Hydrazine network on Cu(111) surface: A Density Functional Theory approach

We have used first-principles calculations, including a correction for the dispersive forces (DFT-D2), to investigate the arrangement of hydrazine (N2H4) molecules upon adsorption on the Cu(111) surface, showing that surface–molecule interactions affect the process most. Our calculations provide insight into the interplay between lateral adsorbate–adsorbate and vertical adsorbate–substrate interactions. We found that the main contributors to the assembly of the hydrazine layers are the binding interactions between the adsorbates and the substrate. The dispersion forces are predominant in both vertical and lateral interactions, whereas hydrogen-bonding is least important and organisation of the N2H4 monolayers is therefore primarily due to the long-range interactions. Optimised geometries for several hydrazine conformations were found to be coverage-dependent. The electronic properties such as charge density and density of states have been calculated for different hydrazine coverages, and indicated that no charge transfer occurs between molecules. Scanning tunnelling microscopy images were simulated, where the observed protrusions arise from the trans conformers. We also found that the effect of hydrazine adsorption on the Cu(111) surface energy is negligible and further investigation of other Cu facets is needed to determine the N2H4 effect on the nanoparticles' morphology. Finally, we have simulated the temperature programmed desorption of different coverages of hydrazine from the Cu(111) resulting in desorption peaks between 150 and 200 K

A DFT Study of Alkaline Earth Metal-Doped FAPbI3 (111) and (100) Surfaces

Density functional theory calculations have been performed to study the effect of replacing lead by alkaline earth metals on the stability, electronic and optical properties of the formamidinium lead triiodide (FAPbI3) (111) and (100) surfaces with different terminations in the form of FAPb1-xAExI3 structures, where AE is Be, Mg or Ca. It is revealed that the (111) surface is more stable, indicating metallic characteristics. The (100) surfaces exhibit a suitable bandgap of around 1.309 and 1.623 eV for PbI5 and PbI6 terminations, respectively. Increases in the bandgaps as a result of Mg- and Ca-doping of the (100) surface were particularly noted in FAPb0.96Ca0.04I3 and FAPb0.8Ca0.2I3 with bandgaps of 1.459 and 1.468 eV, respectively. In the presence of Be, the band gap reduces critically by about 0.315 eV in the FAPb0.95Be0.05I3 structure, while increasing by 0.096 eV in FAPb0.96Be0.04I3. Optimal absorption, high extinction coefficient and light harvesting efficiency were achieved for plain and doped (100) surfaces in the visible and near UV regions. In order to improve the optical properties of the (111)-PbI3 surface in initial visible areas, we suggest calcium-doping in this surface to produce FAPb0.96Ca0.04I3, FAPb0.92Ca0.08I3, and FAPb0.88Ca0.12I3 structures

Adsorption of hydrazine on the perfect and defective copper (111) surface: A dispersion-corrected DFT study

We have investigated the adsorption of hydrazine (N2H4) on perfect and defect-containing copper (111) surfaces by first-principles calculations. The long-range interactions are included in the geometry optimization through the application of the generalised gradient approximation with dispersion correction, DFT-D2 in the method of Grimme. We have studied three types of defects at the surfaces: monoatomic steps, Cu-adatoms and vacancies, where our calculations show that the adsorption energy increases as the coordination of the adsorption sites decreases. The ideal (111) is the most stable surface with the weakest adsorption of hydrazine, whilst the stepped (111) surface is the least stable and hence more reactive surface with the highest adsorption energy, where the hydrazine bridges across the step edge. We found that inclusion of the dispersion correction results in significant enhancement of molecule–substrate binding, thereby increasing the adsorption energy. This strong adsorption results in a bridging adsorption geometry for hydrazine, with a rotation around the Nsingle bondN bond where the torsional angle changes from a gauche towards an eclipsed conformer to help the molecule to bridge through both nitrogen atoms, in agreement with experimental evidence. The core-level binding shifts for the N(1 s) states upon N2H4 adsorption have been calculated at DFT level to provide further insight into the N2H4 adsorption process on the copper surfaces

