ZnO Nanosheets Research Articles

Bimetallic CuPd alloy nanoparticles decorated ZnO nanosheets with enhanced photocatalytic degradation of methyl orange dye

Photocatalytic technology is widely explored as a promising alternative for water treatments. However, low photocatalytic efficiency and selectivity usually limit its practical application. Herein, we develop the synthesis of two-dimensional zinc oxide (ZnO) nanosheets decorated with copper (Cu)-palladium (Pd) bimetallic nanoparticles (NPs) for the degradation of organic dyes in an aqueous solution. Compared to pristine ZnO nanosheets, the prepared CuPd/ZnO composites exhibited superior performance for the photocatalytic degradation of organic dyes under visible-light irradiation. The remarkable improvement of degradation activity was attributable to the enhanced separation and transfer efficiency of photogenerated charge carriers. The highest catalytic efficiency of CuPd/ZnO nanocomposite with the CuPd content of 0.5 wt% exhibited 95.3% removal of methyl orange (MO) (40 mg/L) within 45 min. From the experimental data, we believe this study provides a new avenue for the design and fabrication of high-performance photocatalysts capable of water treatments.

Construction of hierarchical Tourmaline@ZnO/MWCNT micro-nanostructured composite and its conductometric gas sensibility for N-butanol detection

Modification of traditional metal oxides to prepare gas sensors with excellent response and high selectivity for monitoring air pollution, is a pivotal indicator for the development of gas sensing technologies. In this research, the core-shell Tourmaline@ZnO/MWCNT micro-nanostructured composite was successfully constructed and prepared by the uniform co-precipitation and hydrothermal methods, which effectively achieved the high sensitivity to n-butanol. The structure, morphology and surface electron valence state were characterized by employing important analytical techniques. With tourmaline as the inner-core and MWCNT-interspersed ZnO nanosheets as the outer-shell, the uniquely hierarchical micro-nanostructure covered a larger specific surface area, which provided more active sites during the reaction. Meanwhile, the performance assessments demonstrated that the proposed micro-nano structure exhibited exceptional gas-sensing properties, while Tourmaline@ZnO/ 0.9%MWCNT sensor reaching the highest response value to 185.8–100 ppm n-butanol far exceeding other detected gases, additionally with a faster response-recovery time. The presence of tourmaline and the interspersion of MWCNT played a synergistic effect on the enhancement of the properties for ZnO-based gas sensors, which brought about a beneficial impact on the carrier transport. This technical strategy should be of certain significance in the intelligent preparation and extensive application of high-performance sensing devices in the future.

Superhydrophobic surface based on micro/nano structured ZnO nanosheets for high-efficiency anticorrosion

Superhydrophobic surface based on micro/nano structured ZnO nanosheets for high-efficiency anticorrosion

Surface defect-rich ZnO nanostructures with high yellow-orange luminescence

ZnO nanostructures such as nanoislands, nanosheets, microflowers and nanoparticles were obtained successfully using a facile and rapid solution route employing low temperatures and reduced molar concentrations from precursor without using any surfactant agent or additional procedures. In this route, we use ZnCl2 as precursor ranging from 0.05 to 0.4 M and two hydrothermal times (2 and 4 h) to obtain different ZnO morphologies. According to SEM micrographs, the morphology of ZnO nanostructures showed a strong dependence on the ZnCl2 concentration and hydrothermal synthesis time. ZnO microflowers were obtained at 0.05 M during 2 h, while ZnO nanoislands, nanoparticles and nanosheets were observed at 0.05, 0.2 and 0.4 M, respectively, in 4 h. X-Ray diffraction and Raman results showed the wurtzite-type ZnO structure and good crystallinity in all cases. In addition, both techniques confirmed the best crystalline quality in ZnO nanoparticles followed by ZnO nanosheets. Finally, according to photoluminescence measurements, all samples exhibit a high yellow-orange emission, associated to a large number of surface defect states, such as oxygen and zinc interstitials. The largest amount of zinc interstitials and zinc vacancies were observed in ZnO nanoislands, while ZnO microflowers have the highest visible emission (followed by ZnO nanoparticles) which in turn, offered the lowest excitonic recombination from the conduction band to the valence band, which may result in a higher photocatalytic efficiency.

