A Composite Formation Route to Well‐Crystalline Manganese Oxide Nanocrystals: High Catalytic Activity of Manganate–Alumina Nanocomposites

Manganese oxide nanocrystals are combined with aluminum oxide nanocrystals to improve their crystallinity via calcination without a significant increase of crystal size. A nanocomposite, consisting of two metal oxides, can be synthesized by the reaction between permanganate anions and aluminum oxyhydroxide keggin cations. The as‐prepared manganese oxide–aluminum oxide nanocomposite is X‐ray amorphous whereas heat‐treatment gives rise to the crystallization of an α‐MnO₂ phase at 600 °C and Mn₃O₄/Mn₂O₃ and γ‐Al₂O₃ phases at 800 °C. Electron microscopy and N₂ adsorption‐desorption‐isotherm analysis clearly demonstrate that the as‐prepared nanocomposite is composed of a porous assembly of monodisperse primary particles with a size of ～20 nm and a surface area of >410 m² g^?1. Of particular interest is that the small particle size of the as‐prepared nanocomposite is well‐maintained up to 600 °C, a result of the prevention of the growth of manganate grains through nanoscale mixing with alumina grains. The calcined nanocomposite shows very‐high catalytic activity for the oxidation of cyclohexene with an extremely high conversion efficiency of >95% within 15 min. The present results show that the improvement of the crystallinity without significant crystal growth is very crucial for optimizing the catalytic activity of manganese oxide nanocrystals.     

Mesoporous Carbon Nanocube Architecture for High‐Performance Lithium–Oxygen Batteries

One of the major challenges to develop high‐performance lithium–oxygen (Li–O₂) battery is to find effective cathode catalysts and design porous architecture for the promotion of both oxygen reduction reactions and oxygen evolution reactions. Herein, the synthesis of mesoporous carbon nanocubes as a new cathode nanoarchitecture for Li–O₂ batteries is reported. The oxygen electrodes made of mesoporous carbon nanocubes contain numerously hierarchical mesopores and macropores, which can facilitate oxygen diffusion and electrolyte impregnation throughout the electrode, and provide sufficient spaces to accommodate insoluble discharge products. When they are applied as cathode catalysts, the Li–O₂ cells deliver discharge capacities of 26 100 mA h g^?1 at 200 mA g^?1, which is much higher than that of commercial carbon black catalysts. Furthermore, the mesoporous nanocube architecture can also serve as a conductive host structure for other highly efficient catalysts. For instance, the Ru functionalized mesoporous carbon nanocubes show excellent catalytic activities toward oxygen evolution reactions. Li–O₂ batteries with Ru functionalized mesoporous carbon nanocube catalysts demonstrate a high charge/discharge electrical energy efficiency of 86.2% at 200 mA g^?1 under voltage limitation and a good cycling performance up to 120 cycles at 400 mA g^?1 with the curtaining capacity of 1000 mA h g^?1.     

Tuning the Bandgap Character of Quantum‐Confined Si–Sn Alloyed Nanocrystals

Nanocrystals in the regime between molecules and bulk give rise to unique electronic properties. Here, a thorough study focusing on quantum‐confined nanocrystals (NCs) is provided. At the level of density functional theory an approximate (quasi) band structure which addresses both the molecular and bulk aspects of finite‐sized NCs is calculated. In particular, how band‐like features emerge with increasing particle diameter is shown. The quasiband structure is used to discuss technological‐relevant direct bandgap NCs. It is found that ultrasmall Sn NCs have a direct bandgap in their at‐nanoscale‐stable α‐phase and for high enough Sn concentration (≈41%) alloyed Si–Sn NCs transition from indirect to direct bandgap semiconductors. The calculations strongly support recent experiments suggesting a direct bandgap for these systems. For a quantitative comparison many‐body GW + Bethe–Salpeter equation (BSE) calculations are performed. The predicted optical gaps are close to the experimental data and the calculated absorbance spectra compare well with the corresponding measurements.     

