Studi pengaruh penambahan material graphene terhadap karakterisasi, adsorpsi dan aktivitas catalytic nanokomposit LaMnO3/TiO2 dan LaMnO3/ZnO untuk degradasi methylene blue = Study of the effect of graphene material to the characterization, adsorption and catalytic activity of LaMnO3/TiO2 and LaMnO3/ZnO