Understanding the Interface Enhancement Mechanisms of CFRP with the Polydopamine-Polyetheramine Interphase at the Molecular Level.

In this work, polydopamine (PDA) and polyetheramine D230 were selected to construct the PDA-D230 interphase between the carbon fiber (CF) and epoxy matrix. Density functional theory (DFT) and molecular dynamics (MD) simulations were performed to explore the interface enhancement mechanisms of a carbon fiber reinforced polymer (CFRP) with the PDA-D230 interphase from the molecular level. The adsorption characteristics of a PDA molecule on the CF surface were investigated using the DFT method. The results show that stronger π-π stacking interactions are formed due to the structure and orientation preference of the PDA molecule. The interfacial structures and properties of CFRP with the PDA-D230 interphase are derived from MD simulations. The PDA-D230 interphase on the CF surface induces stronger interfacial interaction energy, leading to the better load transfer between the CF and epoxy matrix. The existence of the PDA-D230 interphase on the CF surface can decrease the mean-square displacement (MSD) value and the free volume fraction of CFRP, which restricts the movement of epoxy atoms and inhibits the translational and rotational motion of epoxy chains. Compared with the epoxy using pristine CFs as reinforcement, the interfacial shear stress (ISS) of CFRP with the PDA-D230 interphase is improved by 13.1%. Our results provide valuable insights into the interface characteristics of CFRP with the PDA-D230 interphase, which are of great significance for exploring the strengthening mechanisms for CFRPs with the PDA-D230 interphase.

Catalytic System-Controlled Regioselective 1,2- and 1,4-Carboannulations of [60]Fullerene.

Selective functionalization of fullerenes is an important but challenging topic in fullerene chemistry and synthetic chemistry. Here we present the first example of catalytic system-controlled regioselective 1,2- and 1,4-addition reactions for the flexible and efficient synthesis of novel 1,2- and 1,4-carbocycle-fused fullerenes via a palladium-catalyzed decarboxylative carboannulation process.

Understanding and controlling the formation of single-atom site from supported Cu10 cluster by tuning CeO2 reducibility: Theoretical insight into the Gd-doping effect on electronic metal-support interaction.

Controlling the formation of single-atom (SA) sites from supported metal clusters is an important and interesting issue to effectively improve the catalytic performance of heterogeneous catalysts. For extensively studied CO oxidation over metal/CeO2 systems, the SA formation and stabilization under reaction conditions is generally attributed to CO adsorption, however, the pivotal role played by the reducible CeO2 support and the underlying electronic metal-support interaction (EMSI) are not yet fully understood. Based on a ceria-supported Cu10 catalyst model, we performed density functional theory calculations to investigate the intrinsic SA formation mechanism and discussed the synergistic effect of Gd-doped CeO2 and CO adsorption on the SA formation. The CeO2 reducibility is tuned with doped Gd content ranging from 12.5 % ∼ 25 %. Based on ab initio thermodynamic and ab initio molecular dynamics, the critical condition for SA formation was identified as 21.875 % Gd-doped CeO2 with CO-saturated adsorption on Cu10. Electronic analysis revealed that the open-shell lattice Oδ- (δ < 2) generated by Gd doping facilitates the charge transfer from the bottom-corner Cu (Cubc) to CeO2. The CO-saturated adsorption further promotes this charge transfer process and enhances the EMSI between Cubc and CeO2, leading to the disintegration of Cubc from Cu10 and subsequent formation of the active SA site.

Density Functional Theory Study of Methanol Steam Reforming on Pt3Sn(111) and the Promotion Effect of a Surface Hydroxy Group.