Synthesis of Ceria–Zirconia Nanocrystals with Improved Microstructural Homogeneity and Oxygen Storage Capacity by Hydrolytic Sol–Gel Process in Coordinating Environment

Ceria–zirconia solid solution nanocrystals, (1‐x)CeO₂–xZrO₂, 0 ≤ x ≤ 1, are prepared by sol–gel processing in dodecylamine of solutions obtained by forced hydrolysis of inorganic salts. The as‐prepared nanoparticles have a ceria cubic structure, up to x = 0.35, or are amorphous. Heat‐treatment is carried out at temperatures ranging from 500 to 800 °C, the latter temperature begin suitable to obtain solid solutions throughout the composition range. For all the heating temperatures and x values, the fluorite cubic structure of pure CeO₂ transforms to a mixture (c′) of the cubic c and tetragonal t″ phases for x = 0.35, and to tetragonal t phase only for x = 0.8 at 650 °C, x = 0.65 at 800 °C, and, to a very limited extent, x = 0.5 at 1000 °C. No evidence is obtained at low x values of the t phase, which is detrimental to the oxygen storage capacity. Prolonged heating at 1000 °C demonstrates that only for x = 0.65 a limited separation of CeO₂‐rich nanocrystals occurs. The samples undergo the same transition without simultaneous occurrence of different phases, apart for the two mentioned limited cases. This result is attributed to the intimate mixing of the metal cations even in the early stages of processing. In as‐prepared samples the Zr distribution becomes inhomogeneous when going from x = 0.2 to x = 0.35, but no early phase separations appear. The oxygen storage capacity is favorably influenced by the persistence of the cubic c′ phase.     

Yolk–Shell Structured Assembly of Bamboo‐Like Nitrogen‐Doped Carbon Nanotubes Embedded with Co Nanocrystals and Their Application as Cathode Material for Li–S Batteries

Despite their high theoretical specific capacity (1675 mA h g^?1), the practical application of Li–S batteries remains limited because the capacity rapidly degrades through severe dissolution of lithium polysulfide and the rate capability is low because of the low electronic conductivity of sulfur. This paper describes novel hierarchical yolk–shell microspheres comprising 1D bamboo‐like N‐doped carbon nanotubes (CNTs) encapsulating Co nanoparticles (Co@BNCNTs YS microspheres) as efficient cathode hosts for Li–S batteries. The microspheres are produced via a two‐step process that involves generation of the microsphere followed by N‐doped CNTs growth. The hierarchical yolk–shell structure enables efficient sulfur loading and mitigates the dissolution of lithium polysulfides, and metallic Co and N doping improves the chemical affinity of the microspheres with sulfur species. Accordingly, a Co@BNCNTs YS microsphere‐based cathode containing 64 wt% sulfur exhibits a high discharge capacity of 700.2 mA h g^?1 after 400 cycles at a current density of 1 C (based on the mass of sulfur); this corresponds to a good capacity retention of 76% and capacity fading rate of 0.06% per cycle with an excellent rate performance (752 mA h g^?1 at 2.0 C) when applied as cathode hosts for Li–S batteries.     

Fabrication of ZnO-based metal–insulator–semiconductor diodes by ion implantation

A ZnO-based metal–insulator–semiconductor junction has been fabricated using an isolation layer fabricated by N⁺ ion implantation. I–V dependences show a good rectifying diode-like behavior with a low leakage current of 10⁻⁶ A and a threshold voltage of about 3 V. Ultraviolet light emission under forward bias exhibits a wavelength maximum of 388 nm and a full width at half maximum of 128 meV at room temperature.     

Aligning Single‐Walled Carbon Nanotubes By Means Of Langmuir–Blodgett Film Deposition: Optical,Morphological, and Photo‐electrochemical Studies

An alkoxy‐substituted poly(phenylene thiophene) is used in order to suspend single‐walled carbon nanotubes in an organic solvent. The suspension is spread on the air–water interface of a Langmuir trough and the floating film is characterized by means of Brewster angle microscopy and UV‐visible reflection spectroscopy and the compression isotherm is recorded. The polymer/carbon‐nanotube blend is transferred onto different substrates using the Langmuir–Blodgett technique. AFM measurements indicate the formation of globular structures for the samples transferred at low surface‐pressure values and a tubular morphology for high‐pressure‐deposited samples. AFM analysis is repeated on a sample exposed to soft X‐rays for about 5 h and a highly organized structure of bundles of carbon nanotubes rises up. Samples with different numbers of layers are transferred onto ITO substrates by means of the Langmuir–Blodgett method and are tested as photocathodes in a photo‐electrochemical cell. A V_oc of 0.18 V, an I_sc of 85.8 mA, FF of 40.0%, and η of (6.23 × 10^?3)% are obtained.     

