Flame-made Zn-substituted SnO2 nanoparticulate compound for ultra-sensitive formic acid gas sensing

Abstract This research conducts a detailed study on the sensitivity and selectivity of Zn-substituted SnO2 nanoparticles towards formic acid (HCOOH), an important volatile organic acid (VOA) for various technological applications. SnO2 nanoparticles containing 0.1−1 wt% Zn were made by flame spray pyrolysis (FSP) and sensing films were manufactured by powder pasting and spin coating processes. The physical and chemical properties of the samples were assessed by XRD, EDS, XPS, nitrogen adsorption and electron microscopy. The results indicated that Zn was substitutionally doped in nanocrystalline SnO2 particles. Gas sensing properties of the materials were evaluated towards 50−1000 ppm HCOOH and other volatile organic compounds at varying temperatures from 200 to 400 °C in dry and humid air. The test data revealed that the sensing layer with the optimum Zn content of 0.2 wt% provided a remarkably high response of ~46,374 toward 1000 ppm HCOOH, which was more than two orders of magnitude higher than undoped ones at 350 °C. Additionally, good HCOOH selectivity was achieved against several volatile organic species including formaldehyde, methanol, ethanol, acetone, benzene, xylene, acetic acid, propionic acid, butyric acid, pentanoic acid and lactic acid. Therefore, the flame-made Zn-substituted SnO2 sensors were potential for ultra-sensitive and selective detections of HCOOH in practical applications.