Microwave-assisted synthesis of layer-by-layer ultra-large and thin NiAl-LDH/RGO nanocomposites and their excellent performance as electrodes

In this work, ultra-large sheet NiAl-layered double hydroxide(LDH)/reduced graphene oxide(RGO) nanocomposites were facilely synthesized via in situ growth of NiAl-LDH on a graphene surface without any surfactant or template. It was found that with a microwave-assisted method, NiAl-LDH nanosheets grew evenly on the surface of graphene. With this method, the formation of NiAl-LDH and reduction of graphene oxide were achieved in one step. The unique structure endows the electrode materials with a higher specific surface area, which is favorable for enhancing the capacity performance. The morphology and microstructure of the as-prepared composites were characterized by X-ray diffraction, Brunauer-EmmettTeller surface area measurement, and transmission electron microscopy. The specific surface area and pore volume of the RGO/LDH composite are 108.3 m^2 g^(-1) and 0.74 cm^3 g^(-1), respectively, which are much larger than those of pure LDHs(19.8 m^2 g^(-1) and 0.065 cm^3 g(-1), respectively). The capacitive properties of the synthesized electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy in a three-electrode experimental setup. The specific capacitance of RGO/LDHs was calculated to be 1055 F g^(-1) at 1 Ag^(-1). It could be anticipated that the synthesized electrodes will find promising applications as novel electrode materials in supercapacitors and other devices because of their outstanding characteristics of controllable capacitance and facile synthesis.

Understanding of the major reactions in solution synthesis of functional nanomaterials

This review covers the major reactions involved in the solution synthesis of nanomaterials.It was designed to classify the traditional strategies such as precipitation,reduction,seed growth,etching,and so on into two basic processes which are termed as bottom-up and top-down routines.The discussion is focused on the basic mechanism and principles during the nudeation and growth of nanocrystals,especially in the solution system.This review also presents a prediction for how to utilize these intrinsic processes to artificially construct the desired specific and functional nanostructures.We try to describe the most directive and effective way to control the structures of nanocrystals for researchers who can master the major reaction mechanism and grasp the basic technologies in synthetic nanoscience.

Synthesis of palladium and palladium sulfide nanocrystals via thermolysis of a Pd–thiolate cluster

A novel one-pot approach to synthesize the tiara-like Pd(II) thiolate complex compound, [Pd(SCH_3)_2]_6, was developed. In this strategy, dimethyl sulfoxide(DMSO) was used as a thiolate source instead of methyl mercaptan(CH_3SH). DMSO was first decomposed into CH_3SH and formaldehyde(HCHO); then, the in situ as-formed CH_3SH molecules reacted with palladium acetate, and formed [Pd(SCH_3)_2]_6. By tuning the reaction condition, the morphology of the [Pd(SCH_3)_2]_6 assemblies can change from microprism to nanosphere. The characterization of the pyrolysis product demonstrated that these two kinds of [Pd(SCH_3)_2]_6 assemblies with different shapes could further decompose into palladium or palladium sulfides through different pyrolysis conditions.

Controlled one-pot synthesis of RuCu nanocages and Cu@Ru nanocrystals for the regioselective hydrogenation of quinoline

RuCu nanocages and core–shell Cu@Ru nanocrystals with ultrathin Ru shells were first synthesized by a one-pot modified galvanic replacement reaction. The construction of bimetallic nanocrystals with fully exposed precious atoms and a high surface area effectively realizes the concept of high atom-efficiency. Compared with the monometallic Ru/C catalyst, both the RuCu nanocages and Cu@Ru core–shell catalysts supported on commercial carbon show superior catalytic performance for the regioselective hydrogenation of quinoline toward 1,2,3,4-tetrahydroquinoline. RuCu nanocages exhibit the highest activity, achieving up to 99.6% conversion of quinoline and 100% selectivity toward 1,2,3,4-tetrahydroquinoline. [Figure not available: see fulltext.] © 2015, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

Atomically dispersed Au_1 catalyst towards efficient electrochemical synthesis of ammonia

Tremendous efforts have been devoted to explore energy-efficient strategies of ammonia synthesis to replace Haber-Bosch process which accounts for 1.4% of the annual energy consumption. In this study, atomically dispersed Au_1 catalyst is synthesized and applied in electrochemical synthesis of ammonia under ambient conditions. A high NH＋4 Faradaic efficiency of 11.1 % achieved by our Au_1 catalyst surpasses most of reported catalysts under comparable conditions. Benefiting from efficient atom utilization, an NH＋4 yield rate of 1,305 μg h-1 mg-1Au has been reached, which is roughly 22.5 times as high as that by sup- ported Au nanoparticles. We also demonstrate that by employing our Au_1 catalyst, NH＋4 can be electro- chemically produced directly from N_2 and H_2 with an energy utilization rate of 4.02 mmol kJ-1. Our study provides a possibility of replacing the Haber-Bosch process with environmentally benign and energy-efficient electrochemical strategies.

Interface-induced formation of onion-like alloy nanocrystals by defects engineering

The ability to controlled introduction of defects, particularly twin defects in Pt-based nanocrystals （NCs） provides a possibility to regulate the performance of Pt-based nanocatalyst. However, because of the high internal strain energy existed in twinned structures, the fabrication of defects in Pt-based NCs is sufficiently challenging. Here we demonstrate a ＂low-temperature interface-induced assembly＂ approach that provides precise control over Pt-Cu nanoparticles assembled at the hexadecylamine/water interface, yielding onion-like Pt-Cu NCs exposed a high density of twin defects. Moreover, a bending mechanism is proposed to elucidate the appearance of twin defects and lattice expanding （contraction） based on aberration corrected scanning transmission electron microscopy analysis. This work opens new routes to engineer defects in metal- based alloy NCs, enabling more opportunities in catalysis.

