Synthesis And Properties Of Carbon Nanotube/quantum Dot Nanocomposites

Since their discovery, carbon nanotubes (CNTs) have attracted great attention and increasing research interests due to their special structure as well as unique optical, electrical, mechanical and chemical properties. To optimize the properties of CNTs and expand their application potential, a variety of surface modifications on CNTs were attempted to fabricate CNT-based nanocomposites with superior performance, which have shown broad prospects for applications in the fields of optics, electrics, catalysis, etc. Semiconductor quantum dots (QDs) were provided with more superior performance compared with conventional organic fluorescent dyes. The size-tunable optical properties and high photoluminescence quantum yields have made QDs a novel and ideal optical material for light-emitting diodes, lasers, and biological fluorescent labels. In this thesis, metal sulfide and CdSe nanoparticles were in situ grown on the surface of CNTs via non-covalent modification methods. The CNTs and quantum dots were combined to obtain noval nanocomposites. The as-prepared materials were characterized, and their properties were studied. This thesis includes three chapters.Chapter I summerizes the structure, properties and application potential of carbon nanotubes as well as the characters and application of quantum dots, and put forward the research envisagement for the whole thesis.In Chapter II, SDS and chitosan were layer-by-layer non-covalently coated on multiwalled carbon nanotubes (MWCNTs), then ZnS, CdS, Ag2S and PbS nanoparticles were in situ loaded on the sidewall of CNTs by using the SDS/chitosan coats on CNTs as templates. The resultant CNT/SDS/chitosan/sulfide nanocomposites were characterized by XRD, TEM, FTIR spectra, and UV-vis spectra. In the presence of SDS/chitosan coats on CNTs, metal sulfide nanoparticles with uniform sizes can be well deposited on the surface of CNTs. The effect of reactant concentration on the morphology of the obtained nanocomposites was also studied. The CNT/SDS/chitosan/sulfide nanocomposites may find application potential in nonlinear optics.In Chapter III, CdSe QDs were prepared by a"green chemistry"approach under optimized conditions. TEM, XRD, UV-vis and fluorescence spectroscopy studies revealed that the obtained CdSe quantum dots exhibited good homogeneity and monodispersity, together with excellent fluorescence properties. They can emit a stable green fluorescence under the appropriate excitation energy. Based on the successful preparation of CdSe quantum dots, diluted-acid purified MWCNTs were introduced into the reaction solution during the synthesis process of CdSe QDs, then the QDs were in situ grown on the sidewall of CNTs to produce novel CNT/CdSe nanocomposites. The influences of charging capacity and reaction time upon the morphology and optical properties of the resultant nanocomposites were investigated, and 15 minutes of reaction time and 1.0 mmol/L of precursor concentration were found to be the best conditions for preparing the CNT/CdSe nanocomposites. Under the optimal conditions, the CdSe nanoparticles with uniform size can be well in situ modified on the surface of CNTs to produce nano-composite materials with good fluorescence properties. The nanocomposites may exhibit more novel optical and electrical properties, and they are expected to be employed in the preparation of nano-composite devices with excellent optical, electrical and mechanical properties.