Sintesis dan karakteristik Fe2O3, Mn2O3, Fe2O3/Mn2O3 dan Fe2O3/Mn2O3/Graphene dalam aktivitas foto-fenton untuk mendegradasi limbah pewarna = Synthesized and characterization of Fe2O3, Mn2O3, Fe2O3/Mn2O3 and Fe2O3/Mn2O3/Graphene in photo-fenton activity for dye waste degradation