Methanol steam reforming (MSR) is studied on a Pt3Sn surface using the density functional theory (DFT). An MSR network is mapped out, including several reaction pathways. The main pathway proposed is CH3OH + OH → CH3O → CH2O → CH2O + OH → CH2OOH → CHOOH → COOH → COOH + OH → CO2 + H2O. The adsorption strengths of CH3OH, CH2O, CHOOH, H2O and CO2 are relatively weak, while other intermediates are strongly adsorbed on Pt3Sn(111). H2O decomposition to OH is the rate-determining step on Pt3Sn(111). The promotion effect of the OH group is remarkable on the conversions of CH3OH, CH2O and trans-COOH. In particular, the activation barriers of the O-H bond cleavage (e.g., CH3OH → CH3O and trans-COOH → CO2) decrease substantially by ~1 eV because of the involvement of OH. Compared with the case of MSR on Pt(111), the generation of OH from H2O decomposition is more competitive on Pt3Sn(111), and the presence of abundant OH facilitates the combination of CO with OH to generate COOH, which accounts for the improved CO tolerance of the PtSn alloy over pure Pt.

Understanding the Effect of Grain Boundaries on the Mechanical Properties of Epoxy/Graphene Composites.

This work presents a molecular dynamics (MD) simulation study on the effect of grain boundaries (GBs) on the mechanical properties of epoxy/graphene composites. Ten types of GB models were constructed and comparisons were made for epoxy/graphene composites containing graphene with GBs. The results showed that the tensile and compressive behaviors, the glass transition temperature (Tg), and the configurations of epoxy/graphene composites were significantly affected by GBs. The tensile yield strength of epoxy/graphene composites could be either enhanced or weakened by GBs under a tensile load parallel to the graphene sheet. The underlying mechanisms may be attributed to multi-factor coupling, including the tensile strength of the reinforcements, the interfacial interaction energy, and the inflection degree of reinforcements. A balance exists among these effect factors, resulting in the diversity in the tensile yield strength of epoxy/graphene composites. The compressive yield strength for epoxy/graphene composites is higher than their counterpart in tension. The tensile/compressive yield strength for the same configuration presents diversity in different directions. Both an excellent interfacial interaction and the appropriate inflection degree of wrinkles for GB configurations restrict the translational and rotational movements of epoxy chains during volume expansion, which eventually improves the overall Tg. Understanding the reinforcing mechanism for graphene with GBs from the atomistic level provides new physical insights to material design for epoxy-based composites containing defective reinforcements.

A novel frequency-dependent lattice Boltzmann model with a single force term for electromagnetic wave propagation in dispersive media.

Electromagnetic wave simulation is of pivotal importance in the design and implementation of photonic nano-structures. In this study, we developed a lattice Boltzmann model with a single extended force term (LBM-SEF) to simulate the propagation of electromagnetic waves in dispersive media. By reconstructing the solution of the macroscopic Maxwell equations using the lattice Boltzmann equation, the final form only involves an equilibrium term and a non-equilibrium force term. The two terms are evaluated using the macroscopic electromagnetic variables and the dispersive effect, respectively. The LBM-SEF scheme is capable of directly tracking the evolution of macroscopic electromagnetic variables, leading to lower virtual memory requirement and facilitating the implementation of physical boundary conditions. The mathematical consistency of the LBM-SEF with the Maxwell equations was validated by using the Champman-Enskog expansion; while three practical models were used to benchmark the numerical accuracy, stability, and flexibility of the proposed method.

Two-dimensional metal-organic frameworks as bifunctional electrocatalysts for the oxygen evolution reaction and oxygen reduction reaction (OER/ORR): a theoretical study.

Effective bifunctional catalysts are needed for the two main processes in metal-air batteries (oxygen evolution reaction and oxygen reduction reaction (OER/ORR)) to increase efficiency. Herein, we systematically investigate the stability, electronic structure, and catalytic performance of the OER/ORR of two-dimensional (2D) conducting metal-organic frameworks (MOFs) M3(C6Se6)2 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Ir, and Pt) by first-principles calculations. The results show that Co3(C6Se6)2 has an overpotential of 0.51 V and 0.3 V for the OER and ORR, respectively, and Rh3(C6Se6)2 has an overpotential of 0.53 V and 0.29 V for the OER and ORR, respectively, which are very promising bifunctional catalysts. In addition, Ir3(C6Se6)2 is a very promising ORR catalyst with a low overpotential of 0.34 V. Volcano plots and contour maps of OER/ORR activity versus intermediate adsorption strength were established to describe the activity trend of M3(C6Se6)2 based on the relationship of adsorbed intermediates. Furthermore, the d-band center theory and crystal orbital Hamilton populations (COHPs) were used to relate the OER/ORR activity to the d-electrons of the central metal. Our study not only provides a novel bifunctional electrocatalyst but also provides some references for other 2D MOFs as electrocatalysts.

