Coupling colloidal chemistry with coordination chemistry: Design of hybrid nanomaterials by the assembly of plasmonic nanoparticles and functional coordination complexes

Nanotechnology involves the design, characterization, production and application of structures, devices and systems by the control of the shape and size at the nanometer scale involving different fields. In the last decade, nanotechnology development has boosted the interest in hybrid nanomaterials. These materials are a complimenting combination of two (or more) nanoparticles (NPs) with enhanced performance characteristics that offer exciting opportunities. It allows the possibility of integrating materials with different physical and chemical properties to widen the range of practical applications. In this context, Au NPs have recently attracted a lot of attention due to the great opportunities that Au offers at the nanoscale. In fact, their facile synthesis and functionalization can be exploited for constructing hybrid nanoparticles showing multi-functionality. In this manner, different Au hybrid nanostructures have been developed exhibiting diverse sizes, shapes and compositions displaying novel physicochemical properties, opening the door to potential new applications. On the other hand, Coordination Polymers (CPs) possess besides interesting electronic properties, potential advantages over conventional inorganic nanomaterials such as structural and chemical versatility, high specific area and biodegradability, among others. Therefore, the integration of both Au and CPs in a single heterostructure has emerged as an appealing topic. However, suitable chemical design appears as one of the key factors to improve their applicability. The work described in this thesis is motivated by the purpose of designing and studying novel hybrid nanostructures formed by combining Au NPs with different CPs: i) Prussian Blue and its Analogues (PB and PBA), ii) Spin-Crossover compounds (SCO) and iii) Metal-Organic Frameworks (MOF). Taking into account the numerous possible heterostructures, it will be discussed why these tailored hybrid NPs are the most appropriate for magneto-optical, electrochemical and electrical applications. In chapter 1, it is described the optical properties and the synthesis of Au NPs as well as the main research efforts that have been made to combine CPs incorporating Au functionalities within the overall hybrid nanomaterials. The main results of this thesis are divided into three parts depending on the potential applications: magneto-optics, electrochemistry and electrical conductivity. Chapter 2 deals with the preparation of hybrid systems formed by metallic NPs decorated by electrostatic attraction onto PBA NPs of different sizes and nature. In this approach, the capping agent of the plasmonic NP is modified, thus, allowing to select the plasmonic NP (isotropic or anisotropic) and, therefore, to tune the plasmon band position in a broad range of the visible spectrum. The heterostructure keeps its plasmonic and magnetic properties becoming a suitable hybrid material for magneto-optical applications. In chapter 3, different heterostructures composed of Au and PBA (of NiFe and CoFe) are synthesized and evaluated as electrocatalysts for the oxygen evolution reaction. The core@shell heterostructures are found to be the most appropriate to exploit the Au properties (conductivity and electronegativity). In this way, through a suitable chemical design it can be greatly enhanced the electrochemical activity and stability of the electroactive PBA. In chapter 4, a straightforward protocol is carried out to overgrow a thin SCO over different plasmonic NPs. Moreover, this synthetic route was extended to MOF. It is observed that thanks to the metallic core and the naked surface of the ultrathin SCO/MOF shell, these core@shell NPs are more conductive than the pristine SCO NPs when contacted to electrodes. In future work, further development will be done by taking advantage of the plasmon properties of the plasmonic core to get a light-induced spin transition (SCO) and to promote the adsorption/desorption of guest molecules (MOF) to obtain advanced sensing devices. This Ph.D. thesis is expected to represent a significant advancement in the development of novel heterostructures as a result of the incorporation of Au NPs to CPs

Hybrid nanostructures based on gold nanoparticles and functional coordination polymers: Chemistry, physics and applications in biomedicine, catalysis and magnetism

During the last decade, the scientific community has become interested in hybrid nanomaterials, especially the ones that combine gold nanoparticles with a second functional component. In this context, coordination polymers are materials that possess potential advantages over conventional inorganic nanomaterials and organic compounds such as chemical versatility, easy processability, high specific area, low toxicity, biodegradability and electronic and magnetic functionalities to name a few. In this manner, the wise integration of Au nanoparticles with coordination polymers in different types of nanostructures has allowed extending the scope of properties and applications of these systems, allowing also overcoming some of the limitations of Au nanoparticles for certain applications. Therefore, in this review, we discuss the different reported hybrid nanostructures based on the integration of colloidal Au nanoparticles with coordination polymers exhibiting either physical properties of interest (e.g. ferromagnetism, photo-magnetism, spin switching, etc.) or chemical properties (e.g. electrocatalysis). We have paid particular attention to the enhanced properties and the synergistic effects that can emerge from this association. Along this front, thanks to their improved and/or novel properties, these hybrid materials have become promising nanostructures for several applications, especially in biomedicine, catalysis, magnetism and sensing

