Sheet-like ZnO Research Articles

Porous cellulose gel-regulated flower-like ZnO-Cu nanoparticles for enhancing interfacial catalysis activity and recyclability in environmental catalysis

The recyclability of heterogeneous catalysts directly affects their utilization efficiency, use cost, sustainability, and environmental issues. Herein, the flower-like ZnO-Cu nanoparticles with high interfacial reactivity were in-situ synthesized in the porous cellulose gel to obtain the ZnO-Cu/cellulose composite gel (ZnO-Cu/CCG) catalyst, which possesses superior recycling and reusing stability thanks to the bulk nature of the gel. The ZnO-Cu/CCG catalysts with tunable sheet-like and flower-like ZnO were fabricated by the dissolution of cellulose into zinc chloride (ZnCl2) solvent and regeneration using different coagulating baths (water, ethanol, or isopropanol). The CCG prepared from isopropanol coagulation exhibited the highest specific surface area (291.6 m2/g) and porosity (92.3%). The various network structures of CCG provided different nucleation sites and growing spaces for controllable preparation of ZnO with tunable morphology. The complete removal of methyl orange (MO), Congo red (CR), and methylene blue (MB) required only 80 sec, 3 min, and 5 min, using flower-like ZnO-Cu/CCG catalysts prepared by isopropanol coagulating bath, the pseudo-first-order rate constant (k) is 2.8170 min−1, 1.1330 min−1, and 0.8506 min−1, respectively, much higher than that of the ZnO-Cu powders. Furthermore, the catalytic reusability of ZnO-Cu/CCG can be investigated over 50 successive cycles, in which the catalytic efficiency did not decrease appreciably.

Aqueous Oxytetracycline and Norfloxacin Sonocatalytic Degradation in the Presence of Peroxydisulfate with Multilayer Sheet-Like Zinc Oxide.

Multilayer ZnO sheet-like flakes were synthesized by a simple method of precipitation and characterized by the techniques of X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The findings are proven that the SEM images show the overall morphology of a single sheet-like ZnO nanostructure made from uniformly thick nano-sheets. In an aqueous environment, the acoustic ability of the prepared material was assessed using ultrasound (US) radiation to degrade oxytetracycline (OTC) and norfloxacin (NF). To increase the degradation efficiency, a US/ZnO/peroxodisulfate system was developed by introducing ammonium persulfate ((NH₄)₂S₂O8) and sodium persulfate (Na₂S₂O8), exhibiting excellent synergistic effects. Result show the decomposition efficiency for NF removal with Na₂S₂O8 (64%) appeared to be slightly better than with (NH₄)₂S₂O8 (56%). By contrast, the ultrasonic catalytic efficiency of Na₂S₂O8 (98%) was slightly better than that of (NH₄)₂S₂O8 (94%) for OTC removal. The addition of scavengers to the US/ZnO/peroxodisulfate system through the NF and OTC results in the largest effect of holes. The degradation is considered to be often caused by holes. In this system, the Na₂S₂O8 can have two roles to increase the rate of degradation: (1) The SO₄- formed by Na₂S₂O8 under ultrasonic irradiation directly degraded to norfloxacin on ZnO surface; and (2) S₂O82- behaved as an electron acceptor, inhibiting recombination of electron hole pairs, enabling the development of more ·OH. Therefore, the synergistic effect significantly increases US/ZnO/peroxodisulfate sonocatalytic activity (Hu, S.B., et al., 2017. Aqueous norfloxacin sonocatalytic degradation with multilayer flower-like ZnO in the presence of peroxydisulfate. Ultrasonics Sonochemistry, 38(1), pp.446-454).

Hexylresorcinol calix[4]arene-assisted synthesis of ZnO–Au micro–nano materials with enhanced photodegradation performance to degrade harmful organic compounds

HRCA not only acts as a reducing agent, but also plays a role in morphology regulation in the synthesis of ZnO–Au micro–nano materials. Gold particles deposited on the formed ZnO sheets and prevented the sheet-like ZnO from accumulating.

