ZnO Nanoflakes Research Articles

Access to nanocrystalline, uniform, and fine-grained Ni-P coating with improved anticorrosive action through the growth of ZnO nanostructures before the plating process

In this work, the mild steel surface was modified by the growth of ZnO nanoflakes through a feasible and scalable procedure. The modified surface was used for the coating by the electroless nickel (EN) plating, and the influence of this modification on the morphology, surface roughness, uniformity, the corrosion behavior of Ni-P coating, and also on the deposition rate of EN plating was studied. The SEM micrographs, especially backscatter images, disclosed that the matrix of Ni-P coating with the underneath of ZnO NSs possesses smaller grain size with more uniform distribution compared to the specimen without ZnO NSs. The AFM analysis affirmed the lower surface roughness of this sample. The results of the EIS measurements and the Tafel extrapolation method indicated that the corrosion resistance of this sample is approximately two times higher than that of the sample without zinc oxide (Rp ≈ 35,000 Ω cm2). The role of ZnO NSs in increasing the active nucleation density and the formation of uniform, compact, and fine-grained Ni-P deposit was discussed. Besides, the effects of ZnO NSs on generating scattering centers, restricting the electron transfer, strengthening the Ni-P matrix, and the consequent corrosion behavior, were investigated.

Development of Metal Oxides Heterostructure for Highly Selective CO2 Reduction to Methanol.

Carbon dioxide conversion into valuable chemicals using solar light considered an ideal goal in renewable energy studies. For the purpose of effective photocatalytic materials, a large number of strategies have been studied. Coupling of semiconductors is considered one of the best approaches to design a good photocatalyst for producing selective solar fuels. In this study, we fabricate ZnO/ Co(OH)2 model heterogeneous catalysts for CO2 reduction under visible light irradiation. Firstly, Three ZnO samples with different morphologies and surface area were fabricated by varying preparation methods. It is found that ZnO nanoflakes with a high ratio of {0002} facets possess a higher conversion rate yielding Methanol, Acetaldehyde, and Acetone as the major products of photocatalytic CO2 reduction in a continuous flow gas-phase reaction condition. The obtained ZnO nanoflakes were then treated to form the heterostructure of ZnO/Co(OH)2. When the mass ratio between hexagonal-phased ZnO and Co(OH)2 is varied, the composite catalyst shows selective methanol formation as a major product compared to pristine ZnO phases. The synthesized samples were characterized by means of a multi techniques approach involving powder X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray analysis, transmission electron microscopy, Photoluminescence, UV-Visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and surface area measurements. In conclusion, the results can not only provide the importance indication about the influence of {0002} facets of ZnO, but also demonstrated a strategy for the selective formation of hydrocarbons over the heterostructure semiconductors of ZnO/Co(OH)2 nanocomposites.

Microwave-assisted synthesis of ZnO nanoflakes: structural, optical and dielectric characterization

In this study, we produced ZnO nanoflakes (ZnO-Nfs) by using microwave-assisted techniques. The structural properties of ZnO-Nfs were analyzed by x-ray diffraction (XRD) technique, Raman scattering spectroscopy and field-emission scanning microscopy (FESEM). The Crystallite size (D) and lattice constants of ZnO-Nfs were calculated. The optical properties of ZnO-Nfs were investigated by using UV-visible diffuse reflectance spectrum and photoluminescence (PL) spectra. Also, dielectric constants of ZnO-Nfs were calculated as related to the refractive index (n) an extinction coefficient (k).

Controlled synthesis of CuO decorated defect enriched ZnO nanoflakes for improved sunlight-induced photocatalytic degradation of organic pollutants

We report synthesis and application of a unique heterojunction nanocomposite formed between copper nanoparticles (CNPs) and defect rich ZnO nanoflakes for application towards water remediation. Systemic variation in CNPs functionalization was seen to modulate the optical, structural and photocatalytic properties of the heterojunction, which were found to be well in accordance with the results from TEM, UV-DRS and EPR. The remediation ability of the heterojunction measured in terms of its photocatalytic ability was studied by degrading three different organic dye pollutants Rhodamine 6G (R6G), Methylene Blue (MB) and Methyl Orange (MO) using solar light (850 W/cm2) as the renewable excitation source. CNPs loading density was seen to follow a direct linear relationship to optical absorbance and band gap narrowing. The initial increase in photolytic efficiency is associated with improved visible light response and reduced band gap due to attachment of CNPs while reduction in activity was found to be associated with generation of self-recombination centres in CuO functionalization. Optimized CNP modified ZnO nanoflakes was able to decompose 10 µM of R6G, MB and MO dye solutions in 80, 40 and 60 min respectively.

