Combined Density Functional Theory Research Articles

Machine learning-enabled chemical space exploration of all-inorganic perovskites for photovoltaics

The vast compositional and configurational spaces of multi-element metal halide perovskites (MHPs) result in significant challenges when designing MHPs with promising stability and optoelectronic properties. In this paper, we propose a framework for the design of B-site-alloyed ABX3 MHPs by combining density functional theory (DFT) and machine learning (ML). We performed generalized gradient approximation with Perdew–Burke–Ernzerhof functional for solids (PBEsol) on 3,159 B-site-alloyed perovskite structures using a compositional step of 1/4. Crystal graph convolution neural networks (CGCNNs) were trained on the 3159 DFT datasets to predict the decomposition energy, bandgap, and types of bandgaps. The trained CGCNN models were used to explore the compositional and configurational spaces of 41,400 B-site-alloyed ABX3 MHPs with a compositional step of 1/16, by accessing all possible configurations for each composition. The electronic band structures of the selected compounds were calculated using the hybrid functional (PBE0). Then, we calculated the optical absorption spectra and spectroscopic limited maximum efficiency of the selected compounds. Based on the DFT/ML-combined screening, 10 promising compounds with optimal bandgaps were selected, and from among these 10 compounds, CsGe0.3125Sn0.6875I3 and CsGe0.0625Pb0.3125Sn0.625Br3 were suggested as photon absorbers for single-junction and tandem solar cells, respectively. The design framework presented herein is a good starting point for the design of mixed MHPs for optoelectronic applications.

Adsorption and sensing characteristics of insulating gas C4F7N on 3d late transition metal‐phthalocyanine: Theoretical and experimental study

AbstractHeptafluoroisobutyronitrile (C4F7N) is being considered as a promising alternative to the greenhouse gas SF6 in the electrical industry. However, its biotoxicity necessitates the development of gas sensing technology to detect leaked C4F7N. A combination of density functional theory and experiments was employed to evaluate the adsorption and sensing performance of different metal‐phthalocyanines as potential sensing materials for C4F7N detection. The study included exploring adsorption configurations with adsorption energies, electron transfer, and adsorption distance, as well as comparisons of electronic properties, electron distribution, and density of states (DOS) among the MPcs. Furthermore, gas sensing experiments were conducted using different MPcs to detect 25–100 ppm C4F7N. The results revealed that Mn‐Pc, Fe‐Pc, Co‐Pc, and Zn‐Pc exhibited considerable chemical interactions, while Ni‐Pc and Cu‐Pc showed weaker adsorption strength. These findings were further elucidated based on the electron density and DOS of atomic orbitals. Moreover, gas sensing experiments indicated that Co‐Pc demonstrated a higher response compared to Fe‐Pc at the same concentration of C4F7N. Overall, the theoretical and experimental insights offer valuable guidance for C4F7N detection and provide a systematic approach to screen and explore organometallic polymer‐based gas sensors applicable in various fields.

A combined density functional theory and microkinetics simulations study of electrochemical CO2 reduction on Cu8/SnO2(110): The crucial role of hydrogen coverage

The electrochemical reduction of CO2 (eCO2R) is a promising approach for converting CO2 into valuable chemicals and fuels using renewable energy sources. We investigated the mechanism of eCO2R for a small Cu8 cluster placed on SnO2 containing O vacancies using density functional theory and predicted current density and selectivity by microkinetics simulations within the computational hydrogen electrode model. Low and high H coverages were modeled by Cu8/SnO2-x and Cu8H6/SnO2-x models, using statistical methods to identify their most stable structures. Different CO2 adsorption modes on Cu8/SnO2-x and Cu8H6/SnO2-x surface models, all containing an O vacancy, resulted in distinct reaction pathways, leading to either HCOOH or CO. The preferred formation of HCOOH occurred upon CO2 adsorption on an O vacancy on the Cu8H6/SnO2-x surface, followed by sequential hydrogenation to HCOO and HCOOH. Adsorption of CO2 on Cu8/SnO2-x opened a facile pathway to CO. Electronic structure analysis revealed that differences in charge donation of Cu to the antibonding orbitals of CO2 can explain the predicted selectivity differences. The preferred adsorption mode of CO2 is bidentate at the Cu-SnO2-x interface. Our findings emphasize the role of H coverage on Cu on the selectivity of eCO2R for Cu/SnOx catalysts.

