Electron Density Functional Theory Research Articles

Understanding pillar chemistry in potassium-containing polyanion materials for long-lasting sodium-ion batteries.

K-containing polyanion compounds hold great potential as anodes for sodium-ion batteries considering their large ion transport channels and stable open frameworks; however, sodium storage behavior has rarely been studied, and the mechanism remains unclear. Here, using a noninterference KTiOPO4 thin-film model, the Na+ storage mechanism is comprehensively revealed by in situ/operando spectroscopy, aberration-corrected electron microscopy and density functional theory calculations. We find that incomplete K+/Na+ ion exchange occurs and eventually 0.15 K+ remains as a pillar to stabilize the tunnel structure. The pillar effect substantially maintains the volume change within 3.9%, much smaller than that of K+(Na+) insertion into KTiOPO4(NaTiOPO4) (9.5%; 5%), thus enabling 10,000 cycles. The powder electrode demonstrates comparable capacity and can work efficiently at commercial-level areal capacity of 2.47 mAh cm-2. The quasi-solid-state pouch cell with high safety under extreme abuse also manifests long-term cycling stability. This pillar chemistry will inspire alkali metal ion storage in hosts containing heterogeneous cations.

Enhancing carbamazepine degradation in electrochemical systems: The interplay of sulfur vacancies and absorbed peroxydisulfate in molybdenite electrodes

Achieving high reaction efficiency with low energy input is crucial for electrochemical water remediation processes, yet remains a significant challenge. This study reported a practicable method, utilizing natural molybdenite as particle electrodes in an electro-activated peroxydisulfate (PDS) process (3D system) to develop a cost-efficient electrocatalytic oxidation system. Molybdenite’s unique ability to generate sulfur vacancies during electrocatalysis significantly enhances system efficiency. The 3D system enhanced the rate constant of carbamazepine (CBZ) abatement sixfold compared to the system without molybdenite. Additionally, a substantial decrease in electrical energy per order (EE/O) from 7.13 kWh/m3 to 0.326 kWh/m3 indicates a near 22-fold increase in energy efficiency. Characterizations involving electron microscopies, electrochemical experiments and density functional theory calculations confirm that hydroxyl radicals (•OH) and adsorbed PDS(PDS*) are the main active species. Molybdenite’s surface with plenty of edge-S, released S vacancy during electrocatalytic oxidation, providing adsorption and activation sites for PDS and H2O. This led to more active sites and facilitating the generation of PDS*, lowering the energy barrier for •OH formation and boosting the oxidation performance of the 3D system. The results underscore the constructed 3D system is a robust and energy-efficient method for practical water treatment.

Pt12H24 -: A Cuboctahedral Platinum Hydride Cluster Cage.

The platinum hydride cluster Pt12H24 - is studied in gas phase by a combination of trapped ion electron diffraction and density functional theory computations. We find a cuboctahedral platinum cage with bridge bound hydrogen atoms. This unusual structure is stabilized by Pt-H-Pt multicenter bonds and shows characteristics of spherical aromaticity.

Elaborate construction of a MOF-derived novel morphology Z-scheme ZnO/ZnCdS heterojunction for enhancing photocatalytic H2 evolution and tetracycline degradation

Elaborate construction of novel Z-scheme heterojunction with exceptional morphology derived from metal-organic framework (MOF) have been attracted greatly interest for improving the photocatalytic ability. Herein, a Z-scheme ZnO/ZnCdS heterojunction of rare morphology with ultrathin-nanosheet assembled hierarchical morphology ZnCdS supporting on rich gap ZnO nanospheres were constructed from Zn-based MOF (namely PZH-139) for the first time. This unique feature increased specific surface area, offered abundant mass transport channels and accessible catalytic active sites, accelerated electron migration, which highly elevated photocatalytic property. Furthermore, electron paramagnetic resonance (EPR) measurements and density functional theory (DFT) calculations confirmed the reservation of strong redox capability owing to Z-scheme electron transfer path and the ΔGH* closer to zero of Z-scheme ZnO/ZnCdS system were another two key factors for boosting the photocatalytic activity. As a result, 3-ZnO-700/ZnCdS-160 with optimal morphology showed the best H2 generation performance of 15.43 mmol h−1 g−1 and degradation tetracycline (TC) efficiency of 98.14 %. This work offered a novel and feasible idea for elaborate synthesis of the high-efficiency Z-scheme ZnO/ZnCdS heterojunction with special morphology derived from Zn-MOF.

Bridging electronic and classical density-functional theory using universal machine-learned functional approximations.

