Porous Carbon Materials Based on Graphdiyne Basis Units by the Incorporation of the Functional Groups and Li Atoms for Superior CO₂ Capture and Sequestration

The graphdiyne family has attracted a high degree of concern because of its intriguing and promising properties. However, graphdiyne materials reported to date represent only a tiny fraction of the possible combinations. In this work, we demonstrate a computational approach to generate a series of conceivable graphdiyne-based frameworks (GDY-Rs and Li@GDY-Rs) by introducing a variety of functional groups (R = −NH₂, −OH, −COOH, and −F) and doping metal (Li) in the molecular building blocks of graphdiyne without restriction of experimental conditions and rapidly screen the best candidates for the application of CO₂ capture and sequestration (CCS). The pore topology and morphology and CO₂ adsorption and separation properties of these frameworks are systematically investigated by combining density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations. On the basis of our computer simulations, combining Li-doping and hydroxyl groups strategies offer an unexpected synergistic effect for efficient CO₂ capture with an extremely CO₂ uptake of 4.83 mmol/g at 298 K and 1 bar. Combined with its superior selectivity (13 at 298 K and 1 bar) for CO₂ over CH₄, Li@GDY-OH is verified to be one of the most promising materials for CO₂ capture and separation

On the Gas-Phase Co⁺-Mediated Oxidation of Ethane by N₂O: A Mechanistic Study

The potential energy surface (PES) corresponding to the Co⁺-mediated oxidation of ethane by N₂O has been investigated by using density functional theory (DFT). After initial N₂O reduction by Co⁺ to CoO⁺, ethane oxidation by the nascent oxide involves C–H activation followed by two possible pathways, i.e., C–O coupling accounting for ethanol, Co⁺-mediated β–H shift giving the energetically favorable product of CoC₂H₄⁺ + H₂O, with minor CoOH₂⁺ + C₂H₄. CoC₂H₄⁺ could react with another N₂O to yield (C₂H₄)­Co⁺O, which could subsequently undergo a cyclization mechanism accounting for acetaldehyde and oxirane and/or a direct H-abstraction mechansim for ethenol. Loss of oxirane and ethenol is hampered by respective endothermicity and high kinetics barrier, whereas acetaldehyde elimination is much energetically favorable. CoOH₂⁺ could facilely react with N₂O to form OCoOH₂⁺, rather than Co­(OH)₂⁺ or CoO⁺

A Reaction Mechanism of Methane Coupling on a Silica-Supported Single-Site Tantalum Catalyst

Density functional theory calculations were utilized to study the reaction mechanisms of nonoxidative coupling of methane (NOCM) occurring on a silica-supported single-site tantalum (Ta) catalyst. Two catalytic cycles, namely, catalytic cycles A (CCA) and B (CCB), as well as other competing pathways, were investigated by exploring the potential energy surfaces for the reactions of interest. The supported methyltantalum [(SiO₃)₂Ta–CH₃] and tantalum hydride [(SiO₃)₂Ta–H] catalyzed the reaction of NOCM through CCA and CCB, respectively. CCA and CCB comprise five and six elementary steps, respectively. The two rate-determining states for both catalytic cycles were elucidated. The turnover number of methane conversion catalyzed by the supported methyltantalum was about 10⁵ larger than that catalyzed by the supported tantalum hydride. This large difference indicates that the former species is predominantly responsible for the conversion of methane to ethane

Theoretical Investigation of the Reaction of Mn⁺ with Ethylene Oxide

The potential energy surfaces of Mn⁺ reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO⁺, MnO, MnCH₂⁺, MnCH₃, and MnH⁺ are described in detail. Two types of encounter complexes of Mn⁺ with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn⁺ would insert into a C–O bond or the C–C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO⁺/MnO and MnH⁺ are formed in the C–O activation mechanism, while both C–O and C–C activations account for the MnCH₂⁺/MnCH₃ formation. Products MnO⁺, MnCH₂⁺, and MnH⁺ could be formed adiabatically on the quintet surface, while formation of MnO and MnCH₃ is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a⁵D is calculated to be more reactive than the ground state a⁷S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations

Theoretical Investigation of the Methanol Decomposition by Fe⁺ and Fe(C₂H₄)⁺: A π‑Type Ligand Effect

Density functional theory has been used to probe the mechanism of gas-phase methanol decomposition by bare Fe⁺ and ligated Fe­(C₂H₄)⁺ in both quartet and sextet states. For the Fe⁺/methanol system, Fe⁺ could directly attach to the O and methyl-H atoms of methanol, respectively, forming two encounter isomers. The methanol reaction with Fe⁺ prefers initial C–O bond activation to yield methyl with slight endothermicity, whereas CH₄ elimination is hindered by the strong endothermicity and high-energy barrier of hydroxyl-H shift. For the Fe­(C₂H₄)⁺/methanol system, the major product of H₂O is formed through six elementary steps: encounter complexation, C–O bond activation, C–C coupling, β-H shift, hydride H shift, and nonreactive dissociation. Both ligand exchange and initial C–O bond activation mechanisms could account for ethylene elimination with the ion products Fe­(CH₃OH)⁺ and (CH₃)­Fe­(OH)⁺, respectively. With the assistance of a π-type C₂H₄ ligand, the metal center in the Fe­(C₂H₄)⁺/CH₃OH system avoids formation of unfavorable multi-σ-type bonding and thus greatly enhances the reactivity compared to that of bare Fe⁺

