Publications (9)56.71 Total impact
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Article: Highly Efficient Removal of Organic Dyes from Waste Water Using Hierarchical NiO Spheres with High Surface Area
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ABSTRACT: A facile solvothermal method has been developed for large-scale preparation of uniform spheres of a nickel−ethylene glycol complex (Ni-EG complex) with a hierarchical nanostructure. The dispersibility and hierarchical structure of the Ni-EG particles can be tuned by varying the concentration of additives added. On the basis of experimental observations, a plausible mechanism has been proposed to understand the formation process of the Ni-EG complex spheres. Calcining these as-prepared Ni-EG complex spheres at 300 °C in air results in uniform porous NiO spheres with a high specific surface area of 222 m 2 g −1 . When served as the adsorbent for Congo red in water, the colloidal suspension of the as-prepared NiO hierarchical spheres exhibits a high adsorption capacity for the dye removal, suggesting their potential use in water treatment.The Journal of Physical Chemistry C 01/2012; · 4.80 Impact Factor -
Article: Controlled synthesis of hierarchical NiO nanosheet hollow spheres with enhanced supercapacitive performance
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ABSTRACT: In this work, we report a facile strategy for the controlled synthesis of nickel oxide (NiO) hollow spheres (HSs) assembled from nanosheets (NSs). The Ni 2 CO 3 (OH) 2 NSs are first grown on sulfonated polystyrene (sPS) hollow spheres by a low-temperature solution route. NiO HSs with well preserved morphology are then obtained by calcining the as-prepared sPS@ Ni 2 CO 3 (OH) 2 NSs composite HSs. Because of the hollow interior and hierarchical structure, these NiO nanosheet hollow spheres have a relatively high specific surface area of 62 m 2 g À1 . When evaluated for supercapacitive performance, these hierarchical NiO HSs demonstrate improved electrochemical properties with a high capacitance of 415 F g À1 even at a high charge–discharge current rate of 3 A g À1 and 91% of which can be retained after 1000 charge–discharge cycles.Journal of Materials Chemistry 01/2011; · 5.97 Impact Factor -
Article: Hierarchical nickel sulfide hollow spheres for high performance supercapacitors
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ABSTRACT: Hierarchical NiS hollow spheres assembled from ultrathin nanosheets are synthesized by an efficient template-engaged conversion method. Silica nanospheres were used as templates, and SiO 2 @nickel silicate core-shell nanostructures were first prepared. In the presence of Na 2 S, the nickel silicate shell completely transformed into NiS nanosheets via a hydrothermal treatment, accompanied by the total dissolution of the inner SiO 2 core. This gives rise to uniform hollow nanospheres whose shells are assembled from ultrathin NiS nanosheets. In virtue of the large surface area and enhanced structural stability, the as-prepared NiS hollow spheres exhibit excellent electrochemical performance as electrode materials for supercapacitors. Hollow micro/nanostructures have attracted tremendous research interest in a myriad of applications, such as lithium-ion batteries, 1–4 catalysis, 5–6 chemical sensors 7–9 and biomedical applications, 10–14 due to their unique structural features including well-defined interior voids, low density, large surface area and surface permeability. 15 Templating against colloidal particles is regarded as the most straightforward and effective route towards hollow structures with narrow size distributions and well-defined shapes. 16–18 In general, templating methods involve the growth of a shell of designed materials on various colloidal templates (e.g., monodisperse latex and silica spheres) and subsequent removal of the template to generate the interiors with desirable complexity. The use of templates in principle allows one to manipulate the size and morphology of resultant hollow particles for better control of the local chemical environment and extraordinary properties. However, difficulties ranging from material incompatibility to the collapse or deformation of hollow structures upon template removal are common in practice. The disadvantage of being time-consuming and the general requirement of a tedious multistep procedure also greatly restrict the extensive application of templating methods. Nickel