Hello, thanks for your question. I will need a little more info to help you out. Are the black leaves coming from a tree? What kind of tree? are the leaves sticky, or are there other sticky leaves on the tree?
I suspect you are dealing with sooty mold. It is an issue that arises from the presence of insects, commonly aphids, on plant material. However, it is difficult to say with certainty based on the info provided. here is a link to info on sooty mold:
I hope you find this information helpful,