The present invention relates to a mcthod of producing a inctionalized grapheme nanofluid comprising the steps of preparing exfoliated graphene oxide by treating graphite with acid in the presence of potassium permanganate ;reacting the exfoliated graphene oxide by treating graphite with acid in the presence of potassium permanganate; reacting the exfoliated graphene oxide with saffron in a reaction medium comprising ammnonium solution to obtain functionalized graphene; ultrasonicating the functionalized graphene; and dispering the ultrasonicated functionalized graphene in distilled water to produce the functionalized graphene nanofluid.