Hexagonal Microrods Research Articles

Hydrothermal synthesis and morphological evolution of hexagonal ceria microrod structures

CeriaBTC (CeO2-1,3,5-Benzenetricarboxylic acid) microstructures have been synthesized through hydrothermal methods. Field Emission Scanning Electron Microscopy (FE-SEM) micrographs and X-ray diffraction (XRD) data reveal that the microstructure exhibit hexagonal rod-like structures with average diameters 1.9 ± 0.17 µm and length 5.7 ± 0.19 µm, synthesized at 130 °C for 72 h. Elevating the reaction temperature or duration leads to gradual morphological evolution in micromaterial shape and size (aspect ratio), stabilizing at 3.51. This signifies an ongoing chemical transformation driving morphological alteration. Fourier transform infrared spectroscopy (FT-IR) reveals the presence of an organic linker in the CeriaBTC microrods. Results from XRD, FE-SEM, FT-IR, and thermogravimetric analysis (TGA) suggest a chemical transformation from hexagonal type CeriaBTC to Ceria microrods at higher calcination temperatures of 400 °C for 4 h. The development of hierarchical morphologies, transitioning from hexagonal CeriaBTC rods to Ceria microstructure powder, has been observed to rely on both the orientation of the organic precursor (1,3,5-Benzenetricarboxylic acid) and the specific calcination temperature applied.

2D Co-N-C catalysts derived by 1D CoxZn1-xO hexagonal microrods for oxygen reduction reaction

A novel and feasible strategy to construct 2D Co-N-C catalyst from one-dimensional (1D) CoxZn1-xO microrod is reported. In the strategy, 1D CoxZn1-xO microrods are firstly transformed into CoxZn1-xO@CoZn-ZIF hexagonal core-shell microrods by regulating the reaction conditions of high-pressure vapor-solid transformation, and subsequently pyrolyzed at high temperature to form Co-N-C hexagonal microtubes, which are finally fractured along its edges under the action of thermal stress, evolving gradually to Co-N-C nanosheets. Besides, by investigating the effects of Co doping contents, a catalyst with optimal chemical and structural properties and more highly accessible Co-N4 active sites has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in alkaline media. Among them, Co0.3-N-C NS exhibits superior ORR performance (Eon=1.01 V, E1/2 = 0.87 V), durability and tolerance to methanol than those of commercial Pt/C catalysts (Eon=0.99 V, E1/2 = 0.85 V) in alkaline media.

Synthesis and characterization of hexagonal ceria-BTC microrods for methanol decomposition

BackgroundNovel three-dimensional (3D) hydrated ceria-BTC (CeO2–1,3,5-Benzenetricarboxylic-acid) is the important material due to its unique chemical and physical properties compared to the other materials. A novel 3D ceria nanostructure has been examined as a promising and feasible technique for methanol decomposition. MethodsNovel 3D hydrated ceria-BTC microstructures were successfully synthesized via a hydrothermal route in an aqueous solution. Field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) patterns show that a ceria-BTC framework diameter and length are approximately 1.45–2.4 and 5.5–6.5 µm, respectively, at 130 °C and with pH 2 for 72 h. The hexagonal ceria-BTC microrod comprises organic linkers, which are transformed into hierarchical ceria microrod in the presences of air at 400 °C was confirmed by Fourier transform infrared spectroscopy (FTIR). Significant FindingsThe Ce-O bonding of the hierarchical ceria microrod species has a bond distance and coordination number of 2.44 and 6.89, respectively, which attenuates the Extended X-ray absorption fine structure (EXAFS) spectra. Compared to the ceria powder, the hierarchical ceria microrods produced more oxygen vacancies and Ce3+as shown by the X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) analyses. The ceria microstructure exhibits excellent methanol decomposition activity.

