Search Results (52)

Na-layered Li-containing Mn-based cathodes (Na_xLi_yMn_1-yO₂, NLMOs) with additional Na⁺ storage ability resulting from the anionic redox reaction (ARR) hold great promise for sodium-ion batteries (NIBs). However, practical applications of NLMOs encounter challenges, such as migration of transition metal Mn, loss of lattice oxygen, and voltage decay during cycling. Here, we show that Cu plays an important role in enhancing the ARR via the reductive coupling mechanism (RCM). Results shows that a Cu²⁺/Fe³⁺ modified NLMO sample delivers a Na⁺ storage capacity as high as 174 mA h g⁻¹ at 0.2C, higher than that of a Zn²⁺/Fe³⁺ modified NLMO sample (130 mA h g⁻¹) and NLMO (154 mA h g⁻¹). Both in situ and ex situ characterization results indicate that the obvious improvement in the electrochemical performance of the Cu²⁺/Fe³⁺ modified NLMO is due to the additional overlaps between the Cu 3d and O 2p orbitals, which is beneficial for the RCM. As a result, the ARR is enhanced so as to increase the Na⁺ storage capacity. Full article

A series of fault depressions developed in the Kailu area on the southwestern margin of the Songliao Basin, where thick lacustrine fine-grained sedimentary rocks were widely deposited during the initial faulting stage in the Early Cretaceous. These formations serve as the primary source rocks within the depressions. To investigate the depositional cyclicity framework, paleoenvironmental conditions, and source rock development patterns of fine-grained sedimentary strata, this study focuses on the Naiman Sag, selecting Well Nai-10 for wavelet transform and spectral analysis based on natural gamma ray logs. Combining core, well logging, and geochemical element analyses, Milankovitch cycles within the Yixian Formation were identified. The relationship between theoretical orbital periods and sedimentary cycles in a single well was established, enabling the high-precision identification and classification of fine-grained sedimentary cycles. Furthermore, the study explores the sedimentary response to orbital forcing and the development patterns of source rocks. The results indicate that fine-grained sedimentary strata exhibit distinct Milankovitch cyclicity, with a strong correlation between astronomical periods and sedimentary cycles. Using the 100 kyr short eccentricity cycle as the tuning curve, an astronomical timescale and high-frequency cyclic division for the target interval were established. Under the control of long eccentricity cycles, sedimentation exhibits strong response characteristics: near the peak of short eccentricity cycles, the climate was warm and humid, redox conditions were strong, and precipitation was high, facilitating organic matter accumulation. Based on this response relationship, two ideal enrichment models of mudstone and shale under different paleoclimatic conditions are proposed, providing valuable insights for identifying high-quality source rocks and unconventional hydrocarbons in hydrocarbon exploration. Full article

Dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP) is a highly toxic organophosphorus insecticide, and its persistence in air, water, and soil poses potential threats to human health and ecosystems. Covalent triazine frameworks (CTFs), with their sufficient visible-light harvesting capacity, ameliorated charge separation, and exceptional redox ability, have emerged as promising candidates for the photocatalytic degradation of DDVP. Nevertheless, pure CTFs lack effective oxidative active sites, resulting in elevated reaction energy barriers during the photodegradation of DDVP. In this work, density functional theory (DFT) calculations were employed to investigate the impact of various oxygen-containing acid groups (-COOH, -HSO₃, -H₂PO₃) on DDVP photodegradation performance. First, simulations of the structure and optical properties of modified CTFs reveal that oxygen-containing acid groups induce surface distortion and result in a redshift in the absorption edge. Subsequently, analysis of the density of states, frontier molecular orbitals, surface electrostatic potential, work function, and dipole moment demonstrates that oxygen-containing acid groups enhance CTF polarization, facilitate charge separation, and ameliorate their oxidative capability. Additionally, the free-energy diagram of DDVP degradation uncovers that oxygen-containing acid groups lower the energy barrier by elevating the adsorption and activation capability of DDVP. Notably, -H₂PO₃ presents optimal potential for the photodegradation of DDVP by unique electronic structure and activation capability. This work offers a valuable reference for the development of oxygen-containing acid CTF-based photocatalysts applied in degrading toxic organophosphate pesticides. Full article

