| Περίληψη: | "There's Plenty of Room at the Bottom”, stated by Richard Feynman in 1959, had sparked an extensive research to direct manipulation of atoms and after several decades of research a new technology was born, which is called as “Nanotechnology”. This new technology possess very broad area including fields of science such as surface science, organic chemistry, molecular biology, semiconductor physics, microfabrication, molecular engineering, and so on. Nanotechnology is the engineering of functional systems at the molecular scale and it possess the ability to construct materials from bottom up and top down approaches. It is one of the most important and dynamic technology due to its numerous applications, not only in the areas of electronics, optics, catalysis, environmental engineering and aerospace but also to cosmetics industry, medicine, pharmacy and engineering, etc. In general, nanotechnology can be understood as a technology of design, fabrication and applications of nanostructures and nanomaterials and their fundamental understanding of physical properties and phenomena.
A semiconductor is a material that has an electrical conductivity between a conductor and an insulator. When the size of semiconductor materials is reduced to nanoscale, their physical and chemical properties change drastically due to their large surface area or quantum size effect. Thus, the semiconductor nanomaterials possess special place in nanotechnology as such nanomaterials are not only utilized for the fabrication of highly efficient electronics and optoelectronics devices and systems but also used for bio and environmental applications. Because of various high technological applications, extensive research works have been done for the synthesis, characterizations and applications of semiconductor nanomaterials. However, it is still desirable to prepare semiconductor nanomaterials with environment-friendly precursors and processes with varied size and morphology for their effective utilization in specific applications.
This thesis is focusing on the synthesis, characterizations and environmental applications of variety of semiconductor nanomaterials. The semiconductor nanomaterials studied in this thesis are zinc oxide (ZnO), ytterbium doped ZnO, Samarium oxide (Sm2O3) doped ZnO, Silver (Ag)-doped ZnO, Carbon nanotube (CNTs) decorated ZnO, Copper oxide (CuO), Ytterbium oxide (Yb2O3), Nickel oxide (NiO) and Bismuth subcarbonate (Bi2O2CO3). The chapter is divided into several sections as follows:
Chapter one starts with a brief introduction of the semiconductor nanomaterials and their various synthetic methods. In addition to this, a short review on the targeted applications, i.e. sensing, and photocatalytic, of this thesis was also discussed in this chapter. Finally, the chapter describes the objective and importance of the thesis.
Chapter two deals with the details of the synthesis and characterization techniques used in this thesis.A simple hydrothermal method was used to synthesize variety of semiconductor nanomaterials mentioned above. The synthesized nanomaterials were examined by variety of techniques in terms of their morphological, structural, optical, compositional, electrical and photocatalytic properties. Moreover the prepared nanomaterials were used for various sensing and photocatalytic applications.
Chapter three describes the main results and discussion of the thesis. This chapter is divided into TWO sections, i.e. (I) Environmental applications of semiconductor nanomaterials and (II) Bio-environmental applications of semiconductor nanomaterials. Each of these sections describes the synthesis, detailed characterizations and particular application of a specific semiconductor nanomaterial. Section (I) possesses several sub-sections and marked as 3.1. to 3.7. Fabrication, characterization, picric acid sensor and photocatalytic applications of cauliflower-shaped ZnO nanomaterials are presented in 3.1. Highly-sensitive picric acid chemical sensor based on ZnO nanopeanuts are described in subsection 3.2. Synthesis, detailed characterization and acetone gas sensing applications of Ag-doped ZnO nanoneedles are described in 3.3. Utilization of Ytterbium doped Zinc Oxide nanopencils for chemical sensor application is presented in 3.4. The use of Sm2O3 doped ZnO beech fern hierarchical structures for nitroaniline chemical sensor is presented in 3.5. The development of highly-sensitive and selective ethanol gas sensor based on lance-shaped copper oxide (CuO) nanostructures is demonstrated in 3.6. Fabrication and characterization of highly sensitive and selective alcohol sensors based on porous NiO nanodisks are presented in 3.7. Similarly, section (II) possessses several sub-sections which are marked as 3.8. to 3.11. In these sections, bio-environmental applications of several semiconductor nanomaterials are examined and presented. Subsection 3.8. demonstrates the fabrication and characterization of highly sensitive and selective glucose biosensor based on ZnO decorated carbon nanotubes. Sub section 3.9. exhibits the fabrication characterizations and urea biosensing applications of simply synthesized two-dimensional ytterbium oxide nanodisks. Sub section 3.10 reveals the fabrication and characterization of highly sensitive and selective non-enzymatic mono and disaccharide sugars sensors based on carbon paste electrodes modified with perforated NiO nanosheets. Finally, the fabrication and characterization of highly sensitive and selective cholesterol biosensor based on Bi2O2CO3 nanoplates are presented in section 3.11.
Chapter 4 briefly highlights the overall conclusion and an outlook for further investigations suggested by the work undertaken here for this thesis. It is worthy to mention that all the works presented in this thesis are already published in well-reputed scientific journals.
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