Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 154
Filtrar
Mais filtros

Base de dados
Tipo de documento
Intervalo de ano de publicação
1.
Small ; : e2400885, 2024 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-38616736

RESUMO

The development of pure-blue perovskite light-emitting diodes (PeLEDs) faces challenges of spectral stability and low external quantum efficiency (EQE) due to phase separation in mixed halide compositions. Perovskite quantum dots (QDs) with strong confinement effects are promising alternatives to achieve high-quality pure-blue PeLEDs, yet their performance is often hindered by the poor size distribution and high trap density. A strategy combining thermodynamic control with a polishing-driven ligand exchange process to produce high-quality QDs is developed. The strongly-confined pure-blue (≈470 nm) CsPbBr3 QDs exhibit narrow size distribution (12% dispersion) and are achieved in Br-rich ion environment based on growth thermodynamic control. Subsequent polishing-driven ligand exchange process removes imperfect surface sites and replaces initial long-chain organic ligands with short-chain benzene ligands. The resulting QDs exhibit high photoluminescence quantum yield (PLQY) to near-unity. The resulting PeLEDs exhibit a pure-blue electroluminescence (EL) emission at 472 nm with narrow full-width at half-maximum (FWHM) of 25 nm, achieving a maximum EQE of 10.7% and a bright maximum luminance of 7697 cd m-2. The pure-blue PeLEDs show ultrahigh spectral stability under high voltage, a low roll-off of EQE, and an operational half-lifetime (T50) of 127 min at an initial luminance of 103 cd m-2 under continuous operation.

2.
Langmuir ; 40(13): 6884-6897, 2024 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-38517367

RESUMO

CdS, characterized by its comparatively narrow energy band gap (∼2.4 eV), is an appropriate material for prospective use as a photoanode in photoelectrochemical water splitting. Regrettably, it encounters several obstacles for practical and large-scale applications, including issues such as bulk carrier recombination and diminished conductivity. Here, we have tried to address these challenges by fabricating a novel photoelectrode (ZnO/CdS) composed of one-dimensional ZnO nanorods (NRs) decorated with two-dimensional CdS nanosheets (NSs). A facile two-step chemical method comprising electrodeposition along with chemical bath deposition is employed to synthesize the ZnO NRs, CdS NSs, and ZnO/CdS nanostructures. The prepared nanostructures have been investigated by UV-visible absorption spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy. The fabricated ZnO/CdS nanostructures have shown enhanced photoelectrochemical properties due to the improvement of the semiconductor junction surface area and thereby enhanced visible light absorption. The incorporation of CdS NSs has been further found to promote the rate of the charge separation and transfer process. Subsequently, the fabricated ZnO/CdS photoelectrodes achieved a photocurrent conversion efficiency 3 times higher than that of a planar ZnO NR photoanode and showed excellent performance under visible light irradiation. The highest applied bias photon-to-current conversion efficiency (% ABPE) of about ∼0.63% has been obtained for the sample with thicker CdS NSs on ZnO NRs with a photocurrent density of ∼1.87 mA/cm2 under AM 1.5 G illumination. The newly synthesized nanostructures further demonstrate that the full photovoltaic capacity of nanomaterials is yet to be exhausted.

3.
J Chem Phys ; 160(15)2024 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-38634493

RESUMO

The orthorhombic phase of FeNbO4, a promising anode material for solid oxide fuel cells (SOFCs), exhibits good catalytic activity toward hydrogen oxidation. However, the low electronic conductivity of the material specifically in the pure structure without defects or dopants limits its practical applications as an SOFC anode. In this study, we have employed density functional theory (DFT + U) calculations to explore the bulk and electronic properties of two types of doped structures, Fe0.9375A0.0625NbO4 and FeNb0.9375B0.0625O4 (A, B = Ti, V, Cr, Mn, Co, Ni) and the oxygen-deficient structures Fe0.9375A0.0625NbO3.9375 and FeNb0.9375B0.0625O3.9375, where the dopant is positioned in the first nearest neighbor site to the oxygen vacancy. Our DFT simulations have revealed that doping in the Fe sites is energetically favorable compared to doping in the Nb site, resulting in significant volume expansion. The doping process generally requires less energy when the O-vacancy is surrounded by one Fe and two Nb ions. The simulated projected density of states of the oxygen-deficient structures indicates that doping in the Fe site, particularly with Ti and V, considerably narrows the bandgap to ∼0.5 eV, whereas doping with Co at the Nb sites generates acceptor levels close to 0 eV. Both doping schemes, therefore, enhance electron conduction during SOFC operation.

