Hydrothermal Growth Of ZnO Nanorods Research Articles

Enhanced superhydrophobicity of electrospun carbon nanofiber membranes by hydrothermal growth of ZnO nanorods for oil–water separation

Development of electrospun nanofiber membranes with the selective wettability characteristics for effectively separating oil–water mixtures is an extremely advisable strategy. In this study, a superhydrophobic electrospinning carbon nanofiber (F/ZnO/CNF) membrane was successfully prepared by electrospinning and in-situ growth of ZnO, and subsequent fluorination reaction with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS). Benefiting from the influence of needle-like nanostructure and low surface energy, the as-prepared F/ZnO/CNF membrane shows excellent superhydrophobicity. When the growth duration of ZnO is 3 h, the obtained F/ZnO/CNF-3 membrane possesses outstanding water contact angle (WCA, 159.7°) and splendid oil–water separation efficiency (>99 %). Meanwhile, due to its the superior environmental stability the obtained F/ZnO/CNF-3 membrane exhibits excellent low and high temperature resistance, and enhanced resistance to various organic solvents in the face of a series of harsh environments.

ZnO Nanorods Coated Single-Mode-Multimode-Single-Mode Optical Fiber Sensor for VOC Biomarker Detection.

This work demonstrated a ZnO-coated optical fiber sensor for the detection of a volatile organic compound (VOC) biomarker for diabetes for detecting isopropanol (IPA) markers. A coreless silica fiber (CSF) was connected to a single-mode fiber (SMF) at both ends to achieve a SMF–CSF–SMF structure. CSF is the sensing region where multimode interference (MMI) generates higher light interaction at the interface between the fiber and sensing medium, leading to enhanced sensitivity. Optimization of the CSF length was conducted numerically to attain the highest possible coupling efficiency at the output. Surface functionalization was achieved via hydrothermal growth of ZnO nanorods directly onto the CSF at low temperatures. The optical fiber-based sensor was successfully fabricated and tested with 20%, 40%, 60%, 80%, and 100% of IPA. The sensor response was recorded using an optical spectrometer and analyzed for sensor sensitivity. The fabricated sensor shows the potential to detect isopropanol with the sensitivity of 0.053 nm/%IPA vapor. Further improvement of the sensor sensitivity and selectivity is also proposed for future work.

Combining ZnO inverse opal and ZnO nanorods using ALD and hydrothermal growth

In this paper, we combine the atomic layer deposition synthesis method of inverse opal with the hydrothermal growth of nanorods. From 460 nm polystyrene nanospheres opal crystals were produced using vertical deposition on Si wafers. The opal templates were covered with ZnO by atomic layer deposition. High temperature annealing was used to remove the polystyrene nanospheres to obtain the inverse opal structure. For the hydrothermal growth of ZnO nanorods, two production routes were analysed: hydrothermal reaction before and after the removal of the template. The two paths produced two distinct structures, one with plate like formations and one with nanorods, respectively. Also, the sample modified by the hydrothermal growth after the annealing showed slight differences in optical properties compared to the regular inverse opal. Morphology, composition and structure of the samples were explored using SEM, EDX and XRD. Optical properties were investigated with reflectance UV–Vis spectroscopy. Thermal stability of the polystyrene opal was determined using TG.

Hydrothermal Growth of ZnO Nanorods for Use in Dye-Sensitized Solar Cells

Hydrothermal Growth of ZnO Nanorods for Use in Dye-Sensitized Solar Cells

Optimizing zinc oxide nanorods based DSSC employing different growth conditions and SnO coating

