Unravelling the early oxidation mechanism of zinc phosphide (Zn3P2) surfaces by adsorbed oxygen and water: a first-principles DFT-D3 investigation

Zinc phosphide (Zn3P2) is a novel earth-abundant photovoltaic material with a direct band gap of 1.5 eV. Herein, the incipient oxidation mechanism of the (001), (101), and (110) Zn3P2 surfaces in the presence of oxygen and water, which severely limits the fabrication of efficient Zn3P2-based photovoltaics, has been investigated in detail by means of dispersion-corrected density functional theory (DFT-D3) calculations. The fundamental aspects of the oxygen and water adsorption, including the initial adsorption geometries, adsorption energies, structural parameters, and electronic properties, are presented and discussed. A chemical picture and origin of the initial steps of Zn3P2 surface oxidation are proposed through analyses of Bader charges, partial density of states, and differential charge density isosurface contours. The results presented show that while water interacts weakly with the Zn ions on the Zn3P2 surfaces, molecular and dissociative oxygen species interact strongly with the (001), (101), and (110) surface species. The adsorption of oxygen is demonstrated to be characterized by a significant charge transfer from the interacting surface species, causing them to be oxidized from Zn2+ to Zn3+ formal oxidation states. Preadsorbed oxygen species are shown to facilitate the O–H bond activation of water towards its dissociation, with the adsorbed hydroxide species (OH−) demonstrated to draw a significant amount of charges from the interacting surface sites. Despite the fact that the semiconducting nature of the different Zn3P2 surfaces is preserved, we observe noticeable adsorption induced changes in their electronic structures, with the covered surface exhibiting smaller band gaps than the naked surfaces. The present study demonstrates the importance of the oxygen–water/solid interface to understand the oxidation mechanism of Zn3P2 in the presence of oxygen and water at the molecular level. The study also highlights the need for Zn3P2 nanoparticles to be protected against possible oxidation in the presence of oxygen and moisture via in situ functionalization, wherein the Zn3P2 nanoparticles are exposed to a vapour of organic functional molecules immediately after synthesis

CO2 and H2O coadsorption and reaction on the low-index surfaces of tantalum nitride: a first-principles DFT-D3 investigation

A comprehensive mechanistic insight into the photocatalytic reduction of CO2 by H2O is indispensable for the development of highly efficient and robust photocatalysts for artificial photosynthesis. This work presents first-principles mechanistic insights into the adsorption and activation of CO2 in the absence and presence of H2O on the (001), (010), and (110) surfaces of tantalum nitride (Ta3N5), a photocatalysts of significant technological interest. The stability of the different Ta3N surfaces is shown to dictate the strength of adsorption and the extent of activation of CO2 and H2O species, which bind strongest to the least stable Ta3N5(001) surface and weakest to the most stable Ta3N5(110) surface. The adsorption of the CO2 on the Ta3N5(001), (010), and (110) surfaces is demonstrated to be characterized by charge transfer from surface species to the CO2 molecule, resulting in its activation (i.e., forming negatively charged bent CO2−δ species, with elongated C–O bonds confirmed via vibrational frequency analyses). Compared to direct CO2 dissociation, H2O dissociates spontaneously on the Ta3N5 surfaces, providing the necessary hydrogen source for CO2 reduction reactions. The coadsorption reactions of CO2 and H2O are demonstrated to exhibit the strongest attractive interactions on the (010) surface, giving rise to proton transfer to the CO2 molecule, which causes its spontaneous dissociation to form CO and 2OH− species. These results demonstrate that Ta3N5, a narrow bandgap photocatalyst able to absorb visible light, can efficiently activate the CO2 molecule and photocatalytically reduce it with water to produce value-added fuels

First-principles insights into the interface chemistry between 4-Aminothiophenol and Zinc Phosphide (Zn3P2) nanoparticles

