Combination Of DFT Calculations Research Articles

Dual effect of the coordination field and sulphuric acid on the properties of a single-atom catalyst in the electrosynthesis of H2O2.

Electrocatalytic synthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e- ORR) is the ideal solution for on-site H2O2 production. Herein, we propose a new strategy for creating new 2e- ORR catalysts by introducing electron-deficient B atoms and electron-rich N atoms to regulate the coordination field of metal ions on a graphene substrate. Through the first-principles density functional theory (DFT) calculations, NiN2B2-h was screened out as it had a low overpotential (0.12 V) for 2e- ORR. The Bader charge analysis revealed that B atoms increased the charge density of Ni atoms, leading to moderate binding of O2. Furthermore, the combination of ab initio molecular dynamic (AIMD) calculations and DFT calculations in an H2SO4 environment revealed a new reaction mechanism of H2O2 synthesis, involving proton-transfer between activated O2 and HSO4-. Moreover, the rate-determining step (0.63 eV) of H2O2 desorption in the presence of H2SO4 was different from that of OOH* protonation (0.45 eV) under the gas phase. This difference is attributed to the hydrogen-bond network in the acid solution.

Design and prediction of high potentansa-zirconocene catalyst for olefin polymerizations: combined DFT calculations and QSPR approach

Density functional calculations were carried out to predict activities, regio- and stereoselectivity, and to design newansa-zirconocene catalysts for olefin polymerizations.

Direct oxidation of methane to oxygenates on supported single Cu atom catalyst

Catalytically converting CH4 to chemicals and fuels is of paramount importance but remains a major challenge to simultaneously obtain high activity and selectivity. Here, we report Cu1/ZSM-5 single atom catalyst is highly active (C1 oxygenates productivity of 4800 μmol⋅gcat−1 at 50 °C and 12,000 μmol⋅gcat-1 at 70 °C within 30 min) and selective (C1 oxygenates selectivity of 99 % at 50 °C) for direct CH4 oxidation, comparable to most of those state-of-the-art noble metal catalysts. The combined DFT calculation, electronic microscope, X-ray absorption and electron paramagnetic resonance results confirm that each isolated Cu atom stabilized by four O moieties on the ZSM-5 support possesses uniform Cu1-O4 entity as active site and preferentially activates CH4 instead of CH3OH that is advantageous for highly selective C1 oxygenates production, especially for methanol. Our molecular-level finding on the atomic structure of Cu active site paves the way to design better catalysts for methane conversion.

Borasilylenes in Focus: Topological Effects of Nitrogen Atoms by DFT

DFT calculations in combination with appropriate isodesmic reactions are employed to assess topological effects of nitrogens on thermodynamic parameters of novel mono-, di-, tri-, tetra-, and pentaaza-7-boratricyclo[1,1,1,01,7,07,3,07,5]hexa-2-silylenes (1–20). Despite the enormous steric strain involved in their cubic structures, all our scrutinized singlet and triplet silylenes (1s-20s vs. 1t-20t, respectively) appear as minima on their energy surfaces, for showing singlet ground states. The highest stability (ΔEs−t) is achieved by 1,3,5-triaza-7-boratricyclo[1,1,1,01,7,07,3,07,5]hexa-2-silylene (11), where all the three nitrogens are bonded to the central boron atom. All of our silylenes show the same trend for their calculated ΔEs−t and band gap (ΔEHOMO−LUMO). Isodesmic reactions are employed to compare and contrast nucleophilicity (N), electrophilicity (ω), and heat of hydrogenation (ΔEH) for our 40 silylenes (1s-20s vs. 1t-20t). In fact, we introduce a novel generation of tridimensional silylenes which have the intrinsic potential of expanding the existing boundaries of semiconductors, cumulated multi-dentate ligands, etc..

Rare-Earth Single-Atom La-N Charge-Transfer Bridge on Carbon Nitride for Highly Efficient and Selective Photocatalytic CO2 Reduction.

