ZnO NR Research Articles

Enhancing the performance of photodetectors based on ZnO nanorods decorated with Ag nanoparticles

Zinc oxide nanorods (ZnO NRs) were modified by decorating with silver (Ag) nanoparticles to enhance visible absorption. The morphology, structure and optical properties of the modified ZnO NRs were investigated by scanning electron microscopy, x-ray diffraction and UV–vis absorption spectroscopy. Photodetectors (PDs) based on the modified ZnO NRs successfully detected visible radiation. The result showed high performance of the visible sensor (λ = 400 nm) with a maximum responsivity of 46 mA W−1. The photoconductive gain of Ag/ZnO NR-based PDs was 5.8 times higher than that of pure ZnO NR ones. With their enhanced visible absorption, the multi-modified ZnO NRs are suitable for practical applications, especially in optoelectronic devices operating in the visible region.

Effect of PAA-induced surface etching on the adhesion properties of ZnO nanostructured films

Zinc oxide - polymer interfaces are known to exhibit interesting properties regarding molecular adhesion. This work is aimed at the investigation of the effect of the morphology and surface chemistry on the macroscopic adhesion of a model epoxy-based adhesive to nanorod (ZnO NR) and nanocrystalline (ZnO NC) ZnO-modified surfaces. Both ZnO films have been prepared using hydrothermal synthesis on hot-dip galvanized steel (HDG) surfaces by varying the precursor chemistry in order to control the film morphology. Poly (acrylic acid) (PAA) was used to improve the interfacial adhesion by modifying the morphology and surface chemistry of ZnO nanostructured films. The strong interaction of PAA from a dilute and neutral aqueous solution with the ZnO nanocrystallites was shown to significantly improve the interfacial adhesion by means of a nanoetching process. It was shown that the wet peel-forces correlate well with the considered morphology and surface chemistry.

Au-decorated ZnO nanorod arrays for SERS-active substrates towards trace detection and classification of pentaerythritol tetranitrate

This work proposed a systematic fabrication process towards high-performance SERS-active substrates as the chemical sensors, based on a combination of the hydrothermal-synthesized ZnO nanorods (ZnO NRs) and the decorated Au nano-surface. The fabrication process was first focused on the preparation of the Au/ZnO NRs hybrids. The ZnO NR templates were grown on silicon (100) wafer substrates by the hydrothermal method. Then, the Au films were deposited on the ZnO NR templates by the DC pulse magnetron sputtering technique. The obtained SERS substrates were utilized towards trace detection and classifications of pentaerythritol tetranitrate (PETN), which is commonly used in industrial explosives and improvised explosive devices. The results from field-emission electron microscopy (FE-SEM) and transmission electron microscopy (TEM) indicated the changes in physical morphologies and crystal structure, respectively, based on the variation of the fabrication parameters. The FE-SEM results showed that well-vertical ZnO NRs demonstrated the length of the nanorods before and after the Au decorations. In addition, the hexagonal structures, before and after the Au decorations, were observed with the average diameter of 50 and 181 nm, the nanorod distances of 178 and 81 nm, respectively. The TEM results also confirmed the average size and d-spacing of the ZnO NRs and Au/ZnO NR hybrids, with validated elements/compounds from the EDX mapping technique. Furthermore, the sample surfaces were observed with Raman mapping spectroscopy towards uniformly distributed examination. Finally, the fabricated samples were investigated with trace concentration of PETN towards the limit of detection. The results that our SERS substrates could detect PETN of less than 1 µg/ml, which indicated excellent performance of the trace detection of the explosive substance. The SERS substrates were further used to successfully classify different sources of the PETN substances, with 10 mg/ml, based on the machine learning approach with the principal component analysis.

Tailoring the surface oxygen engineering of a carbon-quantum-dot-sensitized ZnO@H-ZnO1-x multijunction toward efficient charge dynamics and photoactivity enhancement

