ZnO Hollow Microspheres Research Articles

Highly responsive double-shell ZnO hollow microspheres based gas sensor for acetic acid detection in vinegar

Acetic acid sensing materials for environmental and related food quality control requiring high sensitivity and selectivity, and ppb-level detection limit, remain challenging. Double-shell ZnO hollow microspheres were prepared by a surfactant assisted template method, and the resultant gas sensor showed excellent acetic acid sensing performance. The sensor response reached 116 to 100 ppm acetic acid at 270°C with a short response time of 3.2 s. The relationship between acetic acid concentration and the response was established, and the detection limit reached 100 ppb. DFT theory computational results demonstrated the highest adsorption energy of the ZnO gas sensor to acetic acid among all tested gases, proving its high selectivity to acetic acid. Besides, the unique double-shell hollow structure with abundant oxygen vacancy and large surface area might be the other factors that gave rise to its excellent acetic acid gas sensing performance. Based on the gas sensor, a method for fast quantitative detection of acetic acid content in vinegar was developed. The linear relationship between sensor response and acetic acid gas concentration of vaporized white vinegar was established, and the acetic acid content in the vinegar can be quickly determined. The result proved our acetic acid sensor to be a promising candidate for practical applications.

Synergistic Resonances and Charge Transfer in Double-Shelled ZnO Hollow Microspheres for High-Performance Semiconductor-Based SERS Substrates

Synergistic Resonances and Charge Transfer in Double-Shelled ZnO Hollow Microspheres for High-Performance Semiconductor-Based SERS Substrates

Sprayable, thermosensitive hydrogels for promoting wound healing based on hollow, porous and pH-sensitive ZnO microspheres.

A solvothermal method and the subsequent heat treatment process were developed to fabricate hollow ZnO particles with hierarchical pores on a large scale. The as-obtained hollow, porous ZnO microspheres with tunable sizes, high specific surface areas, pH sensitivity, antibacterial properties, and high adsorption capacities showed significant advantages for drug delivery. Sprayable hydrogels containing hollow, porous ZnO microspheres and curcumin nanoparticles (CNPs) were prepared to accelerate wound healing. The water-dispersed CNPs promoted both the migration of fibroblasts and angiogenesis and an aqueous solution of Pluronic F127 (a temperature-sensitive phase-change hydrogel material) was shown to be an effective choice for medical dressings. The experimental data suggest that hollow, porous ZnO microspheres can be loaded with additional CNPs to achieve continuous long-term therapeutic effects.

Development of an innovative ethanol sensing sensor platform based on the construction of Au modified 3D porous ZnO hollow microspheres

The practical production of gas sensor devices poses a significant challenge in terms of designing electronic devices that possess the advantages of a simplistic structure and can be easily and conveniently manufactured through batch processing. Hence, a simple architecture is important in creating new type of gas sensor that could realize experimental purposes in real-life situations. Porous zinc oxide hollow microspheres (ZnO HMS) sensing materials were successfully synthesized via hydrothermal process. The detection of ultra-low gas concentrations, such as 100 ppb ethanol, was achieved using a novel ZnO HMS modified with Au. The ethanol sensing perform of the 1.0 wt%Au-ZnO is 7.7 times and 1.7 times higher than that of the ZnO HMS and 0.5 wt%Au-ZnO. Furthermore, even at a low concentration of 100 ppb, a good sensing response of 1.476 is acquired. Also, we found the low theoretical detection limitation of the 1.0 wt%Au-ZnO was 25.1 ppb.

Core-shell ZnO/BiOBr p-n heterojunction with excellent photocatalytic performance in degradation of tetracycline hydrochloride

Core-shell ZnO/BiOBr heterojunction was prepared by a simple hydrothermal-ionic liquid method. Hollow ZnO microspheres were firstly synthesized by hydrothermal method. Then BiOBr nanosheets were evenly wrapped on the ZnO microspheres through an ionic-liquid method. The prepared dahlia-like core-shell ZnO/BiOBr microspheres had a much larger BET surface area and mesopore volume than that of ZnO. Its visible-light absorption and charge carrier's separation were greatly enhanced due to the synergistic effect of the core-shell nanostructure and formation of ZnO/BiOBr heterojunction. It had an excellent photocatalytic performance in the degradation of tetracycline hydrochloride (TC): 86.76 % TC was degraded after irradiation for 90 min., which was 1.38 times of the pure ZnO and 1.35 times of the BiOBr, respectively.

