Doping Induced Effects on Tungsten Based Oxides Nanostructures and Their Characteristics

Abstract

The tungsten oxide (WO3) nanostructures possess particular importance due to their significant physical, chemical and biological characteristics which allow them to be used in many highly efficient applications like photocatalysis, electrochromic, nanomedicine, sensing and electronic devices. This thesis focuses on the synthesis, characterizations and specific applications of undoped and metal (Fe, Cu, Sn, Co and Ni) doped tungsten oxide nanostructures. The thesis highlights the development of novel synthesis technique which is rapid, consumes less energy and time, is more economical and is easily reproducible. The synthesized nanomaterials were thoroughly characterized using various structural, electrical and optical characterization techniques. The other aspect of the thesis is to use the synthesized nanomaterials for several important novel applications such as visible light driven photocatalysis and anticancer activities. The thesis is divided into several chapters, the detail of which is given below. Chapter 1 gives a brief introduction of the metal based oxide semiconductors. In addition to this, a short review on the targeted applications, such as photocatalytic and anticancer properties with detailed mechanism is presented. Finally, the chapter describes the objectives, importance and problem statement of the thesis. Chapter 2 presents the review of physical and biological properties of WO3 such as crystal structure, morphology, vibrational bands, compositions, band gap, photoluminescence, dielectric, photocatalytic and anticancerous properties. Chapter 3 includes the synthesis details of undoped and metal (Fe, Cu, Sn, Co and Ni) doped WO3 nanostructure, visible light driven photocatalytic and anticancerous (cytotoxicity) procedures and the characterization techniques which have been used in this thesis are discussed.

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Chapter 4 describes the synthesis, characterizations, photocatalytic and anticancer activity of Fe doped WO3 nanostructures. Herein, a series of Fe doped WO3 nanoplates have been synthesized using a facile co-precipitation method. The XRD, SEM, EDX, XPS, FTIR, Raman, LCR, DRS and PL spectroscopy have been used to investigate the Fe doped WO3 nanoplates. This study provides a facile and effective method to prepared Fe doped WO3 nanoplates with enhanced (up to 94 %) visible light driven photocatalytic degradation of methyl red. Most importantly, this is one of the initial reports that Fe doped WO3 nanoplates are an excellent candidate for anticancer applications. The Fe doped WO3 nanoplates have shown highly efficient anticancer activities against human liver (Hep-2) and breast (MCF-7) cancer cells. The percent cell viability of both cancer cells lines is significantly decreased (up to 50%) with Fe doping. Chapter 5 presents the synthesis of Sn doped WO3 nanoplates. Various characterization tools have been employed to study the effect of Sn doping on the structural, optical and dielectric properties of WO3 nanoplates. The visible light driven photodegradation activity of WO3 nanoplates is enhanced up to 83%. Furthermore, the anticancer activity of WO3 nanoplates against MCF-7 cancer cells is also increased with Sn doping which is attributed to several factors such as particle size, defects density and reactive oxygen species (ROS) production. Chapter 6 describes the effect of Cu doping on structural, optical and biocompatible anticancer properties of WO3 nanoplates. The photocatalytic activity is increased up to 80% with Cu doping. Moreover, the differential (biocompatible) anticancer activities of Cu doped WO3 nanoplates against MCF-7 cancer cells and liver (Hep-2) cancer cells are also observed. In chapter 7, the substitution of Co2+ ions on the sites of W6+ ions has been confirmed through X-ray photoelectron spectroscopy (XPS) analysis. The Co doping has been found to be very effective in enhancing the visible light driven photodegradation activity of WO3 nanoplates

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up to 90% which is attributed to trapping of photogenerated electrons by defects. Furthermore, Co doped WO3 nanoplates have also shown good anticancer activities against human breast (MSF-7) and lever (Hep-2) cancer cells. In chapter 8, the effects of Ni doping on the structural, optical, photocatalytic and anticancer activities of WO3 nanoplates were studied. The mineralization degree of organic dye using Ni doped WO3 photocatalyst was determined by total organic carbon analysis (TOC), reaching percentages of mineralization up to 96 % of methyl red in just 2 hour under illumination of visible light. Interestingly, it was also observed that the percent cells viability of human breast (MCF-7) and liver (Hep-2) cancers cells were decreased remarkably up to 30% and 35% respectively with Ni ions doping.