▎ 摘　　要

NOVELTY - The preparation method of graphene film involves (1) preparing black liquor lignin solution having 1-7 %mass methanol, ethanol or acetone as spin coating liquid, (2) taking 200-500 mu L black liquor lignin solution, dripping on a square metal foil by spin coating at speed of 3500-6000 rpm, where the metal foil is copper, nickel, copper-nickel alloy or iron-nickel alloy, (3) heating the metal foil coated with lignin coating at 800-1000 degrees C under the protection of inert gas, maintaining the temperature for 0.5-15 minutes after reaching the set temperature, quickly cooling the metal foil to room temperature, where the protective gas is nitrogen or argon gas, (4) taking polymethylmethacrylate acetone solution, dripping on a surface of the graphene film with a metal foil surface, spin coating, and drying, and (5) etching the metal substrate using 150-350 mL ferric chloride or ferric nitrate solution, and dissolving the polymethylmethacrylate film using acetone. USE - Preparation method of graphene film. ADVANTAGE - The method enables reliable and safe preparation of graphene film which uses rich raw material source, by simple and economical process. DETAILED DESCRIPTION - The preparation method of graphene film involves (1) preparing black liquor lignin solution having 1-7 %mass methanol, ethanol or acetone as spin coating liquid, (2) taking 200-500 mu L black liquor lignin solution, dripping on a square metal foil having thickness of 0.01-0.025 mm and side length of 10-50 mm by spin coating at speed of 3500-6000 rpm, where the metal foil is copper, nickel, copper-nickel alloy or iron-nickel alloy, (3) heating the metal foil coated with lignin coating at 800-1000 degrees C under the protection of inert gas, maintaining the temperature for 0.5-15 minutes after reaching the set temperature, quickly cooling the metal foil to room temperature, where the protective gas is nitrogen or argon gas, (4) taking 200-1000 mu L 2-5 %mass polymethylmethacrylate acetone solution, dripping on a surface of the graphene film with a metal foil surface, spin coating at speed of 500-2000 rpm, and drying at 40 degrees C for 6 hours, and (5) etching the metal substrate using 150-350 mL ferric chloride or ferric nitrate solution with concentration of 1-2 mol/L, and dissolving the polymethylmethacrylate film using acetone.