Preparation Of Nano Zno Based On In-Situ Synthesis Of Zno Quantum Dots And Application In Textile

Quantum dots (QDs), also called semiconductor nanocrystals are of great interest due to their unique properties and potential applications in many fields. When the size of the nanocrystals decreases to the exciton Bohr radius, the energy level becomes discrete from the continuum, and the energy gap increases as the crystal boundary significantly modifies electron distribution, showing a quantum confinement effect. Over the past decade, dramatic progress has been made in the synthesis and application of semiconductor quantum dots. Among the inorganic semiconductors, ZnO semiconductor with a wide direct band gap (3.37eV) and a large exciton binding energy (60meV), is receiving a great deal of attention for their outstanding optoelectronical properties, leading to practical applications in areas such as bioimaging, photovoltaics, and light-emitting diodes. To make full use of their unique properties, much work has still been devoted to the development of new strategies that fabricate monodisperse ZnO QDs with stable properties and improve their application performance further.This dissertation mainly focuses on the preparation of ZnO QDs and the exploration of the application of nano ZnO based on ZnO QDs in textiles. The work can be divided into three parts:(Ⅰ) Sol-gel preparation and characterization of ZnO QDs. In this part the dependence of preparation conditions on the struture and optical properties of ZnO QDs were discussed in detail.(Ⅱ) Introduction of two surface passivation methods to stabilize ZnO QDs. The optical properties of the modified ZnO nanoparticales were studied emphatically.(Ⅲ) Construction of ZnO nanorods on cotton fabrics by using ZnO QDs as seed for hydrothermal growth. The UV-blocking property of the treated cotton fabric was investigated. The following text is the details:1. The ZnO QDs were successfully prepared by sol-gel method, and their crystal structures, sizes and optical properties were characterized. It was found that ZnO QDs had a hexagonal wurtzite crystal structure, and were approximately spherical in shape with the average diameter of4.0nm. UV-vis spectra showed the obvious confinement effect which was consistent with the small size of the as-prepared ZnO nanoparticles. ZnO QDs evinced a UV emission band and a visible emission band that were attributed to different emmsion mechanisms as shown in phtoluminence spectra.2. The effect of preparation conditions such as the concentration of reagents, reaction temperature and alkaline source on the size and optical properties of ZnO nanoparticles was investigated. It was showed that such prearation conditions had an influence on the average size and optical properties of ZnO QDs. In addition, it was demonstrated that the size and emission color of ZnO QDs could be finely tuned by adjusting these preparation conditions. Moreover, the mechanism of growth of ZnO nanocrystals from solution was investigated by UV-vis. The experimental results implied a clear departure from from the widely accepted diffusion controlled coarsening (Ostwald ripening) process but a growth mechanism that was intermediate between the two well-defined limits of diffusion control and kinetic control.3. Poly-inyl pyrrolidone (PVP) as the capping molecules were used during the synthesis of ZnO QDs by the sol-gel process. The capping agent of PVP enhanced the stability of the samples with better monodispersity compared to the bare ZnO QDs. It was also found that the size and PL property of the ZnO nanoparticles could be greatly affected by varing the amount of PVP.4. Another surface modification approach was the preparation of ZnO QDs encapsulated with silica to form ZnO/silica nanocomposites. The results showed that the ZnO/silica nanocomposites improved the water stability as well as dispersibility uniformLy.5. Cotton textile was coated with ZnO nanorods in order to obtain ultraviolet (UV)-blocking properties. The coating process was conducted in mild conditions, which involved the dip-coating of ZnO QDs as seeds, recrystallization of the seed layer and hydrothermal growth of ZnO nanorods. The treated cotton textile was found to be covered with ZnO nanorods densely and uniformLy with approximately0.4-lum in length and150-350nm in diameter observed by SEM, and exhibited an excellent UV protection factor over110. Effects of both hydrothermal growth time and temperature on the morphology of ZnO nanorods and the UV-blocking property were also investigated.