Shape Control and Functional Properties of Copper Chalcogenide Colloidal Nanocrystals

• Autores: Wenhua Li
• Directores de la Tesis: Andreu Cabot Codina (dir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2013
• Idioma: inglés
• Tribunal Calificador de la Tesis: Ramón Álvarez Puebla (presid.), Albert Figuerola Silvestre (secret.), Jessica Rodríguez Fernández (voc.)
• Materias:
  • Química
    • Química inorgánica
  • Ciencias tecnológicas
    • Tecnología de materiales
• Enlaces
  • Tesis en acceso abierto en:  TDX  Dipòsit Digital de la UB 
• Resumen

  • The high quality CuxS nanocrystals were synthesized (Chapter 3) and the profound understanding and skills to prepare colloidal nanocrystals has been obtained and improved. It revealed a very simple synthetic route not only for the systematic investigation on the size control of the copper sulfide nanodisks but also for studying the influence of different stoichiometric ratios on the shape of copper sulfide nanocrystals. An increase of the precursor concentration in the growth solution resulted in the formation of tetradecahedral and dodecahedral nanocrystals. XRD results showed these nanodisks had a similar composition close to Cu1.78S as spherical nanocrystals, however, the tetradecahedral and dodecahedral nanocrystals were characterized with a composition close to Cu1.96S as deduced from their djurleite crystal phase. An oriented attachment was proposed as growth mechanism for polyhedrons growth and the slow nucleation rate allows an accurate control of the size and morphology of CuxS nanocrystals, from spheres and disks to tetradecahedrons and dodecahedrons by tuning the precursor concentration from 0.05 M to 1.0 M and reaction conditions. Dodecahedrons with different size can be easily prepared by elongating the reaction time. These nanocrystals can be used as cathodes in all-vanadium redox flow batteries and showed a significant improvement of the cathodic reaction reversibility, especially the dodecahedrons. The CuxSe nanocubes with mean edge length of 17 nm±0.9 nm were synthesized (Chapter 4). The role of various metal ions playing on shape of CuxSe nanocrystals was discussed during the synthesis. The underlying mechanism was illustrated by preparing copper selenide nanocubes in the presence of Al ions whereas there was no any Al detected on the surface or within the final cubes. The morphology control is proved to be thermodynamically directed during the ripening regime and it exemplified the shape-direction of semiconductor nanocrystals by metal ions for the first time. It is a platform to produce cubic nanoparticles with different composition by cation exchange such as Ag2Te nanocubes. The plasmonic properties of the obtained nanocubes were further characterized and it demonstrated the strong plasmonic absorption peak at 950 nm. A reproducible procedure to prepare highly monodisperse copper telluride nanocubes, nanoplates and nanorods was presented in Chapter 5. The procedure is based on the reaction of a copper salt with trioctylphosphine telluride (TOP-Te) in the presence of Lithium bis(trimethylsilyl) amide (LiN(SiMe3)2), trioctylphosphine (TOP), trioctylphosphine oxide (TOPO) and oleylamine (OLA). The high reaction temperature as 220 °C was found to be necessary to obtain cube-shaped NPs with narrow size distributions. By tuning the precursor ratio of Cu:Te, the size of these nanocubes could be controlled in the range between 10 and 20 nm. When decreasing the reaction temperature to 190 °C and the growth time to 15 min, highly homogeneous copper telluride nanoplates were produced. An increase of the TOP concentration from 0.125 ml to 0.75 ml resulted in the formation of nanorods. It was proposed the LiN(SiMe3)2 to activate the formation of a Cu-oleylamido complex and it is the actual species reacting with TOP-Te. The Cu-oleyamido complexes and/or lithium oleylamine may play a key role stabilizing the NP surface during growth. Copper telluride nanocubes and nanoplates display a strong near-infrared optical absorption at 900nm associated to localized surface plasmon resonances. This plasmon resonance can be exploited for the design of surface-enhanced Raman scattering (SERS) sensors for unconventional optical probes such as nile red containing oxygen based functional groups. This is the first time using Cu-chalcogenide as probes for SERS application and demonstrates its potential interest in future. Preliminary analysis of the use of copper telluride nanocubes as cytotoxic and photothermal agents is also discussed herein.