3D ZnO hollow spheres-dispersed CsPbBr3 quantum dots S-scheme heterojunctions for high-efficient CO2 photoreduction

Efficient electron transfer process and excellent CO2 adsorption capacity are of great significance for improving CO2 photoreduction efficiency. 3D-0D ZnO/CsPbBr3 S-scheme heterojunction hollow spheres were successfully prepared via a simple self-assembled process for efficient CO2 photoreduction. Photocatalytic CO2 reduction experiments showed that the ZnO/CsPbBr3 had the excellent CO2 photocatalytic conversion activity to CO, which was about 2.61 times higher than that of ZnO hollow micro-spheres and 1.9 times higher than that of pure CsPbBr3 quantum dots (QDs). Photoelectrochemical characterization confirmed that the ZnO/CsPbBr3 composite had good photoelectric conversion ability and carrier transfer ability, which was beneficial to the photocatalytic reaction. The suitable band gap structure and DFT calculation results showed that the formation of built-in electric field at the ZnO/CsPbBr3 interface can greatly improve the S-scheme electron transfer ability, which can foster the CO2 photoreduction. Besides, the introduction of 3D structure can improve the dispersion of CsPbBr3 QDs and effectively enhance the CO2 capture ability of the catalyst, which greatly promoted the CO2 photoreduction reaction. The current work can present a novel S-scheme photocatalyst, which is looked forward to providing a certain perception into the advance of novel highly efficient CsPbBr3 QDs-based photocatalysts for CO2 resource utilization.

A novel hollow ZnO microspheres/organosilicone composite for potential application in electronic packaging fields

Current micro-electronic devices and the advent of the 5G era bring more requirements for electronic packaging materials. Herein, we have innovatively fabricated an organosilicone composite with hollow ZnO microspheres (H-ZnO). In this paper, H-ZnO filler was successfully prepared by hydrothermal method without template. We further improve the compatibility between H-ZnO filler and organosilicone matrix by vinyl trimethoxysilane (KH-171). The structures, compositions, size distribution and morphologies of H-ZnO were researched with XRD, FTIR and SEM. Afterwards, composites were prepared with H-ZnO filler and organosilicone, which not only effectively improve thermal conductivity but also keep low dielectric constant. It was found that the dielectric constant of H-ZnO-171/organosilicone is decreased to 2.47 and thermal conductivity reached 0.25 W/mK, which has achieved the synergistic optimization between low dielectric constant and enhance thermal conductivity. In summary, this H-ZnO-171/organosilicone composite could be expected to apply in electronic packaging fields.

Building triple shelled ZnO hollow microspheres decorated TiO2 nanotree to boost light harvesting and reduced charges recombination in dye sensitized solar cell

It is well known that the microstructure of photoanode materials has direct influence on light harvesting and charges recombination in dye sensitized solar cells (DSSC). However, design of photoanode materials for efficient light harvesting and electron transport is still in challenge. Therefore, we developed a hierarchical microstructure of multi shelled ZnO hollow microspheres (MS ZnO HMS) decorated TiO2 nanotree (NT) for DSSCs application with aim to take advantages of enhanced light scattering and enlarged specific area offered by MS ZnO HMS and reduced charges recombination provide by TiO2 NT. The morphology, microstructure and crystalline of ZnO HMS and TiO2 NT have been characterized by SEM, TEM and XRD, confirming the successful building of MS ZnO HMS decorated TiO2 NT. I–V tests show that significant enhancement of short-circuit current density (Jsc) can be achieved by controlling shell numbers of MS ZnO HMS and combining MS ZnO HMS with TiO2 NT. As a result, the triple shelled ZnO HMS (TS ZnO HMS) decorated TiO2 NT (TS ZnO HMS/TiO2 NT) improve the power conversion efficiency (PCE) to 7.40%, which is 138% and 40% higher than DSSCs based on TiO2 NT (3.11%) and TS ZnO HMS (5.27%). IPCE, OCVD and EIS measurements indicate that the combination of TS ZnO HMS with TiO2 NT contribute to the improvement of light harvesting efficiency and prolonging of electron lifetime.