4.
Molecules ; 29(14)2024 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-39064933

RESUMO

The urgent need to shift from non-renewable to renewable energy sources has caused widespread interest in photovoltaic technologies that allow us to harness readily available and sustainable solar energy. In the past decade, polymer solar cells (PSCs) and perovskite solar cells (Per-SCs) have gained attention owing to their low price and easy fabrication process. Charge transport layers (CTLs), transparent conductive electrodes (TCEs), and metallic top electrodes are important constituents of PSCs and Per-SCs, which affect the efficiency and stability of these cells. Owing to the disadvantages of current materials, including instability and high cost, the development of alternative materials has attracted significant attention. Owing to their more flexible physical and chemical characteristics, ternary oxides are considered to be appealing alternatives, where ATiO3 materials-a class of ternary perovskite oxides-have demonstrated considerable potential for applications in solar cells. Here, we have employed calculations based on the density functional theory to study the structural, optoelectronic, and magnetic properties of ATiO3 (A=Li, Na, K, Rb, and Cs) in different crystallographic phases to determine their potential as PSCs and Per-SCs materials. We have also determined thermal and elastic properties to evaluate their mechanical and thermal stability. Our calculations have revealed that KTiO3 and RbTiO3 possess similar electronic properties as half-metallic materials, while LiTiO3 and CsTiO3 are metallic. Semiconductor behavior with a direct band gap of 2.77 eV was observed for NaTiO3, and calculations of the optical and electronic properties predicted that NaTiO3 is the most appropriate candidate to be employed as a charge transfer layer (CTL) and bottom transparent conducting electrode (TCE) in PSCs and Per-SCs, owing to its transparency and large bandgap, whereas NaTiO3 also provided superior elastic and thermal properties. Among the metallic and half-metallic ATiO3 compounds, CsTiO3 and KTiO3 exhibited the most appropriate features for the top electrode and additional absorbent in the active layer, respectively, to enhance the performance and stability of these cells.

5.
Phys Chem Chem Phys ; 25(9): 6797-6807, 2023 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-36789958

RESUMO

ABO4-type materials have shown significant potential for applications as luminescence and photocatalytic materials, and the orthorhombic FeNbO4 (o-FeNbO4) material has also shown excellent promise in catalytic electrodes, unlike other common ABO4 materials. However, little computational work has been carried out on the o-FeNbO4 structure, potentially because it is disordered and thus not straightforward to simulate. In this work, we first confirmed the accuracy of the force field parameters obtained from previous studies through optimizations carried out using the GULP code. Next, we found that one ordered configuration of the stoichiometric o-FeNbO4 structure dominates when analysing the probabilities of cation disorder in three supercells (2 × 2 × 1, 2 × 1 × 2, and 1 × 2 × 2). We then studied the bulk properties of this selected o-FeNbO4 through DFT calculations, including the lattice parameters, the mechanical properties and the electronic structures, where no remarkable differences were observed compared to the monoclinic FeNbO4 structure. Finally, because oxygen mobility is key to the successful application of o-FeNbO4 as an electrode material, we have simulated the diffusion pathways of oxygen through both the stoichiometric and non-stoichiometric structures, where the results show that the existence of oxygen vacancies enhances diffusion and the distribution of the Fe and Nb inside the lattice affects the energy barriers and could therefore impact the oxygen diffusion.