A well-steered coordination environment on photoelectrode can offer fruitful active sites and efficaciously alter atomic and electronic configuration to boost the performance in water oxidation. To enhance the performance of the photocatalytic oxygen-evolution reaction, enriched oxygenous-type carbon quantum dots (CQD) were combined with oxygen-deficient ZnO@H-ZnO1-x homojunctions for the first time. Specifically, hydrogenation created an unstoichiometric H-ZnO1-x surface through oxygen vacancies, which were responsible for the formation of coordinatively unsaturated Zn centers to drive the photoelectrochemical reaction by precise regulation of the charge density, valence-band edge, atomic geometric structure and electronic structure. The enriched photohole reservoir in carboxyl-conjugated CQD was a great benefit for super-rapid charge tunnels, thereby governing the rate of internal and interfacial charge separation and transport in the multijunction. Accordingly, the CQD/H-ZnO1-x/ZnO photoanodes showed a photoactivity enhanced five-fold relative to bare ZnO NR and maintained that high performance for 24 h of operation. Comprehensive analyses, involving electrochemical measurements, time-resolved photoluminescence, X-ray absorption spectra in situ and calculations with density-functional theory were undertaken to elucidate the underlying mechanism of enhancement and the route of directional charge transport as well as the interfacial charge dynamics over the CQD/H-ZnO1-x/ZnO photoelectrode. These findings provide a new track towards photoelectrodes that could yield not only strikingly enhanced photocatalysis but also satisfied stability for realistic application.

3D self-supporting heterostructure NiCo-LDH/ZnO/CC electrode for flexible high-performance supercapacitor

Two kinds of nanostructured ZnO, namely nanorods (ZnO NR) and nanoflakes (ZnO NF) were first prepared on conductive flexible carbon cloth (CC) by a hydrothermal route. Then nickel cobalt layered double hydroxide (NiCo-LDH) nanoflakes were directly hydrothermally deposited on them to construct three-dimensional (3D) self-supporting heterostructure NiCo-LDH/ZnO NR/CC and NiCo-LDH/ZnO NF/CC flexible electrodes. The effects of different nanostructured ZnO on morphology, structure and electrochemical performance of NiCo-LDH/ZnO/CC composite materials were investigated. It is found that NiCo-LDH nanoflakes grown on ZnO NF/CC substrate are more compact and uniform than those on ZnO NR/CC substrate. Moreover, NiCo-LDH/ZnO NF/CC electrode presents better electrochemical properties than NiCo-LDH/ZnO NR/CC electrode with 2.6 times higher specific capacitance (1577.6 F g−1 at 1 A g−1), 2.2 times better rate capability, and 1.5 time greater cycle stability, which may be attributed to the larger contact area and more redox-active sites provided by the NiCo-LDH NFs grown on ZnO NFs. Furthermore, the as-assembled solid-state flexible NiCo-LDH/ZnO NF//AC (active carbon) asymmetric supercapacitor (ASC) delivers a maximal energy density of 51.39 Wh kg−1 (800 W kg−1) with a high operating window of 1.6 V, and exhibits great cyclic stability with 87.3% capacitance retaining after 1000 cycles, which is higher than many reported ASCs. Finally, two packaged ASCs in series successfully lighted a red light-emitting diode (LED, 2.2 V/20 mA), evincing the potentiality of practical application.

ZnO nanorods/sulfophenylporphyrin nanocomposites facilely embedded with special copper for improved photocatalytic hydrogen evolution

Novel and efficient copper-implanted ZnO nanorod/5,10,15,20-tetrakis(4-sulfophenyl)porphyrin composite photocatalysts (ZnO NR-Cu-TSPP) were facilely fabricated. The assembly mechanism was investigated and showed that the TSPP was anchored onto the ZnO NR-Cu through dual interaction, hydrogen bond and coordination interaction. Importantly, the ZnO NR-Cu-TSPP nanocomposite exhibited high photocatalytic activity on account of extended light absorption and greatly enhanced charge separation at the heterointerface. The photocatalytic mechanism revealed that, with the small sized Cu as interfacial linker, not only the interaction between ZnO NR and TSPP was strengthened, but also more active sites for photocatalytic H2 evolution were produced. Furthermore, by the introduction of a certain amount of TSPP, the photocatalytic activity of the nanocomposite can be significantly enhanced, which is higher than those controlled porphyrins with other substituents. Moreover, the composite showed a superior stability according to the cycling tests. This work provides a new idea for fabricating high efficient nano photocatalysts for hydrogen production.

