Hybrid Nanocrystals Research Articles

One-pot surfactant-free synthesis of porous PtAu alloyed nanoflowers with enhanced electrocatalytic activity for ethanol oxidation and oxygen reduction reactions

Well-defined porous PtAu alloyed nanoflowers (PtAu ANFs) were fabricated by a one-pot surfactant-free successive co-reduction approach. Methotrexate, an antimetabolite and antifolate drug, was employed here as the shape-regulator and stabilizer for the first time, while no any seed, polymer, or surfactant was involved during the synthetic process. The as-prepared architectures were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction in details. The as-synthesized hybrid nanocrystals exhibited improved catalytic performances for ethanol oxidation and oxygen reduction in contrast with PtAu-10 NCs, PtAu-50 NPs, and commercial Pt black catalysts, demonstrating their promising applications in fuel cells.

Solid-State Conversion Chemistry of Multicomponent Nanocrystals Cast in a Hollow Silica Nanosphere: Morphology-Controlled Syntheses of Hybrid Nanocrystals.

During thermal transformation of multicomponent nanocrystals in a silica nanosphere, FeAuPd alloy nanocrystals migrate outward and thereby leave a cavity in the silica matrix. Oxidation then converts these nanocrystals back into phase-segregated hybrid nanocrystals, AuPd@Fe3O4, with various morphologies. The FeAuPd-to-AuPd@Fe3O4 transformation was cast by the in situ generated hollow silica mold. Therefore, the morphological parameters of the transformed AuPd@Fe3O4 are defined by the degree of migration of the FeAuPd in the hollow silica nanoshell. This hollow silica-cast nanocrystal conversion was studied to develop a solid state protocol that can be used to produce a range of hybrid nanocrystals and that allows for systematic and sophisticated control of the resulting morphologies.

Pt/Fe₃O₄ Core/Shell Triangular Nanoprisms by Heteroepitaxy: Facet Selectivity at the Pt-Fe₃O₄ Interface and the Fe₃O₄ Outer Surface.

Pt/Fe3O4 core/shell triangular nanoprisms were synthesized using seed-mediated heteroepitaxy. Their well-defined shape, facets, and ordered-assembly allowed detailed analysis of mechanism of the heteroepitaxy. At the Pt-Fe3O4 interface, existence of both lattice and chemical mismatch resulted in facet-selective epitaxy along ⟨111⟩ directions of two lattices. X-ray absorption fine structure measurements demonstrated that the Pt seed nanocrystals were composed of an iron-rich Pt-Fe metallic thin layer sandwiched between the Pt core and a Fe-O outer-surface. The Fe-O outer-surface of the seed nanocrystals presumably offered epitaxial sites for the following deposition of the Fe3O4 shell. Each tip and side of a triangular nanoprism respectively possessed a groove and a ridge, and a (111) plane parallel to the basal planes linked all grooves and ridges. This interesting (111) plane approximately bisected the triangle nanoprisms and located near the Pt-seed. The outer surface of the hybrid nanocrystals was also found to be facet-selective, that is, solely {111} facets of Fe3O4 lattice. These polar {111} facets allowed the surface to be only occupied with high-density iron ions, and thus offered best surface coordination for the electron donating ligands in the solution.

Synthesis and photocatalytic properties of multi-morphological AuCu3-ZnO hybrid nanocrystals