Rapidly Grown Hexagonal Organic Microtubes Using Ionic Liquids for an Enhanced Optical Waveguide Effect

AbstractAn optical waveguide that transmits the electromagnetic waves is a critical component for various optoelectrical applications including integrated optical circuits and optical communications. Among many, the 1D tubular optical waveguide structure enables efficient distant energy transfer via mode selection within the optical microcavity. However, its application is limited due to the complicated fabrication process. Herein, hexagonal tris(8‐hydroxyquinoline) aluminum (Alq3) microtubes with an average longitudinal length of ≈15 µm are self‐assembled within few minutes by utilizing 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF4) ionic liquids. The swift fabrication is enabled by the high electron affinity of BMIMBF4 that forms hexagonal microrods. Also, BMIMBF4 ionic liquid etches the central region of micorods during its growth, forming microtubes with a wall thickness of ≈650 nm. The fabricated Alq3 microtubes show significantly improved waveguide characteristics with reduced optical loss coefficient (0.054 µm−1) compared to that of microrods (0.271 µm−1). The demonstrated method to fabricate Alq3 microtubes with ionic liquid is an efficient approach to utilize organic microstructures as an optoelectrical components for advanced optical communications.

Harnessing plasma-generated reactive species for the synthesis of different phases of molybdenum oxide to study adsorption and photocatalytic activity.

This study employs plasma-liquid interaction technique to synthesize different phases of molybdenum oxide using air and argon as plasma-forming gases. In situ plasma-generated nitrogen species primarily NO3-/NO2- and hydrogen species (H+) facilitate the reduction of the molybdenum precursor anion (Mo7O24-). The reduced Mo species subsequently reacts with reactive oxygen species, forming MoO6 octahedra, which is the building block of a molybdenum oxide crystal. Varied concentrations of NO3-/NO2- and H+ species in air and argon plasma treatment significantly influence the growth process. Air plasma synthesis yields hexagonal molybdenum oxide microrods, which upon calcination changes its phase to orthorhombic 2D layered structure. Moreover, the argon plasma synthesized sample exhibits a mixed phase of hexagonal and orthorhombic molybdenum oxide due to the heavy argon ion bombardment, inducing material porosity and surface oxygen vacancies. The mixed-phase material exhibits superior adsorption and photo-degradation towards cationic dye compared to the other two phases. The higher photocatalytic performance may be responsible for the extended lifetime of the photo-generated charge carriers possessed by the mixed-phase material. Radical scavenging tests have identified holes and hydroxyl radicals as the key reactive species that take part in the photo-degradation process.

Breaking AgInTe2 Quantum Dot Chain to Fabricate AgInTe2-ZnS Janus Nanocrystals.

Colloidal multinary chalcogenides (MnCs) have emerged as excellent optoelectronic materials, where S- and Se-based MnCs show considerable progress; however, the Te counterpart suffers from detrimental surface oxidation. Moreover, Te-based I-III-VI MnCs (e.g., AgInTe2) tend to form a one-dimensional (1-D) anisotropic structure via the self-assembly of surface-oxidized Te, thus restricting the isolation of AgInTe2 quantum dots (QDs). We report successful control of the self-assembly of Te-based MnCs to arrest the growth of AgInTe2 QDs by using a synergistic capping agent (dodecanethiol and oleic acid). The reaction proceeds with several intermediates, including hexagonal microrods (MR), tetragonal QDs in a chain arrangement, and tetragonal MRs. Importantly, we note that the incorporation of ZnS QDs triggers the breaking of the chain arrangement of the AgInTe2 QDs and the emergence of evenly distributed AgInTe2-ZnS Janus nanocrystals with significantly reduced long-term Te-oxidative properties. Arresting the AgInTe2 QD chain and the subsequent Janus nanocrystal formation could have promising opportunities for 1-D charge hopping and efficient charge transport for optoelectronic applications, respectively.