The accuracy of density-functional theory (DFT) calculations is ultimately determined by the quality of the underlying approximate functionals, namely the exchange-correlation functional in electronic DFT and the excess functional in the classical DFT formalism of fluids. For both electrons and fluids, the exact functional is highly nonlocal, yet most calculations employ approximate functionals that are semi-local or nonlocal in a limited weighted-density form. Machine-learned (ML) nonlocal density-functional approximations show promise in advancing applications of both electronic and classical DFTs, but so far these two distinct research areas have implemented disparate approaches with limited generality. Here, we formulate a universal ML framework and training protocol to learn nonlocal functionals that combine features of equivariant convolutional neural networks and the weighted-density approximation. We prototype this new approach for several 1D and quasi-1D problems and demonstrate that functionals with exactly the same hyperparameters achieve excellent accuracy for a diverse set of systems, including the hard-rod fluid, the inhomogeneous Ising model, the exact exchange energy of electrons, the electron kinetic energy for orbital-free DFT, as well as for liquid water with 1D inhomogeneities. These results lay the foundation for a universal ML approach to approximate exact 3D functionals spanning electronic and classical DFTs.

Atomic and electronic structures of the [formula omitted]-FeSi2/Si(001) interface

The atomistic interface structure between β-FeSi2 and Si substrate was investigated by cross-sectional scanning transmission electron microscopy and density functional theory calculations (DFT). A high quality single crystalline β-FeSi2 film was epitaxialy grown on Si(001) substrate. We demonstrate that the β-FeSi2(100) plane is bonded to the Si(001) plane with two Si dimers per unit cell. With such interface structure, DFT band calculations reveal that metallic electronic states are localized at the interface. This finding implies the presence of two dimensional electronic states at the interface of β-FeSi2/Si(001), which may have potential applications in silicon-based electronic devices.

Evolution of strengthening precipitates in Al-4.0Zn-1.8Mg-1.2Cu (at.%) alloy with high Zn/Mg ratio during artificial aging

Evolution of strengthening precipitates, including their types, sizes, volume fraction, and chemical compositions in Al-4.0Zn-1.8Mg-1.2Cu (at.%) alloy during artificial aging, were investigated using anomalous small-angle X-ray scattering (ASAXS), three-dimensional atom probe techniques (APT), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and density functional theory (DFT) calculation. Upon aging, Cu-containing clusters merge with adjacent clusters to form larger clusters, which then act as nucleation sites for GPη' zones. As aging proceeds, GPη' zones grow up to η'I metastable phase with seven atomic layers on {111}Al planes, and this process is controlled by diffusion of Mg atoms. Cu atoms have a low diffusion rate and do not participate into the growth of precipitates within the first 60mins of aging. As aging time increases, Cu atoms enter the η'I metastable phase, leading to a significant increase in Cu content and (Zn+Cu)/Mg ratio; η'I metastable phase grow, and after exceeding about 7nm, gradually transform into the η'II metastable phase with ten atomic layers by adding three new atomic layers at one side. GPη' zones, η'I metastable phase and η'II metastable phase have symmetric interface structures. The precipitation sequence during aging to peak state can be summarized as: atomic clusters → GPη' zones → η'I metastable phase → η'II metastable phase.

Direct quantitative assessment of single-atom metal sites supported on powder catalysts

Rational design of effective catalyst demands a profound understanding of active-site structures. Single-atom supported powder catalysts, depicting unique features like enhanced metal dispersion, hold promise in different applications. Here, we present an approach to directly quantify the detailed structural nature of metal sites in single-atom, high surface area, powder catalysts. By combining advanced high-resolution scanning-transmission electron microscopy, deep learning and density functional theory calculations, we determine, with statistical significance, the exact location and coordination environment of Pd single-atoms supported on MgO nanoplates. Our findings reveal a preferential interaction of Pd single-atoms with cationic vacancies (V-centers), followed by occupation of anionic defects on the {001} MgO surface. The former interaction results in stabilization of PdO species within V-centers, while partially embedded Pd states are found in F-defects. This methodology opens a route to the ultimate structural analysis of metal-support interaction effects, key in the design of advanced nanocatalysts for sustainable and energy-efficient processes.

