Covalent functionalization of multi-wall carbon nanotubes (MWNTs) by nickel(II) Schiff-base complex: Synthesis, characterization and liquid phase oxidation of phenol with hydrogen peroxide

The chemical modification of multi-wall carbon nanotubes (MWNTs) is an emerging area in material science. In the present study, hydroxyl functionalized nickel(II) Schiff-base has been covalently anchored on modified MWNTs. The new modified MWNTs have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron (XPS), thermal analysis, UV–vis, diffuse reflectance (DRS), FT-IR spectroscopy and elemental analysis. The results suggest that the symmetrical Schiff-base; N,N′-bis(4-hydroxysalicylidene)-ethylene-1,2-diamine; H2[(OH)2-salen]; is a bivalent anion with tetradentate N2O2 donors derived from the phenolic oxygen and azomethine nitrogen. The formula was found to be [Ni((OH)2-salen)] for the 1:1 non-electrolytic complex. Multi-wall carbon nanotubes covalently anchored nickel(II) complex ([Ni((OH)2-salen)]@MWNTs) catalyze the oxidation of phenol with H2O2. Oxidation of phenol catalyzed by this complex gave catechol and hydroquinone as major products. A suitable reaction condition has been optimized for [Ni((OH)2-salen)]@MWNTs by considering the effect of various parameters such as reaction time and amount of oxidant, different solvents, concentration of substrate, etc. for the maximum transformation of phenol.