Self-assembly formation of Co quantum dot loaded N-doped porous carbon cathode for quinoline degradation in the electro-Fenton system

Quinoline is high toxicity and difficult biodegradation in oil washing wastewater. Therefore, efficient removal of quinoline contaminant from water bodies poses a major challenge. Hence, Co quantum dot loaded N-doped porous carbon (CoNC) nanosheets grown in situ on carbon cloth were fabricated as cathode for the degradation of quinoline in electro-Fenton system. Under optimal conditions (c(Fe2+) = 0.5 mM, U = -0.3 V, pH = 3), quinoline was completely degraded within 15 min with superior apparent rate constant of 0.385 min−1, which was 19.6 times higher than that of the ZIF-L precursor, due to the abundance of Co QDs active sites and hydrophilicity and electrical conductivity of N-doped porous carbon. In addition, three reaction pathways for quinoline were deduced by combining Density Functional Theory (DFT) calculation and Liquid Chromatography-Mass Spectrometry (LC-MS). More importantly, in situ FTIR and free energy calculations were analyzed to reveal that pathway Ⅰ as spontaneous reaction was the main reaction pathway. Finally, the toxicity of the intermediates was assessed with ECOSAR software and E. coli experiments, and the overall toxicity decreased during the degradation reactions. This work provides novel perspectives on environmental protection by designing in-situ grown cathodes through self-assembly method, thereby effectively purifying pollutants from wastewater.

Novel ultra-low NOx coal combustion technologies based on local microenvironment targeted regulation. Part 1. Selective oxygenation

Developing a novel high-efficiency coal combustion technology with ultra-low NOx emission is urgently needed to sustain the good ecological environment. Here, the targeted regulation of local microenvironment around fuel-N, such as functional groups, radicals, molecular configurations, and reaction atmosphere, is realized by the selective oxidation. The molecular configurations, including pore networks and microcrystalline structure in coal, are well characterized through synchrotron radiation-induced SAXS (small angle X-ray scattering) and WAXS (wide angle X-ray scattering) simultaneously. Furthermore, by combining density functional theory (DFT) and experiments, the effects of the local microenvironment on the nitrogen transformation and NO evolution during the thermal conversion are focused on. The results indicate that for the PPA oxidation, the H radicals attack the adjacent carbon to pyrrole/pyridine nitrogen, promoting the conversion of fuel-N to HCN. On the other hand, for the H2O2 oxidation, disrupting the π bond electron cloud by the CO and C = O on the ortho carbon of pyrrole/pyridine dominates the NH3 generation. Additionally, the increased La (average graphene layer extent), a3 (average interlayer spacing), σ3 (standard deviation of interlayer spacing) and σ1 (standard deviation of the first-neighbor distribution) induce massive smaller pores, promoting the generation of abundant reaction defects inside the particles. Importantly, the intensified adsorption on abundant active sites lead to the decreased HCN and increased NH3 evolution, which is adverse for the interaction between homogeneous and heterogeneous NO reduction. Interestingly, the PAA selective oxidation can reduce NO emission by 31.72 % - 34.30 % during the air combustion, which is far better than the H2O2 oxidation. Overall, the attack of free radicals on nitrogen-containing heterocycles promotes the conversion of fuel-N to HCN, the adsorption of which on char surfaces can further enhance the heterogeneous reduction in a lean oxygen atmosphere. The work here provides a novel route for developing high-efficiency and low-NOx combustion technologies.

Axial coordinated manganeseporphyrin/tetraazaporphyrin-4-(10-phenylanthracen-9-yl)pyridine dyads: self-assembly, structure and spectral properties in ground and excited states.

