Research On Toluene Sensing Performance Of Ni-based Heterojunctioned Materials Derived From Layered Double Hydroxides

Indoor volatile organic compounds(VOCs)have attracted more and more attention because of their potential toxicity,mutagenicity and carcinogenicity.National Standardization Management Committee has made regulations on indoor air quality standards in China(GB/T18883-2002),among which the standards for indoor VOCs have reached dozens of ppb levels.Metal oxide(MOX)gas sensors show more advantages than other types of sensors in terms of sensitivity,manufacturing cost,and integration.So,it's of great practical significance to develop a high-sensitivity MOX gas sensor.Layered double hydroxides(LDHs),as a lamellar material with a unique atomic arrangement,can be used to synthesize various functional materials with uniformly dispersed heterostructures.This paper mainly studies the application of the MOX gas sensor prepared with nickel-based layered double hydroxides as the precursor in the detection of low-concentration toluene vapor.The specific research contents are as follows:(1)Nickel,gallium nitrate and urea were used as raw materials to synthesize nickel-gallium layered double hydroxides(NiGa-LDHs)precursor by a hydrothermal method and a series of toluene gas sensor materials were fabricated by a high temperature calcination in air with an annealing step at hydrogen atmosphere.In the synthesis process,the influence of the metal cation molar ratio of Ni and Ga on the gas sensitivity was explored.The gas sensor material with a Ni/Ga molar ratio of 2.5 showed the highest response at 200? when testing the response to 5 ppm toluen.At the same time,the influence of annealing temperature on the gas sensing performance was studied.Annealing at 300? can help improve the sensor's response to toluene,which can be attributed to the synergy effect of oxygen vacancies and Schottky barriers.(2)Nickel-indium layered double hydroxides(NiIn-LDHs)precursors were synthesized by a co-precipitation method with raw materials of nickel and indium nitrates.A toluene gas sensor material based on NiIn-LDHs precursor was prepared on a high-temperature calcination step.Through exploring the influence of the molar ratio of metal cations in the raw materials on the gas sensing performance during the synthesis process,the results shows that when Ni/In was 3.0,it owned the highest response at 275?.In order to further enhance the gas sensitivity,the sample with the highest response was annealed at a hydrogen atmosphere.The gas sensitivity of the sample annealed at 300? has the greatest enhancement effect compared to the unannealed sample.The enhancement of gas sensitivity can be attributed to the synergistic effect of p-n junction,Schottky barrier and oxygen vacancies.