Photocatalytic CO2 conversion into valuable solar fuels is highly appealing, but lack of directional charge-transfer channel and insufficient active sites resulted in limited CO2 reduction efficiency and selectivity for most photocatalytic systems. Herein, we designed and fabricated rare-earth La single-atoms on carbon nitride with La-N charge-transfer bridge as the active center for photocatalytic CO2 reaction. The formation of La single-atoms was certified by spherical aberration-corrected HAADF-STEM, STEM-EELS, EXAFS, and theoretical calculations. The electronic structure of the La-N bridge enables a high CO-yielding rate of 92 μmol·g-1·h-1 and CO selectivity of 80.3%, which is superior to most g-C3N4-based photocatalytic CO2 reductions. The CO production rate remained nearly constant under light irradiation for five cycles of 20 h, indicating its stability. The closely combined experimental and DFT calculations clearly elucidated that the variety of electronic states induced by 4f and 5d orbitals of the La single atom and the p-d orbital hybridization of La-N atoms enabled the formation of charge-transfer channel. The La-N charge bridges are found to function as the key active center for CO2 activation, rapid COOH* formation, and CO desorption. The present work would provide a mechanistic understanding into the utilization of rare-earth single-atoms in photocatalysis for solar energy conversion.

A combined molecular dynamic simulation, DFT calculations, and experimental study of the eriochrome black T dye adsorption onto chitosan in aqueous solutions

This study aims to evaluate and understand the adsorption of eriochrome black T (EB) by chitosan extracted from local shrimp shells under different experimental conditions. Chitosan samples were characterized by XRD, SEM, and FTIR. Experimental results indicate that the process was pH-dependent with a high adsorption capacity in acidic medium. The adsorption was rapid and kinetic data were suitably correlated to the pseudo-second-order kinetic model. EB molecules were adsorbed on monolayer according to the Langmuir model with an adsorption capacity of 162.3 mg/g. On the other hand, it should be noted that calculated quantum chemical parameters support the experimentally obtained results. The interaction energies calculated for (molecule/chitosan) complexes were in the order of H2EB− > HEB2− (O38) > HEB2− (O48) > EB > H3EB > EB3−, which means that the best and possible adsorption process can take place with H2EB− form. The molecular dynamics (MD) approach was performed to illuminate the nature of the relationship between the EB and the chitosan (110) surface. It was found that the chitosan (110) surface adsorbs EB molecule in a nearby parallel orientation. The higher negative adsorption energy determined for the H2EB− implies that the adsorption mechanism is the typical chemisorption.

Reaction Mechanism of CO2 and Styrene Oxide Catalyzed by Ionic Liquids: A Combined DFT Calculation and Experimental Study.

Bioactive compound 3-aryl-2-oxazolidinone could be synthesized by a green method mixing carbon dioxide, aniline, and ethylene oxide. Our group previously proposed a parallel mechanism for this conversion catalyzed by ionic liquids. Recently, a new study on a similar reaction system of styrene oxide, carbon dioxide, and aniline under the catalysis of K3PO4 gave a different serial mechanism. In order to explore the mechanism of reaction, we conducted a combined theoretical and experimental study on a one-pot conversion of styrene oxide, carbon dioxide, and aniline. In experiments, two isomer products, 3,5-diphenyl-l,3-oxazolidin-2-one and 3,4-diphenyl-l,3-oxazolidin-2-one, were observed. The computational results show that the parallel mechanism is more favored in thermodynamics and in kinetics due to the instability of isocyanate and hardness of its generation. Hence, we believe the previous parallel mechanism is more reasonable under our catalysts and conditions.

Unilaterally Fluorinated Acenes: Synthesis and Solid-State Properties.

The rapid development of organic electronics is closely related to the availability of molecular materials with specific electronic properties. Here, we introduce a novel synthetic route enabling a unilateral functionalization of acenes along their long side, which is demonstrated by the synthesis of 1,2,10,11,12,14‐hexafluoropentacene (1) and the related 1,2,9,10,11‐pentafluorotetracene (2). Quantum chemical DFT calculations in combination with optical and X‐ray absorption spectroscopy data indicate that the single‐molecule properties of 1 are a connecting link between the organic semiconductor model systems pentacene (PEN) and perfluoropentacene (PFP). In contrast, the crystal structure analysis reveals a different packing motif than for the parent molecules. This can be related to distinct F⋅⋅⋅H interactions identified in the corresponding Hirshfeld surface analysis and also affects solid‐state properties such as the exciton binding energy and the sublimation enthalpy.