Self-assembly of new donor-acceptor systems based on (5,10,15,20-tetraphenylporphinato)manganese(III)/(5,10,15,20-tetra-4-tert-butylphenylporphinato)manganese(III)/(octakis(4-tert-butylphenyl)tetraazaporphinato)manganese(III) acetate ((AcO)MnTPP/(AcO)MnTBPP/(AcO)MnTAP) and 4-(10-phenylanthracen-9-yl)pyridine (PyAn) was studied using fluorescence spectroscopy and mass spectrometry. It was found that the coordination complexes of 1:1 composition (dyads) are formed in toluene. The spectral properties, the chemical structures and redox behavior of the dyads were described using 1H NMR, IR, EPR spectroscopy and cyclic voltammetry, respectively. The dynamic processes and the characteristics in the excited state of the dyads were obtained using the femtosecond transient absorption spectroscopy method. Density functional theory (DFT), time-dependent DFT methods were used to elucidate the dyad electronic structures and to establish the differences in their frontier molecular orbitals. The analysis of the lambda parameter and the distance of hole-pair interaction was indicated more favorable charge transfer between the macrocycle and the axial PyAn fragment in (AcO)(PyAn)MnTAP. The calculated values of the zero-field splitting parameters D and E/D, together with the g tensors of the lowest spin-orbit state for (AcO)MnTPP and (AcO)(PyAn)MnTPP were obtained using the combination of DFT and Multireference Perturbation Theory (CASSCF/NEVPT2) simulations. The data obtained develop the fundamental basis in the field of photovoltaics and show the prospects for the study of molecular systems of this class.

DFT and AIMD insights into heterogeneous dissociation of 2-chlorothiophenol on CuO(111) surface: Impact of H2O and OH

Copper oxides are vital catalysts in facilitating the formation of polychlorinated thianthrenes/dibenzothiophenes (PCTA/DTs) through heterogeneous reactions in high-temperature industrial processes. Chlorothiophenols (CTPs) are the most crucial precursors for PCTA/DT formation. The initial step in this process is the metal-catalyzed production of chlorothiophenoxy radicals (CTPRs) from CTPs via dissociation reactions. This work combines density functional theory (DFT) calculations with ab initio molecular dynamics (AIMD) simulations to explore the formation mechanism of the adsorbed 2-CTPR from 2-CTP, with the assistance of CuO(111). Our study demonstrates that flat adsorption configurations of 2-CTP on the CuO(111) surface are more stable than vertical configurations. The CuO(111) surface acts as a strong catalyst, facilitating the dissociation of 2-CTP into the adsorbed 2-CTPR. Surface oxygen vacancies enhance the adsorption of 2-CTP on the CuO(111) surface, while moderately suppressing the dissociation of 2-CTP. More importantly, water molecules and surface hydroxyl groups actively promote the dissociation of 2-CTP. Specifically, water directly participates in the reaction through “water bridge”, enabling a barrier-free process. This research provides molecular-level insights into the heterogeneous generation of dioxins with the catalysis of metal oxides in fly ash from static and dynamic aspects, providing novel approaches for reducing dioxin emissions and establishing dioxin control strategies.

First-Principles Simulation and Materials Screening for Spin-Orbit Torque in 2D van der Waals Heterostructures.

Recent advancements in spin-orbit torque (SOT) technology in two-dimensional van der Waals (2D vdW) materials have not only pushed spintronic devices to their atomic limits but have also unveiled unconventional torques and novel spin-switching mechanisms. The vast diversity of SOT observed in numerous 2D vdW materials necessitates a screening strategy to identify optimal materials for torque device performance. However, such a strategy has yet to be established. To address this critical issue, a combination of density functional theory and non-equilibrium Green's function is employed to calculate the SOT in various 2D vdW bilayer heterostructures. This leads to the discovery of three high SOT systems: WTe2/CrSe2, MoTe2/VS2, and NbSe2/CrSe2. Furthermore, a figure of merit that allows for rapid and efficient estimation of SOT is proposed, enabling high-throughput screening of optimal materials and devices for SOT applications in the future.

Ultrahigh tunneling magnetoresistance ratios in the sandwich-structured full MXene Cr2NO2/Ti2CO2/Cr2NO2 van der Waals heterojunction

