Solar photocatalytic degradation of 2,6-dinitro-p-cresol (DNPC) using multi-walled carbon nanotubes (MWCNTs)-TiO2 composite photocatalysts

Multi-walled carbon nanotubes (MWCNTs)-TiO2 composite photocatalysts with excellent activity were prepared by sol-gel method in order to investigate its photocatalytic activity under solar irradiation for the degradation of 2,6-dinitro-p-cresol (DNPC) in aqueous solution. The prepared composite were analyzed by XRD, FTIR, SEM, TEM, TG-DTA and UV-vis absorption spectra techniques. The results showed that the composite can cause an obvious red shift of UV-vis spectra compared with pure TiO2. The degradation of DNPC by MWCNTs-TiO2 composite photocatalysts under solar irradiation was systematically studied by varying the experimental parameters such as pH value, irradiation time, the initial substrate concentration, reaction temperature, catalyst concentration, etc. The optimal conditions were a DNPC concentration of 33.4 mg L-1 at pH 6.0 with MWCNTs-TiO2 concentration of 6.0 g L-1 under solar irradiation for the illumination of 150 min. The presence of MWCNTs can enhance the photoefficiency of TiO2. The highest efficiency on photodegradation of DNPC can be achieved with an optimal MWCNTs/TiO2 mass ratio of 0.05%. The photocatalytic degradation of DNPC obeys a pseudo-first-order behavior according to the Langmuir-Hinshelwood model, and possible decomposing mechanisms are also discussed. The photocatalyst was used for five cycles with photocatalytic degradation efficiency still higher than 96%. The results of the study showed the feasible and potential use of MWCNTs-TiO2 composite in degradation of toxic organic pollutants. (C) 2009 Elsevier Ltd. All rights reserved.