Yancun Yu

Facile synthesis of a Co3O4-carbon nanotube composite and its superior performance as an anode material for Li-ion batteries

In this work, we report a facile method for the synthesis of a Co3O4–functionalized carbon nanotube (Co3O4–f-CNT) composite via the growth of Co3O4 nanoparticles on the surface of functionalized carbon nanotubes (f-CNTs) by thermal decomposition of cobalt nitrate hexahydrate in ethanol. The composite consists of 13% carbon nanotubes and 87% Co3O4 nanoparticles by weight, and all the Co3O4 particles grew compactly along the carbon nanotube axis with a highly uniform dispersion. When used as an anode material for rechargeable lithium ion batteries, the composite manifested high capacities and excellent cycling performance at high and low current rates. The discharge capacity was 719 mA h g−1 at the 2nd cycle and 776 mA h g−1 at the 100th cycle. Even at a current density of 1 A g−1, the specific capacity still remained at about 600 mA h g−1. This superior electrochemical performance was attributed to the unique nanostructure of the composite. Because almost all of the Co3O4 nanoparticles were immobilized on the surface of f-CNTs, physical aggregation of nanoparticles was avoided during the charge–discharge processes. Furthermore, the good mechanical flexibility of f-CNTs can readily alleviate the massive volume expansion/shrinkage associated with a conversion reaction electrode. Finally, f-CNTs are highly conductive matrices for electrons due to their high conductivity, which can shorten the diffusion path for electrons.

Synthesis of urea derivatives from amines and CO2 in the absence of catalyst and solvent

Urea derivatives are obtained in mild to good yield from the reactions of primary aliphatic amines with CO2 in the absence of any catalysts, organic solvents or other additives. To optimize reaction conditions, experimental variables including temperature, pressure, the concentration of amine, reaction time etc. were studied. Satisfactory yields were obtained at the optimized conditions that are comparable to the presence of catalyst and solvent. The preliminary investigation of the reaction mechanism showed that alkyl ammonium alkyl carbamate was quickly formed as the intermediate, and then the final product was formed by the intramolecular dehydration.

One-step hydrothermal synthesis of SnS2/graphene composites as anode material for highly efficient rechargeable lithium ion batteries

SnS2/graphene nanosheets (SnS2/GNS) composites were synthesized by a one-step hydrothermal method. The composites exhibit remarkably improved Li-storage ability with a good cycling life and high capability superior to that of the pure SnS2 counterpart due to a synergic effect between the graphene and SnS2 nanosheets.

Selective conversion of microcrystalline cellulose into hexitols on nickel particles encapsulated within ZSM-5 zeolite

A highly active and selective Ni/ZSM-5 catalyst was prepared by a simple method. A selectivity of 91.2% to hexitols was obtained at intermediate conversion in the hydrolytic hydrogenation of cellulose.

CO2–expanded ethanol chemical synthesis of a Fe3O4@graphene composite and its good electrochemical properties as anode material for Li-ion batteries

In this work, we have developed a new method to synthesize a Fe3O4@graphene (Fe3O4@GN) composite. First, the precursor was synthesized through the decomposition of ferric nitrate in the presence of graphene oxide in the mixed solvent of CO2–expanded ethanol. Then, the precursor was converted to the Fe3O4@GN composite via thermal treatment in N2 atmosphere. With the help of the CO2–expanded ethanol, Fe3O4 nanoparticles were coated on the surface of GN completely and uniformly with high loading. However, it is difficult to load Fe3O4 particles onto the surface of GN and most of the Fe3O4 particles were deviated away from GN and aggregated to form larger units in pure ethanol. When used as anode for Li-ion batteries (LIBs), the Fe3O4@GN composite with a graphene content of 25 wt% synthesized in CO2–expanded ethanol manifested excellent charge–discharge cycling stability and rate performance compared with the sample synthesized in ethanol. Such improved electrochemical performances should be attributed to the intimate contact between the GN and Fe3O4 nanoparticles in the composite. Since the present method does not need tedious pre-treatment, surfactant, or precipitate, it is a green or sustainable technology and the solvents could be recycled easily after simple phase separation. This facile method can be extended to the synthesis of other metal oxide composites, which are expected to have good performance as anode materials for LIBs and other applications.

