EDA-NOCV analysis of carbene-borylene bonded dinitrogen complexes for deeper bonding insight: A fair comparison with a metal-dinitrogen system

Binding of dinitrogen (N₂ ) to a transition metal center (M) and followed by its activation under milder conditions is no longer impossible; rather, it is routinely studied in laboratories by transition metal complexes. In contrast, binding of N₂ by main group elements has been a challenge for decades, until very recently, an exotic cAAC-borylene (cAAC = cyclic alkyl(amino) carbene) species showed similar binding affinity to kinetically inert and non-polar dinitrogen (N₂ ) gas under ambient conditions. Since then, N₂ binding by short lived borylene species has made a captivating news in different journals for its unusual features and future prospects. Herein, we carried out different types of DFT calculations, including EDA-NOCV analysis of the relevant cAAC-boron-dinitrogen complexes and their precursors, to shed light on the deeper insight of the bonding secret (EDA-NOCV = energy decomposition analysis coupled with natural orbital for chemical valence). The hidden bonding aspects have been uncovered and are presented in details. Additionally, similar calculations have been carried out in comparison with a selected stable dinitrogen bridged-diiron(I) complex. Singlet cAAC ligand is known to be an exotic stable species which, combined with the BAr group, produces an intermediate singlet electron-deficient (cAAC)(BAr) species possessing a high lying HOMO suitable for overlapping with the high lying π*-orbital of N₂ via effective π-backdonation. The BN₂ interaction energy has been compared with that of the FeN₂ bond. Our thorough bonding analysis might answer the unasked questions of experimental chemists about how boron compounds could mimic the transition metal of dinitrogen binding and activation, uncovering hidden bonding aspects. Importantly, Pauling repulsion energy also plays a crucial role and decides the binding efficiency in terms of intrinsic interaction energy between the boron-center and the N₂ ligand.

Active-Site-Specific Structural Engineering Enabled Ultrahigh Rate Performance of the NaLi3Fe3(PO4)2(P2O7) Cathode for Lithium-Ion Batteries

Iron-based mixed-polyanionic cathode Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) has advantages of environmental benignity, easy synthesis, high theoretical capacity, and remarkable stability. From NFPP, a novel Li-replaced material NaLi₃Fe₃(PO₄)₂(P₂O₇) (NLFPP) is synthesized through active Na-site structural engineering by an electrochemical ion exchange approach. The NLFPP cathode can show high reversible capacities of 103.2 and 90.3 mA h g^-1 at 0.5 and 5C, respectively. It also displays an impressive discharge capacity of 81.5 mA h g^-1 at an ultrahigh rate of 30C. Density functional theory (DFT) calculation demonstrates that the formation energy of NLFPP is the lowest among NLFPP, NFPP, and NaFe₃(PO₄)₂(P₂O₇), indicating that NLFPP is the easiest to form and the conversion from NFPP to NLFPP is thermodynamically favorable. The Li substitution for Na in the NFPP lattice causes an increase in the unit cell parameter c and decreases in a, b, and V, which are revealed by both DFT calculations and in situ X-ray powder diffraction (XRD) analysis. With hard carbon (HC) as the anode, the NLFPP//HC full cell shows a high reversible capacity of 91.1 mA h g^-1 at 2C and retains 82.4% after 200 cycles. The proposed active-site-specific structural tailoring via electrochemical ion exchange will give new insights into the design of high-performance cathodes for lithium-ion batteries.

Diastereoselective synthesis of a cyclic diamide-bridged biphenyl as chiral atropos ligand

Chiral compounds with a 1,2-diamine structure motif and their derivatives are of great interest in organic chemistry and are broadly used in asymmetric transformations, as chiral auxiliaries, (co)ligands, and ligand core structure. Here, we present a straightforward, diastereoselective synthesis for a diamide-bridged biaryl ligand. The ring closing reaction of the racemic atropos biphenyl 6,6'-dimethoxy-[1,1'-biphenyl]-2,2'-dicarboxylic acid with (R,R)-diaminocyclohexane yields the diasteromerically and enantiomerically pure cyclic (S_ax ,R,R)-BIPOL, which can be used as a versatile chiral ligand. By NMR spectroscopy, we observed the formation of intermolecular aggregates of the diamide-bridged BIPOL with anhydrous DMSO-d₆ . DFT calculations at the B3LYP/6-31G* level of theory corroborate the high interconversion barrier for the biaryl axis of ΔG^ǂ  = 148.7 kJ mol^-1 and the favoured formation of (S_ax ,R,R)-BIPOL as single stereoisomer.