Optimizing Performance of ZnO Nanorod and Activated Carbon as a Composite Anode for Lithium-Ion Batteries

To obtain the high specific capacity anode for Lithium-ion battery with stable performance is conducted by synthesizing a composite anode of ZnO-nanorods (ZnO-NR) and as a matrix is the activated carbon (AC). In this study, ZnO-NR synthesized a process that uses basic materials hexamethylenetetramine (HMTA) and zinc oxide. Activated carbon has been activated because it has high porosity and good electrical conductivity properties. Variable used is the percentage of ZnO-NR, which is 30wt%, 40wt%, and 50wt%. Characterization of the samples was examined using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Brunauer–Emmett–Teller (BET). The battery performance of the samples was obtained by Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), and Charge-Discharge (CD) testing after being assembled into coin cell batteries. This study discusses the effect of adding activated carbon to ZnO NR composites. The results showed that the ZnO-NR30/AC has the highest specific capacity of 270.9 mAh g-1. According to Brunner-Emmet-Teller (BET) test, the largest surface area was 631.685 m2 g-1. Electrochemical performance is the best obtained by ZnO-NR30/AC.

Highly oriented-ZnO nanorods from hydrothermally depositions: Synthesis and optical properties

A highly (002)-oriented ZnO NRs on the Si/SiO2 substrate was successfully synthesized by the spray-hydrothermal method, where ZnO nanoparticles (ZnO NPs) were used as templates. Interestingly, by varying deposition temperatures from 150 to 350 °C, we successfully modified the orientation of the nanorod from vertical/horizontal to globular. This result is related to the agglomeration of ZnO NPs in the deposition process. Furthermore, globular ZnO NR showed a high electron transfer up to ∼9×1014 Ω−1 cm−1 eV with the presence of an excitonic state. Our results will provide an alternative in designing the structure and morphology of ZnO NR at a more affordable cost for high-performance optoelectronic applications.

Investigation of optical properties of hybrid ZnO/Graphene-based photodetectors

The problem of ozone depletion lies behind the importance of developing a photodetector device, which is used as a preliminary detection step against the risk of solar radiation. At present, hybrid photodetectors are a major concern because they have detection and operational advantages over conventional photodetectors. In this study, we investigated the optical properties and photoresponse of hybrid ZnO/graphene (HZG) systems, of which ZnO nanorod (ZnO NR) was used in the system. Investigations were carried out using spectroscopic ellipsometry (SE) and solar simulators. The results of SE fittings with the effective medium approximation (EMA) method confirmed that the length of ZnO NR was 27.81, 42.67, and 220.46 nm respectively. We note that increasing the size of ZnO NR promotes light absorption to increase significantly. Furthermore, the relationship between light absorption and HZG photoresponse was discussed using a comprehensive analysis.

Room temperature SO2 and H2 gas sensing using hydrothermally grown GO–ZnO nanorod composite films

Graphene based 2D materials with a surfeit of active sites and advantageously high surface to volume ratio are effectively linked to well established nanostructured semiconducting metal oxides for development of nanocomposites with enhanced gas sensing properties. Graphene Oxide (GO), a sister material of graphene, is therefore a natural choice for development of room temperature operated gas sensors. In the current investigation hydrothermally grown GO and ZnO nanorods composite (GO–ZnO–NR) is utilised for room temperature gas sensing of H2 and SO2 gases. Room temperature detection of H2 and SO2 at sub-100 ppm levels with linear variation in response for different concentrations is demonstrated. Morphological and structural analyses are conducted using Scanning electron microscopy, Raman spectroscopy and X-ray diffraction. GO-ZnO-NR composite sensor is seen to exhibit robust sensing response of 5.82 and 5.45 for 100 ppm each of H2 and SO2 gases respectively at room temperature. Further, the delayed response and recovery times exhibited by the sensor for SO2 gas are recognized to be due to formation of strongly adhering SO3 species.

High-performance UV surface photodetector based on plasmonic Ni nanoparticles-decorated hexagonal-faceted ZnO nanorod arrays architecture

We report the photoresponse performance of plasmonic nickel (Ni) nanoparticles (NPs)-decorated ZnO NR arrays-based ultraviolet (UV) surface photodetectors. The ZnO NR arrays were grown on the Si substrate by the facile hydrothermal method, followed by Ni NP decoration on the surface by pulsed laser deposition (PLD) technique. Raman analyses reveal that the grown ZnO NR arrays are in hexagonal wurtzite structure. The field emission scanning electron microscopy (FE-SEM) shows that the grown ZnO NR arrays are vertically aligned, hexagonal faceted, and uniformly distributed on the Si substrate. The 14-fold enhancement in the UV emission upon Ni NP decoration implies the near-field coupling of surface plasmons (SPs) of Ni NPs with the excitons of ZnO NRs. The linear increase in current with the applied voltage indicates good Ohmic contacts between the ZnO NR arrays and the Ag electrodes. The transient photo-response measurements were performed for every twenty seconds (20 s) ON/OFF time and for nine cycles to study its response speed, stability, and repeatability of the photodetectors. The improved photo-response of the Ni NP-decorated ZnO NR arrays is attributed to the near-field coupling of Ni NPs with the underlying ZnO NRs. The decoration of plasmonic Ni NPs provides better optical pathway for the incident light and transfers its hot electrons to the conduction band of ZnO NR arrays gives rise the improved photoresponse.