6.
Phys Chem Chem Phys ; 25(2): 1220-1235, 2023 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-36524712

RESUMO

In order to use classical molecular dynamics to complement experiments accurately, it is important to use robust descriptions of the system. The interactions between biomolecules, like aspartic and glutamic acid, and dissolved ions are often studied using standard biomolecular force-fields, where the interactions between biomolecules and cations are often not parameterized explicitly. In this study, we have employed metadynamics simulations to investigate different interactions of Ca with aspartic and glutamic acid and constructed the free energy profiles of Ca2+-carboxylate association. Starting from a generally accepted, AMBER-based force field, the association was substantially over and under-estimated, depending on the choice of water model (TIP3P and SPC/fw, respectively). To rectify this discrepancy, we have replaced the default calcium parameters. Additionally, we modified the σij value in the hetero-atomic Lennard-Jones interaction by 0.5% to further improve the interaction between Ca and carboxylate, based on comparison with the experimentally determined association constant for Ca with the carboxylate group of L-aspartic acid. The corrected description retrieved the structural properties of the ion pair in agreement with the original biomolecule - Ca2+ interaction in AMBER, whilst also producing an association constant comparable to experimental observations. This refined force field was then used to investigate the interactions between amino acids, calcium and carbonate ions during biogenic and biomimetic calcium carbonate mineralisation.


Assuntos
Aminoácidos , Simulação de Dinâmica Molecular , Aminoácidos/química , Cálcio/química , Ácido Glutâmico , Cátions , Água/química , Ácidos Carboxílicos
7.
Phys Chem Chem Phys ; 25(3): 2498-2509, 2023 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-36602090

RESUMO

Carbon dioxide (CO2) hydrogenation is an energetic process which could be made more efficient through the use of effective catalysts, for example transition metal carbides. Here, we have employed calculations based on the density functional theory (DFT) to evaluate the reaction processes of CO2 hydrogenation to methane (CH4), carbon monoxide (CO), methanol (CH3OH), formaldehyde (CH2O), and formic acid (HCOOH) over the carbon-terminated niobium carbide (111) surface. First, we have studied the adsorption geometries and energies of 25 different surface-adsorbed species, followed by calculations of all of the elementary steps in the CO2 hydrogenation process. The theoretical findings indicate that the NbC (111) surface has higher catalytic activity towards CO2 methanation, releasing 4.902 eV in energy. CO represents the second-most preferred product, followed by CH3OH, CH2O, and HCOOH, all of which have exothermic reaction energies of 4.107, 2.435, 1.090, and 0.163 eV, respectively. Except for the mechanism that goes through HCOOH to produce CH2O, all favourable hydrogenation reactions lead to desired compounds through the creation of the dihydroxycarbene (HOCOH) intermediate. Along these routes, CH3* hydrogenation to CH4* has the highest endothermic reaction energy of 3.105 eV, while CO production from HCO dehydrogenation causes the highest exothermic reaction energy of -3.049 eV. The surface-adsorbed CO2 hydrogenation intermediates have minimal effect on the electronic structure and interact only weakly with the surface. Our results are consistent with experimental observations.

8.
Molecules ; 28(1)2023 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-36615572

RESUMO

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.

9.
Molecules ; 28(18)2023 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-37764301

RESUMO

The increasing demand for clean fuels and sustainable products has attracted much interest in the development of active and selective catalysts for CO conversion to desirable products. This review maps the theoretical progress of the different facets of most commercial catalysts, including Co, Fe, Ni, Rh, and Ru. All relevant elementary steps involving CO dissociation and hydrogenation and their dependence on surface structure, surface coverage, temperature, and pressure are considered. The dominant Fischer-Tropsch synthesis mechanism is also explored, including the sensitivity to the structure of H-assisted CO dissociation and direct CO dissociation. Low-coordinated step sites are shown to enhance catalytic activity and suppress methane formation. The hydrogen adsorption and CO dissociation mechanisms are highly dependent on the surface coverage, in which hydrogen adsorption increases, and the CO insertion mechanism becomes more favorable at high coverages. It is revealed that the chain-growth probability and product selectivity are affected by the type of catalyst and its structure as well as the applied temperature and pressure.

