Aihua Yuan

Montmorillonite-supported magnetite nanoparticles for the removal of hexavalent chromium [Cr(VI)] from aqueous solutions.

Montmorillonite-supported magnetite nanoparticles were prepared by co-precipitation and hydrosol method. The obtained materials were characterized by X-ray diffraction, nitrogen adsorption, elemental analysis, differential scanning calorimetry, transmission electron microscopy and X-ray photoelectron spectroscopy. The average sizes of the magnetite nanoparticles without and with montmorillonite support are around 25 and 15 nm, respectively. The montmorillonite-supported magnetite nanoparticles exist on the surface or inside the interparticle pores of clays, with better dispersing and less coaggregation than the ones without montmorillonite support. Batch tests were carried out to investigate the removal mechanism of hexavalent chromium [Cr(VI)] by these synthesized magnetite nanoparticles. The Cr(VI) uptake was mainly governed by a physico-chemical process, which included an electrostatic attraction followed by a redox process in which Cr(VI) was reduced into trivalent chromium. The adsorption of Cr(VI) was highly pH-dependent and the kinetics of the adsorption followed the Pseudo-second-order model. The adsorption data of unsupported and clay-supported magnetite nanoparticles fit well with the Langmuir and Freundlich isotherm equations. The montmorillonite-supported magnetite nanoparticles showed a much better adsorption capacity per unit mass of magnetite (15.3mg/g) than unsupported magnetite (10.6 mg/g), and were more thermally stable than their unsupported counterparts. These fundamental results demonstrate that the montmorillonite-supported magnetite nanoparticles are readily prepared, enabling promising applications for the removal of Cr(VI) from aqueous solution.

Reduced graphene oxide/nickel nanocomposites: facile synthesis, magnetic and catalytic properties

Graphene, which possesses unique nanostructure and excellent properties, is considered a low cost alternative to carbon nanotubes in nanocomposites. In this paper, we demonstrate a facile in situreduction approach for the synthesis of reduced graphene oxide/Ni (RGO/Ni) nanocomposites with different morphologies. The concentration of nickel ions has a great influence on the morphology of the RGO/Ni nanocomposites and an interesting RGO-wrapped nanostructure was obtained. Magnetic studies reveal a room-temperature ferromagnetic behavior of the RGO/Ni nanocomposites. The catalytic activities of the RGO/Ni nanocomposites were investigated for the reduction of p-nitrophenol by NaBH4. It was found that the nanocomposites show higher catalytic activity compared with the unsupported Ni nanoparticles. The catalytic performance of the RGO/Ni nanocomposites was even better than the RANEY® Ni catalyst. Moreover, after completion of the reaction the nanocomposite catalyst can be easily re-collected from the reaction system by a magnet. Thus, the RGO/Ni nanocomposites obtained in this work may find applications in catalysis, data storage, targeted drug transportation and magnetic resonance imaging technologies.

Facile Fabrication and Enhanced Sensing Properties of Hierarchically Porous CuO Architectures

Hierarchically porous CuO architectures were successfully fabricated via copper basic carbonate precursor obtained with a facile hydrothermal route. The shape of the precursor is preserved after its conversion to porous CuO architectures by calcination. The obtained CuO are systemically characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller N(2) adsorption-desorption analysis. The results reveal that hierarchical CuO microspheres are monoclinic structure and are assembled by porous single-crystal sub-microplatelets. The Brunauer-Emmett-Teller N(2) adsorption-desorption analysis indicates that the obtained CuO has a surface area of 12.0 m(2)/g with pore size of around 30 nm. The gas sensing performance of the as-prepared hierarchical CuO microspheres were investigated towards a series of typical organic solvents and fuels. They exhibit higher sensing response than that of commercial CuO powder. Their sensing properties can be further improved by loading of Ag nanoparticles on them, suggesting their potential applications in gas sensors.

Fabrication, characterization and field emission properties of large-scale uniform ZnO nanotube arrays

Large-scale well-aligned ZnO nanotubes with outer diameters of 100-300 nm and lengths of tens of micrometres have been prepared by a template-based chemical vapour deposition method. The photoluminescence spectrum of the ZnO nanotube arrays consists of a strong violet band at 414 nm, a blue band at 462 nm and a weak shoulder peak at around 480 nm. The field emission of the ZnO nanotube arrays shows a turn-on field of about 7.3 V microm(-1) at a current density of 0.1 microA cm(-2) and emission current density up to 1.3 mA cm(-2) at a bias field of 11.8 V microm(-1).

MOF-derived bi-metal embedded N-doped carbon polyhedral nanocages with enhanced lithium storage

To tackle the issue of the low specific capacity (372 mA h g−1) of graphite as the anode material for lithium-ion batteries (LIBs), an effective and controllable strategy was developed to construct porous bimetallic Co/Zn embedded N-doped carbon (Co–Zn/N–C) polyhedral nanocages via annealing a ZIF-8@ZIF-67 precursor at 800 °C under Ar atmosphere. The results clearly displayed that metallic Co and Zn particles are uniformly dispersed in the carbon matrix. Porous Co–Zn/N–C polyhedral nanocages have a large specific surface area of 349.12 m2 g−1 and contain plenty of micropores and mesopores, which benefit from the carbonization of organic ligands and the catalytic effect of cobalt in the calcination process. As anodes for LIBs, the porous Co–Zn/N–C polyhedral nanocages showed an initial discharge capacity of 809 mA h g−1 and a capacity retention of 702 mA h g−1 after 400 cycles at a current density of 0.2 A g−1. Furthermore, a reversible capacity of 444 mA h g−1 was obtained at a much higher current density of 2 A g−1. The improved electrochemical performance was attributed to the synergistic effect of Zn and Co, the unique porous hollow structure as well as N doping, which relieved the impact of volume changes, maintained perfect electrical conductivity throughout the electrode and enhanced the electrochemical activities of lithium storage.