sulfides with many different phases such as NiS, NiS 2 , b-Ni 3 S 2 , a-Ni 3+x S 2 , Ni 4 S 3+x , Ni 6 S 5 , Ni 7 S 6 , Ni 9 S 8 and Ni 3 S 4 are inexpensive and abundant materials with widespread applications as ceramic tougheners, hydrogenation catalysts and electrode materials, etc. 19–23 Despite the success in the synthesis of various morphologies, including nanochains, 24 hollow spheres 25–26 and layer-rolled struc-tures, 27 the preparation of uniform hierarchical hollow structures of nickel sulfides still remains as a significant challenge. Herein, we report an effective conversion route for controllable synthesis of uniform NiS hollow spheres with a hierarchical structure by template-engaged precipitation of nickel silicates and subsequent in situ chemical conversion to NiS phase. Remarkably, these formed hollow spheres are entirely assembled from ultrathin NiS nanosheets with a thickness of a few nanometres, and simultaneously the silica cores are completely removed during the conversion reaction in a basic solution. When evaluated for potential use in supercapacitors, the NiS hierarchical hollow spheres exhibit excellent electrochemical performance due to their unique structure and high surface area. The scheme in Fig. 1 illustrates our concept for the synthesis of NiS hollow spheres. First, monodisperse silica nanospheres are functionalized with silicate anions in an alkaline solution generated by the hydrolysis of urea. Driven by the interfacial reaction between aqueous solution of nickel nitrate and activated silica nanospheres, uniform deposition of nickel silicate occurs around the scaffold of silica template to form a nickel silicate shell. 28–29 Such SiO 2 @nickel silicate core-shell structures are readily converted into NiS hollow spheres at an elevated temperature by reacting with sodium sulfide (Na 2 S), where the silica cores are etched simultaneously by OH 2 released from the hydrolysis of sulfide ions. Herein Na 2 S not only serves as sulfurizing agent for the phase transformation from nickel silicate to thermodynamically favored nickel sulfide, but also grants the as-formed hollow spheres structural integrity by providing a mild alkaline environment to gradually remove the silica template. As a result of favorable kinetic control over this process, delicate nanosheets are formed as the subunits of the hierarchical hollow spheres.RSC Advances 01/2011; -
Article: Building hematite nanostructures by oriented attachment.
Angewandte Chemie International Edition 01/2011; 50(3):650-3. · 13.45 Impact Factor -
Article: Facile synthesis of metal oxide/reduced graphene oxide hybrids with high lithium storage capacity and stable cyclability.
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ABSTRACT: We report an environment-friendly approach to synthesize transition metal oxide nanoparticles (NPs)/reduced graphene oxide (rGO) sheets hybrids by combining the reduction of graphene oxide (GO) with the growth of metal oxide NPs in one step. Either Fe2O3 or CoO NPs were grown onto rGO sheets in ethanol solution through a solvothermal process, during which GOs were reduced to rGO without the addition of any strong reducing agent, e.g. hydrazine, or requiring any post-high-temperature annealing process. The GO or rGO during the precipitation of metal oxide NPs may act as heterogeneous nucleation seeds to facilitate the formation of small crystal grains. This may allow more efficient diffusion of Li ions and lead to high specific capacities. These metal oxide NPs-rGO hybrids were used as anodes for Li-ion batteries, which showed high capacities and excellent charge-discharge cycling stability in the voltage window between 0.01 and 3.0 V. For example, Fe2O3 NPs/rGO hybrids showed specific capacity of 881 mA h g(-1) in the 90th cycle at a discharge current density of 302 mA g(-1) (0.3 C), while CoO NPs/rGO hybrids showed a lower capacity of 600 mA h g(-1) in the 90th cycle at a discharge current density of 215 mA g(-1) (0.3 C). These nanohybrids also show excellent capacities at high C rate currents, e.g. 611 mA h g(-1) for Fe2O3/rGO sample in the 300th cycle at 2014 mA g(-1) (2 C). Such synthesis technique can be a promising route to produce advanced electrode materials for Li-ion batteries.Nanoscale 12/2010; 3(3):1084-9. · 5.91 Impact Factor -
Article: Shape-controlled synthesis of cobalt-based nanocubes, nanodiscs, and nanoflowers and their comparative lithium-storage properties.
