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1.
Noble metal nanocrystals with different shapes and compositions are embedded in hollow mesoporous metal oxide microspheres through an ultrasonic aerosol spray. Polystyrene (PS) nanospheres are employed simultaneously as a hard template to create hollow interiors inside the oxide microspheres and as the carrier to bring pregrown metal nanocrystals, including Pd nanocubes, Au nanorods, and Au core/Pd shell nanorods, into the oxide microspheres. Calcination removes the PS template and causes the metal nanocrystals to adsorb on the inner surface of the hollow oxide microspheres. The catalytic performances of the Pd nanocube‐embedded TiO2 and ZrO2 microspheres are investigated using the reduction of 4‐nitrophenol as a model reaction. The presence of the mesopores in the oxide microspheres allows the reactant molecules to diffuse into the hollow interiors and subsequently interact with the Pd nanocubes. The embedding of the metal nanocrystals in the hollow oxide microspheres prevents the aggregation of the metal nanocrystals and reduces the loss of the catalyst during recycling. The Pd nanocube‐embedded ZrO2 microspheres are found to exhibit a much higher catalytic activity, a much larger catalytic reaction rate, and a superior recyclability in comparison with a commercial Pd/C catalyst. This preparation approach could potentially be utilized to incorporate various types of mono‐ and multimetallic nanocrystals with different sizes, shapes, and compositions into hollow mesoporous oxide microspheres. Such a capability can facilitate the studies of the catalytic properties of various combinations of metal nanocrystals and metal oxide supports and therefore guide the design and creation of high‐performance catalysts.  相似文献   

2.
Among solution‐processed nanocrystals containing environmentally benign elements, bismuth sulfide (Bi2S3) is a very promising n‐type semiconductor for solar energy conversion. Despite the prompt success in the fabrication of optoelectronic devices deploying Bi2S3 nanocrystals, the limited understanding of electronic properties represents a hurdle for further materials developments. Here, two key materials science issues for light‐energy conversion are addressed: bandgap tunability via the quantum size effect, and photocarrier trapping. Nanocrystals are synthesized with controlled sizes varying from 3 to 30 nm. In this size range, bandgap tunability is found to be very small, a few tens of meV. First principles calculations show that a useful blueshift, in the range of hundreds of meV, is achieved in ultra‐small nanocrystals, below 1.5 nm in size. Similar conclusions are envisaged for the class of pnictide chalcogenides with a ribbon‐like structure [Pn4Ch6]n (Pn = Bi, Sb; Ch = S, Se). Time‐resolved differential transmission spectroscopy demonstrates that only photoexcited holes are quickly captured by intragap states. Photoexcitation dynamics are consistent with the scenario emerging in other metal–chalcogenide nanocrystals: traps are created in metal‐rich nanocrystal surfaces by incomplete passivation by long fatty acid ligands. In large nanocrystals, a lower bound to surface trap density of one trap every sixteen Bi2S3 units is found.  相似文献   

3.
A novel OA/ionic liquid two‐phase system combining the merits of thermal decomposition method, the IL‐based strategy, and the two‐phase approach is introduced to synthesize high‐quality lanthanide‐doped NaGdF4 upconversion nanocrystals with different crystal‐phases in OA‐phase and IL‐phase through a one‐step controllable reaction. Oil‐dispersible cubic‐phase NaGdF4:Yb, Er (Ho, Tm) nanocrystals with ultra‐small size (~5 nm) and monodispersity are obtained in the OA phase of the two‐phase system via an IL‐based reaction. More importantly, water‐soluble hexagonal‐phase NaGdF4:Yb, Er nanocrystals are obtained in the same system simply by adopting an extremely facile method to complete the dual phase‐transition (crystal‐phase transition and OA‐phase to IL‐phase transition) simultaneously. The synthesized lanthanide‐doped NaGdF4 upconversion nanocrystals are effective for dual‐mode UCL imaging and CT imaging in vivo.  相似文献   

4.
NaGdF4:Eu3+, NaEuF4, and NaGdF4 nanocrystals were synthesized in the high‐boiling coordinating solvent N‐(2‐hydroxyethyl)‐ethylenediamine (HEEDA). Phase pure nanomaterials, crystallizing either in the cubic α‐phase or the hexagonal β‐phase, were obtained by adjusting one reaction parameter only, i.e., the molar ratio between metal and fluoride ions in the synthesis. The hexagonal β‐phase is formed, if this molar ratio is close to stoichiometric, whereas the cubic α‐phase is obtained in the presence of excess metal ions. The optical properties of the Eu3+ doped samples are different for the two crystal phases. The results indicate an increased number of oxygen impurities close to Eu3+ ions, if excess metal ions are used in the synthesis.  相似文献   

