▎ 摘　　要

NOVELTY - Preparing graphene oxide by recycling concentrated sulfuric acid comprises (1) mixing flake graphite and concentrated sulfuric acid according to a mass volume ratio of 1: 15-30, performing ultrasonic treatment, reducing the temperature of a material to be below 10° C, and adding potassium permanganate to obtain a material to be reacted, where the mass ratio of the potassium permanganate to the flake graphite is 1.5-2.5: 1, (2) reacting the material to be reacted at 10°C or less for 0.1-0.5 hours, heating to 28-32°C in an ultrasound system, reacting for 1.9-2.1 hours, continuing heating to 38-42°C to react for 1.4-1.6 h, and continuing to raise the temperature to 48-52°C to react for 0.5-1.1 h to obtain a reaction material, (3) performing solid-liquid separation on the reaction material to obtain recovered concentrated sulfuric acid and solid material. USE - The graphene oxide is useful in preparing a graphene thermal conductive film, the thermal diffusion coefficient of the graphene thermal conductive film is 750 mm2/s or more. DETAILED DESCRIPTION - Preparing graphene oxide by recycling concentrated sulfuric acid comprises (1) mixing flake graphite and concentrated sulfuric acid according to a mass volume ratio of 1: 15-30, performing ultrasonic treatment, reducing the temperature of a material to be below 10° C, and adding potassium permanganate to obtain a material to be reacted, where the mass ratio of the potassium permanganate to the flake graphite is 1.5-2.5: 1, (2) reacting the material to be reacted at 10°C or less for 0.1-0.5 hours, heating to 28-32°C in an ultrasound system, reacting for 1.9-2.1 hours, continuing heating to 38-42°C to react for 1.4-1.6 h, and continuing to raise the temperature to 48-52°C to react for 0.5-1.1 h to obtain a reaction material, (3) performing solid-liquid separation on the reaction material to obtain recovered concentrated sulfuric acid and solid material, (4) adding high-purity water to the obtained solid material to obtain a dispersion, where the temperature of the whole process is controlled to be below 60° C; sequentially washing the obtained dispersion by using a sulfuric acid solution having a mass concentration of 2%, 1% and 0.5%, and filtering to obtain an acid-washed solid material, (5) homogenizing the acid-washed solid material to obtain graphene oxide, (6) adding the concentrated sulfuric acid recovered in step (3) to the fuming sulfuric acid to adjust the mass concentration of the recovered concentrated sulfuric acid to 97.5% or more, stirring and filtering by using a filtering device containing a magnetic bar, reacting the filtrate with the crystalline flake graphite again, and repeating the operations (1)- (6).