Step-scheme ZnO@ZnS hollow microspheres for improved photocatalytic H2 production performance

Constructing a step-scheme heterojunction at the interface between two semiconductors is an efficient way to optimize the redox ability and accelerate the charge carrier separation of a photocatalytic system for achieving high photocatalytic performance. In this study, we prepared a hierarchical ZnO@ZnS step-scheme photocatalyst by incorporating ZnS into the outer shell of hollow ZnO microspheres via a simple in situ sulfidation strategy. The ZnO@ZnS step-scheme photocatalysts had a large surface area, high light utilization capacity, and superior separation efficiency for photogenerated charge carriers. In addition, the material simulation revealed that the formation of the step-scheme heterojunction between ZnO and ZnS was due to the presence of the built-in electric field. Our study paves the way for design of high-performance photocatalysts for H2 production.

Construction of hollow NiO/ZnO p-n heterostructure for ultrahigh performance toluene gas sensor

In this work, NiO/ZnO hollow microspheres were successfully fabricated by a simple co-precipitation method. The structural and morphological properties of NiO/ZnO composites were studied by various characterization methods. Gas sensing results revealed that the sensor of NZ-2 and the working temperature was 300 °C showed highest response value (S = 240) and good selectivity to 100 ppm toluene. Compared with pure ZnO hollow microspheres, the sensitivity of NiO/ZnO hollow microspheres is significantly improved by about 20 times. The response/recovery time were 2/33 s respectively at the same time, the detection limit can be reduced to ppb level. The possible mechanism for improvement of gas sensing performance is detailly analyzed, which is mainly due to the unique hierarchical microstructure and the composition of p-n heterojunction at the contact surface between p-type NiO and n-type ZnO structures as well as the catalytic effect of NiO.

Gas Sensing with Double-Shell Zno Hollow Microspheres Prepared by Template-Free Method

Gas Sensing with Double-Shell Zno Hollow Microspheres Prepared by Template-Free Method

Alpha-calcium sulfate hemihydrate used as a water-soluble template for the synthesis of ZnO hollow microspheres

This work develops α-HH microspheres into a water-soluble template for the green synthesis of hollow-architecture catalysts.

Structure and photocatalytic properties of the composite of Al-doped porous ZnO hollow micro-spheres and Ag nanoparticles

Al-doped porous ZnO hollow micro-spheres were prepared using a sol-gel method with a template of agglomerates of polystyrene (PS) nanospheres, and the composite of these ZnO hollow micro-spheres and Ag nanoparticles was prepared with further photo-deposition. The effects of Al doped on the structure and the optical properties of the specimen were investigated by means of x-ray diffractometer, SEM, TEM, an UV-Vis diffuse reflectance analyzer, and photoluminescence (PL) spectroscopy. Different doping concentrations of Al affect not only the existing form of Al atoms in the crystal but also the concentration of the intrinsic defects of ZnO, thus influencing the morphology of the hollow micro-spheres. The appropriate amount of Al doping provides the hollow spheres with a porous, loose morphology, showing the largest specific surface area, which significantly improves the absorbance of light and the number of reaction sites in photocatalysis. For the composite specimen, the introduction of Ag nanoparticles improves the absorbance of light in the visible region because of the surface plasmon resonance: in the PL measurements, because many electrons in the ZnO crystal flow to the surface of Ag nanoparticles due to the difference of energy levels between Ag and ZnO crystals, the intensity of the intrinsic and defect-related emissions of ZnO is reduced. The photocatalytic properties of the specimens were evaluated with the degradation of a methyl orange dye solution under simulated solar irradiation at room temperature. The specimen of porous ZnO hollow micro-spheres with 3% Al dopant concentration demonstrates excellent photocatalytic performance due to its large specific surface area. However, with the designed energy structure, the composite of porous ZnO hollow micro-spheres and Ag nanoparticles exhibits the best photocatalytic performance among the specimens tested by separating electrons and holes in the ZnO crystal.

