Photocatalysis using semiconductor oxides was being investigated extensively for the degradation of dyes in effluent water. This paper reports our findings on visible light induced photocatalytic degradation of azo dye, methyl red mediated nitrogen and manganese codoped nano-titanium dioxide (N/Mn-TiO2). The codoped samples with varying weight percentages were synthesized by sol-gel method and characterized by various analytical techniques. The X-ray diffraction data showed that the synthesized samples were in anatase phase with 2 at 25.3°. UV-visible diffuse reflectance spectral analysis revealed that the presence of dopants in TiO2 caused a significant absorption shift towards visible region and their presence was confirmed by X-ray photoelectron spectral data. The release of hydroxyl radical (major active species in photocatalytic degradation) by the photocatalyst in aqueous solution under visible light irradiation was quantitatively investigated by the photoluminiscent technique (PL). The effect of various experimental parameters like dopant concentration, pH, catalyst dosage, and initial dye concentrations was investigated and optimum conditions were established. The extent of mineralization of methyl red was studied by chemical oxygen demand (COD) assays and the results showed complete mineralization of the dye. 1. Introduction Dyes are the resistant compounds that are found in industrial waste water causing adverse environmental problems. Most of the dyes used in the pigmentation of textiles, leather, paper, ceramics, and food-processing are derived from azo dyes. Approximately 15% of these are lost with waste water during synthesis and processing [1]. This represents a great hazard to human and environmental health due to the toxicity of azo dyes [2]. The treatment of such pollutants can be achieved by heterogeneous photocatalysis due to its efficiency and low cost as well as to the fact that it allows complete degradation of pollutants to carbon dioxide and inorganic acids [3]. TiO2 has attracted a great deal of study for its high photocatalytic activity. But the fatal drawbacks of TiO2 are its wide band gap and high rate of electron-hole () recombination [4]. A number of studies have been reported on the modification of TiO2 in order to extend the absorption of light to the visible region. These include dye sensitization, semiconductor coupling, impurity doping, use of coordination metal complexes, and metal deposition [5]. Among all these methods, codoping TiO2 with a metal and nonmetal is found to be most suitable. According to literature
References
[1]
M. A. Mahmoud, A. Poncheri, Y. Badr, and M. G. Abd El Waned, “Photocatalytic degradation of methyl red dye,” South African Journal of Science, vol. 105, no. 7-8, pp. 299–303, 2009.
[2]
T. Sauer, G. C. Neto, H. J. José, and R. F. P. M. Moreira, “Kinetics of photocatalytic degradation of reactive dyes in a TiO2 slurry reactor,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 149, no. 1–3, pp. 147–154, 2002.
[3]
S. K. Kavitha and P. N. Palanisamy, “Photocatalytic and sonophotocatalytic degradation of reactive red 120 using dye sensitized TiO2 under visible light,” International Journal of Civil and Environmental Engineering, vol. 3, pp. 1–6, 2011.
[4]
C. Kormann, D. W. Bahnemann, and M. R. Hoffmann, “Preparation and characterisation of quantum size titanium dioxide,” The Journal of Physical Chemistry, vol. 92, no. 18, pp. 5196–5201, 1988.
[5]
N. Hariprasad, S. G. Anju, E. P. Yesodharan, and Y. Suguna, “Sunlight induced removal of Rhodamine B from water through semiconductor photocatalysis: effects of adsorption, reaction conditions and additives,” Research Journal of Material Science, vol. 1, pp. 9–17, 2013.
[6]
Y. N. Tan, C. L. Wong, and A. R. Mohamed, “An overview on the photocatalytic activity of nano-doped-TiO2 in the degradation of organic pollutants,” ISRN Materials Science, vol. 2011, Article ID 261219, 18 pages, 2011.
[7]
D. Dvoranova, V. Brezova, M. Mazur, and M. A. Malathi, “Investigations of metal-doped titanium dioxide photocatalysts,” Applied Catalysis B: Environmental, vol. 37, pp. 91–105, 2002.
[8]
J. Zhu, Z. Deng, F. Chen et al., “Hydrothermal doping method for preparation of Cr3+-TiO2 photocatalysts with concentration gradient distribution of Cr3+,” Applied Catalysis B: Environmental, vol. 62, no. 3-4, pp. 329–335, 2006.
[9]
G. Wu, T. Nishikawa, B. Ohtani, and A. Chen, “Synthesis and characterization of carbon-doped TiO2 nanostructures with enhanced visible light response,” Chemistry of Materials, vol. 19, no. 18, pp. 4530–4537, 2007.
[10]
K. R. Patil, S. D. Sathaye, Y. B. Khollam, S. B. Deshpande, N. R. Pawaskar, and A. B. Mandale, “Preparation of TiO2 thin films by modified spin-coating method using an aqueous precursor,” Materials Letters, vol. 57, no. 12, pp. 1775–1780, 2003.
[11]
U. G. Akpan and B. H. Hameed, “The advancements in sol-gel method of doped-TiO2 photocatalysts,” Applied Catalysis A: General, vol. 375, no. 1, pp. 1–11, 2010.
[12]
H. Natori, K. Kobayashi, and M. Takahashi, “Preparation and photocatalytic property of phosphorus-doped TiO2 particles,” Journal of Oleo Science, vol. 58, no. 7, pp. 389–394, 2009.
[13]
K. R. Reyes-Gil, E. A. Reyes-García, and D. Raftery, “Photoelectrochemical analysis of anion-doped TiO2 colloidal and powder thin-film electrodes,” Journal of the Electrochemical Society, vol. 153, no. 7, pp. A1296–A1301, 2006.
[14]
Q. R. Deng, X. H. Xia, M. L. Guo, Y. Gao, and G. Shao, “Mn-doped TiO2 nanopowders with remarkable visible light photocatalytic activity,” Materials Letters, vol. 65, no. 13, pp. 2051–2054, 2011.
[15]
J. Wang, D. N. Tafen, J. P. Lewis et al., “Origin of photocatalytic activity of Nitrogen-doped TiO2 nanobelts,” Journal of the American Chemical Society, vol. 131, no. 34, pp. 12290–12297, 2009.
[16]
J. F. Moulder, W. F. Stickle, P. E. Sobol, and K. D. Bomben, Handbook of X-Ray Electron Spectroscopy, PerkinElmer, Eden Prairie, Minn, USA, 1992.
[17]
H. Czili and A. Horváth, “Applicability of coumarin for detecting and measuring hydroxyl radicals generated by photoexcitation of TiO2 nanoparticles,” Applied Catalysis B: Environmental, vol. 81, no. 3-4, pp. 295–302, 2008.
