Investigation On Preparation And Trace-level H₂S Sensing Performance Of Zinc Oxide Nanowires

ZnO, as a typical semiconducting metal oxide, is the first discovered material which has good gas sensing properties, and also it was the one earliest (1962) proposed to be applied to gas sensor as the sensing materials. It not only has low price and simple preparation but also has big surface-area-to-volume ratio, high electron mobility and good chemical/thermal stability, these making it an advantageous candidate for gas sensitizer. After 40 years of development, the scientific personnel have basically solved the problems of sensitivity and selectivity in ZnO gas sensor, thereafter it was widely used in the detection and control of flammable, toxic and other dangerous gases. Nowadays, the commercial ZnO gas sensor still has some drawbacks, such as poor stability, low selectivity and short service life, that defects severely limited its further promotion in the market.In this paper, we devoted to altering ZnO dimension, constructing ZnO heterostructure and exploring its sensing mechanism. A series of experiments were designed to systematically study the relationship of H2S sensing properties with ZnO’s dimension and composition. Some good research results were obtained and the details are as follows:(1) ZnO nanowires with the diameter of 50-60nm were synthesized by hydrothermal method and their growth regularity was surveyed and mastered. The ZnO’s morphology and composition were characterized and analyzed comprehensively by SEM, TEM, XRD, XPS and GC-MS, and then their sensitivity to different gas was tested. Experimental sensing results show the ZnO nanosize-effect induced the ultra-high and repeatable sensitivity to tens of H2S gas. According to the experimental results and basing on the traditional gas sensing mechanism of surface control type, a new sulfuration-desulfurization gas sensing mechanism was proposed by our group. The novel H2S sensing mechanism is fully clarified by specifically designed experiments, material characterization and theoretical analysis.(2) ZnO nanowires with the diameter of 20-30nm were synthesized by a hydrothermal method, and the key factor influencing the diameter of ZnO nanowires was found. The morphology was characterized by SEM and TEM, its sensitivity to different gas was tested. An exhaustive study of the relationship between ZnO’s sensing performance and its size dimension was accomplished. With respect to the 50nm ZnO, the selectivity and sensitivity of 20nm ZnO are improved significantly, the detection limit has declined from 50ppb to lOppb. It is reducing the diameter of nano ZnO that increase the ZnO reactivity and promote its sensing properties.(3) ZnO/ZnS core-shell heterostructure with the diameter of 200nm was prepared by two-step hydrothermal method. With the help of SEM and EDS, the compound’s external morphology and composition were characterized and analyzed. Its sensitivity to H2S and C2H5OH gas was measured. The results show that the gas sensitivity of ZnO/ZnS heterostructure is better than pure ZnO nanowires. A new practical way of improving sensor sensitivity was found.