Carbon nanotubes (CNTs) doped titania for environmental cleaning application

Introduction: The implementation of the novel significant concept and technology for the development of the advanced constructive material for the environmental cleaning is the thrust area. Nanomaterials and nanotechnologies have opened certain doors for the preparation of effective and better performance based materials. As a part of nanomaterials, titanium dioxide (TiO2) has been exploited widely in photocatalysis reactions targeted at removing organic pollutants from water as one of most effective environmental cleaning application (1). As a photocatalyst, the main limitation with TiO2 is its relatively wide band-gap energy, and as a result, the material cannot be effectively used with the visible light energy (1). To overcome this critical disadvantage, there are different synthetic approaches being applied to reduce band-gap and decrease the recombination rate of the generated electrons and holes and hence, improved photocatalytic efficiency. These approaches include formation of TiO2-composite in which carbon nanotubes (CNTs) making huge impact and proven to be suitable candidates amongst the available materials (2). Therefore, CNTs have great potential to combine with TiO2 to form composite semiconductors, allowing electron exchanges between CNTs and TiO2. Nevertheless, this implicates that CNTs in the composite can help concentrate organic compounds on the composite surface, enhancing the photocatalytic degradation rate (2). In the present work, we have prepared CNT-doped TiO2 by using sol-gel method and explored its photocatalytic activity. Methods: We have prepared CNT-doped TiO2 with 0.01, 0.025, 0.05, 0.075 and 0.1 at % MWCNT (multi-walled carbon nanotubes with diameter of 25-50 nm) content by mixing the required amount of MWCNT in titanium tetra iso-propoxide (TTIP)-methanol solution at room temperature followed by dropwise addition of aqueous ammonia in the solution under stirring till the pH of 9-10. The obtained gel was filtered, washed with methanol, and dried at room temperature for 2 h and then at 80 °C for 12 h and finally the dried gel was calcined for 4 h at 400 °C to get CNT/TiO2 samples. The obtained TiO2/CNTs samples have been characterized for the instrumental methods of analysis and used to evaluate their photocatalytic activity by conducting a photocatalytic degradation study of methylene blue (MB) dye under ultraviolet (UV) irradiation using photocatalytic reactor buildup with magnetic-stirrer and air circulation. Results & Discussions: The Fourier-transform infrared (FTIR) spectra showing characteristics peaks attributed to Ti-O-Ti and Ti-O-C bonds confirming the formation of CNT/TiO2. X-ray diffraction patterns for TiO2 and CNT/TiO2 samples show the distinctive peaks for TiO2 in the anatase phase. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images clearly show a good dispersion and presence of small agglomeration of TiO2 particles on CNTs. The photo-luminescence (PL) emission peak intensity was gradually decreased indicating that loading of CNT onto the TiO2 efficiently separated the photogenerated electron-hole pairs and therefore it was expecting to have good photo-response efficiency. As results of photodegradation study, among the prepared CNT/TiO2 samples, 0.1 at % MWCNT in CNT/TiO2 was exhibited with high percentage (~88%) of MB dye degradation indicating more photocatalytic active compared to other samples and pure anatase TiO2. Conclusions: The preliminary experiment results of decolorization of MB dye under UV light irradiation shows that introduction of CNT into TiO2 matrix has improved a photo-response ability of pure TiO2. Further, optimization in reaction parameters for photocatalytic degradation would lead better efficiency for removal of such toxic dyes and environmental pollutants as well. Keywords: Titanium dioxide, Photocatalysis, Carbon nanotubes, Nanomaterial Acknowledgment: This work was supported by the University Grants Commission, India [No. F.4-2/2006/BSR)/CH/16-17/0049]. References Parangi T and Mishra MK. Titania Nanoparticles as Modified Photocatalysts: A Review on Design and Development. Comments on Inorganic Chemistry. 2019; 39(2); 90-126. Woan K, Pyrgiotakis G and Sigmund W. Photocatalytic Carbon nanotube-TiO2 Composites. Advanced Materials, 2009; 21(21); 2233-2239