Nanocubes Research Articles

Achieving a high cutting-off frequency in the oriented CoFe2O4 nanocubes

An effective way for the improvement of resonance frequency was demonstrated by the orientation of CoFe2O4 nanocubes (NCs) after applying a magnetic field. The magnetic holography image of the oriented CoFe2O4 NC arrays was obtained, and the vortex domain structure was found in single CoFe2O4 NCs, which greatly depends on dipolar interactions. Moreover, the cutting-off frequency of oriented CoFe2O4 NCs of 8.8 GHz is achieved with a slight increase in permeability at an extremely low mass fraction (about 10%). This work provides an effective way for optimizing the high-frequency properties of magnetic nanomaterials above GHz.

Mesoporous Ceria‐Supported Gold Catalysts Self‐Assembled from Monodispersed Ceria Nanoparticles and Nanocubes: A Study of the Crystal Plane Effect for the Low‐Temperature Water Gas Shift Reaction

AbstractMesoporous CeO2 colloidal spheres were obtained by the assembly of CeO2 nanocrystals in two shapes: nanoparticles (NPs) and nanocubes (NCs). CeO2 colloidal spheres assembled by nanoparticles (NPCS) have predominantly exposed {1 1 1} surfaces and that assembled by nanocubes (NCCS) are terminated by {1 0 0} planes. The size and surface area of NPCS and NCCS are comparable. We compared the water gas shift reaction activity over Au/NPCS and Au/NCCS to clarify the nanoscale crystal plane effect of the CeO2 {1 0 0} and {1 1 1} crystal planes. Au/NCCS and NCCS show a better catalytic activity than Au/NPCS and NPCS towards the water gas shift reaction. We used in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to confirm that the water gas shift reaction over Au/NPCS and Au/NCCS follows a formate mechanism and to prove that the formation/decomposition rate of bidentate formates (intermediates) are faster on Au/NCCS and that less monodentate carbonates (inactive species) are accumulated over Au/NCCS. We used X‐ray photoelectron spectroscopy and DRIFTS combined with DFT calculations to demonstrate that more active Auδ+ species could be formed on NCCS than NPCS because of the crystal plane effect. The crystal plane effect is also embodied in the experimental phenomenon that H2O adsorption is more significant on Au/NCCS than Au/NPCS, which is in agreement with the calculation results that H2O adsorption is more facile on CeO2 {1 0 0} than {1 1 1} surfaces.

Shape and Composition Control of Monodisperse Hybrid Pt-CoO Nanocrystals by Controlling the Reaction Kinetics with Additives

Here, we report the effect of Fe(CO)5 additives in the synthesis of branched Pt-CoO nanowires (NWs) and core@shell concave nanocubes (NCs), in a one-pot system. Key to the success of this synthesis is control over the shape of the Pt seeds by controlling the quantity of Fe(CO)5 additive. In the absence of Fe(CO)5, branched Pt-CoO NWs were synthesized through the attachment of small Pt seed particles, followed by the growth of CoO by deposition. On the other hand, Pt@CoO concave NCs were obtained in the presence of Fe(CO)5 because of the stronger adsorption of Co on the Pt (100) surfaces than on the closely packed (111) surfaces. Also, various other conditions including the control of reducing agents, precursor concentrations, and stabilizing agents, were used to verify the effects of reaction kinetics on the synthesis of Pt-CoO nanoparticles. Compared to Pt/graphene oxide (GO) catalyst, branched Pt-CoO NWs supported on GO showed enhanced specific activity toward the oxygen reduction reaction (ORR).