Novel Sol–Gel Nano‐Glass–Ceramics Comprising Ln3+‐Doped YF3 Nanocrystals: Structure and High Efficient UV Up‐Conversion

Transparent glass‐ceramics containing Ln³⁺‐doped YF₃ nanocrystals are successfully obtained under adequate thermal treatment of precursor sol–gel glasses for the first time, to the best of our knowledge. Precipitation of YF₃ nanocrystals is confirmed by X‐ray diffraction and high‐resolution transmission electron microscopy images. An exhaustive structural analysis is carried out using Eu³⁺ and Sm³⁺ as probe ions of the final local environment in the nano‐structured glass–ceramic. Noticeable changes in luminescence spectra, related to relative intensity and Stark structure of band components, along with remarkably different lifetime values, allow us to discern between ions residing in precipitated YF₃ nanocrystals and those remaining in a glassy environment. A large fraction of optically active ions is efficiently partitioned into nanocrystals of small size, around 11 nm. Moreover, bright and efficient up‐conversion, including very intense high‐energy emissions in the UV range, due to 4‐ and 5‐infrared photon processes, are achieved in Yb³⁺–Tm³⁺ co‐doped samples. Up‐conversion mechanisms are analysed in depth by means of intensity dependence on sensitiser Yb³⁺ concentration and pump power.     

Mesoporous Colloidal Superparticles of Platinum‐Group Nanocrystals with Surfactant‐Free Surfaces and Enhanced Heterogeneous Catalysis

Synthesis of colloidal superparticles (CSPs) of nanocrystals, a class of assembled nanocrystals in the form of colloidal particles, has been emerging as a new frontier in the field of nanotechnology because of their potential novel properties originated from coupling of individual nanocrystals in CSPs. Here, a facile approach is reported for the controlled synthesis of mesoporous CSPs made of various platinum‐group nanocrystals that exhibit high colloidal stability and ligand‐free surfaces to significantly benefit their applications in solution‐phase heterogeneous catalysis. The synthesis relies on self‐limiting growth of composite particles through coprecipitation of both Pt‐group nanocrystals (or their precursor compounds) and silver halides on sacrificial substrates of colloidal silver particles. The intermediate silver halides in the composite particles play the critical role in limiting the continuous growth (and/or coalescence) of individual Pt‐group nanocrystals and they can be selectively dissolved to create nanoscale pores in the resulting CSPs.     

Biomimetic Molecule Catalysts to Promote the Conversion of Polysulfides for Advanced Lithium–Sulfur Batteries

To overcome the shuttle effect in Li–S batteries, novel biomimetic molecule catalysts are synthesized by grafting hemin molecules to three functionalized carbon nanotube systems (CNTs–COOH, CNTs–OH, and CNTs–NH₂). The Li–S battery using the CNTs–COOH@hemin cathode exhibits the optimal initial specific capacity (1637.8 mAh g^?1) and cycle durability (up to 1800 cycles). Various in situ characterization techniques, such as Raman spectroscopy, Fourier‐transform infrared reflection absorption spectroscopy, and UV–vis spectroscopy, combined with density functional theory computations are used to investigate the structure–reactivity correlation and the working mechanism in the Li–S system. It is demonstrated that the unique structure of the CNTs‐COOH@hemin composite with good conductivity and adequate active sites resulting from molecule catalyst as well as the strong absorption to polysulfides entrapped by the coordinated Fe(III) complex with Fe? O bond enables the homogeneous dispersion of S, facilitates the catalysis and conversion of polysulfides, and improves the battery's performance.     

Synthesis of Core–Shell Inorganic Nanotubes

New materials and techniques pertaining to the synthesis of inorganic nanotubes have been ever increasing since the initiation of the field in 1992. Recently, WS₂ nanotubes, which are produced now in large amounts, were filled with molten lead iodide salt by a capillary wetting process, resulting in PbI₂@WS₂ core–shell nanotubes. This work features progress in the synthesis of new core–shell nanotubes, including BiI₃@WS₂ nanotubes produced in a similar same manner. In addition, two new techniques for obtaining core–shell nanotubes are presented. The first is via electron‐beam irradiation, i.e., in situ synthesis within a transmission electron microscope. This synthesis results in SbI₃ nanotubes, observed either in a hollow core of WS₂ ones (SbI₃@WS₂ nanotubes), or atop of them (WS₂@SbI₃ nanotubes). The second technique involves a gaseous phase reaction, where the layered product employs WS₂ nanotubes as nucleation sites. In this case, the MoS₂ layers most often cover the WS₂ nanotube, resulting in WS₂@MoS₂ core–shell nanotubes. Notably, superstructures of the form MoS₂@WS₂@MoS₂ are occasionally obtained. Using a semi‐empirical model, it is shown that the PbI₂ nanotubes become stable within the core of MoS₂ nanotubes only above a critical core diameter of the host (>12 nm); below this diameter the PbI₂ crystallizes as nanowires. These model calculations are in agreement with the current experimental observations, providing further support to the growth mechanism of such core–shell nanotubes.     

