특별한 is adjective. You're right.
And speaking of 특별, it is listed as a noun like 특별함 in dictionary.
특별함 is used itself as a noun meaning specialty or distinction.
Meanwhile, I have never seen people using 특별 alone as a noun.
It's rather used like adjective with noun and comes before noun.
특별구역, 특별만남, 특별활동...etc