Unraveling the adsorption-limited hydrogen oxidation reaction at palladium surface via in situ electron microscopy

Palladium (Pd) catalysts have been extensively studied for the direct synthesis of H2O through the hydrogen oxidation reaction at ambient conditions. This heterogeneous catalytic reaction not only holds considerable practical significance but also serves as a classical model for investigating fundamental mechanisms, including adsorption and reactions between adsorbates. Nonetheless, the governing mechanisms and kinetics of its intermediate reaction stages under varying gas conditions remain elusive. This is attributed to the intricate interplay between adsorption, atomic diffusion, and concurrent phase transformation of catalyst. Herein, the Pd-catalyzed, water-forming hydrogen oxidation is studied in situ, to investigate intermediate reaction stages via gas cell transmission electron microscopy. The dynamic behaviors of water generation, associated with reversible palladium hydride formation, are captured in real time with a nanoscale spatial resolution. Our findings suggest that the hydrogen oxidation rate catalyzed by Pd is significantly affected by the sequence in which gases are introduced. Through direct evidence of electron diffraction and density functional theory calculation, we demonstrate that the hydrogen oxidation rate is limited by precursors' adsorption. These nanoscale insights help identify the optimal reaction conditions for Pd-catalyzed hydrogen oxidation, which has substantial implications for water production technologies. The developed understanding also advocates a broader exploration of analogous mechanisms in other metal-catalyzed reactions.

Atomic‐Precision Manipulation of Defects in RuO2 Nanocrystals via Electron‐Beam

AbstractManufacturing nanocrystals with desired structures is the basis for realizing designed properties in their applications. As an important top‐down fabrication technique, although electron beam (e‐beam) has been well used for atomic etching on one hand, it is still challenging to precisely repair the undesired crystal defects on the other. Herein, utilizing the e‐beam probe in a spherical aberration‐corrected scanning transmission electron microscope, the possibility of e‐beam in the atomic‐level‐controllable construction/repair of crystalline defects in ruthenium oxide (RuO2) nanocrystals is systematically explored. It is found that the functional duality of beam effects can be well controlled, with the domination of either constructing or repairing defects in atomic scale, by tuning e‐beam parameters. With the aid of real‐time observation of the atom‐by‐atom repairing process via in situ scanning transmission electron microscopy and density functional theory calculations, the e‐beam‐assisted repairing mechanism is revealed. This work is anticipated to provide insights into controllable top‐down manufacturing nanomaterials at the sub‐nanoscale by e‐beam.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation.

Perylene diimides (PDIs) have garnered considerable attention due to its immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI-PDA, by linking an ortho-substituted PDI with p-phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron transfer dynamics, leading to a ten-fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI-PDA compared to the PDI molecular counterpart, achieving yields exceeding 90%. Electron property studies and density functional theory calculations show that the PDI-PDA with its well-defined crystal structure, enhances π-π stacking and lowers the electron transition barrier. Moreover, the strong electron-withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI-PDA suppressing the rapid recombination of photogenerated electron-hole pairs and improving charge separation efficiency to give high photocatalytic efficiency. This study provides a brief yet effective way for the improvement of the photocatalytic efficiency of commonly used PDI-based dyes by integrating them into a framework skeleton.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation

AbstractPerylene diimides (PDIs) have garnered considerable attention due to their immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI‐PDA, by linking an ortho‐substituted PDI with p‐phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron‐transfer dynamics, leading to a ten‐fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI‐PDA compared to the PDI molecular counterpart, with yields exceeding 90 %. Electron property studies and density functional theory calculations show that the PDI‐PDA with its well‐defined crystal structure, enhances π–π stacking and lowers the electron transition barrier. Moreover, the strong electron‐withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI‐PDA, suppressing the rapid recombination of photogenerated electron‐hole pairs and improving the charge‐separation efficiency to give high photocatalytic efficiency. This study provides a brief but effective way for improving the photocatalytic efficiency of commonly used PDI‐based dyes by integrating them into a framework skeleton.

Utilization of papermaking black liquor as liquid phase for hydrothermal carbonization of corn stalks: The unique role of alkali for production of hydrochar

Papermaking black liquor (BL) contains a large amount of organic matter, alkali, and salt, which has high value in industrial and agricultural production. In the present paper, hydrothermal carbonization (HTC) technology has been employed to deal with BL and corn stalk (CS) under various conditions. A variety of analytical technologies, including Fourier Transform Infrared Spectrometer, X-Ray Diffraction, element analyzer, comprehensive thermal analyzer, scanning electron microscope, chromatography/mass spectrometry, TOC analyzer, and density functional theory (DFT), were used to characterize the physicochemical properties of hydrochar and aqueous phase product. The effects of experimental parameters (temperature, solid-liquid ratio, and time) on the HTC of BL and CS were systematically investigated. The higher energy yield and densification of hydrochar prepared by our HTC technology were obtained at 260 ℃ in 30 min with a solid-liquid ratio of 1:3. Mechanism study indicates that NaOH, which comes from the original BL, could effectively facilitate the cleavage of β–O–4 bond in lignin and β–1–4 glycosidic bond in cellulose and hemicellulose molecules. Hemicellulose and cellulose are more susceptible to degradation relevant to the lignin in the presence of NaOH. Elementary analysis shows that the dosage of BL is important for improving energy densification of hydrochar. The combustion characteristics show that hydrochar presents a thermochemical behavior, which is close to bituminous coal. Owing to hydroxyl ion in NaOH ion pair was consumed in the series of dehydrogenation reactions, pH of HTC aqueous phase product significantly decreases from 11 to 13 in original BL to 4.8–5. Such results indicate that a completely change for the components of BL could be obtained by our HTC technology, which provide a novel idea for the treatment of Papermaking BL without concentration.

