▎ 摘　　要

NOVELTY - Preparing three-dimensional graphene/carbon nanofiber composite material involves performing electrospinning method by adding 11 gram polyacrylonitrile powder, dissolving in 10 mL dimethylformamide solution, and heating at 80-150 degrees C for 1-2 hours to obtain electrospinning solution. 10-20 mL electrospinning solution is transferred to syringe which is fixed on a syringe pump, and electrospinning is carried out at 10-20 kiloVolts. The solution flow rate is 1-3 mL/h, and the collection distance is 10-15 cm. The polyacrylonitrile fiber is placed in a blast drying oven, heated to 300-400 degrees C at a rate of 1-2 degrees C/minute for 1-2 hours for stabilization. The stabilized polyacrylonitrile fiber is placed in the center of the tube furnace and heated from room temperature at a heating rate of 5-10 degrees C/minute to at 800-1000 degrees C under an argon atmosphere for 60 to 100 minutes, then cooled to room temperature with the furnace to obtain carbon nanofibers. USE - Method for preparing three-dimensional graphene/carbon nanofiber composite material as working electrode of biosensor for electrochemical detection of levodopa (claimed). ADVANTAGE - The method enables to prepare three-dimensional graphene/carbon nanofiber composite material which has high detection sensitivity and low detection limit. DETAILED DESCRIPTION - Preparing three-dimensional graphene/carbon nanofiber composite material involves performing electrospinning method by adding polyacrylonitrile powder, dissolving in dimethylformamide solution, heating to obtain electrospinning solution and transferring to syringe which is fixed on a syringe pump, and electrospinning is carried out at 10-20 kiloVolts. The solution flow rate is 1-3 mL/h, and the collection distance is 10-15 cm. The polyacrylonitrile fiber is placed in a blast drying oven, heated to 300-400 degrees C at a rate of 1-2 degrees C/minute for 1-2 hours for stabilization. The stabilized polyacrylonitrile fiber is placed in the center of the tube furnace and heated from room temperature at a heating rate of 5-10 degrees C/minute to at 800-1000 degrees C under an argon atmosphere for 60 to 100 minutes, then cooled to room temperature with the furnace to obtain carbon nanofibers. The flow rate of the argon gas described is 300-500 standard cubic centimeters per minute. The electroless nickel plating method is performed by cutting the carbon nanofiber into a sheet having area of 3 cm2 and soaked in oil solution at 60-80 degrees C for 30-60 minutes to remove oil and washed multiples times with distilled water, immersed in a mixed solution containing ammonium persulfate and concentrated sulfuric acid for 15-30 minutes for coarsening and washed with distilled water. The solution is immersed in a tin(II) chloride solution for 3 to 10 minutes for sensitization and washed multiple times with distilled water. The immersed lead(II) chloride solution is stirred for 3 to 10 minutes for activation and washed multiple times with distilled water, immersed with 25-30 g/L nickel sulfate hexahydrate, 30-35 g/L sodium hypophosphite hydrate, 30-35 g/L sodium citrate and 70-75 g/L ammonium chloride. The electroless nickel plating is started in the electroless nickel plating solution, nickel is plated under alkaline conditions, pH is adjusted by using ammonis hydrate, where pH is 8-10 and reaction temperature is 50-70 degrees C and reaction time is 30-50 minutes, and frozen dried. The chemical vapor deposition is performed by palcing nickel-plated carbon nanofibers are added in a quartz tube furnace, heated at 800-1000 degrees C from room temperature at heating rate of 10-20 degrees C/minute under the protection of argon and hydrogen at 800-1000 degrees C for 10-20 minutes at 800-1000 degrees C. The methane gas is introduced into the tube furnace at a rate of 10-20 standard cubic centimeters per minute for 20 min~30 min, then the quartz tube furnace is is heated at rate of 80-100 degrees C/minute at 800-1000 degrees C and cooled to room temperature to obtain nickel-plated carbon fiber coated with graphene. The flow rate of argon gas is 480-500 standard cubic centimeters per minute, hydrogen gas flow rate is 180-200 standard cubic centimeters per minute. The graphene-coated nickel-plated carbon fiber is immersed in 3-5 moles/L hydrochloric acid for 1-2 hours to remove nickel to obtain graphene/carbon nanofiber composite.