Matías Jobbágy

Electrochemically induced sol-gel depositions have become a widespread, versatile method for fabricating hybrid and nanostructured oxides on conductive substrates. The process is based on the buildup of electrochemically generated OH⁻ in the diffusion layer near the electrode surface. For the electrodeposition of silica thin films, these OH⁻ ions catalyze the gelation of a kinetically stable precursor solution, thereby resulting in an electrochemically controlled process. The control of the diffusion layer has proven pivotal to depositing thin films while preventing the formation of aggregated by-products deeper in the solution. In this work, the silica sol-gel reactions and electrochemical OH⁻ generation were critically analyzed and described to gain insight into the deposition mechanism. A general model is proposed that predicts the pH profile during both stationary and rotating disk electrode depositions under different conditions (i.e., current densities, times, and rotation rates). This model provides insights into the reactive zones where gelation occurs, and explains typical phenomena observed during deposition such as the dependence of film growth rates and aggregate formation on the deposition conditions. The insights and expressions obtained in this work are invaluable when designing future experiments using novel chemistries or setups.

Herein, the Epoxide Route, a one-pot room temperature alkalinization method based on the reaction between a nucleophile and an epoxide, has been employed to synthesize LaPO₄ in the form of a Rhabdophane phase. The intrinsic features of this synthetic approach allow the reaction to be followed by pH monitoring, making possible the identification of the different precipitation steps involved in the formation of the solid. Once demonstrated the effectiveness of this chemical methodology, the size and shape of the LaPO₄ particles were controlled by varying the identity and proportion of the organic co-solvents employed to perform the reaction. By these means, crystalline particles with dumbbell, urchin and needle shapes were obtained, with sizes that ranged from less than 200 nm to more than 5 μm. Finally, luminescent materials in the form of a LnPO₄Rhabdophane structure were easily obtained by the incorporation of Eu^III along the whole composition range. Additionally, photophysical characterization of selected samples was performed, with a promising outcome. The results presented in this work pave the way to obtaining a wide variety of luminescent materials with sizes and morphologies adjustable on demand, by using a simple and reliable synthetic approach.

Calcium phosphates stand among the most promising nanobiomaterials in key biomedical applications, such as bone repairment, signalling or drug/gene delivery. Their intrinsic properties as crystalline structure, composition, particle shape and size define their successful use. Among these compounds, metastable amorphous calcium phosphate (ACP) is currently gaining particular attention due to its inherently high reactivity in solution, which is crucial in bone development mechanisms. However, the preparation of this highly desired (bio)material with control over its shape, size and phase purity remains as a synthetic challenge. In this work, the epoxide route was adapted for the synthesis of pure and stable ACP colloids. By using biocompatible solvents, such as ethylene glycol and/or glycerine, it was possible to avoid the natural tendency of ACP to maturate into more stable and crystalline apatites. Moreover, this procedure offers size control, ranging from small nanoparticles (60 nm) to micrometric spheroids (>500 nm). The eventual fractalization of the internal mesostructured can be tuned, by simply adjusting the composition of the ethylene glycol:glycerine solvent mixture. These findings introduce the use of green solvents as a new tool to control crystallinity and/or particle size in the synthesis of nanomaterials, avoiding the use of capping agents and preserving the natural chemical reactivity of the pristine surface.

A dramatic change in the magnetic behaviour, which solely depends on the parity of the organic linker molecules, has been found in a family of layered Co^II hydroxides covalently functionalized with dicarboxylic molecules. These layered hybrid materials have been synthesized at room temperature using a one‐pot procedure through the epoxide route. While hybrids connected by odd alkyl chains exhibit coercive fields (H_c) below ca. 3500 Oe and show spontaneous magnetization at temperatures (T_M) below 20 K, hybrids functionalized with even alkyl chains behave as hard magnets with H_c>5500 Oe and display a T_M higher than 55 K. This intriguing behaviour was studied by density functional theory with the incorporation of a Hubbard term (DFT+U) calculations, unveiling the structural subtleties underlying this observation. Indeed, the different molecular orientation exhibited by the even/odd alkyl chains, and the orientation of the covalently linked carboxylic groups modify the intensity of the magnetic coupling of both octahedral and tetrahedral in‐plane sublattices, thus strongly affecting the magnetic properties of the hybrid. These findings offer an outstanding level of tuning in the molecular design of hybrid magnetic materials based on layered hydroxides.