Modeling amide-I vibrations of alanine dipeptide in solution by using neural network protocol

Infrared spectroscopy is a powerful tool for the understanding of molecular structure and function of polypeptides. Theoretical interpretation of IR spectra relies on ab initio calculations may be very costly in computational resources. Herein, we developed a neural network (NN) modeling protocol to evaluate a model dipeptide's backbone amide-I spectra. DFT calculations were performed for the amide-I vibrational motions and structural parameters of alanine dipeptide (ALAD) conformers in different micro-environments ranging from polar to non-polar ones. The obtained backbone dihedrals, C = O bond lengths and amide-I frequencies of ALAD were gather together for NN architecture. The applications of built NN protocols for the prediction of amide-I frequencies of ALAD in other solvation conditions are quite satisfactory with much less computational cost comparing with electronic structure calculations. The results show that this cost-effective way enables us to decipher the polypeptide's dynamic secondary structures and biological functions with their backbone vibrational probes.

Insight into the effects of oxygen vacancy on the toluene oxidation over α-MnO2 catalyst

In order to clarify the role of oxygen vacancy (OV), five α-MnO₂ catalysts with abundant OVs are fabricated via a novel and facile redox-precipitation approach and employed to the toluene oxidation in air. The concentration of OVs in α-MnO₂ catalysts is regulated via the alkyl chain length of alcohols, and its correlation with catalytic performances is scientifically investigated based on various characterization technologies and density functional theory (DFT) calculation. The α-MnO₂-C2 catalyst exhibits excellent catalytic activity (T₉₀ = 217 °C), stability, and water resistance for toluene oxidation in air. The OVs can induce the new bandgap states (BGS), which upshift the antibonding orbitals relative to the Fermi level (E_f), eventually favoring the formation of adsorbed active oxygen species. Furthermore, the OVs cause an increase in the amount of Mn³⁺, resulting in the elongated Mn-O bonds due to the strong Jahn-Teller effect of Mn³⁺. Therefore, the synergistic effects of OVs benefit toluene oxidation through L-H and MvK mechanisms over the prepared α-MnO₂-Cx catalysts. This work reveals the important role of OVs in the promotion of toluene catalytic oxidation activity and also may provide new insights for the design of high-performance VOCs oxidation elimination catalyst.

Dual-Atom Metal and Nonmetal Site Catalyst on a Single Nickel Atom Supported on a Hybridized BCN Nanosheet for Electrochemical CO2 Reduction to Methane: Combining High Activity and Selectivity

Atomically dispersed nitrogen-coordinated transition-metal sites supported on graphene (TM-N₄-C) offer promising potential for the electrochemical carbon dioxide reduction reaction (CO₂RR). However, a few TM-N_x-C single-atom catalysts (SAC) are capable of reducing CO₂ to multielectron products with high activity and selectivity. Herein, using density functional theory calculations, we investigated the electrocatalytic performance of a single TM atom embedded into a defective BCN nanosheet for CO₂RR. The N and B atom co-coordinated TM center, namely, TM-B₂N₂, constructs a symmetry-breaking site, which strengthens the overlapping of atomic orbitals, and enables the linear CO₂ to be curved and activated, compared to the weak coupling of CO₂ with the symmetric TM-N₄ site. Moreover, the TM-B₂N₂ sites play a role of dual-atom active sites, in which the TM atom serves as the carbon adsorption site and the B atom acts as the oxygen adsorption site, largely stabilizing the key intermediates, especially *COOH. The symmetry-breaking coordination structures shift the d-band center of the TM atom toward the Fermi level and thus facilitate CO₂ reduction to hydrocarbons and oxygenates. As a result, different from the TM-N₄-C structure that leads to CO as the major product, the Ni atom supported on BCN can selectively catalyze CO₂ conversion into CH₄, with an ultralow limiting potential of -0.07 V, while suppressing the hydrogen evolution reaction. Our finding suggests that introduction of a nonmetal active site adjacent to the metal site provides a new avenue for achieving efficient multi-intermediate electrocatalytic reactions.