Ag+-assisted heterogeneous growth of concave Pd@Au nanocubes for surface enhanced Raman scattering (SERS)

AgNO3 is often used in the preparation of Au nanostructures since Ag-based substances (AgBS) can selectively be adsorbed on Au(100) and significantly modulate the growth of Au nanocrystals. High-index-faceted Au nanostructures have demonstrated excellent performance in catalysis and surface enhanced Raman scattering (SERS), thus attracting the interest of many researchers in the past several decades. Herein, high-index-faceted Pd@Au concave nanocubes (CNCs) were prepared using AgBS as growth-directing agents in the heterogeneous growth of Au on Pd nanocubes (NCs). During the growth of Pd@Au CNCs, Au atoms are initially deposited on the Pd{100} facets leading to the formation of thin Au shells, and then AgBS are quickly adsorbed on the formed Au(100), favoring the growth along and the formation of Pd@Au CNCs. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), high angle annular dark field (HAADF), and scanning transmission electron microscopy EDS (STEM-EDS) were used to systematically investigate the growth of Pd@Au CNCs. We also demonstrated that the high-index-faceted Pd@Au CNCs exhibited excellent SERS performances.

Improved Oxidase Mimetic Activity by Praseodymium Incorporation into Ceria Nanocubes.

Ceria nanocubes (NC) modified with increasing concentrations of praseodymium (5, 10, 15, and 20 mol %) have been successfully synthesized by a hydrothermal method. The as-synthesized Pr-modified ceria nanocubes exhibit an enhanced oxidase-like activity on the organic dye TMB within a wide range of concentrations and durations. The oxidase activity increases with increasing Pr amounts in Pr-modified ceria nanocubes within the investigated concentration range. Meanwhile, these Pr-modified ceria nanocubes also show higher reducibility than pure ceria nanocubes. The kinetics of their oxidase mimetic activity is fitted with the Michaelis-Menten equation. A mechanism has been proposed on how the Pr incorporation could affect the energy level of the bands in ceria and hence facilitate the TMB oxidation reaction. The presence of Pr3+ species on the surface also contributes to the increasing activity of the Pr-modified ceria nanocubes present higher oxidase activity than pure ceria nanocubes.

Pd nanoparticles immobilized on magnetic carbon dots@Fe3O4 nanocubes as a synergistic catalyst for hydrogen generation

In this work, a cube-like Pd/carbon dots@Fe3O4 (Pd/C-dots@Fe3O4) hybrid material has been successfully prepared through a facile ultrasonic assisted chemical reduction method, and used as a highly efficient catalyst for the hydrolytic dehydrogenation of NaBH4 in alkaline media. It is found that the small Pd nanoparticles (NPs) are uniform and well dispersed on the surface of C-dots@Fe3O4 nanocubes (NCs). Benefiting from the advantages of the unique cube-like structure, the super conductivity of carbon dots (C-dots) and the synergistic effect between Pd NPs and C-dots@Fe3O4 support, Pd/C-dots@Fe3O4 NCs exhibits the highest catalytic performance among all the as-prepared samples. The possible reaction mechanism is discussed. Furthermore, the effects of reaction temperature, NaBH4 concentration and NaOH concentration on the catalytic activity of Pd/C-dots@Fe3O4 NCs are studied. Besides, the magnetic properties of Pd/C-dots@Fe3O4 NCs can achieve effective momentum transfer with the assistance of the external magnetic field, and a higher catalytic activity is observed for Pd/C-dots@Fe3O4 NCs in self-stirring mode than in magnetic-stirring mode. This novel catalyst also exhibits good stability and can be easily separated by a magnet, showing great potential for renewable energy applications.

High-Index Facets Bounded Platinum–Lead Concave Nanocubes with Enhanced Electrocatalytic Properties

High-index facets bounded platinum-based alloy nanocrystals usually exhibit enhanced electrocatalytic activity. However, the high surface energy, thermodynamic instability, and lattice mismatch make it a significant challenge to synthesize well-defined bimetallic nanocrystals with high-index facets. Here we developed a one-step wet-chemical synthesis of uniform PtPb concave nanocubes (CNCs) enclosed by {520} high-index facets. The as-prepared PtPb CNCs exhibited high synthetic yield and highly concave structure with an average size of 14 nm. Moreover, the synergistic effects and exposed {520} facets endowed the PtPb CNCs with excellent stability and electrocatalytic mass activity toward the methanol oxidation reaction (MOR), which was 2.16- and 4.62-times higher than PtPb nanocubes (NCs) and commercial Pt/C catalysts, respectively. This work provides a new way for rational design and practical application of efficient catalysts.