Phenothiazine-based photosensitizers bear the intrinsic potential to substitute various expensive organometallic dyes owing to the strong electron-donating nature of the former. If coupled with a strong acceptor unit and the length of N-alkyl chain is appropriately chosen, they can easily produce high efficiency levels in dye-sensitized solar cells. Here, three novel D-A dyes containing 1H-tetrazole-5-acrylic acid as an acceptor were synthesized by varying the N-alkyl chain length at its phenothiazine core and were exploited in dye-sensitized solar cells. Differential scanning calorimetry showed that the synthesized phenothiazine derivatives exhibited behavior characteristic of molecular glasses, with glass transition and melting temperatures in the range of 42–91 and 165–198 °C, respectively. Based on cyclic and differential pulse voltammetry measurements, it was evident that their lowest unoccupied molecular orbital (LUMO) (−3.01–−3.14 eV) and highest occupied molecular orbital (HOMO) (−5.28–−5.33 eV) values were fitted to the TiO₂ conduction band and the redox energy of I⁻/I₃⁻ in electrolyte, respectively. The experimental results were supported by density functional theory, which was also utilized for estimation of the adsorption energy of the dyes on the TiO₂ and its size. Finally, the compounds were tested in dye-sensitized solar cells, which were characterized based on current–voltage measurements. Additionally, for the compound giving the best photovoltaic response, the efficiency of the DSSCs was optimized by a photoanode modification involving the use of cosensitization and coadsorption approaches and the introduction of a blocking layer. Subsequently, two types of tandem dye-sensitized solar cells were constructed, which resulted in an increase in photovoltaic efficiency to 6.37%, as compared to DSSCs before modifications, with a power conversion value of 2.50%. Full article

Oxalate decarboxylase is an Mn- and O₂-dependent enzyme in the bicupin superfamily that catalyzes the redox-neutral disproportionation of the oxalate monoanion to form carbon dioxide and formate. Its best-studied isozyme is from Bacillus subtilis where it is stress-induced under low pH conditions. Current mechanistic schemes assume a monodentate binding mode of the substrate to the N-terminal active site Mn ion to make space for a presumed O₂ molecule, despite the fact that oxalate generally prefers to bind bidentate to Mn. We report on X-band ¹³C-electron nuclear double resonance (ENDOR) experiments on ¹³C-labeled oxalate bound to the active-site Mn(II) in wild-type oxalate decarboxylase at high pH, the catalytically impaired W96F mutant enzyme at low pH, and Mn(II) in aqueous solution. The ENDOR spectra of these samples are practically identical, which shows that the substrate binds bidentate (κO, κO’) to the active site Mn(II) ion. Domain-based local pair natural orbital coupled cluster singles and doubles (DLPNO-CCSD) calculations of the expected ¹³C hyperfine coupling constants for bidentate bound oxalate predict ENDOR spectra in good agreement with the experiment, supporting bidentate bound substrate. Geometry optimization of a substrate-bound minimal active site model by density functional theory shows two possible substrate coordination geometries, bidentate and monodentate. The bidentate structure is energetically preferred by ~4.7 kcal/mol. Our results revise a long-standing hypothesis regarding substrate binding in the enzyme and suggest that dioxygen does not bind to the active site Mn ion after substrate binds. The results are in agreement with our recent mechanistic hypothesis of substrate activation via a long-range electron transfer process involving the C-terminal Mn ion. Full article

Herein, motivated by the excellent redox properties of rod-shaped ceria (CeO₂-NR), a series of TM/CeO₂ catalysts, employing the first-row 3d transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) as active metal phases, were comparatively assessed under identical synthesis and reaction conditions to decipher the role of active metal in the CO₂ hydrogenation process. Notably, a volcano-type dependence of CO₂ hydrogenation activity/selectivity was disclosed as a function of metal entity revealing a maximum for the Ni-based sample. Ni/CeO₂ is extremely active and fully selective to methane (Y_CH4 = 90.8% at 350 °C), followed by Co/CeO₂ (Y_CH4 = 45.2%), whereas the rest of the metals present an inferior performance. No straightforward relationship was disclosed between the CO₂ hydrogenation performance and the textural, structural, and redox properties, whereas, on the other hand, a volcano-shaped trend was established with the relative concentration of oxygen vacancies and partially reduced Ce³⁺ species. The observed trend is also perfectly aligned with the previously reported volcano-type dependence of atomic hydrogen adsorption energy and CO₂ activation as a function of 3d-orbital electron number, revealing the key role of intrinsic electronic features of each metal in conjunction to metal–support interactions. Full article