Construction of 3D copper-chitosan-gas diffusion layer electrode for highly efficient CO2 electrolysis to C2+ alcohols

High-rate electrolysis of CO2 to C2+ alcohols is of particular interest, but the performance remains far from the desired values to be economically feasible. Coupling gas diffusion electrode (GDE) and 3D nanostructured catalysts may improve the efficiency in a flow cell of CO2 electrolysis. Herein, we propose a route to prepare 3D Cu-chitosan (CS)-GDL electrode. The CS acts as a “transition layer” between Cu catalyst and the GDL. The highly interconnected network induces growth of 3D Cu film, and the as-prepared integrated structure facilitates rapid electrons transport and mitigates mass diffusion limitations in the electrolysis. At optimum conditions, the C2+ Faradaic efficiency (FE) can reach 88.2% with a current density (geometrically normalized) as high as 900 mA cm−2 at the potential of −0.87 V vs. reversible hydrogen electrode (RHE), of which the C2+ alcohols selectivity is 51.4% with a partial current density of 462.6 mA cm−2, which is very efficient for C2+ alcohols production. Experimental and theoretical study indicates that CS induces growth of 3D hexagonal prismatic Cu microrods with abundant Cu (111)/Cu (200) crystal faces, which are favorable for the alcohol pathway. Our work represents a novel example to design efficient GDEs for electrocatalytic CO2 reduction (CO2RR).

Cathodoluminescence Properties of Ni-Decorated Hexagonal Cr Microrods for Magneto-Plasmonic Applications

Multifunctional low-dimensional non-noble metal nanostructures exhibiting a broad range of plasmonic resonances and magnetic properties are expected to be innovative materials suitable for advanced device applications. In this work, we synthesized Ni-nanoparticle-decorated Cr microrods from Cr/Ni thin films driven by solid-state dewetting. The Cr microrod exhibits the phase evolution of the Cr(FCC) to Cr(HCP) with temperature confirmed by X-ray diffraction and high-resolution transmission microscopy. Cathodoluminescence (CL) imaging and spectroscopy of a single Cr microrod reveal plasmonic modes in UV (315 nm), vis (563 nm), and IR (705 nm) ranges. With a dewetting temperature, the red-shifted CL emission peaks indicate tunable plasmonic modes. The origin of the three plasmonic modes can be understood from the orbital electron density of states for d–d intraband and s–d interband transitions. The Ni nanoparticles decorated on Cr microrods also show significant room temperature ferromagnetism. The Ni-nanoparticle-designed Cr microrods may expand the range of magneto-plasmonic materials beyond noble metals. The combination of plasmonic and magnetic properties could facilitate emission-sensitive detection and therapy in plasmonic-based optoelectronic technology.

An Investigation of the Thermal Treatment Effects on the Structural, Morphological, and Optical Properties of Hydrothermally Synthesized Hexagonal Molybdenum Oxide Micro-Rods

An Investigation of the Thermal Treatment Effects on the Structural, Morphological, and Optical Properties of Hydrothermally Synthesized Hexagonal Molybdenum Oxide Micro-Rods

Excitonic Mechanisms of Stimulated Emission in Low-Threshold ZnO Microrod Lasers with Whispering Gallery Modes.

Whispering gallery mode (WGM) ZnO microlasers gain attention due to their high Q-factors and ability to provide low-threshold near-UV lasing. However, a detailed understanding of the optical gain mechanisms in such structures has not yet been achieved. In this work, we study the mechanisms of stimulated emission (SE) in hexagonal ZnO microrods, demonstrating high-performance WGM lasing with thresholds down to 10-20 kW/cm2 and Q-factors up to ~3500. The observed SE with a maximum in the range of 3.11-3.17 eV at room temperature exhibits a characteristic redshift upon increasing photoexcitation intensity, which is often attributed to direct recombination in the inverted electron-hole plasma (EHP). We show that the main contribution to room-temperature SE in the microrods studied, at least for near-threshold excitation intensities, is made by inelastic exciton-electron scattering rather than EHP. The shape and perfection of crystals play an important role in the excitation of this emission. At lower temperatures, two competing gain mechanisms take place: exciton-electron scattering and two-phonon assisted exciton recombination. The latter forms emission with a maximum in the region near ~3.17 eV at room temperature without a significant spectral shift, which was observed only from weakly faceted ZnO microcrystals in this study.

