Showing papers by "Shihe Yang published in 2011"
TL;DR: In this article, the formation of sea urchin-like, bimetallic carbonate hydroxide via a sequential crystallization process was facilely converted to porous NiCo2O4 spinel with a conserved morphology, an excellent candidate material for pseudocapacitors.
Abstract: We report kinetic control over and mechanistic studies on the formation of sea urchin-like, bimetallic (Ni, Co) carbonate hydroxidevia a sequential crystallization process, which was facilely converted to porous NiCo2O4 spinel with a conserved morphology, an excellent candidate material for pseudocapacitors. The formation of bimetallic carbonate hydroxide was found to start with the nucleation of monometallic nickel carbonate hydroxide evolving into flower-like microspheres. This was followed by the nucleation and growth of the bimetallic carbonate hydroxide nanorods from and on the nanoplates in the flower-like microspheres by localized dissolution-recrystallization, leading finally to the sea urchin structure. After calcination, a morphology conserved NiCo2O4 spinel nanostructure was formed, which uniquely comprises hierarchical, interconnected pores with high specific surface areas suitable for fast electron and electrolyte transport. This, in tandem with the rich redox reactions of nickel cobaltite spinel and their at least two orders of magnitude higher electric conductivity than those of nickel oxides and cobalt oxides alone, renders the novel nanostructures ideal candidates for pseudocapacitors. Indeed, the porous NiCo2O4 nanostructure with a specific surface area of up to 198.9 m2 g−1 has exhibited higher specific capacitances (658 F g−1 at 1 A g−1) than the monometallic cobalt oxides (60 F/g at 1 A g−1) and nickel oxides (194 F g−1 at 1 A g−) with similar porous nanostructures. Significantly, even at a high current density of 10 A g−1, the pseudocapacitor made of NiCo2O4 porous materials retained high specific capacitances of 530 F g−1 with excellent cycling stability. In all, the simple, scalable syntheses and the excellent supercapacitor performance reported here portend large scale applications of these novel materials in energy storage.
278 citations
TL;DR: Thermal nitridation of reduced graphene oxide sheets yields highly conductive and supercapacitors made of the N-doped graphene electrodes can deliver remarkable energy and power when operated at higher voltages, in the range of 0-4 V.
Abstract: Thermal nitridation of reduced graphene oxide sheets yields highly conductive (∼1000–3000 S m−1) N-doped graphene sheets, as a result of the restoration of the graphene network by the formation of C–N bonded groups and N-doping. Even without carbon additives, supercapacitors made of the N-doped graphene electrodes can deliver remarkable energy and power when operated at higher voltages, in the range of 0–4 V.
266 citations
TL;DR: In this article, the first selective synthesis of α-and β-Bi2O3 nanowires by an oxidative metal vapour transport deposition technique was focused on the first selectivity of α and β-BOWs.
Abstract: This paper is focused on the first selective synthesis of α-and β-Bi2O3 nanowires by an oxidative metal vapour transport deposition technique. The nanowires growth conditions have been systematically investigated, providing insights into the mechanism of nanowires formation. We make a critical comparison of photocatalytic properties of the α- and β-Bi2O3 nanowires by the photo-degradation of Orange G under visible light. The β-Bi2O3 nanowires have shown the highest photo-catalytic activity under visible light of all the tested samples of Degussa TiO2 P25 and α-/β-Bi2O3 nanowires, which can be interpreted by the narrowest band gap of the β-Bi2O3 nanowires for the most effective harvest of the visible light as well as their smallest size for the most facile transfer of photo-excited electrons and the consequent most effective electron-hole separation.
167 citations
TL;DR: In this paper, two kinds of precursor morphologies, oval-shaped and straw-sheaf-shaped, have been selectively prepared by hydrothermal treatment of different functional polyol molecules.
