Composites of Titanate Nanotube and Carbon Nanotube as Photocatalyst with High Mineralization Ratio for Gas-Phase Degradation of Volatile Aromatic Pollutant

Abstract

The nanocomposites of one-dimensional titanate nanotubes and carbon nanotubes (TNT-CNT) have been synthesized by controlling the preparation conditions carefully during the hydrothermal treatment of TiO2 nanoparticles and carbon nanotube (CNT) in a concentrated alkali solution and the subsequent post-treatment. Using the gas-phase degradation of benzene, a volatile aromatic pollutant commonly present in urban atmosphere, as a testing reaction we for the first time have investigated the photocatalytic performance of TNTs and TNT-CNT nanocomposites together. The results show that one-dimensional tubular TNT exhibits enhanced photocatalytic performance toward the gas-phase degradation of benzene as compared to the reference photocatalyst of bare P25-TiO2 nanoparticles. Doping a certain amount of CNT into the matrix of TNT affects the conversion ratio of benzene only slightly; however, the mineralization ratio for degradation of benzene is remarkably increased to about 90%. This observation is particularly interesting because it is markedly different from that over the nanocomposites of TiO2 nanoparticles and CNT. The possible reasons have been put forward based on the results of photocatalytic activity and analysis of detailed characterization results including the transmission electron microscopy and electron spin resonance spectra. We ascribe the high mineralization ratio for benzene degradation over TNT-CNT to the following factors, that is, the unique one-dimensional nanotubular morphology associated with TNT-CNT, enhanced adsorptivity of benzene due to the doping of CNT, and enhanced light absorption intensity. In particular, the former factor of nanotubular morphology plays a more important role on enhancement of the mineralization ratio for degradation of benzene because the latter two factors are also found over the composites of TiO2 nanoparticles and CNT. Moreover, in view of the facile availability of tunable optical properties of TNT via substitution of sodium ions and proton ions in TNT with transition metal ions, there would be a wide scope to optimize the photocatalytic performance of TNT-based one-dimensional materials and their nanocomposites with CNT, which could be an interesting research topic with regard to TiO2-carbon composites as photocatalyst for the environmental remediation.