CO2-assisted template synthesis of porous hollow bi-phase γ-/α-Fe2O3 nanoparticles with high sensor property

In this contribution, monodisperse porous hollow bi-phase γ-/α-Fe2O3 nanoparticles were successfully fabricated based on hard-template method with using carbon colloids as sacrificial templates. A new concept of assembling one kind of metal oxide with different crystalline structures into a single shell was presented for the first time. The critical procedure of coating carbon cores with a uniform layer of oxide was performed in CO2-expanded ethanol, which is a versatile way to produce high-quality hollow oxide nanoparticles. The formation of the novel bi-phase shell was achieved through combining the reduction ability of carbon cores under inert calcination atmosphere and the unique chemical composition of intermediate-shell formed in CO2-expanded ethanol. The porous hollow γ-/α-Fe2O3 nanoparticles with an average diameter of 99 nm not only possess combined properties of γ-Fe2O3 and α-Fe2O3, but also have a large specific surface area of 93.7 m2 g−1 and a high pore volume of 1.056 cm3 g−1, enabling them to have widespread applications in sensors, catalysis, magnetic and electrochemical areas, etc. Herein, such hollow bi-phase γ-/α-Fe2O3 nanoparticles were utilized to prepare a sensor device, and intriguingly it shows higher sensitivity and selectivity to ethanol than γ-Fe2O3 powders and many other porous α-Fe2O3 materials reported recently. The probable sensor mechanism of hollow γ-/α-Fe2O3 nanoparticles was discussed in detail.

An effective medium of H2O and low-pressure CO2 for the selective hydrogenation of aromatic nitro compounds to anilines

Chemoselective hydrogenation of water-insoluble aromatic nitro compounds can be achieved over Ni catalysts in a H2O–compressed CO2 system at 35–50 °C without using any environmentally harmful solvent. The effective CO2 pressure is much lower than the critical pressure of CO2. The hydrogenation of nitro group should be the rate-determining step.

Selective reduction of phenol derivatives to cyclohexanones in water under microwave irradiation

Selective reduction of phenol to cyclohexanone over the Pd/C catalyst in the presence of a hydrogen source of HCOONa/H2O has been studied. Surprisingly, phenol was transformed efficiently to cyclohexanone in an excellent yield of above 98% under microwave irradiation. The influence of some parameters like reaction temperature, time and amount of hydrogen donor, as well as the reaction pathway has been discussed. The combination of microwave irradiation and HCOONa/H2O was certified to be effective for the reduction of phenol as well as its derivatives to their corresponding cyclohexanones.

A new strategy for finely controlling the metal (oxide) coating on colloidal particles with tunable catalytic properties

In this contribution, we present an efficient, versatile and green strategy for finely controlling the metal (oxide) coating on core particles through in situ reaction of precursors in CO2 expanded ethanol without using any precipitants. It not only avoids the formation of free metal (oxide) and/or naked cores, but also permits individual dispersion of all the resultant particles without aggregation. With this method, the composition, thickness, uniformity, and structure of the metal (oxide) shell could be precisely controlled. A wide variety of unreported high-quality core-shell particles with a shell consisting of highly dispersed metal (oxide) nanocrystals or nanoalloys, such as C@Ni, CoO/C, C@Ni&Co and C@Ni&Pd particles have been fabricated, and the properties of the resultant particles were precisely tailored, such as the promising catalytic performance obtained over Ni/C and C@Ni particles in the hydrogenation of nitrobenzene. The present coating strategy is more simple and precisely controllable compared to the conventional deposition method and it is suitable for most precursors and even for multi-component materials, enabling the fabrication of nanostructured materials more easily and precisely.

Selective hydrogenation of citral catalyzed with palladium nanoparticles in CO2-in-water emulsion

CO2-in-Water (C/W) emulsion was formed by using a nonionic surfactant of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (P123), and palladium nanoparticles were synthesized in situ in the present work. The catalytic performance of Pd nanoparticles in the C/W emulsion has been discussed for a selective hydrogenation of citral. Much higher activity with a turnover frequency (TOF) of 6313 h−1 has been obtained in this unique C/W emulsion compared to that in the W/C microemulsion (TOF, 23 h−1), since the reaction was taking place not only in the surfactant shell but also on the inner surface of the CO2 core in the C/W emulsion. Moreover, citronellal was obtained with a higher selectivity for that it was extracted to a supercritical carbon dioxide (scCO2) phase as formed and thus its further hydrogenation was prohibited. The Pd nanoparticles could be recycled several times and still retain the same selectivity, but it showed a little aggregation leading to a slight decrease in conversion.