One‐Pot Self‐Templating Synthesis of Pt Hollow Nanostructures and Their Catalytic Properties for CO Oxidation

Nanoporous Pt hollow nanostructures with octahedral and hexagonal frame‐like morphologies were prepared by a novel one‐pot self‐templating route with no assistance from a preformed template or shape‐directing agent. The hexagonal frame‐like Pt hollow structures exhibited significantly enhanced catalytic activity toward CO oxidation reaction compared to the octahedral Pt hollow nanostructures due to the higher oxidation state of Pt.     

One-step synthesis of SnO2 and TiO2 hollow nanostructures with various shapes and their enhanced lithium storage properties

A versatile one-step method for the general synthesis of metal oxide hollow nanostructures is demonstrated. This method involves the controlled deposition of metal oxides on shaped α-Fe(2)O(3) crystals which are simultaneously dissolved. A variety of uniform SnO(2) hollow nanostructures, such as nanococoons, nanoboxes, hollow nanorings, and nanospheres, can be readily generated. The method is also applicable to the synthesis of shaped TiO(2) hollow nanostructures. As a demonstration of the potential applications of these hollow nanostructures, the lithium storage capability of SnO(2) hollow structures is investigated. The results show that such derived SnO(2) hollow structures exhibit stable capacity retention of 600-700?mA h g(-1) for 50?cycles at a 0.2?C rate and good rate capability at 0.5-1?C, perhaps benefiting from the unique structural characteristics.     

The electronic structures and properties of open-ended and capped carbon nanoneedles

The existence of a family of very thin carbon needlelike nanostructures is predicted: the geometry and stability of several carbon nanoneedles (CNNs) formed by C4 and C6 units have been studied by quantum chemistry computational modeling methods. The structures of carbon nanoneedles are tighter than even the smallest single wall nanotubes (SWNTs) based on (4, 0) naphthacene. The electronic properties, energetic stability of geometrical structures with various terminal units are investigated. The relatively large band gaps, the strong bonding, and additional orbital interactions within the C4 rings and between the C4 layers make the H4(C4)(n)H4 type molecules nonmetallic. We have found indications that if the CNN (3, 0) structures are very long (in the limit of infinite-length), then they are likely to have semiconducting properties and could possibly be used as actual semiconductors. The studied families of CNNs can be considered as carbon nanostructures with unique structural and chemical properties and with possible potential for unusual electronic properties, with likely practical applications as nanomaterials and nanostructure devices.     

High sintering resistance of platinum nanoparticles embedded in a microporous hollow carbon shell fabricated through a photocatalytic reaction

Platinum (Pt) nanoparticles encapsulated in microporous carbon with a hollow structure (nPt@hC) were fabricated on the basis of a titanium(IV) oxide (TiO2) photocatalytic reaction. From the tomogram of a sample studied by using a transmission electron microscope (TEM), the Pt nanoparticles were found to be embedded in the carbon shell and were physically separated from each other by the carbon matrix. Owing to this unique structure, the Pt particles showed high resistance to sintering when subjected to thermal treatment at temperatures up to 800 degrees C. As a result, hydrogenation reactions using various heat-treated nPt@hCs as catalysts indicated that loss of catalytic activity was minimized. Thus, the present system will be a promising system for optimizing catalyst nanostructures utilized in processes requiring rigorous conditions.     

Graphitic carbon nanostructures via a facile microwave-induced solid-state process

A novel approach to fabricate highly graphitic carbon nanostructures such as carbon nanotubes (CNTs), metal/graphitic-shell nanocrystals and hollow carbon nanospheres (HCNSs) in a very short time is demonstrated.     

Carbon‐Incorporated Nickel–Cobalt Mixed Metal Phosphide Nanoboxes with Enhanced Electrocatalytic Activity for Oxygen Evolution

Hollow nanostructures have attracted increasing research interest in electrochemical energy storage and conversion owing to their unique structural features. However, the synthesis of hollow nanostructured metal phosphides, especially nonspherical hollow nanostructures, is rarely reported. Herein, we develop a metal–organic framework (MOF)‐based strategy to synthesize carbon incorporated Ni–Co mixed metal phosphide nanoboxes (denoted as NiCoP/C). The oxygen evolution reaction (OER) is selected as a demonstration to investigate the electrochemical performance of the NiCoP/C nanoboxes. For comparison, Ni–Co layered double hydroxide (Ni–Co LDH) and Ni–Co mixed metal phosphide (denoted as NiCoP) nanoboxes have also been synthesized. Benefiting from their structural and compositional merits, the as‐synthesized NiCoP/C nanoboxes exhibit excellent electrocatalytic activity and long‐term stability for OER.     

