Temperature-induced self-pinning and nanolayering of AuSi eutectic droplets

A process for self-pinning of AuSi eutectic alloy droplets to a Si substrate, induced by a controlled temperature annealing in ultrahigh vacuum, is presented. Surface pinning of AuSi 3D droplets to the Si substrate is found to be a consequence of the readjustment in the chemical composition of the droplets upon annealing, as required to maintain thermodynamic equilibrium at the solid-liquid interface. Structural and morphological changes leading to the pinning of the droplets to the substrate are analyzed. Phase separation is observed upon cooling of the droplets, leading to the formation of amorphous Si-rich channels within the core and the formation of crystalline Si nanoshells on the outside. The mechanism leading to the pinning and surface layering provides new insight into the role of alloying during growth of silicon nanowires and may be relevant to the engineering of nanoscale Si cavities.     

Preparation,characterization and use of new lignocellulose-based bio nanocomposite as a heterogeneous catalyst for sustainable synthesis of pyrimido benzazoles

A sustainable combinatorial synthesis of densely substituted pyrimido [1,2-b] benzazole derivatives in water under microwave irradiation was performed using a new lignocellulose-based bio nanocomposite (BNC) as heterogeneous catalyst. The lignocellulosic waste peanut shells (LCWPS) were turned into a value-added product, a new BNC PS/ZnO, which was prepared via in situ hydrothermal synthesis. The as-prepared BNC was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction spectrum. PS/ZnO has been successfully used in a sustainable catalytic method for the synthesis of pyrimido [1, 2-b] benzazole derivatives in water under microwave irradiation. The time of this reaction was significantly reduced. This catalytic system has a very high turnover number (TON?～?10³) and turnover frequency (TOF?～?10^5?h^?1). This paper presents the benefit of sustainable management of LCWPS, a bio-sourced polymeric carbohydrate for production of new nanocatalyst.     

Pyrrole adsorption on aluminum nitride nanotubes on DFT data

The adsorption behavior of pyrrole molecule with external surface of (5.0) on zigzag aluminum nitride nanotube (AlNNT) was studied using density functional theory calculations. It was found that the adsorption energy (E_ad) of pyrrole on the surface of pristine nanotubes is about–11.99 kcal/mol. However, when nanotubes have been doped with P atom, the adsorption energy of pyrrole was increased. Calculation showed that for the phosphorus-doped nanotube the adsorption energy range is about–9.04 to?12.80 kcal/mol. AlNNT is a suitable adsorbent for pyrrole, so it can be used in adsorption and separation processes involving pyrrole. The doped AlNNT can potentially be used for pyrrole sensors for detection in environmental systems.     

Buchwald‐Hartwig amination reaction of aryl halides using heterogeneous catalyst based on Pd nanoparticles decorated on chitosan functionalized graphene oxide

In this work, graphene oxide was functionalized with chitosan (GO‐Chit) followed by a simple approach for immobilization of palladium nanoparticles onto a chitosan grafted graphene oxide surface. The Pd‐nanocomposite (GO‐Chit‐Pd) was characterized using Transmission Electron Microscopy (TEM), Fourier transforms infrared spectroscopy (FT‐IR), and X‐ray diffraction (XRD) measurements. The catalytic activity of the prepared heterogeneous graphene oxide functionalized chitosan‐palladium (GO‐Chit‐Pd) was investigated in term of C‐N coupling reaction (Buchwald‐Hartwig amination reaction of aryl halides) yielding products of N‐arylamines. The easy purification, convenient operation, and environmental friendliness, combined with a high yield, render this method viable for use in both laboratory research and larger industrial scales. Studying the reusability of the catalyst in this work showed that it could be reused for five times without obvious loss in catalytic activity.     

Nuclephilic ring opening of epoxides promoted by multi-site phase-transfer catalyst:An efficient and eco-friendly route to synthesis of b-hydroxy-thiocyanate

A highly effective and mild protocol for ring opening of epoxides with NH ₄ SCN in the presence of catalytic amount of a multisite phase-transfer catalyst, α,α',α" -N-hexakis(triethylammoniummethylene chloride)-melamine, is developed. A variety of b-hydroxy thiocyanates as important intermediates in agricultural and pharmaceutical chemistry were obtained in high yields with excellent regioselectivity and in short reaction times.     

Ordered mesoporous SBA‐15 functionalized with yttrium(III) and cerium(III) complexes: Towards active heterogeneous catalysts for oxidation of sulfides and preparation of 5‐substituted 1H‐tetrazoles

Mesoporous SBA‐15 was synthesized and modified with 3‐chloropropyltrimethoxysilane and then used in immobilization of creatinine groups, which were employed to introduce Y³⁺ and Ce³⁺ to give rise to two novel yttrium and cerium catalysts: SBA‐15@Creatinine@M (M = Y and Ce). The structures of the SBA‐15@Creatinine@M catalysts were determined using various techniques. These catalysts offered outstanding catalytic performances in the oxidation of sulfides to sulfoxides and in the preparation of 5‐substituted 1H‐tetrazoles. An important characteristic of the SBA‐15@Creatinine@M catalysts is that they are very stable without a considerable decrease in their catalytic performance lasting seven cycles.     

Next-generation quantum theory of atoms in molecules for the S1/S0 conical intersections in dynamics trajectories of a light-driven rotary molecular motor

Next-generation quantum theory of atoms in molecules was applied to analyze, along an entire bond path, intramolecular interactions known to influence the photoisomerization dynamics of a light-driven rotary molecular motor. The 3D bond-path framework set B_0,1 constructed from the least and most preferred directions of electronic motion, provided new insights into the bonding leading to different S₁ state lifetimes including the first quantification of covalent character of a closed-shell intramolecular bond path. We undertook the first use of the stress tensor trajectory T_σ(s) analysis on selected nonadiabatic molecular dynamics trajectories with the electron densities obtained using the ensemble density functional theory method. The stress tensor T_σ(s) analysis was found to be well suited to follow the dynamics trajectories that included the S₀ and S₁ electronic states through the conical intersection and also provided to a new measure to assess the degree of purity of the axial bond rotation for the design of rotary molecular motors.