5.
The high‐yield fabrication of tetrapodal CdSe, CdTe, and CdSexTe1–x nanocrystals is systematically studied. CdSe nanocrystals are prepared by first controlling the synthesis of high‐quality wurtzite CdSe and zinc blende CdSe nanocrystals at a relatively high temperature (260 °C) by selecting different ligands. Then, based on the phase control of the CdSe nanocrystals, two nanoparticle‐tailoring routes (i.e., a seed‐epitaxial route and ligand‐dependent multi‐injecting route) are used, and a high yield of CdSe tetrapods is obtained. CdTe nanocrystals are prepared by adjusting the ligand composition and the ratio of Cd to Te; CdTe tetrapods are synthesized in high yield using a mixed ligand that does not contain alkylphosphonic acids. Moreover, the nanoscale Te powder (Te nanowires/nanorods), which is highly soluble in the ligand solvent, is first used as a Te source to synthesize CdTe nanocrystals, which remarkably enhanced the output of the CdTe nanocrystals in one reaction. Furthermore, composition‐tunable ternary CdSexTe1–x alloyed tetrapods are synthesized on a large scale, for the first time, by thermolyzing the mixture of the organometallic Cd precursor and the mixed (Se + Te) source in a mixed‐ligand solution. The CdSe, CdTe, and CdSexTe1–x nanocrystals are characterized by transmission electron microscopy (TEM), high‐resolution TEM, selected‐area electron diffraction, X‐ray diffraction, and UV‐vis and photoluminescence (PL) spectroscopy. Interesting nonlinear, composition‐dependent absorption and PL spectra are observed for the ternary CdSexTe1–x alloyed nanocrystals. The band‐edge positions of the nanocrystals of CdSe, CdSexTe1–x, and CdTe are systematically studied by cyclic voltammetry.  相似文献   

6.
Composition‐tunable ZnxCd1–xS alloyed nanocrystals have been synthesized by a new approach consisting of thermolyzing a mixture of cadmium ethylxanthate (Cd(exan)2) and zinc ethylxanthate (Zn(exan)2) precursors in hot, coordinating solvents at relatively low temperatures (180–210 °C). The composition of the alloyed nanocrystals was accurately adjusted by controlling the molar ratio of Cd(exan)2 to Zn(exan)2 in the mixed reactants. The alloyed ZnxCd1–xS nanocrystals prepared in HDA/TOP (HDA: hexadecylamine; TOP: trioctylphosphine) solution exhibit composition‐dependent shape and phase structures as well as composition‐dependent optical properties. The shape of the ZnxCd1–xS nanocrystals changed from dot to single‐armed rod then to multi‐armed rod with a decrease of Zn content in the ternary nanoparticles. The alloying nature of the ZnxCd1–xS nanocrystals was consistently confirmed by the results of high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), and UV‐vis absorption and photoluminescence (PL) spectroscopy. Further, the shape‐controlled synthesis of the ternary alloyed nanocrystals was realized by selecting appropriate solvents. Uniform nanodots in the whole composition range were obtained from TOPO/TOP solution, (TOPO: trioctylphosphine oxide) and uniform nanorods in the whole composition range were prepared from HDA/OA solution (OA: octylamine). The effect of the reaction conditions, such as solvent, reaction temperature, and reaction time, on the PL spectra of the alloyed ZnxCd1–xS nanocrystals was also systematically studied, and the reaction conditions were optimized for improving the PL properties of the nanocrystals.  相似文献   

7.
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.  相似文献   

8.
Porous and sub‐micrometer tubes made of textured GaN nanoparticles have been synthesized by an in situ chemical reaction and characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) and Raman spectroscopies. The in situ reaction involves thermal decomposition and nitridation of 1D gallium oxyhydroxide (GaOOH) at temperatures in the range of 700–900 °C. The 1D shape of the precursor GaOOH is maintained in the resultant GaN tubes. The GaN nanocrystals (estimated to be about 15 nm in size) are found to be highly oriented with respect to each other in the tube structure, with the [110] GaN direction parallel to the tube axis. The growth mechanism of the tube structure has also been studied. β‐Ga2O3 is found to be an intermediate phase between the starting GaOOH precursor and the final GaN product. The growth mechanism involves decomposition of GaOOH, which produces β‐Ga2O3 tubes with hollow interiors, and nitridation of β‐Ga2O3, which leads to growth of textured GaN nanocrystals. Based on the growth mechanism, tubular structures with either quasi‐circular or rectangular cross section are selectively synthesized by controlling the heating rate and calcination temperature. This in situ chemical reaction method provides a new route for synthesizing 1D hollow nanostructures.  相似文献   

