Preparation and Ethanol Sensing Properties of ZnO Nanoparticles via a Novel Sol-Gel Method

ZnO nanoparticles were prepared using a novel sol-gel method. Chemical reactions were carried out between zinc acetate and methanol under ambient conditions using monoethanol amine (MEA) as surfactant and subsequent heating at 2 0 0 ° C . The powders were calcined, pressed into pellets, and presintered. The properties of the product were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectra. For gas sensing experiment, ethanol was used as testing gas. The gas sensing results showed that the maximum value for detecting of 1000？ppm ethanol vapor was 25 at an operating temperature of 3 7 0 ° C . 1. Introduction Oxide semiconductor nanostructures have been widely investigated in recent years because of their excellent properties [1] and application in novel optical, electrical, and mechanical devices such as photovoltaic solar cells, luminescence, biomedicine, photocatalysis, light-emitting diodes (LEDs), varistors, and optoelectronic nanodevices [2–6]. ZnO is an n-type II–VI semiconductor with wide band gap of 3.37？eV, large exciton binding energy (~60？meV), strong emission, large saturation velocity (~3.2 × 107？cm/s), and high breakdown voltage [7, 8]. These properties make it a promising material for optoelectronic devices in the ultraviolet (UV) and blue region of the electromagnetic spectrum [9], optical or display devices, solar cells [9, 10] catalysis [11], cantilevers production, piezoelectric applications [6], superficial acoustic waves (SAW) [12], and humidity [11] and gas sensors [13]. Furthermore, ZnO has high transparency, chemical and thermal stability, high conductance, and it is nontoxic, inexpensive, and one of the few oxides that exhibit quantum confinement effects in an experimentally accessible size range [2, 3]. ZnO nanostructures which can come in different shapes such as nanowires, nanobelts, nanorods, nanotubes, and nanoparticles can exhibit interesting physical and chemical properties not found in other nanostructures [14, 15]. ZnO in pure and doped form has been intensively studied, and ZnO gas sensor elements have been prepared and studied in different forms, mostly as thin films, thick films, single crystals, wintered pellets, and hetero junctions while not many have been reported in the bulk form [16, 17]. Various methods have been used for the production of ZnO nanostructures, such as vapor-liquid-solid (VLS) method, reaction-vapor deposition, physical vapor deposition, pulsed-laser deposition, thermal evaporation, metal organic chemical vapor deposition