Defects of multi-walled carbon nanotubes as active sites for benzene hydroxylation to phenol in the presence of H2O2

Multi-walled carbon nanotubes (MWCNTs) with different defect densities have been obtained by heating and ultrasonication in nitric acid solution and used directly as catalyst for the hydroxylation of benzene in the presence of H2O2. The results showed that the catalytic activity increased with increasing defect densities of MWCNTs and had no direct relationship with the MWCNT diameters and oxygen-containing groups. The defects produced by heating and ultrasonication exhibited the same catalytic activities in hydroxylation reaction. The catalysis reaction was proposed to occur via active oxygen attacking benzene process. The active oxygen was generated by H2O2 decomposition on the defect of MWCNTs with dangling incomplete bonding. And cyclic voltammetry tests also showed that the current density of H2O2 decomposition increased along with increasing MWCNT defect densities. Thus, highly defective MWCNTs could accelerate the hydroxylation of benzene.