Biotemplate synthesis of graphitic carbon-doped ZnO tube bundles rich in oxygen vacancies for dual-sensing of NO2/H2S at different temperatures

How to fabricate one chemiresistive sensor for highly dual-selective detection of hazardous NO2 and H2S gases is a challenge owing to the fact that the great majority of gas sensors were designed to monitor only a given harmful gas. For the aim of portable practicality and internet of things, based on green and sustainable concept, natural poplar branches were utilized as template and simply soaked in zinc nitrate solution. Subsequently, the immersed biotemplates underwent air calcination to controllably reproduce two biomorphic ZnO-based materials. Among, the hierarchical tubes (GC/ZnO) prepared by calcination at 450 °C are interconnected by 5.68 wt% in-situ graphitic carbon (GC) and uniform nanoparticles, which possess small mesopores, large specific surface area and massive oxygen vacancies. Such distinctive microstructure not only facilitates rapid gas diffusion into sensing layer and modulates the state of adsorbed oxygen species, but also exposes more active sensing units and promotes surface chemical reactions, thus realizing a portable gas sensor for highly sensing and dual-selective detection of NO2 and H2S. At lower 92 °C or 133 °C, the GC/ZnO sensor exhibits response values of 203 and 65.5 for 10 ppm NO2 or H2S gases, respectively. Meanwhile, it possesses reversible response-recovery, low detection limit, good moisture tolerance and stability during 60 days. In addition, the temperature-controlled dual-response mechanism is also analyzed.