Preparation of non-spherical hollow carbon nanocapsules from nickel nanoprecursors

Hollow carbon nanocapsules (NCs) are prepared from nickel nanoplate precursors through carburizing, decomposition, and leaching steps. The carburizing step was carried out by heating the nickel nanoplates in oleylamine at 250 °C for 4 h. Decomposition was then performed in a nitrogen atmosphere at 530 °C for 3 min. Characterization of the resulting product of the first two steps shows the intermediates to be Ni₃C/Ni–C alloy and Ni/C core–shell nanostructures. Hollow carbon NCs are recovered from the products by leaching the Ni/C core–shell nanostructures in concentrated nitric acid. The NCs are found to have a high specific surface area (1081 m² g⁻¹) and a mesoporous structure (i.e., a pore volume of 2.81 cm³/g and a narrow pore size distribution of 2.9–3.4 nm). In addition, it is found that the hollow carbon NCs retained the same morphology as the original nickel precursors; demonstrating the robustness of the nickel templates and the ability of the carbon shells to maintain a non-spherical shape.     

Colloidal chemical approaches to inorganic micro- and nanostructures with controlled morphologies and patterns

The controlled synthesis of inorganic micro- and nanostructures with tailored morphologies and patterns has attracted intensive interest because the properties and performances of micro- and nanostructured materials are largely dependent on the shape and structure of the primary building blocks and the way in which the building blocks are assembled or integrated. This review summarizes the recent advances on the solution-phase synthesis of inorganic micro- and nanostructures with controlled morphologies and patterns via three typical colloidal chemical routes, i.e., synthesis based on catanionic micelles, reactive templates, and colloidal crystal templates, with focus on the approaches developed in our lab. Firstly, catanionic micelles formed by mixed cationic/anionic surfactants are used as effective reaction media for the shape-controlled synthesis of inorganic nanocrystals and the solution growth of hierarchical superstructures assembled by one-dimensional (1D) nanostructures. Secondly, reactive template-directed chemical transformation strategy provides a simple and versatile route to fabricate both hollow structures and 1D nanostructures. Thirdly, colloidal crystals are employed as very effective templates for the facile solution-phase synthesis of novel inorganic structures with controlled patterns, such as three-dimensionally (3D) ordered macroporous materials and two-dimensionally (2D) patterned nanoarrays and nanonets. Finally, a brief outlook on the future development in this area is presented.     

Fabrication of functional hollow carbon spheres with large hollow interior as active colloidal catalysts

In this study,we have established a facile method to synthesize functional hollow carbon spheres with large hollow interior,which can act as active colloidal catalysts.The method includes the following steps:first,hollow polymer spheres with large hollow interior were prepared using sodium oleate as the hollow core generator,and 2,4-dihydroxybenzoic acid and hexamethylene tetramine(HMT) as the polymer precursors under hydrothermal conditions;Fe 3+ or Ag + cations were then introduced into the as-prepared hollow polymer spheres through the carboxyl groups;finally,the hollow polymer spheres can be pseudomorphically converted to hollow carbon spheres during pyrolysis process,meanwhile iron or silver nanoparticles can also be formed in the carbon shell simultaneously.The structures of the obtained functional hollow carbon spheres were characterized by TEM,XRD,and TG.As an example,Ag-doped hollow carbon spheres were used as colloid catalysts which showed high catalytic activity in 4-nitrophenol reduction reaction.     

A general method for the rapid synthesis of hollow metallic or bimetallic nanoelectrocatalysts with urchinlike morphology

We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100 degrees C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile. Most importantly, the hollow bimetallic nanospheres (Au/Pt and Pd/Pt) obtained here exhibit an area of greater electrochemical activity than other Pt hollow or solid nanospheres. In addition, the approximately 6 nm hollow urchinlike Pt nanospheres can achieve a potential of up to 0.57 V for oxygen reduction, which is about 200 mV more positive than that obtained by using a approximately 6 nm Pt nanoparticle modified glassy carbon (GC) electrode. Rotating ring-disk electrode (RRDE) voltammetry demonstrates that approximately 6 nm hollow Pt nanospheres can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated H(2)SO(4) (0.5 M). Finally, compared to the approximately 6 nm Pt nanoparticle catalyst, the approximately 6 nm hollow urchinlike Pt nanosphere catalyst exhibits a superior electrocatalytic activity toward the methanol oxidation reaction at the same Pt loadings.     