Activation of the MoS2 Basal Plane to Enhance CO Hydrogenation to Methane Activity Through Increasing S Vacancies

The active site of MoS₂ is usually located at the edge of crystalline MoS₂, which has a lower proportion than that from the basal plane, limiting the hydrogenation activity. Therefore, activating the basal plane of MoS₂ is expected to greatly enhance the hydrogenation activity. Herein, we prepared a series of MoS₂ catalysts by acidolysis of ammonium tetrathiomolybdate and subsequently pyrolyzing at high temperature with different atmospheres. Through analysis, we found that the prepared MoS₂ catalysts were curved, which was different from commercial MoS₂. Through X-ray diffraction, transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy characterization, it was found that the MoS₂ catalyst pyrolyzed under a N₂ atmosphere had a larger number of S-vacancies than the MoS₂ catalysts under a H₂ atmosphere. In addition, temperature-programmed reduction results showed that the Mo-S bond energy was decreased with the increasing content of S-vacancies, which might be related to bending. Sulfur-resistant methanation results indicated that the curved MoS₂ exhibited increased CO conversion with the increasing S vacancies. Furthermore, density functional theory calculation was used to simulate the generation of S vacancy and numbers of S vacancies. It was found that with the generation of S vacancy, three unsaturated coordination Mo atoms were exposed around one S vacancy and became new active sites, resulting in enhanced activity. What is more, the higher methanation activity was attributed not only from more S vacancies but also from the decreased activation energy for CO hydrogenation activation.

Tube wall delamination engineering induces photogenerated carrier separation to achieve photocatalytic performance improvement of tubular g-C3N4

Morphology adjustment is a feasible method to change the physicochemical properties of photocatalysts. The issue that excessively thick tube wall of tubular g-C₃N₄ is not conducive to the electron migration from inside to the surface thus inhibiting the separation of photogenerated carriers has always been ignored. Potassium ions were used to regulate the structure of the tubular supramolecular precursor by breaking hydrogen bonds, thereby promoting the synthesis of delaminated laminar tubular g-C₃N₄ (K-CN), which not only shortened the transfer distance of photogenerated electrons but also provided abundant reaction active sites. Experiments and DFT calculations were combined to reveal the details of the physicochemical properties of K-CN. The photocatalytic capacity of K-CN for tetracycline hydrochloride (TCH) degradation and H₂O₂ generation were 83% and 133 μM, respectively. This work not only synthesized a novel delaminated tubular g-C₃N₄ but also provided a strategy and inspiration for structure and performance optimization for tubular g-C₃N₄.

Co-regulation of dispersion, exposure and defect sites on CeO2 (111) surface for catalytic oxidation of Hg0

The additional cost of Hg⁰ capture in coal-fired power plants has facilitated the demand for environmental pollutants mitigation material for Hg⁰ oxidation to Hg²⁺ for an ultra-low Hg emission technology. Herein, a suite of CeO₂-based catalysts were investigated aiming at ultra-low gaseous Hg⁰ emission at coal-fired power stations. Gaseous elemental mercury is feasible to be catalytically oxidized to Hg²⁺. The co-regulated dispersion, exposure and defect sites on CeO₂ (111) surface with 2 wt% Ce and 8 wt% Mo compositions on γ-Al₂O₃ was found to be the most promising catalyst demonstrating a high catalytic oxidation efficiency, a broad operating temperature range and a low activation energy. Specifically, it is shown that the oxidation of Hg⁰ on the Ce-based catalysts can be enhanced by the addition of Mo (up to 8 wt%) via promoting the CeO₂ (111) surface dispersion and exposure. Moreover, insights into the Ce and Mo synergistic interactions showed that it facilitated the formation of defect-containing surface sites. Besides, the co-regulation of dispersion, exposure and defect sites on CeO₂ (111) surface was further studied by DFT calculations. This study provides a feasible approach in optimization of CeO₂-based catalysts for catalytic oxidation of Hg⁰ to achieve efficient removal of environmental pollutants.

