Hierarchical Nanorods Research Articles

Transient Photocurrents and Defect States in Hierarchically Structured ZnO Nanowires

ZnO‐nanostructured thin films can be used as electron transport layers in ordered heterojunction quantum‐dot solar cells. An increased interface between electron and hole‐transporting layers allows for a fast separation of the electron–hole pairs preventing their recombination. Consequently, an improvement of the overall solar cell efficiency is expected. ZnO hierarchical nanorod thin films can provide the desired increase in interface area. In this work, their properties are studied and compared with simple ZnO nanorod films. The ZnO nanorod films are synthesized hydrothermally by placing the quartz/indium‐tin‐oxide substrates in a solution of zinc nitrate hexahydrate and sodium hydroxide at 90 °C. Hierarchical structures are obtained through a second deposition step. Scanning electron microscopy is used to characterize the size and shape of the nanorods. Simple ZnO films display hexagonal nanorods with a diameter of around 150 nm while hierarchical films show additional 40 nm diameter nanorods growing on the side surfaces of the primary 150 nm nanorods. Optical transmittance spectroscopy reveals a bandgap around 3.35 eV. Current–voltage measurements in the high‐field regime of 104 V cm−1 are used to determine the density of trap states Nt through the application of trap‐filled limit current theory.

Rational design of self-assembled copper oxide nanoparticles into hierarchical nanorods with high-surface-area for environmental remediation of wastewater

The coordinated generation of hierarchical structures is a difficult task that necessitates accurate control over a number of variables such as assembly shape, array dimensions, peripheral spacing, and uniformity. In this study, we successfully synthesized self-assembled copper oxide nanomaterials using hydrothermal processes. By aggregating copper oxide nanoparticles (diameter 4–6 nm), we were able to create a hierarchical rod-like morphology with highly homogeneous particle morphology and feature sizes ranging from 50 to 200 nm. We thoroughly investigated the methods of self-assembly of CuO nanorod formations, as well as the influence of templates on the materials' structure. Our analysis included powder X-ray diffraction (XRD), TEM, N2 sorption, and X-ray photoelectron spectroscopic (XPS) methods. N2 adsorption–desorption isotherm indicated high surface areas (125–190 m2/g) and limited pore diameter (less than 5 nm) for different samples. Furthermore, XPS examination demonstrated that the materials have a high concentration of Cu2+ groups, which serve as active sites for dichromate anion adsorption. We further investigated the adsorption process using Langmuir, Freundlich and Weber–Morris models and found that these CuO nanorods can perform as a highly powerful and recyclable adsorbent for hazardous dichromate from wastewater. Our findings have significant implications for the progress of new materials for environmental remediation and other applications.

Built-in electric field in bifunctional electrocatalyst (Ni3S2@Ni9S8) for high-efficiency OER and overall water splitting performance

It is a giant challenge to fabrication inexpensive and efficient bifunctional electrocatalyst to replacing precious metal material in water splitting field. Herein, based on built-in electric field, adsorption intermediates and d-band center theories, Mo and Fe co-engineered Ni3S2@Ni9S8 hierarchical coupling interface is designed. The optimized hierarchical nanorods array facilitate full contact between electrolyte and surface of the catalyst, increasing the number of electrocatalytic sites. Characterizations indicated the successful introduction of Mo and Fe into Ni3S2@Ni9S8 increasing the number of active sites as well as fabricated a unique Ni3S2@Ni9S8 core-shell coupling interface and formed built-in electric field, improving the intrinsic conductivity of the catalyst. The theoretical calculation showing the introduction of Fe and Mo modulate the adsorption energy of the electrocatalyst for the water splitting intermediates, elevating d-band center, so Ni3S2@Ni9S8 catalyst shows excellent electrochemical performance. Specifically, the low overpo tentials of 167 mV is procured at the current density of 10 mA cm−2 for OER in 1 M KOH. Importantly, as a bifunctional electrocatalyst, Ni3S2@Ni9S8 exhibit excellent catalytic activity at a low voltage of 1.62 V to reach a current density of 10 mA cm−2 for 24 h overall water splitting in alkaline condition. These studies provide a feasible and promising strategy for the preparation of inexpensive electrocatalysts and offers more possibilities for further exploration of electrocatalysis in the energy conversion field.