Fast response of hydrogen sensor using palladium nanocube-TiO2 nanofiber composites

In this work, we investigated the properties of resistivity type hydrogen (H2) sensor for monitoring in H2 gas. The H2 sensor was made of Pd nanocube (NCs) and TiO2 nanofiber (NFs) composites. The Pd NCs was synthesized by seed-mediated growth and TiO2 nanofiber was synthesized via electrospinning method. The two nanomaterials are then converted into nanocomposites by ultrasonication process. Pd NCs-TiO2 NFs composite was characterized by scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). The H2 sensing properties including the response/recovery time, the response value and linearity of the synthesized samples were investigated toward to various H2 concentrations (0.6, 0.8 and 1%). The response of H2 sensor is S = 40.8% and the response/recovery time are 25/1 s with 0.6% at working temperature of 150 °C. Moreover, the H2 sensor has excellent cross-selectivity for H2 compared to ethanol, nitrogen dioxide and isopropyl alcohol.

Topochemical Reaction of Exfoliated Layered Cobalt(II) Hydroxide for the Synthesis of Ultrapure Co3O4 as an Oxygen Reduction Catalyst

The liquid exfoliation of hydrotalcite‐like α‐Co(OH)2 in formamide produced a new pink β‐form of Co(OH)2 nanosheets [Ex‐NS‐Co(OH)2] with unique nanoscopic properties: a larger surface area of active hydroxides and a much narrower oxidation–reduction potential for the Co2+ ions in the hydroxide layer than those of the bulk α‐Co(OH)2. These unprecedented properties of Ex‐NS‐Co(OH)2 were applied to the topochemical synthesis of crystalline Co3O4 nanocubes (NCs) with clear edges and no impurity phases from an aqueous solution of Co2+ ions at 70 °C. A Co3O4 NC/C catalyst exhibited good catalytic activity for the oxygen reduction reaction (ORR) and higher stability under a continuous electrochemical operation than that of commercial Pt/C.

High-Performance Rh2P Electrocatalyst for Efficient Water Splitting.

The search for active, stable, and cost-efficient electrocatalysts for hydrogen production via water splitting could make a substantial impact on energy technologies that do not rely on fossil fuels. Here we report the synthesis of rhodium phosphide electrocatalyst with low metal loading in the form of nanocubes (NCs) dispersed in high-surface-area carbon (Rh2P/C) by a facile solvo-thermal approach. The Rh2P/C NCs exhibit remarkable performance for hydrogen evolution reaction and oxygen evolution reaction compared to Rh/C and Pt/C catalysts. The atomic structure of the Rh2P NCs was directly observed by annular dark-field scanning transmission electron microscopy, which revealed a phosphorus-rich outermost atomic layer. Combined experimental and computational studies suggest that surface phosphorus plays a crucial role in determining the robust catalyst properties.

Rapid synthesis strategy of CuO nanocubes for sensitive and selective detection of NO2

Abstract In present work, copper oxide (CuO) films have been successfully synthesized onto a quartz substrate using a simple and catalyst-free thermal evaporation technique and their chemiresistive properties were carried out towards host of target gases. Structural analysis demonstrates the formation of polycrystalline single phase monoclinic CuO. Formation of nanocubes–type of surface morphology of CuO was observed from morphological investigation. Gas sensing results demonstrate that the CuO films, composed of nanocubes (NCs), are highly selective towards oxidizing nitrogen dioxide (NO 2 ) gas than other target gases along with rapid response and recovery times. CuO sensor films exhibit the maximum response value of 76%–100 ppm NO 2 @150 °C. In addition, CuO films are able to sense as low as 1 ppm concentration of NO 2 gas. The effect of operating temperature on the NO 2 sensing properties of CuO films was thoroughly investigated and reported. Impedance spectroscopy was used to study the interaction mechanism between CuO sensor film and NO 2 gas molecules.

