A Quantitative Analysis of the Reduction Kinetics Involved in the Synthesis of Au@Pd Concave Nanocubes

Surface capping has been shown to play a pivotal role in controlling the evolution of metal nanocrystals into different shapes or morphologies. With the synthesis of Au@Pd concave nanocubes as an example, here we demonstrate that the capping agent can also impact the reduction kinetics of a precursor, and thereby its reduction pathway, for the formation of metal nanocrystals with distinct morphologies. A typical synthesis involves the reduction of a Pd^II precursor by ascorbic acid at room temperature in the presence of Au nanospheres as seeds, together with the use of hexadecyltrimethylammonium chloride (CTAC) or hexadecyltrimethylammonium bromide (CTAB) as the capping agent. In the case of CTAC, the Pd^II precursor prevails as PdCl₄²⁻, leading to the formation of Au@Pd concave nanocubes with a rough surface because of the fast reduction kinetics and thus the dominance of solution reduction pathway. When switched to CTAB, the Pd^II precursor changes to PdBr₄²⁻ that features slow reduction kinetics and surface reduction pathway. Accordingly, the Au@Pd concave nanocubes take a smooth surface. This work demonstrates that both reduction kinetics and surface capping play important roles in controlling the morphology of metal nanocrystals and these two roles are often coupled to each other.     

Identification of the hydrogen utilization pathway for the electrocatalytic hydrogenation of phenol

Electrochemical hydrogenation(ECH) of biomass-derived platform molecules is a burgeoning route for the sustainable utilization of hydrogen. However, the noble-metal-catalyzed ECH of phenolic compounds suffers from intense competition with hydrogen evolution reaction. We prepared Pt Rh bimetallic nanoparticles dispersed on highly ordered mesoporous carbon nanospheres, which improves the utilization efficiency of adsorbed hydrogen(Had) to ECH in H–UPD region(0 V vs. RHE).Further analysis reveals(i) the strong overlapping between the d-orbitals of Pt and Rh enhances specific adsorption of phenol;(ii)incorporation of Rh devotes an electronic effect on weakening the alloy–Hadinteraction to increase the FE of ECH. DFT calculations confirm the selectivity difference and the ECH parallel pathways: cyclohexanol and cyclohexanone are formed via hydrogenation/dehydrogenation of the intermediate *C6 H10 OH. These findings deepen our fundamental understanding of the ECH process, and cast new light on exploration of highly efficient electrocatalysts for biomass upgrading.     

Synthesis of Cu2O nanocrystals from cubic to rhombic dodecahedral structures and their comparative photocatalytic activity

In this study, a new series of Cu(2)O nanocrystals with systematic shape evolution from cubic to face-raised cubic, edge- and corner-truncated octahedral, all-corner-truncated rhombic dodecahedral, {100}-truncated rhombic dodecahedral, and rhombic dodecahedral structures have been synthesized. The average sizes for the cubes, edge- and corner-truncated octahedra, {100}-truncated rhombic dodecahedra, and rhombic dodecahedra are approximately 200, 140, 270, and 290 nm, respectively. An aqueous mixture of CuCl(2), sodium dodecyl sulfate, NaOH, and NH(2)OH·HCl was prepared to produce these nanocrystals at room temperature. Simple adjustment of the amounts of NH(2)OH·HCl introduced enables this particle shape evolution. These novel particle morphologies have been carefully analyzed by transmission electron microscopy (TEM). The solution color changes quickly from blue to green, yellow, and then orange within 1 min of reaction in the formation of nanocubes, while such color change takes 10-20 min in the growth of rhombic dodecahedra. TEM examination confirmed the rapid production of nanocubes and a substantially slower growth rate for the rhombic dodecahedra. The rhombic dodecahedra exposing only the {110} facets exhibit an exceptionally good photocatalytic activity toward the fast and complete photodegradation of methyl orange due to a high number density of surface copper atoms, demonstrating the importance of their successful preparation. They may serve as effective and cheap catalysts for other photocatalytic reactions and organic coupling reactions.     

Solvothermal synthesis of zincblende and wurtzite CuInS2 nanocrystals and their photovoltaic application

We report a simple solvothermal synthesis approach to the growth of CuInS(2) nanocrystals with zincblende- and wurtzite-phase structures. Zincblende nanocrystals with particle sizes of 10-20 nm were produced using oleylamine as the solvent. When ethylenediamine was used as the solvent, similarly sized wurtzite nanocrystals with some degree of particle aggregation were formed. Use of a mixture of these solvents gave products with mixed phases including some polyhedral nanostructures. The crystal phases of these nanocrystals were carefully determined by X-ray diffraction and transmission electron microscopy analysis. All the samples exhibit strong absorption from the entire visible light region to the near-infrared region beyond 1300 nm. Pure-phase zincblende and wurtzite CuInS(2) nanocrystals were employed as ink in the fabrication of solar cells. The spray-coated nanocrystal layer was subjected to a selenization process. A power conversion efficiency of ~0.74% and a good external quantum efficiency profile over broad wavelengths have been measured. The results demonstrate that wurtzite and zincblende CuInS(2) nanocrystals may be attractive precursors to light-absorbing materials for making efficient photovoltaic devices.     