Achieving Fast and Durable Lithium Storage through Amorphous FeP Nanoparticles Encapsulated in Ultrathin 3D P-Doped Porous Carbon Nanosheets.

Conversion-type transition-metal phosphide anode materials with high theoretical capacity usually suffer from low-rate capability and severe capacity decay, which are mainly caused by their inferior electronic conductivities and large volumetric variations together with the poor reversibility of discharge product (Li3P), impeding their practical applications. Herein, guided by density functional theory calculations, these obstacles are simultaneously mitigated by confining amorphous FeP nanoparticles into ultrathin 3D interconnected P-doped porous carbon nanosheets (denoted as FeP@CNs) via a facile approach, forming an intriguing 3D flake-CNs-like configuration. As an anode for lithium-ion batteries (LIBs), the resulting FeP@CNs electrode not only reaches a high reversible capacity (837 mA h g-1 after 300 cycles at 0.2 A g-1) and an exceptional rate capability (403 mA h g-1 at 16 A g-1) but also exhibits extraordinary durability (2500 cycles, 563 mA h g-1 at 4 A g-1, 98% capacity retention). By combining DFT calculations, in situ transmission electron microscopy, and a suite of ex situ microscopic and spectroscopic techniques, we show that the superior performances of FeP@CNs anode originate from its prominent structural and compositional merits, which render fast electron/ion-transport kinetics and abundant active sites (amorphous FeP nanoparticles and structural defects in P-doped CNs) for charge storage, promote the reversibility of conversion reactions, and buffer the volume variations while preventing pulverization/aggregation of FeP during cycling, thus enabling a high rate and highly durable lithium storage. Furthermore, a full cell composed of the prelithiated FeP@CNs anode and commercial LiFePO4 cathode exhibits impressive rate performance while maintaining superior cycling stability. This work fundamentally and experimentally presents a facile and effective structural engineering strategy for markedly improving the performance of conversion-type anodes for advanced LIBs.

Polyesters by a Radical Pathway: Rationalization of the Cyclic Ketene Acetal Efficiency.

Radical ring-opening polymerization (rROP) of cyclic ketene acetals (CKAs) combines the advantages of both ring-opening polymerization and radical polymerization thereby allowing the robust production of polyesters coupled with the mild polymerization conditions of a radical process. rROP was recently rejuvenated by the possibility to copolymerize CKAs with classic vinyl monomers leading to the insertion of cleavable functionality into a vinyl-based copolymer backbone and thus imparting (bio)degradability. Such materials are suitable for a large scope of applications, particularly within the biomedical field. The competition between the ring-opening and ring-retaining propagation routes is a major complication in the development of efficient CKA monomers, ultimately leading to the use of only four monomers that are known to completely ring-open under all experimental conditions. In this article we investigate the radical ring-opening polymerization of model CKA monomers and demonstrate by the combination of DFT calculations and kinetic modeling using PREDICI software that we are now able to predict in silico the ring-opening ability of CKA monomers.

Polyesters by a Radical Pathway: Rationalization of the Cyclic Ketene Acetal Efficiency

AbstractRadical ring‐opening polymerization (rROP) of cyclic ketene acetals (CKAs) combines the advantages of both ring‐opening polymerization and radical polymerization thereby allowing the robust production of polyesters coupled with the mild polymerization conditions of a radical process. rROP was recently rejuvenated by the possibility to copolymerize CKAs with classic vinyl monomers leading to the insertion of cleavable functionality into a vinyl‐based copolymer backbone and thus imparting (bio)degradability. Such materials are suitable for a large scope of applications, particularly within the biomedical field. The competition between the ring‐opening and ring‐retaining propagation routes is a major complication in the development of efficient CKA monomers, ultimately leading to the use of only four monomers that are known to completely ring‐open under all experimental conditions. In this article we investigate the radical ring‐opening polymerization of model CKA monomers and demonstrate by the combination of DFT calculations and kinetic modeling using PREDICI software that we are now able to predict in silico the ring‐opening ability of CKA monomers.

