g-Fe 2 O 3 nanoparticles: An easily recoverable effective photo-catalyst for the degradation of rose bengal and methylene blue dyes in the waste-water treatment plant Amit Kumar Dutta, Swarup Kumar Maji, Bibhutosh Adhikary * Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah 711 103, West Bengal, India 1. Introduction The textile dyes with high aromaticity and low biodegradability have emerged as major environmental pollutants [1,2] and nearly 10–15% of the dye is lost in the dyeing process and is released in the waste-water which is an important source of environmental contamination. Considerable amount of water is used for dyeing and finishing of fabrics in the textile industries. The waste-water, from textile mills, causes serious impact on natural water bodies and in the surrounding lands. As dyes are designed to be chemically and photolytically stable, they are highly persistent in natural environments. The improper handling of hazardous chemicals in textile water also has some serious impact on the health and safety of workers putting them into the high-risk bracket for contracting skin diseases like chemical burns, irritation, ulcers, etc. and respiratory problems [3]. Various physical, chemical and biological pre-treatment and post-treatment tech- niques have been developed over the last two decades for the treatment of textile waste water, although most of them were found to be ineffective and expensive [4,5]. Thus, decomposition of organic pollutants using various nanomaterials in the presence of sun light has been a topic of contemporary interest. Semiconduct- ing nanomaterials are especially important for this purpose, as they functions effectively at mild condition and even at very low concentrations. During the past 20 years, many photo-excitable inorganic semiconductors have been used as photo-catalysts to decompose or destroy the organic pollutants [6–11]. The development of facile, cheap and green methods for treatment of organic pollutants has been a focal subject in the field of environmental science and technology. Among many strategies including physical, chemical, biological and photo-catalytic methods, the photo-catalytic method is a promising technology for the treatment of contaminants due to its potential use of sunlight as the energy source to degrade organic pollutants [12– 14]. Organic dyes have the attractive advantages of possessing high molar absorptivity in the visible region, which matches the light source emission spectrum with solar light [15]. TiO 2 is a well- known catalyst for photo-degradation of toxic organic compounds [16–19], however, it is catalytically active only under UV irradiation (l < 387 nm) because of its wide band gap energy (E g  3.2 eV) [20]. Of late, a few non-titania-based several metal oxides (e.g. CuO, ZnO, MnO 2 , Fe 2 O 3 , Fe 3 O 4 , Co 3 O 4 , Al 2 O 3 ) and metal sulfides (e.g. CdS, CuS, ZnS, MnS, Sb 2 S 3 , In 2 S 3 , Bi 2 S 3 , etc.) [21–25] have been found to exhibit visible-light-driven catalytic activity. Obviously, there remains great demand for exploration of inexpensive and environmental friendly materials that might be used for photo-degradation of organic dyes in sun light, especially for effluents of textile waste-water. In this regard, the use of iron oxide nanoparticles, which is commonly known as super paramagnetic nanoparticles (MNPs), as catalyst carriers is very promising due to their large surface area resulting in high catalyst loading capacity, high dispersion, outstanding stability, low-cost Materials Research Bulletin 49 (2014) 28–34 A R T I C L E I N F O Article history: Received 4 February 2013 Received in revised form 9 August 2013 Accepted 16 August 2013 Available online 26 August 2013 Keywords: A. Magnetic materials A. Nanostructures C. Thermogravimetric analysis (TGA) D. Catalytic properties D. Optical properties A B S T R A C T g-Fe 2 O 3 nanoparticles (NPs) were synthesized from a single-source precursor complex [Fe 3 O(C 6 H 5- COO) 6 (H 2 O) 3 ]NO 3 by a simple thermal decomposition process and have been characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and UV–vis spectroscopic techniques. The NPs were highly pure and well crystallized having hexagonal morphology with an average particle size of 35 nm. The prepared g-Fe 2 O 3 (maghemite) NPs show effective photo-catalytic activity toward the degradation of rose bengal (RB) and methylene blue (MB) dyes under visible light irradiation and can easily be recoverable in the presence of magnetic field for successive re-uses. The possible photo-catalytic decomposition mechanism is discussed through the detection of hydroxyl radical (OH  ) by terephthalic acid photo-luminescence probing technique. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +91 3326684561x512; fax: +91 3326682916. E-mail address: bibhutoshadhikary@yahoo.in (B. Adhikary). Contents lists available at ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2013.08.024