Diseño de nanomateriales mediante procesos de molienda mecanoquímica para aplicaciones catalíticas y electroquímicas

The present doctoral thesis project deals with the design of nanomaterials with potential applications in two important fields: 1) the design of energy storage devices and 2) heterogeneous catalysis, in both cases for the development of more sustainable processes that contribute to ameliorate climate change. Today, most of the challenges humanity faces are related to energy and environment, including the scarcity of water and resources, energy requirements and the depletion of fossil fuel sources. In particular, energy demands, whether in the transport sector or for stationary applications, are priorities in all the scientific programs and agendas of the world. Hence, many investigations are currently aimed to find new materials with better electrochemical results for the development of a new generation of sustainable energy storage devices. In addition, the development of a more sustainable chemical industry requires high efficient processes and therefore the preparation of active and selective catalytic systems. Mechanochemical methods have been employed in this doctoral thesis for the design of nanomaterials, including various nanobioconjugates based on proteins and magnetic nanoparticles, as well as metal oxide nanoparticles supported on mesoporous supports and biomass-templated metal oxide nanomaterials. Mechanochemistry offers several advantages regarding its high reproducibility, versatility, simplicity and, specially, to its green character related to the possibility to avoid the use of solvents and additional reagents. Studies on mechanochemistry have greatly increased in the past two decades, nonetheless as an open research line, a lot of efforts still need to be devoted in order to take full advantages of its great potentialities. Biomass valorization has been one of the main issues covered in this thesis, towards both chemicals and materials. Biomass constitutes, together with CO2, one of the most abundant renewable carbon sources. Therefore, the use of biomass-derived platform molecules for the preparation of added-value chemicals, replacing the petro-based chemical industry, is a highly attractive option. In particular, along this thesis, biomass derived platform molecules such as levulinic acid and isoeugenol have been employed for the synthesis of Nheterocycles and vanillin, respectively. It is important to highlight that, through the valorisation of biomass, added value materials can be also obtained, representing an environmentally friendly methodology. In this regard,, several biomass residues, including spent coffee grounds, egg-white form expired eggs and orange peel have been treated by mechanochemical protocols for the preparation of nanostructured materials with controlled morphology and textural properties. In particular, through this work a mechanochemical synthetic strategy have been designed for the preparation of bioconjugates, minimizing reaction times and costs associated with the use of solvents and other reactants. As an alternative to inorganic materials, organic electroactive products, such as proteins have opened new opportunities for the design of innovative energy storage devices with a greater theoretical capacity, safety, sustainability and low cost. Rechargeable batteries and electrochemical supercapacitors (ECs) are among the most representative examples of energy storage devices. The construction of ECs with high energy density and high power has become a priority issue for the development of future devices. Research in this field has focused on the synthesis of active porous nanomaterials such as metal oxides, hydroxides, or carbonbased materials. These materials provide a high capacity, but have several disadvantages including high costs, manufacturing stages, difficult scalability, besides not being respectful with the environment. In order to overcome the inherent drawbacks of conventional inorganic materials, metalloproteins containing heme groups have recently been employed. However, the development of hybrid systems of hemoproteins and nanoparticles (NPs) for the design of sustainable supercapacitors has not yet been deeply investigated, being a highly innovative and relevant idea for the design of materials that could become a potentially applicable product. Therefore, this doctoral thesis also aimed to synthesize hybrid nanostructures of metalloproteins and nanoparticles through a mechanochemical methodology, as a cheap, sustainable, and versatile strategy, for the design of a new generation of electrochemical supercapacitors. Another potential application of these hybrid protein-nanoparticle systems is their use in biomimetic catalysis processes. Inspired by the in vivo synthesis of natural polymers, where enzymes play an important role as catalysts, in vitro enzymatic polymerization has been widely developed to design a wide range of advanced materials. In particular in this project, bioconjugates based on hemoproteins have been used for the preparation of fluorescent carbon-based nanoparticles following a bottom-up strategy. Similarly, carbon quantum dots with fluorescent behavior have been prepared by a top-down metholody from biomass residues and using an iron oxide containing material as catalyst. In summary, mechanochemistry, as a powerful tool, has been successfully employed to produce a wide range of nanomaterials, from bioconjugates to metal oxides, with applications in catalysis and energy storage. Taking into account the above mentioned premises, the objectives of the proposed work are very relevant for the development of a Sustainable Chemistry and to integrate the strategies of Green Chemistry and Engineering

Boosting the Ni-Catalyzed Hydrodeoxygenation (HDO) of Anisole Using Scrap Catalytic Converters

