▎ 摘　　要

NOVELTY - Preparation of three-dimensional graphene involves mixing nickel(II) chloride hexahydrate with deionized water, heating in water bath, adding hydrazine hydrate, turning light purple solution, and heating; placing water bath cylinder on magnetic stirrer, stirring, removing light purple adhering on cup wall using deionized water, cooling, adding sodium hydroxide solution, turning light green, darkening as reaction time increases, reacting, appearing black precipitate on bottom of solution, and taking upper layer as clear solution; washing black precipitate with deionized water and ethanol, filtering, vacuum drying to obtain spherical nickel nanoparticles, placing ceramic ring on ceramic plate, filling loose nickel nanoparticles, placing in center of quartz tube type furnace, heating, and sintering nickel nanoparticles; and introducing methane gas in tube type furnace, cooling furnace, and coating three-dimensional nickel template surface with multi-layer graphene. USE - Method for preparing three-dimensional graphene used as working electrode in electrochemical biosensor for detecting levodopa (claimed). ADVANTAGE - The method solves low sensitivity and poor selectivity when detecting levodopa. The product has small aperture size, large specific surface area and good conductivity. DETAILED DESCRIPTION - Preparation of three-dimensional graphene involves: (A) mixing 0.1-0.3 mol of 80 wt.% nickel(II) chloride hexahydrate with deionized water, heating in 50?oC water bath to completely dissolve nickel(II) chloride hexahydrate, adding 0.4-1.2 mol hydrazine hydrate, turning light purple solution, and heating to 60?oC; (B) placing water bath cylinder on magnetic stirrer, stirring at speed of 300-500 revolutions/minute, removing light purple adhering on cup wall using deionized water, cooling to 50?oC, adding 0.4-1.2 mol of 50 wt.% sodium hydroxide solution, turning light green, darkening as reaction time increases, reacting for 3 hours, appearing black precipitate on bottom of solution, and taking upper layer as clear solution; (C) washing black precipitate with deionized water and ethanol, filtering, vacuum drying at 60-80?oC for 3-4 hours to obtain spherical nickel nanoparticles, placing ceramic ring on ceramic plate, filling loose nickel nanoparticles, placing in center of quartz tube type furnace, heating from room temperature to 700-800?oC at heating speed of 10-2?oC/minute under argon gas and hydrogen gas protection, keeping at 700-800?oC for 30-60 minutes, and sintering nickel nanoparticles to form three-dimensional nickel template; introducing methane gas in tube type furnace at 700-800?oC for 10-20 minutes at flow rate of 5-20 sccm, cooling furnace to room temperature at cooling rate of 100-150?oC/minute, and coating three-dimensional nickel template surface with multi-layer graphene; and dissolving polymethyl methacrylate in ethyl lactate, heating and stirring at 80-120?oC for 1-2 hours to obtain mixed solution, dropping to graphene-coated three-dimensional nickel template, keeping at 150-200?oC for 0.5-1 hour, soaking at 80-90?oC, removing nickel in 3-4 mol/L hydrochloric acid solution for 6-12 hours, soaking in acetone at 60-70?oC for 4-6 hours, cleaning using deionized water, transferring on clean indium tin oxide glass, and freeze-drying for 0.5-1 hour to obtain three-dimensional graphene/indium tin oxide electrode. The ceramic ring has outer diameter of 26.3 mm, inner diameter of 18.2 mm and thickness of 3 mm. The diameter of spherical nickel nanoparticles is 200-500 nm. The flow rate of argon gas is 450-500 sccm. The flow rate of hydrogen is 100-200 sccm. The mass fraction of polymethyl methacrylate in mixed solution is 4-5%.