Chemphyschem最新文献

This study employs first-principles methods to investigate the ORR catalytic activity of As-doped and AsN co-doped graphene. As atoms, as catalytic active sites, exhibit excellent catalytic activity. Due to the strong interaction between As and N, the stability of the As-N co-doped substrate is enhanced. In particular, As-N4 co-doped graphene not only demonstrates the best thermodynamic and kinetic stability, but also has an ORR overpotential of only 0.53 V. We also propose a method to predict the Gibbs free energy change of the system by calculating the adsorption energies of the adsorbates. This approach can streamline the process by eliminating the need to calculate the Gibbs free energy of the ORR system, making it highly advantageous for future studies on the ORR catalytic activity of multi-impurity co-doped graphene.

The centrosymmetric constraint of Friedel's law in standard x-ray diffraction limits its ability to reveal complex molecular symmetry. In contrast, twisted x-ray diffraction with vortex beams, which carry orbital angular momentum, breaks Friedel's law yielding diffraction patterns that reflect the intrinsic symmetry of molecules. Through analytical derivations and numerical simulations, we demonstrate the enhanced sensitivity of twisted x-ray diffraction to the symmetry of M-fold symmetric molecules. Our results show that, while traditional standard x-ray diffraction struggles to distinguish between structurally similar molecules with different symmetries, twisted x-ray diffraction patterns can clearly differentiate these molecules. Additionally, we show that increasing the orbital angular momentum enhances the diffraction resolution and reveals finer symmetry-specific features of the molecules. This positions twisted x-ray diffraction as a promising tool for molecular imaging, capable of revealing intricate structures with complex symmetry.

The rheological behavior of porous ionic liquids comprising ZIF-8 suspensions in two Newtonian ionic liquids - trihexyltetradecylphos- phonium bis(trifluoromethylsulfonyl)imide and tri- hexyltetradecylphosphonium chloride - exhibited distinct and unexpected differences. ZIF-8 suspensions in the bis(trifluoromethylsulfonyl)imide-based liquid showed Bingham behavior with a measurable yield stress, whereas those in the chloride-based liquid remained Newtonian, even at high solid volume fractions of up to 17.4%. Remarkably, the viscosities of these porous liquids were not significantly higher than those of the pure ionic liquids. While explaining these behaviours, we could elucidate how the stability and dynamic properties of porous ionic liquids are governed by the highly structured liquid phases, determined experimentally and using molecular dynamics simulations, and by the balance between particle-particle and ZIF-8-ionic liquid inter- actions, as evidenced by the heat effects measured during particle dispersion.

Ionic liquids are nowadays investigated with respect to their use as electrolytes for high-performance energy storage materials. In this study, we provide a tutorial on how to calculate dynamic properties such as self-diffusion coefficients, ionic conductivities, transference numbers, as well as ion pair and ion cage dynamics, that all play a role in judging the applicability of ionic liquids as electrolytes.  For the case of the ionic liquid ce{[C2C1Im][NTf2]}, we investigate the performance of different force fields.  Amongst them are non-polarizable models employing unity charges, a charge-scaled version of a non-polarizable model, a polarizable model and another non-polarizable model with refined Lennard-Jones parameters. We also study the influence of the system size on the dynamic properties.  While all studied force field models capture qualitatively correct trends, only the polarizable force field and the non-polarizable force field with refined Lennard-Jones parameters provide quantitative agreement to reference data, making the latter model very attractive for the reason of lower computational costs.

Zr-based metal-organic frameworks (MOFs) are typically employed in heterogeneous catalysis due to their porosity, chemical and thermal stability, and well-defined active sites. Density functional theory (DFT) is the workhorse to compute their electronic structure; however, it becomes very costly when dealing with reaction mechanisms involving large unit cells and vast configurational spaces. Semiempirical quantum mechanical (SQM) methods appear as an alternative approach to simulate such chemical systems at low computational cost, but their feasibility to model catalysis with MOFs is still unexplored. Thus, here we present a benchmark study on UiO-66 to evaluate the performance of SQM methods (PM6, PM7, GFN1-xTB, GFN2-xTB) against hybrid DFT (M06). We evaluate defective nodes, ligand exchange reactions, barrier heights, and host-guest interactions with metal nanoclusters. Despite some caveats, GFN1-xTB on properly constrained models is the best SQM method across all studied properties. Under proper supervision, this protocol holds promise for application in exploratory high-throughput screenings of Zr-based MOF catalysts, subject to further refinement with more accurate methods.