10.
Molecules ; 28(2)2023 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-36677718

RESUMO

The imino pyridine Schiff base cobalt(II) and nickel(II) complexes (C1 and C2) and their functionalised γ-Fe3O4 counterparts (Fe3O4@C1 and Fe3O4@C2) were synthesised and characterised using IR, elemental analysis, and ESI-MS for C1 and C2, and single crystal X-ray diffraction for C1, while the functionalised materials Fe3O4@C1 and Fe3O4@C2 were characterized using IR, XRD, SEM, TEM, EDS, ICP-OES, XPS and TGA. Complexes C1, C2 and the functionalised materials Fe3O4@C1 and Fe3O4@C2 were tested as catalysts for the selective transfer hydrogenation of cinnamaldehyde and all four pre-catalysts showed excellent catalytic activity. Complexes C1 and C2 acted as homogeneous catalysts with high selectivity towards the formation of hydrocinnamaldehyde (88.7% and 92.6%, respectively) while Fe3O4@C1 and Fe3O4@C2 acted as heterogeneous catalysts with high selectivity towards cinnamyl alcohol (89.7% and 87.7%, respectively). Through in silico studies of the adsorption energies, we were able to account for the different products formed using the homogeneous and the heterogeneous catalysts which we attribute to the preferred interaction of the C=C moiety in the substrate with the Ni centre in C2 (-0.79 eV) rather than the C=O (-0.58 eV).

11.
Angew Chem Int Ed Engl ; 62(12): e202300149, 2023 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-36692366

RESUMO

Perovskite colloidal quantum wells (QWs) are promising to realize narrow deep-blue emission, but the poor optical performance and stability suppress their practical application. Here, we creatively propose a water-driven synthesis strategy to obtain size-homogenized and strongly confined deep-blue CsPbBr3 QWs, corresponding to three monolayers, which emit at the deep-blue wavelength of 456 nm. The water controls the orientation and distribution of the ligands on the surface of the nanocrystals, thus inducing orientated growth through the Ostwald ripening process by phagocytizing unstable nanocrystals to form well-crystallized QWs. These QWs present remarkable stability and high photoluminescence quantum yield of 94 %. Furthermore, we have prepared light-emitting diodes based on the QWs via the all-solution fabrication strategy, achieving an external quantum efficiency of 1 % and luminance of 2946 cd m-2 , demonstrating state-of-the-art brightness for perovskite QW-based LEDs.

12.
Chemphyschem ; 23(6): e202100781, 2022 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-35040247

RESUMO

As promising materials for the reduction of greenhouse gases, transition-metal carbides, which are highly active in the hydrogenation of CO2 , are mainly considered. In this regard, the reaction mechanism of CO2 hydrogenation to useful products on the Nb-terminated NbC (111) surface is investigated by applying density functional theory calculations. The computational results display that the formation of CH4 , CH3 OH, and CO are more favored than other compounds, where CH4 is the dominant product. In addition, the findings from reaction energies reveal that the preferred mechanism for CO2 hydrogenation is thorough HCOOH* , where the largest exothermic reaction energy releases during the HCOOH* dissociation reaction (2.004 eV). The preferred mechanism of CO2 hydrogenation towards CH4 production is CO2 * →t,c-COOH* →HCOOH* →HCO* →CH2 O* →CH2 OH* →CH2 * →CH3 * →CH4 * , where CO2 * →t,c-COOH* →HCOOH* →HCO* →CH2 O* →CH2 OH* →CH3 OH* and CO2 * →t,c-COOH* →CO* are also found as the favored mechanisms for CH3 OH and CO productions thermodynamically, respectively. During the mentioned mechanisms, the hydrogenation of CH2 O* to CH2 OH* has the largest endothermic reaction energy of 1.344 eV.