Flexible Supercapacitor-Type Rectifier-free Self-Charging Power Unit Based on a Multifunctional Polyvinylidene Fluoride-ZnO-rGO Piezoelectric Matrix.

The development of an effective mechanical to electrical energy conversion device and its functional integration with an energy storage device for self-powered portable gadgets are cutting-edge research fields. However, the generated power and the mechanical stability of these integrated devices are still not efficient to power up portable electronics. We fabricated a rectifier-free piezoelectric nanogenerator (NG) integrated with a supercapacitor (SC). A multifunctional composite matrix was prepared by the incorporation of ultrathin (<10 nm) ZnO nanoflakes and reduced graphene oxide in polyvinylidene fluoride to enhance the piezoelectric output characteristics and mechanical stability of the device while minimizing the additional energy losses during the integration. The as-fabricated SC-based power unit through the energy conversion and storage processes showed a remarkable self-charging performance. We obtained the maximum output voltage, current density, and power density of about 44 V, 1000 nA cm-2, and 193.6 μW cm-2 under the applied mechanical force of 10 N, respectively. The self-charging behavior of the device showed that it can store 1.5 × 10-3 mC within 100 s without resorting to a rectifier. We obtained the total energy density of about 10.34 mW h kg-1 under palm impact. Our results present a step forward in the development of the NG and SC-based flexible and self-charging devices.

Shape-dependant photocatalytic and antimicrobial activity of ZnO nanostructures when conjugated to graphene quantum dots

Abstract To reduce the bandgap and e−/h+ pairs recombination, zinc oxide nanoflakes (ZnO-NFs) and zinc oxide nanorods (ZnO-NRs) were covalently linked to graphene oxide quantum dots (GQDs). Photocatalytic and antimicrobial activity of ZnO nanohybrids (ZnO-NFs@GQDs and ZnO-NRs@GQDs) were investigated. The formation of the distinct ZnO nanoflakes and ZnO nanorods shaped nanoparticles were evidenced by SEM. The bandgap decreased from 2.98 to 2.61 eV and 3.00–2.79 eV for ZnO-NFs@GQDs and ZnO-NRs@GQDs, respectively. Photoluminescence (PL) data showed a similar trend where a larger decrease was obtained for ZnO-NFs@GQDs. Photolysis ruled out adsorption mechanism for the removal of dye. Optical data and PL measurements supported photocatalytic findings that ZnO-NFs@GQDs performed better (80 %) than ZnO-NRs@GQDs (18 %). ZnO-NRs@GQDs however, showed greater bacterial inhibition when tested against E. coli, P. aeruginosa, B. cereus and S. aureus. The antimicrobial efficiency followed the order: ZnO-NFs

Enhancing gas-sensing property and sensing mechanism at molecule level of the hollow microspheres assembled with ZnO nanoflakes exposing {001} facets

The hollow microspheres assembled with ZnO nanoflakes exposing {001} facets have been successfully synthesized by annealing ZnS nanospheres at 550 °C for 2 h. Response of the hollow microspheres assembled from ZnO nanoflakes for ethanol, acetone, or triethylamine is significantly higher than hollow microspheres assembled from ZnO nanorod with dominant {100} facets. The exposed Zn-terminated (001) face is considered to be an active surface for gas sensing. Threefold coordinated Zn (Zn3c) atom with a dangling bond on the Zn-terminated (001) surface serves as a gas-sensing active atom, and thus a gas-sensing mechanism at atomic and molecular level is proposed. The concept of unsaturated Zn3c atoms as a gas-sensing active atoms will be useful for designing of high-performance sensing materials.