Noble metal–semiconductor hybrid nanocrystals represent an important class of materials for many potential applications, especially for photocatalysis. The utilization of transition metals to form alloys with noble metals can not only reduce the preparation costs, but may also offer tunable optical and catalytic properties for a broader range of applications. In this study, we report on the solution synthesis of AuCu3–ZnO hybrid nanocrystals with three interesting morphologies, including urchin-like, flower-like and multipod-like nanocrystals. In the synthetic strategy, Au–Cu bimetallic alloy seeds formed in situ are used to induce the heteroepitaxial growth of ZnO nanocrystals on the surface of bimetallic alloy cores; thus different types of morphologies can be achieved by controlling the reaction conditions. Through high-resolution transmission electron microscopy observations, well-defined interfaces between ZnO and AuCu3 are observed, which indicate that ZnO has a (0001) orientation and prefers to grow on AuCu3 {111} facets. The as-prepared hybrid nanocrystals demonstrate morphology- and composition-dependent surface plasmon resonance (SPR) absorption bands. In addition, much higher photocatalytic efficiency than pure ZnO nanocrystals is observed for the hybrid nanocrystals in the degradation of methylene blue. In particular, the multipod-like AuCu3–ZnO hybrid nanocrystals show the highest catalytic performance, as well as more than three times higher photocurrent density than the pure ZnO sample. The reported synthetic strategy provides a facile route to the effective combination of a plasmonic alloy with semiconductor components at the nanoscale in a controlled manner.

Preparation of multi-branched Au–ZnO hybrid nanocrystals on graphene for enhanced photocatalytic performance

Hybrid nanostructures containing multiple components have received intensive interests. Herein, we report a solution method for the preparation of Au–ZnO/graphene nanocomposites in which multi-branched Au–ZnO hybrid nanocrystals with ZnO nanorods growing on octahedral Au cores are anchored on graphene. The as-prepared hybrid nanocrystal and nanocomposite samples are characterized by transmission electron microscopy, X-ray diffraction and ultraviolet visible spectroscopy. The photocatalytic activity is investigated by the degradation of Rhodamine B (RhB) under ultraviolet light irradiation. The results show that Au–ZnO/graphene nanocomposites not only have optical absorptions in both UV and visible ranges, but also exhibit much enhanced photocatalytic performance compared to pure Au–ZnO hybrid nanocrystals.

Supported NiW catalysts with tunable size and morphology of active phases for highly selective hydrodesulfurization of fluid catalytic cracking naphtha

This article reports a novel method for preparing supported NiW hydrodesulfurization (HDS) catalysts with tunable size and morphology of active phases to achieve highly selective HDS performance in hydro-upgrading fluid catalytic cracking (FCC) naphtha. The proposed approach features the combined use of W-based hybrid nanocrystals (HNCs) as the W precursor and the promoting effect optimization of Ni promoter. The W-based HNCs synthesized under mild hydrothermal conditions are monodispersed particles with an average size of ca. 2nm and show a core–shell structure with W6O192− as the inorganic core and short-chain quaternary ammonium cations as the organic shell. The use of W-based HNCs facilitates the formation of highly dispersed W species and WS2 active phases with enhanced stacking, thus yielding a larger number of accessible Ni–W–S edge sites upon nickel impregnation. Moreover, we found that the advantageous W dispersion in the HNC-derived monometallic catalyst precursor allows further modification of the size and morphology of the active phase via the optimized incorporation of Ni promoter, leading to the formation of Ni–W–S edge sites with a lower percentage of brim sites and thereby resulting in considerably higher selective HDS performance for FCC naphtha than its counterpart prepared by the conventional impregnation method. The proposed approach makes it easy to tune the size and morphology of WS2 nanoparticles, shedding light on the rational design of supported WS2 catalysts for FCC naphtha selective HDS.

Developing nanocrystals for cancer treatment.

Nanocrystals are carrier-free solid drug particles that are sized in the nanometer range and have crystalline characteristics. Due to high drug loading (as high as 100%) - free of organic solvents or solubilizing chemicals - nanocrystals have become attractive in the field of drug delivery for cancer treatment. Top-down and bottom-up approaches have been developed for preparing anticancer nanocrystals. In this review, preparation methods and in vivo performance of anticancer nanocrystals are discussed first, followed by an introduction of hybrid nanocrystals in cancer theranostics.