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ABSTRACT: Facile hydrothermal methods have been developed to synthesize large Co3O4 nanocubes, β-Co(OH)2 hexagonal nanodiscs and nanoflowers. Samples are thoroughly characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller method, and thermogravimetric analysis. The Co3O4 nanocubes have an average size of about 350 nm with a perfect cubic shape, and the β-Co(OH)2 nanodiscs are uniform hexagonal platelets, whereas the β-Co(OH)2 nanoflowers are assembled from large sheetlike subunits. After thermal annealing in air at a moderate temperature, the as-prepared β-Co(OH)2 samples can be converted into spinel Co3O4 without significant alterations in morphology. We have also investigated the comparative lithium storage properties of these three Co3O4 samples with distinct morphologies. The nanoflower sample shows highly reversible lithium storage capability after 100 charge-discharge cycles.ACS Applied Materials & Interfaces 11/2010; 2(12):3628-35. · 4.53 Impact Factor -
Article: One-pot synthesis of uniform carbon-coated MoO(2) nanospheres for high-rate reversible lithium storage.
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ABSTRACT: Uniform carbon-coated MoO(2) nanospheres assembled from small primary nanocrystals have been synthesized by a one-pot hydrothermal method followed by thermal annealing. Because of the desirable structural features, these core-shell MoO(2)@carbon nanospheres exhibit significantly improved electrochemical performance for high-rate reversible lithium storage.Chemical Communications 10/2010; 46(37):6906-8. · 6.17 Impact Factor -
Article: Top-down fabrication of α-Fe2O3 single-crystal nanodiscs and microparticles with tunable porosity for largely improved lithium storage properties.
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ABSTRACT: In this work, we report a facile top-down approach to fabricate uniform single-crystal α-Fe(2)O(3) nanodiscs via selective oxalic acid etching. Phosphate ions are employed as a capping agent to control the etching to along the [001] direction. We also show that α-Fe(2)O(3) melon-like microparticles with contrasting textural properties can be generated using the same approach. The etched particles exhibit a much larger total pore volume and average pore size compared to the pristine ones, thus serving as the possible origin for their greatly enhanced capacity retention when tested as potential anode materials for lithium-ion batteries.Journal of the American Chemical Society 09/2010; 132(38):13162-4. · 9.91 Impact Factor -
Article: Shape-controlled synthesis of porous Co3O4 nanostructures for application in supercapacitors
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ABSTRACT: In this work, we report a facile approach for the shape-controlled synthesis of cobalt carbonate/ hydroxide intermediates. Three different structures, viz., one-dimensional (1D) needle-like nanorods, two-dimensional (2D) leaf-like nanosheets, and three-dimensional (3D) oval-shaped microparticles, have been synthesized through varying experimental parameters such as precursor (cobalt acetate) concentrations and volume ratio of polyethylene glycol to water. Phase-pure tricobalt tetroxide (Co 3 O 4) has been obtained by annealing these as-prepared intermediates without significant alterations in morphology. With relatively high specific surface areas of 86.1–121.5 m 2 g À1 , these products with distinct nanostructures were tested for their potential application in supercapacitors. The results show that these porous Co 3 O 4 structures exhibit promising capacitive properties with high capacitance and good retention. The needle-like nanorods show the highest capacitance of 111 F g À1 , and 88.2% of which can still be maintained after 1000 charge–discharge cycles.Journal of Materials Chemistry 01/2010; · 5.97 Impact Factor
Top co-authors
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Institutions
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2010–2011
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Nanyang Technological University
- School of Chemical and Biomedical Engineering
Singapore, Singapore
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