First principles terahertz spectroscopy of molecular crystals: the crucial role of periodic boundary conditions benchmarked with experimental L-ascorbic acid spectra.

The terahertz (THz) region vibration spectral signatures of molecular crystals can usually be ascribed to the low-frequency vibrational modes related to weak intermolecular interactions, e.g. van der Waals (vdW) interactions or hydrogen bonding. These interactions collectively dictate the compositional units deviating from their equilibrium configurations. The collective movements are intrinsically long-range, and hence the boundary conditions used for theoretical calculation can affect the corresponding potential energy gradients and alter the vibrational features. In this work, we constructed a series of finite-sized cluster models with varying sizes and an extended periodic crystal model for L-ascorbic acid (L-AA) crystals. Density functionals with both semi-local contributions and nonlocal vdW terms, implemented with either atom-centered Gaussian basis or plane waves, were tested. By comparing first principles calculations with experimental time-domain spectra (TDS), we found that the non-local vdW functional opt-B88 combined with a periodic boundary condition is capable of assigning all the experimental features in the 0.2-1.6 THz region. Calculations with cluster models failed in this task. Even worse, the deficiency of the cluster models varied with cluster sizes, and did not converge as the cluster size grew. Our results demonstrate that an appropriate periodic boundary condition is essential to correctly assign and analyze the THz vibration spectra of molecular crystals.

Impacts of different biomass burning emission inventories: Simulations of atmospheric CO2 concentrations based on GEOS-Chem.

Biomass burning has substantial spatiotemporal variabilities. It contributes significantly to the dynamics of global CO2 distributions and variances. Quantifying the impacts of biomass burning emissions on atmospheric CO2 concentrations is essential for global and regional carbon cycles and budgets. In this study, we performed several numerical experiments by switching and replacing inventories to estimate the impacts of four biomass burning emission inventories on atmospheric CO2 concentration simulations in 2006-2010 based on the global chemical transport model, GEOS-Chem. The results highlighted similarities and differences in the annual and seasonal variability of biomass burning emissions and simulated CO2 concentrations at global and regional scales. Based on four different biomass burning emission inventories, we found that biomass burning emissions could lead to a global CO2 concentration increase of 2.4 ppm annually. Africa contributed the largest global CO2 emissions among all continental regions, where the maximum CO2 concentration increase could reach 7.9-13.0 ppm in summer. Model evaluation results showed that simulation using the Quick Fire Emissions Database (QFED) as the model priori biomass burning emission inventory had the best performance compared with the satellite and surface observations. The sensitivity of simulated CO2 concentrations to the uncertainties in different biomass burning emission inventories was high in southern South America and most areas of the Eurasian continent, and low in central Africa and Southeast Asia. This study furthers our understanding of the critical role of biomass burning in atmospheric CO2 and indicates an urgent need to improve the accuracy of biomass burning emission estimates in CO2 simulations.

Theoretical mechanism study on the electrochemical benzylation of [60]fullerene derivatives.

The electrochemical methodology is available for the functionalization of fullerenes. However, intricate and ambiguous issues remain to be identified for some electrochemical reactions. In this work, density functional theory (DFT) calculations reveal that the electron delocalization of C60 in fullerobenzofuran (RF5) and the C60-fused lactone (RL6) declines with the electron injection of electrochemistry, and clear active sites can be obtained to react with the electrophilic agent. Furthermore, the selectivity of the addition reaction depends on the Oδ- site, which is inclined to react with the Cδ+ of C60 after electron injection or the Cδ+ of PhCH2+, forming a new C-O bond.

Synergy of Substrate Chemical Environments and Single-Atom Catalysts Promotes Catalytic Performance: Nitrogen Reduction on Chiral and Defected Carbon Nanotubes.