Relevance of alcoholic solvents in the growth of ZnO nanoparticles and ZnO hierarchical nanorod structures on their optical and opto-electrical properties

We report on the synthesis of ZnO nanoparticles and ZnO hierarchical nanorod structures using four different alcohols i.e. methanol, isopropanol, ethanol, and aqueous ethanol (70% alcohol, 30% water). The syntheses of the nanoparticles were carried out by non-aqueous and hydrothermal routes. In general, absolute alcohol allows a better control of the synthesis reaction and nanoparticles as small as 5 nm were obtained, confirmed by TEM. XPS analysis elucidated the chemical states that were correlated to the synthesis reaction. For the nanorod growth, these four alcohols were used as seeding solvents, followed by hydrothermal ZnO nanorod growth. Here, the seed layer tailored the nanorod diameters and surface defects, which were studied by SEM and photoluminescence spectroscopy. Subsequently, the ZnO nanorods were electrically characterized and exhibited persistent photoconductivity under UV irradiation of 365 nm. The differences in conductivity in dark and under UV irradiation were attributed to the size of the nanorods, defect states, semiconductor band bending and oxygen adsorption–desorption mechanisms. Parameters such as photoresponse and photosensitivity are also calculated in order to evaluate their applicability in UV sensors. This work demonstrates optimization of the physical, chemical, electrical and optical properties of both ZnO nanostructures via the use of alcoholic solvents.

Enhanced rate and specific capacity in nanorod-like core-shell crystalline NiMoO4@amorphous cobalt boride materials enabled by Mott-Schottky heterostructure as positive electrode for hybrid supercapacitors

The supercapacitor electrode materials suffer from structure pulverization and sluggish electrode kinetics under high current rates. Herein, a unique NiMoO4@Co-B heterostructure composed of highly conductive Co-B nanoflakes and a semiconductive NiMoO4 nanorod is designed as an electrode material to exert the energy storage effect on supercapacitors. The formed Mott-Schottky heterostructure is helpful to overcome the ion diffusion barrier and charge transfer resistance during charging and discharging. Moreover, this crystalline-amorphous heterogeneous phase could provide additional ion storage sites and better strain adaptability. Remarkably, the optimized NiMoO4@Co-B hierarchical nanorods (the mass ratio of NiMoO4/Co-B is 3:1) present greatly enhanced electrochemical characteristics compared with other components, and show superior specific capacity of 236.2 mA h g−1 at the current density of 0.5 A g−1, as well as remarked rate capability. The present work broadens the horizons of advanced electrode design with distinct heterogeneous interface in other energy storage and conversion field.

Iron‐incorporated Ni4Mo Hierarchical Nanorod Arrays for Promoted Electrocatalytic Oxygen Evolution Reaction

AbstractIt is great significance to explore rich and efficient transition metal‐based electrocatalysts for the electrolysis of water. Nickel‐molybdenum (Ni−Mo) alloy is considering as one of the most promising electrocatalysts for hydrogen evolution reactions (HER) in alkaline electrolyte, but its catalytic performance for oxygen evolution reaction (OER) is still unsatisfactory. Heteroatom doping by interfering with the electronic structure of the catalysts has been considered to be an effective method to enhance electrocatalytic activities. Herein, we report the synthesis of iron (Fe)‐doped Ni4Mo intermetallic compound with hierarchical nanorod assemblies on nickel foam by hydrothermal and hydrogen‐induced methods, which significantly improve the catalytic performance for OER. The as‐prepared Fe−Ni4Mo/NF shows remarkable activity for alkaline oxygen evolution reaction, requiring only a low overpotential of 271 mV to achieve a current density of 100 mA cm−2. Such performance is significantly better than that of pristine Ni4Mo/NF with overpotential of 400 mV. Density functional theory (DFT) calculation shows that the addition of Fe can significantly reduce the adsorption energy of the intermediate on the catalyst surface, thus facilitating the OER activity. Moreover, an alkaline electrolyzer composed of Fe−Ni4Mo/NF as cathode and anode can provide 10 mA cm−2 current density with only 1.48 V extremely low voltage, and shows excellent long‐term durability of 24 h. These results highlight a heteroatom incorporation engineering strategy into metallic alloys for electrochemical applications.

