Search

The controlled synthesis of metallic nanomaterials has attracted the interest of many researchers due to their shape-dependent physical and chemical properties. However, most of the synthesized nanocrystals cannot be combined with spectroscopy to measure the reaction kinetics, thus limiting their use in monitoring the catalytic reaction process to elucidate its mechanism. As a powerful analytical tool, surface-enhanced Raman spectroscopy (SERS) can be used to achieve in situ monitoring of catalytic reactions by developing bifunctional metal nanocrystals with both SERS and catalytic activities. Herein, we have developed a simple one-pot synthesis method for the large-scale and size-controllable preparation of highly rough hydrangea Au hollow nanoparticles. The growth mechanism of flower-like Au hollow nanostructures was also discussed. The hollow nanostructure with a 3D hierarchical flower shell combines the advantages of hollow nanostructure and hierarchical nanostructure, which possess high SERS activity and good catalytic activity simultaneously. Furthermore, the hydrangea Au hollow crystals were used as a bifunctional nanocatalyst for in situ monitoring of the reduction reaction of 4-nitrothiophenol to the 4-aminothiophenol.

Controllable preparation of nanocrystals (NCs) is a prerequisite to reveal their shape-dependent physicochemical properties. Herein, by using a one-pot synthesis method, ethylene glycol (EG) as a solvent and a reducing agent, poly(diallyldimethylammonium chloride) (PDDA) as a ligand, and AgNO3 as an additive, we successfully prepared octahedral, rhombic dodecahedral (RD), tetrahexahedral (THH) and truncated ditetragonal prism (TDP) Au NCs. And by simply tuning the reaction temperature and thus the reducing power of EG, we not only realized the shape transformation of Au NCs among low-index facet crystals ({111} to {110} facet) and low-index facet crystals to high-index facet crystals ({111} to {210} facet), but also achieved the shape evolution among high-index facet crystals ({210} to {310} facet). At a relatively high reaction temperature of 195 °C, (b.p. 198 °C) stepwise evolution of Au NCs from a {111}-bounded octahedron to a {210}-bounded THH and then to a {310}-bounded TDP was achieved. Furthermore, by simply reducing the reaction temperature to 160 °C, the {111}-bounded octahedral Au NCs would transform into RD Au NCs enclosed with the {110} facet. And the morphology evolution of Au crystals caused by different experimental parameters was systemically investigated. We found that the evolution of the crystal morphology is the result of the synergistic effect of the UPD effect of Ag0 and the oxidative etching of O2/Cl−. In addition, high-index facet THH Au NCs with controllable sizes of 65–120 nm were prepared by adjusting the amount of the PDDA solution added to the growth solution. This work not only provides a new method to synthesize Au NCs with tunable shape and size, but is also helpful in understanding the crystal growth habit.

Controllable morphological metal catalytic materials have always been a focus in research. In the previous work, hexapod AgCl was successfully synthesized. In this paper, hexapod Ag@AgCl microstructures with diverse Ag contents are prepared through NaBH4 reduction. They are characterized by scanning electron microscopy (SEM) and the element distribution is proved by an energy dispersive X-ray spectrometer (EDS). They are porous dendritic microstructures with a large specific surface area and a rough surface, which display high catalytic performance and surface-enhanced Raman spectroscopy (SERS) activity. Furthermore, the hexapod Ag@AgCl microstructure is devoted as a dual catalyst to monitor the reduction of 4-nitrothiophenol (4-NTP) to 4-aminothiophenol (4-ATP) in situ using SERS. Ultraviolet–visible (UV–Vis) spectroscopy was employed to evaluate the catalytic performance of the hexapod Ag@AgCl microstructures. The consequences show that the velocity of reaction became faster with a corresponding increase in silver content and the reaction mechanism was cleared. In addition to preparing a good catalyst, this work also promotes the combination of micro-nano materials and spectroscopy technology.