Abstract: By means of morphology-conserved transformation, we have synthesized hierarchically structured Mn2O3 nanomaterials with different morphologies and pore structures. The key step of this method consists of the formation of a precursor containing the target materials interlaced with the judiciously chosen polyol-based organic molecules, which are subsequently knocked out to generate the final nanomaterials. In the present work, two kinds of precursor morphologies, oval-shaped and straw-sheaf-shaped, have been selectively prepared by hydrothermal treatment of different functional polyol molecules (oval-shape with fructose and straw-sheaf-shape with β-cyclodextrin) and potassium permanganate. Thermal decomposition of the precursors resulted in the formation of mesoporous Mn2O3 maintaining the original morphologies, as revealed by extensive characterization. These novel hierarchical nanostructures with different pore sizes/structures prompted us to examine their potential as anode materials for lithium ion batteries (LIBs). The electrochemical results with reference to LIBs show that both of our mesoporous Mn2O3 nanomaterials deliver high reversible capacities and excellent cycling stabilities at a current density of 200 mA g−1 compared to the commercial Mn2O3 nanoparticles. Moreover, the straw-sheaf-shaped Mn2O3 exhibits a higher specific capacity and a better cycling performance than the oval-shaped one, due to the relatively higher surface area and the peculiar nanostrip structure resulting in the reduced length for lithium ion diffusion. Morphology-conserved transformation yields two kinds of hierarchical mesoporous Mn2O3 nanomaterials with high capacities and cycling stabilities for lithium ion batteries.
157 citations
TL;DR: In this article, a double-layer photoanode for dye-sensitized solar cells is proposed, which consists of highly crystalline TiO2 octahedral nanocrystals and agglutinated mesoporous microspheres.
Abstract: We report the development of a novel double layered photoanode for dye sensitized solar cells made of highly crystalline TiO2 octahedral nanocrystals and agglutinated mesoporous TiO2 microspheres. The underlayer of nanooctahedra serves as a transparent photoanode for copious and strong dye adsorption on the smooth (101) surfaces and for facilitated electron transport. Although the nanooctahedra are extremely small, our synthetic route has ensured a well-faceted crystalline shape with sharp edges and smooth surfaces, resulting in a 7.61% power conversion efficiency, much higher than that of P25 (5.76%). Separately, the overlayer of hierarchical TiO2 mesoporous microspheres plays the multiple roles of efficient light scattering, dye absorption and electrolyte permeation. Especially noteworthy is the agglutination of the microspheres through our 3D necking process, which has yielded an electron diffusion coefficient five times that of the P25 network and four times that of the nanooctahedra network. This is a significant breakthrough in DSSCs, which ensures that the photogenerated electrons in the overlayer can be effectively transported through such highway-like paths and ultimately collected at the FTO electrode. Therefore, in this double layered photoanode we have taken into consideration a number of disparate factors aimed at enhancing the overall DSSC performance. Drawing on the judicious combination of materials synthesis and engineering of nano-architectures and interfaces, solar cells based on this double layered structure have achieved 8.72% power conversion efficiency even with simple device fabrication procedures, showing promise as a new photoanode design for high efficiency dye sensitized solar cells.
147 citations
TL;DR: In this article, a polymer-templated hydrothermal growth method and subsequent calcination to achieve carbon coated hollow CuFe 2O 4 spheres (H-CuFe 2 O 4 @C).
83 citations
TL;DR: Organic–inorganic nanocomposites are one type of advanced material for organic devices because of the expected synergy between the organic and inorganic components, which lead potentially to new physical properties of the composites and various applications in devices.
Abstract: Organic electronics have attracted much attention recently because of the many advantages over inorganic semiconductor devices, including low cost, solution processability, fl exibility, and environmental friendliness. [ 1 ] Organic–inorganic nanocomposites are one type of advanced material for organic devices because of the expected synergy between the organic and inorganic components, which lead potentially to new physical properties of the composites and various applications in devices, including solar cells, [ 2–6 ] phototransistors, [ 7–9 ] memories, [ 10 ]
65 citations
TL;DR: The nonspecific adsorption of charged quantum dots onto a supported zwitterionic lipid bilayer is studied by using quartz crystal microbalance with dissipation (QCM-D) to provide important information on QD-lipid membrane interactions, which will help to develop new drug molecules and efficient drug delivery systems.