Efficient Self-Powered Overall Water Splitting by Ni4 Mo/MoO2 Heterogeneous Nanorods Trifunctional Electrocatalysts.

The exploration of cost-effective multifunctional electrodes with high activity toward energy storage and conversion systems, such as self-powered alkaline water electrolysis, is very meaningful, although studies remain quite limited. Herein, a heterogeneous nickel-molybdenum (NiMo)-based electrode is fabricated for the first time as a trifunctional electrode for asymmetric supercapacitor (ASC), hydrogen evolution reaction, and oxygen evolution reaction. The trifunctional electrode consists of Ni4 Mo and MoO2 (denoted Ni4 Mo/MoO2 ) with hierarchical nanorod heterostructure and abundant heterogeneous nanointerfaces creating sufficient active sites and efficient charge transfer for achieving high performance self-power electrochemical devices. The ASC consists of the as-prepared Ni4 Mo/MoO2 positive electrode, showing a broad potential window of 1.6V, and a maximum energy density of 115.6Whkg-1 , while the alkaline overall water splitting (OWS) assembled using the as-prepared Ni4 Mo/MoO2 as bifunctional catalysts only requires a low cell voltage of 1.48V to achieve a current density of 10mAcm-2 in aqueous alkaline electrolyte. Finally, by integrating the Ni4 Mo/MoO2 -based ASC and OWS devices, an aqueous self-powered OWS is assembled, which self-power the OWS to generate hydrogen gas and oxygen gas, verifying great potential of the as-prepared Ni4 Mo/MoO2 for sustainable and renewable energy storage and conversion system.

Hybrid Carbon Sphere Chain-MnO2 Nanorods as Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc-Air Batteries.

It is now recognized that the development of self-supported and efficient bifunctional air cathodes via the direct growth of earth-abundant catalysts onto the surface of the conductive collector would be a cutting-edge strategy to reduce interfacial resistance, enhance the mechanical tenure, and reduce the final weight and cost of manufacturing of rechargeable Zn-air batteries (ZABs). This work reports an innovative self-supported precious metal-free electrode, comprising carbon sphere chains (CSCs) directly grown onto a carbon paper (CP) substrate, wherein the CSCs have a functionalized surface bearing carbon nanobud defects, oxygen functional groups, and high-density MnO2 hierarchical nanorods (NRs), uniformly coating the surface of CSCs. Not only is the metal-free functionalized CSC catalyst functional for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) but its combination with MnO2 NRs impressively enhances the ORR/OER activities. A homemade ZAB assembled with functionalized CSC/MnO2 air cathode can successfully power a timer for a period of 17 days with no voltage loss, whereas two series-connected ZABs can light up 39 red light-emitting diode (LED) bulbs. The self-supported and earth-abundant-based CSC/MnO2 materials open up an opportunity for lightweight and cost-effective ZABs and metal-air batteries in general.

Enhanced Ion/Electron Migration and Sodium Storage Driven by Different MoS2‐ZnIn2S4 Heterointerfaces

AbstractConstructing hierarchical structures with heterointerfaces is an effective approach for developing high‐efficiency energy‐storage anodes for sodium‐ion batteries. In this study, MoS2@ZnIn2S4 nanorods are designed and fabricated for structural improvement. Theoretical calculations reveal that there are two different MoS2‐ZnIn2S4 heterointerfaces formed by MoS2 with the Zn and In facets of ZnIn2S4, which generate directional built‐in electric fields that provide additional driving forces for facilitating electron transfer. These two heterojunction interfaces, especially the MoS2‐In facet, exhibit enhanced Na+ adsorption energies and reduce Na+ diffusion energy barriers. The multistep reactions of MoS2 and ZnIn2S4 reveal a synergistic effect that promotes the entire electrochemical process. Furthermore, the synthesized hierarchical nanorods composed of nanosheets offer abundant Na+‐storage sites and multidirectional migration pathways and, importantly, accommodate the excessive volume change. Benefiting from the heterointerfaces and hierarchical structure, the composite electrode exhibits excellent electrochemical performance, with high reaction activity and rapid electron/ion diffusion kinetics.

