The present invention relates to the process for the scalable production of Fe3O4/Fe, Sn & Zn doped graphene nanosheets from a naturally abundant seaweed resources such as Sargassum tenerrimum, Sargassum wighti, Ulva faciata, Ulva lactuca and Kappaphycus alvarezii. The granules remained after the recovery of liquid juice from the fresh seaweeds were utilized as a raw material and a deep eutectic solvents (DESs) generated by the complexation of choline chloride and FeCl3, ZnCl2 and SnCl2 were employed as template as well as catalyst for the production graphene nanosheets functionalized with metals. Pyrolysis of the mixture of seaweed granules and DES at 700-900° C. under 95% N2 and 5% H2 atmosphere resulted formation of metal doped graphene sheets with high surface area (120-225 m2·g−1) and high electrical conductivity 2384 mS·m−1 to 2400 mS·m−1. The nanosheets thus obtained could remove substantial amount of fluoride from fluoride contaminated drinking water (95-98%).