9.
Owing to their unique optical, electronic, and catalytic properties, metal nitrides nanostructures are widely used in optoelectronics, clean energy, and catalysis fields. Despite great progress has been achieved, synthesis of defect‐rich (DR) bimetallic nitride nanocrystals or related nanohybrids remains a challenge, and their electrocatalytic application for oxygen evolution reaction (OER) has not been fully studied. Herein, the DR‐Ni3FeN nanocrystals and N‐doped graphene (N‐G) nanohybrids (DR‐Ni3FeN/N‐G) are fabricated through temperature‐programmed annealing and nitridation treatment of NiFe‐layered double hydroxides/graphene oxide precursors by controlling annealing atmosphere. In the nanohybrids, the DR‐Ni3FeN nanocrystals are anchored on N‐G, and mainly show twin crystal defects besides ≈10% of stacking faults. Such nanohybrids can efficiently catalyze OER in alkaline media with a small overpotential (0.25 V) to attain the current density of 10 mA cm?2 and a high turnover frequency (0.46 s?1), superior to their counterparts (the nearly defect‐free Ni3FeN/N‐G), commercial IrO2, and the‐state‐of‐art reported OER catalysts. Except for the superior activity, they show better durability than their counterparts yet. As revealed by microstructural, spectroscopic, and electrochemical analyses, the enhanced OER performance of DR‐Ni3FeN/N‐G nanohybrids originates from the abundant twin crystal defects in Ni3FeN active phase and the strong interplay between DR‐Ni3FeN and N‐G.  相似文献   

10.
IR‐to‐visible up‐conversion fluorescent nanocrystals of hexagonal‐phase NaYF4:20 %Yb,2 %Er and NaYF4:20 %Yb,2 %Tm have been synthesized by decomposition of multiprecursors of CF3COONa, (CF3COO)3Y, (CF3COO)3Yb, and (CF3COO)3Er/(CF3COO)3Tm in oleylamine at 330 °C. The average particle size is 10.5 ± 0.7 nm (from random measurements of 200 particles from five transmission electron microscopy images) and 11.1 ± 1.3 nm (from dynamic‐light‐scattering measurements). The up‐conversion fluorescence intensity of the hexagonal nanocrystals in this work is much higher than that of other cubic‐phase NaYF4:Yb,Er nanocrystals, including the ones in this work (by a factor of 7.5). Mechanisms for nucleation and growth of the hexagonal‐phase nanoparticles are proposed. These nanocrystals are easily dispersed in organic solvents, producing a transparent colloidal solution. The hydrophobic surfaces of the particles are made hydrophilic using a bipolar surfactant. These nanoparticles and their dispersions in various media have potential applications in optical nanodevices and bioprobes.  相似文献   

11.
In this paper, we report a novel synthesis and selective bioseparation of the composite of Fe3O4 magnetic nanocrystals and highly ordered MCM‐41 type periodic mesoporous silica nanospheres. Monodisperse superparamagnetic Fe3O4 nanocrystals were synthesized by thermal decomposition of iron stearate in diol in an autoclave at low temperature. The synthesized nanocrystals were encapsulated in mesoporous silica nanospheres through the packing and self‐assembly of composite nanocrystal–surfactant micelles and surfactant/silica complex. Different from previous studies, the produced magnetic silica nanospheres (MSNs) possess not only uniform nanosize (90 ~ 140 nm) but also a highly ordered mesostructure. More importantly, the pore size and the saturation magnetization values can be controlled by using different alkyltrimethylammonium bromide surfactants and changing the amount of Fe3O4 magnetic nanocrystals encapsulated, respectively. Binary adsorption and desorption of proteins cytochrome c (cyt c) and bovine serum albumin (BSA) demonstrate that MSNs are an effective and highly selective adsorbent for proteins with different molecular sizes. Small particle size, high surface area, narrow pore size distribution, and straight pores of MSNs are responsible for the high selective adsorption capacity and fast adsorption rates. High magnetization values and superparamagnetic property of MSNs provide a convenient means to remove nanoparticles from solution and make the re‐dispersion in solution quick following the withdrawal of an external magnetic field.  相似文献   