Theoretical and experimental insights into the mechanisms of C6/C6 PFPiA degradation by dielectric barrier discharge plasma

As an emerging alternative legacy perfluoroalkyl substance, C6/C6 PFPiA (perfluoroalkyl phosphinic acids) has been detected in aquatic environments and causes potential risks to human health. The degradation mechanisms of C6/C6 PFPiA in a dielectric barrier discharge (DBD) plasma system were explored using validated experimental data and density functional theory (DFT) calculations. Approximately 94.5% of C6/C6 PFPiA was degraded by plasma treatment within 15 min at 18 kV. A relatively higher discharge voltage and alkaline conditions favored its degradation. C6/C6 PFPiA degradation was attributed to attacks of •OH, •O₂^-, and ¹O₂. Besides PFHxPA and C2 -C6 shorter-chain perfluorocarboxylic acids, several other major intermediates including C4/C6 PFPiA, C4/C4 PFPiA, and C3/C3 PFPiA were identified. According to DFT calculations, the potential energy surface was proposed for possible reactions during C6/C6 PFPiA degradation in the discharge plasma system. Integrating the identified intermediates and DFT results, C6/C6 PFPiA degradation was deduced to occur by stepwise losing CF₂, free radical polymerization, and C-C bond cleavage. Furthermore, the DBD plasma treatment process decreased the toxicity of C6/C6 PFPiA to some extent. This study provides a comprehensive understanding of C6/C6 PFPiA degradation by plasma advanced oxidation.

Adsorption of serine at the anatase TiO2/water interface: A combined ATR-FTIR and DFT study

Knowledge of the adsorption reactions between serine and minerals is critical to understanding the geochemical processes of amino acids (i.e., mobility, bioavailability, and degradation) in the environment. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) flow-cell measurements were used to distinguish the inner- and outer-sphere complexation and reveal the dynamic adsorption and desorption processes of each surface complex at the molecular level. Density functional theory (DFT) calculations were applied to determine the structures of the surface complexes and to justify the peak assignments of the serine dissolved in solution and adsorbed on TiO₂. The structures of interfacial serine were governed by pH conditions but were not affected by the changes in adsorption time and serine concentration. The ATR-FTIR spectra and the results of DFT calculations resolved two different bidentate inner-sphere coordination, involving the COO^- group of the serine zwitterion at pH 4-8 and the serine anion at pH 10. The dynamic adsorption processes of these two surface complexes conformed to the pseudo-second-order kinetic model. The stable inner-sphere complexation could not be entirely removed from the TiO₂ surface upon serine desorption. In addition to reducing the migration rate in the environment, the bidentate inner-sphere coordination contributes to the potential degradation of the serine NH₃⁺ and NH₂ groups. Our research provides new insights into serine adsorption and desorption, facilitating further understanding of the fate and transport of amino acids in the environment.

Modulating the Electronic Structure of Nickel Sulfide Electrocatalysts by Chlorine Doping toward Highly Efficient Alkaline Hydrogen Evolution

The exploration of indurative and stable low-cost catalysts for hydrogen evolution reaction (HER) is of great importance for hydrogen energy economy, but it still faces challenges. Herein, we report a Cl-doped Ni₃S₂ (Cl-Ni₃S₂) nanoplate catalyst vertically grown on Ni foam with outstanding activity and durability for HER, which only requires an overpotential of 67 mV to reach a current density of 10 mA cm^-2 in alkaline media and exhibits negligible degradation after 30 h of operation. Both the advanced X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculation validate that Cl doping can optimize the electronic structure and the intrinsic activity of Ni₃S₂. This study devoted to the revelation of the impact of ionic doping on the activity of catalysts at the atomic scale can provide the direction for the rational design of novel and advanced HER electrocatalysts.

Heterojunction-Promoted Sodium Ion Storage of Bimetallic Selenides Encapsulated in a Carbon Sheath with Boosted Ion Diffusion and Stable Structure

Although metallic chalcogenides are deemed as attractive sodium anode materials recently, the electrochemical performance is severely confined by the liability of structural collapse and sluggish ion diffusion kinetics. Herein a composite of carbon-encapsulated bimetallic selenides MoSe₂-Sb₂Se₃ was prepared by a hydrothermal method on the basis of abundant reaction sites, high activity, an extra built-in electric field generated from heterointerfaces, and synergistic effects between the different components. Equally important, the carbon coating is effective to support the structural stability by restraining the vast volumetric variation to achieve the purpose of improving the cycling performance. The density functional theory calculation results indicate that the band gap is narrowed and that the work function is decreased on the interface of the MoSe₂-Sb₂Se₃ heterojunction, leading to an additional driving force stemming from the introduction of the built-in electric field and the formation of the Sb-Se (Se from MoSe₂) bond. Therefore, the resultant composite presents increased reaction kinetics and good electrochemical properties by acquiring a capacity of 376.0 mA h g^-1 over 580 cycles at 2.0 A g^-1 for the half-cell and 276 mA h g^-1 over 750 cycles at 2 A g^-1 for the full-cell. This work highlights bimetallic selenides with facilitated ion transferability with high performance.

