Synthesis and characterization of multinary group 10-11 metal-based nanocrystals

Abstract

[eng] Nanostructured semiconductors have gained significant importance due to their size- and morphology-tunable physical properties, and their ability to play a critical role in various fields such as energy conversion and theragnostic. Hybrid and multinary nanocrystals (NCs) have further enhanced the design complexity of nanostructures, offering new properties and synergies beyond those of individual materials. The thesis focuses on the synthesis and characterization of multinary group 10-11 metal-based chalcogenide nanocrystals, consisting of an introduction chapter and six chapters of results regarding different studied systems.

Chapter 2 presents a new and easy colloidal synthetic method to form Au–Ag2X (X = S, Se) heterodimers. The method involves mixing pre-synthesized faceted Ag2S or hexagonally-shaped Ag2Se NPs with Au NPs by stirring at room temperature. The final product is observed and measured using transmission electron microscopy (TEM) and x- ray diffraction diffractometer (XRD) techniques for preliminary morphological and structural characterization. In-depth chemical and structural characterization is performed using high-resolution TEM and scanning transmission electron microscopy-energy dispersive x- ray spectroscopy (STEM-EDS). The size, shape, ligand and solvent dependence of the reported method are also studied.

Chapter 3 describes the synthesis of the hybrid/multinary Au-Cu-S system using cation exchange (CE) reactions between pre-synthesized Cu2-xS NCs and HAuCl4. The Au/Cu molar ratio and surfactant nature are the key factors for controlling the crystallographic structures of the final products. The use of non-reducing surfactant (tetraoctylammonium bromide, TOAB) promotes mainly the CE between two precursors, resulting in the formation of void nanostructures. The use of reducing surfactant (dodecylamine, DDA) results in the growth of metallic Au domain on the surface of Cu2-xS NCs NCs. At the highest Au/Cu ratio, Au2S phase is presented, indicating the completion of the full CE reaction. In addition, at an Au/Cu ratio of 6, the ternary phase composed of Au-Cu-S is formed with either of the above-mentioned surfactants.

Chapter 4 focuses on the synthesis of the Ag-Cu-Se ternary system by a reaction between premade Ag2Se NPs and CuIPPh3 under stirring at room temperature. Two ternary phases are observed in the final product at different Cu/Ag molar ratios, one of which is eucairite AgCuSe and the other one is a new, unreported ternary phase composed of Ag, Cu, and Se. A quaternary system is also synthesized based on the reaction of the obtained ternary Ag-Cu-Se phase with an Au(I)-complex.

Chapter 5 includes the reproduction of ternary Pt-Cu-Se NPs with two different Pt/Cu molar ratios and assessments of their catalytic activities as photocatalysts for the production of hydrogen from aqueous ethanolic solutions. The synthesis of photocatalysts is carried out

by a ligand-assisted CE reaction, and their activities are measured using UV-visible absorption spectroscopy, XRD, TEM, and photoelectrochemical measurements.

In conclusion, the thesis provides valuable insights into the synthesis and characterization of multinary group 10-11 metal-based chalcogenide nanocrystals. The studies reveal the importance of controlling the crystallographic structures of the final products by tuning the Au/Cu molar ratio and surfactant nature in the hybrid/multinary Au-Cu-S system. The synthesis of new ternary phases and quaternary systems highlights the potential

[spa] Los semiconductores nanoestructurados son esenciales en la conversión de energía y la teranóstica. Para mantenerse al día con los avances tecnológicos, se están diseñando nanoestructuras cada vez más complejas, como los nanocristales híbridos y multinarios, lo que lleva a nuevas propiedades y sinergias que surgen de la composición de diferentes materiales. En el Capítulo 2, se presenta un método simple y efectivo para sintetizar heterodímeros Au- Ag2X (X = S, Se) mediante la mezcla de nanopartículas Ag2X pre-sintetizadas con nanopartículas de Au a temperatura ambiente. El estudio también investiga el impacto del tamaño de partícula, forma, ligandos y solventes en el proceso de síntesis. En el Capítulo 3, se describe la síntesis de sistemas híbridos/multinarios de Au-Cu-S mediante reacciones de intercambio catiónico entre NCs de Cu2-xS pre-sintetizados y HAuCl4. La naturaleza del surfactante y la relación molar Au/Cu juegan un papel crucial en el control de las estructuras cristalográficas de los productos finales. El Capítulo 4 se centra en la síntesis de un sistema ternario (Ag-Cu-Se) mediante la reacción de NPs preformados de Ag2Se con CuIPPh3. Los resultados muestran la presencia de dos fases ternarias en el producto final, una de las cuales es eucairita AgCuSe y otra que aún no se ha reportado. También se realizó la síntesis de un sistema cuaternario, mostrando la presencia de los cuatro elementos en una sola NP. En el Capítulo 5, se describe la síntesis y caracterización de materiales ternarios Pt-Cu-Se como co-catalizadores en capas semiconductoras de g-C3N4 para la reacción de evolución de hidrógeno (HER). Los experimentos catalíticos demuestran su efectividad para HER. El Capítulo 6 discute la preparación de un experimento in situ utilizando un microscopio electrónico de transmisión en celda líquida para estudiar la reacción entre Ag2S NPs y Au (III)- TOAB. El Capítulo 7 se centra en la síntesis y caracterización de tres microestructuras de oro diferentes (microrods, esféricas y prismas con base cuadrada) utilizando ensamblajes organometálicos de oro (I) supramoleculares como plantillas, con una pequeña adición de NPs de Ag como agentes reductores.