Binding modes of carboxylic acids on cobalt nanoparticles

Owing to their high saturation magnetisation, cobalt nanoparticles hold significant potential for the hyperthermia treatment of tumours. Covalent binding of carboxylic acids to the nanoparticles can induce biocompatibility, whilst also preventing the formation of surface oxides which reduce the magnetic properties of cobalt. Understanding the origin of the acid–metal interaction is key, yet probably the most experimentally challenging step, for the rational design of such entities. In this density functional theory study, we use static calculations to establish that a 57-atom Co cluster is the smallest model able to reproduce the adsorption behaviour of carboxylic acids, and ab initio metadynamics to obtain the structure and the free energy landscape for its interaction with valeric acid. Our simulations show that a bridging bidentate binding mode has a stronger affinity compared to monodentate binding, with energetically high transition barriers between the two. A chelate interaction mode of two carboxyl oxygen atoms can be formed as an intermediate. These results clarify the organic–inorganic interactions in the cobalt–acid system, providing a basis for the rational design of biocompatible metallic nanoparticles

Challenges in dye-sensitised solar cells: a theoretical study

Up to now, the market of solar cells has been dominated by the conventional silicon devices. Recently, a new class of solar cells, known as dye-sensitised solar cells (DSSCs) have emerged. They are based on the hybrid chromophore/TiO2 semiconductor interface, and the low cost of manufacturing and the flexibility make them a very promising alternative to the traditional silicon cells. With this thesis, we aim at investigating theoretically, by means of density functional theory atomistic simulations, some of the current challenges in DSSCs. In particular, we will focus on the binding mode of the most common anchoring groups to TiO2, the coating of TiO2 with a second oxide such as Al2O3 to increase the efficiency, the issues related to the island growth mode during the atomic layer deposition of Al2O3 on TiO2, and the use of the delta self-consistent field method for the excitations of natural anthocyanidins. The idea is to provide experimentalists with useful guidelines for the design of devices with improved efficiencies

Delta Self-Consistent Field Method for Natural Anthocyanidin Dyes

We present an application of the ∆ self-consistent field (∆SCF) method, which we have implemented and tested in the DFT code CONQUEST, on the study of excited states of natural anthocyanidin dyes. We show that ∆SCF allows relaxation of the atomic structure for systems in excited states by following gradients on the excited Born-Oppenheimer surface. We compare the vertical excitation energies of some anthocyanidins in gasphase to results from time-dependent density functional theory (TDDFT) and experiments. To reproduce a typical dye-sensitised solar cell interface, we adsorb cyanidin on TiO2 anatase (101), focussing on the shift of the lowest excitation energy due to the adsorption. We have found that important modifications occur in the excited state geometry of the adsorbed cyanidin

Initial Oxygen Incorporation in the Prismatic Surfaces of Troilite FeS

We present a theoretical investigation of the prismatic (011̅0) surface of troilite in an oxidizing environment, which aims to elucidate the presence of oxygen detected experimentally in the pyrrhotite Fe1–xS nanoparticles. We find that atomic oxygen adsorbs in Fe–O–Fe bridging motifs, which are thermodynamically stable under ambient conditions. During the first oxidation steps, the formation of the S–O bond is less favored than Fe–O, suggesting that the sulfur oxides detected experimentally form only subsequently. We predict, moreover, that substitution of sulfur for oxygen can occur. The appearance of Fe–O–Fe–O–Fe bridging motifs due to successive adsorptions points toward a clustering growth of the oxidic units. In agreement with the experimental observations, the oxidation of troilite is exothermic, where the equilibrium between adsorption and substitution is influenced by the presence of Fe vacancies

A surface oxidised Fe-S catalyst for the liquid phase hydrogenation of CO₂

Rapidly increasing anthropogenic carbon dioxide (CO_{2}) emissions, coupled with irreversible climate change and depleting fossil fuel reserves, have significantly increased the drive for CO_{2} utilisation. Iron sulfide as a catalyst for the hydrogenation of CO_{2} has been discussed in the literature for decades, especially in an origin-of-life context, but little experimental evidence exists in the literature for its feasibility. Here we report the catalytic properties of pyrrhotite (Fe_{1−x}S) for the hydrogenation of CO_{2} into formate. Advanced material characterisation methods in combination with computational studies have allowed us to identify surface S–Fe–O moieties as active sites for the reaction

CO2 interaction with violarite (FeNi2S4) surfaces: a dispersion-corrected DFT study