Study of structural, optical and electrochemical properties of ZnO nanostructures and ZnO-PANI nanocomposites

In this study, different morphologies like plate, flower, spherical particles and flakes of ZnO, which have been prepared by simple sol gel method using Sodium dodecyl Sulphate (SDS), Trisodium Citrate, and Cetyl trimethyl ammonium bromide (CTAB) as different stablizers have been reported. These products have been systematically investigated by UV-Visible spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), x-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Photoluminesecence (PL) techniques. ZnO-PANI nanocomposites films prepared on ITO, and characterzied by XRD and electrochemical techniques. Microstructural details like lattice parameters, lattice volume, crystalline size and crystal phase have been determined from reitveld refinement method of X-diffraction pattern. FESEM technique shows that ZnO nanostructures morphology can be changed from ZnO nanoplate like shape to ZnO nanoflowers assembled with nanorods, ZnO nanoflakes and ZnO spherical particles when Trisodium Citrate, CTAB and SDS used as additives, respectively. Photoluminescence technique shows that there is slight red shift in the UV region and blue shift in the visible region with the addition of surface active molecules to ZnO, with concomitant decrease in the relative intensity of emission peaks. This indicates that the defects in the ZnO structure have been decreased as CTAB, SDS and Trisodium citrate added into the precursor solution. Cyclic voltammetry results reveal that the current intensity of PANI enhances with the addition of ZnO and surfactant modified ZnO. The urea biosensor, fabricated using urease enzyme on the trisodium citrate assisted ZnO/PANI/ITO nanocomposites, exhibits linearity in the concentration range of 10–80 mg dl−1 with detection limit of 2 mg dl−1 and sensitivity 7.30 μA mM−1 cm−2.

Effect of Al thickness on the structural and ethanol vapor sensing performance of ZnO porous nanostructures prepared by microwave-assisted hydrothermal method

Highly porous ZnO nanoflakes were successfully prepared using a microwave-assisted hydrothermal method. The presence of aluminum changes the environment of the preparation reaction, which controlled the crystallographic orientation. The unique morphology and properties of ZnO nanoflakes may be due to the effect of microwave irradiation and the ambient condition. The approach is very simple and there is rapid growth of around 3 μm ZnO within 30 min. The mechanism of the construction of unique ZnO nanoflake growth using the present approach is proposed. Hence, the prospective performance of ethanol vapor sensing for the rapid growth of ZnO porous nanostructures was investigated.

Excellent antibacterial activities in the dark of ZnO nanoflakes with oxygen vacancies on exposed {21̄1̄0} facets

We report that the oxygen vacancies on exposed {21̄1̄0} facets are able to generate both ˙O−2 by single-electron transfer and O2−2 by two-electron transfer.

Highly sensitive and ultra-fast responsive ammonia gas sensor based on 2D ZnO nanoflakes

Detecting ammonia in ambient air with high sensitivity and ultra-fast responsivity is crucial given its implications on human health. The response of such sensors should also be reversible to use them for continuous monitoring. Herein, we report a reversible ammonia (NH3) sensor based on 2D ZnO nanoflakes at 250 °C. The sensor exhibited a maximum response of 80% and sub-15 s response and recovery times upon exposure of 0.6–3 ppm NH3. Further, we formulated and corrected the baseline drift with a simple and straightforward baseline manipulation method. The excellent response of the sensor indicates the feasibility of using it in diverse applications where high sensitivity and rapid response are crucial.

SiO2 -Coated ZnO Nanoflakes Decorated with Ag Nanoparticles for Photocatalytic Water Oxidation.

Many strategies have been adopted to improve the photoinduced features of zinc oxide nanostructures for different application fields. In this work, zinc oxide has been synthesised and decorated by plasmonic metal nanoparticles to enhance its photocatalytic activity in the visible range. Furthermore, an insulating layer of SiO2 has been grown between the surface of zinc oxide nanoflakes and silver nanoparticles. A synthetic procedure that allows the accurate modulation of the insulating layer thickness in the range 5-40 nm has been developed. Evidences highlight the crucial role of the SiO2 layer in dramatically increasing photocatalytic water oxidation promoted by the nanostructure under both UV and visible illumination. An ideal thickness value of about 10 nm has been demonstrated to guarantee the plasmon-induced resonance energy-transfer process and to quench the Förster resonance energy-transfer mechanism; thus, optimising the local surface plasmon resonance effect and water oxidation properties.