Synthesis of ultrathin carbon dots-coated iron oxide nanocubes decorated with silver nanoparticles and their excellent catalytic properties

A facile ultrasonic method has been successfully developed for the fabrication of multifunctional Fe3O4@carbon dot/Ag (Fe3O4@C-dot/Ag) nanocubes (NCs), and the resulting materials are well characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Vibrating sample magnetometer (VSM) and fluorescence measurements. The Ag nanoparticles (NPs) are uniform and well dispersed on the surface of Fe3O4@C-dot, while maintaining the shape and the size of the core-shell Fe3O4@C-dot NCs. In addition, its catalytic activities are evaluated by measuring the reduction of p-nitroaniline (p-NA) and crystal violet (CV), and the composite materials exhibit excellent catalytic activity towards reduction of p-NA and CV dye, which is superior to most reported catalysts. The good catalytic performance of Fe3O4@C-dot/Ag NCs may be attributed to the specific characteristics of its nanostructure and the synergistic effect on the delivery of electrons between Ag NPs and Fe3O4@C-dot NCs. Furthermore, the as-prepared catalysts also show good activity for the reduction of other nitrobenzene analogs. The effect of solvent and reducing agent was also studied on the catalytic activity of Fe3O4@C-dot/Ag NCs. Most importantly, the Fe3O4@C-dot/Ag catalyst shows excellent recycling stabilities, which can be potentially applied in the fields of catalysis and green chemistry.

PdCu@Pd Nanocube with Pt-like Activity for Hydrogen Evolution Reaction.

The electronic properties of metal surfaces can be modulated to weaken the binding energy of adsorbed H-intermediates on the catalyst surface, thus enhancing catalytic activity for the hydrogen evolution reaction (HER). Here we first prepare PdCu alloy nanocubes (NCs) by coreduction of Cu(acac)2 (acac = acetylacetonate) and Na2PdCl4 in the presence of oleylamine (OAm) and trioctylphosphine (TOP). The PdCu NC coated glassy carbon electrode is then anodized at a constant potential of 0.51 V vs Ag/AgCl at room temperature in 0.5 M H2SO4 solution for 10 s, which converts PdCu NCs into core@shell PdCu@Pd NCs that show much enhanced Pt-like activity for the HER and much more robust durability. The improvements in surface property and HER activity are rationalized based on strain and ligand effects that enhance the activity of the edge-exposed Pd atoms on core@shell PdCu@Pd structure. This work opens up a new perspective for simultaneously reducing metal Pd cost and achieving excellent performance toward the HER.

A Plasmonic Coupling Substrate Based on Sandwich Structure of Ultrathin Silica‐Coated Silver Nanocubes and Flower‐Like Alumina‐Coated Etched Aluminum for Sensitive Detection of Biomarkers in Urine

Interactions between substrate and plasmonic nanostructures can give rise to unique optical properties and influence performance in plasmonic biosensing applications. In this study, a substrate with low refractive index and roughness based on flower-like alumina-coated etched aluminum foil (f-Al2 O3 /e-Al) has been fabricated. Silver@silica (Ag@SiO2 ) nanocubes (NCs) assemble in an edge-edge configuration when deposited on this substrate. The rough surface texture of f-Al2 O3 /e-Al provides a pathway for coupling of incident light to surface plasmons. The Ag@SiO2 /f-Al2 O3 /e-Al substrate exhibits a coupling efficiency of laser light sources into surface plasmon hotspots for both surface-enhanced Raman scattering (SERS) and metal-enhanced photoluminescence (MEPL). Moreover, the shelf life of this substrate is significantly improved due to a reduction in oxygen diffusion rate mediated by the ultrathin silica spacer and the flower-like Al2 O3 dielectric layer. Creatinine and flavin adenine dinucleotide are biomolecules present in human blood and urine. With advanced label-free SERS and MEPL techniques, it is possible to detect these biomarkers in urine, allowing cheap, noninvasive, yet sensitive analysis. The approach explored in this work can be developed into a powerful encoding tool for high-throughput bioanalysis.