In this study, the structure, magnetism, energy-band, and spin-dependent electron transport properties of the Cr2NO2/Ti2CO2/Cr2NO2 magnetic tunnel junction (MTJ) were investigated using a combination of density functional theory and non-equilibrium Green’s function methods. The calculation band structures indicate that Cr2NO2 MXene is an “ideal” half-metal with a magnetic moment of 5.00 μB. Ti2CO2 MXene is an indirect band-gap semiconductor, and the Cr2NO2/Ti2CO2-stacked heterojunction reserve 100 % spin polarization because of the weak Van der Waals interface interaction. For the equilibrium state of the most stable Cr2NO2/Ti2CO2/Cr2NO2 MTJ, the total transmission coefficient for parallel configuration is about eleven orders of magnitude larger than that for anti-parallel configuration. An ultrahigh tunneling magnetoresistance (TMR) ratio of 1.92×1013\\% can be detected. For the non-equilibrium state, our calculation results show that the Cr2NO2/Ti2CO2/Cr2NO2 MTJ has a good transport performance when bias voltage ranges from 0 V to 0.1 V. The minimum TMR ratio of 7.51×1012% is detected at the bias voltage of 0.09 V, which can be considered as an excellent TMR ratio. Therefore, the Cr2NO2/Ti2CO2/Cr2NO2 MTJ is an excellent candidate for spintronic device application.

Chromium immobilization in basic magnesium sulfate cement: Experimental and density functional theory studies

This study investigated the effects of different concentrations of Cr(III) on the properties of basic magnesium sulfate cement (BMSC). In addition, the hydration process of BMSC with different concentrations of Cr(III) was studied using isothermal calorimetry and in-situ pH monitoring. A combined experimental approach and density functional theory simulation was further employed to investigate the solidification mechanism of Cr(III) in BMSC. The results indicated that Cr(III) affected the hydration heat, pH value, compressive strength and setting time of BMSC, and the influence became more obvious with the increase of Cr(III) concentration. In addition, the solidification efficiency of Cr(III) in BMSC was up to 99.9%; the efficient solidification of Cr(III) in BMSC primarily operated through ion exchange interactions, as revealed by density functional theory simulation and phase analysis results. Furthermore, the BMSC matrix after being immersed in simulated acid rain solutions for 28 days had a compressive strength of over 45MPa, showing remarkable resistance to acids.

Exploring the impact of annealing temperature on morphological, structural, vibrational and electron paramagnetic resonance properties of starch-mediated spinel CoAl2O4: Experimental and DFT study

In the present work, CoAl2O4 nanoparticles were successfully synthesized using the simple auto-combustion sol-gel method employing starch as an organic fuel source. The effect of the annealing temperature on the structural, vibrational, morphological, and magnetic properties is studied. The obtained spherical nanoparticles have grain sizes ranging from 23.54 nm to 46.50 nm. X-ray diffraction (XRD) patterns reveal the formation of a face centered cubic (fcc) spinel phase with the Fd-3m space group for all prepared samples. The calculated average crystallite sizes exhibit an increase from 24.65 nm to 56.27 nm, consistent with the observed grain sizes. Density Functional Theory (DFT) calculations are applied to reach the optimized cell parameters as well as to confirm the structural properties of the synthetized CoAl2O4 nanoparticles. Geometry optimization of the CoAl2O4 spinel oxide is performed using the CASTEP module of Materials Studio software. The optimized unit cell, lattice parameter and unit cell volume were obtained from this simulation. The combined experimental and density functional theory study of structural properties of CoAl2O4 revealed that an increase in the calcination temperature leads to an increase in the volume of the unit cell and hence to an increase in the particles size. Fourier-transform infrared spectroscopy (FTIR) further corroborated these findings by demonstrating subtle shifts in characteristic CoAl2O4 absorption peaks with varying annealing temperatures. These peak shifts suggest a potential redistribution of Al³⁺ and Co2⁺ ions between tetrahedral and octahedral sites within the spinel structure. Electron paramagnetic resonance (EPR) spectroscopy revealed a magnetic state transition as a function of both the annealing temperature and the resulting crystallite size. Occupancy fluctuations of Al³⁺ and Co2⁺ ions at specific sites have also impacted on the nanoparticles color since the hue of the material depends on the valence state and the cationic coordination environment in the CoAl2O4 crystal lattice. Correlations between structural, vibrational, magnetic and color properties are presented to understanding how synthesis parameters influence CoAl2O4 characteristics which is essential for tailoring materials for specific applications.

Electronic Interaction of Epoxy Resin with Copper at the Adhered Interface.

