ZnO Hollow Spheres Research Articles

Highly efficient ethanol sensor based on controllable synthesized ZnO hollow flower spheres

Highly efficient ethanol sensor based on controllable synthesized ZnO hollow flower spheres

In-situ construction of carbon-doped ZnO hollow spheres for highly efficient dimethylamine detection

Pure ZnO and carbon-doped ZnO hollow spheres were successfully synthesized by a hydrothermal-calcination process. The doping content of carbon in ZnO was controlled by different calcination temperatures at 500 ℃ and 600 ℃ (named as ZnO-500 and ZnO-600). Systematic material characterization indicates that mesoporous ZnO hollow spheres are featured in abundant defects induced by in-situ carbon doping. Used as gas sensing materials, the response of ZnO-600 towards 200 ppm dimethylamine (83.6) is 28.6 times and 2.5 times higher than that of Pure ZnO (2.9) and ZnO-500 (32.8) at the optimum operating temperature of 240 ℃. Remarkably, the response of ZnO-600 toward 1 ppm dimethylamine is as high as 7.2, and simultaneously the limit of detection is as low as 108 ppb. In addition, ZnO-600 hollow spheres hold excellent gas-sensing performance in response-recovery speed, selectivity, repeatability, long-term stability, and water resistance towards dimethylamine. The boosted dimethylamine sensing performance of ZnO-600 is mainly attributed to synergistic effects of the unique mesoporous microstructure and rich defects induced by in-situ carbon doping. This work provides a promising material for dimethylamine detection, the properties of which can be improved for practical applications in the future. Furthermore, this contribution gives new insights into nonmetal-doped metal oxide nanostructures for high-performance gas sensors via surface defect control.

Hollow Spherical ZnO with Mesoporous Shell for Highly Enhanced Gas Sensitivity and Selectivity

In this work, ZnO hollow spheres (ZnO-HS) with mesoporous shells were successfully synthesized via a facile two-step method. The hollow structure provides sufficient space and active sites for adsorbing gases. The mesoporous shells assembled from nanoparticles facilitate the diffusion of gas molecules into the inner space and ensure full contact with ZnO. Consequently, ZnO-HS-600 gas sensors deliver a satisfactory response to volatile organic compounds (VOCs) and an excellent response-recovery time at the optimal working temperature of 300 °C, i. e., acetone (9 and 5 s), ethanol (10 and 6 s), and methanol (12 and 14 s), respectively. By combining the theoretical calculation and the experimental observation, the relationship between the structure and performance has been established. The results demonstrate that ZnO-HS-600 materials meet the regional depletion condition, i. e., L 2Ls , further explaining its superior response-recovery time. Our work provides a prospective strategy for high-performance ZnO gas sensors via structural design and theoretical calculations.

Noble metal modified (002)-oriented ZnO hollow spheres for the degradation of a broad range of pollutants

Zinc oxide hollow spheres were fabricated by applying sucrose-derived carbon spheres as templates that were eliminated through calcination. For this purpose, two synthesis methods were examined and compared, chemical impregnation and solvothermal method. The most suitable ZnO hollow structure was selected for noble metal deposition (Au and Pt at 1 wt%) to further increase the photocatalytic activity. The photocatalytic activity was examined by the decomposition of three different model pollutants (phenol, Na-ibuprofen and diuron) under UV irradiation. The as-synthesized hollow sphere structures and its noble metal composites were further examined by XRD, SEM, IR, DRS, PL. The templates did not modify the structure of ZnO only the morphology and contributed to the preservation of the original structure during calcination. The structural, optical and photocatalytic activity was correlated with both the application of carbon sphere template, and noble metal deposition respective their role in the improvement of the photocatalytic activity.

Physical and Electrochemical Properties of Graphene Decorated with ZnO Hollow Spheres for Supercapacitor Applications

Single-layer graphene-ZnO hollow sphere (SLG-ZnO(HS)) composites were successfully prepared through facile one-step solvothermal synthesis route. The morphological structures of the samples were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Hollow spheres consisting of ZnO nanoparticles with a diameter of approximately 30 nm are decorated to both sides of the SLG sheets. The electrochemical performances were tested by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance (EIS). The SLG-ZnO(HS) composite electrode synthesized at a concentration of 0.25 mM Zn precursor exhibited an enhanced specific capacitance of 34.7 F/g at a scan rate of 1 mV/s with energy and power densities of 5.39 W h/kg and 1.73 kW/kg, respectively.