Abstract: Understanding how the composition and environmental conditions of membranes influence their interactions with guest species is central to cell biology and biomedicine. We herein study the nonspecific adsorption of charged quantum dots (QDs) onto a supported zwitterionic lipid bilayer by using quartz crystal microbalance with dissipation (QCM-D). It is demonstrated that (1) the adsorption of charged QDs is charge-dependent in a way similar to but much stronger than that of the capping molecules by reason of size effect; (2) the adsorption behavior of charged QDs is dominated by electrostatic interaction, which can be well described by an “adsorption window”; (3) the “adsorption window” can be broadened by exploiting the bridge role of Ca2+ ions; and (4) by introducing a cationic lipid into the zwitterionic lipid bilayer, one can achieve preferential adsorption of anionic QDs but suppression of the cationic QD adsorption. Our QCM-D data also indicates that these different adsorption traits effect different ...
57 citations
TL;DR: The structure of the fluorescent C60 nanoparticles was deduced as a ∼5 nm sphere with a solid core of aggregated C60 and an anionic shell of C603−, which renders the nanoparticles water soluble.
Abstract: Aqueous solutions of fluorescent ultrafine C60 nanoparticles have been successfully prepared by an electrochemical method, which involves reducing a C60 film to C603− anions in the presence of tetrabutylammonium (TBA+) cations in acetonitrile solution and transferring to water. The nanoparticles are highly emissive in the visible region. The structure of the fluorescent C60 nanoparticles was deduced as a ∼5 nm sphere with a solid core of aggregated C60 and an anionic shell of C603−, which renders the nanoparticles water soluble. The photostable and nontoxic C60 nanoparticles can easily penetrate into live cells, and are thus primed for a host of biomedical applications.
42 citations
TL;DR: Compared were the performances of glucose biosensors with GOx immobilized on mesoporous SiO(2) by physical adsorption and by covalent binding to 3-aminopropyltrimethoxysilane (APTMS) modified SiO (2) using glutaraldehyde as the cross-linker.
39 citations
TL;DR: In this article, the authors provide mechanistic insight into the self-assembly involved in the controlled synthesis of mesoporous TiO2 microspheres with tunable sizes (200, 400, and 600 nm on average).
TL;DR: In this paper, the transition temperatures for the α or β to δ and the δ to liquid phase for α- and β-Bi 2 O 3 nanowires were investigated.
TL;DR: The promise of the C( 60) hollow structures as Pt catalyst supports is heightened by the significantly enhanced catalytic activity toward methanol oxidation for a given amount of C(60) used, which demonstrates their potential application in fuel cells.
Abstract: Large-scale single-crystalline hollow nanobowls of pure C(60) were prepared by applying a sonophysical strategy in a binary organic solution. Through the simple adjustment of the concentration of the C(60) /m-xylene solution and the volume ratio of m-xylene to acetonitrile, C(60) nanorings, nanoplates, nanorods, and nanowires were also selectively synthesized. The promise of the C(60) hollow structures as Pt catalyst supports is heightened by the significantly enhanced catalytic activity toward methanol oxidation for a given amount of C(60) used, which demonstrates their potential application in fuel cells.
TL;DR: By means of the high reversibility of the thermosensitive phase transition of the P(NIPAM-co-MAA) microspheres, SERS activity of the silver nanoparticle network embedded in the microsphere can be well controlled by thermal-induced variation of special separation.
Abstract: By in situ reduction of Ag(+) ions pre-dispersed inside thermosensitive microspheres of poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P(NIPAM-co-MAA)), a 3D copolymer-supported network of silver nanoparticles is created and extensively characterized by surface-enhanced Raman scattering (SERS). The effective dispersion and the suitable density of the silver nanoparticles in the composite microspheres are demonstrated by the thermal-induced SERS signal and its high reproducibility during thermocycling. When the temperature of the system increases above 32 °C, spatial separation of the silver nanoparticles decreases and the numbers of Ag nanoparticles and P(NIPAM-co-MAA) microspheres under illumination spot increase as a result of the shrinkage of the P(NIPAM-co-MAA) chains, leading to the ramp of the SERS effect. By means of the high reversibility of the thermosensitive phase transition of the P(NIPAM-co-MAA) microspheres, SERS activity of the silver nanoparticle network embedded in the microsphere can be well controlled by thermal-induced variation of special separation.
