Hybrid Nanocrystals Research Articles

Trimetallic WMoNi diesel ultra-deep hydrodesulfurization catalysts with enhanced synergism prepared from inorganic–organic hybrid nanocrystals

Supported WMoNi diesel ultra-deep hydrodesulfurization (HDS) catalysts with enhanced synergetic effects among metal species were prepared with W- and Mo-based hybrid inorganic–organic nanocrystals (HNCs) as the W/Mo precursors. The W- and Mo-based HNCs are monodispersed particles with similar structure. The thus-obtained supported WMoNi catalyst has superior hydrogenation and direct desulfurization activities for dibenzothiophene HDS and dramatically higher fluid catalytic cracking diesel HDS performance than WMoNi/Al2O3 prepared by the impregnation method. This benefits from the bimetallic catalyst precursor WMo/Al2O3, which has highly dispersed W and Mo species and high sulfidability and thus generates a large number of metal sulfide slabs after sulfidation. The highly dispersed W/Mo sulfide slabs provide abundant edge sites for dispersing Ni species, facilitating both textural and chemical synergisms among the sulfide phases and yielding more synergetic NiWMoS active phases. The approach opens a novel route to optimizing the synergetic effects among metal species in supported WMoNi catalysts for diesel ultra-deep HDS.

Time-resolved photoluminescence studies in Eu-doped SiO2 – HfO2 – ZnO glass-ceramic waveguides

Fabrication of ZnO-HfO2 hybrid nanocrystals embedded 70 SiO2-(30−x) HfO2-xZnO (x=0, 2, 5, 7 and 10mol%) ternary glass-ceramic planar waveguides doped with 1mol% Eu-ions, by sol-gel process and dip-coating technique has been reported. The effect of varying ZnO concentration on the growth and structural evolution of ZnO-HfO2 hybrid nanocrystals were investigated using transmission electron microscopy and other spectroscopic tools. Time-resolved PL measurements were performed to estimate the PL emission lifetimes of Eu2+ and Eu3+, present in two different local environments in the ternary matrix, as a function of ZnO concentration. Eu3+ ions exhibit double exponential decay profile for the D05→F27 emission, while the decay curves of Eu2+ ions are single exponential. The variations in the PL emission decay profiles are used as a probe to investigate the changes in the local environments of the rare-earth ions in the glass-ceramic waveguides.

Near‐Field Energy Transfer Using Nanoemitters For Optoelectronics

Effective utilization of excitation energy in nanoemitters requires control of exciton flow at the nanoscale. This can be readily achieved by exploiting near‐field nonradiative energy transfer mechanisms such as dipole‐dipole coupling (i.e., Förster resonance energy transfer) and simultaneous two‐way electron transfer via exchange interaction (i.e., Dexter energy transfer). In this feature article, we review nonradiative energy transfer processes between emerging nanoemitters and exciton scavengers. To this end, we highlight the potential of colloidal semiconductor nanocrystals, organic semiconductors, and two‐dimensional materials as efficient exciton scavengers for light harvesting and generation in optoelectronic applications. We present and discuss unprecedented exciton transfer in nanoemitter–nanostructured semiconductor composites enabled by strong light–matter interactions. We elucidate remarkably strong nonradiative energy transfer in self‐assembling atomically flat colloidal nanoplatelets. In addition, we underscore the promise of organic semiconductor–nanocrystal hybrids for spin‐triplet exciton harvesting via Dexter energy transfer. These efficient exciton transferring hybrids will empower desired optoelectronic properties such as long‐range exciton diffusion, ultrafast multiexciton harvesting, and efficient photon upconversion, leading to the development of excitonic optoelectronic devices such as exciton‐driven light‐emitting diodes, lasers, and photodetectors.