Pd-dispersed CuS hetero-nanoplates for selective hydrogenation of phenylacetylene

We have exploited a new and distinctive combination method that ＂disperses＂ elemental Pd into CuS nanoplates. Pd was successfully dispersed by means of the concomitant transformation of CuS into an amorphous sulfide, which formed an intimate metal-sulfide contact via cation exchange and underwent a subsequent reduction. A series of such Pd-dispersed CuS hetero-nanoplates were synthesized with tailored proportions and compositions. By efficient utilization of noble metal atoms and stable anchored active sites, the optimal catalytic performance for the semihydrogenation of phenylacetylene, a probe reaction, was achieved with high selectivity, activity, and stability. We believe that the synthetic strategy described in our study is a feasible means of developing effective metal-sulfide catalysts for organic reactions.

Free-standing palladium-nickel alloy wavy nanosheets

Two-dimensional nanomaterials （2DNMs） have attracted increasing attention due to their unique properties and promising applications. Unlike 2DNMs with lamellar structures, metal ultrathin 2DNMs are difficult to synthesize and stabilize because they tend to form close-packed crystal structures. Most reported cases consist of monometallic and heterogeneous nanostructures. The synthesis of metal alloy 2DNMs has been rarely reported. Here, we report the synthesis of PdNi alloy wavy nanosheets （WNSs） using an enhanced CO-confinement strategy. This strategy is also suitable to the synthesis of other Pd-based alloy WNSs such as PdCu, PdFe, and even a trimetallic PdFeNi.

Photosynthetic conversion of CO_2 to acetic acid by an inorganic-biological hybrid system

Since 7000 BCE,humans have fermented sugars into ethanol,and since work by Louis Pasteur in the 1850s,we have known that microorganisms are responsible for this miraculous feat of chemical synthesis[1].Since then,the ability of biological organisms to cheaply and selectively transform chemicals into useful products has been exploited on a global scale from agriculture to biotechnological synthesis of pharmaceutical compounds.Recently,pho-

Pd3 cluster catalysis: Compelling evidence from in operando spectroscopic, kinetic, and density functional theory studies

Identification of metal cluster catalysis is a topic that is being investigated since a long time. Here, we report a Pd3 metal cluster catalytic reaction investigated by means of operando studies. We discovered that atomically defined tri-nuclear palladium (Pd3) is a surprisingly active catalyst for the cycloisomerization of 2-phenylethynylaniline. Operando1H NMR spectroscopy and X-ray extended absorption fine structure (EXAFS) measurements have indicated that the structural integrity of such a catalyst remains intact throughout the reaction, which has also been confirmed by an ex situ X-ray photoelectron spectroscopy (XPS) study and catalyst recycling experiments. Kinetic data derived from operando IR spectroscopy measurements have shown that Pd3is the active catalytic species. Density functional theory calculations have revealed a reaction pathway consistent with the kinetic data, further supported by NMR titration and X-ray crystal structure studies. Overall, the present study presents a clear example of metal cluster catalysis. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

Hybrid atomic layers based electrocatalyst converts waste CO_2 into liquid fuel

Electrocatalyst that converts carbon dioxide to useful fuels,using electricity generated from renewable sources,is generally regarded as a potentially'clean'strategy of turning trash into treasure under mild conditions[1,2].Lots of studies have demonstrated that electroreduction of CO2contains several elementary steps of adsorption,activation,dissociation and desorption,among which the most

Defective molybdenum sulfide quantum dots as highly active hydrogen evolution electrocatalysts

Molybdenum disulfide （MoS2）, a promising non-precious electrocatalyst for the hydrogen evolution reaction with two-dimensional layered structure, has received increasing attention in recent years. Its electrocatalytic performance has been limited by the low active site content and poor conductivity. Herein, we report a facile and general ultrafast laser ablation method to synthesize MoS2 quantum dots （MS-QDs） for electrocatalytic HER with fully exposed active sites and highly enhanced conductivity. The MS-QDs were prepared by ultrafast laser ablation of the corresponding bulk material in aqueous solution, during which they were partially oxidized and formed defective structures. The as-prepared MS-QDs demonstrated high activity and stability in the electrocatalytic HER, owing to their very large surface area, defective structure, abundance of active sites, and high conductivity. The present MS-QDs can also find application in optics, sensing, energy storage, and conversion technologies.

Co_2C nanoprisms with strong facet effect for Fischer-Tropsch to olefins reaction

Lower olefins refer to ethylene,propylene and butylene,which are vital building block in the chemical industry.They are fundamental chemicals of the greatest consumption among the organic chemicals all over the world.Large amount of chemical products,such as packing materials,cosmetics,synthetic rubber,coatings are the derivatives of lower olefins.In traditional petrochemical industry,lower olefins are mainly derived from oil-based feedstocks.

Perfectly planar CoB^-18 as a motif for metallo-borophenes

Over the past decade, extensive collaborative experimental and theoretical researches have systematically elucidated the structures and chemical bonding of boron clusters as a function of size and have revealed an intriguing set of structures, ranging from planar hydrocarbon-analogs to nanotubular and fullerenelike structures （borospherenes） [1-7]. Small boron clusters have the propensity for planarity with delocalized σ and π electrons over the whole molecular plane, giving rise to the concept of multiple aromatidty.