Synthesis of silica nanotubes with orientation controlled mesopores in porous membranes via interfacial growth

Silica nanotubes with mesopores perforating the wall were synthesized on the channel surface of porous anodic alumina (PAA) or polycarbonate membranes via interfacial growth. Transmission and scanning electron microscopy characterizations indicated that the mesopore orientation can be regulated from perpendicular to the wall to circling the axis when the thickness of the silica nanotube wall increases from about 15 to 40-60 nm, without any modification of the channel surface or external forces, just by optimizing the amount of the tetraethoxysilane confined in the channels of PAA. Mesopores in the silica nanotube wall arrange hexagonally when the diameter of the silica nanotubes is larger than 200 nm.