Hierarchical ZnO Nanostructures Research Articles

Bimetallic Co-Mn catalysts for synergistic enhancement of VOC gas-sensing performance of ZnO hierarchical nanostructures.

The synergistic effect between bonding dissimilar metals is a very effective way to improve the performance of metal catalysts. In this work, we prepared a series of bimetallic co-doped ZnO hierarchical nanostructures by controlling Mn and Co contents. The gas-sensing properties of the sensors based on the bimetallic co-doped ZnO hierarchical nanostructures were studied systematically through different volatile organic compound (VOC) vapors for the temperature range from 160 to 400 °C. In the testing of normal butanol gas by the bimetallic co-doped ZnO sensor, its performance was tens of times higher than that of pure zinc oxide, and the response values to other VOCs tested were very low, which also indicates that the sensor has good selectivity. The promoted performance is attributed to the increase of adsorbed oxygen content on the surface of the sensor material due to the bimetallic synergistic enhancement effect. XPS spectra of O 1s region of the sensor show that the adsorbed oxygen content is 22.4%, which is higher than that of the pure ZnO (8.5%). The synergistic effect between bimetallic Mn and Co leads to electron enrichment on the surface of ZnO. Electron enrichment can not only promote the activation of ZnO, but also can help to improve the gas-sensing performance.

Simple Template-Mediated Fabrication of ZnO Nanotube Arrays and Their Application in Flexible Ultraviolet Photodetectors

ZnO, as an important semiconductor, has been extensively studied for a wide range of applications. To date, with the development of micro/nano manufacturing technology, various hierarchical ZnO nanostructures have been fabricated and explored, showing encouraging success in advanced photodetectors. ZnO nanotube structure has a high surface-to-volume ratio, and versatile hollow channels, which are promising for sensing applications. Typical nanotube arrays primarily rely on advanced nanofabrication technologies. Simple and low-cost fabrication strategies are still lacking. Herein, we report a simple template fabrication method to obtain vertically aligned ZnO nanotube arrays. Using flexible, etched polyimide membranes as the template, ZnO nanotube arrays can be prepared in situ by dip-coating the sample into a zinc acetate solution followed by heating. Different hierarchical ZnO nanotube structures were obtained with the nanotube arrays when the method was combined with hydrothermal growth. We have demonstrated that the structures may be used in flexible and transparent photodetectors. Our work provides a facile approach for fabricating ZnO nanotube arrays and expands the application of ZnO nanotube structures to flexible and transparent photodetectors.

Correction to: Morphological evolution of 3D ZnO hierarchical nanostructures by diethylene glycol-assisted sol–gel synthesis for highly effective photocatalytic performance

Correction to: Morphological evolution of 3D ZnO hierarchical nanostructures by diethylene glycol-assisted sol–gel synthesis for highly effective photocatalytic performance

Amine-functionalized ZnO hierarchical nanostructures for enhanced photocatalytic decomposition under visible light illumination

Nanostructures of ZnO have been synthesized using Benzylamine (BA) and Diethylamine (DEA) as passivating agent for environmental remidiation. Hexagonal ZnO formation were revealed from the X-ray diffraction patterns. The oxidation states of Zn 2p and O 1s were confirmed by X-ray photoelectron spectroscopy. Morphological analysis revealed the formation of nanoparticles at lower concentration of BA and DEA, with increasing the concentration of BA and DEA branched nanoflakes were observed. The photocatalytic degradation of MB in aqueous solution has been found by employing ZnO as photocatalysts by illuminating visible light and maximum degradation efficiency was observed for sample DZ0.4. Further various photocatalytic reaction parameters such as effect of pH and dye concentration was investigated and the optimum pH and dye concentration were 11 and 10 ppm, respectively.

Morphological evolution of 3D ZnO hierarchical nanostructures by diethylene glycol-assisted sol–gel synthesis for highly effective photocatalytic performance

Morphological evolution of 3D ZnO hierarchical nanostructures by diethylene glycol-assisted sol–gel synthesis for highly effective photocatalytic performance

Ultrasensitive Electrochemical Detection and Plasmon-Enhanced Photocatalytic Degradation of Rhodamine B Based on Dual-Functional, 3D, Hierarchical Ag/ZnO Nanoflowers.

