New electrochemical strategies for synthesising micro- and nano- structures

Abstract

Nowadays, researchers have spent considerable effort on the development of new materials, with new properties and characteristics, and new methods of synthesis, in order to meet the demands of a market that is constantly evolving. In this sense, “New electrochemical strategies for synthesising micro- and nano-structures” proposes, generalizes and discusses the development of novel electrochemical methods, strategies or media to prepare different kinds of micro- and nanostructured materials. The leitmotiv could be focused on the possibility of preparing micro-patterned (Cu), nanoparticulated (Co, CoNi, CoPt), composited (CoPt-Ni), mesoporous (CoNi, CoPt, Pt, CoNi@Pt or CoNi@Au) or nanopowdered (CoPt) deposits with various shape (films, nanorods or nanowires) by using the proposed strategies (Electrochemical nano-Fabrication using Chemistry and Engineering (EnFACE) technology or classical/ionic liquid microemulsions as a soft electrodeposition templates) to obtain micro/nanomaterials for specific magnetic, catalytic or biomedical applications.

The present thesis is organized in eight chapters, in which several published scientific papers in international journals with our original results have been included in order to discuss and analyze our work. The first one introduces the electrodeposition (Chapter 1) – history, theoretical fundaments, advantages and disadvantages and introduce the state-of-the-art of electrochemical micro- and nano-fabrication –, which is fundamental in order to understand our work. The aims and the experimental details of our research are presented and detailed in chapter 2 and chapter 3, respectively. It is important emphasize that “New electrochemical strategies for synthesising

micro- and nano-structures” could be grouped into three main areas, according the aims introduced above:

(a) The optimization of EnFACE technology as an alternative method to classical masked-electrodeposition to prepare metallic microstructures on large conductive substrates, with the final objective of proposing this technology as a scalable, economic and environmentally-friendly synthesis approach to microfabrication; this could be relevant in the electronics and sensors industries. This work is presented in chapter 4;

(b) Proposing, discussing and analyzing the use of different types of classical microemulsions as new electrochemical media for synthesising nanostructures — that is, a new shape-controlled electrodeposition approach based on the use of soft-template systems. In this sense, the possibility of obtaining different types of Co-based structures with varied geometries and shapes as a function of the microemulsions conditions has been demonstrated. However, the low or moderate deposition rates and efficiencies leading us to explore and propose the use of alternative (water-in-ionic liquid) microemulsions as soft-template electrochemical media with improved conductivity and low environmental impact for shape-controlled electrodeposition. These electrodeposition media were tested to prepare magnetic nanostructured materials (nanoparticulated CoPt magnetic films or CoPt-Ni composites) with controlled size, composition and magnetism. Based on our results, the use of water –in-ionic liquid (W/IL) microemulsions have been revealed to be a versatile, green, simple and inexpensive approach to 1) synthesizing nanoparticles with controlled size and composition, and therefore magnetic behavior, by controlling the droplet size and aqueous solution concentration respectively, or 2) developing layers of composites using a one-step procedure, in which simultaneous electrodeposition from aqueous droplets and continuous ionic liquid components could take place. This work is presented in chapter 5;

(c) Proposing, generalizing and discussing new electrochemical strategies (electrodeposition in water-in-ionic liquid, bicontinuous and ionic liquid-in-water microemulsions) for synthesising mesoporous nanomaterials ((Pt, CoPt, CoNi, CoNi @Au or CoNi@Pt) for catalysis (the

electrooxidation of methanol or ethanol in order to propose competitive electrocatalysts with poor- Pt content for fuel cell reactions) or drug delivery with enhanced therapeutic effect as a consequence of their magnetic stimulation. This results are presented in chapter 6.

Lastly, to complete the thesis, the main conclusions obtained are collected in chapter 7, while a summary of the thesis in Catalan language is given in chapter 8.

En aquesta tesi s’estudien i proposen noves estratègies de síntesi de micro- i nano-estructures metàl·liques amb potencials aplicacions en els camps de l’electrònica, catàlisi i alliberament de fàrmacs.

El leitmotiv de la tesi serien (a) l’optimització de la preparació de micro-estructures de coure sobre grans àrees superficials, mitjançant la tecnologia EnFACE (Electrochemical nano-Fabrication using Chemistry and Engineering); demostrar, analitzar i generalitzar la viabilitat d’utilitzar (b) microemulsions clàssiques i (c) microemulsions base líquid iònic, com a plantilles toves, per a la síntesi diferents tipus de nano-estructures magnètiques (nanopartícules, compòsits, materials mesoporosos), permetent modular-ne les seves propietats, forma i característiques; i finalment (d) testar l’ús de les nano-estructures mesoporoses com a electro-catalitzadors per l’oxidació d’alcohols o vehicles intel·ligents per a l’alliberament de fàrmacs en medis cel·lulars.

La tesi s’estructura en vuit capítols i inclou diverses publicacions en revistes científiques. En el primer capítol s’introdueix breument l’estat de l’art de l’electrodeposició de micro- i nano-materials, així com una breu ressenya històrica i els fonaments imprescindibles per a la comprensió del treball. El capítol 2 introdueix els objectius, mentre que en el capítol 3 es descriuen i detallen les condicions experimentals i equips emprats per a la síntesi, caracterització i aplicació dels materials fabricats. El capítol 4 es focalitza en la micro-fabricació fent una breu introducció a l’estat de l’art, així com discutir i optimitzar l’ús de la tecnologia EnFACE per a la micro-fabricació d’estructures de coure sobre substrats de grans dimensions. El capítol 5 es centra en la

discussió i anàlisi de la viabilitat de l’ús de microemulsions clàssiques i base líquid-iònic per a l’electrodeposició amb forma controlada, basada en l’ús de plantilles toves. Finalment, el capítol 6 explora i estableix unes condicions de síntesi de nano-fils mesoporosos de diferents materials (base Co i Pt) per a la preparació d’electro-catalitzadors amb grans àrees superficials i alta activitat catalítica per a l’oxidació d’alcohols així com el seu ús com a vehicles dosificadors de fàrmacs. Finalment, el capítol 7 resumeix les conclusions de la tesi i el 8 presenta un resum en català.