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ABSTRACT: Uniform and stable micro-sized SnO(2) hollow spheres are prepared by templating against polystyrene microspheres. After being coated with a thin layer of amorphous carbon, the as-obtained SnO(2)@carbon hollow microspheres are shown to exhibit improved lithium storage properties, delivering a reversible capacity of 570 mA h g(-1) after 50 cycles at a high current density of 400 mA g(-1).
Nanoscale 05/2012; 4(12):3651-4. · 5.91 Impact Factor
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ABSTRACT: In this work, we demonstrate an interesting polystyrene microsphere-assisted synthesis of hierarchical MoS(2) spheres composed of ultrathin nanosheets. The as-prepared sample exhibits promising lithium storage properties with improved cyclic capacity retention and rate capability.
Nanoscale 11/2011; 4(1):95-8. · 5.91 Impact Factor
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Chemistry 11/2011; 17(47):13142-5. · 5.93 Impact Factor
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Advanced Functional Materials 09/2011; 21(21):4120 - 4125. · 10.18 Impact Factor
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ABSTRACT: A novel one-dimensional hierarchically structured TiO(2) (1DHS TiO(2)) was synthesized by a solvothermal method using multiwalled carbon nanotubes (MWCNTs) as a template and evaluated for the immobilization of protein and biosensing applications. Characterization studies showed that the 1DHS TiO(2) possessed an anatase crystalline structure and a large surface area with narrow pore size distribution. Fast direct electron transfer was observed for glucose oxidase (GOx) immobilized on the 1DHS TiO(2), and excellent electrocatalytic performance for glucose detection can be obtained without a mediator. The glucose sensor based on the GOx/1DHS TiO(2)-modified electrode had a high sensitivity of 9.90 μA mM(-1) cm(-2) and a low detection limit of 1.29 μM. The fabricated biosensor displayed good selectivity and long-term stability, indicating that the novel structured TiO(2) is a promising material for the immobilization of biomolecules and the fabrication of third-generation biosensors.
ACS Nano 08/2011; 5(9):7617-26. · 10.77 Impact Factor
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ABSTRACT: In this work, we employ new chemistry to grow tin oxide nanosheets in the gel matrix of sulfonated polystyrene hollow spheres. After calcination in air, hierarchical hollow spheres assembled from SnO(2) nanosheets can be obtained. In virtue of the porous shell structure and internal voids, these SnO(2) hierarchical nanosheet hollow spheres exhibit improved lithium storage capability.
Nanoscale 08/2011; 3(9):3586-8. · 5.91 Impact Factor
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ABSTRACT: We demonstrate a new hydrothermal method to directly grow SnO(2) nanosheets on a graphene oxide support that is subsequently reduced to graphene. This unique SnO(2)/graphene hybrid structure exhibits enhanced lithium storage properties with high reversible capacities and good cycling performance.
Chemical Communications 07/2011; 47(25):7155-7. · 6.17 Impact Factor
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Chemistry - An Asian Journal 06/2011; 6(9):2278-81. · 4.50 Impact Factor
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ABSTRACT: We have designed a unique hybrid structure by directly growing ultrathin anatase TiO(2) nanosheets onto graphene support for fast lithium storage. With exposed (001) high-energy facets, these TiO(2) nanosheets serve as ideal hosts for fast and efficient lithium storage. On the other hand, the graphene support serves as a highly conductive substrate that is beneficial to the high-rate performance.
Chemical Communications 05/2011; 47(20):5780-2. · 6.17 Impact Factor
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ABSTRACT: We report an interesting approach for efficient synthesis of SnO(2) hollow spheres inside mesoporous silica "nanoreactors". The as-prepared products are shown to have a uniform size distribution and good structural stability. When evaluated for their lithium storage properties, these SnO(2) hollow spheres manifest improved capacity retention.