TiO2-CeO2/g-C3N4 S-scheme heterostructure composite for enhanced photo-degradation and hydrogen evolution performance with combined experimental and DFT study

The g-C₃N₄/TiO₂ nanocomposites (NCs) are fabricated by optimization of calcination and subsequent hydrothermal technique decorated with CeO₂ nanoparticles (NPs) to build the g-C₃N₄/TiO₂-CeO₂ hybrid NCs. The chemical and surface characterizations of structural, morphological, elemental composition, optical, photo-degradation, HER performance and the DFT computation has been efficiently analyzed. The g-C₃N₄/TiO₂-CeO₂ composite photocatalysts (PCs) exhibit photocatalytic improved performance (∼97 %) for MB aqueous dye related to pristine g-C₃N₄ and g-C₃N₄/TiO₂ composite PCs. The obtained k value of the g-C₃N₄/TiO₂/CeO₂ heterostructure composite PCs has around 0.0262 min^-1 and 6.1, 2.6 and 1.5 times higher than to g-C₃N₄ (0.0043 min^-1), g-C₃N₄/CeO₂ (0.0099 min^-1) and g-C₃N₄/TiO₂ (0.0180 min^-1) PCs respectively. Likewise, the synergistic probable S-scheme charge separation mechanism based on scavengers' tests and other values, which leads to effective separation of photo-excited (e^--h⁺) pairs, whereas high degradation and more H₂O molecules have photo-reduction to H₂. The H₂ evolution reaction (HER) and the electrochemical impedance spectroscopy (EIS) of the as-obtained samples were explored via electrochemical study. This exertion recommends that the rational strategy and building of g-C₃N₄/TiO₂-CeO₂ nano-heterostructures were beneficial for developing visible-light-driven recyclable PCs for ecological refinement.

Multifunctional capacity of CoMnFe-LDH/LDO activated peroxymonosulfate for p-arsanilic acid removal and inorganic arsenic immobilization: Performance and surface-bound radical mechanism

Organoarsenic contaminants existing in water body threat human health and ecological environment due to insufficient bifunctional treatment technologies for organoarsenic degradation and inorganic arsenic immobilization. In order to safely and efficiently treat organoarsenic contaminants discharged into the aquatic environment, Co-Mn-Fe layered double hydroxide (CoMnFe-LDH) and Co-Mn-Fe layered double oxide (CoMnFe-LDO) were fabricated and employed as peroxymonosulfate (PMS) activator for organoarsenic degradation and inorganic arsenic immobilization, and p-arsanilic acid (p-ASA) was selected as target pollutant. Results demonstrated that the satisfactory removal of p-ASA (100.0%) in both CoMnFe-LDH/PMS and CoMnFe-LDO/PMS systems was obtained within 30 min, and substantial inorganic arsenic adsorption could be achieved (below 0.5 mg/L) in two systems with converting major inorganic arsenic species to arsenate. As XPS, ESR and quenching experiment revealed, the existence and generation of surface-bound radicals in two systems were identified. Based on density functional theory calculation and XPS analysis, the catalytic mechanism of CoMnFe-LDO/PMS system that PMS could be activated via direct electron transfer from adsorbed p-ASA was clarified, which differed from PMS activation via coupling with surface hydroxyl groups in CoMnFe-LDH/PMS system. Catalytic performance assessment under various critical operation parameters indicated that CoMnFe-LDH presented more stable ability of p-ASA removal in a wide pH range and complex aquatic environment. The recycle experiment demonstrated the excellent stability and reusability of CoMnFe-LDH(LDO). Besides, seven degradation products of p-ASA in CoMnFe-LDH/PMS system including phenolic compounds, azophenylarsonic acid, nitrobenzene and benzoquinne were identified by UV-Vis spectra and LC-TOF-MS analysis, and the corresponding degradation pathway was proposed. In summary, compared to CoMnFe-LDO/PMS, CoMnFe-LDH/PMS holds great promise for the development of an oxidation-adsorption process for efficient control of organoarsenic pollutant.

