Sentiment data for Emoji
Total of 972 emoji is not really that big not to be able to label them manually, but I doubt that they will work as a good ground truth. Sources like Twitter are full of irony, sarcasm and other tricky settings where emotional symbols (such as emoji or emoticon) mean something different from normal interpretation. For example, someone may write "xxx cheated their clients, and now they are cheated themselves! ha ha ha! :D". This is definitely negative comment, but author is glad to see xxx company in trouble and thus adds positive emoticon. These cases are not that frequent, but definitely not suitable for ground truth. 

Much more common approach is to use emoticon as a seed for collecting actual data set. For example, in this paper authors use emoticon and emotional hash tags to grab lexicon of words useful for further classification.