Deposition of ZnO Nanocrystals on Fe3O4 Nanocubes and Their Special Luminescent and Magnetic Properties

With increasing miniaturization, it is extremely important to maintain the magnetization stability at small scale. Herein, more efforts and interests focus on the interface of magnetic core and semiconductor shell to obtain desired magnetic and/or luminescent properties. Here, Fe3O4 nanocubes are synthesized via a thermal decomposition followed by coating ZnO nanocrystals. To create a large interface, large Fe3O4 nanocubes with 78 ± 3 nm average side‐length are synthesized through adjusting the ratio of iron precursor to stabilizer. The average diameter of the particular ZnO nanostructures coated on the nanocubic Fe3O4 is around 10 ± 2 nm. In addition to the photoluminescent properties of the ZnO‐coated nanostructures, core‐shell Fe3O4@ZnO nanostructures demonstrate enhanced UV absorption at 360 nm, which has a 20 nm blueshift compared to bulk ZnO. The superparamagnetic properties of Fe3O4@ZnO core–shell hybrid nanocrystals at room temperature are dominated by the ferromagnetic properties when the temperature is lower than the Blocking temperature, 235.7 K. The observed exchange bias and temperature‐dependent magnetization can result from the interfacial interphase between ZnO and Fe3O4. The anisotropy contributed by the interfacial interphase allows the nanostructures to maintain stable magnetization in miniaturized devices.

Highly Luminescent Hybrid SiO<SUB>2</SUB>-Coated CdTe Quantum Dots Retained Initial Photoluminescence Efficiency in Sol–Gel SiO<SUB>2</SUB> Film

A highly luminescent silica film was fabricated using tetraethyl orthosilicate (TEOS) and 3-aminopropyltrimethoxysilane (APS) through a controlled sol-gel reaction. The pre-hydrolysis of TEOS and APS which resulted in the mixture of TEOS and APS in a molecular level is a key for the formation of homogenous films. The aminopropyl groups in APS play an important role for obtaining homogeneous film with high photoluminescence (PL). Red-emitting hybrid SiO2-coated CdTe nano-crystals (NCs) were fabricated by a two-step synthesis including a thin SiO2 coating via a sol-gel process and a subsequent refluxing using green-emitting CdTe NCs. The hybrid SiO2-coated CdTe NCs were embedded in a functional SiO2 film via a two-step process including adding the NCs in SiO2 sol with a high viscosity and almost without ethanol and a subsequent spinning coating. The hybrid SiO2-coated CdTe NCs retained their initial PL efficiency (54%) in the film. Being encapsulated with the hybrid NCs in the film, no change on the absorption and PL spectra of red-emitting CdTe NCs (632 nm) was observed. This indicates the hybrid NCs is stable enough during preparation. This phenomenon is ascribed to the controlled sol-gel process and a hybrid SiO2 shell on CdTe NCs. Because these films exhibited high PL efficiency and stability, they will be utilizable for potential applications in many fields.

Freeze-dried PVP–Ag+ precursors to novel AgBr/AgCl–Ag hybrid nanocrystals for visible-light-driven photodegradation of organic pollutants

AgBr/AgCl–Ag nanocrystals with various molar Br-to-Ag ratios (RBr/Ag=0, 1/3, 1/2, 2/3, 1) and different photoreduction times (0–20min) were synthesized via stepwise liquid–solid reactions using the freeze-dried PVP–Ag+ hybrid as the Ag source, followed by a photoreduction reaction. The AgBr/AgCl–Ag7.5(1:2) nanocrystals obtained take on a spherical morphology with a particle-size range of 58±15nm. The photocatalytic performance of AgBr/AgCl–Ag nanocrystals was evaluated by photodegrading organic dyes, 4-chlorophenol and isopropanol under artificial visible light (λ⩾420nm, 100mWcm−2). For the decomposition of rhodamine B, the AgBr/AgCl–Ag7.5(1:2) nanocrystals has a photodegradation rate of ∼0.87min−1, ∼159 times higher than that (∼0.0054min−1) of TiO2 (P25), whereas the AgCl–Ag and AgBr–Ag nanocrystals have photodegradation rates of 0.35min−1 and 0.45min−1, respectively. The efficient separation of photogenerated electron–hole pairs in the ternary system consisting of AgBr, AgCl and Ag species plays a key role in the enhancement of photocatalytic performance.