Ionized cocatalyst to promote CO2 photoreduction activity over core–triple-shell ZnO hollow spheres

Ionized cocatalyst to promote CO2 photoreduction activity over core–triple-shell ZnO hollow spheres

In-Situ Construction of Carbon-Doped ZnO Hollow Spheres for Highly Efficient Dimethylamine Detection

In-Situ Construction of Carbon-Doped ZnO Hollow Spheres for Highly Efficient Dimethylamine Detection

Investigation on synergistic effect of rGO and carbon quantum dots-embedded ZnO hollow spheres for improved photocatalytic aqueous pollutant removal process

Investigation on synergistic effect of rGO and carbon quantum dots-embedded ZnO hollow spheres for improved photocatalytic aqueous pollutant removal process

EPR Investigation on Electron Transfer of 2D/3D g‐C3N4/ZnO S‐Scheme Heterojunction for Enhanced CO2 Photoreduction

AbstractPhotocatalytic conversion of CO2 into useful products is a promising technology from environmental and economic viewpoints. However, the efficiency of current photocatalytic materials is still unsatisfactory. In this work, a robust S‐scheme heterojunction composed of 3D ZnO hollow spheres wrapped by 2D g‐C3N4 layers is fabricated. The electrostatic attraction between both components not only facilitates the exfoliation of g‐C3N4 layers but also strengthens the photocatalyst framework. The prepared g‐C3N4/ZnO photocatalyst afforded an enhanced CH4 production rate, which is ≈40 and 7 times higher than those of pure ZnO and g‐C3N4, respectively. The improved activity is attributed to the extended light absorption and suppressed charge carrier recombination. Moreover, apart from traditional techniques, electron paramagnetic resonance (EPR) is used to probe charge movement in the fabricated S‐scheme heterojunction. An observable shift of the relevant EPR peak is noticed after the construction of g‐C3N4/ZnO heterostructure, indicating the electron transfer process. This study sheds light on S‐scheme heterojunctions as efficient candidates for CO2 photocatalytic conversion.

Sustained CO2-photoreduction activity and high selectivity over Mn, C-codoped ZnO core-triple shell hollow spheres

Solar conversion of CO2 into energy-rich products is one of the sustainable solutions to lessen the global energy shortage and environmental crisis. Pitifully, it is still challenging to attain reliable and affordable CO2 conversion. Herein, we demonstrate a facile one-pot approach to design core-triple shell Mn, C-codoped ZnO hollow spheres as efficient photocatalysts for CO2 reduction. The Mn ions, with switchable valence states, function as “ionized cocatalyst” to promote the CO2 adsorption and light harvesting of the system. Besides, they can capture photogenerated electrons from the conduction band of ZnO and provide the electrons for CO2 reduction. This process is continuous due to the switchable valence states of Mn ions. Benefiting from such unique features, the prepared photocatalysts demonstrated fairly good CO2 conversion performance. This work is endeavoured to shed light on the role of ionized cocatalyst towards sustainable energy production.

A novel synthesis of Ag@ZnO yolk-shell and ZnO hollow sphere nanostructures and comparison of their photocatalytic performances

ZnO hallow spheres and Ag@ZnO yolk-shell nanostructures were synthesized using a hydrothermal method and their dye absorption and photocatalytic performances were investigated. For ZnO hollow spheres preparation, carbon sphere templates were used and ZnO hollow spheres with average size of 200 nm were obtained. Also, Ag@C core-shell spheres with diameters of 350 nm were prepared by a hydrothermal method and were used as template to prepare Ag@ZnO yolk-shell spheres. The samples were characterized using XRD, SEM, TEM, EDX and FT-IR measurements. The results confirmed the formation of yolk-shell nanostructure. The average diameters of ZnO shells and Ag cores, 300 and 55 nm were measured respectively. Then Congo red dye absorption of ZnO hollow spheres and Ag@ZnO yolk-shells were examined. The results showed that the ZnO hollow spheres were a better dye absorbent, but Ag@ZnO yolk-shells had better photocatalytic performance probably due to presence of Ag nanoparticles as a plasmonic material.

