Nanocapsules based on carbon nanotubes-graft-polyglycerol hybrid materials

Abstract

In this work the effect of a conjugated macromolecule on the conformation of CNT wasstudied. Typically polyglycerol (PG) was covalently grafted onto the surface ofmulti-wall carbon nanotubes (MWCNTs) and MWCNT-graft-PG (MWCNT-g-PG) hybrid materials were obtained. Dynamic light scattering (DLS)experiments showed an average diameter around 100 nm for MWCNT-g-PG hybrid materials in water. The difference between this size and the expected size for MWCNT-g-PG hybrid materials (the length of pristine MWCNTs was several micrometers)was assigned to the effect of the grafted PG on the conformation ofMWCNT in the solution state. Transmission electron microscopy (TEM)evaluations showed a change in the shape and conformation of MWCNT-g-PG hybrid materials during the time so that they were in a core–shell shape in a freshsample but over time they changed to dendritic- and finally nanocapsule-like structures.According to ultraviolet–visible (UV–vis) experiments it was found that MWCNT-g-PG hybrid materials were able to encapsulate small guest molecules such as ferrocene,confirming nanocapsule-like structures for hybrid materials in the solution state. Based onthese observations it was suggested that non-covalent interactions between highly hydrophilicPG and highly hydrophobic MWCNT led to changes in the conformation of MWCNT froma linear to nonlinear state. In order to investigate the role of hydroxyl end functionalgroups of PG as being responsible for non-covalent interactions such as hydrogen bonding,they were reacted with opened MWCNTs (MWCNT–COOH) to achieve MWCNT-g-PG-g-(MWCNT)n structures. TEM images showed an extended conformation for MWCNT-g-PG-g-(MWCNT)n hybrid materials which confirmed the key role of hydroxyl end functionalgroups of PG on the conformation of MWCNTs. To evaluate the ability of MWCNT-g-PG-g-(MWCNT)n hybrid materials to encapsulate and support guest molecules, palladiumnanoparticles were loaded and transported by these hybrid materials and their reactivitytoward Heck reactions was also investigated.