The unbridled emissions of gases derived from the use of fossil fuels have led to an excessive concentration of carbon dioxide (CO2) in the atmosphere with concomitant problems to the environment. It is therefore imperative that new cost-effective catalysts are developed to mitigate the resulting harmful effects through the activation and conversion of CO2 molecules. In this paper, we have used calculations based on the density functional theory (DFT), including two semi-empirical approaches for the long-range dispersion interactions (-D2 and -D3), to explore the interaction of CO2 with the surfaces of spinel-structured violarite (FeNi2S4). This ternary sulfide contains iron ions in the highest possible oxidation state, while the nickel atoms are in the mixed 2+/3+ valence state. We found that CO2 interaction with violarite is only moderate due to the repulsion between the oxygen lone pairs and the electronic clouds of the sulfur surface atoms. This suggests that the CO2 activation is not dictated by the presence of nickel, as compared to the pure iron-isomorph greigite (Fe3S4). These results differ from findings in (Ni,Fe) ferredoxin enzymes, where the Ni/Fe ratio influences the redox potential, which suggests that the periodic crystal structure of violarite may hinder its redox capability

Mixing thermodynamics and electronic structure of the Pt1−xNix (0 ≤ x ≤ 1) bimetallic alloy

The development of affordable bifunctional platinum alloys as electrode materials for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains one of the biggest challenges for the transition towards renewable energy sources. Yet, there is very little information on the optimal ratio between platinum and the transition metal used in the alloy and its impact on the electronic properties. Here, we have employed spin-polarised density functional simulations with long-range dispersion corrections [DFT–D3–(BJ)], to investigate the thermodynamics of mixing, as well as the electronic and magnetic properties of the Pt1−xNix solid solution. The Ni incorporation is an exothermic process and the alloy composition Pt0.5Ni0.5 is the most thermodynamically stable. The Pt0.5Ni0.5 solid solution is highly ordered as it is composed mainly of two symmetrically inequivalent configurations of homogeneously distributed atoms. We have obtained the atomic projections of the electronic density of states and band structure, showing that the Pt0.5Ni0.5 alloy has metallic character. The suitable electronic properties of the thermodynamically stable Pt0.5Ni0.5 solid solution shows promise as a sustainable catalyst for future regenerative fuel cells

Thermal Properties and Segregation Behavior of Pt Nanowires Modified with Au, Ag, and Pd Atoms: A Classical Molecular Dynamics Study

Platinum nanowires (NWs) have been reported to be catalytically active toward the oxygen reduction reaction (ORR). The edge modification of Pt NWs with metals M (M = Au, Ag, or Pd) may have a positive impact on the overall ORR activity by facilitating diffusion of adsorbed oxygen, Oads, and hydroxyl groups, OHads, between the {001} and {111} terraces. In the present study, we have employed classical molecular dynamics simulations to investigate the segregation behavior of Au, Ag, and Pd decorating the edges of Pt NWs. We observe that, under vacuum conditions, Pd prefers to diffuse toward the core rather than stay on the NW surface. Ag and Au atoms are mobile at temperatures as low as 900 K; they remain on the surface but do not appear to be preferentially more stable at edge sites. To effect segregation of Au and Ag atoms toward the edge, we propose annealing in the presence of different reactive gas environments. Overall, our study suggests potential experimental steps required for the synthesis of Pt nanowires and nanoparticles with improved Oads and OHads interfacet diffusion rates and consequently an improved ORR activity

Genotype-by-Diet Interactions for Larval Performance and Body Composition Traits in the Black Soldier Fly, Hermetia illucens

Further advancing black soldier fly (BSF) farming for waste valorisation and more sustainable global protein supplies critically depends on targeted exploitation of genotype-phenotype associations in this insect, comparable to conventional livestock. This study used a fully crossed factorial design of rearing larvae of four genetically distinct BSF strains (FST: 0.11–0.35) on three nutritionally different diets (poultry feed, food waste, poultry manure) to investigate genotype-by-environment interactions. Phenotypic responses included larval growth dynamics over time, weight at harvest, mortality, biomass production with respective contents of ash, fat, and protein, including amino acid profiles, as well as bioconversion and nitrogen efficiency, reduction of dry matter and relevant fibre fractions, and dry matter loss (emissions). Virtually all larval performance and body composition traits were substantially influenced by diet but also characterised by ample BSF genetic variation and, most importantly, by pronounced interaction effects between the two. Across evaluated phenotypes, variable diet-dependent rankings and the lack of generally superior BSF strains indicate the involvement of trade-offs between traits, as their relationships may even change signs. Conflicting resource allocation in light of overall BSF fitness suggests anticipated breeding programs will require complex and differential selection strategies to account for pinpointed trait maximisation versus multi-purpose resilience

The Future of Neutrino Mass Measurements: Terrestrial, Astrophysical, and Cosmological Measurements in the Next Decade. Highlights of the NuMass 2013 Workshop. Milano, Italy, February 4 - 7, 2013

The third Workshop of the NuMass series ("The Future of Neutrino Mass Measurements: Terrestrial, Astrophysical, and Cosmological Measurements in the Next Decade: NuMass 2013") was held at Dipartimento di Fisica "G. Occhialini, University of Milano-Bicocca in Milano, Italy, on 4-7 February 2013. The goal of this international workshop was to review the status and future of direct and indirect neutrino mass measurements in the laboratory as well as from astrophysical and cosmological observations. This paper collects most of the contributions presented during the Workshop