I prepared reduced graphene oxide (rGO )coating Co3O4 composites (denoted as rGO/Co3O4) employing a temperate coprecipitation method and using GO-MOFs . For comparision,I plan to prepare rGO sandwiching Co3O4 composites (denoted as Co3O4-rGO-Co3O4) employing eco-friendly reduction of graphene oxide(GO) to rGO.What is the suitable eco-friendly reductant for this synthesis?