From 3D ZIF Nanocrystals to Co–Nx/C Nanorod Array Electrocatalysts for ORR,OER, and Zn–Air Batteries

Designing a highly active electrocatalyst with optimal stability at low cost is must and non‐negotiable if large‐scale implementations of fuel cells are to be fully realized. Zeolitic‐imidazolate frameworks (ZIFs) offer rich platforms to design multifunctional materials due to their flexibility and ultrahigh surface area. Herein, an advanced Co–N_x/C nanorod array derived from 3D ZIF nanocrystals with superior electrocatalytic activity and stability toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) compared to commercial Pt/C and IrO₂, respectively, is synthesized. Remarkably, as a bifunctional catalyst (E_{j = 10} (OER) ? E_1/2 (ORR) ≈ 0.65 V), it further displays high performance of Zn–air batteries with high cycling stability even at a high current density. Such supercatalytic properties are largely attributed to the synergistic effect of the chemical composition, high surface area, and abundant active sites of the nanorods. The activity origin is clarified through post oxygen reduction X‐ray photoelectron spectroscopy analysis and density functional theory studies. Undoubtedly, this approach opens a new avenue to strategically design highly active and performance‐oriented electrocatalytic materials for wider electrochemical energy applications.     

碳纳米管薄膜的电泳沉积及其场发射性能研究

利用电泳沉积法在铝片上制备了碳纳米管薄膜冷阴极。通过扫描电镜、Raman光谱观察分析了表面形貌和结构,并对场发射性能进行了测试。经过研磨处理的碳纳米管薄膜样品,开启电场为2V／μm,当电场强度为4V／μm时电流密度达到2600μA／cm^2,发光点密度大于10^4／cm^2。     

Light‐Switchable Single‐Walled Carbon Nanotubes Based on Host–Guest Chemistry

A new type of light‐switchable “smart” single‐walled carbon nanotube (SWNTs) is developed by the reversible host–guest interaction between azobenzene‐terminal PEO (AzoPEO) and pyrene‐labeled host attached on the sidewalls of nanotubes via π–π stacking. The SWNTs hybrids not only are well dispersed in pure water, but also exhibit switchable dispersion/aggregation states upon the alternate irradiation of UV and visible light. Moreover, the SWNTs hybrids dispersion is preliminarily used as coating fluid to form transparent conductive films. The dispersant AzoPEO is removed by the contamination‐free UV treatment, decreasing the resistance of the films. This kind of light‐switchable SWNTs hybrids, possessing a ‘‘green’’ trigger and intact structure of the nanotube, may find potential applications in sensor of biomedicines, device fabrication, etc. Additionally, such a reversible host–guest interaction system may open up the possibility to control the dispersion state of SWNTs by other common polymers.     

Advanced Catalysts Derived from Composition‐Segregated Platinum–Nickel Nanostructures: New Opportunities and Challenges

Composition segregation, resulting from the rearrangement of atom positions and different enrichment behaviors of different atoms in alloys, has been linked to their enhanced performances in catalytic applications due to the strong electronic effect and largely improved number of available active sites. Hence, composition‐segregated metallic nanostructures have been actively pursued to prepare better‐performing nanocatalysts. Moreover, they also act as an emerging platform to develop unusual nanostructures with desirable functionalities. An overview about the recent advances in preparing unusual nanostructures with desirable functionalities such as highly open 3D structures (concave, frame, porous, etc.) and composites with suitable interfaces (metal–metal, metal–oxide, metal–sulfide, metal–boride, metal–organic, metal–hydroxide interfaces, etc.) based on composition‐segregated metallic nanostructures which can boost heterogeneous catalytic reactions with superior performances is provided here. The different strategies developed so far for the synthesis of composition‐segregated metallic nanostructures are also discussed. Finally, the challenges of the composition‐segregated nanostructure and their functionalized materials are discussed, as well as some perspectives are highlighted on the fine regulation and multifunctionalities of nanostructures, which provide a powerful material foundation for the potential electrocatalysis, organic catalysis, and energy conversion of multicomponent metal nanostructures.     