Z‐scheme CuSbS2/ZnO Heterojunction for Enhanced Photocatalytic Degradation of RhB

AbstractThe heterojunction structure photocatalysts are very promising for photocatalytic degradation dyes to resolve the organic industrial wastewater. In this work, an effective and solar light‐driven Z‐scheme heterojunction photocatalyst CAS/ZnO was prepared by two steps microwave irradiation method. The ZnO nanosheets were successfully compounded with CAS tetragonal particles aggregate. As the ZnO concentration increased, the absorbance decreased but the specific surface area increased. Rhodamine B (RhB) was tested for photodegradation by photocatalysts under a solar simulation in 120 min, and 3 M displayed the highest degradation rate (100 %), highest rate constant (0.021 min−1) and optimum stability. Furthermore, the main reactive species were superoxide radicals (O2−.) and hydroxyl radicals (HO⋅). Also, mechanism of the Z‐scheme migration of photon‐generated carrier and photocatalytic degradation was proposed. This paper provides a new Z‐scheme heterojunction CAS/ZnO photocatalyst for the treatment of organic pollutants.

Significant butanol gas sensor based on unique Bi2MoO6 porous microspheres and ZnO nanosheets composite nanomaterials

The heterostructure of metal oxide and other materials is one of the important ways for the development of electronic devices. The Bi 2 MoO 6 (BMO)/ZnO composites were synthesized by secondary hydrothermal method. The morphology and crystal structure of the compound were characterized by scanning electron microscopy, EDS mapping, X-ray photoelectron spectroscopy, transmission electron microscopy, nitrogen physical adsorption and X-ray diffraction. The synthesis technology and gas sensitivity of BMO and BMO/ZnO composites were discussed. The results showed that BMO and BMO/ZnO had better butanol gas sensitivity, faster response rate, lower working temperature, and good stability. Compared with methanol, benzene, methyl alcohol, ethanol, and acetone, BMO/ZnO sensor showed good selectivity to butanol at 270 ℃. The response time and recovery time for 100 ppm butanol were about 6 s and 33 s, respectively, the response value up to 128. The n-n type BMO/ZnO composites with unique microstructure has abundant diffusion channels, and the research work provides a valuable reference for the low-cost preparation of high-performance butanol sensors. The energy band, potential barrier and charge transfer of BMO/ZnO composites are discussed, and the optimization of their gas sensitivity is analyzed in detail. • The three-dimensional porous nanospheres Bi 2 MoO 6 were successfully synthesized. • The Bi 2 MoO 6 /ZnO composite were synthesized by hydrothermal method. • The Bi 2 MoO 6 /ZnO composite were employed as gas sensor for the detection of butanol gas.

Effect of iron doping concentration on the structure and photocatalytic activity of ZnO nanosheets under visible light irradiation

Undoped and Fe-doped ZnO nanosheets have been successfully synthesized by hydrothermal method using zinc acetate as the source of Zn2+, iron(III) nitrate as the doping source, urea as media to control the solution pH and polyethylene glycol as structure-directing agents. The obtained materials were characterized by means of XRD, TEM, BET, FT-IR and UV-Vis-DRS. The results show that ZnO has a hexagonal wurtzite structure and that the Fe3+ ions were well incorporated into the ZnO nanosheets crystal lattice. As the Fe/Zn molar ratios increased from 0.05% to 0.1% results in increased absorption in the visible region of the spectrum, a slightly decreased optical band gap and increased photocatalytic activity in comparison with the undoped ZnO. The photocatalytic activity was evaluated based on photodegradation of methylene blue (MB) in aqueous solutions under visible light irradiation. The optimum Fe doping at the molar ratios of Fe/Zn = 0.1% showed the highest photocatalytic activity and was 2.19 times higher than that of undoped ZnO. The kinetic studies showed the decomposition of MB followed pseudo first-order kinetics with the rate constant were determined kapp = 7.33×10-2 min−1.

Acoustofluidic bubble-driven micromixers for the rational engineering of multifunctional ZnO nanoarray

Acoustofluidics that combines acoustics with microfluidics represents an emerging and promising technology for the efficient mixing of fluids and synthesis of functional nanomaterials. However, it remains a great challenge to the controllable synthesis of three-dimensional functional nanostructures in a confined space. Herein, we introduce a robust acoustofluidic bubble-driven micromixer for the controllable synthesis of functional nanoarray inside the glass capillary toward efficient photodegradation and metal ion enrichment. The acoustofluidic micromixer functions with microbubbles-induced acoustic streaming from arrow-patterned microchannels. The morphology, density, and size of ZnO nanorods and nanosheets array can be precisely adjusted by reactant type, seeding phase, and reaction time. ZnO nanorod array exhibits approximately 90% degradation efficiency of R6G even after ten cycles, which are significantly better than ZnO nanosheet array and blank control groups. Enrichment tests of heavy metal ions show that ZnO nanoarray performs better enrichment performance of Cu2+ than that of Ag+. In addition, both photodegradation and enrichment capabilities can be well regulated by tuning the flow rates (i.e., the residence time). These findings provide important guidelines for the rational design of functional nanomaterials and shed new light on the fabrication of advanced lab-on-a-chip devices.

