The properties of the hydrated amorphous polyamide (PA) membrane and its binding with alginate are investigated through molecular dynamics simulations. The density of the hydrated membrane, surface morphology, and water diffusion near and inside the membrane are compared to other studies. Particular focus is given to the steered molecular dynamics (SMD) simulation of the binding between the PA membrane and an alginate model. The PA surface composition is determined on the basis of experimental measurements of the oxygen/nitrogen (O/N) ratio. The surface model is built using a configurational-bias Monte Carlo technique. The consistent valence force field (CVFF) is used to describe the atomic interactions in the membrane-foulant system. Simulation results show that the carboxylate groups in both the PA surface and alginate exhibit strong binding with metal ions. This binding mechanism plays a major role in the PA-alginate fouling through the formation of an ionic binding bridge. Specifically, Ca(2+) ions have stronger binding with the carboxylate group than Na(+) ions, while the binding breakdown time is shorter for Ca(2+) than Na(+) because of the comparably higher hydration free energy of Ca(2+) ions with water molecules.

We perform molecular dynamics (MD) simulations to investigate the cross-linked polyamide (PA) membrane, the aggregation of alginate molecules in the presence of Ca(2+) ions, and their molecular binding mechanism in aqueous solution. We use a steered molecular dynamics (SMD) approach to simulate the unbinding process between a PA membrane and an alginate gel complex. Simulation results show that Ca(2+) ions are strongly associated with the carboxylate groups in alginate molecules, forming a web structure. The adhesion force between alginate gel and PA surface during unbinding originates from several important molecular interactions. These include the short-range hydrogen bonding and van der Waals attraction forces, and the ionic bridge binding that extends much longer pulling distances due to the significant chain deformations of alginate gel and PA membrane.

The structure and dynamics of water–methane fluids between clay surfaces are investigated through the grand-canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The chemical potentials of water and methane at the temperatures and pressures corresponding to different burial depths are calculated. These chemical potentials are used in the GCMC simulations to determine the water and methane contents in the clay interlayer at a burial depth of 6 km. The results are used as initial inputs for further MD simulations to investigate the static and dynamic properties of the confined fluid. Simulation results show that initial clay swelling is dominated by water adsorption into clay interlayer, followed by the formation of methane hydrates as the basal spacing increases. Methane content in clay is found to increase in a step fashion, from initial inner-sphere complex to both inner- and outer-sphere structures. It is found that methane is not fully coordinated by water molecules due to the low density of water content in Na-montmorillonite clay.

We carried out umbrella sampling and molecular dynamics (MD) simulations to investigate molecular interactions between sulfobetaine zwitterions or between sulfobetaine brushes in different media. Simulation results show that it is more energetically favorable for the two sulfobetaine zwitterions or brushes to be fully hydrated in aqueous solutions than in vacuum where strong ion pairs are formed. Structural properties of the hydrated sulfobetaine brush array and its antifouling behavior against a foulant gel are subsequently studied through steered MD simulations. We find that sulfobetaine brush arrays with different grafting densities have different structures and antifouling mechanisms. At a comparably higher grafting density, the sulfobetaine brush array exhibits a more organized structure which can hold a tightly bound hydration water layer at the interface. Compression of this hydration layer results in a strong repulsive force. However, at a comparably lower grafting density, the brush array exhibits a randomly oriented structure in which the antifouling of the brush array is through the deformation of the sulfobetaine branches.

