Preparation Of Three-Dimensional Graphene And Its Gas Sensing Properties

Since the first report in 2004,graphene has received tremendous attention due to its unique two-dimensional honeycomb structure,low electronic noise,ultrahigh electron mobility and specific surface area,electrical conductivity at room temperature,and excellent mechanical properties;its high specific surface area and electron mobility make this material have great potential in the field of gas sensing.Herein,we prepared three-dimensional foamed graphene and tubular graphene on nickel foam and nickel nanowires through chemical vapor deposition(CVD),and further explored their sensing performances for NO2.The specific research and experimental contents are as follows:(1)With methanol as carbon source gas,graphene was synthesized on nickel foam via CVD.Furthermore,high-quality and small-layer graphene was obtained by controlling the reaction temperature and methanol concentration.Subsequently,graphene foam was obtained through etching the nickel foam substrate.The sensing measurement results showed that the three-dimensional foamed graphene-based sensor can response to NO2 reversibly with high sensitivity and excellent selectivity.For 50 ppm NO2 gas,the response of the gas sensor was?33.07%.When NO2 concentration decreased to 500 ppb,it still showed a response of 22.00%.Comparison of three consecutive 50 ppm NO2 gas tests demonstrated that the three-dimensional foamed graphene-based sensor can response to NO2 repeatedly within 300 s.With the aid of the UV lamp,it can return to the original resistance value within 200s.In addition,the sensor exhibited a larger resistance change on exposure to NO2 more than 10 times than other contrast gases.(2)Nickel nanowires can be synthesized via chemical reduction in magnetic field.Through CVD method,graphene was synthesized on nickel wire.By changing reaction temperature and methanol concentration,high-quality and thin graphene was obtained.After etching the nickel wires and assembling it on fork finger electrode,the three-dimensional tubular graphene-based sensor was successfully fabricated.The three-dimensional tubular graphene-based device showed a resistance change of 16.4%on exposure to 50 ppm NO2 at room temperature.When the concentration of NO2 drops to an ultra-low concentration(100 ppb),it still showed a response of 5.5%.The good repeatability of the sensor can be demonstrated by three cycles of continuous testing at low NO2 concentration of 5 ppm,the maximums of response for which were basically maintained at 9%.When exposed to NO2,the sensor can reach the highest response value within 400 s and return to the initial state within 300 s with the aid of the UV lamp.In addition,the three-dimensional tubular graphene-based device showed relative lower response(<1%)to other contrast gases than to NO2,suggesting the excellent selectivity for NO2.In this paper,gas sensors were successfully fabricated from two three-dimensional graphene materials.At room temperature and atmospheric enviroent,the devices showed high sensitivity,repeatability and selectivity on exposure to NO2,which have great potential in NO2 gas molecular detection.