working as prepositions, there are many differences between 对and 向:
1, 向= indicating time, place and direction
e.g. 一直向前走。
对=indicating the objects ( someone or something)
e.g. 说说你对这件事的看法。
2, 向 can be used to express " from...", but 对can not .
e.g.他向我借了自行车。
3, 对 can be used to express the relationship between people and someone/ something, means "treat" , but 向 can not.
e.g. 老师对我特别好。
sometimes, 对and 向 are interchangable when they are followed by the object of an action: e.g. 他对我笑了笑。/ 他向我笑了笑。