Correction to: Fabrication of SiO2–ZnO NP/ZnO NR hybrid coated cotton fabrics: the effect of ZnO NR growth time on structural and UV protection characteristics

Correction to: Fabrication of SiO2–ZnO NP/ZnO NR hybrid coated cotton fabrics: the effect of ZnO NR growth time on structural and UV protection characteristics

Quantitative evaluation of the antibacterial factors of ZnO nanorod arrays under dark conditions: Physical and chemical effects on Escherichia coli inactivation

Although zinc oxide nanorod (ZnO NR) arrays are a nanomaterial that offers efficient bactericidal activity, they have not been systematically evaluated to quantitatively investigate their disinfection mechanism under dark conditions. In this study, ZnO NR arrays of different lengths (0.5–4 μm) were uniformly grown via hydrothermal synthesis. The longer arrays exhibited higher Escherichia coli (E. coli) inactivation efficiency up to 94.2% even under darkness for 30 min. When the NR arrays were coated via Al2O3 atomic layer deposition, the inactivation efficiency was decreased to 56.4% because the generation of reactive oxygen species (ROS) and the leaching of Zn2+ ions were both hindered by the surficial coverage of defect sites. The morphological effect, i.e., the mechanical rupture of E. coli on the surface, contributed 56.4% of the bactericidal efficiency; chemical effects, i.e., ROS formation and zinc ion release, contributed the remaining 37.8% under dark conditions. The bactericidal effect of fabricated ZnO NR arrays was further validated in bottled and pond water spiked with E. coli, exhibiting 87.5% and 80.4% inactivation efficiencies, respectively, within 30 min. Understanding these antibacterial mechanisms is not only of significance for research in this and related fields but also beneficial for potential application in various fields, e.g., biomedical and antifouling areas.

Biodetection using a ZnO nanorod-based microfluidic device with a concentration gradient generator

An effective microfluidic device with a concentration gradient generator for cancer biomarker detection is developed by integrating ZnO NR arrays into microchannels.

Fabrication of SiO2–ZnO NP/ZnO NR hybrid coated cotton fabrics: the effect of ZnO NR growth time on structural and UV protection characteristics

In the original published article, the figure 4f was wrongly processed with the same part of figure 5f.

Sonochemical synthesis and anchoring of zinc oxide on hemin-mediated multiwalled carbon nanotubes-cellulose nanocomposite for ultra-sensitive biosensing of H2O2.

In this work, the metal oxide and biopolymer nanocomposites on multiwalled carbon nanotubes (MWCNT) were prepared using a simple sonochemical method. The hexagonal nanorods of zinc oxide (ZnO NR) were synthesized by probe sonication (frequency=20kHz, amplitude=50) method and were integrated on ultrasonically functionalized MWCNT-cellulose nanocrystals (MWCNT-CNC) for the first time. The stable hemin bio-composites also were prepared using the bath sonication (37kHz of frequency, 150W of power) method, and was used for the selective and ultrasensitive electrochemical detection of H2O2. The UV-Vis spectroscopy studies confirmed the presence of native hemin on MWCNT-CNC/ZnO NR nanocomposite. Cyclic voltammetry studies revealed that an enhanced redox electrochemical behaviour of hemin was observed on hemin immobilised MWCNT-CNC/ZnO NR nanocomposite than that of other hemin modified electrodes. Also, the MWCNT-CNC/ZnO NR/hemin modified SPCE showed 2.3 folds higher electrocatalytic activity with a lower reduction potential (-0.2V) towards H2O2 than that of other investigated hemin modified electrodes including hemin/MWCNT and hemin/CNC-ZnO. The fabricated biosensor displayed a stable amperometric response (-0.2V vs Ag/AgCl) in the linear concentration of H2O2 ranging up to 4183.3µM with a lower detection limit of 4.0nM.