12.
Widespread deployment of metal–organic frameworks (MOFs) for CO2 capture remains challenging due to the great energy‐penalty associated with their regeneration. To overcome this challenge, a new type of photodynamic carbon capture material synthesized by incorporating Ag nanocrystals with UiO‐66 (Ag/UiO‐66) framework is presented. Upon the irradiation of visible light, Ag nanocrystals within the composites serve as “nanoheaters” to convert photon energy into thermal energy locally. Driven by such light‐induced localized heat (LLH), the adsorbed CO2 within MOFs is remotely released. The CO2 desorption capacity of such Ag/UiO‐66 composites can be readily regulated by control over their Ag contents and the applied light intensity. Up to 90.5% of CO2 desorption is achieved under the investigated conditions. Distinct from the traditional light‐responsive MOFs for gas trigger release, currently developed LLH‐driven CO2 release method not only offers a promising solution to the heat‐insulating nature of MOFs, but also demonstrates a potentially low energy method to remotely regenerate MOF adsorbents given the utilization of naturally abundant visible light as efficient stimulus.  相似文献   

13.
A simple, one‐step synthetic route to prepare ordered mesoporous silica monoliths with controllable quantities of metal oxide nanocrystals in their channels is presented. The method is based on the assisted assembly effect for mesostructure‐directing of the metal complexes formed by the interaction of metal ions with the –O– groups of copolymers. Highly ordered hexagonal silica monoliths, loaded with various metal oxide nanocrystals, including those of Cr2O3, MnO, Fe2O3, Co3O4, NiO, CuO, ZnO, CdO, SnO2, and In2O3, can be obtained by this one‐step pathway. In the NiO/SiO2 nanocomposite, nickel oxide nanorods with face‐centered cubic lattices are formed at low doping ratios, and they can be transformed into nanowires by increasing the quantities of the precursors. In the Fe2O3/SiO2 nanocomposites, a one‐dimensional assembly of iron oxide nanoparticles is observed. In the In2O3/SiO2 nanocomposites, single crystal nanowires with high aspect ratios are obtained. For the other metal oxide nanocomposites, including Cr2O3, MnO, Co3O4, CuO, ZnO, CdO, and SnO, only crystalline nanorods are obtained. N2 sorption results of the metal oxide/SiO2 mesostructured nanocomposites reveal that nanocrystals inside the pores do not severely decrease the pore volume or the Brunauer–Emmett–Teller (BET) surface area of the mesoporous silica host. The bandgaps of SnO2 and In2O3 nanocrystals, calculated from UV‐vis spectra, are much larger than the corresponding bulk materials, implying the quantum confinement effect in the small particles. Co3O4/SiO2 mesostructured nanocomposites catalyze the complete combustion of CH4. These studies provide a new and simple method for templating synthesis of metal oxide nanostructures.  相似文献   

14.
A homogeneous and disordered assembly of densely packed nanocrystals is generated without the assistance of organic molecules, from an aqueous solution at room temperature. The densely packed nanocrystals of tin dioxide (SnO2) and titanium dioxide (TiO2), 2–3 nm in size, form glassy macroscopic transparent objects of 2–10 mm. The monodisperse nanocrystals, which have a surface hydrated layer and are synthesized in aqueous solution, are densely packed in an homogeneous and disordered assembly through the evaporation of water as the dispersion medium. The formation of transparent bulk objects on the macroscopic scale originates from the homogeneous and disordered nature of the densely packed nanocrystals. The resultant homogeneous architectures are distinguishable from the typical inhomogeneous and disordered aggregates of nanoparticles observed after evaporation of the dispersion medium. Among superstructures based on nanocrystals, such as superlattices and mesocrystals, the resultant homogeneous and disordered assembly can be regarded as a new class of solid‐state material.  相似文献   

15.
The exploration of highly efficient nonprecious metal bifunctional electrocatalysts to boost oxygen evolution reaction and oxygen reduction reaction is critical for development of high energy density metal‐air batteries. Herein, a class of CuS/NiS2 interface nanocrystals (INs) catalysts with atomic‐level coupled nanointerface, subtle lattice distortion, and plentiful vacancy defects is reported. The results from temperature‐dependent in situ synchrotron‐based X‐ray absorption fine spectroscopy and electron spin resonance spectroscopy demonstrate that the lattice distortion of 14.7% in CuS/NiS2 caused by the strong Jahn–Teller effect of Cu, the strong atomic‐level coupled interface of CuS and NiS2 domains, and distinct vacancy defects can provide numerous effective active sites for their excellent bifunctional performance. A liquid Zn‐air battery with the CuS/NiS2 INs as air electrode displays a large peak power density (172.4 mW cm?2), a high specific capacity (775 mAh gZn?1), and long cycle life (up to 83 h), making the CuS/NiS2 INs among the best bifunctional catalysts for Zn‐air battery. More remarkably, the flexible CuS/NiS2 INs‐based solid‐state Zn‐air batteries can power the LED after twisting, making them be promising in portable and wearable electronic devices.  相似文献   