Accurate prediction of the structures, stabilities, and electronic structures of hybrid inorganic/organic systems is an essential prerequisite for tuning their electronic properties and functions. Herein, the interface chemistry between the 4-aminothiophenol (4ATP) molecule and the (001), (101), and (110) surfaces of zinc phosphide (Zn3P2) has been investigated by means of first-principles density functional theory calculation with a correction for van der Waals interactions. In particular, the atomic-level insights into the fundamental aspects of the 4ATP adsorption, including the lowest-energy adsorption configurations, binding energetics, structural parameters, and electronic properties are presented and discussed. The 4ATP molecule is demonstrated to bind most strongly onto the least stable Zn3P2(001) surface (Eads = −1.91 eV) and least strongly onto the most stable Zn3P2(101) surface (Eads = −1.21 eV). Partial density of states analysis shows that the adsorption of 4ATP on the Zn3P2 surfaces is characterized by strong hybridization between the molecule’s sulfur and nitrogen p-orbitals and the d-orbitals of the interacting surface Zn ions, which gave rise to electron density accumulation around the centers of the newly formed Zn–S and Zn–N chemical bonds. The thermodynamic crystal morphology of the nonfunctionalized and 4ATP-functionalized Zn3P2 nanoparticles was obtained using Wulff construction based on the calculated surface energies. The stronger binding of the 4ATP molecule onto the less stable (001) and (110) surfaces in preference to the most stable (101) facet resulted in the modulation of the Zn3P2 nanocrystal shape, with the reactive (001) and (110) surfaces becoming more pronounced in the equilibrium morphology

Adsorption and Desulfurization Mechanism of Thiophene on Layered FeS(001), (011), and (111) Surfaces: A Dispersion-Corrected Density Functional Theory Study

Layered transition-metal chalcogenides have emerged as a fascinating new class of materials for catalysis. Here, we present periodic density functional theory (DFT) calculations of the adsorption of thiophene and the direct desulfurization reaction pathways on the (001), (011), and (111) surfaces of layered FeS. The fundamental aspects of the thiophene adsorption, including the initial adsorption geometries, adsorption energies, structural parameters, and electronic properties, are presented. From the calculated adsorption energies, we show that the flat adsorption geometries, wherein the thiophene molecule forms multiple π-bonds with the FeS surfaces, are energetically more favorable than the upright adsorption geometries, with the strength of adsorption decreasing in the order FeS(111) > FeS(011) > FeS(001). The adsorption of the thiophene onto the reactive (011) and (111) surfaces is shown to be characterized by charge transfer from the interacting Fe d-band to the π-system of the thiophene molecule, which causes changes of the intramolecular structure including loss of aromaticity and elongation of the C–S bonds. The thermodynamic and kinetic analysis of the elementary steps involved in the direct desulfurization of thiophene on the reactive FeS surfaces is also presented. Direct desulfurization of thiophene occurs preferentially on the (111) surface, as reflected by the overall exothermic reaction energy calculated for the process (ER = −0.15 eV), with an activation energy of 1.58 eV

Structures and Properties of As(OH)3 Adsorption Complexes on Hydrated Mackinawite (FeS) Surfaces: A DFT-D2 Study