Hollow ZnO microspheres self-assembled from rod-like nanostructures: morphology-dependent linear and Kerr-type nonlinear optical properties

Hollow nanostructures have attracted attention because of their unique physiochemical properties and broad potential applications in electronics, optics and photonics. In this study, a facile hydrothermal approach was developed to fabricate hollow ZnO microspheres via self-assembled rod-like nanostructures. The morphology-controlled synthesis was conducted by altering hydrothermal treatment temperature (150, 200 and 250 °C) in solutions containing zinc acetate dihydrate precursor and glycerol as the stabilizing agent. The morphological observations indicated that hydrothermally grown ZnO architectures could be reasonably adjusted by modulating hydrothermal reaction temperature. Possible growth routes are proposed to elucidate the formation process of ZnO microspheres with the rod-like nanostructures. Morphology-dependent absorbance and emission along with red-shifts with improved crystalline qualities were observed with increasing hydrothermal growth temperature. Kerr-type nonlinear optical characteristics examined using single-beam Z-scan technique in the near infrared spectral range under nanosecond Nd-YVO4 laser pulses showed positive values of nonlinear refraction providing an evidence of self-focusing behaviors at the excitation wavelength of 1064 nm in all the samples studied. The highest Kerr-type nonlinear susceptibility was estimated to be 2.31 × 10–6 esu for hollow ZnO microspheres grown at 250 °C, suggesting synergistic effects of surface morphologies on optical nonlinearities.

Core-double shell ZnO@In2O3@ZnO hollow microspheres for superior ethanol gas sensing

• ZnO@In 2 O 3 @ZnO hollow microspheres have been prepared. • The heterojunctions were created at the interface of In 2 O 3 and both inner and outer ZnO. • The sensor exhibits enhanced gas-sensing properties toward ethanol. • The sensing mechanism is appropriately speculated. Core-double shell-structured ZnO@In 2 O 3 @ZnO microspheres consisting of ZnO hollow microspheres, an In 2 O 3 interlayer, and a ZnO outer layer were synthesized by decorating In 2 O 3 and ZnO on the surface of ZnO hollow microspheres. The ZnO hollow microspheres with a size of 1.4 μm provided a good matrix for the adhesion of In 2 O 3 and ZnO. Both In 2 O 3 and the ZnO shells have a loose microstructure, which provided numerous gas diffusion channels and active sites for gas diffusion and gas sensing reaction. The surface defects and electronic structure of ZnO and ZnO@In 2 O 3 @ZnO were examined by photoluminescence (PL) and ultraviolet photoelectron spectroscopy (UPS). The gas sensing properties of the ZnO hollow microspheres, ZnO@In 2 O 3 core-shell microspheres, and ZnO@In 2 O 3 @ZnO core-double shell microspheres were compared using ethanol as the target gas. The response of ZnO@In 2 O 3 @ZnO toward 100 ppm ethanol was 453.2 at the optimum operating temperature of 200 °C, which was 2 and 30 times higher than that of ZnO@In 2 O 3 and ZnO. Even at a concentration of 1 ppm, the response of ZnO@In 2 O 3 @ZnO reached 53.2, indicating its excellent gas-sensing performance at low concentrations. The superior gas sensing properties of ZnO@In 2 O 3 @ZnO were attributed to its high specific surface area, abundant surface defects, and radial electronic modulation mechanism.

Surface modification and reconstruction of ZnO hollow microspheres for selective electroreduction of CO2 to CO

Surface chemistry can be modified by introducing another component on the surface of catalyst due to the regulation of configuration and electronic properties. Herein, the nanostructured ZnO hollow microspheres were fabricated for selective CO2 reduction to CO. The addition of CuO weakens the strength of adjacent Zn-O bond and improves the formation of more zero-valence Zn. Small CuO entities can provide the active sites for CO2 adsorption, and the presence of surface defects due to Zn2+ reduction could enhance initial dissociation from CO2 to CO. More interestingly, the 3CuO/ZnO catalyst underwent reconstruction during electrocatalysis, and multi-shelled hollow spheres evolved into a thin flaky structure. The extended surface area of flaky morphology enhances the catalytic stability despite the occurrence of ZnO reduction. This study highlights the importance of surface modification for CO2 selective reduction to CO but also provides some insights on reconstruction during electrochemical reduction of CO2.