Synthesis of Ni-Au-ZnO ternary magnetic hybrid nanocrystals with enhanced photocatalytic activity.

The functional synergy between the metal and the semiconductor in metal-semiconductor hybrid nanocrystals with specific structures and morphologies makes them suitable candidates for a wide range of applications. To date, the synthesis and the corresponding properties of ternary metal-semiconductor hetero-nanostructures, especially for hybrid nanocrystals containing magnetic metals, are seldom discussed and thus worthy of extensive research. In this study, we report a nonaqueous approach for the synthesis of Ni-Au-ZnO ternary hybrid nanocrystals with three morphologies, including nanomultipods, matchstick-like nanorods and nanopyramids. In the synthetic strategy, the Ni precursor dissolved in oleylamine was injected into a hot solution containing preformed Au-ZnO nanocrystals with specific morphologies. Then Ni prefers to grow on the unoccupied surfaces of Au, thus forming a hybrid hetero-nanostructure which retains the main morphologies of Au-ZnO nanocrystals. The ultraviolet-visible spectra not only show the band gap absorption of ZnO but also exhibit a broadened and weakened surface plasmon resonance (SPR) band of Au. The Ni-Au-ZnO nanocrystals exhibit much higher photocatalytic efficiency than pure ZnO in the degradation of Rhodamine B. Meanwhile, these hybrid nanocrystals are superparamagnetic at room temperature and can be readily recycled by a magnetic field for reuse. The as-prepared ternary Ni-Au-ZnO hybrid nanocrystals possess plasmonic, magnetic and enhanced photocatalytic properties, and thus are expected to find wide applications in the future.

Enhanced colloidal stability and antibacterial performance of silver nanoparticles/cellulose nanocrystal hybrids.

The aggregation of nanoparticles has been shown to significantly reduce the activity of nanomaterials, resulting in inferior performance. As an alternative to the use of traditional capping agents, stabilization of unstable nanoparticles with water-dispersible and biocompatible carriers is a promising strategy. A bioinspired coating strategy was developed and the hybrid nanoparticles displayed excellent colloidal stability that significantly improved antibacterial activity when silver nanoparticles (AgNPs) were used as a model. Cellulose nanocrystals (CNCs) were first modified with dopamine, followed by in situ generation and anchoring of AgNPs on the surface of CNCs through the reduction of silver ions by polydopamine coated CNCs. The results indicated that the dispersion stability of AgNPs was significantly enhanced by the CNC, which in turn resulted in more than fourfold increase in antibacterial activity based on antibacterial studies using Escherichia coli and Bacillus subtilis.

Efficient aqueous-processed hybrid solar cells from a polymer with a wide bandgap

Efficient aqueous processed polymer–nanocrystal hybrid solar cells are demonstrated based on MPPV with a wide band gap. A PCE of 5.18% is achieved which is the highest for solar devices via an aqueous process. This work may provide a new way to develop hybrid solar cells.

Surface-Initiated Group-Transfer Polymerization – A Catalytic Approach to Stimuli-Responsive Silicon Nanocrystal Hybrid Materials

ABSTRACTSilicon nanocrystals are photoluminescent materials with a tremendous scope in various niche applications especially the generation of hybrid materials. Our approach for the preparation of stimuli responsive SiNC hybrid materials is based on the application of surface-initiated group-transfer polymerization. As a first step we used photografting of ethyleneglycol di(methacrylate). Then we impregnated remaining methyl acrylic surface groups with the catalyst Cp2YCH2TMS(thf). We performed polymerization studies regarding catalyst and diethyl vinylphosphonate (DEVP) concentrations, highlighting that surface grafting is dependent upon catalyst concentration and independent from added monomer amount. Furthermore, we successfully polymerized methyl methacrylate, dimethyl vinylphosphonate and diisopropyl vinylphosphonate from the SiNC surface.

