The design of hierarchical zinc oxide (ZnO) microstructures modified with silver (Ag) nanoparticles have emerged as an effective approach for improving the hydrogen gas sensing performance. Here, we report a simple, low-cost chemical co-precipitation method to obtain the Ag/ZnO hollow microstructures and morphologically characterized them by field emission scanning electron microscopy (FESEM). FESEM images revealed the clear hollow hexagonal tube-like morphology. The existence of Ag in ZnO was confirmed by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). UV visible absorption and photoluminescence (PL) spectra were also recorded to observe the effect of Ag nanofiller on the optical properties of ZnO. Furthermore, the gas sensing properties of the as-prepared bare ZnO and Ag/ZnO sensor were investigated. The thoroughly sensing experiments demonstrated that after modification with Ag nanoparticles the ZnO sensor shows superior sensitivity 479 % towards 300 ppm hydrogen gas concentration, whereas 101 % response was noted for the pure ZnO sensor at 250 °C working temperature. Meanwhile, Ag/ZnO hybrids exhibited excellent selectivity, fast response, and recovery time and also obtained a good and stable response signal at 5 ppm H2 exposure, which indicated that the lower concentration measurement is also attainable. This enhancement in the sensing performance of Ag/ZnO structures towards hydrogen is due to the chemical and electronic sensitization effect of Ag nanoparticles. As a result, such microstructure is attributed to more oxygen species and active sites, and it enhances the sensitivity of a sensor. Moreover, this type of hybrid opens a new path and supports the next generation of innovative materials to fabricate highly selective and sensitive H2 gas sensing devices.

An efficient hydrogen gas sensor based on hierarchical Ag/ZnO hollow microstructures

Superhydrophobic ZnO Nanowires: Wettability Mechanisms and Functional Applications

Zinc oxide (ZnO) nanorods have been extensively investigated, owing to their extraordinary applications in numerous fields, spatially microchip technology, solar cells, sensors, photodetectors, photocatalysts and many others. Recently, using ZnO nanorods, as photocatalysts, are receiving increasing attention in environmental defense applications. This mini review summarizes some remarkable applications for ZnO nanorods. First, the various chemical and physical procedures that were used to produce ZnO nanorods are identified through symmetric matrices and heterogeneous structures, then the authors explain how to use these methods to produce ZnO nanorods. This mini review, also, discusses the applications of ZnO nanorods in many fields, especially in field release, emission properties, and electron transference. Last but not least, the appropriate conclusions for future research using ZnO nanorods have been successfully explained.

Synthesis, properties and uses of ZnO nanorods: a mini review

Ultraviolet (UV) photodetectors (PDs) based on high-quality well-aligned ZnO nanorods (NRs) were fabricated using both modified and conventional chemical bath deposition (CBD) methods. The modified chemical bath deposition (M-CBD) method was made by adding air bubbles to the growth solution during the CBD process. The viability and effectiveness of M-CBD were examined by developing UV PDs based on ZnO NRs. The ZnO nano-seed layer was coated on a glass substrate utilizing radiofrequency (RF) sputtering. The impact of the different growth-times on morphology, growth rate, crystal structure, and optical and chemical properties were investigated systematically using different characterization techniques, such as field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) analysis, UV-VIS double beam spectrometer, and energy dispersive X-ray analysis (EDX), respectively. The Al/ZnO UV PDs based on ZnO nanorods were fabricated with optimum growth conditions through the two methods of preparation. This study showed that the synthesized ZnO NRs using the M-CBD method for different growth times possess better properties than the conventional method under similar deposition conditions. Despite having the highest aspect ratio and growth rate of ZnO NRs, which were found at 4 h growth duration for both methods, the aspect ratio of ZnO NRs using the M-CBD technique was comparatively higher than the conventional CBD method. Besides, the UV PDs fabricated by the M-CBD method at 5 V bias voltage showed high sensitivity, short response time, quick recovery time, high gain, low dark current, and high photocurrent compared with the UV PD device fabricated by the conventional CBD method.

Fabrication and Characterization of High-Quality UV Photodetectors Based ZnO Nanorods Using Traditional and Modified Chemical Bath Deposition Methods.

Nanostructured ZnO has got a lot of interest as a suitable material for various applications especially sensing, energy conversion and storage. ZnO nanostructures can be synthesized in a number of ways. It is one of the materials that can be prepared in a variety of morphologies including hierarchical nanostructures. This review article presents a review of current research activities on growth of ZnO Nanorods. The article covers various water based routes of synthesis, and is further characterized by the type of substrate used for the growth. The growth factors involved in the hydrothermal and chemical bath deposition methods are discussed. These factors include the variety of precursors, time, temperature and the seeding method employed. At the end, applications such as gas sensing and improvement in opto-electric properties in relation to the morphology are discussed.

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A review on synthesis and optoelectronic applications of nanostructured ZnO

In this study, the effects of different precursor concentrations on the growth and characteristics properties of the zinc oxide (ZnO) nanorods (NRs) synthesized by using modified and conventional chemical bath deposition (CBD) methods were investigated. The morphologic, structural and optical properties of synthesized ZnO NRs with different precursor concentrations were studied using various characterization techniques. The experimental results show that the varying precursor concentration of the reactants has a remarkable and significant effect on the growth and characteristics properties of ZnO NRs. In addition, the characteristic properties of ZnO NRs grown using the modified method showed significantly improved and enhanced properties. The average length of grown ZnO NRs increased with increased precursor concentration; it can be seen that longer ZnO NRs have been investigated using the modified CBD methods. The ZnO NRs synthesized at 0.05 M using the modified method were grown with high aspect ratios than the ZnO NRs grown using conventional means which were 25 and 11, respectively. The growth rate increased with increased precursor concentration; it can be observed that a higher growth rate was seen using the modification CBD method. Furthermore, XRD results for the two cases reveal that the grown ZnO samples were a nanorod-like in shape and possessed a hexagonal wurtzite structure with high crystal quality. No other phases from the impurity were observed. The diffraction peaks along (002) plane became higher, sharper and narrower as precursor concentration increased, suggesting that the crystalline quality of ZnO NRs grown using the modified method was more enhanced and better than conventional methods. However, optical studies show that the transmittance at each concentration was more than two times higher than the transmittance using the modified CBD method. In addition, optical studies demonstrated that the ZnO NRs grown by using modified and conventional methods had a direct Eg in the range of (3.2–3.26) eV and (3.15–3.19) eV, respectively. It was demonstrated in two methods that ZnO NRs grown at a precursor concentration 0.05 M gave the most favorable result, since the NRs had best characteristic properties.

https://www.mdpi.com/2073-4352/10/5/386/pdf

Munirah Abullah Almessiere

Papers

Enhancement of ZnO Nanorods Properties Using Modified Chemical Bath Deposition Method: Effect of Precursor Concentration

Fabrication and Characterization of High-Quality UV Photodetectors Based ZnO Nanorods Using Traditional and Modified Chemical Bath Deposition Methods.