13.
Phys Chem Chem Phys ; 24(17): 10451-10464, 2022 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-35441635

RESUMO

The rapid development of applications relying on magnetism at the nanoscale has put a spotlight on nanoparticles with novel morphologies that are associated with enhanced electronic and magnetic properties. In this quest, nanoalloys combining highly magnetic cobalt and weakly reactive gold could offer many application-specific advantages, such as strong magnetic anisotropy. In the present study, we have employed density functional theory (DFT) calculations to provide a systematic overview of the size- and morphology-dependence of the energetic order and magnetic properties of AuCo nanoparticles up to 2.5 nm in diameter. The core-shell icosahedron was captured as the most favourable morphology, showing a small preference over the core-shell decahedron. However, the magnetic properties (total magnetic moments and magnetic anisotropy) were found to be significantly improved within the L10 ordered structures, even in comparison to monometallic Co nanoparticles. Atom-resolved charges and orbital moments accessed through the DFT analysis of the electronic level properties permitted insight into the close interrelation between the AuCo nanoparticle morphology and their magnetism. These results are expected to assist in the design of tailored magnetic AuCo nanoalloys for specific applications.


Assuntos
Ouro , Nanopartículas Metálicas , Anisotropia , Cobalto/química , Ouro/química , Magnetismo , Nanopartículas Metálicas/química
14.
Phys Chem Chem Phys ; 24(34): 20104-20124, 2022 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-35983830

RESUMO

Greigite (Fe3S4), with its ferredoxin-like 4Fe-4S redox centres, is a naturally occurring mineral capable of acting as a catalyst in the conversion of carbon dioxide (CO2) into low molecular-weight organic acids (LMWOAs), which are of paramount significance in several soil and plant processes as well as in the chemical industry. In this paper, we report the reaction between CO2 and water (H2O) to form oxalic acid (H2C2O4) on the partially oxidised greigite Fe3S4(001) surface by means of spin-polarised density functional theory calculations with on-site Coulomb corrections and long-range dispersion interactions (DFT+U-D2). We have calculated the bulk phase of Fe3S4 and the two reconstructed Tasker type 3 terminations of its (001) surface, whose properties are in good agreement with available experimental data. We have obtained the relevant phase diagram, showing that the Fe3S4(001) surface becomes 62.5% partially oxidised, by replacing S by O atoms, in the presence of water at the typical conditions of calcination [Mitchell et al. Faraday Discuss. 2021, 230, 30-51]. The adsorption and co-adsorption of the reactants on the partially oxidised Fe3S4(001) surface are exothermic processes. We have considered three mechanistic pathways to explain the formation of H2C2O4, showing that the coupling of the C-C bond and second protonation are the elementary steps with the largest energy penalty. Our calculations suggest that the partially oxidised Fe3S4(001) surface is a mineral phase that can catalyse the formation of H2C2O4 under favourable conditions, which has important implications for natural ecosystems and is a process that can be harnessed for the industrial manufacture of this organic acid.


Assuntos
Dióxido de Carbono , Ácido Oxálico , Catálise , Ecossistema , Ferro , Sulfetos/química , Água
15.
Proteins ; 89(5): 521-530, 2021 05.
Artigo em Inglês | MEDLINE | ID: mdl-33320391

RESUMO

The accumulation of advanced glycation end-products is a fundamental process that is central to age-related decline in musculoskeletal tissues and locomotor system function and other collagen-rich tissues. However, although computational studies of advanced glycation end-product cross-links could be immensely valuable, this area remains largely unexplored given the limited availability of structural parameters for the derivation of force fields for Molecular Dynamics simulations. In this article, we present the bonded force constants, atomic partial charges and geometry of the arginine-lysine cross-links DOGDIC, GODIC, and MODIC. We have performed in vacuo Molecular Dynamics simulations to validate their implementation against quantum mechanical frequency calculations. A DOGDIC advanced glycation end-product cross-link was then inserted into a model collagen fibril to explore structural changes of collagen and dynamics in interstitial water. Unlike our previous studies of glucosepane, our findings suggest that intra-collagen DOGDIC cross-links furthers intra-collagen peptide hydrogen-bonding and does not promote the diffusion of water through the collagen triple helices.