NiSe@Ni12P5 hierarchical nanorod arrays coupled on nickel-copper foam for highly efficient urea oxidation

Electrocatalytic urea oxidation reaction (UOR) is one of the most promising energy-saving alternatives to anodic oxygen evolution reaction (OER), and the development of efficient and stable catalysts for UOR is crucial. Therefore, in this paper, hierarchical structure NiSe@Ni12P5/NCF with Ni12P5 nanorod arrays coupled with NiSe nanospheres are synthesized on bare nickel-copper foam (NCF) by exogenous phosphorylation and subsequent electrodeposition methods. The catalytic performance of hierarchical structure NiSe@Ni12P5/NCF in urea-assisted electrolytic water reaction is studied in focus. The results show that the potential of NiSe@Ni12P5/NCF was only 1.267 V and 1.412 V vs RHE at current densities of 10 mA cm−2 and 100 mA cm−2, respectively, in addition to no significant activity decay after 140 h stability test. This is attributed to the fact that the introduction of NiSe regulated the interfacial charge distribution, creating an interfacial coupling effect that can greatly increase the original catalytic species, as well as the NiOOH species generated during the UOR process as true active sites, which ultimately improving the electrocatalytic UOR performance of NiSe@Ni12P5/NCF. This study provides a new idea for the preparation of hierarchical selenide - phosphides for electrochemical applications.

Free-standing 3D core-shell architecture of Ni3S2@NiCoP as an efficient cathode material for hybrid supercapacitors

The design and discovery of free-standing hybrid electrode materials with large absolute capacity and high cycling stability for energy storage become desirable and are still challenging. In this work, we demonstrate that the hybrid supercapacitor (HSC) device is assembled by 3D core–shell hierarchical nanorod arrays of Ni3S2@NiCoP nanocomposite for the first time. The Ni3S2@NiCoP nanocomposite is successfully synthesized through a facile stratagem containing hydrothermal process and the subsequent electrodeposition method. The 3D architecture of Ni3S2@NiCoP hybrid electrode composed of vertically aligned “hyperchannel” 1D Ni3S2 nanorods and highly conductive interconnected 2D nanosheets of NiCoP is beneficial to fast electron transfer kinetics, thus leading to enhancing the ionic and electronic conductivity, kinetics of redox reaction, and synergistic behavior of active species. The fabricated HSC device with Ni3S2@NiCoP electrode delivers outstanding areal capacity of 109 µAh cm−2 at a current density of 1 mA cm−2, brilliant energy density of 74.9 Wh kg−1 at a power density of 700 W kg−1, and prominent cyclic performance of 92% capacity retention even after 144-h floating test. This work demonstrates that the core–shell hierarchical nanorod arrays of Ni3S2@NiCoP can be viewed as one of the novel battery-type electrode materials for high-performance HSCs.

Hierarchical nanorods of graphene oxide decorated SnO2 with high photocatalytic performance for energy conversion applications

Tin oxide (SnO2) hierarchical nanorods are decorated with different weight percentages (1, 2 and 3%) of graphene oxide (GO) were prepared through sol–gel method. The produced hierarchical nanorods (HNRs SnO2@GO) have a tetragonal rutile structure with considerable crystallinity, according to X-ray diffraction examination. The produced SnO2@GO nanocomposites encompasses the distinctive bands of SnO2 and GO according to a FTIR investigation. SEM was used to examine the morphology of the produced nanocomposite materials, revealing hierarchal nanoparticles of SnO2 wrapped on graphene sheets. EDX analysis reveals that all the samples are made up of Sn and O elements (for SnO2) and Sn, O, and C elements (for SnO2 and GO composite). The photocatalytic performance of the prepared GO decorated SnO2 samples were studied for methylene blue (MB) dye degradation under visible light irradiation. Therefore, the 2% weight of GO with SnO2 exhibits the high degradation efficiency of 96% for MB dye which is applicable for energy conversion devices.