The multiply depolarized composite cathode consisted of Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO) and a combinatory conductive network of graphene (GN) + carbon nanotubes (CNTs) in the active material and GN coating at the interface of current collector is synthesized via pasting LMNCO/GN/CNTs composite slurry on GN coated Al foil. The interlaced GN + CNTs conductive network improves both the electronic conductivity and Li ion transport and stabilizes the structure of composite. The GN coating at the interface of current/active materials interlaces with GN + CNTs in the active materials and improves the adhesion and reduces the resistance between the active material and current collector. Consequently, the LMNCO composite cathode exhibits superior rate capacities of 132 mAh g−1 at 5C and 97 mAh g−1 at 10C, high cycling capacity retentions of 86% at 1C and 85% at 2C after 100 cycles, respectively and lower voltage fading. This combinatory conductive network is much more efficient for reducing the resistance and polarization of electrode than any single conductive network of GN + CNTs, CNTs, GN or GN coating.

Shape transformation of Au crystals from a {111}-bounded octahedron to a {730}-bounded tetrahexahedron (THH) and then to a {310}-bounded truncated ditetragonal prism (TDP) was achieved by a one pot synthesis method. The transformation of the crystal morphology is the result of the synergistic effect of Ag+ and O2/Cl-. This work not only provides a way to prepare high-index faceted Au micro/nanocrystals, but also provides new insights into the crystal growth habit.

In this work, we have synthesized hexapods AgCl crystals with mace pods for the first time. Diallyldimethylammonium chloride (DDA)-controlled stepwise evolution of AgCl crystals from octahedron to hexapods with mace pods are achieved by one-pot method. The intermediates have been captured which show the basic process of crystal growth. In this process, octahedra AgCl crystals firstly grow along the direction and then change to grow in the direction. At the same time, the size of AgCl grow from 2 μm to 20 μm. Due to the poor absorption of visible light by AgCl, sodium borohydride(NaBH4) is used to reduce AgCl hexapods with mace pods crystals. By changing the mole ratio(R) of NaBH4 to AgCl, the new structure was reduced to obtain a series of Ag@AgCl microstructures. Visible light catalysis effects of the Ag@AgCl microstructures on degradation of methyl orange (MO) were investigated. The Ag@AgCl microstructures with R = 0.02 have a high photocatalytic performance, which completely degrades MO in 40 minutes.

Calcium-looping technology has been identified as one of the most favorable CO2 capture techniques for the implementation of carbon capture, utilization, and storage (CCUS); however, the rapid deactivation of CaO sorbents due to sintering is currently a major barrier of this technology. We report for the first time an environmentally benign and cost-effective strategy to reduce sintering by adding waste-derived nanosilica, synthesized from photovoltaic waste (SiCl4), into Cao-based sorbents through a simple dry mixing procedure. The as-synthesized sorbent (90% CaCO3–W) resulted in final CO2 uptake of 0.32 g(CO2) g(CaO)−1 within 5 min of carbonation. Even under the most severe calcination conditions (at 920 °C in pure CO2), it still maintained a stable capture capacity, with CO2 uptake of 0.23 g(CO2) g(CaO)−1 after 30 cycles. Additionally, the CO2 uptake percentage reached ∼90% in the fast carbonation stage (∼20 s), which is of great significance for real applications. The most likely stabilization mechani...

The sulfidation/oxidation and carburization resistances of a Ni3Al(Mo) (IC-6) alloy at high temperatures were investigated in this work. The corrosion kinetics of the IC-6 alloy was found to follow parabolic rate law in an environment of high partial pressures of sulfur (∼10−5 atm) and low partial pressures of oxygen (

In the fall of 2012 the Stanford University materials science course Solar Cells, Fuel Cells and Batteries: Materials for the Energy Solution was offered as a flipped class and a massively open online course (MOOC). To the best of our knowledge, this was the first materials science MOOC. Here we describe how the course was implemented, and present results on performance, demographics and other observations that were made. Finally, we provide some perspectives for the future of the implementation of these engineering MOOCs.