Effect of seed layer thickness, growth time and tin oxide coating was studied for optimized performance in ZnO nanorods (NRs) based Dye-sensitized solar cells (DSSCs). Three different seed layer thickness of 150 nm, 250 nm and 350 nm were used for hydrothermal growth of ZnO NRs varying the growth time from 12 to 20 h. Among all devices, cell fabricated employing ZnO NRs grown for 20 h using 150 nm thick seed layer yielded the highest power conversion efficiency (PCE) of 0.25%, with a short circuit current density (Jsc) of 1.549 mA/cm2, open circuit voltage (Voc) of 0.5 V and a fill factor of 32.68. A significant increase in short circuit current density was observed by employing tin oxide coating on zinc oxide nanorods based DSSCs compared to simple ZnO based DSSCs. This increase of Jsc is attributed to better electron transfer, increased dye loading, more charge carriers generation and lower recombination of charge carriers. The DSSC fabricated with SnO coated ZnO NRs also showed an increase in open circuit voltage and fill factor because of the higher conduction band edge of SnO as compared to ZnO. A maximum efficiency of 0.81% was achieved when seed layer thickness was kept at 150 nm, hydrothermal growth of ZnO NRs was continued for 20 h, and 2 h of SnO coating was performed followed by 350 °C annealing. An increase of 224%, 61.39% and 38% was observed for PCE, short circuit current density (Jsc) and open circuit voltage (Voc) respectively, compared to the device fabricated without SnO coating of ZnO NRs with the same seed layer thickness and growth time. Scanning electron microscopy was performed to visualize and understand function of tin oxide coating on zinc oxide nanorods used in dye-sensitized solar cell.

Selective growth of ZnO nanorods by thickness contrast in In-doped ZnO quantum dots seed layer

Selective growth of ZnO nanorods (NRs) have been demonstrated using thickness contrast in In-doped ZnO (IZO) quantum dot (QD) seed layer. The use of IZO QD as a seed layer has enabled the direct growth of ZnO NRs on soft substrates such as polyethylene terephthalate (PET) and polydimethylsiloxane (PDMS). Depending on the annealing temperature, the seed layers show different grain sizes: as the annealing temperature increases, the seed grain size also increases accordingly. Interestingly, the hydrothermal growth of ZnO NRs has been found to depend on the seed grain size: the larger grain seed sample shows earlier start of growth compared to smaller seed grain counterpart. The same growth behavior has been found in the growth of ZnO NRs on seed layers having different thickness, due again to the difference in seed grain size. To advantageously exploit the observed growth behavior, the IZO QDs seed layers have been patterned by soft lithographic technique, which led to the formation of alternating thin/thick region periodically. On this patterned seed surface, the thin regions showed earlier start of NRs growth compared to thick regions, enabling the spatially selective growth of ZnO NRs. When applied for acetone gas sensors, the selectively grown sample showed better performance than the non-selectively grown counterpart. The low resistance in air, due to increased amount of chemisorbed oxygen, has been found to be responsible for the inferior sensor performance with non-selectively grown sample.

ZnO NANORODS GROWN ON PLASTIC PVC SUBSTRATE FOR ENVIRONMENTAL APPLICATION

In this work, the hydrothermal growth of ZnO nanorods (NRs) on plastic PVC substrate is presented. It was shown that ZnO NRs with high density and high crystallinity can be successfully grown by implementing saturated nutrition solution of zinc nitrate hexahydrate (Zn[NO3]2·6H2O) and hexamethylenetetramine (C6H12N4) without the assistance of a seed layer. The morphologies of the ZnO nanorods investigated by scanning electron microscope (SEM) demonstrated hexagonal structures. The crystallinity of the ZnO NRs was studied by photoluminescence (PL) spectroscopy. The as-grown ZnO NRs were then utilized for photocatalytic degradation of methylene blue.

Seedless Hydrothermal Growth of ZnO Nanorods as a Promising Route for Flexible Tactile Sensors.

