Modification of multiwall carbon nanotubes with ruthenium(II) terpyridine complex

Multiwall carbon nanotubes (MWCNTs, 1–3 μM in length and 20–25 nm in diameter) were initially functionalized with a 2,2′:6′2″-terpyridine-chelated ruthenium(II) complex by covalent amidation. The resulting functionalized ruthenium MWCNTs (RuMWCNTs, 1–2 μM in length and 10–20 nm in diameter) were characterized by thermogravimetric analysis, X-ray photoelectronic spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and scanning electron microscopy (SEM). Thermogravimetric experiments of RuMWCNTs show that the functional group coverage of terpyridine–rutheniun–terpyridine (tpy–Ru–tpy) is 0.7036 mmol/1.0 g carbon. The XPS results show N1s and Ru3d5/5 signals, confirming the presence of tpy–Ru–tpy groups on the surface of MWCNTs. The FTIR spectra of the RuMWCNTs display the typical stretching mode of the carboxyl group (amide I) and a combination of amide N–H and C–N stretching mode (amide II). The Raman D- and G-line peak intensity ratio of RuMWCNTs (ID/IG 2.21) exceeds that of pristine MWCNTs (ID/IG 1.93), suggesting covalent bonding of tpy–Ru–tpy to MWCNTs and supporting the disruption of the graphitic integrity due to the proposed covalent functionalization. High-resolution SEM images confirm that tpy–Ru–tpy moieties are interconnected or attached as aggregated structures (100–200-nm range) on the surfaces of the carbon nanotubes after functionalization. The electrical property of RuMWCNTs depicts higher resistance (10.10 M Ω) than that of OX-MWCNTs (15.38 kΩ).