Is it legal to sell my art if I used some emoticons in it?

If the art can be considered fine art it might meet the requirements for Fair Use under Copyright law. To be considered Fine Art in this context, it might need to be a single original work of art. Think of the Andy Warhol paintings of Campbell Soup cans. If you need a further examination of whether your art might violate copyright or trademark, please discuss with a lawyer.

There shouldn't be a problem with using them in a work of art. They're just another form of fonts which can't be copyrighted, they're not trade or service marks, and art is usually considered a protected form of speech.