16.
17.
In nature, charge recombination in light‐harvesting reaction centers is minimized by efficient charge separation. Here, it is aimed to mimic this by coupling dye‐sensitized TiO2 nanocrystals to a decaheme protein, MtrC from Shewanella oneidensis MR‐1, where the 10 hemes of MtrC form a ≈7‐nm‐long molecular wire between the TiO2 and the underlying electrode. The system is assembled by forming a densely packed MtrC film on an ultra‐flat gold electrode, followed by the adsorption of approximately 7 nm TiO2 nanocrystals that are modified with a phosphonated bipyridine Ru(II) dye (RuP). The step‐by‐step construction of the MtrC/TiO2 system is monitored with (photo)electrochemistry, quartz‐crystal microbalance with dissipation (QCM‐D), and atomic force microscopy (AFM). Photocurrents are dependent on the redox state of the MtrC, confirming that electrons are transferred from the TiO2 nanocrystals to the surface via the MtrC conduit. In other words, in these TiO2/MtrC hybrid photodiodes, MtrC traps the conduction‐band electrons from TiO2 before transferring them to the electrode, creating a photobioelectrochemical system in which a redox protein is used to mimic the efficient charge separation found in biological photosystems.  相似文献   

18.
Metal oxide/polymer hybrids are prepared from polystyrene nanoparticles functionalized at the surface with phosphonate and phosphate groups. The polymer particles are synthesized with specifically designed surface‐active monomers (surfmers) and used as nucleation surfaces for the controlled in situ crystallization of cerium, iron, and zinc oxide nanocrystals. The formation of the metal oxide is driven by the addition of a base to suspensions of the polymer particles containing the corresponding precursor. The crystal formation at the particle surface is studied for the different hybrid systems by X‐ray diffraction and transmission electron microscopy (TEM). The potential catalytic activity of CeO2/polymer hybrid particles is proven with the example of the photodegradation of rhodamine B. For the case of magnetic iron oxide‐functionalized latex, a superparamagnetic behavior is found above a blocking temperature of 225 K. ZnO/polymer hybrids present a strong yellow visible photoluminescence. The approach is shown to be versatile not only in terms of the variety in the metal oxides deposited on the surface, but also because the crystallization can take place in both aqueous and alcoholic media.  相似文献   

19.
Direct synthesis (co‐condensation reaction) and post‐synthesis reaction (grafting) are combined for the first time to efficiently fabricate bifunctionalized ordered mesoporous materials (OMMs). Ethylenediamine‐containing OMMs (ED‐MCM‐41) were first synthesized via direct synthesis and then further modified by the phenyl (PH) group in a supercritical fluid (SCF) medium via grafting reaction, resulting in OMMs with ED and PH groups (PH‐ED‐MCM‐41). X‐ray diffraction (XRD) patterns, N2 sorption properties, transmission electron microscopy (TEM), 29Si and 13C magic angle spinning (MAS) NMR, chemical analysis, and hydrothermal treatment were used to characterize the bifunctionalized materials. Experiments show that bifunctionalized OMMs can be efficiently prepared by modifying the directly synthesized monofunctionalized OMMs via grafting reaction in a supercritical fluid medium. Both functional groups are distributed uniformly at the surfaces. The advantage of bifunctionalized OMMs over monofunctionalized OMMs was illustrated by introducing thiol groups into ED‐MCM‐41 materials and the subsequent formation of CdS nanocrystals inside thiol‐ and ED‐functionalized MCM‐41 (HS‐ED‐MC‐41). Because of the variety of the functional groups that can be introduced into OMMs by direct synthesis or post‐synthesis reaction, it is expected that the present strategy could provide a generally applicable approach to the design of OMMs with two functional groups.  相似文献   

20.
Monodisperse fullerene‐like polyoxometalate‐based microspheres are synthesized using a single‐phase approach which is quick, easier to control surfactant to polyoxometalate (POM) molar ratios and result in better control over the size‐distribution range. Noble‐metal nanocrystals are successfully incorporated in the surfactant encapsulated complex multilayered spherical assemblies without any change in their layered morphology. Combining the merits of fullerene‐like POMs and monodisperse noble metal nanocrystals, these monodisperse hybrid spheres show interesting composition‐ and size‐dependent photochemical properties.  相似文献   

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