Computational Study of Key Mechanistic Details for a Proposed Copper (I)-Mediated Deconstructive Fluorination of N-Protected Cyclic Amines

Using calculations, we show that a proposed Cu(I)-mediated deconstructive fluorination of N-benzoylated cyclic amines with Selectfluor^® is feasible and may proceed through: (a) substrate coordination to a Cu(I) salt, (b) iminium ion formation followed by conversion to a hemiaminal, and (c) fluorination involving C-C cleavage of the hemiaminal. The iminium ion formation is calculated to proceed via a F-atom coupled electron transfer (FCET) mechanism to form, formally, a product arising from oxidative addition coupled with electron transfer (OA + ET). The subsequent β-C-C cleavage/fluorination of the hemiaminal intermediate may proceed via either ring-opening or deformylative fluorination pathways. The latter pathway is initiated by opening of the hemiaminal to give an aldehyde, followed by formyl H-atom abstraction by a TEDA²⁺ radical dication, decarbonylation, and fluorination of the C3-radical center by another equivalent of Selectfluor^®. In general, the mechanism for the proposed Cu(I)- mediated deconstructive C-H fluorination of N-benzoylated cyclic amines (LH) by Selectfluor^® was calculated to proceed analogously to our previously reported Ag(I)-mediated reaction. In comparison to the Ag(I)-mediated process, in the Cu(I)-mediated reaction the iminium ion formation and hemiaminal fluorination have lower associated energy barriers, whereas the product release and catalyst re-generation steps have higher barriers.

One-pot molten salt method for constructing CdS/C3N4 nanojunctions with highly enhanced photocatalytic performance for hydrogen evolution reaction

The construction of heterojunction photocatalysts for efficiently utilizing solar energy has attracted considerable attention to solve the energy crisis and reduce environmental pollution. In this study, we use the energy released from an easily-occurred exothermic chemical reaction to serve as the drive force to trigger the formation of CdS and C₃N₄ nanocomposites which are successfully fabricated with cadmium nitrate and thiourea without addition of any solvents and protection of inert gas at initial temperature, a little higher than the melting point of thiourea. The as-prepared CdS/C₃N₄ materials exhibit high efficiency for photocatalytic hydrogen evolution reaction (HER) with the HER rate as high as 15,866 μmol/(g∙hr) under visible light irradiation (λ > 420 nm), which is 89 and 9 times those of pristine C₃N₄ and CdS, respectively. Also, the apparent quantum efficiency (AQE) of CdS/C₃N₄-1:2-200-2 (CdS/C₃N₄-1:2-200-2 means the ratio of Cd to S is 1:2 and the reaction temperature is set at 200°C for two hours) reaches 3.25% at λ = 420 ± 15 nm. After irradiated for more than 24 hr, the HER efficiencies of CdS/C₃N₄ do not exhibit any attenuation. The DFT calculation suggests that the charge difference causes an internal electric field from C₃N₄ pointing to CdS, which can more effectively promote the transfer of photogenerated electrons from CdS to C₃N₄. Therefore, most HER should occur on C₃N₄ surface where photogenerated electrons accumulate, which largely protects CdS from photo-corrosion.

Lattice Matching and Halogen Regulation for Synergistically Induced Uniform Zinc Electrodeposition by Halogenated Ti3C2 MXenes

Dendrite growth and low Coulombic efficiency caused by uneven diffusion and electrodeposition of Zn²⁺ ions have emerged as a barrier to exploit the Zn metal anode. In this work, we demonstrate the stoichiometric halogenated MXenes (Ti₃C₂Cl₂, Ti₃C₂Br₂, and Ti₃C₂I₂) as an artificial layer that can induce the uniform Zn deposition. The efficient redistribution effect results from the coherent heterogeneous interface reconstruction and regulated ion tiling by halogen surficial termination. The synergetic effects of high lattice matching (90%) between the adopted MXenes and Zn, as well as the positive halogen regulation, Zn²⁺ ions are guided to nucleate uniformly on the most extensive (000l) crystal plane of the MXene matrix and grow in a planar manner. In terms of Zn ion regulation, Cl termination is found to be more effective than O/F, Br, and I due to its moderate adsorption and diffusion coefficiency for Zn²⁺ ions. The Ti₃C₂Cl₂-Zn anode achieves a life extension of over 12 times (840 h at 2 mA cm^-2//1 mAh cm^-2) over that of the bare Zn anode and serves more than 9000 cycles in a battery with a Ti₃C₂I₂ cathode at a high rate of 3 A g^-1. Given the abundance of lattice parameters and terminations of MXene materials, the developed strategy is expected to be extended to other metal anode systems.