Additional file 1: of Insights into the H2/CH4 Separation Through Two-Dimensional Graphene Channels: Influence of Edge Functionalization

Supporting information. Fig. S1. Final configurations of the 1:1 H2/CH4 mixture permeating through the 2D channel of pristine and edge-functionalized GMs (DOCX 4515 kb

Dithiafulvenyl Unit as a New Donor for High-Efficiency Dye-Sensitized Solar Cells: Synthesis and Demonstration of a Family of Metal-Free Organic Sensitizers

This work identifies the dithiafulvenyl unit as an excellent electron donor for constructing D−π–A-type metal-free organic sensitizers of dye-sensitized solar cells (DSCs). Synthesized and tested are three sensitizers all with this donor and a cyanoacrylic acid acceptor but differing in the phenyl (<b>DTF-C1</b>), biphenyl (<b>DTF-C2</b>), and phenyl–thiopheneyl–phenyl π-bridges (<b>DTF-C3</b>). Devices based on these dyes exhibit a dramatically improved performance with the increasing π-bridge length, culminating with DTF-C3 in η = 8.29% under standard global AM 1.5 illumination

Analysis of Petroleum Aromatics by Laser-Induced Acoustic Desorption/Tunable Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Laser-induced acoustic desorption coupled with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (LIAD/SVUVPI-MS) is employed to analyze aromatics prepared under different conditions from Lungu atmospheric residue (LGAR), i.e., the primary aromatics separated directly from LGAR, and the secondary aromatics after hydrogenation of LGAR and its resins. The mass spectra of the primary aromatics present a bimodal normal distribution in the range of 200–900 Da, in which the relative intensity of the two peaks changes significantly with the SVUV photon energies (9.0, 11.0, and 14.0 eV), indicating that at least two categories of compounds with different ionization energies (IEs) are included, i.e., polycyclic aromatics (IEs < 10.0 eV) in the mass range of 400–900 Da, and aliphatic and alicyclic compounds (IEs close to 11.0 eV) in 200–400 Da. Also detected in the aromatics are metalloporphyrins. Furthermore, the mass spectra of the secondary aromatics separated from LGAR and its resins at different hydrogenation temperatures (390, 400, 410, and 420 °C) are also recorded. The results indicate that the hydrogenation process, especially at higher temperatures, results in removal of alkyl-side and bridge chains in the aromatics, and the secondary aromatics from LGAR resins contain more alkyl side and bridge chains and metal compounds than those from LGAR

New Paradigm for Allosteric Regulation of Escherichia coli Aspartate Transcarbamoylase

For nearly 60 years, the ATP activation and the CTP inhibition of Escherichia coli aspartate trans­carbamoylase (ATCase) has been the textbook example of allosteric regulation. We present kinetic data and five X-ray structures determined in the absence and presence of a Mg²⁺ concentration within the physiological range. In the presence of 2 mM divalent cations (Mg²⁺, Ca²⁺, Zn²⁺), CTP does not significantly inhibit the enzyme, while the allosteric activation by ATP is enhanced. The data suggest that the actual allosteric inhibitor of ATCase in vivo is the combination of CTP, UTP, and a divalent cation, and the actual allosteric activator is a divalent cation with ATP or ATP and GTP. The structural data reveals that two NTPs can bind to each allosteric site with a divalent cation acting as a bridge between the triphosphates. Thus, the regulation of ATCase is far more complex than previously believed and calls many previous studies into question. The X-ray structures reveal that the catalytic chains undergo essentially no alternations; however, several regions of the regulatory chains undergo significant structural changes. Most significant is that the N-terminal region of the regulatory chains exists in different conformations in the allosterically activated and inhibited forms of the enzyme. Here, a new model of allosteric regulation is proposed

Metallic Iron–Nickel Sulfide Ultrathin Nanosheets As a Highly Active Electrocatalyst for Hydrogen Evolution Reaction in Acidic Media

We report on the synthesis of iron-nickel sulfide (INS) ultrathin nanosheets by topotactic conversion from a hydroxide precursor. The INS nanosheets exhibit excellent activity and stability in strong acidic solutions as a hydrogen evolution reaction (HER) catalyst, lending an attractive alternative to the Pt catalyst. The metallic α-INS nanosheets show an even lower overpotential of 105 mV at 10 mA/cm² and a smaller Tafel slope of 40 mV/dec. With the help of DFT calculations, the high specific surface area, facile ion transport and charge transfer, abundant electrochemical active sites, suitable H⁺ adsorption, and H₂ formation kinetics and energetics are proposed to contribute to the high activity of the INS ultrathin nanosheets toward HER