Immobilization of cobalt doped rutile TiO2 on carbon nanotubes walls for efficient photodegradation of 2,4-dichlorophenol under visible light

In this work, we focused on improvement of rutile-type TiO2 degradation efficiency by cobalt doping and decorating on carbon nanotubes walls (CNTs) (Co-TiO2/CNTs). We also synthesized pure TiO2, Co-TiO2 and TiO2/CNTs samples for control experiments. The textural and morphology features of the samples were characterized by a range of analyses including: XRD, FESEM/EDX. FTIR, TEM, UV-Vis DRS and N2 physisorption. The XRD results indicated that we obtained rutile phase as the major phase for TiO2 with crystal size between 18-22 nm. The band gap energy of the samples calculated from DRS analysis and Kubelka-Munk spectra and obtained 2.88, 2.38, 2.97 and 2.20 eV for TiO2, Co-TiO2, TiO2/CNTs and Co-TiO2/CNTs respectively. The effectiveness of the samples was examined through degradation of 2,4-dichlorophenol (2,4-DCP) as a model of organic pollutants in the synthetic wastewater under visible light. We achieved 27% and 50% visible light degradation of 2,4-DCP in the presence of pure TiO2 and Co-TiO2/CNTs after 180 min irradiation, respectively. The high visible light activity of Co-TiO2/CNTs sample could be approved that the presence of cobalt and CNTs reduced the band gap energy and sensitize TiO2 surface to visible light. The mechanism for degradation of 2,4-DCP by Co-TiO2/CNTs photocatalyst under visible light was proposed.