Tribological properties and anti-wear mechanism of ZnO@graphene core-shell nanoparticles as lubricant additives

Abstract Graphene is regarded as a promising, environmentally friendly candidate for lubricant additives. This work presents a coated nanocomposite with hard-core and soft-shell as lubricant nanoadditive. Three morphological ZnO nanoparticles are synthesized as the core to prepare ZnO@graphene core-shell nanoadditives. A four-ball machine is used to evaluate the anti-friction and anti-wear properties. The effects of ZnO morphology and concentration on the tribological behaviors and worn-out appearance are discussed. The compositional variation of wear scar is characterized to explore the possible anti-wear mechanisms. Researches suggest sheet-like ZnO is more ideal morphology, and ZnO@graphene hard core-soft shell nanostructure is more suitable for dynamic friction environment. The synergistic effect can effectively maintain load capacity and stability of lubricating film, exhibiting excellent tribological property.

The Structural and Electrical Properties of the Au/n-Si (MS) Diodes With Nanocomposites Interlayer (Ag-Doped ZnO/PVP) by Using the Simple Ultrasound-Assisted Method

In this paper, Au/Ag-doped ZnO/polyvinyl pyrrolidone (PVP)/n-Si [metal-polymer-semiconductor (MPS)] Schottky Barrier Diodes (SBDs) were fabricated. The structural properties of the Ag-doped ZnO/PVP nanocomposites have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analyses. The XRD pattern indicated that the samples have high purity ZnO and Ag materials and have not observed other peaks. The mean crystallite size of nanoparticles was calculated using Debye-Scherer's equation and the measured sizes reveal clearly the formation of small nanocrystals. The SEM and EDX results show the sheetlike ZnO nanostructures and also confirm the presence of Zn, O, and Ag materials with the nonstoichiometric ratio. The values of ideality factor (n), zero-bias barrier height (Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B0</sub> ), and series resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> ) of the MPS-type SBD were obtained from both the thermionic emission (TE) and Cheung function and the observed some discrepancy between them was due to the voltage-dependent of these parameters and the nature of the calculation method. The value of surface states (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ss</sub> ) was changed from 2.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> at (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> - 0.44) eV to 8.19 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> at (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> - 0.69) eV and these values are more suitable for the MPS-type SBD. The values of doping-donor atoms (ND), depletion layer width (WD), and B [capacitance-voltage (C-V)] were obtained from the reverse bias C-2-V plot as a function of frequency. While the value of ND decreases with increasing frequency, WD increases almost as exponentially. However, there is a good relationship between Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> (C-V) and ln(f).

Facile synthesis of ZnO nanosheets: Structural, antibacterial and photocatalytic studies

Two dimensional (2D) hexagonal sheet-like Zinc Oxide nanostructures (ZnO NSs) have been synthesized by Sodium Dodecyl Sulphate (SDS)-assisted atmospheric microplasma electrochemical technique at room temperature. The synthesized nanostructures were investigated by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), UV–Visible spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. The viable formation mechanism of sheet-like ZnO NSs has been proposed. XRD pattern confirmed the ZnO NSs of fine crystallinity with hexagonal phase. Rietveld refinement of XRD patterns provides accurate values for the lattice parameters. The sharp UV absorption peak at 363 nm suggested the synthesis of high-quality crystalline ZnO NSs. These NSs also showed significant antibacterial activities against various bacterial strains. In addition, ZnO NSs displayed excellent Photocatalytic activity in the degradation of Rhodamine B (Rhd B) dye in aqueous solution.

Effect of ZnO nanostructures on the optical properties of white light-emitting diodes.

White light produced by blue LEDs with yellow phosphor is the most widely used methods, but it results in poor quality in angular CCT uniformity. In this work, a novel technique was introduced to solve this problem by integrating different ZnO nanostructures into white light-emitting diodes. The experiment of ZnO doped films and the simulation of Finite-Difference Time-Domain (FDTD) were carried out. The result indicated scattering effect of ZnO nanoparticles could improve uniformity of scattering energy effectively. Moreover, the effect of ZnO nanostructures on white light-emitting diodes (wLEDs) devices was also investigated. The CCT deviation of wLEDs devices would decrease from 3455.49 K to 96.30 K, 40.03 K and 60.09 K when the node-like (N-ZnO), sheet-like (S-ZnO) and rod-like ZnO (R-ZnO) respectively applied. The higher CCT uniformity and little luminous flux dropping were achieved when the optimal concentrations of N-ZnO, S-ZnO, and R-ZnO nanostructures were 0.25%, 0.75%, and 0.25%. This low-cost and green manufacturing method has a great impact on development of white light-emitting diodes.