Acoustics and thermal studies of conventional heat transfer fluids mixed with ZnO nano flakes at different temperatures

The present investigation is mainly focused upon the effect of adding zinc oxide nano particles in the conventional heat transfer fluid involving the mixture of ethylene glycol & water (EG-water). Efforts have been made to synthesize zinc oxide nano particles by precipitation technique and to blend with EG-water to prepare nanofluids using ultrasonication. From the characterization, the shapes of the particles were found to be agglomerated nano flakes. The ultrasonic velocity and transport properties have been measured to characterize the nanofluids and they also shed light on the molecular environment of the dispersed phase at different temperatures. The dynamic viscosity shows the nanofluids to be non-Newtonian fluids at very less shear rate. In addition, the stability of the nanofluid is being interpreted from UV-visible study.

Tuning the defects and luminescence of ZnO:(Er, Sm) nanoflakes for application in organic wastewater treatment

A series of ZnO nanoflakes modified with rare earth ions of Er and Sm were prepared by a simple chemical solution deposition approach. It was found that the doping content of rare-earth ions was dominant for the defects in the nanoflakes and the ability of photocatalytic degradation for rhodamine B (RhB). The ZnO:(Er, Sm) nanoflakes exhibited a superior photocatalytic activity compared to undoped ZnO mainly due to the longer lifetime of photogenerated electrons-hole pairs in the process of photocatalytic reaction, and Zn0.98Sm0.01Er0.01O nanoflakes could degrade 96.5% RhB within 60 min under UV light irradiation. PL results provided a strong evidence for the existence of VO defect, which was also found to be responsive for the enhanced photocatalytic activity of ZnO:(Er, Sm) nanoflakes. And the peaks at 515 nm and 550 nm could be attributed to the transitions of $$^{2} H_{11/2} \to^{4} I_{15/2}$$ and $$^{4} S_{3/2} \to^{4} I_{15/2}$$ from Er3+ ions, indicating the realization of green luminescence.

Low-Temperature Solution Process of Al-Doped ZnO Nano-flakes for Flexible Perovskite Solar Cells

Herein we report on the selective synthesis and direct growth of nanostructures using an aqueous chemical growth route. Specifically, Al-doped ZnO (AZO) nanoflakes (NFs) are vertically grown on indium tin oxide (ITO) coated flexible polyethylene terephthalate (PET) sheets at low temperature and ambient environment. The morphological, optical, and electrical properties of the NFs are investigated as a function of the Al content. Furthermore, these AZO-NFs are integrated into perovskite solar devices as the electron transport layer (ETL) and the fabricated devices are tested for photovoltaic performance. It was determined that the doping of AZO-NFs significantly increases the performance metrics of the solar cells, mainly by increasing the short-circuit current of the devices. The observed enhancement is primarily attributed to the improved conductivity of the doped AZO-NF, which facilitates charge separation and reduces recombination. Further, our flexible solar cells fabricated through this low temperature process demonstrate an acceptable reproducibility and stability when exposed to a mechanical bending test. Keywords: Solution process, Perovskite solar cells, ZnO nanoflakes

Self-assembly of free-standing hybrid film based on graphene and zinc oxide nanoflakes for high-performance supercapacitors

A free-standing hybrid film combining graphene and zinc oxide nanoflakes used as electrode materials was prepared by facile filtration self-assembly and thermal reduction process. The as-prepared ZnO nanoflakes were inserted into the graphene sheets to form unique layer-layer structure. The hybrid film can be directly employed as binder-free and self-supported electrode material for supercapacitors (SCs). The max specific capacitance of fabricated zinc oxide nanoflakes/reduced graphene oxide (ZnO/rGO) SCs is as high as 167.2 F g−1 at a scan rate of 5 mV s−1, which is nearly 50% higher than pure rGO (111.4 F g−1) and more than twice as much as ZnO nanoflakes (71.1 F g−1). The enhanced electrochemical performance could be due to the efficient utilization of electroactive ZnO nanoflakes and high conductive graphene sheets network and the good synergistic effect between them. The free-standing hybrid film also exhibits an excellent cycling capability, retention of the initial capacity over 90% after 2000 cycles. The EIS analysis of the hybrids showed low electrical resistance, improving ion diffusion capacity and surface charge transfer performance of the working electrode. It holds a potential for high performance electrochemical energy storage applications.