Reactive mineral–water interfaces exert control on the bioavailability of contaminant arsenic species in natural aqueous systems. However, the ability to accurately predict As surface complexation is limited by the lack of molecular-level understanding of As–water–mineral interactions. In the present study, we report the structures and properties of the adsorption complexes of arsenous acid (As(OH)3) on hydrated mackinawite (FeS) surfaces, obtained from density functional theory (DFT) calculations. The fundamental aspects of the adsorption, including the registries of the adsorption complexes, adsorption energies, and structural parameters are presented. The FeS surfaces are shown to be stabilized by hydration, as is perhaps to be expected because the adsorbed water molecules stabilize the low-coordinated surface atoms. As(OH)3 adsorbs weakly at the water–FeS(001) interface through a network of hydrogen-bonded interactions with water molecules on the surface, with the lowest-energy structure calculated to be an As–up outer-sphere complex. Compared to the water–FeS(001) interface, stronger adsorption was calculated for As(OH)3 on the water–FeS(011) and water–FeS(111) interfaces, characterized by strong hybridization between the S-p and O-p states of As(OH)3 and the surface Fe-d states. The As(OH)3 molecule displayed a variety of chemisorption geometries on the water–FeS(011) and water–FeS(111) interfaces, where the most stable configuration at the water–FeS(011) interface is a bidentate Fe–AsO–Fe complex, but on the water–FeS(111) interface, a monodentate Fe–O–Fe complex was found. Detailed information regarding the adsorption mechanisms has been obtained via projected density of states (PDOS) and electron density difference iso-surface analyses and vibrational frequency assignments of the adsorbed As(OH)3 molecule

Computational study of the interactions of small molecules with the surfaces of iron-bearing minerals

This thesis presents a comprehensive computational study of the bulk and surface properties of two major iron-bearing minerals: hematite (α-Fe2O3) and mackinawite (tetragonal FeS), and subsequently unravels the interactions of a number of environmentally important molecules with the low-Miller index surfaces of these iron-bearing minerals using a state-of-the-art methodology based on the density functional theory (DFT) techniques. First, we have used the Hubbard corrected DFT (GGA+U) calculations to unravel the interactions of a single benzene molecule with the (0001) and (01 2) surfaces of α-Fe2O3 under vacuum conditions. α-Fe2O3 is correctly described as a charge-transfer insulator, in agreement with the spectroscopic evidence when the optimized value for U = 5 eV is employed. The benzene molecule is shown to interact relatively more strongly with the (01 2) surface via cation-π interactions between the π-electrons of benzene ring and the surface Fe d-orbitals than with the (0001) where van der Waals interactions are found to play important role in stabilizing the molecule at the surface. In the second part of this thesis, DFT calculations with a correction for van der Waals interactions (DFT-D2 scheme of Grimme) have been used to simulate the bulk properties, surface structures and reactivity of layered mackinawite (FeS). We demonstrate that the inclusion of van der Waals dispersive interaction sensibly improves the prediction of interlayer separation distance in FeS, in good agreement with experimental data. The effect of interstitial impurity atoms in the interlayer sites on the structure and properties of FeS is also investigated, and it is found that these contribute considerably to the mechanical stability of the FeS structure. From the geometry optimization of the low-Miller index surfaces of FeS, we have shown the (001) surface terminated by sulfur atoms is by far the most energetically stable surface of FeS. The calculated surface energies are used successfully to reproduce the observed crystal morphology of FeS. As an extension to the surface studies, we have used the DFT-D2 method to model the adsorption mechanism of arsenious acid (As(OH)3), methylamine (CH3NH2) and nitrogen oxides (NO and NO2) molecules on the low-Miller index FeS surfaces under vacuum conditions. The As(OH)3 molecule is demonstrated to preferentially form bidentate adsorption complexes on FeS surfaces via two O‒Fe bonds. The calculated long As−Fe and As−S interatomic distances (> 3 Å) clearly suggest interactions via outer sphere surface complexes with respect to the As atom, in agreement with the experimental observations. The growth modifying properties of methylamine, the capping agent used in the synthesis of FeS, are modelled by surface adsorption. The strength of the interaction of CH3NH2 on the different FeS surfaces is shown to increase in the order: (001) < (011) < (100) < (111) and an analysis of the nature of bonding reveals that the CH3NH2 molecule interacts preferentially with the surface Fe d-orbitals via the lone-pair of electrons located on the N atom. Our simulated temperature programmed desorption process shows that methylamine is stable up to about 180 K on the most reactive (111) surface, which is comparable to the experimental desorption temperatures predicted at metallic surfaces. Finally, the catalytic properties of FeS as a nanocatalyst for the adsorption, activation and decomposition of environmentally important NOx gases have been explored, where we consider the nature of binding of the NOx species to the FeS surfaces and their dissociation reaction mechanisms