The catalytic activities of single-atom catalysts (SACs) are strongly influenced by the local chemical environments of their substrates, by which the electronic structures of the SACs can be effectively tuned. Together with the freedom of available reactive metallic centers, it would be feasible to maximize the catalytic performance by means of a synergetic optimization in the chemical space spanned by the features of both the substrate and the catalytic center. In this work, using first-principles calculations, we systematically assessed the synergetic effect between the substrate geometric/electronic structures and the catalytic centers on the electrocatalytic nitrogen reduction reaction (NRR). Carbon nanotubes with different chirality, defects, and chemical functionalization were used to support 15 transition metal atoms. Three SACs, TiN4CNT(3,3), TiN4CNT(5,5), and VN4CNT(3,3), simultaneously possess high NRR selectivities (w.r.t hydrogen evolution) and low overpotentials of 0.35, 0.35, and 0.37 V, respectively. Electronic structure analysis elucidated that larger metal atoms anchored on CNTs with higher curvature and doped by N atoms facilitate the rupture of the N-N bond in *NH2NH2 to lower the overpotentials. The synergy of substrate chemical environments and single atomic catalysis is a promising strategy to optimize the catalytic performance.

Enhancing the Photoinduced Interlayer Charge Transfer and Spatial Separation in Type-II Heterostructure of WS2 and Asymmetric Janus-MoSSe with Intrinsic Self-Build Electric Field.

Two-dimensional heterostructure manipulation is promising to overcome the high recombination rates and limited redox abilities of photogenerated electron-hole pairs in a single photocatalyst. The built-in electric field (Ehetero) in the type-II heterojunction is normally unfavorable for the desired charge transfer, which is an important but easily neglected issue that needs to be solved. Here, on the basis of the density functional theory (DFT) and the nonadiabatic molecular dynamics (NAMD) calculations, we obtain a type-II band alignment in Janus-MoSSe/WS2 heterostructure, which meets the band-edge position requirement for water splitting. Importantly, the intrinsic self-build electric field (Eself) of Janus-MoSSe can effectively weaken the hindrance effect of Ehetero for charge transfer by constructing a suitable Se-S stacking configuration, improving charge separation efficiency in the Janus-MoSSe/WS2 heterostructure. Our work provides a materials-by-design paradigm and interlayer charge-transfer dynamics understanding of heterostructure engineering against asymmetric structures lacking reflection symmetry.

Polysaccharide and conjugate vaccines to Streptococcus pneumoniae generate distinct humoral responses.

Streptococcus pneumoniae is a major cause of community-acquired pneumonia, bacteremia, and meningitis in older adults worldwide. Two pneumococcal vaccines containing S. pneumoniae capsular polysaccharides are in current use: the polysaccharide vaccine PPSV23 and the glycoconjugate vaccine PCV13. In clinical trials, both vaccines elicit similar opsonophagocytic killing activity. In contrast to polysaccharide vaccines, conjugate vaccines have shown consistent efficacy against nasopharyngeal carriage and noninvasive pneumonia overall and for some prevalent individual serotypes. Given these different clinical profiles, it is crucial to understand the differential immunological responses induced by these two vaccines. Here, we used a high-throughput systems serology approach to profile the biophysical and functional features of serum antibodies induced by PCV13 and PPSV23 at 1 month and 1 year. In comparison with PPSV23, PCV13 induced higher titers across antibody isotypes; more durable antibody responses across immunoglobulin G (IgG), IgA, and IgM isotypes; and increased antigenic breadth. Although titers measured in opsonophagocytic activity (OPA) assays were similar between the two groups, confirming what was observed in clinical studies, serum samples from PCV13 vaccinees could induce additional non-OPA antibody-dependent functions, including monocyte phagocytosis and natural killer cell activation. In a multivariate modeling approach, distinct humoral profiles were demonstrated in each arm. Together, these results demonstrate that the glycoconjugate PCV13 vaccine induces an antigenically broader, more durable, polyfunctional antibody response. These findings may help explain the increased protection against S. pneumoniae colonization and noninvasive pneumonia and the longer duration of protection against invasive pneumococcal disease, mediated by PCV13.