Enhancing the photocatalytic performance of surface - Treated SnO2 hierarchical nanorods against methylene blue dye under solar irradiation and biological degradation

Surfactant -treated tin oxide (SnO2) hierarchical nanorods were successfully synthesized through hydrothermal technique. The X-ray diffraction analysis showed the prepared SnO2 possesses tetragonal rutile structure having appreciable crystallinity with crystallite sizes in the range of 110 nm–120 nm. UV–visible diffuse reflectance absorption spectra confirm that the better visible light absorption band of SnO2 hierarchical nanorods have red shift compared to the pure SnO2. Fourier transform infrared spectroscopy (FTIR) study evident that the as-prepared SnO2 nanorods encompass the characteristic bands of SnO2 nanostructures. The morphological analyses of prepared materials were performed by FESEM, which shows that hierarchal nanorods and complex nanostructures. EDX analyses disclose all the samples are composed of Sn and O elements. The photocatalytic performance of the prepared surfactant treated SnO2 hierarchical nanorods was evaluated using methylene blue (MB) dye removal under direct natural sunlight. Recycling experiment results of CTAB - SnO2 nanorods and photocatalytic reaction mechanism also discussed in detail.

MOF-on-MOF Strategy to Construct a Nitrogen-Doped Carbon-Incorporated CoP@Fe-CoP Core-Shelled Heterostructure for High-Performance Overall Water Splitting.

The design and preparation of efficient and low-cost catalysts for water electrolysis are crucial and highly desirable to produce eco-friendly and sustainable hydrogen fuel. Herein, we prepared nitrogen-doped carbon-incorporated CoP@Fe-CoP core-shelled nanorod arrays grown on Ni foam (CoP@Fe-CoP/NC/NF) through phosphorization of ZIF-67@Co-Fe Prussian blue analogue (ZIF-67@CoFe-PBA). The hierarchical nanorod arrays combined with the core-shelled structure offer favorable mass/electron transport capacity and maximize the active sites, thus enhancing the electrochemically active surface area. The synergistic effect of the bimetallic components and the nitrogen-doped carbon matrix endow the composite with an optimized electronic structure. Benefiting from the above superiorities of morphological and chemical compositions, this self-supported CoP@Fe-CoP/NC/NF heterostructure can drive alkaline hydrogen evolution reaction and oxygen evolution reaction with overpotentials of 97 and 270 mV to yield 100 mA cm-2, respectively. The two-electrode alkaline electrolyzer constructed by this heterostructure shows a low cell voltage of 1.58 V to yield 10 mA cm-2, superior to the precious-metal-based electrocatalyst apparatus (IrO2∥Pt/C). This study offers a feasible and facile approach to develop efficient electrocatalysts for water electrolysis, which applies to other electrochemical energy conversion and storage applications.

Correction to “Accelerated, Mesoporogen-Free Synthesis of Hierarchical Nanorod ZSM-48 Assisted by Hydroxyl Radicals”

Correction to “Accelerated, Mesoporogen-Free Synthesis of Hierarchical Nanorod ZSM-48 Assisted by Hydroxyl Radicals”

Accelerated, Mesoporogen-Free Synthesis of Hierarchical Nanorod ZSM-48 Assisted by Hydroxyl Radicals

Hierarchical ZSM-48 was synthesized at an accelerated rate, ca. 2 times faster than the conventional route. This is due to the hydroxyl radical (•OH), induced by persulfate ions, that accelerate th...

Low-operating temperature and remarkably responsive methanol sensors using Pt-decorated hierarchical ZnO structure

Highly responsive methanol sensors working at low temperatures are developed using hierarchical ZnO nanorods decorated by Pt nanoparticles. The sensing materials are fabricated following a 3-step process: electrospinning of ZnO nanofibers, hydrothermal growth of hierarchical ZnO nanorods on the nanofibers and UV-assisted deposition of Pt nanoparticles. The morphology, structure and properties of the materials are examined by field-effect scanning electron microscopy, transmission electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy, UV–Vis absorption spectroscopy, and electrical measurements. The methanol sensing performance is investigated at different working temperatures in the range of 110 °C–260 °C. It is observed that the surface modification of the ZnO hierarchical nanorods by Pt nanoparticles results in a remarkable enhancement of the sensing response toward methanol, which can reach approximately 19 500 times higher than that of the unmodified ZnO nanorods-based sensor. In addition, this modification enables lower working temperatures with an optimum range of 140 °C–200 °C. Based on the achieved results, a methanol sensing mechanism of the Pt/ZnO structure is proposed.