Controllable growth of single-crystalline zinc oxide nanosheets under ambient condition toward ammonia sensing with ultrahigh selectivity and sensitivity

To date, the synthesis of crystalline ZnO nanostructures was often performed under high temperatures and/or high pressures with tiny output, which limits their commercial applications. Herein, we report the progress on synthesizing single-crystalline ZnO nanosheets under ambient conditions (i.e., room temperature (RT) and atmospheric pressure) based on a sonochemistry strategy. Furthermore, their controllable growth is accomplished by adjusting the pH values of solutions, enabling the tailored crystal growth habits on the polar-charged faces of ZnO along c-axis. As a proof of concept for their potential applications, the ZnO nanosheets exhibit highly efficient performance for sensing ammonia at RT, with ultrahigh sensitivity (S = 610 at 100 ppm), excellent selectivity, rapid detection (response time/recover time = 70 s/4 s), and outstanding detection limit down to 0.5 ppm, superior to those of all pure ZnO nanostructures and most ZnO-based composite counterparts ever reported. The present work might open a door for controllable production of ZnO nanostructures under mild conditions, and facilitate the exploration of modern gas sensors for detecting gaseous molecules at RT, which underscores their potential toward practical applications in opto-electronic nanodevices.

Achieving efficient photocatalytic uranium extraction within a record short period of 3 min by Up-conversion erbium doped ZnO nanosheets

As an important strategic resource and environmental pollutant, uranium has high toxicity and economic value. Photocatalytic reduction of soluble hexavalent uranium (U(VI)) is a green and economic method to achieve uranium extraction, whereas the reported photocatalyst commonly requires a long period of > 1 h to reach a high extraction efficiency (>90%). Herein, we reported the ultrafast photocatalytic uranium extraction by up-conversion Er doped ZnO nanosheets. In the initial U(VI) concentration of 200 mg/L, the Er doped ZnO with 4% doping level (Er0.04-ZnO) nanosheets achieved 91.8% within 3 min, which was at least a magnitude shorter relative to ever-reported materials. The Er0.04-ZnO nanosheets reached a high removal efficiency of 96.1% in 10 min, with a considerable U(VI) extraction capacity of 3036 mg/g. The mechanistic study showed that the Er doping induced the up-conversion properties and increases the carrier density, thus enhancing the light adsorption and accelerating the U(VI) extraction.

Synthesis of Boron-Doped Zinc Oxide Nanosheets by Using Phyllanthus Emblica Leaf Extract: A Sustainable Environmental Applications.

The use of Phyllanthus emblica (gooseberry) leaf extract to synthesize Boron-doped zinc oxide nanosheets (B-doped ZnO-NSs) is deliberated in this article. Scanning electron microscopy (SEM) shows a network of synthesized nanosheets randomly aligned side by side in a B-doped ZnO (15 wt% B) sample. The thickness of B-doped ZnO-NSs is in the range of 20–80 nm. B-doped ZnO-NSs were tested against both gram-positive and gram-negative bacterial strains including Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumonia, and Escherichia coli. Against gram-negative bacterium (K. pneumonia and E. coli), B-doped ZnO displays enhanced antibacterial activity with 26 and 24 mm of inhibition zone, respectively. The mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), mean free path (MFP), half-value layer (HVL), and tenth value layer (TVL) of B-doped ZnO were investigated as aspects linked to radiation shielding. These observations were carried out by using a PTW® electron detector and VARIAN® irradiation with 6 MeV electrons. The results of these experiments can be used to learn more about the radiation shielding properties of B-doped ZnO nanostructures.

Correction to Effectively Tuning the Ratio of CO and H2 into Syngas through CO2 Electrochemical Reduction over a Wide Potential Range on a ZnO Nanosheet via Ni Doping

Correction to Effectively Tuning the Ratio of CO and H₂ into Syngas through CO₂ Electrochemical Reduction over a Wide Potential Range on a ZnO Nanosheet via Ni Doping

Construction of 0D/2D Schottky Heterojunctions of ZnO and Ti3C2 Nanosheets with the Enriched Transfer of Interfacial Charges for Photocatalytic Hydrogen Evolution.