Hydrothermal growth of ZnO nanorods has been widely used for the development of tactile sensors, with the aid of ZnO seed layers, favoring the growth of dense and vertically aligned nanorods. However, seed layers represent an additional fabrication step in the sensor design. In this study, a seedless hydrothermal growth of ZnO nanorods was carried out on Au-coated Si and polyimide substrates. The effects of both the Au morphology and the growth temperature on the characteristics of the nanorods were investigated, finding that smaller Au grains produced tilted rods, while larger grains provided vertical rods. Highly dense and high-aspect-ratio nanorods with hexagonal prismatic shape were obtained at 75 °C and 85 °C, while pyramid-like rods were grown when the temperature was set to 95 °C. Finite-element simulations demonstrated that prismatic rods produce higher voltage responses than the pyramid-shaped ones. A tactile sensor, with an active area of 1 cm2, was fabricated on flexible polyimide substrate and embedding the nanorods forest in a polydimethylsiloxane matrix as a separation layer between the bottom and the top Au electrodes. The prototype showed clear responses upon applied loads of 2–4 N and vibrations over frequencies in the range of 20–800 Hz.

A flexible tactile sensor using seedless hydrothermal growth of ZnO nanorods on fabrics

A flexible and cost-effective electromechanical device for tactile sensing based on ZnO nanorods (ZnO NRs) grown on fabrics is developed. Sensing performance and the electromechanical properties of ethylcellulose/polyurethane-coated ZnO NRs on fabric substrates were tested by the LCR meter, force transducer, vibrator, and pulse analyzer. The peak-to-peak output voltage at an applied force of 21.5 N dropped considerably for the wool-, nylon-, and PP substrates and reached to the order of 3.84 mV, 1.8 mV and 4.1 mV, respectively. Furthermore, the frequency dependency of the dissipation factors revealed abrupt changes at low frequencies, while these changes were negligible at high frequencies.

Synthesis, growth mechanism and effect of sputtering pressure on 3D ZnO nanostructures with trunk-branch nanorods

Three-dimensional (3D) ZnO nanostructures, hierarchical nanorods with trunks and branches, were synthesized via a multi-step growth method. The ZnO trunk-branch nanorods are immobilized on glass substrates and their fabrication technologies include the deposition of ZnO seed crystals by magnetron sputtering and the hydrothermal growth of ZnO nanorods without any directing agents. The sputtering pressure for the deposition of ZnO seed crystals was varied and the corresponding effect on the morphology and microstructure of 3D ZnO nanostructures was characterized by various spectroscopic and microscopic techniques. The growth mechanism of ZnO trunk-branch nanorods was discussed and their optical property was also explored. The multi-level constructions of ZnO nanorods would benefit their photo-related functional applications.

Rapid Hydrothermal Growth of ZnO Nanorods on a Magnetron Sputtered Thick ZnO Seed Layer

In this work, we report rapid hydrothermal growth of ZnO nanorods on a magnetron sputtered thick ZnO seed layer. The ZnO seed layer on the glass substrarte is monocrystalline and formed by 600 °C annealing for 1 hour after magnetic sputtering. The morphology of the ZnO grain in the ZnO seed layer plays a critical role in the growing of the ZnO nanorods, and the slant ZnO grain results in the slant ZnO nanorod and connected ZnO nonrods. It is found that the average growth of the ZnO nanorods is ~75 nm/minute. The rapid grow rate may be owing to the monocrystallie and the pure water solution of the growth solution.

The Role of ALD-ZnO Seed Layers in the Growth of ZnO Nanorods for Hydrogen Sensing.

Hydrogen is one of the most important clean energy sources of the future. Because of its flammability, explosiveness, and flammability, it is important to develop a highly sensitive hydrogen sensor. Among many gas sensing materials, zinc oxide has excellent sensing properties and is therefore attracting attention. Effectively reducing the resistance of sensing materials and increasing the surface area of materials is an important issue to increase the sensitivity of gas sensing. Zinc oxide seed layers were prepared by atomic layer deposition (ALD) to facilitate the subsequent hydrothermal growth of ZnO nanorods. The nanorods are used as highly sensitive materials for sensing hydrogen due to their inherent properties as oxide semiconductors and their very high surface areas. The low resistance value of ALD-ZnO helps to transport electrons when sensing hydrogen gas and improves the sensitivity of hydrogen sensors. The large surface area of ZnO nanorods also provides lots of sites of gas adsorption which also increases the sensitivity of the hydrogen sensor. Our experimental results show that perfect crystallinity helped to reduce the electrical resistance of ALD-ZnO films. High areal nucleation density and sufficient inter-rod space were determining factors for efficient hydrogen sensing. The sensitivity increased with increasing hydrogen temperature, from 1.03 at 225 °C, to 1.32 at 380 °C after sensing 100 s in 10,000 ppm of hydrogen. We discuss in detail the properties of electrical conductivity, point defects, and crystal quality of ALD-ZnO films and their probable effects on the sensitivity of hydrogen sensing.