Peculiarities of erbium incorporation into ZnO microrods at high doping level leading to upconversion and the morphology change. Influence on excitonic as well as shallow donor states

Heavily Er-doped zinc oxide (ZnO) microrods with nominal compositions, ZnO:Er(2, 10, 30%), were prepared by the hydrothermal growth method. The crystallographic phases present in the as grown and annealed materialswere determined. The presence of the hexagonal Wurtzite ZnO phase in the form of the hexagonal shape nanoplatelets and microrods was confirmed. Moreover, the Er2O3phase in the form of nanosheets has been revealed as well. Erbium is partly incorporated into the ZnO hosts. It was thinning upon erbium doping level contributing to erbium oxide. This effect was even more pronounced upon annealing in air. Moreover, the influence of erbium doping and annealing on paramagnetic shallow donor centers has been studied. There were two types of these centers, both affected by the erbium presence. The increase of the neutral zinc vacancies amount upon erbium doping has been proven. Annealing in air moderated the charge distribution between them. Moreover, upconversion processes between the two erbium ions were observed and explained. The surface distribution of excitonic emission centers was studied. The larger the erbium content the weaker the exciton luminescence. The smaller the ZnO microrods the stronger the exciton emission.

Heteroepitaxial Growth of Vertically-Aligned GaN Single-Crystalline Microrod Arrays on Silicon Substrates.

The heteroepitaxial growth of vertically aligned gallium nitride (GaN) single-crystalline microrod arrays on silicon substrates was achieved with high reproducibility by using the plasma-enhanced chemical vapor deposition (PECVD) method in the furnace. By reducing the plasma power from 70 to 15 W, the crystal morphology of GaN varied from thin films to microrod arrays with the decreased V/III gas ratio. The growth of GaN crystals occurred in the vertical direction of the substrate and in the lateral direction of the growth axis via the self-catalytic vapor-liquid-solid mechanism (VLS mechanism) and the vapor-solid mechanism (VS mechanism), respectively, contributing to the formation of inverted hexagonal GaN cone microrods. Furthermore, the morphology of inverted hexagonal GaN cone microrods shows extremely small contact areas between the microrods and the substrate, suggesting the potential to solve the problems of stress accumulation and poor crystalline qualities of heteroepitaxy. With the raised growth temperature of GaN from 930 to 980 °C, the material quality was improved and the high crystalline qualities were obtained, owing to the successful surface migration of gallium atoms. However, the density of GaN microrods became lower with the increased growth temperature because the spatial temperature gradient was reduced and the evaporation of gallium was enhanced, leading to fewer gallium atoms precipitating and remaining on the substrate. The growth direction of vertically aligned GaN single-crystalline microrod arrays with the (002) crystal plane is along the [0001] orientation (c axis) and normal to the substrate surface, which may bring about many device applications in future studies.

Electro‐Optic Effect of ZnO Microcavity and Active Dynamic Lasing Mode Modulation

AbstractElectro‐optic effect, as a physical effect of electric field modulating refractive index, is widely applied to modulate lasing modes dynamically. However, the modulation is operated passively in general. It means that the lasing is generated in a resonance cavity and the modes are regulated externally in different materials and spaces. It will be highly favorable for optoelectronic integration and other applications when a gain medium with electro‐optic effect is applied to design an optical microcavity, integrating optical pumping and electro‐optic modulation. In this work, a hexagonal ZnO microrod is pumped optically to generate UV lasing with an electric field applied to modulate dynamically the resonance wavelength. When the electric field is parallel to the ZnO C‐axis, the refractive index variation is correlated linearly with the electric field strength (Pockels effect). When the electric field is perpendicular to the ZnO C‐axis, the refractive index variation shows a quadratic increase tendency with the increase of the electric field strength (Kerr electro‐optic effect). The whispering‐gallery lasing modes are dynamically modulated by applying an electric field successfully. In one word, lasing generation and modulation are integrated in the same microcavity based on both 1st and 2nd order electro‐optic effect.

