Recycling end-of-life polycarbonate in steelmaking: Ab initio study of carbon dissolution in molten iron

The scarcity of fossil fuels as carbon resources has motivated the steelmaking industry to search for new carbon sources such as end-of-life polymeric products. Using ab initio molecular dynamics simulation, we demonstrate that 41% of polycarbonate's carbon content is readily dissolved in molten iron's interface at T = 1823 K which is comparable to graphite with ∼58% carbon content dissolution. More importantly, we demonstrate that polycarbonate's hydrogen content does not dissolve in molten iron but rather escapes in gaseous form. Therefore, waste polycarbonate constitutes a feasible carbon source for steelmaking. © 2014 American Chemical Society

The effects of copper doping on photocatalytic activity at (101) planes of anatase TiO2: A theoretical study

© 2016 Elsevier B.V. Copper dopants are varyingly reported to enhance photocatalytic activity at titanium dioxide surfaces through uncertain mechanisms. In order to interpret how copper doping might alter the performance of titanium dioxide photocatalysts in aqueous media we applied density functional theory methods to simulate surface units of doped anatase (101) planes. By including van der Waals interactions, we consider the energetics of adsorbed water at anatase surfaces in pristine and copper doped systems. Simulation results indicate that copper dopant at anatase (101) surfaces is most stable in a 2+ oxidation state and a disperse configuration, suggesting the formation of secondary CuO phases is energetically unfavourable. In agreement with previous reports, water at the studied surface is predicted to exhibit molecular adsorption with this tendency slightly enhanced by copper. Results imply that the enhancement of photoactivity at anatase surfaces through Cu doping is more likely to arise from electronic interactions mediated by charge transfer and inter-bandgap states increasing photoexcitation and extending surface-hole lifetimes rather than through the increased density of adsorbed hydroxyl groups

Theoretical insights into the hydrophobicity of low index CeO <inf>2</inf> surfaces

© 2019 The hydrophobicity of CeO 2 surfaces is examined here. Since wettability measurements are extremely sensitive to experimental conditions, we propose a general approach to obtain contact angles between water and ceria surfaces of specified orientations based on density functional calculations. In particular, we analysed the low index surfaces of this oxide to establish their interactions with water. According to our calculations, the CeO 2 (111) surface was the most hydrophobic with a contact angle of Θ = 112.53° followed by (100) with Θ = 93.91°. The CeO 2 (110) surface was, on the other hand, mildly hydrophilic with Θ = 64.09°. By combining our calculations with an atomistic thermodynamic approach, we found that the O terminated (100) surface was unstable unless fully covered by molecularly adsorbed water. We also identified a strong attractive interaction between the hydrogen atoms in water molecules and surface oxygen, which gives rise to the hydrophilic behaviour of (110) surfaces. Interestingly, the adsorption of water molecules on the lower-energy (111) surface stabilises oxygen vacancies, which are expected to enhance the catalytic activity of this plane. The findings here shed light on the origin of the intrinsic wettability of rare earth oxides in general and CeO 2 surfaces in particular and also explain why CeO 2 (100) surface properties are so critically dependant on applied synthesis methods

Ab Initio Investigation of Water Adsorption and Hydrogen Evolution on Co<inf>9</inf>S<inf>8</inf> and Co<inf>3</inf>S<inf>4</inf> Low-Index Surfaces

Copyright © 2018 American Chemical Society. We used density functional theory approach, with the inclusion of a semiempirical dispersion potential to take into account van der Waals interactions, to investigate the water adsorption and dissociation on cobalt sulfide Co9S8 and Co3S4(100) surfaces. We first determined the nanocrystal shape and selected representative surfaces to analyze. We then calculated water adsorption and dissociation energies, as well as hydrogen and oxygen adsorption energies, and we found that sulfur vacancies on Co9S8(100) surface enhance the catalytic activity toward water dissociation by raising the energy level of unhybridized Co 3d states closer to the Fermi level. Sulfur vacancies, however, do not have a significant impact on the energetics of Co3S4(100) surface

Suppression of magnetism and Seebeck effect in Na<inf>0.875</inf>CoO<inf>2</inf> induced by Sb<inf>Co</inf> dopants

© 2020, The Author(s). We examined the electronic property of Sb-doped Na0.785CoO2 using density functional calculations based on GGA+U formalism. We demonstrated that Sb dopants were the most stable when replacing Co ions within the complex Na0.875CoO2 lattice structure. We also showed that the SbCo dopants adopted the + 5 oxidation state introducing two electrons into the host Na0.875CoO2 compound. The newly introduced electrons recombined with holes that were borne on Co4+ sites that had been created by sodium vacancies. The elimination of Co4+ species, in turn, rendered Na0.875(Co0.9375Sb0.0625)O2 non-magnetic and diminished the compound’s thermoelectric effect. Furthermore, the SbCo dopants tended to aggregate with the Na vacancies keeping a minimum distance. The conclusions drawn here can be generalised to other highly oxidised dopants in NaxCoO2 that replace a Co

