Received 22 March 2013, revised 10 June 2013, online published 19 July 2013 Defence Science Journal, Vol. 63, No. 4, July 2013, pp. 435-441, DOI: 10.14429/dsj.63.4870  2013, DESIDOC 1. INTRODUCTION Titanium dioxide is a benchmark photocatalyst for the successful decontamination of the organic pollutants in both liquid and gas phases. Although TiO 2 has several advantages, it has two critical limitations for large scale technical applications. They are (i) electron hole recombination which limits its effciency 1 . (ii) it absorbs only 2-3% of the solar light impinging on the earth’s surface as it can be excited only under UV irradiation with wavelengths shorter than 400 nm. To overcome the limitations innumerable methods have been applied to enhance the photocatalytic activity of TiO 2 by increasing active sites of reaction, retardation of electron– hole recombination and visible light catalysis by modifcation of band–gap 2-4 . Recently, among carbon materials, after the discovery of carbon nanotubes 5 , TiO 2 -MWCNTs composites have attracted much attention of researchers because of the remarkable electrical 6-7 , mechanical 8 and thermal 9 properties of MWCNTs and the promising applications of TiO 2 -MWCNTs composites for the big problem of pollutions 10 due to their high capability to conduct electrons and adsorb hydrophobic organic pollutants, hardly adsorbed by TiO 2 nanoparticles themselves 11,12 . The synergistic effect of carbon nanotubes on the activity of composite catalyst can be explained in terms of its action as adsorbent and dispersing agent. Further MWCNTs consisting of multiple layers of graphite superimposed and rolled in on them to form tubular shape conductive structure might facilitate the separation of the photo- generated electron/hole pairs at the TiO 2 -CNT interface leading to the faster rates of photocatalytic oxidation and enhancement in the effciency of titanium dioxide. Different techniques have been employed for the preparation of TiO 2 -CNTs composites. Mostly TiO 2 is coated on the surface of CNT. The composites can be prepared by various methods 13,14 which includes sol-gel, 15-18 impregnation 19 , electro-spinning, 20,21 electrophoretic deposition 22 , chemical vapor deposition 23 and hydrothermal method 24 . Among this sol-gel has been used extensively for mechanical mixing of CNT-TiO 2 composites 25,26 . Composites prepared by hydrothermal methods are mostly found to give better results as it favors a decrease in agglomeration among particles, narrow particle size distribution, phase homogeneity and controlled particle morphology. In the present study, we have prepared TiO 2 -MWCNTs nanocomposites by in-situ deposition of TiO 2 on the MWCNTs by hydrothermal treatment. 2. EXPERIMENTAL 2.1 MWCNTs Functionalization The pristine MWCNTs (Multi Walled Carbon Nanotubes) were purchased from Plasma Chem. GmbH Berlin, having diameters of 5-20 nm, lengths of 1-10 μm and carbon purity is minimum 95%. Purifcation and functionalisation of MWCNTs is needed to remove impurities and to improve the solubility of MWCNTs in water by introducing anionic groups on their surfaces 27 . In a typical purifcation treatment, 1g pristine MWCNTs were sonicated in the equal volume of conc. HCl for 1 hr and allowed to settle down, after settling yellow coloured supernatant acid was observed. This colour indicates that there is a Fe impurity present in the pristine MWCNTs. This Fe impurity has been removed by repeating same procedure Preparation, Characterisation and Photocatalytic Applications of TiO 2 -MWCNTs Composite Kirti D. Shitole, Roshan K. Nainani, and Pragati Thakur * University of Pune, Pune-411 007, India * E-mail:prthakur@chem.unipune.ac.in ABSTRACT The nanocomposite of TiO 2 -MWCNTs has been synthesised by simple hydrothermal route showing signifcant enhancement in the photocatalytic activity for the degradation of methyl orange dye (MO). Several characterisations employed were X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy- dispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM), Raman spectroscopy.XRD pattern shows the formation of anatase phase in prepared TiO 2 which was retained in TiO 2 -MWCNTs composite as well. The Raman spectrum of prepared TiO 2 -MWCNT shows the interface integration of TiO 2 and MWCNTs which is further supported by TEM data. Complete decolorisation and degradation of dye using TiO 2 -MWCNTs nanocomposite has been observed only in 45 minutes of UV irradiation. 65 per cent reduction in chemical oxygen demand (COD) value of treated dye shows substantial mineralisation of dye by composite catalyst. Dye degradation reactions were found to follow frst order kinetics. Keywords: MWCNTs, TiO 2 , methyl orange, photocatalysis 435 brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by Defence Science Journal