Zn0.97-xCu0.03VxO (x = 0, 0.02, 0.04) hexagonal tube and microrods structures: Optical, refractive index, electrical and solar photocatalytic properties

The optical, refractive index, electrical, dielectric and solar photocatalytic properties of pure and Zn0.97-xCu0.03VxO (x = 0, 0.02, 0.04) compositions synthesized by coprecipitation method have been studied. Pure single phase of hexagonal wurtzite structure of ZnO was confirmed by XRD and Rietveld refinement analysis. The SEM obviously illustrated that Cu doping and Cu/V codoping have great impacts on morphology of ZnO particles. Remarkably, incorporation of Cu ions converts the spherical shape of the pure ZnO particles to open hexagonal tube and microrods structures while Cu/V ions lead to formation of mixed particles possess microrods and very fine spherical shapes. Optically, lowering in the optical band gap energy of ZnO with formation of long tails extend to visible light wavelengths (460 nm) were detected due to insertion of Cu and Cu/V ions. Based on Ravindra, Moss, Hervé, Reddy, and Kumar models, hexagonal Zn0.97Cu0.03O exhibits the highest refractive index values of 2.1558, 2.3509, 2.2961, 2.7368 and 2.3355, respectively. At different frequencies, 3 wt% Cu doping enhanced the room temperature electrical conductivity values of ZnO and further improvements were seen due to insertion of V3+/4+ ions plus Cu2+ dopant. Zn0.95Cu0.03V0.02O composition revealed a colossal dielectric constant of 1947 at 50 Hz and at nearly all frequency it possesses the highest values. The low cost solar photocatalytic test showed that both Zn0.97Cu·03O and Zn0.93Cu0.03V0.04O catalysts have high efficiencies of 81% and 82% to degrade the organic Congo red pollutant in 90 min.

Upconversion‐Enabled In Situ Growth of Silver Nanostructures Mediated by Cavity Resonance in Single Microrod (Adv. Mater. Interfaces 15/2022)

Upconversion-Enabled Growth of Silver Nanostructures In article number 2200029, Huilin He, Yan Jun Liu, and co-workers demonstrate that the upconversion emission from the hexagonal NaYF4 microrods under the near-infrared laser excitation enables the photochemical reaction to grow the Ag nanoparticles (AgNPs). Additionally, AgNPs aggregate along the leaked sites of cavity-induced resonances inside the microrod, forming a grating-like Ag nanostructure.

Upconversion‐Enabled In Situ Growth of Silver Nanostructures Mediated by Cavity Resonance in Single Microrod

Solution-based photochemical reaction is widely utilized in the syntheses of metallic nanocrystals. Although seedless photochemical reaction can avoid pre-treatments, it relies on long, high-energy radiation. Here, this work demonstrates an upconversion-enabled seedless photochemical approach to synthesize grating-like silver nanostructures on a hexagonal NaYF4 microrod via a near-infrared laser excitation. Experimental results show that upconversion emission enables the nucleation and growth of Ag nanoparticles. Meanwhile, the emission can be also precisely tuned and enhanced by in situ growth of silver nanoparticles on the NaYF4 and NaYF4@SiO2 microrods. The maximum enhancement factor of 2 in overall emissions is achieved for the NaYF4@SiO2 microrod. This fabrication approach and results visually confirm the cavity resonance of excitation light inside the microrod via the distribution of Ag nanostructures. Moreover, the in situ grown Ag nanostructures provide a tunable far-field upconversion emission via the plasmonic effect, which is potentially useful for tunable microlasers, biosensing, antibacterial, and catalytic applications.

Novel homo-epitaxial approaches in solvothermal synthesis for preparing surface tethered uni-directionally oriented zinc oxide micro and nano structured arrays

Surface aligned, uni-directionally grown, hexagonal nanorod bundles and microrod pillared arrays of zinc oxide (ZnO), were synthesized through a simple, homo-epitaxial growth approach. A uniform layer of ZnO seed was initially prepared on cleaned glass substrates by dip coating and calcination. Uni-directionally oriented ZnO micro– nano structures were subsequently developed on the seeded glass substrates through solvothermal methods, by employing equi-molar solutions of zinc nitrate and hexamethylenetetramine. The reaction parameters that control the surface morphologies and crystal orientations were explored. A solution exchange process was also carried out to prepare perpendicularly aligned ZnO nanorod arrays. The structural and functional features of the resultant samples were studied and discussed with the help of X-ray diffractometry, scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence spectrophotometry. A plausible structure dependent growth mechanism of the morphologically varied ZnO was also proposed.

