i asked them not to use the word but they still used the f word quiet frequently
You should consult with a local employment attorney about what action(s) you could take. Foul language does not always constitute sexual harassment nor is it always illegal. Speak to an attorney about the details of your employment, your interactions with and observations of this coworker and any knowledge management has of his actions. You can search for an attorney on Avvo or contact the National Employment Lawyers Association for a referral.
If a local lawyer cannot help you, then perhaps you can go the boss or the human resource department and ask, in a nice and professional way, for help in maintaining a productive work environment for you that does not include undue profanity.
Try to be positive if you take that approach.
Not legal advice. Just friendly advice.