A better understanding of the aggregation states of adhesive molecules in the interfacial region with an adherend is crucial for controlling the adhesion strength and is of great inherent academic interest. The adhesion mechanism has been described through four theories: adsorption, mechanical, diffusion, and electronic. While interfacial characterization techniques have been developed to validate the aforementioned theories, that related to the electronic theory has not yet been thoroughly studied. We here directly detected the electronic interaction between a commonly used thermosetting adhesive, cured epoxy of diglycidyl ether of bisphenol A (DGEBA) and 4,4'-diaminodiphenylmethane (DDM), and copper (Cu). This study used a combination of density functional theory (DFT) calculations and femtosecond transient absorption spectroscopic (TAS) measurements as this epoxy adhesive-Cu pairing is extensively used in electronic device packaging. The DFT calculations predicted that π electrons in a DDM molecule adsorbed onto the Cu surface flowed out onto the Cu surface, resulting in a positive charge on the DDM. TAS measurements for the Cu/epoxy multilayer film, a model sample containing many metal/adhesive interfaces, revealed that the electronic states of excited DDM moieties at the Cu interface were different from those in the bulk region. These results were in good accordance with the prediction by DFT calculations. Thus, it can be concluded that TAS is applicable to characterize the electronic interaction of adhesives with metal adherends in a nondestructive manner.

Exploring long-range fluorine–carbon J-coupling for conformational analysis of deoxyfluorinated disaccharides: A combined computational and NMR study

In this study, we investigated the potential of long-range fluorine–carbon J-coupling for determining the structures of deoxyfluorinated disaccharides. Three disaccharides, previously synthesized as potential galectin inhibitors, exhibited through-space fluorine–carbon J-couplings. In our independent conformational analysis of these disaccharide derivatives, we employed a combination of density functional theory (DFT) calculations and nuclear magnetic resonance (NMR) experiments. By comparing the calculated nuclear shieldings with the experimental carbon chemical shifts, we were able to identify the most probable conformers for each compound. A model comprising fluoromethane and methane molecules was used to study the relationship between molecular arrangements and intermolecular through-space J-coupling. Our study demonstrates the important effect of internuclear distance and molecular orientation on the magnitude of fluorine–carbon coupling. The experimental values for the fluorine–carbon through-space couplings (TSCs) of the disaccharides corresponded with values calculated for the most probable conformers identified by the conformational analysis. These results unlock the broader application of fluorine–carbon TSCs as powerful tools for conformational analysis of flexible molecules, offering valuable insights for future structural investigations.

Enhanced photodegradation of methylene blue by Zr-doped TiO2:A combined DFT and experimental investigation

The effective mitigation of effluents in water has attracted researchers as a foremost task for addressing environmental concerns. To overcome these concerns, TiO2 (labeled as PCT-1) and Zr-doped TiO2 (labeled as PCT-2) nano catalysts are prepared by an efficient sol–gel protocol and their photocatalytic degradation performance of methylene blue (MB) is investigated. The structural integrity of nanostructures is determined by analytical tools. More than 96 % MB degradation is observed when PCT-2 is subjected to ultraviolet light for 180 min. Nanosized PCT-2 exhibits attractively advanced photocatalytic performance than PCT-1 owing to lower electron–hole pair recombination (3.02 eV) as well as superior photon capture via oxidation by photocatalytic response (confirmed through active species trapping scavenger tests). Furthermore, the results of bandgap are also confirmed by spin-polarized density functional theory (DFT) computations. The findings of this study indicate that band tuning is an attractive photocatalytic system for improving catalytic performance.

Sulfur migration mechanism of pig manure in supercritical water: A combined experimental and DFT study

Pig manure (PM) is a high concentration organic waste rich in sulfur, and its biofuel contains various sulfur-containing pollutants, which reduces the safety of the products. Supercritical water (SCW) can dissolve most organic matter, which is a technology worthy of further study. In order to reduce sulfur pollution in the process of PM resource utilization and better control the conversion path of sulfur, it is necessary to explore the migration mechanism of sulfur in the whole PM-SCW gasification process. The experimental results indicated that H2S was the only gaseous product. Only inorganic compounds (S2-, S2O32- and SO42-) were detected in the liquid. Sulfur in the solid mainly included thiol/thioether, thiophene and sulfone. The influence of different reaction conditions (temperature, residence time, PM concentration and catalysts) on sulfur migration was studied in a batch reactor. It was worth noting that the catalysts had a significant effect on H2S absorption. The lowest H2S yield was 3.2 * 10−4 mol/kg and more than 70% of the sulfur was distributed in the liquid under the condition of addition of K2CO3. While, the RTH2110 fixed most of the sulfur of PM (the maximum value reached 50.94%) in the solid. Thus, adding the catalysts flexibly can choose composition of the products. Furthermore, six possible pathways of sulfur migration in the solid were designed and the kinetic parameters were calculated by density functional theory (DFT). The results provided a basis for controlling sulfur in PM. Subsequently, the sulfur migration pathways during PM-SCW gasification process were comprehensively summarized through the combination of experiment and DFT. It provided a method for sulfur treatment in PM, which had guiding significance for the realization of pollution-free treatment of PM.