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Tuning the interfacial perimeter and structure is crucial to understanding the origin of catalytic performance. This paper describes the design, characterization, and application of CeO2 modified Au@SBA-15 (Au-CeO2@SBA-15) catalysts in selective oxidation of benzyl alcohol. The reaction results showed that Au-CeO2@SBA-15 catalysts exhibited higher catalytic activity compared with Au@SBA-15 and Au/CeO2 catalysts under identical conditions along with the high selectivity towards benzaldehyde (>99%). The turnover frequency of benzyl alcohol over the Au-100CeO2@SBA-15 catalyst is about nine-fold and four-fold higher than those of Au@SBA-15 and Au/CeO2 catalysts, respectively. The supported catalysts were characterized by N2 adsorption-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, scanning transmission electron microscopy-energy dispersive spectrometry, and X-ray photoelectron spectroscopy. It was found that the Au and small CeO2 nanoparticles (∼5 nm) were homogeneously mixed in the channels of SBA-15, which led to an increase in the interfacial area between Au and CeO2 and consequently a better catalytic performance of Au-CeO2@SBA-15 catalysts for the selective oxidation of benzyl alcohol to benzaldehyde compared with that of Au/CeO2. The prevention of agglomeration and leaching of Au nanoparticles by restricting them inside the mesopores of SBA-15 was conducive to the stable existence of large quantities of Au-CeO2 interface, which leads to high stability of the Au-CeO2@SBA-15 catalyst.

Trigonal tellurium (Te) is a chiral semiconductor that lacks both mirror and inversion symmetries, resulting in complex band structures with Weyl crossings and unique spin textures. Detailed time-resolved polarized reflectance spectroscopy is used to investigate its band structure and carrier dynamics. The polarized transient spectra reveal optical transitions between the uppermost spin-split H 4 and H 5 and the degenerate H 6 valence bands (VB) and the lowest degenerate H 6 conduction band (CB) as well as a higher energy transition at the Lpoint. Surprisingly, the degeneracy of the H 6 CB (a proposed Weyl node) is lifted and the spin-split VB gap is reduced upon photoexcitation before relaxing to equilibrium as the carriers decay. Using ab initio density functional theory (DFT) calculations, we conclude that the dynamic band structure is caused by a photoinduced shear strain in the Te film that breaks the screw symmetry of the crystal. The band-edge anisotropy is also reflected in the hot carrier decay rate, which is a factor of two slower along the c-axis than perpendicular to it. The majority of photoexcited carriers near the band-edge are seen to recombine within 30 ps while higher lying transitions observed near 1.2 eV appear to have substantially longer lifetimes, potentially due to contributions of intervalley processes in the recombination rate. These new findings shed light on the strong correlation between photoinduced carriers and electronic structure in anisotropic crystals, which opens a potential pathway for designing novel Te-based devices that take advantage of the topological structures as well as strong spin-related properties.

The synthesis, characterization, and application of silica-supported Cu-Au bimetallic catalysts in selective hydrogenation of cinnamaldehyde are described. The results showed that Cu-Au/SiO 2 bimetallic catalysts were superior to monometallic Cu/SiO 2 and Au/SiO 2 catalysts under identical conditions. Adding a small amount of gold (6Cu-1.4Au/SiO 2 catalyst) afforded eightfold higher catalytic reaction rate compared to Cu/SiO 2 along with the high selectivity (53%, at 55% of conversion) toward cinnamyl alcohol. Characterization techniques such as x-ray diffraction, H 2 temperatureprogrammed reduction, ultraviolet-visible spectroscopy, transmission electron microscopy, Fourier-transform infrared spectra of chemisorbed CO, and x-ray photoelectron spectroscopy were employed to understand the origin of the catalytic activity. A key genesis of the high activity of the Cu-Au/SiO 2 catalyst was ascribed to the synergistic effect of Cu and Au species: the Au sites were responsible for the dissociative activation of H 2 molecules, and Cu 0 and Cu 1 sites contributed to the adsorption-activation of C@C and C@O bond, respectively. A combined tuning of particle dispersion and its surface electronic structure was shown as a consequence of the formation of Au-Cu alloy nanoparticles, which led to the significantly enhanced synergy. A plausible reaction pathway was proposed based on our results and the literature.(a) 6Cu/SiO 2 , (b) 6Cu-0.4Au/SiO 2 , (c) 6Cu-0.9Au/SiO 2 , (d) 6Cu-1.4Au/SiO 2 , (e) 6Cu-1.9Au/SiO 2 , (f) 2Au/SiO 2 , and (g, h) 6Cu-1.4Au/SiO 2 . [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] 3304 Scheme 2. Schematic illustration of the structural changes of the xCu-yAu/SiO 2 under H 2 reduction condition and the possible mechanism of catalysis.