Insights into the Mechanism of Hydroxyl Radical Mediated Oxidations of 2-Aminopurine: A Computational and Sonochemical Product Analysis Study.

Mechanistic details of hydroxyl radical (•OH) mediated oxidations of 2-aminopurine (2AP) in the aqueous phase have been established in this study via a combination of DFT calculations (at the M05-2X/6-311+G(d,p) level with SMD solvation) and sonochemical end product analyses by the LC-Q-TOF-MS/MS method. Rate constants and branching ratios for single electron transfer (SET), two H-abstractions (HA), and seven radical adduct formation (RAF) reactions of •OH with 2AP were evaluated using transition state theory (TST). The RAF at the C8-position of 2AP is noted as the dominant process, which constitutes almost 46.1% of overall reaction routes. The SET mechanism accounts for the second major pathway (39.6%) followed by RAF at the C6-position (14.3%). Formations of 14 transformation products (TPs, i.e., the nonradical end products) in the sonochemical reactions of •OH with 2AP have been identified by means of the LC-Q-TOF-MS/MS technique. Among the 14 TPs (designated as TP1 to TP14), the lowest and highest mass to charge ratio (m/z) were respectively observed at 129 and 269 in ESI-MS positive ionization mode. The identities of all TPs have been proposed on the basis of elemental composition of [M + H]+ ions and their respective MS-MS fragmentation pattern. Four TPs (including guanine) are considered as obtained directly from primary transients by radical elimination, radical-radical combination/disproportionation reactions. The remaining 10 TPs are postulated as a result of successive self- and/or cross-reactions of primary transients/four first generation TPs with reagents such as •OH, O2, and solvent H2O molecules.

Properties and Reactivities of Niclosamide in Different Media, a Potential Antiviral to Treatment of COVID-19 by Using DFT Calculations and Molecular Docking

In this work, the structural, electronic, topological and vibrational properties of potential antiviral to treatment of COVID-19, niclosamide (NCL) have been studied in different media together with its reactivities by combination of DFT calculations with molecular docking. Properties of two most stable conformers of niclosamide (C1 and C2) were reported in gas phase and water, ethanol and chloroform solvents. Calculations using the integral equation formalism variant polarised continuum (IEFPCM) and solvation methods in the different solutions have revealed solvation energy values for C1 and C2 in aqueous solution (GC= -78.43 and -64.53 kJ/mol, respectively) comparable with that observed for the antiviral agent zalcitabine (-78.92 kJ/mol). Probably, the high stability of C1, predicted by NBO studies, explains the experimental existence of C1 in the solid phase. Comparisons of frontier orbitals with eleven antiviral agents have evidenced the high reactivity of C2 slightly higher than brincidofovir, an antiviral agent used in the treatment to ebola disease. Possibly, the presence of deactivating groups (NO2 and Cl) in the chloro-4-nitrophenyl and hydroxybenzamide rings of both forms of NCL could explain the higher reactivities predicted in the different media. Here, the harmonic force fields and force constants for both forms are reported together with the assignments of 80 vibration modes expected in the experimental infrared spectrum of NCL. The predicted UV-Vis spectra in the different solvents suggest the presence of both forms of NCL in solution. Molecular docking results were discussed basing on the type of interaction between the ligands and several amino acid residues.

Site-Specific Activity of Pt Single Crystal Surfaces for Oxygen Reduction Reaction

Development of industrial electrocatalysts with improved performance strongly relies on the fundamental understanding of the model systems. Pt(111) surface is probably the simplest, the most fundamental and thus also the most classic model systems for studying the hydrogen and oxygen electrocatalysis, among others. While the wide terrace has long been taken for granted to be the playground of the electrocatalytic reactions, here we demonstrate that such a hypothesis is far incomplete. By combining DFT calculations with experimental measurements, we unravel a 1-2 nm zone with 50% to 5000% activity enhancement for oxygen reduction reaction, which are induced by intrinsic strain that is generated because of the release of surface stress. We further demonstrate how this mechanistic understanding can be utilized to improve the activity of both model electrocatalysts and industrial electrocatalysts.