The sensitive detection and degradation of synthetic dyes are pivotal to maintain safety owing to the adverse side effects they impart on living beings. In this work, we developed a sensitive electrochemical sensor for the nanomolar-level detection of rhodamine B (RhB) using a dual-functional, silver-decorated zinc oxide (Ag/ZnO) composite-modified, screen-printed carbon electrode. The plasmon-enhanced photocatalytic degradation of organic pollutant RhB was also performed using this nanocomposite prepared by embedding different weight percentages (1, 3, and 5 wt%) of Ag nanoparticles on the surface of a three-dimensional (3D), hierarchical ZnO nanostructure based on the photoreduction approach. The structure and morphology of an Ag/ZnO nanocomposite were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental mapping, ultraviolet-visible (UV-vis) spectroscopy, and X-ray diffraction (XRD). The electrochemical sensor exhibited a very high sensitivity of 151.44 µAµM−1cm−2 and low detection limit of 0.8 nM towards RhB detection. The selectivity, stability, repeatability, reproducibility, and practical feasibility were also analyzed to prove their reliability. Furthermore, the photocatalysis results revealed that 3 wt% of the Ag/ZnO hybrid nanostructure acquired immense photostability, reusability, and 90.5% degradation efficiency under visible light. Additionally, the pseudo-first-order rate constant of Ag-3/ZnO is 2.186 min−1 suggested promising activity in visible light photocatalysis.

Branches of ZnO nanostructure grown on sub-microrod template with seed layer coated by ultrasonic-assisted immersion technique: effect of surface energy on the growth of branches

Branches of ZnO nanostructure were hydrothermally grown on seed layer coated on sub-microrod template by ultrasonic-assisted immersion technique. Zinc acetate, monoethanolamine, and isopropanol were used as a precursor, stabilizer, and solvent for coating seed layer, respectively. The crystallization of seed layer, which was confirmed by x-ray diffractometer (XRD) and x-ray photoelectron spectrometer (XPS), was facilitated by ultrasonic irradiation. The sol concentration was adjusted to be 20 and 50 mM with the coating cycles of 8 and 16 for controlling the uniformity and surface energy of seed layer. The increase of sol concentration and coating cycles led to the increase of crystal orientation in (002) plane causing the improvement of seed layer’s surface energy which was estimated from water contact angle of the template. Atomic force microscope (AFM) was revealed that the seed layer did not cover the template only at the lowest condition of both sol concentration and coating cycles. However, the roughness and maximum peak-to-valley value tended to be increased for other conditions and dropped for the last condition which was suitable to vertically grow branches. After the growth of branches, the morphology of hierarchical ZnO nanostructure was investigated by field-emission scanning electron microscope (FESEM). It was found that the branches were vertically grown on the surface of rod template in every condition except the lowest sol concentration and coating cycles. Moreover, when the sol concentration and coating cycle of seed layer were increased, the branch density was also increased.

Fabrication of tunable hierarchical ZnO nanostructures via an anodization process

The size and morphology of nanomaterials replicate optical, electrical, and mechanical properties and their applications. In this paper, for the first time, ZnO hierarchical nanostructures were grown on Zn foil through electrochemical anodization in the presence of fluoride ions at room temperature in water/glycerol electrolyte. Fluoride ions are vital for development of chelation reactions and the formation of ZnO hierarchical nanostructures. XRD analysis confirmed the ZnO crystal phase to be wurtzite, and the Raman analysis confirmed the crystal phase to be wurtzite hexagonal. The surface morphology of ZnO reveals that the nanostructures grown on Zn foil are hierarchical nanoflowers with an even distribution. The identified binding energies from the XPS spectrum confirmed the Zn2+ state. Such unique hierarchical architectured ZnO can be used for designing high-performance optoelectronic devices such as LED lights, photodiodes, nanosensors, and solar cells.

Efficient performance acetone sensor based on squirrel-tail like Ni doped ZnO hierarchical nanostructure

Highly sensitive, rapidly responsive and excellently selective sensor towards acetone vapor was developed utilizing open space Ni doped ZnO hierarchical nanostructures. The acetone sensing behavior was examined at different working temperatures and various Ni doping content as the variable. The response (Ra/Rg) to 18,000 ppm acetone was 330 operated at 280 °C with the response and recovery time of ~1 and 298 s, respectively. An excellent selectivity of sensor based on the open space Ni doped hierarchical nanostructure towards acetone vapor compared with other vapors such as ethanol, methanol, 2-propanol and toluene was observed. The high performance of the Ni doped ZnO hierarchical nanostructure based sensors can be explained by a combination of several factors including the high porosity ZnO structure, enhanced oxygen absorption capability after Ni doping and sensing measurement at the optimal working temperature. The acetone sensing mechanism of the Ni doped ZnO sensor is also discussed in detail. The morphology and characteristics of the samples were examined by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrical measurements.

