Photodegradation of organic dyes based on anatase and rutile TiO 2 nanoparticles† Ashish Gautam, Anuraj Kshirsagar, Rahul Biswas, Shaibal Banerjee and Pawan K. Khanna * The present work highlights a simple nanochemistry based clean and efficient process for effective degradation of various organic dyes by use of anatase and rutile TiO 2 nanoparticles. Based on photodegradation studies it was observed that at certain experimental parameters, rutile TiO 2 was as effective as anatase for the degradation of indigo carmine (IC) dye in aq. solution. However, anatase TiO 2 was found to be much more efficient against methylene blue (MB), methyl orange (MO), rhodamine B (RB) and eriochrome black T (EBT) under short UV irradiation. The photodegradation study of these organic dyes was also performed under long UV irradiation employing both anatase and rutile titania and the results showed similar trends. However, only EBT photodegradation indicated equal photocatalytic activity by both phases. The catalytic degradation of the organic dyes was studied by degradation kinetics. The maximum degradation efficiency using anatase and rutile titania photocatalysts was found to be 88% and 77% in the case of MB under short UV irradiation while about 65% was found in the case of EBT under long UV irradiation. The reuse of photocatalyst even after five cycles retained the degradation efficiency of 83% and 71% respectively for anatase and rutile when tested against MB. 1. Introduction Dye pollutants, found in the waste water from various chemical industries such as paints, dyes and textile etc. are a major concern for a clean environment as such pollutants can adversely affect the environment causing health hazards to living organisms. 1–3 Safe and effective disposal and degradation of harmful organics from such polluted water is needed. Currently, the methods employed for the degradation/ decomposition of harmful dyes are either by dye adsorption onto a certain solid support or their catalytic decomposition in the form of gaseous molecules via green chemical reactions. 4 The absorption method is normally employed where precious metal catalysts are part of the degradation process. However, degradation through chemical reactions may involve liberation of harmful gases into the atmosphere. 4b Owing to such limitations, it is need of the present time that suitable, robust and green non-toxic materials as well as processes are designed and practiced to handle the issue of environmental pollution. Nanotechnology has played a vital role in recent time to handle such issues in more effective manners. Oen metal oxide nano-particles have been employed for degradation of organic dyes. Advancement in photocatalysis research led to use of oxygen rich metal oxides nano-particles for promotion of the oxidation of organic molecules facilitating green decomposi- tion. 5,6 Amongst the metal oxide materials, nano-TiO 2 offers advantages due to its band-gap in the desired UV-Visible spec- tral range as a photocatalyst. Besides its optical properties, TiO 2 has been found to be a non-toxic and stable material, which is available at lower cost. The common forms of this metal oxide are known to be anatase and rutile with the former one being the strongest oxidizer among the two whereas presence of rutile with anatase only enhances its photocatalytic activity. TiO 2 (oen anatase) is known to be an effective photocatalyst and has found varied applications for its role in photocatalytic processes thus making it an environmentally friendly candidate for waste water treatment and water purication. 6–8 It has been documented in literature that, the exposure of nano-TiO 2 to UV radiations results in the formation of hydroxyl radicals (cOH) which eventually initiates the oxidation of the organic pollutants in water and completes the degradation process. The dye pollutants so-oxidized and decomposed lead to carbon dioxide and water. 5 Additionally, TiO 2 nano-particles have been attractive because of their variety of industrial applications as well as due to their potential applicability in dye sensitized solar cells and photocatalysis. 8 Rutile phase of TiO 2 is particularly useful in cosmetics. 9,10 Reportedly, rutile TiO 2 nano- particles are never easy to synthesize by chemical methods however, phase pure anatase TiO 2 can be converted to rutile phase by high temperature sintering process between 500  C to Nanochemistry Laboratory, Dept. of Applied Chemistry, Defence Institute of Advanced Technology (DIAT-DU), DRDO, Govt. of India, Pune-411025, India. E-mail: pawankhanna2002@yahoo.co.in † Electronic supplementary information (ESI) available: UV, weight loss upon sintering, tabulated XRD and XPS, SEM/EDS, FTIR, BET, TGA etc. See DOI: 10.1039/c5ra20861k Cite this: RSC Adv. , 2016, 6, 2746 Received 8th October 2015 Accepted 21st December 2015 DOI: 10.1039/c5ra20861k www.rsc.org/advances 2746 | RSC Adv. , 2016, 6, 2746–2759 This journal is © The Royal Society of Chemistry 2016 RSC Advances PAPER