The development of cost-effective co-catalysts of high photocatalytic activity and recyclability is still a challenge in the energy transformation domain. In this study, 0D/2D Schottky heterojunctions, consisting of 0D ZnO and 2D Ti3C2, were successfully synthesized by the electrostatic self-assembling of ZnO nanoparticles on Ti3C2 nanosheets. In constructing these heterojunctions, Ti3C2 nanosheets acted as a co-catalyst for enhancing the transfer of excitons and their separation to support the photocatalytic response of ZnO. The as-prepared ZnO/Ti3C2 composites demonstrate an abbreviated charge transit channel, a huge interfacial contact area and the interfacial electrons’ transport potential. The extended optical response and large reactive area of the ZnO/Ti3C2 composite promoted the formation of excitons and reactive sites on the photocatalyst’s surface. The ZnO/Ti3C2 Schottky heterojunction showed significantly high photocatalytic activity for hydrogen production from a water–ethanol solution under the light illumination in the visible region. The hydrogen evolution overoptimized the ZnO/Ti3C2 composition with 30 wt.% of Ti3C2, which was eight times higher than the pristine ZnO. These findings can be helpful in developing 0D/2D heterojunction systems for photocatalytic applications by utilizing Ti3C2 as a low-cost co-catalyst.

Experimental investigations to enhance the tribological behaviour of biodegradable oil by using manganese doped ZnO/FMWCNTs nanomaterials as lubricant additive

A novel binary hybrid nanomaterial of functionalized multi-walled carbon nanotubes (FMWCNTs) anchored on the surface of manganese doped zinc oxide nanosheets Mn0.10ZnO0.90 (MnZnO) were synthesized by using simple hydrothermal method. Further, the nanomaterials such as zinc oxide (ZnO), functionalized multiwalled carbon nanotubes (FMWCNTs) and ZnO/FMWCNTs hybrid nanomaterials have also been considered to evaluate the influence of doping of manganese in ZnO nanosheets on the tribological properties. The individual nanomaterials and synthesized hybrid nanomaterials were characterized by employing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), Thermo gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) techniques. The tribological performances of ZnO nanoparticles, FMWCNTs, ZnO/FMWCNTs and MnZnO/FMWCNTs hybrid nanomaterials dispersed in castor oil were investigated by a reciprocating ball on disk tribo tester. The castor oil with optimum concentration of 0.10 wt% MnZnO/FMWCNTs hybrid nanomaterials exhibited the superior tribological performance than the castor oil, ZnO, FMWCNTs and ZnO/FMWCNTs hybrid nanomaterial additives and reduced the coefficient of friction and wear volume by 26.21 % and 89.09 % respectively. The outstanding lubricating behaviour of MnZnO/FMWCNTs hybrid nanomaterial are corresponds to the synergistic mechanism of Mn doped ZnO nanosheets and FMWCNTs and formation of boundary film on the frictional surface. The surface characteristics and chemical composition of the worn bronze specimen lubricated with various nanomaterial additives have been examined using FESEM, EDS, optical profilometer and X-ray photoelectron spectroscopy.

Detection of L-Aspartic Acid with Ag-Doped ZnO Nanosheets Using Differential Pulse Voltammetry.

Here, a sensitive voltametric electrochemical sensor probe was fabricated to reliably trace the detection of L-aspartic acid in phosphate-buffered medium using a glassy carbon electrode (GCE) layered with a film of wet-chemically prepared Ag2O-doped ZnO nanosheets (NSs). EDS, FESEM, XPS, and X-ray diffraction analyses were implemented as characterizing tools of prepared NSs to confirm the structural and compositional morphology, binding energies of existing atoms, and the crystallinity of synthesized NSs. The differential pulse voltammetry (DPV) was applied to the trace detection of L-aspartic acid, and exhibited a wide detection range of 15.0~105.0 µM, a limit of detection (3.5 ± 0.15 µM), and good sensitivity (0.2689 µA µM−1 cm−2). Besides these the precious reproducibility, stability, and efficient responses were perceived from the voltametric analysis of aspartic acid. Moreover, the proposed aspartic acid was subjected to experiments to potentially detect aspartic acid in real biological samples. Therefore, the development of an enzyme-free sensor by applying this method will be a smart technical approach in the near future.

