Structure of palladium nanoparticles under oxidative conditions

Using density functional theory (DFT) and thermodynamic considerations we study the shape and stability of Pd nanoparticles in oxygen-lean and oxygen- rich atmospheres. We find that at very high oxygen coverage cubes exposing (100) faces will form, which are stabilized due to the formation of a Image o/√(5) x √(5)R27° overlayer. The shape of oxygen-covered Pd and Pt nanoparticles is compared in this study

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Density functional study of molecular adsorption on the CU(011) surface: oxalic acid and 2,5 pyrazine di-carboxylic acid

Highly ordered self-assembled organic monolayers (SAM) on metallic surfaces have attracted considerable attention recently due to their possible applications as opto-electronic devices (organic light-emitting diodes (OLED), organic field-effect transistors (OFET), solar cells, etc) as well as due to their use in a vast number of economically important surface processes (such as catalysis in chemical production, corrosion protection, control of surface properties like wettability or friction, molecular sensing, etc). For all these applications, a fundamental understanding of the surface-molecule bonding (in terms of bonding strength, charge injection barriers) and of the molecule-molecule interactions (in terms of steric interactions, hydrogen bonding, etc.) is essential, as these factors significantly affect the performance and the stability of the molecular-deposited systems. We have performed using the VASP code density functional theory calculations to examine the structural, electronic, vibrational and optical properties of oxalic acid molecules (HOOC – COOH) and of 2,5 pyrazine di-carboxylic acid molecules (PDA,HOOC – C4N2H2 – COOH) in vacuum and adsorbed onto the Cu(011) surface. A series of experimentally accessible quantities such as adsorption geometries, binding energies, Ultraviolet Photoelectron Spectroscopy (UPS) spectra, work-function values, Scanning Tunneling Microscopy (STM) images, Reflection Adsorption Infrared Spectroscopy (RAIRS) spectra has been calculated and compared with the available experimental data. The main results are: (a) For the experimental found vertical orientations of the adsorbed molecules (oxalic acid, PDA) the orientation of the vacuum exposed COOH H atom ("up" or "down") is a crucial structural property. This largely influences both the 2D organization of the molecular layer, as well as its reactivity. Thus, if the H atom is found to be stable in an up-orientation, it has a smaller chance to get involved in inter-molecular hydrogen bonds. If the H atom is however down-oriented, it will promote the formation of inter-molecular hydrogen bonds with consequences on the molecular layer stability and ordering. From the reactivity point of view, a H atom up-oriented means that this can be replaced/substituted easiest by a molecule which has a reactive positive side group. If the H atom is down- oriented, the most natural replacement will be that of the entire OH group by a molecule having a negative side group. (b) The H atom has a decisive influence on the value of the dipole moment of molecule layer and thus on the work function of the Cu-molecular-layer system. A change from "up" to "down" in the position of the H atom causes a change in work function of ~ 1.5 eV (for the oxalic acid layer) and of ~ 2.5 eV for the PDA layer. This is an interesting result as a lot of work is put nowadays in finding efficient ways for the in-situ variation of the systems work-function. (c) For both investigated systems ( Cu-oxalic, Cu-PDA ) we find that the hole injection barrier (HIB) is smaller than the electron injection barrier (EIB). For the Cu-oxalic system HIB ~ 0.75 eV and EIB ~ 2.86 eV. For Cu-PDA system HIB ~ 1.1 eV and an EIB ~ 1.5 eV. These systems are therefore p-type organic semiconductors and good candidates for the anode in opto-electronic components. (d) The simulated STM images show characteristic differences for the up-and down-conformations, allowing one to know what kind of organization is present on the surface. (e) The calculated infra-red spectrum is found to be in good agreement with the experimental one

Basic quantum‐chemical concepts, the chemical bond revisited

Quantum‐chemical functions as Partial density of States and Crystal orbital Hamiltonian population are introduced. They are essential to understand the electronic nature of the chemical bond. The electronic structure of diatomic molecules and solid state materials, mainly the transition metals will be discussed. As an illustration the relation between transition metal structure and valence electron distribution is presented

How molecular is the chemisorptive bond?

