Converting nitrobenzene to freestanding polyaniline tube arrays has been successfully carried out in a "water-oil-water" triphasic reaction system, where catalytic reduction of nitrobenzene to aniline and aniline polymerization reactions were synergistically integrated. With optimized control over molecular diffusion and reaction at separate solid/liquid and liquid/liquid interfaces, polyaniline nanostructures could be synthesized with different morphologies. The paired molecular diffusion and reaction rate is revealed as the dominating factor that determines the feasibility of the reaction system to produce a patterned array structure. Slow molecular diffusion leads to a better ordered three-dimensional (3D) assembling structure. This work demonstrates a new approach to control 3D assembling structures