Journal of the American Chemical Society 01/2011; 133(1):21-3. · 9.91 Impact Factor
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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
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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;
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ABSTRACT: We report a simple approach for synthesizing uniform hollow spheres assembled from anatase TiO 2 nanosheets with large amount of exposed (001) facets. These hierarchical TiO 2 hollow spheres possessing a high specific surface area of 134.9 m 2 g À1 manifest a high Coulombic efficiency for lithium extraction, excellent capacity retention, and superior rate behaviour owing to the hollow structure and unique crystal faceting of the building blocks. Titania (TiO 2) is of great importance for both fundamental studies and technological applications such as energy storage 1–5 and photo-catalysis. 6,7 Among titania polymorphs, anatase TiO 2 is most widely studied. 8 The surface energies of (001) and (101) facets of anatase TiO 2 have been calculated to be 0.90 and 0.44 J m À2 , respectively. 9 Therefore, anatase nanocrystals are dominantly bound by energeti-cally favored (101) facets. Those high-energy (001) facets are more likely to form during the earliest stages of crystal growth; however, they are quickly eliminated during further growth. 10 Thus, growth of nano/microanatase TiO 2 crystals with exposed (001) facets is highly challenging. Recently, Yang et al. reported the pioneering work on anatase TiO 2 microcrystals with 47% exposed (001) facets. 11 Following that a series of research works on synthesis of sheet-like anatase TiO 2 single-crystals with as high as 89% exposed (001) facets have been reported. 6,12–14 Despite the high percentages of (001) facets, the specific surface area of these TiO 2 nano/microcrystals is generally low because of the relatively large crystal size along the [001] direc-tion. The absolute amount of (001) facets is more relevant for prac-tical applications, for example, photocatalysis. How to get high surface area nano/microanatase TiO 2 crystals with exposed (001) facets is the second challenge. By reducing the thickness in the [001] direction and increasing the two-dimensional lateral size of the (001) planes, Wu et al. synthesized anatase TiO 2 nanosheets (NSs) with thickness of less than 1 nm by employing a facile nonaqueous route. 15 In their method, pure anatase TiO 2 is obtained by removing the stabilizing agent (oleylamine) through calcination, which will likely lead to condensation and destruction of the NS structure. Preventing the aggregation of these nano/microcrystals with large amount of exposed (001) facets is the third challenge. One promising way to obtain stable ultrathin NSs is to grow them into a three-dimension-ally (3-D) self-organized architecture, as nicely demonstrated for ultrathin zeolite and TiO 2 NSs most recently. 5,16,17 Constructing hollow structure from building blocks of anatase TiO 2 nanosheets with exposed (001) facets represents the next challenge. Hollow structures are advantageous for many applica-tions. 1,18,19 For example, hollow structures can improve reversible lithium storage capabilities. This can be explained in terms of multiple factors. First, the cavities in the hollow structure may provide extra active sites for the storage of lithium ions, which is beneficial for enhancing the specific capacity. Second, the hollow structure is often associated with larger surface area and reduced effective diffusion distance for lithium ions, leading to better rate capabilities. More importantly, the void space in hollow structures buffers against the local volume change during lithium insertion/extraction and is able to alleviate the problem of pulverization and aggregation of the elec-trode material, hence improving the cycling performance. 18 Herein, we report a simple synthesis of hollow spheres composed of anatase TiO 2 NSs with large amount of exposed (001) facets. Our strategy is based on in situ growth of anatase TiO 2 NSs with exposed (001) facets in the sulfonated gel matrix of polystyrene hollow spheres (PHS) (Fig. S1) as illustrated in Scheme 1. 20,21 Due to the presence of hydrophilic functional groups within the polymeric gel shell, TiO 2 NSs will grow within the polymer gel matrix and develop into a hierarchical structure. Use of PHS templates can effectively reduce the amount of gas out flux during the template removal by combustion. As a result, hollow spheres assembled from TiO 2 NSs can be well preserved. After being annealed in nitrogen or air, the PHS@TiO 2 -NSs are converted into carbon@TiO 2 -NSs or TiO 2 NSs, respectively.
Journal of Materials Chemistry 01/2011; · 5.97 Impact Factor
