Carbon-nanotube-templated microfabrication (CNT-M) of porous materials is demonstrated. Partial chemical infiltration of 3D carbon-nanotube structures with silicon results in a mechanically robust material, structured from the 10 nm scale to the 100 mu m scale. The nanoscale dimensions are determined by the diameter and spacing of the resulting silicon/carbon nanotubes, while the microscale dimensions are controlled by the lithographic patterning of the CNT growth catalyst. We demonstrate the utility of this hierarchical structuring approach by using CNT-M to fabricate thin-layer-chromatography (TLC) separations media with precise microscale channels for fluid-flow control and nanoscale porosity for high analyte capacity. Chemical separations done on the CNT-M-structured media outperform commercial high-performance TLC media.