Nano/Micro-Structured ZnO Rods Synthesized by Thermal Chemical Vapor Deposition with Perpendicular Configuration.

Under a one-step process, catalyst-free growth of one-dimensional (1D) ZnO hierarchical nanostructures was performed on ZnO-seeded Si substrate by thermal chemical vapor deposition with a perpendicular setup. The morphological and crystallographic properties of the nano/micro-structured ZnO rods were investigated with varying growth temperature and growth time. X-ray diffraction patterns of 1D ZnO double-structured rods showed the hexagonal wurtzite structure. The morphology and crystal structure of the ZnO double-structured rods were sensitive to the growth temperature and growth time. From Raman scattering and photoluminescence spectra, the orientation and size effects of the ZnO double-structured rods were discussed in relation to growth temperatures and growth times.

Hierarchical ZnO nanostructure flowers loaded with AgI nanoparticles for photodegradation of methylene blue under UV visible radiation

Hierarchical ZnO spherical flowers loaded with different weight contents of AgI nanoparticles were synthesized by deposition-precipitation method at room temperature and tested for photodegradation of methylene blue (MB) under UV visible light irradiation. The as-prepared photocatalysts were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) connected with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). XRD patterns and SEM images of ZnO and AgI/ZnO hierarchical spherical flowers present pure phase of hexagonal wurtzite ZnO structure flowers and hexagonal wurtzite ZnO flowers supported with cubic AgI nanoparticles with size range of 80–90 nm on top. The photodegradation of MB was increased with increasing in the weight content of the loaded AgI nanoparticles on the surface of ZnO flowers. The 10% AgI/ZnO nanocomposites have the highest photocatalytic efficiency in degrading MB by h+ and ●OH as the main active species under visible light irradiation within 60 min.

Nghiên cứu chế tạo và tính chất quang của cấu trúc nano phân nhánh ZnO/NiO

NiO/ZnO hierarchical nanostructures were synthesized by a combination of electrospinning, hydrothermal and ultraviolet (UV)-assisted deposition. Initially, ZnO nanofibers were synthesized by electrospinning method following thermal oxidation. Subsequently, ZnO hierarchical nanostructures were synthesized by hydrothermal method using ZnO nanofibers as templates. Finally, NiO nanoparticles were deposited on ZnO surface by UV-assisted deposition method. Morphology and characteristics of the material were determined by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) and photoluminescence spectrum (PL). The results showed that the NiO/ZnO hierarchical nanostructures with high open space were obtained. NiO/ZnO crystals showed hexagonal structure of ZnO without phase formation of NiO. PL spectra of the NiO/ZnO material showed emission peaks shift towards longer wavelengths in the visible region with increasing the content of NiO nanoparticles.

Modified interfaces of twisted root-like 2D configured ZnO hierarchical nanostructures through surface lattice coating of NiO/graphene and their enhanced UV photodetection properties

The formation of edges in 2D configured nanomaterials are special sites which possess different arrangements of atoms and properties compared to that of plain nanomaterials. Herein, a novel strategy is used to synthesize the self-assembled 2D configured edges with twisted building blocks of glucose reduced graphene oxide (grGO)-incorporated NiO-coated ZnO NRs via soft chemical route. It is envisioned that the present hierarchical nanostructures will stimulate the performances of UV photodetection due to these combinations of materials. The as-prepared samples such as ZnO nanorods (NRs), NiO-ZnO NRs, grGO-ZnO NRs and grGO-incorporated NiO-ZnO NRs are designed using Ag interdigitated electrodes. Remarkably, the as-fabricated grGO-incorporated NiO-ZnO NRs shows enhanced photodetection properties when compared to those of bare ZnO NRs, NiO-ZnO NRs and grGO-ZnO. Especially, the grGO-incorporated NiO-ZnO NRs photodetector exhibits the highest UV on/off ratio of 3 × 104 which is ~60 times better than that of bare ZnO NRs photodetector. The results reveal that the development of p-n junction along grGO coating at the surface of NiO-ZnO enhances the relaxation dynamics of ZnO NRs by reducing the photocarriers contact with O2 species due to surface passivation. The present grGO-NiO-ZnO photodetectors might opening up a new opportunities for future optoelectronic devices.

