Gas Sensing Properties of Metal Cation Doping Oxide Semiconductors with Hierarchical Nanostructures

Abstract

Introduction Due to their high sensitivity to the target gases and simplicity in preparation, metal-oxide semiconductors such as SnO2, α-Fe2O3, ZnO, In2O3 and NiO [1-3] have been extensively investigated as sensing materials in the past ten years. Although exciting results have been reported, the development of more highly sensitive and markedly selective gas sensors based on hierarchical oxides nanostructures remains a challenge. In order to meet the increasing demands for making sensors work in more complicated systems and under more harsh conditions, many efforts have been taken such as element doping, heterostructure constructing, and adding catalyst. Among these methods, doping has been reported to be a very simple and feasible way to enhance the gas sensing properties of oxides via altering its structure and grain size or introducing an impurity level and surface defects etc. From this point of view, we adopted metal cations in-situ doping method to adjust the surface NiO nanostructures, aiming to realize the efficient detection of VOCs gases. Method The chemiresistive gas sensor is mainly composed of four parts: 1. A 4 mm long ceramic tube (internal diameter: 0.8 mm, external diameter: 1.2 mm), where a pair of gold electrodes with four Pt wires have been installed originally. 2. Sensing material layer (thickness: ~ 42 um) on the surface of ceramic tube. Taking the material based sensor as an example here. Mix the obtained powder with deionized water to form a slurry and coat the slurry uniformly on the whole surface of the ceramic tube. Then put the well-coated tube in the muffle furnace heating at 500 °C for 3 h in air. 3. A Ni-Cr alloy coil heater, it was inserted through the well-coated and sintered ceramic tube, controlling the working temperature via the flowing current. 4. A hexagon base, which supported the well-coated and sintered ceramic tube through welding. After ageing, the as-prepared sensors were tested through the static test system at a laboratory conditions (20 °C, 10% RH). Results and Conclusions The results indicated that the sensor based on 4.0 at% W-doped NiO sample showed the best gas sensing properties with a ppb-level detection limit (100 ppb), an ultra-high response and a good selectivity to acetone compared to pure NiO. The sensor based on 2.15 at% Al-NiO nanorod-flowers showed the greatly enhanced gas sensing performances to ethanol.