Copper acetate-facilitated transfer-free growth of high-quality graphene for hydrovoltaic generators.

Direct synthesis of high-quality graphene on dielectric substrates without a transfer process is of vital importance for a variety of applications. Current strategies for boosting high-quality graphene growth, such as remote metal catalyzation, are limited by poor performance with respect to the release of metal catalysts and hence suffer from a problem with metal residues. Herein, we report an effective approach that utilizes a metal-containing species, copper acetate, to continuously supply copper clusters in a gaseous form to aid transfer-free growth of graphene over a wafer scale. The thus-derived graphene films were found to show reduced multilayer density and improved electrical performance and exhibited a carrier mobility of 8500 cm2 V-1 s-1. Furthermore, droplet-based hydrovoltaic electricity generator devices based on directly grown graphene were found to exhibit robust voltage output and long cyclic stability, in stark contrast to their counterparts based on transferred graphene, demonstrating the potential for emerging energy harvesting applications. The work presented here offers a promising solution to organize the metal catalytic booster toward transfer-free synthesis of high-quality graphene and enable smart energy generation.

Improved nitrogen reduction activity of NbSe2 tuned by edge chirality.

Efficient catalysts for the electroreduction of N2 to NH3 are of paramount importance for sustainable ammonia production. Recently, it was reported that NbSe2 nanosheets exhibit an excellent catalytic activity for nitrogen reduction under ambient conditions. However, existing theoretical calculations suggested an overpotential over 3.0 V, which is too high to interpret the experimental observations. To reveal the underlying mechanism of the high catalytic activity, in this work, we assessed NbSe2 edges with different chirality and Se vacancies by using first principles calculations. Our results show that N2 can be efficiently reduced to NH3 on a pristine zigzag edge via the enzymatic pathway with an overpotential of 0.45 V. Electronic structure analysis demonstrates that the N2 molecule is activated by the back-donation mechanism. The efficient tuning of the local chemical environments by edge chirality provides a promising approach for catalyst design.

Machine learning recognition of protein secondary structures based on two-dimensional spectroscopic descriptors.

Protein secondary structure discrimination is crucial for understanding their biological function. It is not generally possible to invert spectroscopic data to yield the structure. We present a machine learning protocol which uses two-dimensional UV (2DUV) spectra as pattern recognition descriptors, aiming at automated protein secondary structure determination from spectroscopic features. Accurate secondary structure recognition is obtained for homologous (97%) and nonhomologous (91%) protein segments, randomly selected from simulated model datasets. The advantage of 2DUV descriptors over one-dimensional linear absorption and circular dichroism spectra lies in the cross-peak information that reflects interactions between local regions of the protein. Thanks to their ultrafast (∼200 fs) nature, 2DUV measurements can be used in the future to probe conformational variations in the course of protein dynamics.

Ultrafast stimulated resonance Raman signatures of lithium polysulfides for shuttling effect characterization: An ab initio study.

The shuttling effect is a crucial obstacle to the practical deployment of lithium sulfur batteries (LSBs). This can be ascribed to the generation of lithium polysulfide (LiPS) redox intermediates that are soluble in the electrolyte. The detailed mechanism of the shuttling, including the chemical structures responsible for the loss of effective mass and the dynamics/kinetics of the redox reactions, are not clear so far. To obtain this microscopic information, characterization techniques with high spatial and temporal resolutions are required. Here, we propose that resonance Raman spectroscopy combined with ultrafast broadband pulses is a powerful tool to reveal the mechanism of the shuttling effect. By combining the chemical bond level spatial resolution of resonance Raman and the femtosecond scale temporal resolution of the ultrafast pulses, this novel technique holds the potential of capturing the spectroscopic fingerprints of the LiPS intermediates during the working stages of LSBs. Using ab initio simulations, we show that, in addition to the excitation energy selective enhancement, resonance Raman signals of different LiPS intermediates are also characteristic and distinguishable. These results will facilitate the real-time in situ monitoring of LiPS species and reveal the underlying mechanism of the shuttling effect.