Here, we used a combination of laser-induced experiments and density functional theory (DFT) calculations to study the mechanism of growth of carbonaceous species on the Mg surface. Experimental observations revealed that the carbon deposit forms upon laser illumination on the Mg surface, with the deposit being clearer and better structured in the presence of 1,3-butadiene (C4H6) compared to ethylene (C2H4) gas. DFT thermodynamic and kinetic calculations of C2-C4 hydrocarbons interaction on low-index Mg(0001) were used to explain this experimental observation. Our results on Mg(0001) showed that the cis isomer of C4H6 binds more strongly than its trans isomer via a [4+2] cycloaddition mechanism. We also investigated the adsorption of two units of C2H4 and C4H6 molecules, as well as the subsequent dehydrogenation stages that produce radical species responsible for chain growth mechanisms. The results showed that free energy of dehydrogenation of two units of cis-C4H6 [i. e. cis-C8H12] is lower than the dehydrogenation of trans conformer of C4H6 and C2H4 molecule, indicating that the dehydrogenation of two units of cis-C4H6 facilitates the initiation of growth of carbonaceous species on Mg surfaces. Therefore, the DFT calculations pinpoint the origin of the experimental observation of clearer carbon deposits on the Mg surface.

Elucidating the significance of low-energy electrons in the rupture of DNA/RNA and the process involved in it is crucial in the field of radiation therapy. Capturing of the incident electron in one of the empty molecular orbitals and the formation of a temporary negative ion (TNI) is considered to be a stepping stone towards the lesion of DNA/RNA. This TNI formation manifests itself as a resonance peak in the cross-sections determined for the electron-molecule interaction. In the present work, we have reported the integral (ICS), differential (DCS), and momentum transfer (MTCS) cross-sections for the elastic scattering of low-energy electrons from the isomers, 2H-pyran and 4H-pyran (C5H6O), which are analogues of the sugar backbone of DNA. The single-center expansion method has been employed for the scattering calculations. Further, we have used the time delay approach to identify and analyze the resonance peaks. Our results for the ICS and DCS compare well with the only data available in the literature. MTCS data for 2H-pyran and 4H-pyran have been reported for the first time. Moreover, we have also identified an extra peak for each molecule, from time delay analysis, which might be a potential resonance.

Since hydrogen is a promising alternative to fossil fuels due to its high energy density and environmental friendliness, water electrolysis for hydrogen production has received widespread attentions wherein the development of active and stable catalytic materials is a key research direction. This article designs a dual transition metal doped functional graphene for hydrogen evolution reaction via density functional theory calculations. Among varied combinations, 16 candidates are screened out that are expected to be stable as reflected by the criterion of formation energy Ef < 0 and active due to its free energy of hydrogen adsorption ∆GH within the window of ±0.3 eV. Considering its feasibility in structural modification and electronic adjustment due to the strong dd orbital couplings, the homogeneous dual-atom moiety delivers improved performance toward hydrogen evolution in comparison with the single-atom counterpart. Owing to the good resistance of electrochemical dissolution, the work figures out the potential combinations of Cu2C3N3, Rh2C6, Rh2C3N3 and Rh2N6 endowed with the ∆GH values of -0.03, 0.12, -0.21, and 0.06 eV, respectively, being comparable to the benchmark Pt materials. Therefore, this study provides a new direction for the experimental synthesis of highly active carbon-based electrocatalysts and highlights the well-tuning ability posed by dual-atom interaction.

Photoluminescence (PL) quenching mechanism and dynamics of carbon nanodots (CNDs) with molecular electron donor and acceptor is investigated by means of time resolved emission spectroscopy. CNDs are prepared by direct pyrolysis from two different precursors, di-ammonium citrate and tri-ammonium citrate, and at two different temperatures 150 °C and 180 °C and 40 hours under ambient conditions. Despite the small changes in the pyrolysis temperature rather significant differences are observed in the structure, PL quantum yield, and hence observation of the important characteristics of PL quenching kinetics in the presence of benzophenone and dimethoxybenzene as an electron acceptor and donors, respectively. Molecular dynamic simulations of CNDs in the presence of molecular quenchers support the spectroscopic data and the photophysical behavior of CNDs, and the distinct PL quenching dynamics are attributed to the hydrogen bonding interaction in case of BP and the π π-stacking interaction in case of DMB as PL quencher.

A halobenzene molecule contains several sites that are capable of acting in an electron-donating capacity within a H-bond.  One set of such sites comprise the lone electron pairs of the halogen (X) atoms on the periphery of the ring.  The π-electron system above the ring plane can also fulfill this function in many cases.  DFT calculations are applied to compare and contrast the propensity of these two site types to engage in such a H-bond within the context of mono, di, tri, tetra, and hexasubstituted halobenzenes.  The X atoms chosen for study comprise the full set: F, Cl, Br, and I.  It is found that even when the electrostatic potential of the X lone pair is more negative than that above the ring, it is the latter position which is the preferred binding site of HCl in most cases.  This preference switches over to the X lone pair only for higher order of substitution, with n=4 or 6.  This pattern is explained in large measure by the higher contribution of dispersion when the proton donor is located above the ring.