Thermodynamic and Kinetic Study of Carbon Dioxide Hydrogenation on the Metal-Terminated Tantalum-Carbide (111) Surface: A DFT Calculation

The need to reduce our reliance on fossil fuels and lessen the environmentally harmful effects of CO2 have encouraged investigations into CO2 hydrogenation to produce useful products. Transition metal carbides exhibit a high propensity towards CO2 activation, which makes them promising candidates as suitable catalysts for CO2 hydrogenation. Here, we have employed calculations based on the density-functional theory to investigate the reaction network for CO2 hydrogenation to product molecules on the tantalum-terminated TaC (111) surface, including two routes from either HCOOH* or HOCOH* intermediates. Detailed calculations of the reaction energies and energy barriers along multiple potential catalytic pathways, along with the exploration of all intermediates, have shown that CH4 is the predominant product yielded through a mechanism involving HCOOH, with a total exothermic reaction energy of −4.24 eV, and energy barriers between intermediates ranging from 0.126 eV to 2.224 eV. Other favorable products are CO and CH3OH, which are also produced via the HCOOH pathway, with total overall reaction energies of −2.55 and −2.10 eV, respectively. Our calculated thermodynamic and kinetic mechanisms that have identified these three predominant products of the CO2 hydrogenation catalyzed by the TaC (111) surface explain our experimental findings, in which methane, carbon monoxide, and methanol have been observed as the major reaction products

Development and use of a computer program to detect potentially inappropriate prescribing in older adults residing in Canadian long-term care facilities

BACKGROUND: Inappropriate prescribing has been estimated to be as high as 40% in long-term care. The purpose of this study was to develop a computer program that identifies potentially inappropriate drug prescriptions and to test its reliability. METHODS: Potentially inappropriate prescriptions were identified based on modified McLeod guidelines. A database from one pharmacy servicing long-term care facilities in Ontario was utilized for this cross-sectional study. Prescription information was available for the 356 long-term care residents and included: the date the prescription was filled, the quantity of drug prescribed and the eight-digit drug identification number. The pharmacy database was linked to the computer-based program for targeting potential inappropriate prescriptions. The computer program's reliability was assessed by comparing its results to a manual search conducted by two independent research assistants. RESULTS: There was complete agreement between the computer and manual abstraction for the total number of potentially inappropriate prescriptions detected. In total, 83 potentially inappropriate prescriptions were identified. Fifty-three residents (14.9%) received at least one potentially inappropriate prescription. Of those, twenty (37.7%) received two potential inappropriate prescriptions and eight (15.1%) received 3 or more potential inappropriate prescriptions. The most common potential inappropriate prescriptions were identified as long-term use of non-steroidal anti-inflammatory agents and tricyclic antidepressants with active metabolites. CONCLUSION: A computer program can accurately and automatically detect inappropriate prescribing in residents of long-term care facilities. This tool may be used to identify potentially inappropriate drug combinations and educate health care professionals

Mechanism of Photocatalytic Reduction of CO2 by Ag3PO4(111)/g-C3N4 Nanocomposite: A First-Principles Study

Density functional theory (DFT) calculations have been performed to investigate the electronic structure and photocatalytic activity of a hybrid Ag3PO4(111)/g-C3N4 structure. Due to Ag(d) and O(p) states forming the upper part of the valence band and C(p), N(p), and Ag(s) the lower part of the conduction band, the band gap of the hybrid material is reduced from 2.75 eV for Ag3PO4(111) and 3.13 eV for monolayer of g-C3N4 to about 2.52 eV, enhancing the photocatalytic activity of the Ag3PO4(111) surface and g-C3N4 sheet in the visible region. We have also investigated possible reaction pathways for photocatalytic CO2 reduction on the Ag3PO4(111)/g-C3N4 nanocomposite to determine the most favored adsorption geometries of reaction intermediates and the related reaction energies. For CO2 reduction, our findings demonstrate that the Ag3PO4(111)/g-C3N4 heterostructure thermodynamically exhibits a higher selectivity toward CH4 production than that of CH3OH. The CO2 reduction process takes place through either HCOOH* or HOCOH* as an intermediate species, where the highest exothermic reaction energy of −2.826 eV belongs to the hydrogenation of t-COOH* to HCOOH* and the lowest reaction energy of −0.182 eV for hydrogenations of CH2O* to CH2OH* and HCO* to c-HCOH*. Our results from charge density difference calculations of the Ag3PO4(111)/Ag/g-C3N4 revealed that the charge transfer between the Ag3PO4(111) slab and g-C3N4 monolayer occurs through mediation of atomic Ag, thus proposing a Z-scheme mechanism. Moreover, a smaller band gap energy of 0.73 eV is calculated for this ternary nanocomposite due to the midgap states of the atomic Ag at the interface. These results provide in depth understanding of the reaction mechanism in the reduction and conversion of CO2 to useful chemicals via an Ag3PO4 and g-C3N4-based nanocomposite photocatalyst under visible light

