There have been some low-tech centrifuge designs based on salad spinners - I would think you could make an insert to fit into one that could hold test tubes wit

There have been some low-tech centrifuge designs based on salad spinners - I would think you could make an insert to fit into one that could hold test tubes without too much trouble, though I don't know if it would be powerful enough to separate the graphene well. A good experiment...