Ultra Responsive and Highly Selective Ethanol Gas Sensor Based on Au Nanoparticles Embedded ZnO Hierarchical Structures

Ultra sensitive and highly selective sensor towards ethanol (C2H5OH) vapor was developed from Au embedded open space ZnO hierarchical nanostructures. The ethanol sensing behaviors were examined at different working temperatures and various quantities of Au nanoparticles as the variable. The response of the Au/ZnO nanostructure based sensor at the optimal working temperature of 220 °C towards ethanol vapor is 167 times higher than that of the pristine ZnO structure at the optimal working temperature of 260 °C. In addition, the developed sensor exhibited excellent selectivity to ethanol compared with other vapors such as methanol, acetone, 2-propanol and toluene. The ethanol sensing mechanism of the Au embedded ZnO sensor structure is also proposed. The morphology and characteristics of the fabricated samples were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and electrical measurements. This finding offers a new way of thinking for the design and development of ethanol sensors based on Au nanoparticles embedded ZnO hierarchical structures.

Recent Advances in Zinc Oxide Nanostructures with Antimicrobial Activities.

This article reviews the recent developments in the synthesis, antibacterial activity, and visible-light photocatalytic bacterial inactivation of nano-zinc oxide. Polycrystalline wurtzite ZnO nanostructures with a hexagonal lattice having different shapes can be synthesized by means of vapor-, liquid-, and solid-phase processing techniques. Among these, ZnO hierarchical nanostructures prepared from the liquid phase route are commonly used for antimicrobial activity. In particular, plant extract-mediated biosynthesis is a single step process for preparing nano-ZnO without using surfactants and toxic chemicals. The phytochemical molecules of natural plant extracts are attractive agents for reducing and stabilizing zinc ions of zinc salt precursors to form green ZnO nanostructures. The peel extracts of certain citrus fruits like grapefruits, lemons and oranges, acting as excellent chelating agents for zinc ions. Furthermore, phytochemicals of the plant extracts capped on ZnO nanomaterials are very effective for killing various bacterial strains, leading to low minimum inhibitory concentration (MIC) values. Bioactive phytocompounds from green ZnO also inhibit hemolysis of Staphylococcus aureus infected red blood cells and inflammatory activity of mammalian immune system. In general, three mechanisms have been adopted to explain bactericidal activity of ZnO nanomaterials, including direct contact killing, reactive oxygen species (ROS) production, and released zinc ion inactivation. These toxic effects lead to the destruction of bacterial membrane, denaturation of enzyme, inhibition of cellular respiration and deoxyribonucleic acid replication, causing leakage of the cytoplasmic content and eventual cell death. Meanwhile, antimicrobial activity of doped and modified ZnO nanomaterials under visible light can be attributed to photogeneration of ROS on their surfaces. Thus particular attention is paid to the design and synthesis of visible light-activated ZnO photocatalysts with antibacterial properties

AgBr nanoparticles–ZnO flowers nanocomposites used for photodegradation of methylene blue solution illuminated by ultraviolet-visible radiation

Different weight contents of AgBr nanoparticles supported on hierarchical ZnO nanostructure flowers were synthesized by precipitation-deposition method at room temperature. The nanocomposites were investigated for photocatalytic degradation of methylene blue (MB) under ultraviolet (UV)-visible light irradiation. The analytical results show that AgBr nanoparticles with size range of 60–80 nm were supported on hierarchical ZnO nanostructure flowers with ∼4 µm diameter. The photodegradation was improved by AgBr nanoparticles loaded on ZnO nanopetals. In this research, 10 wt% AgBr–ZnO nanocomposites have the highest photodegradation of MB under UV-visible light irradiation.

