A poly-epoxy surface explored by Hartree-Fock ΔSCF simulations of C1s XPS spectra

Spiral Square Nanosheets Assembled from Ru Clusters

Spiral two-dimensional (2D) nanosheets exhibit unique physical and chemical phenomena due to their twisted structures. While self-assembly of clusters is an ideal strategy to form hierarchical 2D structures, it is challenging to form spiral nanosheets. Herein, we first report a screw dislocation involved assembled method to obtain 2D spiral cluster assembled nanosheets (CANs) with uniform square morphology. The 2D spiral Ru CANs with a length of approximately 4 μm and thickness of 20.7 ± 3.0 nm per layer were prepared via the assembly of 1-2 nm Ru clusters in the presence of molten block copolymer Pluronic F127. Cryo-electron microscopy (cryo-EM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) demonstrate the existence of screw dislocation in the spiral assembled structure. The X-ray absorption fine structure spectrum indicates that Ru clusters are Ru³⁺ species, and Ru atoms are mainly coordinated with Cl with a coordination number of 6.5. Fourier-transform infrared (FT-IR) spectra and solid-state nuclear magnetic resonance hydrogen spectra (¹H NMR) indicate that the assembly process of Ru clusters is formed by noncovalent interactions, including hydrogen bonding and hydrophilic interactions. Additionally, the Ru-F127 CANs exhibit excellent photothermal conversion performance in the near-infrared (NIR) region.

Exceptional Photocatalytic Activities of rGO Modified (B,N) Co-Doped WO3 , Coupled with CdSe QDs for One Photon Z-Scheme System: A Joint Experimental and DFT Study

Artificial Z-scheme, a tandem structure with two-step excitation process, has gained significant attention in energy production and environmental remediation. By effectively connecting and matching the band-gaps of two different photosystems, it is significant to utilize more photons for excellent photoactivity. Herein, a novel one-photon (same energy-two-photon) Z-scheme system is constructed between rGO modified boron-nitrogen co-doped-WO₃ , and coupled CdSe quantum dots-(QDs). The coctalyst-0.5%Rh_x Cr₂ O₃ (0.5RCr) modified amount-optimized sample 6%CdSe/1%rGO3%BN-WO₃ revealed an unprecedented visible-light driven overall-water-splitting to produce ≈51 µmol h^-1 g^-1 H₂ and 25.5 µmol h^-1 g^-1 O₂ , and it remained unchanged for 5 runs in 30 h. This superior performance is ascribed to the one-photon Z-scheme, which simultaneously stimulates a two photocatalysts system, and enhanced charge separation as revealed by various spectroscopy techniques. The density-functional theory is further utilized to understand the origin of this performance enhancement. This work provides a feasible strategy for constructing an efficient one-photon Z-scheme for practical applications.

Porous Carbon Substrate Improving the Sensing Performance of Copper Nanoparticles Toward Glucose

An accurate sensor to rapidly determine the glucose concentration is of significant importance for the human body health, as diabetes has become a very high incidence around the world. In this work, copper nanoparticles accommodated in porous carbon substrates (Cu NP@PC), synthesized by calcinating the filter papers impregnated with copper ions at high temperature, were designed as the electrode active materials for electrochemical sensing of glucose. During the formation of porous carbon, the copper nanoparticles spontaneously accommodated into the formed voids and constituted the half-covered composites. For the electrochemical glucose oxidation, the prepared Cu NP@PC composites exhibit much superior catalytic activity with the current density of 0.31 mA/cm2 at the potential of 0.55 V in the presence of 0.2 mM glucose. Based on the high electrochemical oxidation activity, the present Cu NP@PC composites also exhibit a superior glucose sensing performance. The sensitivity is determined to be 84.5 μA /(mmol.L) with a linear range of 0.01 ~ 1.1 mM and a low detection limit (LOD) of 2.1 μmol/L. Compared to that of non-porous carbon supported copper nanoparticles (Cu NP/C), this can be reasonable by the improved mass transfer and strengthened synergistic effect between copper nanoparticles and porous carbon substrates.