The importance of intermediates ring-opening in preventing photocatalyst deactivation during toluene decomposition

The deactivation of photocatalysts is the main barrier that diminishes the commercial value of photocatalytic air-purification technology. It is essential to explore the intrinsic origins for the deactivation and develop effective strategy to address this key issue. This work investigates the intrinsic reasons for VOCs-decomposition induced intermediates accumulation on the surface of TiO2 (P25) based on the combined experiments and DFT calculations. The main culprit of deactivation is the accumulation of benzaldehyde intermediate on the surface of P25 because of its high reaction energy of aromatic ring opening. This will lead to the facilitated conversion of benzaldehyde to benzoic acid that will thus occupy the active sites on the surface of P25. However, the wide gap β-Ga2O3 achieved the excellent deactivation resistance during prolonged VOCs degradation, which is derived from that the fact that the adsorbed intermediates will be activated on the surface of β-Ga2O3 and strengthen the aromatic ring opening via •OH radicals, thus realizing efficient mineralization of the ring-containing intermediates into inorganic small molecules (CO2 and H2O). This work points out that the deactivation-resistant property of photocatalyst is closely related to the adsorption activation and the ring-opening characteristics of the intermediates, which could provide a new perspective in development of efficient and deactivation-resistant photocatalysts for practical applications.

A novel in-situ chemical oxidation channel – Selective pH-dependence of refractory β-lactam antibiotics in the synergistic mechanism of persulfate and g-C3N4 under visible light

The degradation characteristics of four typical structures of β-lactam antibiotics were studied during the synergistic oxidation mechanism of persulfate (PS) and mesoporous g-C3N4 (MCN) under visible light irradiation including amoxicillin (AMX), cefotaxime (CFX), meropenem (MER), and sulbactam (SUL). Notably, the degradation of SUL in the MCN/PS system exhibits a pH-dependence different from the other three antibiotics. In this work, a novel oxidation channel for such persistent organic pollutant was revealed. Initially, SUL was bound specifically with PS via the addition reaction caused by the electron transfer between the oxygen atoms of the sulfoxide group of SUL and the HSO3− group generated by the protonation of PS. The reaction was carried out under acidic conditions and generated the SUL-O-SO2H byproducts. Successively, the adduct was further oxidized by the free radicals and singlet oxygen until the intermediate products were completely mineralized. The environmental factors of the reaction, such as the presence of humic acid and the cation-anion interactions, were also considered. In this work, the degradation pathways of SUL, the hydrolysis of the β-lactam ring, the decarboxylation, and the deamination reaction based on the combination of DFT calculations and the HPLC-QTOF-MS/MS analysis are elucidated. The toxicity of the byproducts was also calculated via the USEPA TEST. The findings improve the understanding of the reaction mechanism of the persulfate and the photocatalytic systems and provide new ideas for the oxidative degradation of refractory organic contaminants.

Electronic Properties of Oxidized Cyclometalated Diiridium Complexes: Spin Delocalization Controlled by the Mutual Position of the Iridium Centers.

