▎ 摘　　要

NOVELTY - Preparing graphene oxide involves mixing the graphite raw material, concentrated sulfuric acid and potassium permanganate to obtain a graphene dispersion liquid, performing a first filtering process on the graphene dispersion liquid to obtain a primary filter cake and a primary filtrate, performing a second filtering treatment on the primary filtrate to remove manganese ion (Mn2+) and potassium ion (K+) in the filtrate to obtain a secondary filtrate, subjecting the primary filter cake and secondary filter liquid to a secondary mixing treatment and performing a third filtering treatment to obtain a secondary filter cake i.e. graphene oxide. USE - Method for preparing graphene oxide. ADVANTAGE - The method enables to utilize graphene oxide dispersion liquid as a purification reagent to remove Mn2+and K+in the graphene oxide to 1-50 ppm and 10-100 ppm, respectively, thus improving the degree of purification of graphene oxide and reducing the preparation cost. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: 1. the graphene oxide, which is prepared by the method; 2. a composite film, which is prepared by the graphene oxide; and 3. a method for preparing a composite film, which involves: a. providing the graphene oxide; b. coating the graphene oxide to obtain a graphene oxide film; c. carrying out a heat treatment to the oxidation graphene film; d. carbonizing and graphitizing the film to obtain the graphene film; and e. rolling the graphene film to obtain the composite film.