Wet Chemical Preparation Of NiO-based Network Films And Their Gas Sensing Properties

With the problem of environmental pollution becoming more and more serious in recent years,the detection of harmful gases becoming a topic of much concern,the appearance of gas sensor has attracted people’s attention.As gas-sening performance is closely related to the morphological structure of the material,the gas-sening performance can be optimized by increasing the specific surface area of the material to improve the adsorption of the target gas.Based on this requirement,we not only report NiO-based network films prepared by the wet chemical preparation,but also study their morphologies and gas-sensing performances.The following are our main results.Polycrystalline cubic NiO films are formed by precursor films via chemical bath deposition after 400°C heat treatment.NiO films appear with the network-like structure consisting of interconnected nano flakes with the thickness of about 200–300 nm.The nano flakes become nanoporous,which the width of the hole is about 5 nm.The NiO nanosheet array gas sensor was fabricated by in-situ growth and heat treatment on an alumina substrate with Pt interdigitated electrodes.The testing results found that the best working temperature is 200°C,and can detect the concentration of H₂S gas as low as 10 ppm.The sensitivity of this gas sensor is up to 78.4under the condition of 200°C and H₂S concentration of 50 ppm.Compared with NO₂,NH₃,SO₂and CO,NiO array membrane has better selectivity to H₂S gas.However,the study showed that the stability to H₂S gas was poor.On the basis of preparation of nano-structured NiO films by chemical bath deposition method,SnO₂/NiO composite films were further synthesized by combining with SnO₂.The morphology of SnO₂/NiO films is to cover the surface of the nano-sheet array with a uniform thin film.The thickness of nano-sheet films increased,with a thickness from 30 nm to 50 nm,forming a more stable porous structure,which the width of the hole is about 200–500 nm.According to the gas sensor based on SnO₂/NiO films testing,the optimal temperature is 200°C,and the lowest detection limit is 10ppm.Similarly,at 200°C and 50 ppm H₂S,the better sensitivity of the gas sensor made of SnO₂/NiO film is 82.It exhibites high response to H₂S gas among other test gases.What’s more,with rapid response and recovery,it has a small fluctuation and long-term stability.The comprehensive analysis indicates that SnO₂/NiO thin film gas sensor has better gas sensitive performance than NiO thin film gas sensor.The NiO films and nickel films prepared by sol-gel are polycrystalline films,both of which have a FCC structure.Consisting of densely packed nanoparticles,the as-prepared NiO films are smooth and uniform.The nickel thin films present porous structure.The width of the pore is ca.100 nm,and its length can reach hundreds of nanometers.According to the gas-sensor testing,at200°C,under the condition of 100 ppm H₂S,the sensitivity of the NiO thin gas sensor is 2.44,which is only 1.63%of that of the network-like NiO thin film gas sensor obtained by chemical bath deposition.Nickel thin film gas sensor has no dynamic response and poor sensitivity.