Concave Co3O4 octahedral mesocrystal: polymer-mediated synthesis and sensing properties

Co3O4 mesocrystals with concave octahedral structures were successfully prepared by a facile, polymer-mediated route. The Co3O4 mesocrystals are obtained from the oriented aggregation of primary nanocrystals from their six identical [100] directions. After a thorough investigation of their structure as a function of the adopted preparation parameters such as reaction time and the amount of polymer, the gas sensing performance of the Co3O4 mesocrystals was studied with formaldehyde and ethanol as probe analytes. It was found that they show high sensitivity and good response and recovery characteristics. As compared with Co3O4 powder, the Co3O4 mesocrystals exhibit 1.8-fold and 1.4-fold enhancement in gas responses to 100 ppm of formaldehyde and ethanol, respectively.

Facile synthesis of a metal–organic framework-derived Mn2O3 nanowire coated three-dimensional graphene network for high-performance free-standing supercapacitor electrodes

This study presents a facile strategy to construct three-dimensional graphene network (3DGN) and metal–organic framework (MOF)-derived metal oxide composites as free-standing electrodes for supercapacitors for the first time. A Mn-based MOF is first grown in situ on a 3DGN substrate through a simple solution immersion method, and then a high-temperature treatment has resulted in the formation of a 3DGN decorated with Mn2O3 with a nanowire stacking flower-like morphology. The structure and morphology of the as-prepared samples are investigated by powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy analysis, scanning electron microscopy, elemental mapping, and transmission electron microscopy. The designed 3DGN/Mn2O3 electrode material exhibits a high specific capacitance of 471.1 F g−1 (0.21 F cm−2) at 0.2 A g−1, good rate capability of 57.3% at 5 A g−1 relative to the initial value at 0.2 A g−1, and excellent long-cycle stability without decaying after 1800 charge–discharge cycles. The remarkable electrochemical performances originate from the synergistic effect of the high electrical conductivity and large surface area of the 3DGN along with the superior pseudocapacitance activity of Mn2O3 nanowires. This result suggests that the 3DGN/MOF-derived metal oxide composites are promising and efficient binder-free electrode materials for high-performance supercapacitors.

Three unique two-fold interpenetrated three-dimensional networks with PtS-type topology constructed from [M(CN)4]2− (M = Ni, Pd, Pt) as “square-planar” building blocks

Three unique three-dimensional cyanide-based networks with {4284} PtS-type topology, ZnM(CN)4 (M = Ni(1), Pd(2), Pt(3)), have been synthesized deliberately from [M(CN)4]2− as “square-planar” building blocks and characterized by single crystal X-ray diffraction.

Co3O4 nanostructures with a high rate performance as anode materials for lithium-ion batteries, prepared via book-like cobalt–organic frameworks

The self-assembly of cobalt coordination frameworks (Co-CPs) with a two-dimensional morphology is demonstrated by a solvothermal method. The morphology of the Co-CPs has been controlled by various solvothermal conditions. The two-dimensional nanostructures agglomerated by Co3O4 nanoparticles remained after the pyrolysis of the Co-CPs. The as-synthesized Co3O4 anode material is characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge measurements. The morphology of Co3O4 plays a crucial role in the high performance anode materials for lithium batteries. The Co3O4 nanoparticles with opened-book morphology deliver a high capacity of 597 mA h g-1 after 50 cycles at a current rate of 800 mA g-1. The opened-book morphology of Co3O4 provides efficient lithium ion diffusion tunnels and increases the electrolyte/Co3O4 contact/interfacial area. At a relatively high current rate of 1200 mA g-1, Co3O4 with opened-book morphology delivers an excellent rate capability of 574 mA h g-1.

Two octacyanometallate-based Ni(II)W(V) bimetallic assemblies with metamagnetism

Reactions of the precursors [Ni(macrocyclic ligand)](2+) with [W(CN)(8)](3-) afford two octacyanotungstate-based assemblies, (H(2)L(1))(0.5)[Ni(L(1))][W(CN)(8)]·2DMF·H(2)O (L(1) = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) (1) and [Ni(L(2))](3)[W(CN)(8)](2)·4H(2)O (L(2) = 3,10-dipropyl-1,3,5,8,10,12-hexaazacyclotetradecane) (2). Single crystal X-ray diffraction shows that 1 consists of anionic one-dimensional (1D) linear chains, while 2 is built of 2D graphite-like layers with (6, 3) topology. Magnetic studies reveal that both complexes exhibit metamagnetic behavior from the spin-canted antiferromagnet to the ferromagnet induced by field.