Unusual ferrimagnetic ground state in rhenium ferrite

Through comprehensive density functional calculations, we predict the stability of a rhenium-based ferrite, ReFe2O4, in a distorted spinel-based structure. In ReFe2O4, all Re and half of the Fe ions occupy the octahedral sites while the remaining Fe ions occupy the tetrahedral sites. All Re ions are predicted to be at a + 4 oxidation state with a low spin configuration (S = 3/2), while all Fe ions are predicted to be at a + 2 oxidation state with a high-spin state configuration (S = 2). Magnetically, ReFe2O4 adopts an unconventional ferrimagnetic state in which the magnetic moment of Re opposes the magnetic moments of both tetrahedral and octahedral Fe ions. The spin–orbit coupling is found to cause a slight spin canting of ~ 1.5°. The predicted magnetic ground state is unlike the magnetic alignment usually observed in ferrites, where the tetrahedral cations oppose the spin of the octahedral cations. Given that the density of states analysis predicts a half-metallic character driven by the presence of Re t2g states at the Fermi level, this compound shows promise towards potential spintronics applications

High-Performance Thermoelectric Oxides Based on Spinel Structure

© 2020 American Chemical Society. High-performance thermoelectric oxides could offer a great energy solution for integrated and embedded applications in sensing and electronics industries. Oxides, however, often suffer from low Seebeck coefficient when compared with other classes of thermoelectric materials. In search of high-performance thermoelectric oxides, we present a comprehensive density functional investigation, based on GGA+U formalism, surveying the 3d and 4d transition-metal-containing ferrites of the spinel structure. Consequently, we predict MnFe2O4 and RhFe2O4 have Seebeck coefficients of ±600 μV K-1 at near room temperature, achieved by light hole and electron doping. Furthermore, CrFe2O4 and MoFe2O4 have even higher ambient Seebeck coefficients at ±700 μV K-1. In the latter compounds, the Seebeck coefficient is approximately a flat function of temperature up to ∼700 K, offering a tremendous operational convenience. Additionally, MoFe2O4 doped with 1019 holes/cm3 has a calculated thermoelectric power factor of 689.81 μW K-2 m-1 at 300 K and 455.67 μW K-2 m-1 at 600 K. The thermoelectric properties predicted here can bring these thermoelectric oxides to applications at lower temperatures traditionally fulfilled by more toxic and otherwise burdensome materials

Critical role of Fock exchange in characterizing dopant geometry and magnetic interaction in magnetic semiconductors

We demonstrate the significance of the Fock exchange in accurately describing dopant geometry on the superexchange interaction between the magnetic ions in doped semiconductors. The result emphasizes the important role of the Coulombic and electronic contributions to the Hellmann-Feynman forces, which have been overlooked in methods using generalized gradient approximation and local density approximation functionals. Using hydrogen-doped ZnO:Co as an example, we show that the hybrid functional can result in a new geometry of hydrogenic complex, which mediates ferromagnetic interaction through a combination of double exchange and Jahn-Teller effect. © 2014 American Physical Society

High-performance Na ion cathodes based on the ubiquitous and reversible O redox reaction

© 2018 The Royal Society of Chemistry. Utilising reversible oxygen redox in Na and transition metal oxides offers unprecedented opportunities for the design of high voltage, high capacity and affordable cathodes for application in rechargeable Na-ion batteries. Through a judicious materials search and theoretical investigations, we identified new compounds with excellent energy storage properties that rely on oxygen states for charge compensation during the redox reaction. According to our predictions, Na2-xMoO4 demonstrates a voltage of 4.743 V and an energy density of ∼617.3 W h kg-1. These values exceed the performance of most commercialised Na-ion cathode materials. Furthermore, both Na4-xZr5O12, demonstrating a voltage of 3.583 V, and Na1-xPd2PO3, demonstrating a voltage of 2.630 V, exhibit a meagre absolute volume change of ∼1% during the sodiation/desodiation process. Because of this minor volume change, these compounds are suitable for all-solid-state battery applications. An examination of the electronic structures of these compounds reveals that O states are always present at the top of the valence band regardless of the presence of 4d transition metal species or their oxidation states. This feature is attributed to the exceedingly substantial 4d-2p hybridisation over the entire valence band which also prevents the bonding of oxidised O ions in the desodiated compounds, thus preventing irreversible oxygen loss