Bimetallic PtAu superlattice arrays: Highly electroactive and durable catalyst for oxygen reduction and methanol oxidation reactions

Abstract Superlattice arrays, an important type of nanomaterials, have wide applications in catalysis, optic/electronics and energy storage for the synergetic effects determined by both individual metals and collective interactions. Herein, a simple one-pot solvothermal coreduction approach is developed for facile preparation of bimetallic PtAu alloyed superlattice arrays (PtAu SLAs) in oleylamine, with the assistance of urea via hydrogen bonding induced self-assembly. Urea is essential in morphology-controlled process and prevents PtAu nanoparticles from the disordered aggregation. The characterization and formation mechanism of PtAu SLAs are investigated in details. The as-synthesized hybrid nanocrystals exhibit enhanced electrocatalytic performances for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in alkaline electrolyte in comparison with commercial Pt-C (50%, wt.%) and Pt black catalysts.

Plasmon-enhanced photocatalytic hydrogen production on Au/TiO2 hybrid nanocrystal arrays

In recent years, hybrid nanostructure consisted of plasmonic metals and different dielectrics have attracted much attention for their intriguing plasmonic properties. Recent studies have also shown that by introducing plasmonic metals, the photocatalytic efficiency of semiconductor can improve via plasmon-enhanced light absorption. In this work, we have demonstrated excellent photocatalytic properties for hydrogen production using hexagonal close-packed core-shell Au/TiO2 hybrid nanocrystal arrays. Under both ultra-violet and visible light, significant increase in the hydrogen production from methanol (20%) solution splitting was achieved with the hybrid Au/TiO2 nanocrystal arrays in comparison with bare TiO2 thin film as well as randomly distributed Au/TiO2 nanocrystals. From the finite difference time domain (FDTD) simulation, the significant increase (up to 60%) in hydrogen production can be correlated to strong and optimum coupling of the enhanced electric field from localized surface plasmon resonance in Au/TiO2 nanocrystal arrays. In addition to allowing more accurate measurement of plasmonic enhancement, the ordered nanostructures have been shown to be especially amenable to the systematic analysis of lateral coupling of plasmonically enhanced electric field. As a result, optimal structures with appropriate spacing of core-shell metal-dielectric nanocrystals, metal core size and dielectric shell thickness for maximum enhancement can be designed.

High-quality Cu2ZnSnS4 and Cu2ZnSnSe4 nanocrystals hybrid with ZnO and NaYF4: Yb, Tm as efficient photocatalytic sensitizers

A chloroform-assistant Se dissolution in oleylamine without trioctylphosphine and alkylthiol as the green precursor was used for facile and robust synthesis of quaternary selenide nanocrystals. The S2− modified hydrophilic Cu2ZnSnS4 and Cu2ZnSnSe4 nanocrystals were first prepared by a one-pot thermal decomposition route, followed by a bi-phase hydrophilic treatment process. As a proof of concept, the as-obtained hydrophilic nanocrystals were hybridized with ZnO microspheres as photosensitizers to achieve visible light-driven photocatalytic application; on the other hand, hybridized with NaYF4: Yb, Tm microplates to achieve near-infrared light-driven photocatalytic application. These photosensitized hybrids as photocatalysts expanded the light absorption from ultraviolet to visible even near-infrared region, which showed excellent photocatalytic Rhodamine B degradation under visible and near-infrared irradiation compared to pure ZnO and NaYF4: Yb, Tm, respectively. Therefore, these hydrophilic Cu2ZnSnS4 and Cu2ZnSnSe4 nanocrystals are proved as efficient photocatalytic sensitizers due to the efficient utilization of the visible light and emissions upconverted from near-infrared light.