Novel in situ growing carbon nanocoils onto steel mesh as positive electrode and hexagonal-MoO3 micro-rod array onto carbon fabric as negative electrode for assembling dual-asymmetric supercapacitors with redox active gel eleectrolyte

Intrinsically functionalized carbon nanocoils (CNCs) are in-situ grown onto the microwire surface of stainless steel mesh (SS) in an alcohol flame. The CNCs are deposited without using any additional catalysts and the flame growth mechanism is proposed. Such a unique structure with functionalized CNCs directly growing onto SS micro-wires in the mesh current collector makes it an excellent binder-free CNC/SS electrode. It exhibits ultrahigh capacitance in a iron ion based redox active electrolyte, where an remarkable areal capacitance of 4160 mF/cm 2 at 20 mA/cm 2 can be achieved. Meanwhile, hexagonal MoO 3 microrods are grown vertically onto carbon fibers and their electrochemical behaviors in normal H 2 SO 4 electrolyte are investigated. Finally, novel dual-asymmetric supercapacitors (DASCs) with the configuration of CNC/H 2 SO 4 +PVA + Fe 2+/3+ //H 2 SO 4 +PVA/h-MoO 3 are assembled. The device exhibits an excellent areal capacitance of 1502 mF/cm 2 at 3 mA/cm 2 , and a remarkable ultrahigh energy density of 252.4 μW h/cm 2 at the power energy of 1.6 mW/cm 2 as well. The research is expected to promote the development of SCs with high energy density through the design and assembly of all their main components, including the direct growth of active materials onto current collectors and the appropriate utilizing the redox active gel electrolyte. • A facile method for growing carbon nanocoils on stainless steel mesh was developed. • The flame catalytic growth mechanism of CNCs on stainless steel mesh was proposed. • Arrays of vertical h-MoO 3 hexagonal micro-rods was grown onto carbon fabric. • Novel dual-asymmetric supercapacitor with redox active gel electrolyte was assembled. • Remarkable capacitance of 1.5F/cm 2 and energy density of 252.4 μWh/cm 2 was realized.

Two-round quasi-whispering gallery mode exciton polaritons with large Rabi splitting in a GaN microrod.

We investigate the exciton polaritons and their corresponding optical modes in a hexagonal GaN microrod at room temperature. The dispersion curves are measured by the angle-resolved micro-photoluminescence spectrometer, and two types of exciton polaritons are identified with the help of the finite-difference time-domain simulation. By changing the pump position, the photon part of the exciton polaritons is found to switch between the quasi-whispering gallery modes and the two-round quasi-whispering gallery modes. The exciton polaritons formed by the latter are observed and distinguished for the first time, with a giant Rabi splitting as large as 2Ω = 230.3 meV.

Highly Regulated Supramolecular Assembly of 2-O-Methylated α-Cyclodextrin to Construct Vertically Oriented Microrods on Graphite.

Precisely controlling self-assembled molecules to fabricate highly ordered nano/microstructures is a challenging task. Here, a simple precipitation technique with common solvents forms supramolecular microstructures with highly regulated molecular arrangements from a methylated derivative of α-cyclodextrin at the 2-O position (2-Me-α-CD). The formation of a head-to-tail channel assembly of 2-Me-α-CD through host-guest complexation with a solvent molecule such as benzene or cyclohexane yields well-defined hexagonal microrods. Specifically, the self-assembly of 2-Me-α-CD forms vertically aligned hexagonal microrods on a highly ordered pyrolytic graphite (HOPG) surface via epitaxial growth. This work should provide insight into the design of supramolecular building blocks for controlled self-assembly.