Four cyclometalated diiridium complexes, with IrCp*Cl (Cp*=η5 -C5 Me5 - ) termini bridged by 1,4- and 1,3-bis(p-tolyliminoethyl)benzene (1, 2), or 1,4- and 1,3-bis(2-pyridyl)benzene (3, 4), were prepared and characterized by nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray diffraction (complexes 1, 2, and 4). The two iridium centers in complexes 1 and 3 are thus bound at the central benzene ring in the para-position (trans-Ir2), whereas those in complexes 2 and 4 are in the meta-position (cis-Ir2). Cyclic voltammograms of all four complexes show two consecutive one-electron oxidations. The potential difference between the two anodic steps in 1 and 3 is distinctly larger than that for 2 and 4. The visible-near-infrared (NIR)-short-wave infrared (SWIR) absorption spectra of trans-Ir2 monocations 1+ and 3+ are markedly different from those of cis-Ir2 monocations 2+ and 4+ . Notably, strong near-infrared electronic absorption appears only in the spectra of 1+ and 3+ whereas 2+ and 4+ absorb only weakly in the NIR-SWIR region. Combined DFT and TD-DFT calculations have revealed that (a) 1+ and 3+ (the diiridium-benzene trans-isomers) display the highest occupied spin-orbitals (HOSO) and the lowest unoccupied spin-orbital (LUSO) evenly delocalized over both molecule halves, and (b) their electronic absorptions in the NIR-SWIR region are attributed to mixed metal-to-ligand and ligand-to-ligand charge transfers (MLCT and LLCT). In contrast, cis-isomers 2+ and 4+ do not feature this stabilizing π-delocalization but a localized mixed-valence state showing a weak intervalence charge-transfer (IVCT) absorption in the SWIR region.

Synergistic Pt-WO3 Dual Active Sites to Boost Hydrogen Production from Ammonia Borane.

SummaryDevelopment of synergistic heterogeneous catalysts with active sites working cooperatively has been a pursuit of chemists. Herein, we report for the first time the fabrication and manipulation of Pt-WO3 dual-active-sites to boost hydrogen generation from ammonia borane. A combination of DFT calculations, structural characterization, and kinetic (isotopic) analysis reveals that Pt and WO3 act as the active sites for ammonia borane and H2O activation, respectively. A trade-off between the promoting effect of WO3 and the negative effect of decreased Pt binding energy contributes to a volcano-shaped activity, and Pt/CNT-5W delivers a 4-fold increased activity of 710.1 molH2·molPt−1·min−1. Moreover, WO3 is suggested to simultaneously act as the sacrificial site that can divert B-containing by-products away from Pt sites against deactivation, yielding an increase from 24% to 68% of the initial activity after five cycles. The strategy demonstrated here could shed a new light on the design and manipulation of dual-active-site catalysts.

High-Performance K-CO2 Batteries Based on Metal-Free Carbon Electrocatalysts.

Metal-CO2 batteries have attracted much attention owing to their high energy density and use of greenhouse CO2 waste as the energy source. However, the increasing cost of lithium and the low discharge potential of Na-CO2 batteries create obstacles for practical applications of Li/Na-CO2 batteries. Recently, earth-abundant potassium ions have attracted considerable interest as fast ionic charge carriers for electrochemical energy storage. Herein, we report the first K-CO2 battery with a carbon-based metal-free electrocatalyst. The battery shows a higher theoretical discharge potential (E⊖ =2.48 V) than that of Na-CO2 batteries (E⊖ =2.35 V) and can operate for more than 250 cycles (1500 h) with a cutoff capacity of 300 mA h g-1 . Combined DFT calculations and experimental observations revealed a reaction mechanism involving the reversible formation and decomposition of P121 /c1-type K2 CO3 at the efficient carbon-based catalyst.

High‐Performance K–CO2 Batteries Based on Metal‐Free Carbon Electrocatalysts

AbstractMetal–CO2 batteries have attracted much attention owing to their high energy density and use of greenhouse CO2 waste as the energy source. However, the increasing cost of lithium and the low discharge potential of Na–CO2 batteries create obstacles for practical applications of Li/Na–CO2 batteries. Recently, earth‐abundant potassium ions have attracted considerable interest as fast ionic charge carriers for electrochemical energy storage. Herein, we report the first K–CO2 battery with a carbon‐based metal‐free electrocatalyst. The battery shows a higher theoretical discharge potential (E⊖=2.48 V) than that of Na–CO2 batteries (E⊖=2.35 V) and can operate for more than 250 cycles (1500 h) with a cutoff capacity of 300 mA h g−1. Combined DFT calculations and experimental observations revealed a reaction mechanism involving the reversible formation and decomposition of P121/c1‐type K2CO3 at the efficient carbon‐based catalyst.