Design of Bistable Gold@Spin‐Crossover Core-Shell Nanoparticles Showing Large Electrical Responses for the Spin Switching

A simple chemical protocol to prepare core-shell gold@spin-crossover (Au@SCO) nanoparticles (NPs) based on the 1D spin-crossover [Fe(Htrz)2(trz)](BF4) coordination polymer is reported. The synthesis relies on a two-step approach consisting of a partial surface ligand substitution of the citrate-stabilized Au NPs followed by the controlled growth of a very thin layer of the SCO polymer. As a result, colloidally stable core@ shell spherical NPs with a Au core of ca. 12 nm and a thin SCO shell 4 nm thick, are obtained, exhibiting a narrow distribution in sizes. Differential scanning calorimetry proves that a cooperative spin transition in the range 340-360 K is maintained in these Au@SCO NPs, in full agreement with the values reported for pristine 4 nm SCO NPs. Temperature-dependent chargetransport measurements of an electrical device based on assemblies of these Au@SCO NPs also support this spin transition. Thus, a large change in conductance upon spin state switching, as compared with other memory devices based on the pristine SCO NPs, is detected. This results in a large improvement in the sensitivity of the device to the spin transition, with values for the ON/OFF ratio which are an order of magnitude better than the best ones obtained in previous SCO devices

Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

Layered double hydroxides (LDHs) are low dimensional materials that act as benchmark catalysts for the oxygen evolution reaction (OER). Many LDH properties affecting the OER have been studied to reach the optimal efficiency but no systematic studies concerning the influence of the interlayer space have been developed. In this context, these materials allow a large tunability in their chemical composition enabling the substitution of the interlayer anion and therefore modifying exclusively the basal space. Here, we synthesize by anion exchange reactions a surfactantintercalated family of NiFe-LDHs with increasing basal spacing ranging from 8.0 to 31.6 Å (one of the largest reported so far for a NiFe-LDH) while the electrochemical OER performance of this family of compounds was explored to analyse the interlayer distance effect keeping similar morphology, dimensions and metallic composition. Results show the increase of the LDH basal space undergo to lower Tafel slopes, higher electrochemical surface area and a reduction of the resistance related to the chemisorption of oxygen leading to better kinetic behaviour, showing an optimum enhancement of the electrocatalytic performance for the NiFe-dodecyl sulphate (basal space of 25 Å). Interestingly, the NiFe-dodecyl sulphate exhibits optimum proton diffusion values, indeed a further increment in the basal space compromises the onset potential, a fact that could be related to an increase in the hydrophobicity between the layers. Moreover, by judicious tuning of the interlayer space, it is possible to reach a Tafel slope value for the most spaced LDH (NiFe-octadecyl sulphate, basal space of 31.6 Å), similar to the one obtained for exfoliated NiFe nanosheets, showing a much better long‐time stability due to the three‐dimensional robustness of the catalysts. This work illustrates the importance of molecular engineering in the design of novel highly active catalysts and provides important insights into the understanding of basic principles of oxygen evolution reaction in NiFe-LDHs

Boosting the supercapacitive behavior of CoAl-layered double hydroxides via tuning the metal composition and interlayer space

Layered double hydroxides (LDHs) are promising supercapacitor materials due to their wide chemical versatility, earth abundant metals and high specific capacitances. Many parameters influencing the supercapacitive performance have been studied such as the chemical composition, the synthetic approaches, and the interlayer anion. However, no systematic studies about the effect of the basal space have been carried out. Here, two-dimensional (2D) CoAl-LDHs were synthesized through anion exchange reactions using surfactant molecules in order to increase the interlayer space (ranging from 7.5 to 32.0 Å). These compounds exhibit similar size and dimensions but different basal space to explore exclusively the interlayer distance influence in the supercapacitive performance. In this line, Co:Al ratios of 2:1, 3:1 and 4:1 were explored. In all cases, an enhancement of the specific capacitance was observed by increasing the basal space, reaching ca. 50 % more than the value obtained from the less-spaced 2:1 CoAl-LDH (up to ca. 750 - 1100 F.g-1 at 1 A.g-1). This increment mainly occurs because of the increase in the electrochemical surface area (up to ca. 260 %) and the higher electrolyte diffusion. Interestingly, best performance is achieved for the lowest Co:Al ratio (i. e. the highest Al content) revealing the important role of the electrochemically inert Al in the structure