Preparation of Ce-doped ZnO hollow spheres and their application as a light scattering layer in dye-sensitized solar cells

Ce-doped ZnO hollow spheres (Ce@ZHSp) with various Ce-contents of 0, 0.25, 0.50 and 1.0 mol% were synthesized via a template-free hydrothermal method. The calcined samples were characterized using XRD, FESEM, TEM, BET–BJH and UV–Vis spectroscopic techniques. The analytical results showed that all the samples possessed a hexagonal wurtzite structure. The crystallite size of Ce@ZHSp decreased with increasing Ce-content. Calcined samples had a hollow sphere morphology with an average diameter range of 4.63–5.16 µm. Diffuse reflectance was increased by adding an appropriate Ce-dopant of 0.25 mol% into the ZnO hollow spheres. The energy-conversion efficiency of a dye-sensitized solar cell was examined under the A.M. 1.5 direct spectrum. These results showed that the highest efficiency was derived from a bilayer photoanode using 0.25 mol% Ce-doped ZnO hollow spheres as a light scattering layer. This finding was related to an increase in the amount of dye adsorption and a photonic reflection effect originating from the relatively larger particle sizes with higher porosity compared to the other samples.

Noble Metal Modified (002)-Oriented ZnO Hollow Spheres for the Degradation of a Broad Range of Pollutants

Noble Metal Modified (002)-Oriented ZnO Hollow Spheres for the Degradation of a Broad Range of Pollutants

Synthesis of 3D flower-like ZnO/ZnCo2O4 composites with the heterogeneous interface for excellent electromagnetic wave absorption properties

Reasonable structure and composition are essential for electromagnetic wave absorption (EMW). Herein, ZnO hollow spheres were prepared with carbon spheres as templates and then synthesized ZnO/ZnCo2O4 composites by the solvothermal method and annealing treatment. The flower-like ZnCo2O4 material was produced by self-assembly of ZnCo2O4 nanosheets. The absorbing material with the complex structure has multiple scattering and reflection, conduction loss, resonance, and eddy current loss characteristics. Furthermore, the addition of ZnO hollow spheres has a significant impact on electromagnetic parameters and absorption properties. As a result, the addition of ZnO hollow spheres can greatly enhance the complex permittivity of the ZnO/ZnCo2O4 composites and obtain excellent EMW absorbing properties. It is worth noting that ZnO/ZnCo2O4 composites show the best EMW absorption properties when the ZnO hollow spheres were added up to 5 mg. The minimum reflection loss is −55.42 dB and a matching thickness of 1.99 mm while the maximum effective absorption bandwidth can also reach 7.44 GHz with a matching thickness of 2.4 mm. Our research can prove that the structure and composition have a significant influence on the properties of the absorbing material, which provides ideas for the development of absorbing materials with high-performance.

Fabrication of flexible polyaniline@ZnO hollow sphere hybrid films for high-performance NH3 sensors

In this study, a simple inexpensive gas sensor, which uses polyaniline@ZnO hollow sphere hybrid films, is prepared with different mole percentages of ZnO hollow spheres (5–30 mol%) and combining hydrothermal and in-situ chemical oxidative polymerization methods. Polyaniline@ZnO hollow sphere hybrids are loaded on flexible polyethylene terephthalate substrates for rapid and selective detection of ammonia at room temperature. The morphology, structure, chemical functional group information and the specific surface area are, respectively, characterized by field emission-scanning electron microscopy, X-ray diffraction, Fourier transform infrared and N2 adsorption–desorption techniques. The best sensing performance is realized for the polyaniline@20 mol% ZnO hollow sphere hybrid sensor, which is exposed to 10 ppm ammonia at room temperature. Moreover, this sensor exhibits a low detection limit of 500 ppb, excellent selectivity and good response/recovery times (140/136 s). This good sensing performance can be attributed to the hollow structure of ZnO and the p–n heterojunction between the polyaniline and ZnO hollow spheres.

Carbon quantum dots supported ZnO sphere based photocatalyst for dye degradation application

A Carbon quantum dots supported ZnO hollow Sphere (ZnO/C-dots) were synthesized through a solvothermal method using polyethylene glycol 400 (PEG 400) as a solvent. The phase and crystal structure of as-prepared ZnO/C-dots photocatalyst were characterized by powder X-ray diffraction (XRD). The surface morphology and size of the composite were analyzed using field emission scanning microscopy (FE-SEM). The optical properties of the as-prepared nanocomposites were examined using UV–visible (UV–Vis) spectrometer. The photocatalytic activity of pure ZnO and ZnO/C-dots nanocomposites were evaluated by the degradation of methylene blue (MB) under UV–Visible light irradiation. The ZnO/C-dots nanocomposites exhibited maximum photocatalytic MB dye degradation efficiency of 96% which is much higher that the pure ZnO (63%). The enhanced photocatalytic activity of ZnO/C-dots is due to the extended light absorption in the visible region and suppressed photoexcited electron-hole pair recombination rate. Moreover, the activity of photocatalyst after five cycles exhibits high stability, which is vital for the sustainable photocatalytic procedures. It is concluded that the prepared ZnO/C-dots composite have low cost, good stability and has a great potential application for Photocatalytic dye degradation.