Synergistic effect of a cobalt dopant and Au nanoparticles on the photocatalytic activity of ZnO nanorods

The photocatalytic performance of zinc oxide nanorods (ZnO NRs) still needs improvement. In this regard, the addition of noble-metal nanoparticles (NPs) and doping with transition metals can be employed. In this study, nanocomposites of ZnO NR/Au and Co-doped ZnO NR/Au NPs were synthesized by ultrasonic spray pyrolysis and hydrothermal method and subsequently used as photocatalysts for the degradation of methylene blue. Results revealed that pure ZnO NRs exhibit a degradation rate of only 28.8%, while ZnO NR/Au NPs exhibit a degradation rate of 37.3%, and Co-doped ZnO NR/Au NPs exhibit the highest degradation rate of up to 46.5%. Based on these results, the presence of Au on the ZnO NR surface can enhance the photocatalytic activity due to its key role as an electron sink, which reduces the recombination rate of electrons and holes, while the incorporation of Co into ZnO NRs can also enhance the number of crystal defects, which can widen the visible-light absorption spectrum.

Cellular Stemness Maintenance of Human Adipose-Derived Stem Cells on ZnO Nanorod Arrays.

Ever-growing tissue regeneration and other stem cell therapies cause pressing need for large population of self-renewable stem cells. However, stem cells gradually lose their stemness after long-term in vitro cultivation. In this study, a ZnO nanorod (ZnO NR) array is used to maintain the stemness of human adipose-derived stem cells (hADSCs). The results prove that after culturing hADSCs on ZnO NRs for 3 weeks, the stemness genes and protein expression level are higher than that on culture plates and ZnO film. ZnO NRs can maintain stemness of hADSCs without inhibiting the cell proliferation and oriented differentiation capabilities. KLF4 (Kruppel-like factor 4) is a Zn2+ -binding gene that plays a vital role in cell proliferation and differentiation. Sustained Zn2+ release and the increased expression of KLF4 can be detected, suggesting that ZnO NRs have efficiently released Zn2+ for stemness maintenance. Taken together, the nanotopography of ZnO NRs and the Zn2+ release synergistically facilitate stemness maintenance. This study has provided a powerful tool for directing cell fate, maintaining stemness, and realizing the expansion of stem cells in vitro, which will open a new route for the manufacture of large populations of stem cells and fulfilling the growing demand for the cell therapy market.

Photocorrosion suppression and photoelectrochemical (PEC) enhancement of ZnO via hybridization with graphene nanosheets

Graphene-ZnO nanocomposites with different morphologies (nanoparticles and nanorods) were synthesized by alkali precipitation and solvothermal process. The influence of graphene nanosheets on photocatalytic and photoelectrochemical (PEC) activity of graphene-ZnO nanorods (ZnO/GNR) and graphene/ZnO nanoparticles (ZnO/GNP) was investigated. ZnO/GNR showed greatly increased photocatalytic degradation of methyl orange (MO): 2-, 2.5- and 3.5-fold higher under UV light and 1.6-, 4.7-, and 11-fold higher under visible light than that for ZnO/GNP, ZnO NR and ZnO NP, respectively. In addition, ZnO/GNR showed remarkable photocorrosion suppression (∼0.5%) compared to 10, 35 and 45% for ZnO/GNP, ZnO NR and ZnO NP, respectively. Furthermore, PEC results indicated a remarkable 6-fold enhancement photocurrent density for ZnO/GNR compared to ZnO NR. This enhancement is attributed to the crucial role of graphene in the electron transfer from ZnO NR into graphene sheets increasing the electron lifetime, leading to a minimized charge recombination.

Growth of highly uniform size-distribution ZnO NR arrays on sputtered ZnO thin film via hydrothermal with PMMA template assisted

This paper demonstrates a fabrication approach to control size distribution of zinc oxide nanorod arrays (ZnO NRAs) when using a polycrystalline seed layer. Through perfect matching between a physical confinement using a periodic PMMA template and a chemical confinement via hydrothermal method, highly ordered ZnO NRAs are accomplished. This matching relies on the restricted nucleation sites where the seed layer's grain size as well as number of grains along the template's aperture become dominant factors. In the experiment, various dimensions of periodic templates and precursor concentrations were carried on. The optimum condition shows single-ZnO NR arrays with good uniformity. Multiple rod array appears in the template with larger holes' dimension as it allows multiple nucleation sites to be formed. The effect of spacing between holes in the template is also included. The results demonstrate an effective and cost-effective way for tailoring uniformity of single ZnO NRAs on the polycrystalline seed layer.