Fabrication of mesoporous silica-coated CNTs and application in size-selective protein separation†

In this study, we report a simple method to coat mesoporous silica onto carbon nanotubes (CNTs) via a two-step procedure. Mesoporous CNTs@SiO2 composites have been obtained by extracting cetyltrimethylammonium bromide (CTAB) via an ion-exchange procedure after silica-coated carbon nanotubes were synthesized with the aid of the cationic surfactant CTAB. The coating process was explicitly investigated, and a possible formation mechanism of the mesoporous CNTs@SiO2 was proposed, which reveals that the ratio of CTAB/CNTs plays a critical role in the coating process. Furthermore, the pore size of the as-prepared mesoporous silica could be exactly controlled by using different amounts of the bromide surfactant CTAB. The obtained mesoporous CNTs@SiO2 composite nanomaterial was evaluated with three typical proteins, cytochrome c (Cyt c), bovine serum albumin (BSA) and lysozyme (Lyz), with different molecular sizes. The adsorption and desorption of binary mixtures of Cyt c and BSA, Cyt c and Lyz, and a ternary mixture of Cyt c, BSA and Lyz showed that the mesoporous CNTs@SiO2 are effective and highly selective adsorbents for Cyt c. The as-prepared mesoporous CNTs@SiO2 composites have shown effective performance in size-selective adsorption of biomacromolecules, demonstrating great potential in biomacromolecular separation.