TL;DR: In this paper, high magnesium calcite microspheres (HMCMs) have been obtained, which consist of vertically aligned single crystal nanorod building blocks and show good mechanical properties.
Abstract: Mg2+ ions and acidic proteins are both controlling elements in biomineralization. The present study combines the two types of additives (Mg2+ ions and a denatured collagen protein (gelatin)) to direct the mineralization of CaCO3. We find that the polymorphs and morphologies critically depend on gelatin concentration at a given Mg2+ concentration. Moreover, at a given gelatin concentration, the Mg molar percentages in the mother liquor, although not a determining factor for the polymorphs, can affect the crystal micro- and nano-structures. The controlled crystallization can be rationalized by the interplay between Mg2+ and gelatin, which mutually enhances their uptake and regulate the concomitant mineralization. We have obtained high magnesium calcite microspheres (HMCMs), which consist of vertically aligned single crystal nanorod building blocks. Such HMCMs show good mechanical properties (Er = 28.91 ± 2.97 GPa; H = 1.37 ± 0.07 GPa), akin to the central stereo of the spine skeleton of Paracentrotus. lividus (Er = 32.20 ± 3.26 GPa; H = 1.76 ± 0.70 GPa).1 The remarkable mechanical properties should be ascribed to the hierarchical structure, the anisotropic arrangement, and the centrally aligned calcite nanorods separated by the cohesive gelatin matrix, which can effectively dissipate energy under force loading.
TL;DR: In this paper, the authors used ZnO nanotetrapods for photoanodes of dye-sensitized solar cells (DSSCs) in their group.
Abstract: In this paper, we reviewed recent systematic studies of using ZnO nanotetrapods for photoanodes of dye-sensitized solar cells (DSSCs) in our group. First, the efficiency of power conversion was obtained by more than 3.27% by changes of conditions of dye loading and film thickness of ZnO nanotetrapod. Short-circuit photocurrent densities (Jsc) increased with the film thickness, Jsc would not be saturation even the film thickness was greater than 35 μm. The photoanode architecture had been charactered by good crystallinity, network forming ability, and limited electron-hopping interjunctions. Next, DSSCs with high efficiency was devised by infiltrating SnO2 nanoparticles into the ZnO nanotetrapods photoanodes. Due to material advantages of both constituents described as above, the composite photoanodes exhibited extremely large roughness factors (RFs), good charge collection, and tunable light scattering properties. By varying the composition of the composite photoanodes, we had achieved an efficiency of 6.31% by striking a balance between high efficiency of charge collection for SnO2 nanoparticles rich films and high light scattering ability for ZnO nanotetrapods rich films. An ultrathin layer of ZnO was found to form spontaneously on the SnO2 nanoparticles, which primarily was responsible for enhancing open-circuit photovoltage (Voc). We also identified that recombination in SnO2/ZnO composite films was mainly determined by ZnO shell condition on SnO2, whereas electron transport was greatly influenced by the morphologies and sizes of ZnO crystalline additives. Finally, we applied the composite photoanodes of SnO2 nanoparticles/ZnO nanotetrapods to flexible DSSCs by low temperature technique of “acetic acid gelation-mechanical press-ammonia activation.” The efficiency has been achieved by 4.91% on ITO-coated polyethylenenaphtalate substrate. The formation of a thin ZnO shell on SnO2 nanoparticles, after ammonia activation, was also found to be critical to boosting Voc and to improving inter-particles contacts. Mechanical press, apart from enhancing film durability, also significantly improved charge collection. ZnO nanotetrapods had been demonstrated to be a better additive than ZnO particles for the improvement of charge collection in SnO2/ZnO composite photoanodes regardless of whether they were calcined.
TL;DR: A novel surface-enhanced Raman scattering (SERS) approach for accurate quantification of mononucleotides of deoxyribonucleic acid (DNA) is described and can be similarly precise but the SERS measurement is simple, rapid and potentially cheap.
