  We prove that Morrison and Nieh's categorification of the su(3) quantum knot
invariant is functorial with respect to tangle cobordisms. This is in contrast
to the categorified su(2) theory, which was not functorial as originally
defined. We use methods of Bar-Natan to construct explicit chain maps for each
variation of the third Reidemeister move. Then, to show functoriality, we
modify arguments used by Clark, Morrison, and Walker to show that induced chain
maps are invariant under Carter and Saito's movie moves.