Controlled spatial dispersion of CdSe tetrapod nanocrystals with amphiphilic block copolymer particles

Abstract We report, for the first time, a nanoscale control of the spatial distribution of semiconducting tetrapod (TP) nanocrystals within block copolymer particles. Polystyrene (PS) block copolymer (BCP)/CdSe TP nanocrystal hybrid particles were prepared by the nanoprecipitation of TP/BCP mixtures into methanol. The BCPs consisted of short, polar terminal block bearing methyl disulfide anchoring moiety which serves both to bind to CdSe TP surfaces as well as to drive self-assembly during nanoprecipitation into polar solvent systems. The resulting BCP/TP hybrid particles showed various spatial distribution and the number density of TPs with respect to individual polymer particles depending on the degree of polymerization of the block copolymer as well as the nature of the solvent in which nanoprecipitation was done.

Solution Synthesis, Surface Passivation, Optical Properties, Biomedical Applications, and Cytotoxicity of Silicon and Germanium Nanocrystals.

Silicon and germanium nanocrystals (NCs) are attractive materials owing to their unique size and surface-dependent optical properties. The optical properties of silicon and germanium NCs make them highly suitable for a range of applications, including bioimaging, light-emitting diodes, and solar cells. In this review, the solution synthesis, surface passivation, optical properties, biomedical applications, and cytotoxicity of silicon and germanium NCs are compared and contrasted. Over the last 10 years, synthetic protocols have improved considerably, with size control readily achieved. Investigations have begun into a range of silicon and germanium nanostructures, including doped, alloy, and metal-semiconductor hybrid NCs, which represent the next generation of silicon and germanium nanomaterials. Silicon and germanium NCs are actively researched for a wide array of biomedical applications, including, long-term in vivo cellular imaging, fluorescent nanocarriers for drug delivery, and as contrast agents for magnetic resonance imaging (MRI). Cytotoxicity studies have shown the low toxicity of Si NCs, while demonstrating that Ge NCs are less toxic than CdSe NCs at similar concentrations, giving these materials a strong future in nanomedicine applications.

Synthesis and properties of covalently linked photoluminescent magnetic magnetite nanoparticle-silicon nanocrystal hybrids

Silicon nanocrystals (SiNCs) are quantum dots that do not contain toxic metals and exhibit a photoluminescent response that may be tailored via changes in particle dimension as well as surface chemistry. Herein, we present a promising hybrid nanomaterial that combines the favourable properties (e.g., photoluminescence, biocompatibility, and surface chemistry) of SiNCs with the magnetic characteristics of Fe 3 O 4 nanoparticles (NPs). Linking these two complementary nanomaterials via DCC coupling has yielded a new advanced hybrid material that possesses the characteristics of its constituents and affords a photoluminescent system that responds to permanent magnets.

Correlation between CdSe QD Synthesis, Post-Synthetic Treatment, and BHJ Hybrid Solar Cell Performance.

In this publication we show that the procedure to synthesize nanocrystals and the post-synthetic nanocrystal ligand sphere treatment have a great influence not only on the immediate performance of hybrid bulk heterojunction solar cells, but also on their thermal, long-term, and air stability. We herein demonstrate this for the particular case of spherical CdSe nanocrystals, post-synthetically treated with a hexanoic acid based treatment. We observe an influence from the duration of this post-synthetic treatment on the nanocrystal ligand sphere size, and also on the solar cell performance. By tuning the post-synthetic treatment to a certain degree, optimal device performance can be achieved. Moreover, we show how to effectively adapt the post-synthetic nanocrystal treatment protocol to different nanocrystal synthesis batches, hence increasing the reproducibility of hybrid nanocrystal:polymer bulk-heterojunction solar cells, which usually suffers due to the fluctuations in nanocrystal quality of different synthesis batches and synthesis procedures.