Effective destruction of perfluorooctanoic acid by zero-valent iron laden biochar obtained from carbothermal reduction: Experimental and simulation study

This study investigated the degradation of perfluorooctanoic acid (PFOA) on zerovalent iron-laden biochar (BC-ZVI) prepared by carbothermal reduction. Results show that over 99% PFOA can be removed by BC-ZVI in hydrothermal conditions under 240 °C within 6 h. The maximum defluorination rate of 63.2% was achieved after 192 h, and this outcome was significantly better than biochar (BC) and zero-valent iron (ZVI) alone. The short-chain perfluorinated compounds (PFCs) and perfluoroheptanal were detected in the liquid phase after degradation, suggesting that the degradation of PFOAs by BC-ZVI followed the Kobel decarboxylation process. XRD and SEM-EDS analyses strongly suggested that carbothermal reduction could avoid the agglomeration of ZVI loaded onto biochar, which helped make the PFOA degradation more efficient. The frontier molecular orbital theory calculated by density functional theory revealed there were two possibilities for ZVI loading on BC (edged or internal loading), while the edge loaded ZVI had a greater tendency to provide electrons for the defluorination of PFOA than internally loaded ZVI.

A simple pyridine based fluorescent chemosensor for selective detection of copper ion

A feasibly constructed novel pyridine based receptor (S) has been reported for the selective detection of copper ion over other metal ions. The metal sensing ability of receptor with diverse metal ions were studied by colorimetry, absorption and emission spectroscopic systems in CH₃CN/H₂O (7:3, v/v). This receptor reveals a drastic color converts from vapid to yellow and cyan under normal light and UV light with copper ion. Further, S-Cu²⁺ complex exhibits new UV-Visible band at 419 nm and intense fluorescence band at 494 nm upon the excitation at 388 nm. The stoichiometric binding ratio of receptor with metal ion was confirmed with Job's method and ESI-Mass also further supported the complexation. Besides, limits of detection of Cu²⁺ were calculated to be 0.25 μM. The limiting capacity of receptor with Cu²⁺ ion was additionally explored by quantum chemical calculation. Moreover, this receptor was effectively utilized for the measurement of Cu²⁺ ion in various water tests.

Elucidation of a mechanism for the heterogeneous electro-fenton process and its application in the green treatment of azo dyes

Vast efforts are directed today toward the development of efficient, green methods for the degradation of toxic compounds, especially those that are water-soluble. Though Fenton reactions are commonly used in wastewater treatment, their mechanisms and the active species involved remain obscure due to their mechanistic complexity. In this work, the mechanism of an electro-Fenton reaction, in which a FeLaO₃ catalyst was entrapped in a sol-gel matrix, was studied in the presence of azo dyes as the model for toxic compounds. Increased knowledge about this important mechanism will confer greater control over related processes and enable a more efficient and green degradation method. DFT calculations showed that in the presence of Fe(IV), OH are formed under acidic conditions and that both the iron and hydroxyl species function as oxidation reagents in the degradation process. The structure of the formed Fe(IV) embedded in the solid matrix was not the typical tetravalent structure. Entrapment in the sol-gel matrix stabilized the catalyst, enhanced its efficiency and enabled it to be recycled. Sol-gel matrices constitute a simple method for the degradation of stable and toxic compounds under extreme pH conditions. The findings of this study are highly significant for the treatment of typically acidic wastewaters.

Enhanced oxygen transfer over bifunctional Mo-based oxametallacycle catalyst for epoxidation of propylene

Activation of inert propylene to produce propylene oxide (PO) is critical, but still faces some challenges in realizing higher PO selectivity and productivity. Herein, a temperature-controlled phase transfer catalyst (MoOO·DMF) is prepared for the liquid-phase epoxidation of propylene with tert-butyl hydroperoxide (TBHP) as oxidant, which exhibit the selectivity of 90.6% and the productivity of 1286.42·h^-1 for PO (catalyst/propylene = 0.77 mol‰). Some experimental factors (solvent types, reaction temperature, contact time, the dosage of catalyst, TBHP and substrate) were investigated, and the reaction kinetics and thermodynamics are discussed. MoOO·DMF has the characteristic of both homogeneous and heterogeneous catalysts, which can be dissolved in the solvent at higher temperatures and separated from the solvent after reaction by lowering the temperature. Importantly, MoOO·DMF has a wonderful epoxidation performance for many olefins (e.g., light olefins, linear α-olefins, cyclic olefins and others). The mechanisms are proved by in-situ FT-IR, ESR and HRMS spectrum to be the selective oxygen transfer from tert-butyl peroxide radical and the MoOO bridge in MoOO·DMF to propylene. Density functional theory (DFT) calculations show that the MoOO bridge in catalyst is the key role for the activation of both the OH bond in TBHP and the CC bond in propylene, thus enhanced the epoxidation of propylene.

