You think biology plays no part in determining what you "know [...] is wrong" or what you "feel a moral duty" about? What makes you think that?Free will is freedom from hard determinism. It is the freedom to act against what your biology is telling you to do. When you resist the temptation to do something you really want to do, simply because you know it is wrong and you feel a moral duty not to do what your biology is telling you to do, that is free will.
I think it's all biology.
Wouldn't you agree that if you end up not doing something, there is an important sense in which you didn't "really want to do" it? So, how can your definition of "free will" ever be satisfied, then?