Flexible NO 2 gas sensors based on sheet-like hierarchical ZnO 1− x coatings deposited on polypropylene papers by suspension flame spraying

Abstract 2D sheet-like ZnO coatings composed of nanoparticles were deposited on flexible polypropylene papers equipped with gold electrodes in three steps. Firstly, sheet-like ZnO powder was synthesized by direct precipitation method. Then, the as-synthesized powders were dispersed in anhydrous ethanol to form feedstock suspension. At last, the feedstock suspension was injected into the acetylene-oxygen flame to deposit ZnO coatings. X-ray diffraction and field-emission microscopy results revealed that the coatings were hexagonal phase and porous hierarchical structure. With an increase in spray distance, the coatings exhibited a morphology with smaller particle size and sheet thickness. Photoluminescence and X-ray photoelectron spectra indicated that large amounts of oxygen vacancies were introduced into the coatings, and oxygen vacancy concentration increased with the spray distance. UV–vis spectra showed that the light absorption of the coatings was extended to visible light region, and wider absorption range was obtained when the spray distance was increased. The ZnO coatings exhibited good responses to sub-ppm level NO2 at room temperature under white LED light illumination, and the coating deposited with longer spray distance presented a better NO2 sensing performance.

Soft jet plasma-assisted synthesis of Zinc oxide nanomaterials: Morphology controls and antibacterial activity of ZnO

This manuscript discusses about size and shape-selective preparation of Zinc oxide nanomaterials (ZnO NMs) using simple and handy soft jet plasma source. The soft jet was operated in an atmospheric pressure with low energy consumption and utilized ambient air as a feed gas. The plasma synthesized ZnO NMs exhibited variety of surface morphology such as nanorods, nanosheets and micro-size flowers as compared to the conventional low temperature synthesized powders which showed spherical shape. The precursor concentrations and kinds of precursors were strongly influenced into the NMs morphology and possible growth mechanism in the presence of plasma has been proposed. It is suggested here that the soft jet plasma is an effective tool to control size and shape of ZnO NMs especially when the preparations demanding low temperature, surfactant free and cost-effective synthesis. The prepared ZnO NMs were tested for its shape dependent anti-bacterial property against Gram-positive bacteria namely S. iniae and S. parauberis and two Gram-negative bacteria such as E. coli and V. anguillarum. The flower-like ZnO NMs showed more powerful anti-bacterial activity than rod or sheet-like ZnO structures.

Comparative spectroscopic approach for the dye loading optimization of sheet-like ZnO photoanodes for dye-sensitized solar cells

The peculiarly critical sensitization of zinc oxide with Ru-based dyes is the serious problem that prevents this semiconductor oxide from achieving photoconversion efficiencies in dye-sensitized solar cells (DSCs) comparable to those obtained with TiO2. Within this framework, methodologies for the optimization of the sensitization procedure of this material in acidic environments prove to be essential. In this paper, in view of streamlining the critical sensitization procedure of sheet-like zinc oxide-based DSC photoanodes with Ru-based dye, a comparative study on active and passive evaluations of N719 dye loading on sheet-like ZnO nanostructures are reported. For the active in-situ spectroscopic approach, a home-made set-up has been appropriately designed and developed for real time monitoring the dye adsorption on the ZnO-based photoanodes, whereas the standard passive dye loading measurements were performed after the electrodes had been sensitized for different time periods in the dye solutions of different concentrations. The dye adsorption results are carefully analyzed and correlated to the photovoltaic conversion efficiency and the incident photon-to-electron conversion efficiency (IPCE) of the corresponding ZnO-based DSCs, fabricated by employing our customized microfluidic architecture. The obtained results show that the real time monitoring of the dye absorption can be successfully employed for optimizing the sensitization conditions of ZnO-based photoanodes for DSCs. When applied online in a large scale production system for dye-sensitized solar cells, the proposed active method will permit to save both time and materials.

