Fabrication of different silica nanotubes and examination of their catalytic activity in organic solvents

Silica nanotubes (SNTs) with different geometrical architectures and comparable pore sizes were fabricated inside the one-dimensional (1D) channels of anodic alumina membrane (AAM) using different nonionic Brij template surfactants. Experimental results revealed the formation of SNTs with ordered 1D, two-dimensional (2D), three-dimensional (3D), and wormlike mesostructures. Cytochrome C (Cyt C) was chosen as a hemoprotein to be immobilized inside the SNTs. Under the same starting Cyt C concentration, the amount immobilized was found to be dependent on the SNT mesostructure. Unlike native Cyt C, which lost its activity while interacting in organic solvents, Cyt C entrapped within silica nanotube hybrid membrane (SNM) showed remarkable catalytic conversion activity in organic solvents, with wormlike mesostructure being favorable over ordered mesostructures. This could be ascribed to facile access to active centers of Cyt C due to the random orientations of wormlike SNTs.