(A)(II):Cu(+) center was more easily formed than the less laser active F(A)(I):Au(+) center. The Glasner-Tompkins empirical relation was generalized to include F(A) centers at the low coordinated surfaces of silver bromide thin film. As far as color photographic sensitization is concerned, the lowest unoccupied molecular orbitals of the selected dye molecules in the excited states were high enough for electron injection. F(A) defect formation and rotational diffusion of silver clusters reduced the energy gaps between the excited dye molecules and the lower edges of the conduction bands and allowed for hole injection. About 54-60% of the reduction of silver ions at the flat surface of AgBr was attributed to the host anions and F(A) defect formation, leaving about 40-46% for the reduction of photoelectrons as well as the electrons of the developer or dye molecules. The unrelaxed rotational diffusions of the central Ag(4) by 90 degrees decreased the latter percentage, but were severely hindered by activation energy barriers.