Decorating ZnO nanoflakes on carbon cloth: Free-standing, highly stable lithium-ion battery anodes

Abstract A facile chemical bath deposition method to grow 10-nm-thick ZnO nanoflakes (NFs) on carbon cloth (CC) was developed; further, free-standing, flexible lithium-ion -battery (LIB) anodes with good electrical contact between current collector and the active substance were prepared. The as-prepared ZnO NFs/CC-based LIB anodes showed a high specific capacity of 1754 mAh g−1 at a current density of 0.1 A g−1, a capacity retention of almost 52.9% at a current density of 2 A g−1, as well as high rate capability. Moreover, the anodes demonstrated a high capacity with reversiblity of approximately 1650 mAh g−1 and only 6% capacity fading at a current density of 0.1 A g−1, even after 100 cycles. These results imply that the synthesized, unique ZnO NFs/CC nanostructures can be employed as high-efficiency anode materials for flexible LIBs.

Synthesis and characterization of ZnO nanoflakes anchored carbon nanoplates for antioxidant and anticancer activity in MCF7 cell lines

ZnO nanoparticles with flakes-like structures were synthesized by simple wet chemical route using triethanolamine as a mild base. The well distributed ZnO nanoflakes onto carbon nanoplates (ZnO/C) were prepared by wet impregnation method. The crystalline structure and purity of the synthesized samples was inspected using XRD. The shape, structural morphology and elemental composition analysis was studied using FESEM and EDS. The probable anticancer activity of the synthesized samples was studied through their activity on human breast cancer MCF7 cell line. Exposure of breast cancer cells to ZnO and ZnO/C resulted in a dose dependent loss of cell viability, and the characteristic apoptotic features such as early and late apoptosis by dual staining. The results exhibited an enhanced antioxidant activity in the ZnO/C treated cells. This present study demonstrated that the ZnO and ZnO/C can be suggested as compounds with potential activity to induce apoptosis probable anticancer activity agents.

Facile synthesis of novel ZnO/Nd-doped BiOBr composites with boosted visible light photocatalytic degradation of phenol

Novel ZnO/Nd-BiOBr composites were facilely synthesized via a surfactant-free chemical approach. The ZnO nanoflakes were loaded on the surface of Nd-BiOBr nanosheets with intimately contact. The synthesized ZnO/Nd-BiOBr demonstrated significantly higher visible light photocatalytic degradation of phenol compared to those of ZnO, BiOBr and Nd-BiOBr. The enhanced photocatalytic activity of ZnO/Nd-BiOBr was attributed to the effective separation of photogenerated electron-hole in the heterojunction structure as proven via the photoluminescence spectra. In addition, the ZnO/Nd-BiOBr showed good stability in phenol degradation for four irradiation cycles. The radical trapping experiments indicated that the hydroxyl radicals played key role in the photodegradation process.

SiO2 shell on ZnO nanoflake arrays for UV-durable superhydrophobicity on Al substrate

ZnO nanoflaker arrays were fabricated on Al substrates by hydrothermal route at the temperature of 90 °C. Then the arrays were coated with SiO2 film by pulsed laser deposition (PLD) process with different deposition time, and finally hydrophobized with hexadecyltrimethoxysilane (HDTM). It is found that the SiO2 film have little effect on the superhydrophobic property of ZnO nanoflaker arrays. However, it has greatly improved the UV-durability of the superhydrophobicity of ZnO nanoflaker arrays. The water contact angles were almost unchanged even after UV exposure for 40 h when the deposition time is about 10 min. Thus, the SiO2/ZnO/Al structure his paper may provide an effective and simple to design UV-durable superhydrophobic surface.