High-performance fluorinated polyimide/pure silica zeolite nanocrystal hybrid films with a low dielectric constant

A simple strategy for preparing the low-κ FPI hybrids with enhanced properties.

Growing ordered and stable nanostructures on polyhedral nanocrystals

Using both theoretical analysis and phase field simulation, we reveal robust and facile self-assembly routes, which allow the growth of different stable and ordered nanostructures on various polyhedral nanocrystals (NCs) heteroepitaxially. Our studies show that by increasing the NC's size, transitions from formal growth to ordered quantum dots on the facets and further to ordered quantum dots on the corners take place. The predicted morphologies and their transitions are in excellent agreement with existing widely scattered experimental results. Our study presents a facile and potentially practical route for mass-producing hybrid NCs with well-defined size, shape, composition, and architecture.

A Review of Graphene Supported Electrocatalysts for Direct Methanol Fuel Cells

As a fascinating two-dimensional nanomaterial, graphene is attractive for electrocatalytical application in direct methanol fuel cells due to its unique structure and outstanding physical properties. Graphene and its derivatives have been widely used as a support material to improve electrocatalytical activity of catalyst particles for methanol and ethanol oxidations. In this review, discussion is focused on the graphene supported monometallic and bimetallic nanocrystals hybrid materials for electrocatalysts. Additionally, the nitrogen-doped graphene utilized for promising support material in electrocatalysts was also mentioned. We believe that the article will be useful to researchers interested in graphene-based catalyst and related materials for direct methanol fuel cells and provide the present status of the subject.

Improving Polymer/Nanocrystal Hybrid Solar Cell Performance via Tuning Ligand Orientation at CdSe Quantum Dot Surface

Achieving superior solar cell performance based on the colloidal nanocrystals remains challenging due to their complex surface composition. Much attention has been devoted to the development of effective surface modification strategies to enhance electronic coupling between the nanocrystals to promote charge carrier transport. Herein, we aim to attach benzenedithiol ligands onto the surface of CdSe nanocrystals in the "face-on" geometry to minimize the nanocrystal-nanocrystal or polymer-nanocrystal distance. Furthermore, the "electroactive" π-orbitals of the benzenedithiol are expected to further enhance the electronic coupling, which facilitates charge carrier dissociation and transport. The electron mobility of CdSe QD films was improved 20 times by tuning the ligand orientation, and high performance poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT):CdSe nanocrystal hybrid solar cells were also achieved, showing a highest power conversion efficiency of 4.18%. This research could open up a new pathway to improve further the performance of colloidal nanocrystal based solar cells.

Seed‐Induced Growth of Flower‐Like Au–Ni–ZnO Metal–Semiconductor Hybrid Nanocrystals for Photocatalytic Applications

The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications.

One-step synthesis of hybrid nanocrystals with rational tuning of the morphology.

Metal-sulfide hybrid nanocrystals (HNCs) have been of great interest for their distinguished interfacial effect, which gives rise to unique catalytic properties. However, most of the reported metal-sulfide HNCs were synthesized via two-step approaches and few were fabricated based on the one-step strategies. Herein, we report a facile one-pot synthesis of CuPt-Cu2S, Pt-Cu2S HNCs, and CuPt nanocubes by simply changing the Pt precursor types. 1-Hexadecanethiol (HDT) was employed in this system to mediate the reduction of metal precursors and also as capping agent and sulfur source. Moreover, CuPd-Cu2S and Au-Cu2S HNCs were successfully prepared by using this one-step method. The catalytic properties of the obtained three nanocrystals were investigated in hydrogenation of cinnamaldehyde. Results show that CuPt-Cu2S HNCs exhibited the highest conversion rate and the highest selectivity toward hydrocinnamaldehyde while 3-phenyl-1-propanol was the only product over Pt-Cu2S HNCs.