Facile synthesis of cationic surfactant-treated hierarchical nanorods SnO2@CdO nanocomposite photocatalyst for degradation of methylene blue under sunlight

CTAB-treated hierarchical nanorods cadmium oxide nanorods loaded tin oxide (SnO2@CdO/CTAB) nanocomposite has been prepared by simple chemical co-precipitation technique. The X-ray diffraction pattern analysis revealed the as-prepared CTAB-treated nanocomposites possess tetragonal rutile structure having appreciable crystallinity with crystallite sizes in the range of 100–115 nm. The diffuse reflectance absorption spectrophotometer investigation confirms that the efficient absorption band of SnO2@CdO/CTAB nanocomposites have red shift over the SnO2. Fourier transform infrared spectroscopy (FTIR) investigation confirms the prepared SnO2@CdO/CTAB nanocomposites encompass the characteristic bands of both SnO2 and CdO. The morphology of the prepared nanocomposites were performed by FESEM and shows that hierarchal nanorods structure. The EDX analyses revealed all the samples are composed of Sn and O elements. The photocatalytic performance of the prepared SnO2@CdO/CTAB hierarchical nanorods nanocomposites was evaluated via methylene blue (MB) dye removal under direct natural sunlight irradiation.

Controlled Growth of Hierarchical Bi2Se3/CdSe‐Au Nanorods with Optimized Photothermal Conversion and Demonstrations in Photothermal Therapy

AbstractIntegrating multiple mechanisms to maximize photothermal conversion efficiency is a significant strategy but remains challenging to construct therapeutic agents toward photothermal tumor treatment. Here, an approach to synthesize asymmetric Bi2Se3/CdSe‐Au hierarchical nanorods with excellent photothermal conversion is reported. Ag wetting‐layer is firstly grown to help overcome the interfacial lattice mismatch and promote the site‐selective growth of AgCdSe onto one end or side surface of Au nanorods. Subsequently, extraction of Ag+ ions out of lattice is observed during cation exchange reaction and epitaxial growth of Bi2Se3 shell. Bi2Se3/CdSe heterojunction with type‐II band alignment is formed and located at the plasmonic hotspots of Au nanorods, which experiences enhanced light absorption and accelerates the charge separation of photo‐excited carriers. Under excitation of near‐infrared 808 nm laser, the matchstick‐like Bi2Se3/CdSe‐Au nanorods show an excellent photothermal conversion, with 4.3 times temperature increment (ΔT) than that of bare Au nanorods. Moreover, in vitro and in vivo experiments verify them as excellent photothermal therapeutic agents.

One-Dimensional CdS/Carbon/Au Plasmonic Nanoarray Photoanodes via In Situ Reduction-Graphitization Approach toward Efficient Solar Hydrogen Evolution.

Photoelectrochemical (PEC) hydrogen evolution has been acknowledged as a promising "green" technique to convert solar energy into clean chemical fuel. Photoanodes play a key role in determining the performance of PEC systems, spurring numerous efforts to develop advanced materials as well as structures to improve the photoconversion efficiency. In this work, we report the rational design of a plasmonic hierarchical nanorod array, composed of oriented one-dimensional (1D) CdS nanorods decorated with a uniformly wrapped graphite-like carbon (CPDA) layer and Au nanoparticles (Au NPs), as highly efficient photoanode materials. An interfacial in situ reduction-graphitization method has been conducted to prepare the CdS/CPDA/Au nanoarchitecture, where polydopamine (PDA) coating was used as a C source and a reductant. The CdS/CPDA/Au nanoarray photoanode demonstrates superior photoconversion efficiency with a photocurrent density of 8.74 mA/cm2 and an IPCE value (480 nm) of 30.2% (at 1.23 V vs RHE), under simulated sunlight irradiation, which are 12.7 and 13.5 times higher than pristine CdS. The significant enhancement of PEC performance is mainly benefited from the increase of the entire quantum yield and efficiency due to the formation of a Schottky rectifier, localized surface plasmon resonance (LSPR)-enhanced light absorption, and promoted hot-electron injection from interlayered graphene-like carbon. More importantly, thanks to the inhibited charge carrier recombination process and transferred oxidation reaction sites, the fabricated CdS/CPDA/Au photoelectrode exhibits lengthened electron lifetimes and better photostability, illustrating its wonderful potential for future PEC application.