The present invention relates to controlled growth of carbon nanotube (CNT) arrays via chemical vapor deposition (CVD) using novel porous anodic aluminum oxide (AAO) templates, which have been seeded with transition metal catalysts. The resulting CNT bundles may be dense and long and can be used for numerous applications. Further, the porous AAO templates and the CNTs grown thereby, can be functionalized and used for separation of chemical species, hydrogen storage, fuel cell electrocatalyst and gas flow membranes, other catalytic applications, and as a bulk structural material.