A first-principles study of bilayer 1T'-WTe2/CrI3: a candidate topological spin filter

The ability to manipulate electronic spin channels in 2D materials is crucial for realizing next-generation spintronics. Spin filters are spintronic components that polarize spins using external electromagnetic fields or intrinsic material properties like magnetism. Recently, topological protection from backscattering has emerged as an enticing feature that can be leveraged to enhance the robustness of 2D spin filters. In this work, we propose and then characterize one of the first 2D topological spin filters: bilayer CrI3/1T’-WTe2. To do so, we use a combination of density functional theory, maximally localized Wannier functions, and quantum transport calculations to demonstrate that a terraced bilayer satisfies the principal criteria for being a topological spin filter: namely, that it is gapless, exhibits spin-polarized charge transfer from WTe2 to CrI3 that renders the bilayer metallic, and has a topological boundary which retains the edge conductance of monolayer 1T’-WTe2. In particular, we observe that small negative ferromagnetic moments are induced on the W atoms in the bilayer, and the atomic magnetic moments on the Cr are approximately 3.2 μB/Cr compared to 2.9 μB/Cr in freestanding monolayer CrI3. Subtracting the charge and spin densities of the constituent monolayers from those of the bilayer further reveals spin-orbit coupling-enhanced spin-polarized charge transfer from WTe2 to CrI3. We demonstrate that the bilayer is topologically trivial by showing that its Chern number is zero. Lastly, we show that interfacial scattering at the boundary between the terraced materials does not remove WTe2’s edge conductance. Altogether, this evidence indicates that BL 1T’-WTe2/CrI3 is gapless, magnetic, and topologically trivial, meaning that a terraced WTe2/CrI3 bilayer heterostructure in which only a portion of a WTe2 monolayer is topped with CrI3 is a promising candidate for a 2D topological spin filter. Our results further suggest that 1D chiral edge states may be realized by stacking strongly ferromagnetic monolayers, like CrI3, atop 2D nonmagnetic Weyl semimetals like 1T’-WTe2.

Multiexcitonic and optically bright states in subunits of pentacene crystals: A hybrid DFT/MRCI and molecular mechanics study.

A hybrid quantum mechanics/molecular mechanics setup was used to model electronically excited pentacene in the crystal phase. Particularly interesting in the context of singlet fission (SF) is the energetic location of the antiferromagnetically coupled multiexcitonic singlet state, 1(TT), and the ferromagnetically coupled analog in relation to the optically bright singlet state. To provide photophysical properties of the accessible spin manifold, combined density functional theory and multi-reference configuration interaction calculations were performed on pentacene dimers and a trimer, electrostatically embedded in the crystal. The likelihood of a quintet intermediate in the SF process was estimated by computing singlet-quintet electron spin-spin couplings employing the Breit-Pauli Hamiltonian. The performance of the applied methods was assessed on the pentacene monomer. The character of the optically bright state and the energetic location of the 1(TT) state depend strongly on the relative orientation of the pentacene units. In the V-shaped dimers and in the trimer, the optically bright state is dominated by local and charge transfer (CT) excitations, with admixtures of doubly excited configurations. The CT excitations gain weight upon geometry relaxation, thus supporting a CT-mediated SF mechanism as the primary step of the SF process. For the slip-stacked dimer, the energetic order of the bright and the 1(TT) states swaps upon geometry relaxation, indicating strong nonadiabatic coupling close to the Franck-Condon region-a prerequisite for a coherent SF process. The multiexcitonic singlet, triplet, and quintet states are energetically too far apart and their spin-spin couplings are too small to bring about a noteworthy multiplicity mixing.