Lattice Transparency of Graphene.

Here, we demonstrated the transparency of graphene to the atomic arrangement of a substrate surface, i.e., the "lattice transparency" of graphene, by using hydrothermally grown ZnO nanorods as a model system. The growth behaviors of ZnO nanocrystals on graphene-coated and uncoated substrates with various crystal structures were investigated. The atomic arrangements of the nucleating ZnO nanocrystals exhibited a close match with those of the respective substrates despite the substrates being bound to the other side of the graphene. By using first-principles calculations based on density functional theory, we confirmed the energetic favorability of the nucleating phase following the atomic arrangement of the substrate even with the graphene layer present in between. In addition to transmitting information about the atomic lattice of the substrate, graphene also protected its surface. This dual role enabled the hydrothermal growth of ZnO nanorods on a Cu substrate, which otherwise dissolved in the reaction conditions when graphene was absent.

Flexible piezoelectric nanogenerators based on a transferred ZnO nanorod/Si micro-pillar array

Flexible piezoelectric nanogenerators (PNGs) based on a composite of ZnO nanorods (NRs) and an array of Si micro-pillars (MPs) are demonstrated by a transfer process. The flexible composite structure was fabricated by hydrothermal growth of ZnO NRs on an electrochemically etched Si MP array with various lengths followed by mechanically delaminating the Si MP arrays from the Si substrate after embedding them in a polydimethylsiloxane matrix. Because the Si MP arrays act as a supporter to connect the ZnO NRs electrically and mechanically, verified by capacitance measurement, the output voltage from the flexible PNGs increased systematically with the increased density ZnO NRs depending on the length of the Si MPs. The flexible PNGs showed 3.2 times higher output voltage with a small change in current with increasing Si MP length from 5 to 20 μm. The enhancement of the output voltage is due to the increased number of series-connected ZnO NRs and the beneficial effect of a ZnO NR/Si MP heterojunction on reducing free charge screening effects. The flexible PNGs can be attached on fingers as a wearable electrical power source or motion sensor.

A promising carbon fiber-based photocatalyst with hierarchical structure for dye degradation

To fabricate a novel photocatalyst, ZnO seeds were uniformly deposited on carbon fibersviaatomic layer deposition followed by hydrothermal growth of ZnO nanorods, then Pt nanoparticles were deposited by DC magnetron sputtering.

Microstructure-Dependent Visible-Light Driven Photoactivity of Sputtering-Assisted Synthesis of Sulfide-Based Visible-Light Sensitizer onto ZnO Nanorods.

The ZnO-CdS core-shell composite nanorods with CdS shell layer thicknesses of 5 and 20 nm were synthesized by combining the hydrothermal growth of ZnO nanorods with the sputtering thin-film deposition of CdS crystallites. The microstructures and optical properties of the ZnO-CdS nanorods were associated with the CdS shell layer thickness. A thicker CdS shell layer resulted in a rougher surface morphology, more crystal defects, and a broader optical absorbance edge in the ZnO-CdS rods. The ZnO-CdS (20 nm) nanorods thus engaged in more photoactivity in this study. When they were further subjected to a postannealing procedure in ambient Ar/H2, this resulted in the layer-like CdS shell layers being converted into the serrated CdS shell layers. By contrast, the ZnO-CdS nanorods conducted with the postannealing procedure exhibited superior photoactivity and photoelectrochemical performance; the substantial changes in the microstructures and optical properties of the composite nanorods following postannealing in this study might account for the observed results.