Confining MoSe2 Nanosheets into N-Doped Hollow Porous Carbon Microspheres for Fast-Charged and Long-Life Potassium-Ion Storage

The potassium-ion battery (PIB) is the most promising alternative to a lithium-ion battery (LIB). Exploitation of a suitable electrode material is crucial to promote the development of PIBs. The MoSe₂ material has attracted much attention due to its high theoretical capacity, unique layered structure, and good conductivity. However, the potassium storage property of MoSe₂ has been suffering from structural fragmentation and sluggish reaction kinetic caused by large potassium ions upon insertion/extraction, which needs to be further improved. Herein, the MoSe₂ nanosheets are confined into N-doped hollow porous carbon microspheres (MoSe₂@N-HCS) by spray drying and high-temperature selenization. It delivers a superior rate performance of 113.7 mAh g^-1 at 10 A g^-1 and remains at a high capacity of 158.3 mAh g^-1 at 2 A g^-1 even after 16 700 cycles for PIBs. The excellent electrochemical performance can be attributed to unique structure, N-doping, and robust chemical bonds. The storage mechanism of MoSe₂ for potassium ions was explored. The outstanding properties of MoSe₂@N-HCS make it a promising anode material for PIBs.

A novel free-standing metal organic frameworks-derived cobalt sulfide polyhedron array for shuttle effect suppressive lithium-sulfur batteries

Metal-organic-frameworks-derived nanostructures have received broad attention for secondary batteries. However, many strategies focus on the preparation of dispersive materials, which need complicated steps and some additives for making electrodes of batteries. Here, we develop a novel free-standing Co₉S₈polyhedron array derived from ZIF-67, which grows on a three-dimensional carbon cloth for lithium-sulfur (Li-S) battery. The polar Co₉S₈provides strong chemical binding to immobilize polysulfides, which enables efficiently suppressing of the shuttle effect. The free-standing S@Co₉S₈polyhedron array-based cathode exhibits ultrahigh capacity of 1079 mAh g^-1after cycling 100 times at 0.1 C, and long cycling life of 500 cycles at 1 C, recoverable rate-performance and good temperature tolerance. Furthermore, the adsorption energies towards polysulfides are investigated by using density functional theory calculations, which display a strong binding with polysulfides.

Fragmentation efficiency of phenethylamines in electrospray ionization source estimated by theoretical chemistry calculation

Small molecules with polar functional groups, including substituted phenethylamines, are commonly analyzed by liquid chromatography-mass spectrometry (LC-MS) with electrospray ionization (ESI). Analyte molecules are mostly detected in protonated and cation-adducted forms through positive-ion electrospray ionization-mass spectrometry (ESI-MS). However, the ESI of substituted phenethylamines commonly provides an intense signal of fragment ions by ESI in-source collision-induced dissociation (IS-CID), which hinders the unambiguous identification of phenethylamines. This phenomenon was approximated as a unimolecular dissociation model, and the dissociation efficiency was evaluated by various quantum chemistry calculations to determine the ESI IS-CID efficiency. The calculated results were consistent with the experimental data, when the dissociation threshold energy of phenethylamines was calculated using the post-Hartree-Fock (post-HF) method, CCSD(t)/cc-pVTZ//MP2(full)/6-311++G(d,p). In contrast to post-HF methods, the utilization of density functional theory calculations with a suitable functional is recognized as an accurate and competitive low-cost approach. In particular, ωB97-XD, M06-2X-D3, and recently developed Minnesota functionals, such as M11, MN12-SX, and MN15, provided reliable results, as in the case of the post-HF method. The results obtained by the recently developed double hybrid functionals, DSD-PEBP86-D3(BJ), PBE0-DH, and PBE-QIDH, were also reliable. The consideration of ESI IS-CID can facilitate the identification of analyte molecules because most phenethylamines, except for N-methylated analogs, provide an intense signal in the ESI mass spectrum.