Direct Growth of Freestanding ZnO Tetrapod Networks for Multifunctional Applications in Photocatalysis, UV Photodetection, and Gas Sensing

Abstract

Growth of freestanding nano- and microstructures with complex morphologies is a highly desired aspect for real applications of nanoscale materials in various technologies. Zinc oxide tetrapods (ZnO-T), which exhibit three-dimensional (3D) shapes, are of major importance from a technological applications point of view, and thus efficient techniques for growth of different varieties of tetrapod-based networks are demanded. Here, we demonstrate the versatile and single-step synthesis of ZnO-T with different arm morphologies by a simple flame transport synthesis (FTS) approach, forming a network. Morphological evolutions and structural intactness of these tetrapods have been investigated in detail by scanning electron microscopy, X-ray diffraction, and micro-Raman measurements. For a deeper understanding of the crystallinity, detailed high-resolution transmission electron microscopic studies on a typical ZnO tetrapod structure are presented. The involved growth mechanism for ZnO tetrapods with various arm morphologies is discussed with respect to variations in experimental conditions. These ZnO-T have been utilized for photocatalytic degradation and nanosensing applications. The photocatalytic activities of these ZnO-T with different arm morphologies forming networks have been investigated through the photocatalytic decolorization of a methylene blue (MB) solution under UV light illumination at ambient temperature. The results show that these ZnO-T exhibit strong photocatalytic activities against MB and its complete degradation can be achieved in very short time. In another application, a prototype of nanoelectronic sensing device has been built from these ZnO-T interconnected networks and accordingly utilized for UV detection and H2 gas sensing. The fabricated device structures showed excellent sensing behaviors for promising practical applications. The involved sensing mechanisms with respect to UV photons and H2 gas are discussed in detail. We consider that such multifunctional nanodevices based on ZnO tetrapod interconnected networks will be of interest for various advanced applications.

Hybridization of Zinc Oxide Tetrapods for Selective Gas Sensing Applications

“…3,[12][13][14] Concentration of all tested gases (H2, ethanol vapour (EtOH), CO and CH4) was 100 ppm, as in previous works. 3,15 The relative humidity (RH) value during the measurements was set at normal ambient conditions of 30% RH, and was continuously measured by a standard hygrometer inside the test chamber. The gas response was calculated as the ratio between the electrical current under gas exposure (Igas) and the electrical current through the sensor in the ambient air (Iair).…”

“…[3][4][12][13][14] As above mentioned, before the integration of ZnO-T-MexOy and ZnO-TZnxMe1-xOy (Me = Fe, Cu, Al) hybrid networks into the sensor structure, the as-produced samples were subjected to thermal annealing in an electrical furnace at 1150 ºC for 5 h in air.…”

“…[1][2][3] Nanoarchitectures of semiconducting oxides are becoming important advanced materials with a large variety of exceptional properties for an extensive utilization, ranging from ultraviolet (UV) and gas sensing to biomedical and catalyst applications. [2][3] However, the rapid progress in nanotechnologies includes the continuous search of novel materials with new and unique functionalities, which is in focus of many research groups around the world. [1][2][3][4][5][6] In this context, fabrication of three-dimensional (3-D) networks of interconnected ZnO tetrapods (ZnO-T) has been a very important step for progress in engineering, science and nanotechnology.…”

“…[2][3] However, the rapid progress in nanotechnologies includes the continuous search of novel materials with new and unique functionalities, which is in focus of many research groups around the world. [1][2][3][4][5][6] In this context, fabrication of three-dimensional (3-D) networks of interconnected ZnO tetrapods (ZnO-T) has been a very important step for progress in engineering, science and nanotechnology. 1,[3][4][6][7][8] Recently the research group of Rainer Adelung has demonstrated a fast and simple synthesis of highly porous interconnected ZnO-T networks by a crucible flame transport synthesis (C-FTS) approach and burner flame transport synthesis (B-FTS).…”

Synthesis of ZnO with Enhanced Photocatalytic Activity: A Novel Approach Using Nanocellulose

“…As an n-type semiconductor (Maryam and Aziz 2016), ZnO has excellent optoelectrical behavior due to its natured wide band gap and large exciton binding energy. Nanoscale ZnO is a next-generation semiconductor material with potential applications in the catalytic and luminescent fields (Mishra et al 2015). These outstanding properties, which are to some degree attributable to small-size effects, allow wide applications of nano-ZnO in wastewater treatment, sterilization, and environmental protection (Memarian et al 2011).…”