Emergence of critical thickness and multifaceted role of stacking faults in high misfit hexagonal ferrites films

Polarization in improper ferroelectrics is believed to be robust against the depolarizing field. However, this characteristic appears to be disrupted in hexagonal ferrite and manganite, leading to a controversial debate regarding the origin of the critical thickness. In this study, we design hexagonal TbFeO3 (h-TFO) films which exhibits a critical thickness exceeding 5 nm at room temperature and an exceptionally long suppression layer in thicker films. It is explained that the critical thickness effect originates from the synergistic interplay of the interface, strain, and vacancies, which is confirmed by combining scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) and density functional theory (DFT). This explanation is equally applicable to the polarization suppression near the stacking fault (SF). Finally, we find that the SF reduces the suppression length to an extent, and contributes to changes in the topological order of the domain in h-TFO film. Our study provides a more comprehensive understanding of the origin of critical thickness and the multifaceted role of the SF in ferroelectrics.

Cobalt single atom anchored at C2N3 for activating peracetic acid to ultrafast degrade drugs at 4 °C

Low temperature weakens the catalytic degradation efficiency of contaminants in advanced oxidation processes. C2N3, a preeminent catalyst support material, was prepared by the pyrolysis of HNO3 pretreated melamine. The Co SA/C2N3 was prepared by the pyrolysis-induced-vaporization strategy, and used to activate peracetic acid (PAA) to degrade drugs. The Co SA/C2N3-650-2+PAA system can completely remove acyclovir within 3 min at 4 °C, and achieved excellent removal rate under the various influencing factors. The system showed outstanding degradation performance in repeated use experiment and simulated wastewater experiment. Co SA/C2N3-650-2 was cross-linked to the calcium alginate sponge, and exhibited superior practicability in microreactor experiment. The electron paramagnetic resonance (EPR), quenching experiment and density functional theory (DFT) calculations certificated that the non-radical pathway was primary mechanism in which 1O2 played a major role. The Co(Ⅱ)N3 sites and PAA bound to form Co(IV) by electron transfer, which attacked the external peroxygen of PAA to produce 1O2. This study proposes a novel pathway for the generation of 1O2 and provides an efficient SA catalyst for degradation of drugs in cold regions.

Fe(Ⅲ)-doped ZnIn2S4-modified graphene oxide in-situ for the degradation of tetracycline hydrochloride in simulated sunlight

To improve the efficiency of photocatalytic reactions, it is important to understand how to achieve fast directional migration and separation of photogenerated carriers at the interface. Here, Fe(III)-doped ZnIn2S4 (ZIS)-coated graphene oxide (GO) composite (GZF) was in-situ prepared via the low-temperature water bath method. Ultrathin Fe(III)-doped ZIS nanosheets were uniformly grown upright on the GO surface. The prepared samples were studied via, such as, X-ray diffraction, scanning electron microscopy combined with energy-dispersive spectroscopy, transmission electron microscopy, ultraviolet spectroscopy, N2 adsorption–desorption measurements, X-ray photoelectron spectroscopy, and electron spin resonance. Compared with ZnIn2S4 (ZIS)-coated graphene oxide (GZ), the GZF exhibit a 2.26-fold increase in the photocatalytic degradation performance of tetracycline hydrochloride (TCH) in simulated sunlight. Through density functional theory calculations, found that Fe(III) doping introduces new energy levels into ZIS, which effectively narrow its bandgap and thus enhance its light absorption efficiency. It was found that h+, ·O2−, and 1O2 were the major reactive oxygen species involved in the photocatalysis, and the effect of pH on the catalytic degradation of TCH was examined. Electron spin resonance and density functional theory results indicate that Fe(III) acts as an electron trap in the ZIS structure to promote the separation of photogenerated electron-hole pairs, which in turn enhances the photocatalytic efficiency of GZF-25.

