Photocatalytic Studies of Undoped and Doped ZnS Nanostructures

Abstract

The present work deals with the synthesis and characterization of undoped and doped ZnS nanoparticles (NPs). Studies related to nanocomposites (NCs) and core shell nanoparticles (CSNPs) have also been discussed. The entire work has been divided into seven chapters. Chapter 1 deals with the introduction about the conventional methods used for degradation of organic pollutants. Role of photocatalysis in degrading organic pollutants is described. Also, various chemical reactions occurring in the process are discussed. The main factors which affect the catalytic activity of a photocatalyst are described in detail. Further, approaches developed to synthesize NPs have also been discussed. Methods to prevent agglomeration of NPs and to stabilize them are explained. A brief introduction about ZnS and its application in photocatalysis is also provided. In Chapter 2, reported work which describes synthesis, structural, optical and photocatalytic studies of ZnS is reviewed. Effect of various parameters like synthesis method, reaction temperature and doping with metal or non metal ions on optical and photocatalytic properties of ZnS has been described in detail. Besides this, other techniques developed to enhance the photocatalytic activity of ZnS at nanoscale has also been discussed. At the end of the chapter, the reasons for selecting main objectives behind this work are presented. Chapter 3 describes the details of the synthesis procedure to prepare ZnS using different chemicals. Details of different techniques which have been employed to characterize as prepared samples like X-Ray diffraction (XRD) technique, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Fourier transfer infrared (FTIR) spectroscopy, UV-Vis spectroscopy and photoluminescence (PL) spectroscopy including their model number have been provided. The set up used to perform photocatalytic experiments has been given in the end of the chapter. A brief introduction about the model pollutant selected for the entire photocatalytic study is also provided. In Chapter 4, the studies of undoped ZnS NPs prepared via chemical precipitation route have been discussed. In the next section of this chapter, photocatalytic degradation of crystal violet has been carried out with the aim to study photocatalytic properties of as prepared ZnS NPs. Effect of UV irradiation on photocatalytic properties of ZnS has also been investigated. At the end of the chapter, effect of pH of the solution (in which the NPs are being synthesized) on optical and photocatalytic properties of undoped ZnS has also been discussed. Chapter 5 describes the studies of doped ZnS NPs prepared via chemical precipitation route. Effect of doping ZnS with metal ions like Cu, Mn, Ni on photocatalytic properties of as xxi prepared ZnS NPs has been studied. Structural, optical and photocatalytic properties of thioglycerol capped and Ag2S modified ZnS have also been discussed. In Chapter 6, studies related to NCs of ZnS/ZnO and ZnS/Ag2S prepared via chemical precipitation route have been presented. At the end of the chapter, a brief introduction has been given about core shell particles. Structural and optical studies of as synthesized ZnSZnO CSNPs have also been done to demonstrate their photocatalytic activity in degrading the organic pollutants. Chapter 7 summarizes the results of the study made on ZnS which has been synthesized under different conditions. UV irradiation of undoped ZnS has shown better photocatalytic activity towards crystal violet. ZnS synthesized at pH 12 has shown superior photocatalytic properties as compared to that of samples synthesized at pH 5.6, 8 and 10. Doping of ZnS with Cu impurities has led to the enhancement in photocatalytic activity of ZnS. However, at higher concentration of Cu, photocatalytic activity has decreased. Doping with Ni and Mn ions has reduced the photocatalytic activity of ZnS. It has been concluded that dopant ions may reduce or enhance the photocatalytic activity of a semiconductor depending upon the type of transition involved in the emission pathway. Ag2S modified ZnS has shown better catalytic activity at higher AgNO3 content. All the prepared NCs have shown better photocatalytic activity towards crystal violet as compared to ZnS alone. ZnS-ZnO CSNPs have served as a better photocatalyst as compared to bare or organically passivated semiconductor ZnS NPs.