ZnO-nanorods/graphene heterostructure: a direct electron transfer glucose biosensor.

ZnO-nanorods/graphene heterostructure was synthesized by hydrothermal growth of ZnO nanorods on chemically reduced graphene (CRG) film. The hybrid structure was demonstrated as a biosensor, where direct electron transfer between glucose oxidase (GOD) and electrode was observed. The charge transfer was attributed to the ZnO nanorod wiring between the redox center of GOD and electrode, and the ZnO/graphene heterostructure facilitated the transport of electrons on the hybride electrode. The glucose sensor based on the GOD-ZnO/CRG/Pt electrode had a high sensitivity of 17.64 μA mM−1, which is higher than most of the previously reported values for direct electron transfer based glucose biosensors. Moreover, this biosensor is linearly proportional to the concentration of glucose in the range of 0.2–1.6 mM. The study revealed that the band structure of electrode could affect the detection of direct electron transfer of GOD, which would be helpful for the design of the biosensor electrodes in the future.

Role of hexamine: growth of multiarmed ZnO nanorods and evidence of merging due to lateral growth

The role of hexamine in the growth of 1D ZnO nanostructures, so far is only assumed, unpredictable and not well explained. Further, the role of hexamine in the growth of 1D ZnO nanostructure by hydrothermal method, especially at the higher concentrations (0.08 M and above) has not yet been well reported. The present study is designed to investigate the role of hexamine in lateral and vertical side growth of ZnO nanorods with different concentrations (0.08 M and above) of hexamine by keeping the concentration of zinc nitrate hexahydrate at 0.1 M. The influence of hexamine in the hydrothermal growth of ZnO nanorods is studied with various characterization tools. The results show that hexamine strongly influence the morphology of ZnO nanostructure and single rod structure transforming into multiarmed structure with increase in hexamine concentration. The growth mechanism of multiarmed ZnO nanorods with respect to hexamine is effectively investigated and discussed in detail from the basic nucleation theories. Lateral growth and merging of rods on the surface is evidenced at the higher concentration of hexamine.

Low-temperature seeding and hydrothermal growth of ZnO nanorod on poly(3,4-ethylene dioxythiophene):poly(styrene sulfonic acid)

This work reports a low-temperature seeding process for hydrothermal growth of ZnO nanorods on flexible polymeric materials. The process involved decomposition of zinc (II) amine complex below 100°C to form ZnO seeds, followed by hydrothermal growth using zinc nitrate hexahydrate and hexamethylenetetramine under 90°C. The method enabled the growth of ZnO nanorods on the polymeric film (e.g. PET) or the p-type conducting polymer poly(3,4-ethylene dioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) film. The UV response of the ZnO/PEDOT:PSS nanostructure was investigated.

Superhydrophobic and anti-reflective ZnO nanorod-coated FTO transparent conductive thin films prepared by a three-step method

A ZnO nanorod-coated FTO film was prepared by sputtering an AZO layer on FTO glass, thermal annealing of the AZO/FTO film, and hydrothermal growth of ZnO nanorods at 70 °C on the annealed AZO/FTO film using zinc foils as zinc source. Two other ZnO nanorod-coated FTO films were also prepared by hydrothermal growths of ZnO nanorods on the FTO glass and the unannealed AZO/FTO film respectively for comparison purpose. The results were observed in detail using X-ray diffraction, scanning electron microscopy, water contact/sliding angle measurement, spectrophotometry and four-point probe measurement. The ZnO nanorods on the annealed AZO/FTO film were found to exhibit denser distribution and better orientation than those on the FTO glass and the unannealed AZO/FTO film. As a result, the ZnO nanorod-coated annealed AZO/FTO film demonstrated superhydrophobicity, high transparency and low reflectance in the visible range. Also this film had the lowest sheet resistance of 4.0 Ω/sq, implying its good electrical conductivity. This investigation provides a valuable reference for developing multifunctional transparent conductive films.