Highly Sensitive and Selective HCHO Sensor Based on Co Doped ZnO Hollow Microspheres Activated by UV Light

Low power consumption or even detecting harmful gases at room temperature is the future development trend of gas sensors. In this work, Co doped ZnO hollow microspheres were prepared by a facile water bath method. Co doping increases the electron density of ZnO and promotes the adsorption of oxygen on the surface. The surface band bending caused by oxygen adsorption further promotes the separation efficiency of photogenerated charge. The sensing results showed that 1.5 mol% Co doped ZnO exhibited the highest response of 111.6 to 50 ppm formaldehyde (HCHO) activated by UV light (6.8 mW/cm2) at room temperature. Moreover, the detection of limit can reach to 100 ppb, and the response and recovery time is 32 and 44 s, respectively. The excellent gas-sensing performance could be attributed to the increase in adsorbed negative oxygen species on the surface, the improved separation efficiency of photogenerated charge, and the porous and hollow microstructure of ZnO. In addition, the sensor possessed excellent reproducibility, selectivity, and a certain ability of moisture resistance.

Synthesis of ZnO core/shell hollow microspheres to boost light harvesting capability in quantum dots-sensitized solar cell

Although ZnO hollow microspheres (HMS) is beneficial to improving light scattering, this superiority is crippled by poor specific surface area of ZnO HMS. We designed ZnO core/shell hollow microspheres (CSHMS) by carbonaceous microspheres template method for application in QDSSC. In comparison to ZnO nanoparticles (NPs) and ZnO HMS, ZnO CSHMS increased QDs loadings and enhanced light scattering, leading to the boost of light harvesting capability and photovoltaic performance. As a result, the power conversion efficiency of QDSSC based on ZnO CSHMS is 76.22% and 21.74% higher than QDSSCs based on ZnO NPs and ZnO HMS, respectively.

Synthesis of ZnO Hollow Microspheres and Analysis of Their Gas Sensing Properties for n-Butanol

ZnO hollow microspheres with a diameter of approximately 1.4 μm were successfully synthesized by a facile one-step chemical precipitation method using trisodium citrate dihydrate as a morphology control agent. The ZnO hollow microspheres consisted of nanoplates and had good dispersibility. Control experiments revealed that trisodium citrate dihydrate played an important role in regulating the morphologies of ZnO products. The morphology of the ZnO product evolved from nanowires to hollow microspheres with the addition of trisodium citrate dihydrate. The sensor response of ZnO hollow microspheres toward 100 ppm n-butanol reached 86.6 at the optimum operating temperature of 340 °C, which was approximately three times higher than that of ZnO nanowires. In addition, the ZnO hollow microspheres also displayed good selectivity and long-term work stability toward n-butanol. The excellent gas sensing performance of ZnO hollow microspheres may be ascribed to the unique hollow sphere structure with high exposed polar crystal surface.

Template-free synthesis and photocatalytic activity of hierarchical hollow ZnO microspheres composed of radially aligned nanorods

In this work, hierarchical hollow ZnO microspheres with an average diameter of 3.5 μm are successfully synthesized via a simple template-free solvothermal route. And these microspheres are constructed by anisotropic single-crystalline ZnO nanorods which grows along the [0001] c-axis direction because of the selective adsorption of ethylene glycol. It is noted that ethylene glycol plays a crucial role in promoting the growth and aggregation of nanorod by comparing the effect of other solvents, such as water, ethanol, isopropanol and glycerol. Furthermore, the photocatalytic activity of as-obtained hollow ZnO microspheres is evaluated by the degradation of methylene blue (MB) in aqueous solution. The photocatalytic performance reveals that these hollow ZnO microspheres can not only efficiently degradate the dye, but also show good stability during the cycling photodegradation.