ZnO hollow sphere prepared by flame spray pyrolysis serves as an anti-reflection layer that improves the performance of dye-sensitized solar cells

In this study we investigated the use of sub-micrometer ZnO hollow spheres as anti-reflection layers (ARLs) in dye-sensitized solar cells (DSSCs). The ZnO hollow sphere was synthesized by flame spray pyrolysis (FSP) followed by post-heating treatment. The ZnO hollow sphere was analyzed via x-ray diffraction (XRD), which revealed a hexagonal-wurtzite structure. A scanning electron microscope (SEM) image showed a uniform and spherical hollow particle with a narrow size distribution of the diameter: dav ~900 nm. In this research, the DSSCs were fabricated via manual screen printing with TiO2 nanoparticles (20 nm) as transparent layers and ZnO hollow spheres as anti-reflection layers. The performance of the DSSCs was investigated using a Keithley 2440 source meter under an AM 1.5 G solar simulator with a power intensity of 100 mW/cm2. The addition of the ZnO anti-reflecting layers resulted in a four-fold improvement in the efficiency of these DSSCs. In this study, we also noted that the photocurrent density was dependent on the size of the crystals in the ZnO ARLs. The photocurrent was further improved when crystal size was increased via heat treatment. As a result, the DSSCs using ZnO hollow spheres annealed at 900 °C and coated onto TiO2 film achieved a PCE of 2.61% (Voc of 0.75 V, Jsc of 10.03 mA cm−2, ad FF of 0.35), whereas DSSCs using TiO2 with a non-annealed ZnO ARL achieved a PCE of only 2.18% (Voc of 0.78 V, Jsc of 6.78 mA cm−2, and FF of 0.34), and the DSSCs with only TiO2 showed a paltry PCE of 0.64%.

Nanostructural Cu-Doped ZnO Hollow Spheres as an Economical and Recyclable Catalyst in the Synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-diones and Pyrazolo[1,2-a][1,2,4]triazole-1,3-diones

In the synthesis of organic compounds, heterogeneous catalysts have gained significance versus their homogeneous counterparts, due to both environmental and economic concerns. 1–4 Homogeneous catal...

High performing photocatalytic ZnO hollow sub-micro-spheres fabricated by microwave induced self-assembly approach

The development of high-performing photocatalytic materials is highly sought after, but challenging, especially for environmental applications. Herein, we report on a microwave induced self-assembly approach for the fabrication of uniform submicron ZnO hollow spheres (ZOHS) with shell walls of nano diameter. This approach is more efficient, greener and swifter than methods that have been previously reported on. The microwave induced self-assembly method is an interesting approach to produce well-defined and uniform ZnO hollow-structured spheres as revealed by TEM, SEM, XRD, IR, TGA and BET analysis. Of particular interest is the practical relevance of the photocatalytic performance of the obtained hollow-structured ZnO was explored through the photodegradation of Rhodamin B (RhB). The ZOHS exhibited higher photocatalytic performance when compared with its solid counterparts (at room temperature) as revealed by UV–Vis analysis.

STUDIES OF SEM, EDS, XRD, UV-Vis, PCTA (2 DYES -8TIMININGUV) IN TZZ: TiO2/ ZnO WITH (1:2) RATIO

Carbon spheres as template with hydrothermal method we prepared TiO2,ZnO, and TiO2/ ZnO composite hollow spheres of 1:2. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), EDS and UV-Vis. Photo degradation activity of composite hollow spheres is studied for two dyes Methylene Blue(MB), and RhodamineB(RhB)at different time intervals (0-270min) under UV Lamp(54 watts).The results are systematically analysed and reported at the end ,the degradation efficiency of TiO2/ ZnO (1;2) hollow spheres is about 90% within 270 min.