The role of counter-ions in crystal morphology, surface structure and photocatalytic activity of ZnO crystals grown onto a substrate

In this contribution, we present an experimental and theoretical investigation of the role of counter-ions in the crystal morphology, surface structure, and photocatalytic activity of hierarchical ZnO nanostructures. The effect of zinc precursor (nitrate, acetate and, sulfate) along the synthesis of ZnO nanostructures grown directly onto a substrate by means of a simple hydrothermal method was analyzed in detail. Scanning electron microscopy images showed a preferential growth of ZnO nanostructures along the c-axis, with a slight reduction in the orientation depending on the choice of the Zn source. Theoretical calculations based on the Wulff theory allowed us to better understand the morphological changes and directly relate the photocatalytic performance at the different exposed surfaces of the as-observed crystal shapes. Our results showed that photocatalytic activities in the discoloration of organic dyes became superior for hierarchical ZnO nanostructures obtained from zinc nitrate. This finding was explained by X-ray photoelectron and photoluminescence spectroscopies, which revealed that in addition to, the attached counter-ions and the abundance of carboxylate groups and organic residuals on ZnO surfaces, the presence of surface defects are determinant to enhance the photocatalytic performance of the material.

PHOTODEPOSITION SYNTHESIS AND CHARACTERIZATION OF Ag/ZnO NANOCOMPOSITES FOR PHOTODEGRADATION OF METHYLENE BLUE AND METHYL ORANGE

In this work, Ag nanoparticles were deposited on hierarchical ZnO nanostructure flowers by photodeposition method. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) coupled with energy dispersive spectrometer (EDS), Fourier transform infrared (FTIR) spectrometry and X-ray photoelectron spectroscopy (XPS). Photocatalytic performance of the asprepared ZnO and Ag/ZnO nanocomposites was investigated through photodegradation of methylene blue (MB) and methyl orange (MO) as cationic and anionic dye models under UV light irradiation. The analytical results showed that the spherical metallic Ag nanoparticles with 10–12 nm diameter were deposited on nanosheets as petals of hierarchical ZnO nanostructure flowers. The photodegradation efficiencies of MB and MO by Ag/ZnO nanocomposites were higher than that by pure ZnO sample because of the electronic transfer through Ag/ZnO heterojunctions.

Facile synthesis of Cr doped hierarchical ZnO nano-structures for enhanced photovoltaic performance

Transition metal doped ZnO has been widely used in various research areas such as optoelectronics, chemical sensors, solar cells and photo catalysts. Herein, we fabricated Cr-doped ZnO nanospheres by a facile solvothermal treatment for enhanced photovoltaic performance. A systematic study of the structural and optical properties of Cr doped ZnO were investigated by scanning electron microscopy (SEM), X-ray diffraction technique (XRD), Ultra violet-Visible spectroscopy (UV–Vis) respectively. XRD patterns confirm that the samples have hexagonal (wurtzite) structure with no additional peaks, which suggests that Cr ions replaces the regular Zn sites in the ZnO crystal structure. Furthermore, doped ZnO nanospheres were employed in the hybrid solar cells in combination with P3HT and gave better current densities than their corresponding undoped counterparts. The increase in solar cell efficiency of doped ZnO nanospheres is solely due to the improvement in the charge separation efficiency in the 4% Cr doped ZnO nanospheres. Optoelectronic analysis of the Cr doped ZnO hybrid solar cell showed comparable results of JSC −3.7 (mAcm−2), VOC 0.44 (V), Fill Factor 0.49 and Efficiency (ƞ) 0.79 (%). The enhanced photovoltaic activity of the Cr doped hierarchical ZnO nanostructures provides an interesting grounds for the design and enhancement of the low cost, feasible synthesis of photovoltaic nanostructure materials.

Anisotropic growth and strain-induced tunable optical properties of Ag–ZnO hierarchical nanostructures by a microwave synthesis method

Effective surface-enhanced Raman scattering (SERS) substrate with hierarchical nanostructure is successfully fabricated by architecturing Ag nanoparticles on the surface of one dimensional (1-D) semiconducting ZnO nanospikes. The influence of anisotropic growth and strain in the ZnO nanostructures through microwave treatment with the different time interval of microwave exposure. Based on the obtained physiochemical characterization results, the Ag–ZnO hierarchical nanostructures facilitates to modify the band structure due to the formation of heterojunction and thus drastically improves the SERS sensing capacity towards the various chemically harmful species. It is proposed that the anisotropic growth and strain-induced effect would be a unique strategy for designing and development of high-performance chemical and real-time molecular sensors.