Chemical Interactions at the Al/Poly-Epoxy Interface Rationalized by DFT Calculations and a Comparative XPS Analysis

A metal-polymer interface is pertinent to numerous technological applications, especially in spatial sectors. The focus of this work is to elaborate on the metallization process of the poly-epoxy surface with aluminum thin films, using atomistic details. To this end, X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum and density functional theory calculations are employed. The interfacial bonding between Al atoms and the poly-epoxide surface, represented by a dimer model, is studied by determining adsorption energies and by simulating XPS spectra. The latter simulations are mainly performed using the ΔKS method, taking into account the initial and the final state effects. Simulated atom-by-atom metal deposition on model epoxy systems is attempted to further elucidate energetics of metallization and preferential arrangement of metal atoms at the interface. A fair agreement obtained between XPS experiments and computations rationalizes the interaction mechanism at the atomic scale explaining the formation of the Al/poly-epoxy interface. Electronic structure properties highlight the charge transfer from the Al atom(s) to dehydrogenated model epoxy system.

Model of the DGEBA-EDA Epoxy Polymer: Experiments and Simulation Using Classical Molecular Dynamics

Polyepoxy samples are synthesized from diglycidylether of bisphenol A (DGEBA) and ethylene diamine (EDA) monomers at a stoichiometric ratio of 2 DGEBA : 1 EDA in model conditions in order to promote a high degree of polymerization and a low density of defects and to try to approach the ideal models obtained by simulation. A slow polymerization (>24 h at ambient temperature) and a postcuring achieved in an inert atmosphere lead to a conversion degree of 92±2% and a midpoint glass transition temperature of 391±1 K. In parallel, a model is created with a multistep cross-linking procedure. In this work, all-atom molecular dynamics (MD) simulations are performed with LAMMPS and the GAFF 1.8 force field. In the initial liquid mixture of reactants (600 molecules), proper mixing is demonstrated by the calculation of the partial radial distribution functions (RDF), which show a minimum intermolecular distance of 2.8 Å and similar distributions for EDA-EDA, DGEBA-DGEBA, and DGEBA-EDA molecules in the simulation boxes. Then, in alternation with MD equilibrations, cross-linking is performed on frozen configurations by creating covalent bonds between reactive pairs within a reaction radius of 3 Å. The resulting boxes show conversion rates of 90-93% and densities close to the experimental value. Finally, a cooling ramp from 700 K to 25 K is applied in order to monitor the specific volume and the coefficient of volumetric thermal expansion (CVTE) of the polymer and to derive the glass transition temperature. Experimental thermomechanical analyses (TMA) compares well with simulations for both the specific volume and the CVTE evolutions with temperature. Whereas the uncertainty remains high with the fitting procedure used, we calculate a glass transition temperature of 390±8 K which compares very well with the experimental values (391±1 K from DSC and 380 K from TMA).

Molecular dynamics simulations of EPON-862/DETDA epoxy networks: structure, topology, elastic constants, and local dynamics

Structural, topological, mechanical and dynamical properties of EPON-862/DETDA epoxy networks are investigated with Molecular Dynamics (MD) simulations. The epoxy networks are composed of the resin Diglycidyl Ether Bisphenol F (DGEBF), also known as EPON-862, and the hardener Diethyl Toluene Diamine (DETDA). Systems with four different crosslinking degrees are examined; the effect of the degree of crosslinking on studied properties is thus determined. The computed quantities are retrieved by employing several simulation strategies and numerical methods of statistical mechanics in order to gain a rigorous and solid understanding of the aforementioned properties as well as to assess the accuracy and applicability of the methods employed. We quantify and analyze the local structure of the EPON-862/DETDA epoxy networks through the partial pair distribution functions, the Faber-Ziman partial structure factors and through simulated X-ray diffraction patterns, demonstrating good agreement with an experimental spectrum from a similar epoxy resin. The topology of the networks is examined with the aim of assessing percolation of connectivity, the properties of network fragments (subnetworks), and the distribution of functionalities of the crosslinks. The elastic constants of the systems are retrieved by employing two equilibrium (analysis of volume fluctuations, Parrinello-Rahman strain fluctuation relation) and one nonequilibrium (uniaxial tension/compression deformations at prescribed rate) method. Finally, the glass temperatures of the systems are estimated by calculating the density as a function of temperature and by analyzing the reorientational dynamics of bond vectors which describe relaxation processes at the segment level.