利用Ostwald熟化作用合成空心碳纳米材料

以淀粉等易获得的生物质为碳前驱物, 亚铁盐为添加剂, 采用水热法制备了碳材料. 实验发现, 在反应过程中, 首先生成了被无定形碳包裹的铁氧化物纳米棒, 形成碳/铁氧化物的核/壳结构. 在进一步的反应中, 铁氧化物核自发溶解, 最终得到了空心的碳纳米棒. 讨论了铁氧化物自发溶解的原因, 认为空心碳纳米棒的形成是由Ostwald熟化现象造成的. 当以葡萄糖或环糊精为碳前驱物时, 得到的是空心碳球, 这可能与各种碳前驱物不同的表面活性剂作用有关.     

One‐Step Synthesis of SnO2 and TiO2 Hollow Nanostructures with Various Shapes and Their Enhanced Lithium Storage Properties

A versatile one‐step method for the general synthesis of metal oxide hollow nanostructures is demonstrated. This method involves the controlled deposition of metal oxides on shaped α‐Fe₂O₃ crystals which are simultaneously dissolved. A variety of uniform SnO₂ hollow nanostructures, such as nanococoons, nanoboxes, hollow nanorings, and nanospheres, can be readily generated. The method is also applicable to the synthesis of shaped TiO₂ hollow nanostructures. As a demonstration of the potential applications of these hollow nanostructures, the lithium storage capability of SnO₂ hollow structures is investigated. The results show that such derived SnO₂ hollow structures exhibit stable capacity retention of 600–700 mAh g^?1 for 50 cycles at a 0.2 C rate and good rate capability at 0.5–1 C, perhaps benefiting from the unique structural characteristics.     

Structure and thermodynamics of carbon and carbon/silicon precursors to nanostructures

The structures at the Hartree-Fock level, as well as the energetics, are reported for the unsaturated system C(36)H(16), its Si-doped analogue C(32)Si(4)H(16), and several smaller, unsaturated fragments. Structural effects on the electronic distribution are discussed in terms of a localized orbital energy decomposition. The standard heats of formation are calculated based on homodesmic and isodesmic reactions and the G2(MP2,SVP) method with a valence double-zeta plus polarization basis. The origin of the observed explosion of the all-carbon system (C(36)H(16)) to form carbon nanotubes was investigated by exploring a possible initial reactive channel (dimerization), which could lead to the formation of the observed onion-type nanostructures.     

Biomolecule-assisted route to prepare titania mesoporous hollow structures

Amino acids, as a particularly important type of biomolecules, have been used as multifunctional templates to intelligently construct mesoporous TiO(2) hollow structures through a simple solvothermal reaction. The structure-directing behaviors of various amino acids were systematically investigated, and it was found that these biomolecules possess the general capability to assist mesoporous TiO(2) hollow-sphere formation. At the same time, the nanostructures of the obtained TiO(2) are highly dependent on the isoelectric points (pI) of amino acids. Their molecular-structure variations can lead to pI differences and significantly influence the final TiO(2) morphologies. Higher-pI amino acids (e.g., L-lysine and L-arginine) have better structure-directing abilities to generate nanosheet-assembled hollow spheres and yolk/shell structures. The specific morphologies and mesopore size of these novel hollow structures can also be tuned by adjusting the titanium precursor concentration. Heat treatment in air and vacuum was further conducted to transform the as-prepared structures to porous nanoparticle-assembled hollow TiO(2) and TiO(2)/carbon nanocomposites, which may be potentially applied in the fields of photocatalysts, dye-sensitized solar cells, and Li batteries. This study provides some enlightenment on the design of novel templates by taking advantage of biomolecules.     

Self-assembly of Co-based nanosheets into novel nest-shaped nanostructures: Synthesis and characterization

We report the first observation of the formation of novel Co-based three-dimensional (3D) self-assembly hollow nanostructures, i.e., nest-shaped nanospheres composed of sheet-like particles, via reduction of cobalt salt with sodium tetrahydroboride in cetyltrimethylammonium bromide (CTAB)-cyclohexane-NH4F aqueous solutions. It was found that the cyclohexane has a significant influence on the formation of the nest-shaped Co-based nanospheres, because when the experiments are carried out in the absence of cyclohexane, only sheet-like particles are formed. NH4F plays also an important role in the formation of the hollow nanostructures because without this salt mainly solid spherical structures, composed of sheet-like particles, instead of nest-shaped structures are obtained. The nanostructures are mainly formed by Co, but also a minor amount (17%) of Co2B is present in the final compounds. The structures are characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and field-emission scanning electron microscopy (FESEM). A possible mechanism for the formation of the novel Co-based nanostructures is proposed.     