This work investigated the substitution of the aldehyde with a pyran functional group in D-π-aldehyde dye to improve cell performance. This strategy was suggested by recent work that synthesized D-π-aldehyde dye, which achieved a maximum absorption wavelength that was only slightly off the threshold for an ideal sensitizer. Therefore, DFT and TD-DFT were used to investigate the effect of different pyran substituents to replace the aldehyde group. The pyran groups reduced the dye energy gap better than other known anchoring groups. The proposed dyes showed facile intermolecular charge transfer through the localization of HOMO and LUMO orbitals on the donor and acceptor parts, which promoted orbital overlap with the TiO₂ surface. The studied dyes have HOMO and LOMO energy levels that could regenerate electrons from redox potential electrodes and inject electrons into the TiO₂ conduction band. The lone pairs of oxygen atoms in pyran components act as nucleophile centers, facilitating adsorption on the TiO₂ surface through their electrophile atoms. Pyrans increased the efficacy of dye sensitizers by extending their absorbance range and causing the maximum peak to redshift deeper into the visible region. The effects of the pyran groups on photovoltaic properties such as light harvesting efficiency (LHE), free energy change of electron injection, and dye regeneration were investigated and discussed. The adsorption behaviors of the proposed dyes on the TiO₂ (1 1 0) surface were investigated by means of Monte Carlo simulations. The calculated adsorption energies indicates that pyran fragments, compared to the aldehyde in the main dye, had a greater ability to induce the adsorption onto the TiO₂ substrate. Full article

Pt supported on carbon (Pt/C) is deemed as the state-of-the-art catalyst towards oxygen reduction reactions (ORRs) in chemical and biological fuel cells. However, due to the high cost and scarcity of Pt, researchers have focused on the development of Earth-abundant non-precious metal catalysts, hoping to replace the traditional Pt/C catalyst and successfully commercialize the chemical and biological fuel cells. In this regard, electrocatalysts made of transition metals emerged as excellent candidates for ORRs, especially the electrocatalysts made of Fe and Co in combination with N-doped carbons, which produce potentially active M-N₄-C (M=Co, Fe) ORR sites. At present, however, the transition metal-based catalysts are popular; recently, electrocatalysts made of rare earth metals are emerging as efficient catalysts, due to the fact that rare earth metals also have the potential to form rare earth metal-N₄-C active sites, just like transition metal Fe-N₄-C/Co-N₄-C. In addition, mixed valance states and uniqueness of f-orbitals of the rare earth metals are believed to improve the redox properties of the catalyst that helps in enhancing ORR activity. Among the rare earth metals, Ce is the most interesting element that can be explored as an ORR electrocatalyst in combination with the N-doped carbon. Unique f-orbitals of Ce can induce distinctive electronic behavior to the catalyst that helps to form stable coordination structures with N-doped carbons, in addition to its excellent ability to scavenge the OH^● produced during ORRs, therefore helping in catalyst stability. In this study, we have synthesized Ce/N-C catalysts by a metal–organic framework and pyrolysis strategy. The ORR activity of Ce/N-C catalysts has been optimized by systematically increasing the Ce content and performing RDE studies in 0.1 M HClO₄ electrolyte. The Ce/N-C catalyst has been characterized systematically by both physicochemical and electrochemical characterizations. The optimized Ce/N-C-3 catalyst exhibited a half-wave potential of 0.68 V vs. RHE. In addition, the Ce/N-C-3 catalyst also delivered acceptable stability with a loss of 70 mV in its half-wave potential when compared to 110 mV loss for Pt/C (10 wt.%) catalyst, after 5000 potential cycles. When Ce/N-C-3 is used as a cathode catalyst in dual-chamber microbial fuel cells, it delivered a volumetric power density of ~300 mW m⁻³, along with an organic matter degradation of 74% after continuous operation of DCMFCs for 30 days. Full article

The role of dopants (Sm, Tb and Pr) on the water–gas shift performance of CeO₂-based materials was studied. Modification of CeO₂ with Sm significantly improved the water–gas shift performance. The catalytic activities of doped CeO₂ were increased when compared with the catalytic activities of pure ceria (65% conversion at 600 °C for Ce5%SmO and 50% conversion at 600 °C for CeO₂). The key factors driving the water–gas shift performance were reduction behavior and oxygen vacancy concentration. In the redox mechanism of the WGS reaction, CeO₂ plays a crucial role in transferring oxygen to CO through changes in the oxidation state. Therefore, Sm is effective in catalyzing the water–gas shift activity because the addition of Sm into CeO₂ decreases the surface reduction temperature and alters the oxygen transportation ability through the redox mechanism. XRD results suggested that Mⁿ⁺ (M = Sm, Tb and Pr) incorporate into ceria lattice to form a solid solution resulting in unit cell enlargement. The defect structure inside the CeO₂ lattice generates a strain on the oxide lattice and facilitates the generation of oxygen vacancies. XANES analysis revealed that Sm reduced CeO₂ easily by transporting its electron into the d-orbitals of Ce, thus giving rise to more Ce³⁺ at the CeO₂ surface. The presence of Ce³⁺ is a result of oxygen vacancy. Therefore, the high content of Ce³⁺ provides more oxygen vacancies. The oxygen vacancy formation results in easy oxygen exchange. Thus, reactive oxygen species can be generated and easily reduced by CO reactant, which enhances the WGS activity. Full article

