The present study outlines a one-step route to the preparation and functionalization of graphene nanosheets from graphene oxide using tea polyphenols as a simultaneous reductant and functionalization reagent. This method uses a “green” reductant and is free of additional functionalization reagents, thus it is environmentally friendly, simple, and low-cost. The resulting functionalized graphene nanosheets have a mostly single-layer structure, are stable, and have very good water dispersibility. The structure, composition, and morphology of the resulting material were characterized by using various methods including, X-ray diffraction (XRD), UV/Vis spectroscopy, Raman spectroscopy, detailed X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Among other possible applications of the functionalized graphene, we discuss its use as an adsorbent for heavy-metal ions in aqueous solutions.