3-D phase diagram of HPC/H2O/H3PO4 tertiary system

A 3-D phase diagram of the HPC/H₂O/H₃PO₄ tertiary system against various temperatures was established. Four distinct phases—the completely separated phase (S), the cloudy suspension phase (CS), the liquid crystalline miscible phase (LC), and the isotropically miscible phase (I)—were identified. The S phase shrank as the temperature increased, revealing that the HPC solubility increased with temperature, regardless of the LCST (lower critical solution temperature) characteristic. The addition of H₃PO₄ suppressed the formation of LC phase. However, as the temperature was raised sharply from 50 to 70?°C, the LC phase could only be maintained at high H₃PO₄ concentration region; it was a triangular shape, and the top apex of the triangle was the temperature-invariant L* point (HPC/H₂O/H₃PO₄ 38/9/53?wt%). The CS phase expanded considerably into the H₂O-rich but H₃PO₄-poor region when the temperature continued to increase over 48?°C. The LCST points of the CS phase that contained 0 and 15?wt% of H₃PO₄ were 34 and 38?°C, respectively. These CS results demonstrate that H₃PO₄ suppresses the occurrence of LCST behavior. Additionally, the binodal curve exhibits a weak or even zero dependence of binodal temperature on the HPC concentration at HPC concentrations of less than 30?wt% in a pure water system. A hypothesis concerning the sequential desorption of water molecules was proposed to explain such behavior.     

蒸馏法测定一次性筷子中二氧化硫浸出量的不确定度评定

依照GB 19790.1-2005,GB 19790.2-2005和GB/T 5009.34-2003(第二法),选取含量接近法规限值的代表性样品,从基准物质和标准滴定溶液溯源,探索测定一次性筷子中二氧化硫浸出量的数学模型,对检测过程中引入的不确定度进行了分类和量化,系统地评定了各个不确定度分量,得到该方法的相对标准不确定度为0.0043.     

Properties and Iterative Methods for the Lasso and Its Variants

The lasso of Tibshirani （1996） is a least-squares problem regularized by the l1 norm. Due to the sparseness promoting property of the l1 norm, the lasso has been received much attention in recent years. In this paper some basic properties of the lasso and two variants of it are exploited. Moreover, the proximal method and its variants such as the relaxed proximal algorithm and a dual method for solving the lasso by iterative algorithms are presented.     

Synthesis of Ag2O nanocrystals with systematic shape evolution from cubic to hexapod structures and their surface properties

We report the development of a facile method for the synthesis of Ag(2)O crystals with systematic shape evolution from cubic to edge- and corner-truncated cubic, rhombicuboctahedral, edge- and corner-truncated octahedral, octahedral, and hexapod structures by mixing AgNO(3), NH(4)NO(3), and NaOH at molar ratios of 1:2:11.8. A sufficient volume of NaOH solution was first added to a mixture of AgNO(3) and NH(4)NO(3) solution to promote the formation of Ag(NH(3))(2)(+) complex ions and the growth of Ag(2)O nanocrystals with good morphological control. The crystals are mostly submicrometer-sized. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterization has been performed to determine the crystalline surface facets. A band gap value of approximately 1.45 eV has been found for the octahedral Ag(2)O crystals. By changing the molar ratios of AgNO(3)/NH(4)NO(3)/NaOH to 1:2:41.8, corner-depressed rhombicuboctahedra and elongated hexapods were obtained as a result of enhanced crystal growth along the [100] directions. Smaller nanocubes with average sizes of approximately 200 and 300 nm and octapods can also be prepared by adjusting the reagent molar ratios and their added volumes. Both the octahedra and hexapods with largely silver atom-terminated {111} surface facets responded repulsively and moved to the surface of the solution when dispersing in a solution of positively charged methylene blue, but can be suspended in a negatively charged methyl orange solution. The cubes and octapods, bounded by the {100} faces, were insensitive to the molecular charges in solution. The dramatic facet-dependent surface properties of Ag(2)O crystals have been demonstrated.     

Circular permutation of the starch-binding domain: inversion of ligand selectivity with increased affinity

Proteins containing starch-binding domains (SBDs) are used in a variety of scientific and technological applications. A circularly permutated SBD (CP90) with improved affinity and selectivity toward longer-chain carbohydrates was synthesized, suggesting that a new starch-binding protein may be developed for specific scientific and industrial applications.