Dual-ligand Zn-based MOF as a fluorescent probe for the detection of HSO4−

The development of fluorescent probes for the recognition of HSO4− is important for social security and human health. In this work, Zn-MOF ([(Zn2+)(L+)2(H2O)2]∙6(H2O) ∙2(FDCA2−)) materials were synthesized using Zn2+ as the metal center and 1,3,5-triimidazolylbenzene (L) and 2,5-furan dicarboxylic acid (FDCA) as the bi-conjugate. The characterization was carried out by single crystal X-ray diffraction, powder X-ray diffraction (PXRD), thermogravimetric analysis (TG), Zeta potential, and scanning electron microscopy (SEM). The fluorescence sensing experiments showed that Zn-MOF can be used as a fluorescent probe, which produces an obvious fluorescence burst in a short time, and has a good selectivity for the detection of HSO4−, with a low limit of detection (LOD) as low as 0.18 μM, and a good immunity to interference. The recognition mechanism of Zn-MOF was explored by electron transfer analysis methods and density functional theory (DFT) calculations, which indicated that the fluorescence burst mechanism was hydrogen bond formation.

Unraveling degradation mechanism and reaction efficacy of sulfamethoxazole via reactive oxygen species dominated radical process

Herein, the Ti4O7 electrode was combined for the first time with various oxidants to generate reactive oxygen species for the removal of different organic pollutants in an electrochemical oxidation (EO) system. The removal efficiency of organic pollutants, reaction mechanism, and degradation pathway were evaluated by electrochemical tests, reaction kinetics, electron paramagnetic resonance, quantum chemical, and density functional theory calculations. As a result, nearly 100 % removal efficiency of sulfamethoxazole (SMX) was achieved within 12 min with a high kinetic rate constant of 0.259 min−1, and the kinetic rate constant was strongly dependent on the electrostatic potential. The O2 site on the peroxymonosulfate (PMS) molecule dominated the radical generation for the removal of SMX via the radical and non−radical process. This current study offers a novel approach toward the electrochemical activation of PMS in the elimination and degradation of various organic pollutant from wastewater.

Molecular Insights into Adhesion at Interface of Geopolymer Binder and Cement Mortar.

The degradation of concrete and reinforced concrete structures is a significant technical and economic challenge, requiring continuous repair and rehabilitation throughout their service life. Geopolymers (GPs), known for their high mechanical strength, low shrinkage, and durability, are being increasingly considered as alternatives to traditional repair materials. However, there is currently a lack of understanding regarding the interface bond properties between new geopolymer layers and old concrete substrates. In this paper, using advanced computational techniques, including quantum mechanical calculations and stochastic modeling, we explored the adsorption behavior and interaction mechanism of aluminosilicate oligomers with different Si/Al ratios forming the geopolymer gel structure and calcium silicate hydrate as the substrate at the interface bond region. We analyzed the electron density distributions of the highest occupied and lowest unoccupied molecular orbitals, examined the reactivity indices based on electron density functional theory, performed Mulliken charge population analysis, and evaluated global reactivity descriptors for the considered oligomers. The results elucidate the mechanisms of local and global reactivity of the oligomers, the equilibrium low-energy configurations of the oligomer structures adsorbed on the surface of C-(A)-S-H(I) (100), and their adsorption energies. These findings contribute to a better understanding of the adhesion properties of geopolymers and their potential as effective repair materials.

Influence of Na2SO4-NaCl-ZnO co-doping on the thermochemical energy storage in CaO looping

In recent years, calcium-looping as one of the thermochemical energy storage technologies has attracted much attention. However, the poor cycling stability of conventional calcium-based materials limits the application of the calcium-looping. In this work, we prepare a novel calcium-based composite by Na2SO4-NaCl-ZnO co-doping. The properties of the composites are investigated by thermogravimetric analysis, X-ray photoelectron spectroscopy, in-situ X-ray diffraction, electron paramagnetic resonance, scanning electron microscope and Density Functional Theory calculations. The results indicate the Na2SO4 + NaCl-(CaO+0.5ZnO) composite is the most cost-effective material. After one cycle, the effective conversion of the composite is 89.8 %, which is 59.8 % higher than CaO. After 80 cycles, the effective conversion of composites decay 36.5 %. The enhancement mechanism is attributed to the formation of the high Taman temperature coordination compounds and oxygen vacancies generated by the coordination effect, and the rapid transport of oxygen ions derived from the oxo-Grotthuss effect. In addition, the averaged thermal energy density of Na2SO4 + NaCl-(CaO+0.5ZnO) is 2057 J/g after 80 cycles, which is a 43.9 % improvement compared to CaO. This work paves the way for the application of calcium-based thermochemical energy storage technology via achieving fast reaction rates and good cycling stability.