Tailoring the carbon nanostructures grown on the surface of Ni-Al bimetallic nanoparticles in the gas phase

A gas-phase, one-step method for producing various aerosol carbon nanostructures is described. The carbon nanostructures can be selectively tailored with either straight, coiled, or sea urchin-like structures by controlling the size of Ni-Al bimetallic nanoparticles and the reaction temperature. The carbon nanostructures were grown using both conventional spray pyrolysis and thermal chemical vapor deposition. Bimetallic nanoparticles with catalytic Ni (guest) and non-catalytic Al (host) matrix were reacted with acetylene and hydrogen gases. At the processing temperature range of 650-800 °C, high concentration straight carbon nanotubes (S-CNTs) with a small amount of coiled carbon nanotubes (C-CNTs) can be grown on the surface of seeded bimetallic nanoparticle size <100 nm, resulting from consumption of the melting Al matrix sites; sea urchin-like carbon nanotubes (SU-CNTs) of small diameter (～10±4 nm) can be grown on the bimetallic nanoparticle size >100 nm, resulting from the significant size reduction of the available Ni sites due to thermal expansion of molten Al matrix sites without consumption of Al matrix. However, at the processing temperature range of 500-650 °C, C-CNTs can be grown on the bimetallic nanoparticle size <100 nm due to the presence of Al matrix in the bimetallic nanoparticles; SU-CNTs of large diameter (～60±13 nm) can also be grown on the bimetallic nanoparticle size >100 nm due to the isolation of Ni sites in the Al matrix.     

Fabrication of gold nano- and microstructures in ionic liquids--a remarkable anion effect

Gold nano- and microstructures such as polyhedral crystals, large single-crystalline nanoplates, hollow trapeziform crystals, holey polyhedra, and dendrites were produced via microwave heating of HAuCl(4).4H(2)O in a variety of ionic liquids (ILs) in the absence of capping agents (polymers or surfactants) or additional reducing agents. The influence of the IL anions and cations on the topology (size, shape, etc.) of gold materials was studied in detail. The anions of the ILs control the topology of materials, whereas the cations used in the experiments exert less influence. It was also found that the HAuCl(4) concentration, reaction temperature, and heating method are key parameters that help to control the topological structures of the gold materials. For example, the thickness of the large single-crystalline nanoplates could be adjusted from 16 to 320 nm by varying the HAuCl(4) concentration and reaction temperature. This easy synthetic approach to gold nano- and microstructures is a seedless, one-step, fast, template-free route that shows good reproducibility and may be further developed to produce other types of metal nanostructures that satisfy specific applications.     

Template-free fabrication of hexagonal ZnO microprism with an interior space

Well-faceted hexagonal ZnO microprisms with regular interior space have been successfully prepared by a template-free hydrothermal synthetic route. The morphologies of the products depend on the experimental conditions such as the solvent, the concentration of ammonia aqueous solution, and the reaction temperature. Through manipulation of the aging time, the as-prepared ZnO can be controlled as a monodispersed hexagonal twinning solid or as hollow microprisms. Moreover, the evolution process of the hollow ZnO nanoarchitecture after reaction for 2, 6, 12, and 24 h has been investigated by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). A possible growth mechanism has also been proposed and discussed. Furthermore, the photoluminescence (PL) measurement exhibits the unique emitting characteristic of hollow ZnO nanostructures.     

Synthesis of ultra-long hollow chalcogenide nanofibers

Electrospinning and galvanic displacement reaction are combined to fabricate ultra-long hollow chalcogen and chalcogenide nanofibers in a cost-effective and high throughput manner. This procedure exploits electrospinning to fabricate ultra-long sacrificial nanofibers with controlled dimensions and morphology, thereby imparting control over the composition and shape of the nanostructures evolved during galvanic displacement reaction. It is believed to be a general route to form various ultra-long hollow semiconducting nanofibers.     

Carbon Nanotubes/Heteroatom‐Doped Carbon Core–Sheath Nanostructures as Highly Active,Metal‐Free Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells

A facile, scalable route to new nanocomposites that are based on carbon nanotubes/heteroatom‐doped carbon (CNT/HDC) core–sheath nanostructures is reported. These nanostructures were prepared by the adsorption of heteroatom‐containing ionic liquids on the walls of CNTs, followed by carbonization. The design of the CNT/HDC composite allows for combining the electrical conductivity of the CNTs with the catalytic activity of the heteroatom‐containing HDC sheath layers. The CNT/HDC nanostructures are highly active electrocatalysts for the oxygen reduction reaction and displayed one of the best performances among heteroatom‐doped nanocarbon catalysts in terms of half‐wave potential and kinetic current density. The four‐electron selectivity and the exchange current density of the CNT/HDC nanostructures are comparable with those of a Pt/C catalyst, and the CNT/HDC composites were superior to Pt/C in terms of long‐term durability and poison tolerance. Furthermore, an alkaline fuel cell that employs a CNT/HDC nanostructure as the cathode catalyst shows very high current and power densities, which sheds light on the practical applicability of these new nanocomposites.