Zinc-Blende CdS Nanocubes with Coordinated Facets for Photocatalytic Water Splitting

To develop catalysts that are efficient and stable under aggressive catalytic conditions, we detail a synthetic approach to producing zinc-blende cadmium sulfide (CdS) nanocubes (NCs), a metastable CdS polymorph that is terminated by coordinated facets. The hydrogen generation activity of these CdS NCs (∼11.6 mmol g–1 h–1) was nearly 4 times higher than that of wurtzite CdS nanoparticles (∼2.7 mmol g–1 h–1) and 2 times higher than that of irregularly shaped zinc-blende CdS nanoparticles (∼5.9 mmol g–1 h–1). Furthermore, the NCs also exhibited much improved long-term performance compared to the performance of these controlled photocatalysts. Finally, the density functional theory calculation and site-specific Au photodeposition demonstrate that the improved activity and stability can be attributed to the enhanced charge-flow steering and coordinated facet terminations.

Nano cube of CaSnO3: Facile and green co-precipitation synthesis, characterization and photocatalytic degradation of dye

In this work, nanocubes of CaSnO3 have been prepared by a simple and green co-precipitation method. In this technique, for preparation of calcium stannate, we have used from a complex structure of calcium as a new precursor and the synthesis of CaSnO3 have been done in water as a green solvent. Using of complexing precursors were created a congestion in reaction medium. Different conditions have been studied in synthetic approaches and optimized the effect of different parameters on the morphology of product such as precipitation agent (alkaline), pH, temperature, the rate of stirrer, surfactants and the mole ratio of surfactants for preparation product and obtain the best product in terms of quality and morphology. By using of this CaSnO3, two types of azo dyes (acid blue 92 and acid brown 14) have been degraded at presence of ultraviolet light from aqueous solution. Results display that the powder shows appropriate catalytic behavior for degradation of dyes (77% acid brown 14 and 67% acid black 92). Therefore these nano-cube structures have been used as photocatalysts in presence of UV light for degradation of azo dyes.

Shell-Thickness-Controlled Synthesis of Core-Shell Pd@Pt Nanocubes and Tuning of Their Oxygen Reduction Activities

An approach to control Pt shell thickness in the synthesis of Pd@Pt core-shell nanocubes (NCs) has been successfully developed. Tuning the Pt and Pd precursor concentration ratio (Pt4+/Pd2+) in the reaction mixture allowed precise control over the Pt shell thickness in the range of 0.3–4.9 nm. At low Pt4+/Pd2+ ratios (≤1/4), the deposition of Pt occurred via a layer-by-layer mode, whereas layer-by-layer deposition followed by Pt island growth was possible at higher Pt4+/Pd2+ ratios (1/3, 1/2, and 1). Additionally, rotating ring-disk electrode experiments determined the shell-thickness-dependent specific activities (SAs) and mass activities (MAs) of these Pd@Pt NCs, which acted as oxygen reduction catalysts in NaOH solution. Among these core-shell catalysts, the Pd1@Pt1/6 NCs (0.3 nm Pt shell) displayed the highest SA (0.4398 mA cm–2) and MA (2.915 mA μg–1) values, which were 3.38 and 2.53 times higher than the corresponding values for Pt nanoparticles (SA = 0.13 mA cm–2, MA = 1.15 mA μg–1). These results, supported by X ray photoelectron spectroscopy observations, indicate that the high activity of Pd1@Pt1/6 NCs is due to the modified electronic properties of the Pt shell influenced by the Pd NC core.

An anti-fouling nanoplasmonic SERS substrate for trapping and releasing a cationic fluorescent tag from human blood solution.