DFT-D2 Study of the Adsorption and Dissociation of Water on Clean and Oxygen-Covered {001} and {011} Surfaces of Mackinawite (FeS)

We present a dispersion-corrected density functional theory study of the adsorption and dissociation reactions of oxygen and water on the {001} and {011} surfaces of mackinawite (FeS). A chemical picture of the initial steps of the mackinawite {001} and {011} surfaces oxidation process in the presence of oxygen and water is presented in the present investigation. Our results show that, while water interacts weakly with the Fe ions on both surfaces and only oxidizes them to some extent, atomic and molecular oxygen interact strongly with the FeS{011} surface cations by drawing significant charge from them, thereby oxidizing them from Fe2+ to Fe3+ formal oxidation state. We show from our calculated adsorption energies and activation energy barriers for the dissociation of H2O on the clean and oxygen-covered FeS surfaces, that preadsorbed oxygen could easily activate the O–H bond and facilitate the dissociation of H2O to ferric-hydroxy, Fe3+–OH– on FeS{011}, and to zerovalent sulfur-hydroxyl, S0–OH– on FeS{001}. With the aid of preadsorbed O atom, the activation energy barrier for dissociating hydrogen atom from H2O decreases from 1.73 to 1.19 eV on the FeS{001}, and from 0.83 to 0.14 eV on the FeS{011}. These findings provide molecular-level insight into the mechanisms of mackinawite oxidation, and are consistent with experimental results, which have shown that oxygen and water are necessary for the oxidation process of mackinawite and its possible transformation to pyrite via greigite

Теоретико-методологічні засади адаптивного інноваційного розвитку

Подано визначення змісту управління адаптивним інноваційним розвитком, заснованого на використанні його здібностей до трансформації з урахуванням особливостей зовнішнього та внутрішнього середовища суб’єкта сукупності дій, необхідних для здійснення впливу на процеси в усіх сферах управління, що забезпечує інноваційну, організаційно-управлінську, технічну, фінансову та кадрову стійкість. Ключові слова: інновації, інноваційний розвиток, адаптація, адаптивність, механізм, система, процес.Представлено определение содержания управления адаптивным инновационным развитием, основанным на использовании его способностей к трансформации с учетом особенностей внешней и внутренней среды субъекта совокупности действий, необходимых для осуществления влияния на процессы во всех областях управления, обеспечивающих инновационную, организационно-управленческую, техническую, финансовую и кадровую устойчивость. Ключевые слова: инновации, инновационное развитие, адаптация, адаптивность, механизм, система, процесс.The paper presents the definition of management of adaptive innovation-based development that is based on the use of its ability to transform in view of external and internal environment of the subject of actions necessary for making influence on the processes in all areas of management, providing innovative, organizational, administrative, technical, financial and personnel stability of the production company. Keywords: innovation, innovation-based development, adaptation, adaptability, mechanism, system, process

Наукові засади розвитку інституту юридичної риторики: в контексті теорії юридичної аргументації

Саме аргументація в юридичній риториці є одним із ключових компонентів, який позначається на результативності та якості юридичного дискурсу. Тому для наукового дослідження юридичної риторики як науким провідне значення має вивчення теорії юридичної аргументації, як складової загальної теорії аргументації.Именно аргументация в юридической риторике является одним из ключевых компонентов, который проявляет себя в результативности и качестве юридического дискур­са. Поэтому для научного исследования юридической риторики как науки приоритетное значение имеет изучение теории юридической аргументации, как составляющей общей теории аргументации.The argument in legal rhetoric is one of key components who prover in productivity and quality of a legal discourse. Therefore for scientific research of legal rhetoric science priority has studyind of the legal argument, as making general of the argument