Trends in adsorption energies as a function of transition metal differ for adsorbates that are attached atop a surface atom or are adsorbed onto a high coordination site. When adsorption onto early and late transition metals is compared variation in relative bond energies of adsorbates attached to different sites is large. A theoretical understanding is provided based on the analysis of the electronic structure of the respective chemical bonds. The electronic structure analysis is based on partial density of states (PDOS) and bond order overlap population densities from crystal orbital Hamiltonian population (COHP) calculations available from DFT electronic structure computations. This is complemented by calculations of Bader charge densities and electron density topology properties. Variation of the respective bond energies depends on the symmetry of the molecular orbitals that form the chemical bond. The key electronic structure parameters are the position of the Fermi level in the bonding or antibonding molecular orbital partial density of states region of the chemical bond and chemical bond polarity. These are very different for adsorbates adsorbed onto the same transition metal surface, but which have different coordination with surface metal atoms. The adsorption energies and the respective electronic structures of adatoms H, C and O and molecular fragments CHx (x = 1–3) are compared with those of the analogous molecules that contain a single transition metal atom. When adsorbed atop, trends in bond energies are remarkably similar to those of the corresponding molecules. The difference in bond energies of adsorbates and transition metal molecules, i.e. the embedding energy, is shown to consist of three contributions: quenching of the sometimes high molecular spin states, weakening of the adsorbate–surface interaction energy and weakening of the metal–metal atom bond energies next to the adsorbate. Conventional scaling rules of the interaction energies of adsorbed CHx (0 < x ≤ 3) fragments are satisfied only for adsorbates in high coordination sites. For the early transition metals a breaking of this rule is found for C and CH or N and NH when adsorbed atop a transition metal surface or when they are part of a transition metal molecule. The M–C bond energy is found to be only stronger than that of the M–CH bond as long as the Fermi level or the HOMO is located in the antibonding molecular orbital partial density of states of the chemical bond

Chemical bonding and reactivity of transition metal surfaces

Quantum‐chemistry of chemisorption is discussed based on partial density of states and crystal orbital hamiltion population analyses of the eelectronic structures of chemical bonds. In a second part of the chapter activation of small molecules on transition metals is introduced. Emaphasis is on the analysis of transition states

Chemical bonding and reactivity of transition metal surfaces

Quantum‐chemistry of chemisorption is discussed based on partial density of states and crystal orbital hamiltion population analyses of the eelectronic structures of chemical bonds. In a second part of the chapter activation of small molecules on transition metals is introduced. Emaphasis is on the analysis of transition states

Tuning the hematite (110) surface properties to enhance its efficiency in photoelectrochemistry

We present the analysis of the role of the substitutional doping on the electronic structure of Fe2O3– hematite – (110) surface. The presence of a heteroatom in different crystallographic positions in the surface layer of hematite influences the band structure– additional donor or acceptor states appear in the band gap depending on the type and charge of the heteroatom. The modifications play a role in altering the absorption coefficient, however to a minor extent in the visible light range. On the other hand, all investigated substitutions seem advantageous for the oxygen evolution reaction, as for this reaction the vacuum potential is located inside the band gap. Additionally, the differences in partial charges and binding energy suggest that the substitution site can play a role in preferential binding of the reaction intermediates

Ab-initio study of doped salt hydrates crystal stabilities for thermochemical heat storage

In order to move towards a sustainable energy economy, a reliable energy storage technology is necessary. Thermochemical heat storage based on reversible physico-chemical processes, like sorption of water in hygroscopic chloride-based salts, is a highly appealing approach. This concept allows one to store heat over long periods of time in relative compact systems. Promising materials for this process are MgCl2·nH2O and CaCl2·nH2O (n=0,1,2,4,6), which undergo chemical reactions between the different hydrates at the desired operating temperatures. However, challenges remain related to the kinetics and stability of these salt hydrates. Another challenge is the formation of HCl through hydrolysis of MgCl2·nH2O at high temperatures. Doped salts have the potential to overcome these challenges. Therefore, density functional theory (DFT) studies are performed on MgCl2·2H2O with varying contents of Ca, and on CaCl2·2H2O with varying contents of Mg. Advanced chemical bonding approaches (DDEC6 bond order and charges, Bader topological analysis) are used to describe the relevant chemical bonds within these doped structure. These tools allow to quantitatively and qualitatively describe the doped crystals, and provide insight in the strength and nature of its interatomic interactions. Important trends in structure stability of the doped salts are revealed. It is confirmed that doping MgCl2·nH2O increases its resistivity towards hydrolysis. However, too high amount of doping (above 39%), can result in metastable crystal structures