Use of carbon dots to enhance UV-blocking of transparent nanocellulose films

High-efficient transparent UV-blocking nanocellulose (NC) films were successfully assembled by pressured-extrusion of the composites of carbon dots (CDs), 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical mediated oxidized nanocellulose (ONC) and ZnO nanostructures. ONC nanofibrils were firstly extracted from bamboo fibers and subsequently prepared by applying TEMPO oxidation. The as-obtained CDs-ONC-ZnO films exhibited high visible light transparency, excellent thermal stability and enhanced UV-blocking properties. Compared to the previously designed NC-ZnO films, CDs-ONC-ZnO films presented significant increase of UV-blocking ratio (UVR) with the same amounts of ZnO. Moreover, the UVR of CDs-ONC-s-ZnO film with 4wt% sheet-like ZnO (s-ZnO) at 300nm and 225nm is 92.74% and 98.99%, better than the same condition of CDs-ONC-b-ZnO film added with belt-like ZnO (b-ZnO) and CDs-ONC-p-ZnO film added with commercial particulate ZnO (p-ZnO). An interesting discovery is that when adding 4wt% p-ZnO, the UVR of CDs-ONC-p-ZnO film is very close to the value of NC-s-ZnO film with the same amount of s-ZnO.

Mesostructured zinc oxide architectures with high photocatalytic activity

Several photocatalysts with different architectures were synthesized via a facile hydrothermal approach in the presence of diverse structure-directing reagents at varied concentrations. It was found that the concentration of the directing reagents played a crucial role in the architecture of the obtained products. Flower-like ZnO architectures were synthesized at a high concentration of PVP, while pencil-like mesocrystals (MCs) at a low concentration. The flower shaped assembly was composed of leaf-like ZnO MCs. More interestingly, the MCs were assembled with ZnO nanocrystals aligned along [111] direction. The photocatalytic activities of the samples were examined by photocatalytic degradation of methylene blue, and the results indicated that the flower-like architectures exhibited highest performance, compared with those of ZnO nanocrystals, pencil shaped ZnO mesocrystal, and the sheet-like ZnO MCs. This could be attributed to not only the hierarchical architecture of the assembly, high crystallinity, and large surface area, but also the unique mesoscopic structure of ZnO MCs.

Effect of Preparation Technology of Nano-ZnO on Its Morphology and Photocatalytic Activity

Using Zn(NO3)2•6H2O and NaOH as raw materials, hydrothermal method was employed to prepare nano-ZnO by changing the proportion of materials and adding surfactant. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that at n(OH−):n(Zn2+) = 4:1, the nano-ZnO had a sheet-like structure with average thickness of 80 nm; at (OH−):n(Zn2+) = 10:1, nano-ZnO had a pencil-like structure with the diameter of 220 nm. Rhodamine was used as pollutant to carry out photocatalytic experiments. The results indicated that the photocatalytic performance of sheet-like ZnO was superior to that of pencil-like ZnO. As to the influence of different surfactants, the ZnO had a rod-like structure with the addition of dodecyltrimethylammonium bromide (DTAB), and its photocatalytic performance was enhanced. The photocatalytic performance of ZnO prepared with the addition of Sodium dodecylbenzenesulfonate (DBS) was also improved, though by a smaller extent compared with the addition of DTAB.

Preparation of cribriform sheet-like carbon-coated zinc oxide with improved electrochemical performance

Cribriform sheet-like carbon-coated ZnO are prepared using pyrrole as the carbon source. It is found that a sheet-like precursor will form when polymerizing pyrrole in the presence of ZnO particles. After the carbonization of precursor, cribriform sheet-like carbon-coated ZnO can be obtained. Morphology and structure analysis of as-prepared carbon-coated ZnO is conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The carbon overlayer not only present a barrier layer on the surface of the ZnO particles, which keeps relative high discharge capacity by inhibiting the active materials in electrode from dissolving into electrolyte, but also modify the surface status of ZnO particles so as to obtain more uniform current distribution and improved conductivity. As a result, when evaluated as an anode material for Zn/Ni cell, carbon-coated ZnO exhibit a more stable cycle performance than bare ZnO electrode.

