Synthesis And Application Of Poly(Ethylene Glycol) Functionalized Multiwalled Carbon Nanotubes

In this paper, poly(ethylene glycol) (PEG) functionalized multiwalled carbon nanotubes (MWNT-PEG) and isocyanatopropyltriethoxysilane (IPTES) functionalized multiwalled carbon nanotubes (MWNT-IPTES) were prepared using the grafting-onto method. Then silica (SiO2) nanotubes were synthesized through sol-gel process using MWNT-PEG and MWNT-IPTES as the templates, respectively. In addition, the inclusion interaction between MWNT surface anchored PEG chains andα-cyclodextrin (α-CD) was also investigated. The main contents were as follows:(1) Synthesis of MWNT-PEG and MWNT-IPTES. Firstly, the hydroxyl functionalized multiwalled carbon nanotubes (MWNT-OH) was treated with excess toluene 2,4-diisocyanate (TDI), after which the residual isocyanate groups were reacted with PEG (Mn = 400, 1000, 2000, and 4000 g/mol) to form MWNT-PEG. The MWNT-PEG was further treated with IPTES to give MWNT-IPTES. FTIR, TGA, UV-vis, and TEM techniques were employed to characterize the synthesized MWNT-PEG and MWNT-IPTES. The results indicated that the PEG was successfully grafted onto the surface of MWNT. In addition, TGA results indicted that 100 percent of–OH on the surface of MWNT-PEG was reacted with IPTES.(2) MWNT templated synthesis of SiO2 nanotubes. SiO2 nanotubes were synthesized via sol-gel process using MWNT-PEG and MWNT-IPTES as the templates, respectively. Through the hydrolysis of tetracthoxysilane (TEOS), a continuous coating of SiO2 was deposited over the surface of MWNT-PEG to form core–shell structures. Hollow silica structures were finally obtained after calcining process. The as-prepared hollow products were characterized with FTIR, SEM, TEM and EDX. A shorter diameter ranged from 35 to 80 nm and a thin wall (about 6 nm) structure of hollow SiO2 nanotubes were obtained according to the SEM and TEM photographs. The effects of the concentration of the reactants and the templates on the formation of SiO2 nanotubes were also investigated. The results indicated that the diameter of the SiO2 nanotubes and their thickness of wall were increased with the increasing of the concentration of TEOS. Moreover, SiO2 nanotubes could not be obtained using neat PEG or MWNT-OH as the templates.(3) The inclusion complexation between MWNT-PEG andα-CD. MWNT-PEG samples were used to form inclusion complexes (ICs) withα-CD through the grafted PEG chains being threaded withα-CD rings in aqueous solution. The FTIR, TGA, UV-vis, and SEM techniques were employed to characterize the formed ICs. The ICs formation time was monitored by UV-vis spectroscopy, and the results indicated that the inclusion interaction between MWNT surface anchored PEG chains andα-CD was dependent on the molecular weight of PEG. The grafted PEG with molecular weights of 4000 and 2000 g/mol, respectively, can form ICs withα-CD, while the grafted PEG with molecular weights of 1000 and 400 g/mol, respectively, are difficult to form ICs withα-CD due to the steric hindrance from nanotubes. The stoichiometry value determined by TGA indicated that the ratio of ethylene glycol (EG) unit toα-CD in the resulted ICs was about 15:1. In addition, the morphology of the ICs was observed by scanning electron microscopy (SEM).