International Conference on Multidisciplinary Research & Practice Page | 91 Volume I Issue VII IJRSI ISSN 2321-2705 Use of Spinels to Overcome the Limitation of Semiconductors as a Photocatalyst for Degradation of Dyes from Industrial Waste Water : A Review Julie Pardiwala # , Femina Patel * , Sanjay Patel # # Department of Chemical Engineering, Institute of Technology, Nirma University, Ahmedabad, INDIA Abstract— This review paper presents the use of spinels in photocatalytic conversion to generate e - /h + which in turn produce reactive oxygen species through redox processes for the degradation of the contaminants . Spinel ferrites have a relatively narrow band gap (̴ 1.9 eV) making them capable of such processes. Spinels (mixed oxides of composition AB 2 O 4 with A(II) and B(III) cations) are an important family of crystalline systems and are an important class of mixed-metal oxides extensively used MFe 2 O 4 (M=Mn, Fe, Co, Ni) and semiconductors TiO 2 use for different photocatalytic process for degradation of industrial dyes under visible light, dark/sunlight, microwave irradiation. Spinel-type oxides materials with narrow band gap, high sunlight utilization efficiency, good electrical and magnetic property, reused, stable, and cheap have been proven to be efficient in the degradation of pollutants like industrial organic dye (wastewater) involving methylene blue, methyl orange, rhodamine B, reactive black 5. Semiconductor used in photocatalytic degradation process is difficult to separate from liquid solution after reaction, broad band gap, corrode in water which probably produced secondary pollution and increased costs. Synthesis of nano-sized spinels from sol–gel, co-precipitation, solution combustion, citrate. Different techniques to characterize ferrites are XRD, XPS, SEM, TEM, BET analytical methods are UV-visible spectro photo meter, FTIR, COD,TOC. This review paper discusses introduction about dyes, phtocatalytic degradation techniques, semiconductor used as photocatalyst and spinel-type oxides as novel photo-catalyst to overcome the limiotation of semiconductor. Synthesis and characterization of spinel-type oxides and mechanism of degradation of dyes using spinel-type oxides. Keywords— Dyes; Band gap; Photocatalyst; Spinel and Semiconductor; Sol-gel,citrate, co-precipetation I. INTRODUCTION yes are organic compounds consisting of two main groups of compounds, chromophores (responsible for color of the dye) and auxochromes (responsible for intensity of the color) [1]. The pollution of water resources by the dyes from industries such as textile, paper, plastic, leather, cosmetics and photographic, has become a serious environmental problem because of their toxicity, affecting the quality of life for generation to come [2]. Spinel ferrites, with a general formula of MFe2O4 where M represents a metal cation, are chemically and thermally stable magnetic materials that have been used for many applications [3, 4, 5]. Their magnetic properties make them useful in magnetic resonance imaging (MRI), electronic devices, information storage, and drug delivery. [4] Separation of these catalysts from treated water, especially from a large volume of water, is expensive and time consuming, which limited their application in industrial fields. It is realized that introducing the magnetic catalysts is a good choice to deal with the catalysts separation and reuse problems [5, 6, 7, 8, 9, 10, 11, 12, 13, 14]. Spinel AB 2 O 4 (mixed oxides of composition AB 2 O 4 with A(II) and B(III) cations) are an important family of crystalline systems and are an important class of mixed- metal oxides extensively used ferrites MFe 2 O 4 (Ni, Mn, Zn, Co, Cu, etc) Spinel ferrites have a relatively narrow band gap (̴ 1.9 eV) making photocatalytic process possible. Semiconductors having broad band gap > 3.0unable to capture the solar radiation also it is very difficult to separate it out from waste water as it is very costly. Semiconductors are defined having to be between an insulator and conductor[15, 16, 17, 18]. The band gap of semi conductor are given in table 1. TABLE I BAND GAP OF SEMICONDUCTORS Semi conductor Band gap TiO2 3.0-3.2 Diamond 5.4 WO3 2.7 ZnO 3.2 SnO2 3.5 SrTiO3 3.4 Fe2O3 2.2 A broad range of experimental conditions was established in order to reduce the colour and organic load of dye containing effluent wastewater [17]. The ideal photocatalyst should process the following Properties like photoactivity, biological and chemical inertness, stability toward photocorrosion, suitability towards visible or near UV light, low cost, and lack of toxicity [8]. Since 1972, when Fujishima and Honda discovered the photocatalytic splitting of water using TiO 2 electrodes; research on the heterogeneous photocatalysis started growing rapidly but semiconductors have sone disadvantages [18]. Spinel overcomes all the limitation of semiconductor as it has a narrow band gap, high magnetic and electrical property, low cost, high stability, can be reused and recycled for other process many times without any decrease in its activity. D