Morphological, Photocatalytic and Bactericidal Properties of ZnO Powders Prepared by a Precipitation Method

Structural, optical and photocatalytic properties of ZnO powders prepared by a precipitation method were systematically investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), UV-Vis diffuse reflectance measurement and UV-Vis absorbance measurement. The antibacterial activity was tested by a broth microdilution method. All calcined ZnO powders exhibited a hexagonal wurtzite structure. The ZnO powders formed various shapes depending upon the concentration of n-propylamine used. The Eg value of ZnO powders depended upon defect concentration. The photocatalytic property of ZnO powders depended on the particle shape and defect concentration. The best photocatalytic efficiency of 100% was observed from the ZnO powders prepared at R = 2 after irradiating by the blacklight for 90 min. All ZnO powders can damage only S. aureus and the agglomerated sheet-like ZnO powders prepared at R = 2 showed the best antibacterial property with a MIC value of 1.5625 mg/mL.

Transparent nanocellulose hybrid films functionalized with ZnO nanostructures for UV-blocking

Transparent nanocellulose films functionalized with sheet-like ZnO nanostructures presented excellent UV-blocking performance in a wide range from 200 to 375 nm.

Improved Cycling Performance of Cellular Sheet-Like Carbon-Coated ZnO as Anode Material for Zn/Ni Secondary Battery

A novel cellular sheet-like carbon coated ZnO has been constructed with the assistance of chemical polymerization of pyrrole, followed by carbonization treatment. When evaluated as an anode material for Zinc/Nickel rechargeable battery, the carbon-coated ZnO electrode exhibits improved reversibility and cycling performance compared with bare ZnO electrode. The carbon coating is believed to better retain active material in electrode upon prolonged cycle and to improve the conductivity of material. This facile strategy using chemical polymerization followed with carbonization could also be applied to prepare other carbon-coated material.

Controlled Growth of ZnO Nanoparticles with Different Morphologies Using Sol-Gel Technique

A low temperature sol-gel approach was demonstrated to prepare ZnO nanoparticles with controlled morphologies. By changing the concentration of NH4OH, the ZnO nanoparticles evolves from sphere-like, star-like and sheet-like structures. No peak of additional phase was observed in the XRD patterns except the diffraction peaks of ZnO. The estimated crystallite size of ZnO nanoparticles decreases with the increase of NH4OH. It is also found that the morphology of nanoparticles affects the optical bandgap of ZnO. The optical bandgap of sphere-like,star-like, and sheet-like ZnO nanoparticles are 3.55 eV, 3.48 eV and 3.45 eV, respectively. The growth mechanism of ZnO nanoparticles was discussed.

Photocatalytic Activity of CuO/ZnO Heterostructure Nanocrystals under UV-Visible Light Irradiation

The p-n junction photocatalysts, p-CuO (at. 0-25%)/n-ZnO nanocomposite were prepared through hydrothermal method without using any organic solvent or surfactant. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-Ray spectroscopy, and UV-vis spectroscopy. The results demonstrated that the CuO/ZnO nanocomposite presented a two-dimensional morphology composed of sheet-like ZnO nanostructures adorned with CuO nanoparticles. The photocatalytic activity of CuO/ZnO with different Cu/Zn molar rations and pure ZnO synthesized by the identical synthetic route were evaluated by degrading methylene blue (MB) dye under UV-visible light irradiation. The CuO/ZnO with Cu/Zn molar ratio of 4% exhibits the highest photocatalytic activity compared that of the other photocatalysts under the identical conditions. It is mainly attributed to the increased charge separation rate in the nanocomposite and the extended photo-responding range.

Hydrothermal growth of upright-standing ZnO sheet microcrystals

Abstract Large-scale upright-standing ZnO sheet microcrystals were fabricated on Zn substrate using sodium oxalate as structure-directing agent by a hydrothermal method at low temperature (70 °C) without any surfactant. The sheets are about 3–5 μm in dimension and 100–300 nm in thickness. The strong and narrow diffraction peaks of ZnO indicate that the sample has a good crystallinity and size. The morphology of sheet-like ZnO varied with the concentrations of sodium oxalate and reaction time. The sheet-like ZnO would transform into rod-like ones when sodium oxalate was substituted by equivalent sodium acetate. The formation of sheet-like ZnO is attributed to the preferable adsorption of oxalate anions on (0 0 0 1) face of ZnO, which inhibits the intrinsic growth of ZnO. Additionally, the continuous growth in six (0 1 −1 0) directions that have the lowest surface energy leads to the formation of hexagonal sheets.