Co‐ and Ni‐based layered hydroxides constitute a unique class of two‐dimensional inorganic materials with exceptional chemical diversity, physicochemical properties and outstanding performance as supercapacitors and overall water splitting catalysts. Recently, the occurrence of Co(III) in these phases has been proposed as a key factor that enhance their electrochemical performance. However, the origin of this centers and control over its contents remains as an open question. We employed the Epoxide Route to synthesize a whole set of α‐NiCo layered hydroxides. The PXRD and XAS characterization alert about the occurrence of Co(III) as a consequence of the increment in the Ni content. DFT+U simulation suggest that the shortening of the Co−O distance promotes a structural distortion in the Co environments, resulting in a double degeneration in the octahedral Co 3d orbitals. Hence, a strong modification of the electronic properties leaves the system prone to oxidation, by the appearance of Co localized electronic states on the Fermi level. This work combines a microscopic interpretation supported by a multiscale crystallochemical analysis, regarding the so‐called synergistic redox behavior of Co and Ni, offering fundamental tools for the controllable design of highly efficient electroactive materials. To the best of our knowledge, this is the first computational–experimental investigation of the electronic and structural details of α‐NiCo hydroxides, laying the foundation for the fine tuning of electronic properties in layered hydroxides.

A new one‐pot homogeneous methodology at room temperature to obtain Au nanoparticles (AuNP) on the basis of the epoxide route is presented. The proposed method takes advantage of the homogenous generation of OH⁻ moieties driven by epoxide ring‐opening, mediated by chloride nucleophilic attack. Once reached alkaline conditions, the reducing medium allows the quantitative formation of AuNP under well‐defined kinetic control. A stabilizing agent, such as polyvinylpyrrolidone (PVP) or cetyltrimethylammonium chloride (CTAC), is required to maintain the AuNP stable. Meanwhile their presence dramatically affects the reduction kinetics and pathway, as demonstrated by the evolution of the UV/Vis spectra, small‐angle X‐ray scattering (SAXS) patterns, and pH value along the reaction. In the presence of PVP nanogold spheroids are obtained following a similar reduction mechanism as that observed for control experiments in the absence of PVP. However, if CTAC is employed a stable complex with Au^III is formed, leading to a different reaction pathway and resulting in ellipsoidal‐like shaped AuNP. Moreover, the proposed methodology allows stabilize the growing AuNP, by coupling their formation with nonalkoxidic sol–gel reactions, leading to nanocomposite gels with embedded metallic nanoparticles. The epoxide route thus offers a versatile scenario for the one‐pot preparation of new metal nanoparticles–inorganic/hybrid matrices nanocomposites with valuable optical properties.

Pesticides represent a significant source of contamination for urban and suburban surface, ground and seawaters. Whole-cell algal biosensors are sensitive, cheap and adaptable early-warning systems, which are capable of detecting pesticides both in situ and continuously in discharges and receiving ecosystems. Here we designed and optimized a new biosensor with a microalgae immobilization method based on double encapsulation in alginate beads/silica gel, which has been proven safe for algae in previous studies. Pesticide detection was assessed by chlorophyll fluorescence disturbance using the two algae strains Chlorella vulgaris and Pseudokirchneriella subcapitata. Three pesticides (diuron, atrazine and isoproturon) were used to optimize and assess the sensor's performance. The first step was to select the optimal silica hydrogel (based on porosity and optical properties) to design the sensor. Two parameters were adjusted to obtain the best contact between microalgae and pesticides, optimizing pesticide detection: algal concentrations in the alginate beads and thickness of the silica gel around the algal beads. Finally, the biosensor's performance was assessed with pesticide solutions and the lowest detection limit was obtained with C. vulgaris exposed to diuron (10 μg L⁻¹).

The ultimate control of the interfaces of nanocomposite materials is essential to tailor and improve their physical/chemical properties in applications such as catalysis and energy storage and production. Fabrication and co-assembly of a variety of nanostructured colloids are promising ways to design the interface of materials in the nano-scale toward high functionality. In this study, we demonstrate the synthesis of colloids of nanocluster-sized (∼2 nm) cobalt and nickel hydroxides and their assembly into microparticles that present hetero-nanointerfaces. The electrochemical properties were investigated to elucidate the effect of the hetero-nanointerface. Microparticles with hetero nanostructures composed of cobalt and nickel hydroxide nanoclusters revealed improved mass specific capacity (91.4 mA h g⁻¹) compared with the respective microparticles with homo-nanointerfaces (cobalt hydroxide, 15.8 mA h g⁻¹; nickel hydroxide, 64.4 mA h g⁻¹). Further investigation suggests that the introduced hetero-nanointerface leads to lower charge transfer resistance and improved electrochemical properties. The synthetic concept demonstrated here is expected to create unique hetero-nanointerfaces for various materials with a wide-range of chemical compositions towards improved and novel functionalities.