Strain Effect on Optoelectronic and Thermoelectric Properties of the Perovskite NaGeI3

In this research, we investigate the impact of strain on the optoelectronic and thermoelectric properties of the NaGeI3 perovskite by employing a combination of density functional theory (DFT) and Boltzmann transport theory. Initially, we examine the NaGeI3 material’s structural, electronic, and optical properties using the generalized gradient approximation (GGA). The results reveal that this material proves the behavior of a semiconductor with a p-type character and possesses interesting optical properties. Furthermore, we outline the thermoelectric properties of the material, including the Seebeck coefficient, the electrical and thermal conductivities, the figure of merit (ZT), and the power factor (PF). Our investigations indicate that the Seebeck coefficient exhibits positive and increasing values with the application of strain. This confirms the p-type semiconductor behavior observed in the studied material. Additionally, the NaGeI3 compound demonstrates significantly high values of the ZT when compared with the existing thermoelectric materials, both at room and high-temperature values. This suggests that the NaGeI3 compound stands as a promising potential candidate for optoelectronic and/or thermoelectric applications.

Ultrasound catalytic ozonation to remove 5-hydroxy-1,3-phthalic acid from strongly alkaline and high-salt solutions: Aiding nuclear waste disposal and human health

As a typical precipitation inhibitor and the main component of plasticizers, 5-hydroxy-1,3-phthalic acid (5-HPA) seriously threatens the nuclear waste disposal and human health. OH, 1O2, and O2− induced by the ultrasound catalytic ozonation (US/O3) process achieves a removal rate of 60.67 % of 5-HPA in strongly alkaline and high-salt solutions within 60 min, which is significantly higher than the O3 alone process. This technology is highly resistant to inorganic anions that coexist in industrial production, but the mineralization process is inhibited. Ozone utilization and mass transfer are significantly improved by ultrasound, including reducing the ozone bubble size by 38 %, increasing the ozone utilization rate from 52 % to 75 %, increasing the volumetric mass transfer coefficient by 61 %, and increasing the specific interfacial area by 60 %, reducing the molar ratio of ozone to TOC from 0.45 to 0.23. Through a combination of Density functional theory (DFT) and GC–MS, four pathways for removing 5-HPA are clearly proposed, which are significantly different from the evolution behavior in acidic systems. The US/O3 system has significant application potential in reducing the threat of 5-HPA to nuclear waste disposal and human health.

A combination of DFT and kMC to study on the formation mechanism of ethyl acetate during the gas-phase synthesis of vinyl acetate from ethylene on PdAu(100) surface

Vinyl acetate (VAc) is an important chemical raw material for the production of polyvinyl alcohol and polyvinyl acetate, among others. The preparation of vinyl acetate over PdAu catalysts using ethylene, oxygen and acetic acid as raw materials is one of the mainstream processes for the production of vinyl acetate in the world. The by-product ethyl acetate in this process is more difficult to be completely removed, and it is an impurity component in vinyl acetate products that needs to be strictly controlled in content. However, studies on the mechanism of ethyl acetate generation have not been reported, which limits the improvement of the purity of vinyl acetate products and the optimization of the ethyl acetate separation process. In this paper, the mechanism of ethyl acetate generation during ethylene vinyl acetate reaction on PdAu catalysts was systematically investigated using a combination of density functional theory (DFT) and kinetic Monte Carlo (kMC) simulations.The results show that the species tend to adsorb to the Pd-Au bridge sites, diagonal Pd-Pd vacancies, and diagonal Pd-Au vacancies of PdAu(100), and the Pd on the catalyst surface interacts more strongly with the adsorbed species. The dominant pathway for the generation of ethyl acetate on PdAu(100) is CH2CH2* + O*→ CH2CH* + H* → CH3CH* + CH3COO* → CH3COOCHCH3* + H* → CH3COOCH2CH3*, where the hydrogenation of CH2CH* to CH3CH* is the rate-control step in the dominant pathway for the generation of ethyl acetate. This step has an energy barrier of 1.09 eV and a reaction heat of 0.90 eV. The study of the generation mechanism of the by-product ethyl acetate in this paper is hoped to provide more targeted guidance and suggestions for the modification of Pd-Au catalysts, so as to reduce the generation of ethyl acetate as a by-product, to reduce the energy consumption required for the separation, and to enhance the purity of vinyl acetate products.