Mixed Nanocrystals Research Articles

High-Valent Ni Species Induced by Inactive MoO2 for Efficient Urea Oxidation Reaction.

The microenvironment tuning of Ni species, a promising non-precious catalyst, is significant in the energy and environmentally relevant urea electro-oxidation reaction (UOR). Herein, we found that the high-valent Ni species induced by the inactive MoO2 in mixed nanocrystals of NiO/MoO2 were effective for urea oxidation. The redox interaction of MoO2 and NiO revealed by the spectroscopic analysis well supported the formation of high-valent Ni species and the changes in the surface chemical state. High catalytic activity and stability for urea oxidation were observed by a series of electrochemical measures compared to the counterpart catalysts of MoO2 and NiO. The optimal NiO/MoO2 hybrid catalyst showed a UOR activity of 73.1 mA cm-2 at 1.50 V, which was about 12-fold that of the NiO catalyst. In addition, largely improved catalytic kinetics and catalytic stability for UOR were also demonstrated. Because of the inactive activity of MoO2 and the low performance of NiO, the largely improved preference can be affirmatively attributed to the efficient catalytic synergism of NiO/MoO2 in the mixed nanocrystals. The current finding clarifies the catalytic promotion effect of the inactive Mo species on Ni-based catalysts for urea oxidation, which would be instructive for Ni/Mo-relevant catalyst development.

Carbonaceous FexP Synthesized via Carbothermic Reduction of Dephosphorization Slag as Hydrogen Evolution Catalyst for Water Splitting

Developing the high-efficiency and cheap non-noble catalysts towards hydrogen evolution reaction (HER) is of significance for water splitting. Herein, for the first time, we report a simple method of acid leaching combined with carbothermic reduction with dephosphorization slag to construct a carbonaceous FexP/C catalyst. In alkaline medium, the corresponding overpotential when the output current density was 10 mA cm−2 (η10) was only 145 mV. Additionally, there was no obvious attenuation after 3000 cycles, which showed significantly better activity and stability than that of non-carbonaceous FexP catalysts prepared by gas–solid phosphating. The structure and composition of FexP/C were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and inductively coupled plasma atomic emission spectrometer. The electrochemical properties of the electrode were evaluated by cyclic voltammetry, linear scanning voltammetry, electrochemical impedance spectroscopy, and cyclic stability. The results showed that the prepared FexP/C was composed of FeP-Fe2P mixed nanocrystals supported on amorphous carbon. Compared with FexP, the synergistic catalysis of the FeP and Fe2P phases as well as the interactive support effect between the FeP-Fe2P mixed nanocrystals and the amorphous carbon support will attribute the rich active sites for electrocatalytic reaction and reduce the charge transfer resistance. Thus, FexP/C has good hydrogen evolution activity and stability. Overall, the preparation of catalysts with high additional value based on dephosphorization slag was preliminarily explored.

Laser-assisted synthesis of Fe-Cu oxide nanocrystals

In the current paper, the production of homogeneous mixed nanocrystals based on Fe and Cu was successfully accomplished despite these two transition metals exhibiting extremely low miscibility in their phase diagram. The synthesis was carried out by the laser-mediated reduction of metal salts that were dissolved in different kinds of solvents, water, acetone and ethylene glycol. The greatest value of the methodology is that it allows the generation of mixed nanocrystals formed by transition metals with low miscibility in the presence of different solvents, taking metal salts as precursor agents, which are conventionally used in traditional wet synthesis techniques, but in contrast with the most popular approaches, the process requires neither special conditions nor hazardous reducing agents. Therefore, the presented methodology represents a clean and promising alternative for the synthesis of mixed nanocrystals composed of materials with low miscibility.

Design and Synthesis of Spherical Multicomponent Aggregates Composed of Core-Shell, Yolk-Shell, and Hollow Nanospheres and Their Lithium-Ion Storage Performances.

Micrometer-sized spherical aggregates of Sn and Co components containing core-shell, yolk-shell, hollow nanospheres are synthesized by applying nanoscale Kirkendall diffusion in the large-scale spray drying process. The Sn2 Co3 -Co3 SnC0.7 -C composite microspheres uniformly dispersed with Sn2 Co3 -Co3 SnC0.7 mixed nanocrystals are formed by the first-step reduction of spray-dried precursor powders at 900 °C. The second-step oxidation process transforms the Sn2 Co3 -Co3 SnC0.7 -C composite into the porous microsphere composed of Sn-Sn2 Co3 @CoSnO3 -Co3 O4 core-shell, Sn-Sn2 Co3 @CoSnO3 -Co3 O4 yolk-shell, and CoSnO3 -Co3 O4 hollow nanospheres at 300, 400, and 500 °C, respectively. The discharge capacity of the microspheres with Sn-Sn2 Co3 @CoSnO3 -Co3 O4 core-shell, Sn-Sn2 Co3 @CoSnO3 -Co3 O4 yolk-shell, and CoSnO3 -Co3 O4 hollow nanospheres for the 200th cycle at a current density of 1 A g-1 is 1265, 987, and 569 mA h g-1 , respectively. The ultrafine primary nanoparticles with a core-shell structure improve the structural stability of the porous-structured microspheres during repeated lithium insertion and desertion processes. The porous Sn-Sn2 Co3 @CoSnO3 -Co3 O4 microspheres with core-shell primary nanoparticles show excellent cycling and rate performances as anode materials for lithium-ion batteries.