Assuntos
Arginina/química , Colágeno/química , Dipeptídeos/química , Produtos Finais de Glicação Avançada/química , Lisina/química , Arginina/metabolismo , Sítios de Ligação , Colágeno/metabolismo , Reagentes de Ligações Cruzadas/química , Dipeptídeos/metabolismo , Produtos Finais de Glicação Avançada/metabolismo , Ligação de Hidrogênio , Imidazóis/química , Lisina/análogos & derivados , Lisina/metabolismo , Simulação de Dinâmica Molecular , Ligação Proteica , Conformação Proteica , Eletricidade Estática , Água/química , Água/metabolismo
16.
Faraday Discuss ; 229(0): 35-49, 2021 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-34075915

RESUMO

Acetic acid (CH3-COOH) is an important commodity chemical widely used in a myriad of industrial processes, whose production still largely depends on homogeneous catalysts based on expensive rare metals. Here, we report a computational study on the formation of CH3-COOH from carbon dioxide (CO2) as an alternative chemical feedstock on the {111} surface of the low-cost greigite Fe3S4 catalyst. We have used density functional theory calculations with a Hubbard Hamiltonian approach and long-range dispersion corrections (DFT+U-D2) to simulate the various stages of the direct combination of C1 species of different composition to produce glyoxylic acid (CHO-COOH) as a key intermediate in the formation of CH3-COOH. Three reaction mechanisms are considered: (i) the main pathway where the direct formation of the C-C bond takes place spontaneously, followed by a step-wise reduction of CHO-CHOO to CH3-COOH; and the competitive pathways for the non-promoted and H-promoted elimination of hydroxy groups (OH) and water (H2O), respectively from (ii) the carboxyl; and (iii) the carbonyl end of the glyoxylate intermediates. The thermodynamic and kinetic profiles show that the energies for the intermediates on the main pathway are very similar for the two catalytic sites considered, although the activation energies are somewhat larger for the exposed tetrahedral iron (FeA) ion. In most cases, the intermediates for the deoxygenation of the carboxylic acid are less stable than the intermediates on the main pathway, which suggests that the molecule prefers to lose the carbonylic oxygen. The suitable surface properties of the Fe3S4{111} surface show that this material could be a promising sustainable catalyst in future technologies for the conversion of CO2 into organic acid molecules of commercial interest.

17.
Faraday Discuss ; 230(0): 87-99, 2021 07 16.
Artigo em Inglês | MEDLINE | ID: mdl-33960357

RESUMO

We present several in silico insights into the MAX-phase of early transition metal silicon carbides and explore how these affect carbon dioxide hydrogenation. Periodic density functional methodology is applied to models of Ti4SiC3, V4SiC3, Nb4SiC3 and Zr4SiC3. We find that silicon and carbon terminations are unstable, with sintering occurring in vacuum and significant reconstruction taking place under an oxidising environment. In contrast, the metal terminated surfaces are highly stable and very active towards CO2 reduction. However, we predict that under reaction conditions these surfaces are likely to be oxidised. These results are compared to studies on comparable materials and we predict optimal values for hydrogen evolution and CO2 reduction.

18.
Faraday Discuss ; 230: 30-51, 2021 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-33884381

RESUMO

Increasing carbon dioxide (CO2) emissions, resulting in climate change, have driven the motivation to achieve the effective and sustainable conversion of CO2 into useful chemicals and fuels. Taking inspiration from biological processes, synthetic iron-nickel-sulfides have been proposed as suitable catalysts for the hydrogenation of CO2. In order to experimentally validate this hypothesis, here we report violarite (Fe,Ni)3S4 as a cheap and economically viable catalyst for the hydrogenation of CO2 into formate under mild, alkaline conditions at 125 °C and 20 bar (CO2 : H2 = 1 : 1). Calcination of violarite at 200 °C resulted in excellent catalytic activity, far superior to that of Fe-only and Ni-only sulfides. We further report first principles simulations of the CO2 conversion on the partially oxidised (001) and (111) surfaces of stoichiometric violarite (FeNi2S4) and polydymite (Ni3S4) to rationalise the experimentally observed trends. We have obtained the thermodynamic and kinetic profiles for the reaction of carbon dioxide (CO2) and water (H2O) on the catalyst surfaces via substitution and dissociation mechanisms. We report that the partially oxidised (111) surface of FeNi2S4 is the best catalyst in the series and that the dissociation mechanism is the most favourable. Our study reveals that the partial oxidation of the FeNi2S4 surface, as well as the synergy of the Fe and Ni ions, are important in the catalytic activity of the material for the effective hydrogenation of CO2 to formate.