Can N, S Cocoordination Promote Single Atom Catalyst Performance in CO2 RR? Fe-N2 S2 Porphyrin versus Fe-N4 Porphyrin.

Single atom catalysts (SACs) are promising electrocatalysts for CO2 reduction reaction (CO2 RR), in which the coordination environment plays a crucial role in intrinsic catalytic activity. Taking the regular Fe porphyrin (Fe-N4 porphyrin) as a probe, the study reveals that the introduction of opposable S atoms into N coordination (Fe-N2 S2 porphyrin) allows for an appropriate electronic structural optimization on active sites. Owing to the additional orbitals around the Fermi level and the abundant Fe dz2 orbital occupation after S substitution, N, S cocoordination can effectively tune SACs and thus facilitating protonation of intermediates during CO2 RR. CO2 RR mechanisms lead to possible C1 products via two-, six-, and eight-electron pathways are systematically elucidated on Fe-N4 porphyrin and Fe-N2 S2 porphyrin. Fe-N4 porphyrin yields the most favorable product of HCOOH with a limiting potential of -0.70 V. Fe-N2 S2 porphyrin exhibits low limiting potentials of -0.38 and -0.40 V for HCOOH and CH3 OH, respectively, surpassing those of most Cu-based catalysts and SACs. Hence, the N, S cocoordination might provide better catalytic environment than regular N coordination for SACs in CO2 RR. This work demonstrates Fe-N2 S2 porphyrin as a high-performance CO2 RR catalyst, and highlights N, S cocoordination regulation as an effective approach to fine tune high atomically dispersed electrocatalysts.

One-step Ethylene Purification from an Acetylene/Ethylene/Ethane Ternary Mixture by Cyclopentadiene Cobalt-Functionalized Metal-Organic Frameworks.

The separation of ethylene (C2 H4 ) from a mixture of ethane (C2 H6 ), ethylene (C2 H4 ), and acetylene (C2 H2 ) at normal temperature and pressure is a significant challenge. The sieving effect of pores is powerless due to the similar molecular size and kinetic diameter of these molecules. We report a new modification method based on a stable ftw topological Zr-MOF platform (MOF-525). Introduction of a cyclopentadiene cobalt functional group led to new ftw-type MOFs materials (UPC-612 and UPC-613), which increase the host-guest interaction and achieve efficient ethylene purification from the mixture of hydrocarbon gases. The high performance of UPC-612 and UPC-613 for C2 H2 /C2 H4 /C2 H6 separation has been verified by gas sorption isotherms, density functional theory (DFT), and experimentally determined breakthrough curves. This work provides a one-step separation of the ternary gas mixture and can further serve as a blueprint for the design and construction of function-oriented porous structures for such applications.

Computational study on the mechanism of hydroboration of CO2 catalysed by POCOP pincer nickel thiolate complexes: concerted catalysis and hydride transfer by a shuttle.

Hydroboration of carbon dioxide (CO2) catalysed by bis(phosphinite) (POCOP) pincer nickel complexes is among the most efficient homogeneous processes for the reduction of CO2 to the methanol level. Although both POCOP pincer nickel hydride and thiolate complexes are effective catalysts, the latter is far more effective under the same conditions. The mechanism for nickel hydride complexes catalysed reactions is well-established. However, that for nickel thiolate complex catalysed reactions remains elusive. In this work, the mechanism for the reduction of CO2 catalysed by POCOP pincer nickel thiolate complexes was investigated using density functional theory. The calculated results indicated that the reaction occurs via a concerted catalytic process involving two active species and the hydride is transferred by a shuttle species. Specifically, the reaction proceeds through four cycles: formation of two active species (cycle I) followed by further reaction of these two species to form a hydride transfer shuttle which is responsible for hydride transfers CO2→HCOOBcat (cycle II), HCOOBcat→CH2O (cycle III) and CH2O→catBOCH3 (cycle IV). The calculated mechanism is in good agreement with the experimental observation that the reaction is exothermic with simultaneous HBcat degradation.