Plasmon-assisted spin transition in gold nanostar@spin crossover heterostructures

Aquí presentamos el diseño de nanopartículas core@shell formadas por un núcleo de nanoestrella de Au metálico y una capa cruzada de espín basada en el polímero de coordinación [Fe(Htrz)2(trz)](BF4). Este procedimiento es general y se ha extendido a otras morfologías metálicas (nanovarillas, nanotriángulos). Gracias al efecto fototérmico derivado de las propiedades plasmónicas de la nanoestrella de Au, el 60 % de los centros de hierro experimentan una transición de espín térmico dentro de la histéresis térmica provocada por una irradiación de baja intensidad con un láser de 808 nm. En comparación con otras morfologías de Au, la gran ventaja de la forma de nanoestrella surge de los puntos calientes creados en las ramas de la nanoestrella. Estos puntos calientes dan lugar a grandes absorciones NIR, lo que los convierte en nanoestructuras ideales para convertir de manera eficiente la luz en calor utilizando luz de baja energía, como la que proporciona un láser de 808 nm.03866

The design of magneto-plasmonic nanostructures formed by magnetic Prussian Blue-type nanocrystals decorated with Au nanoparticles

We have developed a general protocol for the preparation of hybrid nanostructures formed by nanoparticles (NPs) of molecule-based magnets based on Prussian Blue Analogues (PBAs) decorated with plasmonic Au NPs of different shapes. By adjusting the pH, Au NPs can be attached preferentially along the edges of the PBA or randomly on the surface. The protocol allows tuning the plasmonic properties of the hybrids in the whole visible spectrum

Liquid phase exfoliation of carbonate-intercalated layered double hydroxides

Direct exfoliation of a carbonate layered double hydroxide (LDHs) has been achieved by using a novel horn‐probe sonic tip, avoiding the development of time‐consuming anion‐exchange reactions. Most suitable solvents were chosen based on the Hildebrand solubility parameters and the thickness of the exfoliated nanosheets confirmed unambiguously the successful delamination

Magnetic PiezoBOTs: a microrobotic approach for targeted amyloid protein dissociation

Piezoelectric nanomaterials have become increasingly popular in the field of biomedical applications due to their high biocompatibility and ultrasound-mediated piezocatalytic properties. In addition, the ability of these nanomaterials to disaggregate amyloid proteins, which are responsible for a range of diseases resulting from the accumulation of these proteins in body tissues and organs, has recently gained considerable attention. However, the use of nanoparticles in biomedicine poses significant challenges, including targeting and uncontrolled aggregation. To address these limitations, our study proposes to load these functional nanomaterials on a multifunctional mobile microrobot This microrobot is designed by coating magnetic and piezoelectric barium titanate nanoparticles on helical biotemplates, allowing for the combination of magnetic navigation and ultrasound-mediated piezoelectric effects to target amyloid disaggregation. Our findings demonstrate that acoustically actuated PiezoBOTs can effectively reduce the size of aggregated amyloid proteins by over 80% in less than 10 minutes by shortening and dissociating constituent amyloid fibrils. Moreover, the PiezoBOTs can be easily magnetically manipulated to actuate the piezocatalytic nanoparticles to specific amyloidosis-affected tissues or organs, minimizing side effects. These biocompatible PiezoBOTs offer a promising non-invasive therapeutic approach for amyloidosis diseases by targeting and breaking down protein aggregates at specific organ or tissue sites

Continuous‐Flow Synthesis of High‐Quality Few‐Layer Antimonene Hexagons

2D materials show outstanding properties that can bring many applications in different technological fields. However, their uses are still limited by production methods. In this context, antimonene is recently suggested as a new 2D material to fabricate different (opto)electronic devices, among other potential applications. This work focuses on optimizing the synthetic parameters to produce high-quality antimonene hexagons and their implementation in a large-scale manufacturing procedure. By means of a continuous-flow synthesis, few-layer antimonene hexagons with ultra-large lateral dimensions (up to several microns) and a few nanometers thick are isolated. The suitable chemical post-treatment of these nanolayers with chloroform gives rise to antimonene surfaces showing low oxidation that can be easily contacted with microelectrodes. Therefore, the reported procedure offers a way to solve two critical problems for using antimonene in many applications: large-scale preparation of high-quality antimonene and the ability to set electrical contacts useful for device fabrication.PNICTOCHEM 804110 (G.A.)PID2019-111742-GA-I00CIDEGENT/2018/00