Large-scale production of CdO/Cd(OH)2 nanocomposites for non-enzyme sensing and supercapacitor applications.

Recent advancements in electrode design are substantially linked to state-of-the-art nanomaterial fabrications. Herein, we report a simple one-pot hydrothermal synthesis of Cd(OH)2 with a platelet-like morphology, which was subsequently annealed at relatively high temperatures to produce a CdO/Cd(OH)2 nanocomposite for the first time. It was found that the control of thermal treatment allowed tunable charge transport across the nanometre scale due to the presence of CdO and Cd(OH)2 mixed nanocrystals. The CdO/Cd(OH)2 nanocrystals offer interesting prospects for the electrocatalytic oxidation of nitrite ions and for supercapacitor applications. The CdO/Cd(OH)2 nanocomposite was blended with a trace amount of gold NPs for enhancing the electrochemical conductivity and electrocatalytic capability for nitrite oxidation with a sensitivity of 32.9 μA mM−1. It afforded a promising electrocatalyst in a wide concentration range up to 10 mM with a low detection limit of 0.87 μM. Furthermore, the CdO/Cd(OH)2 nanocomposite electrode was showed to be a highly active and stable supercapacitor, achieving a high specific capacitance in an alkaline medium of about 145 F g−1 at a discharge current of 2.0 A g−1. These results have revealed that the presence of mixed oxide/hydroxide nanocrystals in nanoscale dimensions will be very interesting for various electrochemical applications and provide for a new class of nanodevices based on electrochemistry with unique capabilities.

Mechanochemical synthesis and in vitro studies of chitosan-coated InAs/ZnS mixed nanocrystals

In this paper, InAs/ZnS mixed nanocrystals were synthesized by dry high-energy milling approach in the first step. The obtained nanocrystals were characterized from structural point of view by X-ray diffraction analysis and Raman spectroscopy, and from the morphological point of view by scanning electron microscopy. In the next step, the nanocrystals were subjected to wet ultra-fine milling in order to obtain a nanosuspension of chitosan-coated InAs/ZnS nanocrystals with bio-imaging properties. The stability of the nanosuspension was examined by zeta potential and particle size distribution measurements. The prepared nanosuspension was stable with high values of zeta potential. Its optical properties were also studied using UV–Vis and PL spectroscopies. The determined fluorescent properties confirming the potential in bio-imaging applications were verified on cancer cell lines Caco-2, HCT116, HeLa, and MCF7.

A simple and effective method for controllable synthesis of silver and silver oxide nanocrystals

Silver (Ag) and silver oxide (Ag2O) colloidal nanocrystals are easily interconvertable and important for many similar applications; however, they have not been synthesized using the same method. Here we report a simple and effective method for synthesizing well-dispersed, hydrophilic, and colloidal Ag, Ag2O, and Ag–Ag2O mixed nanocrystals, which are 10–50 nm in diameter, sphere-like, and passivated with the same stabilizer polyvinylpyrrolidone (PVP). The method is denoted as alternating voltage induced electrochemical synthesis (AVIES). It involves only a transformer, two pieces of identical Ag wires, a stirring plate, and a PVP-containing electrolyte solution. The control of Ag and/or Ag2O nanocrystals is achieved by tuning the electrolyte identity, the stirring rate, and the applied voltage. Toward exploring practical applications of heterogeneous catalysis and antibacterial therapy, we have employed the synthesized NCs to catalyze the reduction of 4-nitrophenol and fabricated Ag NCs-loaded electrospun carbon fibers, respectively. Moreover, the revealed crystal-formation mechanism is surprising and interesting: the intermediate states for producing Ag nanocrystals are Ag2O nano-islands formed in situ on the electrode, and not the Ag+ ions in solution formed in situ through electrochemical etching.

Microstructures and photovoltaic properties of fullerene-based organic-inorganic hybrid solar cells

C60-based bulk heterojunction solar cells were fabricated, and the electronic and optical properties were investigated. C60 were used as n-type semiconductors, and copper oxides, CuInS2 and diamond were used as p-type semiconductors. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed. Nanostructures of the solar cells were investigated by transmission electron microscopy, electron diffraction and X-ray diffraction, which indicated formation of mixed nanocrystals.