Highly sensitive and selective acetone gas sensors based on modified ZnO nanomaterials

In this work, Fe-doped ZnO (Fe–ZnO) porous nanosheets gas sensors were fabricated to detect acetone gas. The pure and 0.5, 1, 3 mol% Fe–ZnO nanosheets were synthesized through a hydrothermal method. The crystalline structure, morphology, and composition were identified by XRD, SEM, TEM, BET, and XPS. At the optimal working temperature of 365 °C, the 0.5% Fe–ZnO sensor to 100 ppm acetone gas can reach the maximum response of 105.7, which is 3.68 times higher than that of the pure ZnO device. Meanwhile, it also shows a response of 2.3 at the low detecting limit of 1 ppm, indicating its good response at low gas concentrations. The sensor exhibits well repeatability and selectivity. The improvement in gas-sensitive performance is related to the reduction in the bandgap and the increase in oxygen vacancies of the material after doping. All experimental results show that Fe–ZnO porous flake particles have excellent potential for fabricating efficient acetone sensing materials.

Synthesis of the Porous ZnO Nanosheets and TiO2/ZnO/FTO Composite Films by a Low-Temperature Hydrothermal Method and Their Applications in Photocatalysis and Electrochromism

In this paper, porous zinc oxide (ZnO) nanosheets were successfully prepared by a simple low-temperature hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) tests showed that the synthesized product was ZnO with porous sheet structure. The diameter of porous nanosheets was about 100 nm and the thickness was about 8 nm. As a photocatalyst, the degradation efficiencies of porous ZnO nanosheets for methyl orange (MO), methylene blue (MB) and Rhodamine B (RhB) were 97.5%, 99% and 96.8%, respectively. In addition, the degradation efficiency of ZnO for mixed dyes (Mo, MB and RhB) was satisfactory, reaching 97.7%. The photocatalytic stability of MB was further tested and remained at 99% after 20 cycles. In the experiment, ZnO/FTO (fluorine-doped tin oxide) composites were prepared by using ZnO as the conductive layer. Titanium dioxide (TiO2) was deposited on the surface of ZnO/FTO by electrodeposition, so as to obtain a TiO2/ZnO/FTO composite. By studying the electrochromic properties of this composite, it was found that the TiO2/ZnO/FTO composite shows a large light modulation range (55% at 1000 nm) and excellent cycle stability (96.6% at 200 cycles). The main reason for the excellent electrochromic properties may be the synergistic effect between the porous structure and the polymetallic oxides. This study is helpful to improve the photocatalytic efficiency and cycling stability of metal oxides, improve the transmittance of thin films and provide a new strategy for the preparation of ZnO composite materials with excellent photocatalytic and electrochromic properties.

Ratiometric optical temperature sensing based on greenish-white light emitting ZnO nanosheets and rhodamine 6G composite

In this report, the composites of ZnO nanosheets (NS) and rhodamine 6G (Rh6G) dye were prepared for possible exploration of ratiometric temperature sensing performances. Intense greenish-white color emissions are observed due to the contribution of well-separated emission bands of ZnO (cyan-green) and Rh6G (orange-red). The temperature-dependent photoluminescence measurement in the 83-493 K range with 355 nm excitation shows that the emission intensity of the two bands decreases gradually with an increase in the temperature. A composition-dependent sensitivity is observed with the maximum relative sensitivity of 0.87 % K−1 for the lower Rh6G content case. The individual ZnO NS and Rh6G also show a similar trend in the temperature dependency as that of the composites. The composites exhibit high stability for continuous heating and cooling cycles at 473 and 83 K. Hence the ZnO+Rh6G composites can be used as a self-referencing optical temperature probe for stable wide range sensing applications.

Defect‐Assisted Electron Tunneling for Photoelectrochemical CO2 Reduction to Ethanol at Low Overpotentials

AbstractA Si/ZnO/Cu2O p‐n‐p heterojunction potential well with electron tunnels is fabricated for selective photoelectrochemical CO2 reduction to ethanol. This heterojunction is formed by growing n‐type ZnO nanosheets between defect‐rich p‐type Cu2O nanoparticles and nanoporous p‐type Si. Due to the existence of this potential well, the photogenerated electrons are trapped and accumulate inside n‐ZnO at low biases with the assistance of a ≈0.6 V built‐in potential, and escape into the Cu2O defect band. Under simulated sunlight, the Si/ZnO/Cu2O photocathode exhibits an onset potential of 0.2 V versus reversible hydrogen electrode (RHE) for aqueous photoelectrochemical CO2 reduction. Due to the confined electron energy in tunneling, the product selectivity is substantially tuned from CO or formate to ethanol, with an excellent Faradaic efficiency of ethanol over 60% at 0 V versus RHE.

Effectively Tuning the Ratio of CO and H2 into Syngas through CO2 Electrochemical Reduction over a Wide Potential Range on a ZnO Nanosheet via Ni Doping

Effectively Tuning the Ratio of CO and H₂ into Syngas through CO₂ Electrochemical Reduction over a Wide Potential Range on a ZnO Nanosheet via Ni Doping