19.
Phys Chem Chem Phys ; 23(46): 26482-26493, 2021 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-34806732

RESUMO

Zinc phosphides (ZnP2 and Zn3P2) are emerging absorber materials for photovoltaic applications owing to their abundancy and non-toxic nature. Herein, we provide a comprehensive characterisation of the surface structure, composition, stabilities, morphology, and electronic properties of both bare and hydrated/hydroxylated low-Miller index surfaces of ß-ZnP2 by means of density functional theory (DFT) calculations. Mechanistic insights into the fundamental aspects of water adsorption and dissociation, including the adsorption geometries, energetics, and structural parameters along the reaction path are systematically characterised. The stabilities of the surfaces under dry and wet conditions are discussed in detail and the predicted phase diagrams for the water adsorption are presented. Using calculated surface energies, we have derived the equilibrium morphology of the ß-ZnP2 nanocrystals under vacuum and upon hydration or hydroxylation. Atomic-level insights into the origin of the incipient oxidation of ß-ZnP2 surfaces are provided through analysis of Bader charges, which reveal that the Zn sites to which H2O and OH species are bound undergo oxidation due to the transfer of charge to the adsorbed species. Adsorption-induced changes to the electronic properties before and after hydration/hydroxylation were characterised by the work function and partial density of states. The results highlight the need for protection of ß-ZnP2 nanocrystals against possible oxidation in the presence of water through post-synthesis organic functionalisation.

20.
J Chem Phys ; 154(19): 194701, 2021 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-34240906

RESUMO

In the hybrid sulfur (HyS) cycle, the reaction between SO2 and H2O is manipulated to produce hydrogen with water and sulfuric acid as by-products. However, sulfur poisoning of the catalyst has been widely reported to occur in this cycle, which is due to strong chemisorption of sulfur on the metal surface. The catalysts may deactivate as a result of these impurities present in the reactants or incorporated in the catalyst during its preparation and operation of the HyS cycle. Here, we report a density functional theory investigation of the interaction between S, SO, and SO3 with the Pt (001), (011), and (111) surfaces. First, we have investigated the adsorption of single gas phase molecules on the three Pt surfaces. During adsorption, the 4F hollow sites on the (001) and (011) surfaces and the fcc hollow site on the (111) surface were preferred. S adsorption followed the trend of (001)4F > (011)4F > (111)fcc, while SO adsorption showed (001)4F > (011)bridge/4F > (111)fcc and SO3 adsorption was most stable in a S,O,O bound configuration on the (001)4F > (011)4F > (111)fcc sites. The surface coverage was increased on all the surfaces until a monolayer was obtained. The highest surface coverage for S shows the trend (001)S = (111)S > (011)S, and for SO it is (001)SO > (011)SO > (111)SO, similar to SO3 where we found (001)SO3 > (011)SO3 > (111)SO3. These trends indicate that the (001) surface is more susceptible to S species poisoning. It is also evident that both the (001) and (111) surfaces were reactive toward S, leading to the formation of S2. The high coverage of SO3 showed the formation of SO2 and SO4, especially on the (011) surface. The thermodynamics indicated that an increased temperature of up to 2000 K resulted in Pt surfaces fully covered with elemental S. The SO coverage showed θ ≥ 1.00 on both the (001) and (011) surfaces and θ = 0.78 for the (111) surface in the experimental region where the HyS cycle is operated. Lower coverages of SO3 were observed due to the size of the molecule.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA