Radiation-induced grafting of carbon nanotubes on HPLC silica microspheres: theoretical and practical aspects

Multi-walled carbon nanotubes (MWCNTs) were for the first time grafted by gamma radiation to silica microspheres in presence of polybutadiene (PB) as the linking agent, obtaining a novel hybrid material with chromatographic properties, with an alternative approach to the existing procedures.
The synthesis entails the one-pot  radiation-induced grafting of MWCNTs onto silica microspheres in presence of PB as linking agent. PB also serves as coating layer of the silica particles, to which MWCNTs are anchored through stable chemical bonds formed via radical chain reaction with the polymer. The product (MWCNT-PB modified silica) resulted in MWCNT bundles interlaying the silica particles which acted as support and as a spacer. This new material highlights the unquestionable properties of CNTs also when grafted in a composite, thus allowing to dispose of a more robust material whose properties are still related to the nanotube structure. The grafting was confirmed by Raman spectroscopy. Surface area, determined by BET isotherms, resulted 132 m2 g-1, about 34% lower than that of pure silica, pointing to the cross-linking effect of PB in the silica matrix. The evaluation of MWCNT-PB modified silica as a LC stationary phase was performed by separation of aromatics, with satisfactory resolution and reproducibility, while structural selectivity was proved by isomers separation. Nice resolution was obtained also for acid/basic compounds as barbiturates. Comparison with a commercial C18 sorbent highlighted the advantage in using the CNT column for separating aromatic hydrocarbons. Control experiments on the PB-coated silica column proved the key role of MWCNTs in the chromatographic performance.