▎ 摘　　要

NOVELTY - Synthesizing functionalized graphene using a plant extract comprises (1) preparing a mixed solution in which the layers are separated into supernatant/supernatant solution by mixing graphite with plant extract, applying ultrasonic waves for a predetermined time, and allowing to stand, (2) taking only the supernatant from the mixed solution, separating/obtaining graphene functionalized with a hydrophilic functional group from the supernatant, and (3) washing and drying the obtained functionalized graphene to obtain a graphene powder functionalized with a hydrophilic functional group. The plant extract is of Gallnut, Armoracia rusticana, Morus nigra, Mentha, Panax ginseng, Moringa oleifera, Murraya koenigii, and Nelumbo nucifera. USE - The graphene is useful for producing gold nanoparticle-functionalized graphene complex (claimed). ADVANTAGE - The functionalized graphene: is environmentally friendly and structurally stable; has physical/chemical resistance and electrical conductivity, high thermal conductivity and thermal resistance. The complex has UV protection properties, and antioxidant properties and has peroxidase mimic activity. The method does not use strong acid or toxic substance. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: functionalized graphene prepared by above mentioned method; producing gold nanoparticle-functionalized graphene complex comprising (a) dispersing functionalized-graphene in a dispersion medium, (b) adding a gold precursor to the prepared graphene dispersion while stirring to form gold nanoparticles on the surface of the functionalized graphene, and (c) centrifugation, washing, and drying to obtain a functionalized graphene-gold nanoparticle complex; gold nanoparticle-functionalized graphene composite prepared by above mentioned method; and natural enzyme substitute comprising the gold nanoparticle-functionalized graphene complex.