Writing in college has a very specific target audience- your classmates or your professor/instructor. Particularly when writing essays , your professor or instructor expects you to write formally (using proper etiquette, grammar, style, and tone).
If you were writing a letter to the President of the United States, or even the President of your company, you would not use exclamation points and emoticons. Would you? You would not do this when writing for your professor / instructor either.