Hydrothermal growth of zinc oxide nanostructures for environmental applications | |
| Author | Baruah, Sunandan |
| Call Number | AIT Diss no.ISE-11-01 |
| Subject(s) | Zinc oxide Nanostructures |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Nanotechnology, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ISE-11-01 |
| Abstract | Nanostructures of zinc oxide (ZnO) were synthesized by hydrothermal processes in mild growth conditions. The size and morphology of nanostructures could be controlled through variations in growth conditions like reactant concentration, pH of growth solutions, temperature and time. Nanostructured ZnO in the form of nanoparticles, nanowires, nanorods, tapered nanorods, nanoflowers, nanoplates, broccoli structure, microballs, etc. were successfully synthesized. Tetrahedrally coordinated 0 2 • and Zn2+ in ZnO crystal assisted the growth of different morphologies. ZnO nanorods were extensively studied during this thesis work and control on the dimension and preferential orientation of the nanorods could be achieved which could grown be on a wide variety of substrates like gla8s, alumina, aluminium, stainless steel, polyethylene, polypropylene, etc. through seeding with ZnO nanoparticles. Photocatalysis using metal oxide semiconductors is an attractive way of degrading toxic water borne contaminants and volatile organic compounds into benign forms. ZnO nanostructures were engineered for enhanced visible light photocatalysis for water purification using solar energy. In addition to their sizes and morphologies, the electronic and optical properties of ZnO nanostructures are strongly dependent on the nature and concentration of point defects present in their crystals formed during the crystallization process. Synthesis of ZnO nanoparticles through faster nucleation and growth during synthesis lead to higher defect concentrations in the nanoparticles. ZnO nanoparticles and nanorods formed by microwave assisted synthesis exhibited 8 to 15% increase in visible light photocatalytic activity than conventionally hydrolyzed samples or transition metal (Mn) doped ZnO nanostructures. Optical absorption and photoluminescence spectra confirmed the presence of high concentration of defects in these nano structures. Possible mechanisms of energy transfer between nanostructured ZnO and adsorbed dyes like methylene blue and N719 ruthenium dye has been studied though time correlated single photon count (TCSPC) spectroscopy to follow the electron-hole pair creation and recombination upon excitation with light. Correlation of photodegradation and TCSPC studies showed that defect engineered ZnO nanoparticles obtained through microwave assisted hydrolysis led to a faster initial degradation r.ate of methylene blue as compared to the conventionally synthesized nanoparticles. By using picosecond resolved Forster resonance energy transfer (FRET) technique it was observed that the excited ZnO NPs resonantly transfer visible optical radiation to the dye N719. The energy transfer mechanism on overall efficiency of a model ZnO nanoparticles (NP) based Dye sensitized solar cell (DSSC) was also explored. It was found that the efficiency of a ZnO NP-based solar cell depends significantly on the presence of high~energy photons in the solar radiation. ZnO is mildly soluble in water, which can have both positive and negative implications in photocatalytic application for the purification of water. Zn2 + ions can add an essential nutrient to the purified water in a dose beneficial to humans but the gradual dissolution may require replenishment of the photocatalyst. In a quest to further improve the physical and chemical properties, preliminary study on the hydrothermal growth of zinc stannate nanoparticles was carried out. The hydrothermally grown zinc stannate nanoparticles were checked for its photocatalytic activity and as a sensing material for the detection of liquefied petroleum gas, ethanol, acetone and ammonia. |
| Year | 2010 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ISE-11-01 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Industrial Systems Engineering (DISE) |
| Academic Program/FoS | Industrial Systems Engineering (ISE) |
| Chairperson(s) | Dutta, Joydeep; |
| Examination Committee(s) | Kumar, Sivanappan;Chanchana Thanachayanont;Mahajan, Devinder; |
| Scholarship Donor(s) | Asian Institute of Technology Fellowship; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2010 |