In bioenvironmental detection, surface-enhanced Raman scattering (SERS) signals are greatly affected by anti-specific biomolecule adsorption, which generates strong background noise, reducing detection sensitivity and selectivity. It is thus necessary to modify the SERS substrate surface to make it anti-fouling to maintain excellent SERS signals. Herein, we propose a zwitterionic copolymer, namely poly(glycidyl methacrylate-co-sulfobetaine methacrylate) (poly(GMA-co-SBMA)), for the surface modification of SERS substrates, which were fabricated and characterized spectroscopically. The copolymer was grafted onto Ag nanocubes (NCs) on an Ag surface with massive nanogaps via 1,2-ethanedithiol, which acted as a metal-insulator-metal (MIM) substrate. The high density of poly(GMA-co-SBMA) grafted near NCs favored the formation of connections between adjacent NCs, causing strong surface plasmon resonance at these junctions. With the zwitterionic-copolymer-modified surface, the adhesion of large biomolecules in platelet-rich plasma (PRP) solution can be effectively resisted, as determined from immunoassay and fibrinogen adsorption results. The SERS signals for malachite green (MG) in PRP solution (10-6 M) were effectively distinguished using the copolymer-grafted MIM substrate. MG was deposited on adjacent copolymer-grafted NCs, which amplified the SERS signals. Moreover, the copolymer connected adjacent NCs, inducing the electromagnetic effect at copolymer-grafted surfaces, which improved the SERS mechanism. The hydration process restructured the MG-trapped copolymer-grafted surface, decreasing the number of MG characteristic peak regions and increasing that of the copolymer regions. These results reveal that grafting a copolymer onto an MIM substrate allows MG to be easily trapped and released in complex biomatrices and increases surface reproducibility due to anti-fouling, leading to high SERS enhancement.

Shape-tunable Pt-Ir alloy nanocatalysts with high performance in oxygen electrode reactions.

For the first time, shape-tunable Pt-Ir alloy nanocatalysts including both single-crystalline (nano-octahedra (NOs), nano-truncated octahedra (NTOs), nanocubes (NCs)) and polycrystalline (nanocluster flowers (NCFs), nanowires (NWs), nano-short-chains (NSCs), and nano-octahedral stars (NOSs)) ones were synthesized with a facile one-pot solvothermal method, via precise control of the facet-selective agents (Br- and I-). The surface effects of Pt-Ir alloy nanocatalysts for oxygen electrode reaction in acidic solution were intensively investigated. Pt-Ir alloy nanocatalysts showed enhanced catalytic activities for the oxygen evolution reaction (OER), which were 1.6 to 2.0 times those of the commercial Ir/C catalyst and the Pt/C-Ir/C mixture at an overpotential of 0.25 V. The catalytic activity for the OER exhibited a positive correlation with the proportion of surface IrOx species, but was restricted by the surface alloying effect. Besides the change of the intermediate adsorption state, the dissociation of water was also confirmed to be effective as the rate-determining step of the Pt-Ir alloy nanocatalysts. The catalytic activity for the oxygen reduction reaction (ORR) decreased with the increase of surface IrOx species. Pt-Ir nano-short-chains (NSCs) exhibited 1.3 times the catalytic activity as that of the commercial Pt/C catalyst at 0.80 V and 0.85 V, owing to the higher proportion of the (110) facets with irregular step sites exposed after the annealing treatment at 350 °C. The unique structure could prevent the mass transfer process from being obstructed by adsorbed bisulfate anions and oxidized species on the surfaces. Pt-Ir NSCs exhibited a catalytic efficiency of 46.7% and were considered to be a promising URFC catalyst.

Efficient all p-type heterojunction photocathodes for photoelectrochemical water splitting.

In this paper, Co3O4 nanostructures with different morphologies (nanoparticles (NPs), nanosheets (NSs) and nanocubes (NCs)) are directly grown on an ITO substrate using a hydrothermal method. Sb2S3 is loaded onto Co3O4 to construct a Co3O4/Sb2S3 heterojunction, which is used as an all p-type photocathode for photoelectrochemical (PEC) water splitting for the first time. The specific morphologies of Co3O4 have been discussed in detail. The improved PEC properties of the Co3O4/Sb2S3 heterojunction are characterized. Among them, the outstanding photocurrent density of the Co3O4 NC/Sb2S3 heterojunction photocathode is accessed by -1.32 mA cm-2 at -0.4 V vs. RHE. The enhanced PEC properties result from more active sites of specific crystal planes, excellent optical performance, suitable band gradient alignment and increased charge separation and charge transfer rate.