The two-dimensional layered heterostructure have been demonstrated as an effective method for achieving efficient photocatalytic hydrogen production. In this work, we propose, for the first time, the creation of van der Waals heterostructures from monolayers of SiH and g-C₃N₄ using first-principle calculations. We also systematically investigated additional properties for the first time, such as the electronic structure and optical behavior of van der Waals heterostructures composed of SiH and g-C₃N₄ monolayers. The results of this study show that the SiH/g-C₃N₄ heterostructure is categorized as a type-II heterostructure, which has a bandgap of 2.268 eV. Furthermore, the SiH/g-C₃N₄ heterostructure interface was observed to efficiently separate and transfer photogenerated charges, resulting in an enhanced photocatalytic redox performance. Moreover, the calculation of HOMO (Highest occupied molecular orbital) and LUMO (Least unoccupied molecular orbital) and charge density difference can further confirm that the SiH/g-C₃N₄ heterojunction is a type-II heterojunction, which has excellent photocatalytic hydrogen production and water decomposition performance. In addition, the SiH/g-C₃N₄ heterostructure exhibited excellent HER (Hydrogen evolution reaction) efficiency. This is essential for the process of photocatalytic water splitting. In SiH/g-C₃N₄ heterojunctions, the redox potential required for water splitting is spanned by the band edge potential. Calculating the absorption spectra, it was discovered that the SiH/g-C₃N₄ heterostructure possesses outstanding optical properties within the visible-light range, implying its high efficiency in photocatalytic hydrogen production. This research provides a broader research direction for the investigation of novel efficient photocatalysts and offers effective theoretical guidance for future efficient photocatalysts. Full article

Redox-induced magnetic transformation in organic diradicals is an appealing phenomenon. In this study, we theoretically designed twelve couples of diradicals in which two nitroxide (NO) radical groups are connected to the redox-active couplers including p-benzoquinonyl, 1,4-naphthoquinyl, 9,10-anthraquinonyl, naphthacene-5,12-dione, pentacene-6,13-dione, hexacene-6,15-dione, pyrazinyl, quinoxalinyl, phenazinyl, 5,12-diazanaphthacene, 6,13-diazapentacene, and 6,15-diazahexacene. As evidenced at both the B3LYP and M06-2X levels of theory, the calculations reveal that the magnetic reversal can take place from ferromagnetism to antiferromagnetism, or vice versa, by means of redox method in these designed organic magnetic molecules. It was observed that p-benzoquinonyl, 1,4-naphthoquinyl, 9,10-anthraquinonyl, naphthacene-5,12-dione, pentacene-6,13-dione, and hexacene-6,15-dione-bridged NO diradicals produce antiferromagnetism while their dihydrogenated counterparts exhibit ferromagnetism. Similarly, pyrazinyl, quinoxalinyl, phenazinyl, 5,12-diazanaphthacene, 6,13-diazapentacene, and 6,15-diazahexacene-bridged NO diradicals present ferromagnetism while their dihydrogenated counterparts show antiferromagnetism. The differences in the magnetic behaviors and magnetic magnitudes of each of the twelve couples of diradicals could be attributed to their distinctly different spin-interacting pathways. It was found that the nature of the coupler and the length of the coupling path are important factors in controlling the magnitude of the magnetic exchange coupling constant J. Specifically, smaller HOMO-LUMO (HOMO: highest occupied molecular orbital, LUMO: lowest unoccupied molecular orbital) gaps of the couplers and shorter coupler lengths, as well as shorter linking bond lengths, can attain stronger magnetic interactions. In addition, a diradical with an extensively π-conjugated structure is beneficial to spin transport and can effectively promote magnetic coupling, yielding a large |J| accordingly. That is, a larger spin polarization can give rise to a stronger magnetic interaction. The sign of J for these studied diradicals can be predicted from the spin alternation rule, the shape of the singly occupied molecular orbitals (SOMOs), and the SOMO-SOMO energy gaps of the triplet state. This study paves the way for the rational design of magnetic molecular switches. Full article