TL;DR: In this paper, the authors studied the crystallization of calcite from an amorphous calcium carbonate (ACC) precursor inside a three-dimensional insoluble chitosan scaffold.
Abstract: Biominerals provide excellent mechanical properties for skeletal support and protection, rivaling and even outperforming those of many engineered ceramics fabricated at high temperatures and pressures. However, the mechanisms of biomineralization are still poorly understood. To make progress in this direction, here we study the crystallization of calcite (thermodynamically the most stable CaCO 3 phase) from an amorphous calcium carbonate (ACC) precursor inside a three-dimensional insoluble chitosan scaffold. A hydrated ACC phase with complete disorder is found to first nucleate from citrate-calcium ion pairs and subsequently transform into stabilized ACC nanoparticles with a short-range order of calcite, which then crystallize and grow into calcite nanocrystals via the transient ACC phase, instead of direct crystallization from the hydrated ACC precursor as reported previously. The calcite nanocrystals are aggregated and collectively oriented into rough rhombohedral calcite mesocrystals, and eventually evolve into smooth mesocrystals. Mechanical property characterizations of the novel bio-inspired nanocomposites show a strong dependence on the content of the constituent inorganic nanocrystals. Furthermore, the reduced elastic modulus is closely related to the interfacial interaction strength between the inorganic nanocrystals and the organic matrix, whereas the hardness is dependent on the crystallinity of the constituent inorganic mesocrystals in the nanocomposites.
TL;DR: In this paper, the role of functional groups in controlling the polymorph and morphology of magnesium-containing calcium carbonate has been investigated and it was shown that functional groups of organic molecules added into the starting amorphous precursor reactant rather than added in the transformation process can influence the polymorph selection.
Abstract: Mineralization can be divided into the nucleation of amorphous precursors and the subsequent amorphous to crystalline transformation. Although the biomimetic transformations from amorphous precursors to different crystalline phases have been reported in a variety of settings, the issue on what determines the polymorph selection and morphology remains elusive. The present work studied the roles of organic molecules with different functional groups added in the nucleation process and added in the transformation process in controlling the polymorph and morphology of magnesium-containing calcium carbonate. We find that polymorph selection is controlled by the functional groups of organic molecules added into the starting amorphous precursor reactant rather than added in the transformation process. Specifically, when added in the first process, hydroxyl and amine groups induced a preferential transformation from amorphous to the thermodynamically metastable aragonite and carboxyl groups to the thermodynamically most stable calcite, whereas little difference was effected when these functional groups were introduced in the second process. Our work has important implications in in vivo polymorph selections of aragonite and calcite from amorphous precursors by functional groups of the omnipresent biomolecules such as proteins and polysaccharides.
TL;DR: In this article, the effects of oxygenic versus oxygen-free environments on colloidal CdSe nano-tetrapods and quantum dots (QDs) were studied using both continuous and time-resolved photoluminescence (PL) measurements.
Abstract: The effects of oxygenic versus oxygen-free environments on colloidal CdSe nano-tetrapods and quantum dots (QDs) were studied using both continuous and time-resolved photoluminescence (PL) measurements. The decays of PL intensities for tetrapods and QDs in oxygen-free solution (chloroform) and in air (on silicon) can be well fitted by a bi-exponential function. Based on the emission-energy dependence of carrier lifetimes and the amplitude ratio of the fast-decay component to the slow-decay component, the fast and slow PL decays of CdSe nanocrystals are attributed to the recombination of delocalized carriers in the core states and localized carriers in the surface states, respectively. The PL intensities of CdSe nano-tetrapods and QDs were found to be five times and an order of magnitude higher in air than in vacuum, respectively, which is explained by the passivation of surface defects by the polar gas (oxygen) absorption. The lower enhancement in PL intensities of CdSe nano-tetrapods is explained by the special morphology of the tetrapods.
TL;DR: In this article, the hollow gold tetrapod was prepared for the first time by using ZnO tetrapods as a template, HAuCl 4 as a gold source and ascorbic acid as a reducing reagent.