Electrocatalytic activity of undoped and Mn-doped Zn(S,Se)-carbon nanocomposites

Electrocatalytic materials for applications, e.g. in fuel cells are often composites of (conducting) carbon variants and nanosized metal particles, typically from the family of platinum or nickel. They share some common problems (most notably a tendency to agglomeration and poisoning, e.g. by CO or H2), which prevent their use in contact with, e.g. raw biogenic methane or ethanol. Highly purified fuels or reformation to hydrogen are therefore necessary for such purposes. As a potential alternative, this study describes electrocatalytic activity of composites of undoped and Mn-doped Zn(S,Se) nanoparticles and carbon in contact with ethanol. The results on ethanol oxidation on such electrodes in short-circuit mode are reported, as well as values for the open circuit voltage achieved so far. The focus of this report is the variation of the Se/S ratio in mixed nanocrystals of ZnS and ZnSe. The influence on the electrocatalytic activity by the varying band gap energy and absolute positions of the electronic levels of the doped as well as undoped chalcogenide nanoparticles is reported.

Fabrication and Characterization of Fullerene-Based Bulk Heterojunction Solar Cells with Porphyrin, CuInS2, Diamond and Exciton-Diffusion Blocking Layer

Fullerene-based bulk heterojunction solar cells were fabricated, and the electronic and optical properties were investigated. C60 were used as n-type semiconductors, and porphyrin, CuInS2 and diamond were used as p-type semiconductors. An effect of exciton-diffusion blocking layer of perylene derivative on the solar cells between active layer and metal layer was also investigated. Optimized structures with the exciton-diffusion blocking layer improved conversion efficiencies. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed. Nanostructures of the solar cells were investigated by transmission electron microscopy, electron diffraction and X-ray diffraction, which indicated formation of mixed nanocrystals.

Fabrication and characterization of inorganic-organic hybrid solar cells based on CuInS2

Chalcopyrite compounds/fullerene solar cells based on copper-indium-disulphide and C60 were produced. Two-types of devices with heterojunction and bulk heterojunction structures were examined and characterized. The bulk heterojunction structure provided better efficiency compared to that of the heterojunction structure. Nanostructures of the solar cells were confirmed as mixed nanocrystals by transmission electron microscopy. A photovoltaic mechanism of the present solar cells was discussed on the basis of the experimental results.

Formation and Characterization of Bulk Hetero-Junction Solar Cells Using C<SUB>60</SUB> and Perylene

Polymer bulk hetero-junction solar cells were fabricated and the electronic and optical properties were investigated. C60 and perylene were used as n-type semiconductors, and copper phthalocyanine, zinc phthalocyanine and pentacene were used as p-type semiconductors. Energy levels of the molecules were calculated, and HOMO levels were localized around the main chains of the zinc phthalocyanine and pentacene. Nanostructures of the solar cells were confirmed as mixed nanocrystals by transmission electron microscopy and electron diffraction. [doi:10.2320/matertrans.MB200807]

コア/シェル型CuInSe2/ZnSeナノ結晶の合成と混晶化による蛍光特性の変化

コア/シェル型CuInSe2/ZnSeナノ結晶の合成と混晶化による蛍光特性の変化

Optical response of mixed Ag-Cu nanocrystals produced by pulsed laser deposition

Ag - Cu mixed nanocrystals (NCs) have been embedded in an amorphous Al2O3 matrix by alternate ablation of pure metal and Al2O3 targets. The composition of the NCs has been varied from pure Cu to pure Ag. Structural analysis by high-resolution electron microscopy (HREM) has shown that in the whole range of compositions, the NCs have average in-plane diameters in the range 3–4nm and are wider in the in-plane direction than their height, the aspect ratio being 1.4–1.6. The optical properties of the resulting nanocomposite films have instead a strong dependence on the NCs composition. A single surface plasmon resonance (SPR) has been observed whose wavelength blueshifts from that of Cu to that of Ag as the Ag content increases, thus allowing the SPR to be tuned over a broad interval (424–572nm). Although the nucleation and growth mechanisms have been found to depend on the metal that was deposited first, the optical response has no significant sensitivity to the deposition sequence and thus, it is concluded that more controllable results are achieved by depositing the lighter element first. Finally, HREM together with selective area electron diffraction show that the Ag-CuNCs are most likely formed by metastable solid solutions of Ag and Cu.

Dynamics of Formation and Evaporation of Mixed Alkali Halide Nanocrystals: A Case of Comparable Lattice Energies

Abstract : The relative intensity distribution of the (Rb(n)K(14-n)I(13)(+) mixed nanocrystals containing a 'magic' number of 14 metal cations and 13 iodide anions is examined. These nanocrystals were generated through sputtering of mixed RbI/KI solids using fast atom bombardment, and analyzed by use of a double-focusing sector-field mass spectrometer. The relative intensities of the observed peaks is found to have a 'bimodal' distribution with a maximum near n=7. This observation is explained by assuming: (a) a rate of formation that is proportional to the number of isomers that can be formed for each mixed nanocrystal, and (b) a rate of dissociation that is insensitive to the composition of the mixed nanocrystal. The later assumption leads to the conclusion that the internal energies of these mixed nanocrystals are similar and independent of their composition. The conclusion is supported by the results of Monte Carlo simulation annealing as well as by the similarity of the known lattice energies of KI and RbI bulk crystals.