Hybrid density functional theory has been employed to study the influence of interfacial oxygen (O), sulfur (S) and zinc (Zn) vacancies on the optoelectronic properties of ZnO/ZnS heterostructure. The results show that the O, S, and Zn vacancies can decrease cell volume of the ZnO/ZnS heterostructure, leading to slight deformation from the perfect heterostructure. The quasi-band gap of ZnO/ZnS heterostructure is remarkably reduced compared to the ZnO surface. Hence, the visible light response is enhanced in ZnO/ZnS heterostructure, which can be further improved by creating an interfacial S or O vacancy. Moreover, the removal of S or O atoms can generate lone electrons in the system, which can enhance n-type conductivity of the heterostructure. The O and S vacancies improve the contribution of the atomic orbitals of Zn_ZnO (Zn atom in ZnO), Zn_ZnS (Zn atom in ZnS), S and O to the valence band maximum (VB) of the heterostructure; while the Zn-vacancy remarkably improves the contribution of S states to the conduction band minimum (CB). The resultant type-II band alignment and large difference between the migration speed of electrons and holes can efficiently separate the photogenerated electron-hole pairs. The CB edge positions are more negative than the redox potentials of CO₂/CO and H₂O/H₂, and the VB edge positions are more positive than the redox potential of O₂/H₂O. Hence, all the systems under investigation can be potentially used as efficient photocatalysts for various applications like CO₂ reduction and water splitting. Full article

Redox properties of monoiminoacenaphthenes (MIANs) were studied using various electrochemical techniques. The potential values obtained were used for calculating the electrochemical gap value and corresponding frontier orbital difference energy. The first-peak-potential reduction of the MIANs was performed. As a result of controlled potential electrolysis, two-electron one-proton addition products were obtained. Additionally, the MIANs were exposed to one-electron chemical reduction by sodium and NaBH₄. Structures of three new sodium complexes, three products of electrochemical reduction, and one product of the reduction by NaBH₄ were studied using single-crystal X-ray diffraction. The MIANs reduced electrochemically by NaBH₄ represent salts, in which the protonated MIAN skeleton acts as an anion and Bu₄N⁺ or Na⁺ as a cation. In the case of sodium complexes, the anion radicals of MIANs are coordinated with sodium cations into tetranuclear complexes. The photophysical and electrochemical properties of all reduced MIAN products, as well as neutral forms, were studied both experimentally and quantum-chemically. Full article

Modifying non-precious metal porphyrins at the meso-position is sufficient to further improve the ability to activate O₂ and the selectivity of the corresponding redox products. In this study, a crown ether-appended Fe(III) porphyrin complex (FeTC₄PCl) was formed by replacing Fe(III) porphyrin (FeTPPCl) at the meso-position. The reactions of FeTPPCl and FeTC₄PCl catalysed by O₂ oxidation of cyclohexene under different conditions were studied, and three main products, 2-cyclohexen-1-ol (1), 2-cyclohexen-1-one (2), and 7-oxabicyclo[4.1.0]heptane (3), were obtained. The effects of reaction temperature, reaction time, and the addition of axial coordination compounds on the reactions were investigated. The conversion of cyclohexene reached 94% at 70 °C after 12 h, and the selectivity toward product 1 was 73%. The geometrical structure optimization, molecular orbital energy level analysis, atomic charge, spin density, and density of orbital states analysis of FeTPPCl, FeTC₄PCl, as well as the oxygenated complexes (Fe-O₂)TCPPCl and (Fe-O₂)TC₄PCl formed after adsorption of O_2, were carried out using the DFT method. The results of thermodynamic quantity variation with reaction temperature and Gibbs free energy variation were also analysed. Finally, based on experimental and theoretical analysis, the mechanism of the cyclohexene oxidation reaction with FeTC₄PCl as a catalyst and O₂ as an oxidant was deduced, and the reaction mechanism was obtained as a free radical chain reaction process. Full article

The cobalt complex (I) with cyclopentadienyl and 2-aminothiophenolate ligands was investigated as a homogeneous catalyst for electrochemical CO₂ reduction. By comparing its behavior with an analogous complex with the phenylenediamine (II), the effect of sulfur atom as a substituent has been evaluated. As a result, a positive shift of the reduction potential and the reversibility of the corresponding redox process have been observed, also suggesting a higher stability of the compound with sulfur. Under anhydrous conditions, complex I showed a higher current enhancement in the presence of CO₂ (9.41) in comparison with II (4.12). Moreover, the presence of only one -NH group in I explained the difference in the observed increases on the catalytic activity toward CO₂ due to the presence of water, with current enhancements of 22.73 and 24.40 for I and II, respectively. DFT calculations confirmed the effect of sulfur on the lowering of the energy of the frontier orbitals of I, highlighted by electrochemical measurements. Furthermore, the condensed Fukui function f ⁻ values agreed very well with the current enhancement observed in the absence of water. Full article