Si-containing 3D cage-functionalized graphene oxide grafted with Ferrocene for high-performance supercapacitor application: An experimental and theoretical study

In this work, graphene oxide sheets were functionalized with Octa(aminopropyl)silsesquioxane. Then, Octa(aminopropyl)silsesquioxane-functionalized graphene oxide (GO-Amine-SSQ) was grafted with Ferrocene through Friedel-Craft reaction. Structural properties of the prepared composite (GO-Amine-SSQ-Fc) were analyzed by XPS, FT-IR, XRD, Raman, SEM, TEM, and BET tests. Results confirmed the successful synthesis and high porosity. Next, the electrochemical properties of GO-Amine-SSQ-Fc were characterized by CV, GCD, and EIS techniques in the 3E system. The GO-Amine-SSQ-Fc electrode showed a specific capacitance of 574 F g−1 at 1 A g−1, retention capacitance of 90.1% after 10,000 charge-discharge cycles, low resistance, and efficient diffusion of ions. After confirming the excellent electrochemical performance of this electrode, a symmetric supercapacitor system (GO-Amine-SSQ-Fc//GO-Amine-SSQ-Fc) was tested by CV and GCD techniques, to determine practical application of system. GO-Amine-SSQ-Fc//GO- Amine-SSQ-Fc system recorded a specific capacitance of 304 F g−1 at 0.5 A g−1, retention capacitance of 92.5% over 10,000 charge-discharge cycles, and specific energy of 10.14 Wh kg−1 at a specific power of 500 W kg−1. Also, the results of computational methodology show that the interaction of SSQ, Fc and GO layer in GO-Amine-SSQ-Fc composite, makes it effective as an electrode material for supercapacitors. This excellent performance, as a result of the unique structure of Amine-SSQ groups and the superior electrochemical behavior of Ferrocene groups, suggests that GO-Amine-SSQ-Fc composite has great potential for energy storage devices

Persistent Quantum Coherence and Strong Coupling Enable Fast Electron Transfer across the CdS/TiO2 Interface: A Time-Domain ab Initio Simulation

Fast transfer of photoinduced electrons and subsequent slow electron–hole recombination in semiconductor heterostructures give rise to long-lived charge separation which is highly desirable for photocatalysis and photovoltaic applications. As a type II heterostructure, CdS/TiO2 nanocomposites extend the absorption edge of the light spectrum to the visible range and demonstrate effective charge separation, resulting in more efficient conversion of solar energy to chemical energy. This improvement in performance is partly explained by the fact that CdS/TiO2 is a type II semiconductor heterostructure and CdS has a smaller energy band gap than UV-active TiO2. Ultrafast transient absorption measurements have revealed that electrons generated in CdS by visible light can quickly transfer into TiO2 before recombination takes place within CdS. Here, using time-domain density functional theory and nonadiabatic molecular dynamics simulations, we show how electronic subsystems of the CdS and TiO2 semiconductors are coupled to their lattice vibrations and coherently evolve, enabling effective transfer of photoinduced electrons from CdS into TiO2. This very fast electron transfer, and subsequent slow recombination of the transferred electrons with the holes left in CdS, is verified experimentally through the proven efficient performance of CdS/TiO2 heterostructures in photocatalysis and photovoltaic applications