Engineering of the Heterointerface of Porous Carbon Nanofiber–Supported Nickel and Manganese Oxide Nanoparticle for Highly Efficient Bifunctional Oxygen Catalysis

Constructing heterointerfaces between metals and metal compounds is an attractive strategy for the fabrication of high performance electrocatalysts. However, realizing the high degree of fusion of two different metal components to form heterointerfaces remains a great challenge, since the different metal components tend to grow separately in most cases. Herein, by employing carboxyl‐modified carbon nanotubes to stabilize different metal ions, the engineering of abundant Ni|MnO heterointerfaces is achieved in porous carbon nanofibers (Ni|MnO/CNF) during the electrospinning–calcination process. Remarkably, the resulting Ni|MnO/CNF catalyst exhibits activities that are among the best reported for the catalysis of both the oxygen reduction and oxygen evolution reactions. Moreover, the catalyst also demonstrates high power density and long cycle life in Zn–air batteries. Its superior electrochemical properties are mainly ascribed to the synergy between the engineering of oxygen‐deficient Ni|MnO heterointerfaces with a strong Ni/Mn alloying interaction and the 1D porous CNF support. This facile anchoring strategy for the initiation of bimetallic heterointerfaces creates appealing opportunities for the potential use of heteronanomaterials in practical sustainable energy applications.     

High‐Performance Oxygen Reduction Electrocatalyst Derived from Polydopamine and Cobalt Supported on Carbon Nanotubes for Metal–Air Batteries

The development of nonprecious metal‐based electrocatalysts for the oxygen reduction reaction holds the decisive key to many energy conversion devices. Among several potential candidates, transition metal and nitrogen co‐doped carbonaceous materials are the most promising, yet their activity and stability are still insufficient to meet the needs of practical applications. In this study, a core–shell hybrid electrocatalyst is developed via the self‐polymerization of dopamine and cobalt on carbon nanotubes (CNTs), followed by high‐temperature pyrolysis. The polymer‐derived carbonaceous shell contains abundant structural defects and facilitates the formation of Co? N/C active sites, whereas the graphitic carbon nanotube core provides high electrical conductivity and corrosion resistance. These two components separately fulfill different functionalities, and jointly afford the catalyst with excellent electrochemical performance. In 1 m KOH, Co? N/CNT exhibits a positive half‐wave potential of ≈0.91 V, low peroxide yield of <7%, as well as great stability. When used as the air catalyst of primary Zn–air and Al–air batteries, this hybrid electrocatalyst enables large discharge current density, high peak power density, and prolonged operation stability.     

Nitrogen‐Dopant‐Induced Organic–Inorganic Hybrid Perovskite Crystal Growth on Carbon Nanotubes

Interfacial engineering of organic–inorganic halide perovskites in conjunction with different functional materials is anticipated to offer novel heterojunction structures with unique functionalities. Unfortunately, complex material compositions and structures of the organic–inorganic hybrid materials make it difficult to tailor a desirable intermolecular interaction at the interface. Spontaneous and highly specific nucleation of perovskite crystals, that is, methylammonium lead iodide perovskite (CH₃NH₃PbI₃, MAPbI₃) at nitrogen‐doped carbon nanotube (NCNT) surfaces for the self‐assembly of MAPbI₃/NCNT hybrids is reported. It is demonstrated that the lone‐pair electrons of pyridinic nitrogen‐dopant sites at NCNTs mediate specific interactions with the cationic component in the perovskite structure and serve as the nucleation sites via coordinate bonding formation, as supported by X‐ray photoelectron spectroscopy and density functional theory calculation. The potential suitability of MAPbI₃/NCNT hybrids is presented for highly sensitive and selective NO₂ sensing layer. This work suggests a reliable self‐assembly route to the molecular level hybridization of organic–inorganic halide perovskites by employing the substitutional dopant sites at graphene‐based nanomaterials.     

Manipulating Polysulfide Conversion with Strongly Coupled Fe3O4 and Nitrogen Doped Carbon for Stable and High Capacity Lithium–Sulfur Batteries

Li–S batteries are among the most promising energy storage technologies but their commercialization faces substantial challenges, largely due to difficulties in controlling their reaction pathways under practical conditions. Here, the synthesis of strongly coupled Fe₃O₄ and N‐doped carbon directly in flexible carbon cloth is demonstrated, as well as their novel use for hosting sulfur with outstanding performance for Li–S batteries. It is discovered that the synergistic effects of Fe₃O₄ and N‐carbon bring strong adsorption toward lithium polysulfide, and ensure nearly complete conversion of short‐chain polysulfide to Li₂S during discharge. The Li₂S solids generated on these novel hosts are extremely reactive and can be readily charged back to S without a noticeable overpotential. The critical roles of Fe₃O₄ and N‐doped carbon are studied and direct correlations are established between their surface concentration/crystallinity and the Li₂S₄ to Li₂S conversion capacity. This novel manipulation of polysulfide conversion allows to fabricate freestanding and flexible sulfur cathodes that deliver a specific capacity of 1316 mAh g^?1 at 0.1C and stable cycling for 1000 cycles at 0.2C under a high sulfur loading of ≈4.7 mg cm^?2.