Enhanced Ultraviolet Photon Capture in Ligand-Sensitized Nanocrystals

The small absorption cross sections (e < 10 M–1 cm–1) characteristic of Laporte-forbidden transitions in the f-elements have limited the practical implementation of lanthanide nanoparticles in solar capture devices. While various strategies designed to circumvent the problems of low f–f oscillator strengths have been investigated, comparatively little work has explored the utility of organic ligands with high absorption coefficients (e ≈ 103–105 M–1 cm–1) in sensitizing excited states in lanthanide nanocrystals. Here, we detail the photophysics of NaGd1–xEuxF4 nanoparticles featuring surface display of the ligand 3,4,3-LI(1,2-HOPO), an aromatic antenna functioning as the terminal light absorber in this system. The result is a ligand–nanocrystal hybrid that converts UV (250–360 nm) light into red Eu(III) luminescence with an external quantum yield of 3.3%. We analyze this sensitization process, responsible for a 104-fold increase in luminescence relative to metal-centered excitation, through a quantitative...

Chloride Ion Mediated Synthesis of Metal/Semiconductor Hybrid Nanocrystals.

A synthetic route to prepare metal-semiconductor hybrid nanoparticles is presented, along with the possibility to tune the ratio of primary to secondary nucleation and the morphology of the semiconductor material grown on the metal nanoparticle seeds. Gold and cobalt-platinum nanoparticles are employed as metal seeds, on which CdS or CdSe is grown. Using transmission electron microscopy, absorption spectroscopy (UV-vis), and powder X-ray diffraction as characterization techniques, a significant influence of chloride ions on the type of nucleation (that is, secondary or primary nucleation) as well as on the shape of the resulting heterostructures is observed. Partially replacing the commonly used cadmium precursor CdO by varying amounts of CdCl2 opens access to rod-like, multiarmed, flower-like, and bullet-like structures. The results suggest that neither pure CdO nor pure CdCl2 as precursors but only a mixture of both make these structures obtainable. In this article, the influence of the chloride ion concentration during semiconductor growth on metal seeds is investigated in depth. The morphology of the resulting heterostructures is characterized carefully, and a growth mechanism is suggested. Furthermore, it is shown that this synthetic approach can be transferred to seeds of various metals such as platinum, gold, and cobalt platinum.

Eu-doped ZnO–HfO2 hybrid nanocrystal-embedded low-loss glass-ceramic waveguides

We report on the sol–gel fabrication, using a dip-coating technique, of low-loss Eu-doped 70SiO2 – HfO2–xZnO (x = 2, 5, 7 and 10 mol%) ternary glass-ceramic planar waveguides. Transmission electron microscopy and grazing incident x-ray diffraction experiments confirm the controlled growth of hybrid nanocrystals with an average size of 3 nm–25 nm, composed of ZnO encapsulated by a thin layer of nanocrystalline HfO2, with an increase of ZnO concentration from x = 2 mol% to 10 mol% in the SiO2–HfO2 composite matrix. The effect of crystallization on the local environment of Eu ions, doped in the ZnO–HfO2 hybrid nanocrystal-embedded glass-ceramic matrix, is studied using photoluminescence spectra, wherein an intense mixed-valence state (divalent as well as trivalent) emission of Eu ions is observed. The existence of Eu2+ and Eu3+ in the SiO2–HfO2–ZnO ternary matrix is confirmed by x-ray photoelectron spectroscopy. Importantly, the Eu-doped ternary waveguides exhibit low propagation losses (0.3 ± 0.2 dB cm–1 at 632.8 nm) and optical transparency in the visible region of the electromagnetic spectrum, which makes ZnO–HfO2 nanocrystal-embedded SiO2–HfO2–ZnO waveguides a viable candidate for the development of on-chip, active, integrated optical devices.

Three-dimensional controlled growth of monodisperse sub-50 nm heterogeneous nanocrystals.

The ultimate frontier in nanomaterials engineering is to realize their composition control with atomic scale precision to enable fabrication of nanoparticles with desirable size, shape and surface properties. Such control becomes even more useful when growing hybrid nanocrystals designed to integrate multiple functionalities. Here we report achieving such degree of control in a family of rare-earth-doped nanomaterials. We experimentally verify the co-existence and different roles of oleate anions (OA−) and molecules (OAH) in the crystal formation. We identify that the control over the ratio of OA− to OAH can be used to directionally inhibit, promote or etch the crystallographic facets of the nanoparticles. This control enables selective grafting of shells with complex morphologies grown over nanocrystal cores, thus allowing the fabrication of a diverse library of monodisperse sub-50 nm nanoparticles. With such programmable additive and subtractive engineering a variety of three-dimensional shapes can be implemented using a bottom–up scalable approach.

Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties.

Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.

Photoinduced ultrafast charge separation in colloidal 2-dimensional CdSe/CdS-Au hybrid nanoplatelets and corresponding application in photocatalysis.

Multicomponent hybrid nanocrystals (HNC) consisting of a semiconductor and metallic domains are an important class of nanostructured materials demonstrating useful applications and interesting basic knowledge. In this scenario, Au nanoparticle (NP) islands of ∼2 nm have been grown on unique two dimensional (2D) CdSe/CdS core@shell hexagonal nanoheteroplatelets of 20 nm diameter to form unprecedented 2D CdSe/CdS-Au HNCs and detailed optical characterization has been carried out to determine the dimensionality based electron transfer dynamics on the ultrafast scale. Steady state optical absorption studies show that upon growing Au NPs onto the 2D nanoplates, a new band appears in the red region of the spectra (500-800 nm), which suggests a strong interaction between the exciton of the core-shell and the plasmon of the metal NPs. Fluorescence studies showed the quenching of emission of the semiconductor domains upon the growth of the metallic domains. Detailed optical and TRPL studies suggested efficient charge transfer from the 2D CdSe/CdS to the Au domains, irrespective of excitation wavelength. Femtosecond transient absorption studies suggest that the electron transfer from the 2D hybrid nanocrystals to the metal domain is on an ultrafast time scale (∼800 fs). No evidence is observed for charge transfer from the 2 nm Au domains to the semiconductor seeds. The broad absorption in the visible region of the hybrid nanocrystals and the ultrafast charge transfer facilitates very efficient photo-catalytic reactions under direct sun light, as a case study.

Plasmonic fluorescent CdSe/Cu2S hybrid nanocrystals for multichannel imaging and cancer directed photo-thermal therapy.

A simple, crude Jatropha curcas (JC) oil-based synthesis approach, devoid of any toxic phosphine and pyrophoric ligands, to produce size and shape tuned CdSe QDs and a further copper sulfide (Cu2S) encasing is presented. The QDs exhibited excellent photoluminescent properties with narrow band gap emission. Furthermore, the Cu2S shell rendered additional cytocompatibility and stability to the hybrid nanomaterial, which are major factors for translational and clinical applications of QDs. The nanocomposites were PEGylated and folate conjugated to augment their cytoamiability and enhance their specificity towards cancer cells. The nanohybrids possess potentials for visible, near infrared (NIR), photoacoustic (PA) and computed tomography (μCT) imaging. The diverse functionality of the composite was derived from the multi-channel imaging abilities and thermal competence on NIR laser irradiation to specifically actuate the photo-thermal ablation of brain cancer cells.

Facile hydrothermal synthesis of SnCoS4/graphene composites with excellent electrochemical performance for reversible lithium ion storage

An SnCoS4/graphene composite with uniformly distributed SnCoS4 hybrid nanocrystals was prepared by a one-pot hydrothermal route and exhibits excellent electrochemical performance for reversible lithium storage.

Synthesis of plasmonic Au–CuS hybrid nanocrystals for photothermal transduction and chemical transformations

Plasmonic Au–CuS heterodimers were prepared by tuning Cu–S reactivity, which shows synergistically enhanced optical absorption and can be further chemically transformed to hybrids like Au–CuInS2 and Au–Cu2ZnSnS4.

Surface modification of CdSeS nanocrystals for polymer hybrid solar cells

We report synthesis of Fluorene–Carbazole derivatives as caping agent for CdSeS nanocrystals to improve the performance of polymer nanocrystal hybrid solar cells.