The large availability and renewable nature of lignin makes its upgrading to bioproducts of particular interest for sustainable development. The hydrodeoxygenation (HDO) of anisole specifically represents a model reaction for the conversion of lignin to biofuels through the removal of the aromatic carbon-oxygen bonds. To date, a range of Ni-based catalysts have been reported as highly active systems for the HDO of anisole. However, there has been a substantial lack of consideration given to the environmental characteristics of these catalytic systems, in contrast with the scope of the sustainable production of biofuels. Herein, Ni-based SiO2 catalysts are prepared by a solventless and highly efficient mechanochemistry approach, having a considerably lower environmental impact as compared to standard impregnation methods. Importantly, scrap catalytic converters (SCATs) are employed as co-catalysts, proving the possibility of enhancing the catalytic HDO of anisole, with a scarcely exploited waste material. The results demonstrate that the combined use of Ni/SiO2 as catalysts and Ni/SCATs as co-catalysts remarkably boosts the rate of the conversion of anisole up to more than 50% by achieving an almost complete conversion of anisole in only 40 min instead of at 200 °C and 4 MPa H2

Improving electrochemical hydrogen evolution of Ag@CN nanocomposites by synergistic effects with α-rich proteins

A graphitic carbon nitride nanostructure has been successfully functionalized by incorporation of different silver contents and subsequent modification with an α-rich protein, namely hemoglobin. Mechanochemistry has been employed, as an efficient and sustainable procedure, for the incorporation of the protein. A complete characterization analysis has been performed following a multitechnique approach. Particularly, XPS data exhibited considerable differences in the C 1s region for the Hb/xAg@CN, ensuring the successful protein anchorage on the surface of the graphitic carbon nitride-based materials. The as-synthesized nanomaterials delivered impressive performance toward hydrogen evolution reactions with an overpotential of 79 mV at a current density of 10 mA/cm2 for Hb/20Ag@CN nanohybrids, which is comparable with the most efficient HER electrocatalysts reported in the literature. The outstanding HER properties were associated with the unique synergistic interactions, quantitatively measured, between AgNPs, Hb tertiary architecture, and the graphitic carbon nitride networks

Versatile protein-templated TiO2 nanocomposite for energy storage and catalytic applications

A protein-templated titania nanocomposite (PT-TiO2) was successfully synthesized by a water-free mechanochemical approach. A biomass valorization strategy was developed by employing egg white from expired eggs to control the morphology and textural features of the prepared titania. A remarkable enhancement of the surface area was achieved, in comparison with the synthesis of the material in absence of the biomass-derived template. Several techniques, such as scanning electron microscopy-mapping and CNHS analysis, supported the presence of carbon, nitrogen and sulfur residues in the obtained composite. Catalytic performance of PT-TiO2 was explored in the oxidation of diphenyl sulfide, displaying promising results in terms of conversion, selectivity and stability. The effect of the oxidant agent was additionally investigated by using hydrogen peroxide, urea hydrogen peroxide, oxygen and t-butyl-hydroperoxide. On the other hand, PT-TiO2 nanocomposite was successfully proved as anodic material for lithium-ion batteries delivering a reversible capacity of 107 mAh g–1 at 0.1C with an excellent Coulombic efficiency of 100% from the second cycle. In addition, the as-synthesized material showed significant capacity retention values of 76% among the 2nd cycle and 100th cycle. PT-TiO2 resulted to be a versatile material with potential catalytic and energy storage applications

Ultrastable CoxSiyOz Nanowires by Glancing Angle Deposition with Magnetron Sputtering as Novel Electrocatalyst for Water Oxidation

Cobalt is one of the most promising non‐noble metal as electrocatalyst for water oxidation. Herein, a highly stable silicon‐cobalt mixed oxide thin film with a porous columnar nanostructure is proposed as electrocatalyst for oxygen evolution reaction (OER). CoOx and CoxSiyOz layers with similar thickness were fabricated at room temperature by magnetron sputtering in a glancing angle configuration (MS‐GLAD) on tin‐doped indium oxide (ITO) substrates. After characterization, a comparative study of the electrocatalytic performance for OER of both layers was carried out. The excellent long‐term stability as electrocatalyst for OER of the porous CoxSiyOz thin film demonstrates that the presence of silicon on the mixed oxide network increases the mechanical stability of the Si/Co layer, whilst maintaining a considerable electrocatalytic response

Mechanochemically Synthesized Supported Magnetic Fe-Nanoparticles as Catalysts for Efficient Vanillin Production

Magnetically separable nanocatalysts were synthesized by incorporating iron nanoparticles on a mesoporous aluminosilicate (Al-SBA-15) through a mechanochemical grinding pathway in a single step. Noticeably, magnetic features were achieved by employing biomass waste as a carbon source, which additionally may confer high oxygen functionalities to the resulting material. The resulting catalysts were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, porosimetry, and magnetic susceptibility. The magnetic nanocatalysts were tested in the selective oxidative cleavage reaction of isoeugenol and vanillyl alcohol to vanillin. As a result, the magnetic nanocatalysts demonstrated high catalytic activity, chemical stability, and enormous separation/reusability qualities. The origin of catalytic properties and its relationship with the iron oxide precursor were analyzed in terms of the chemical, morphological, and structural properties of the samples. Such analysis allows, thus, to highlight the superficial concentration of the iron entities and the interaction with Al as key factors to obtain a good catalytic response

Thermal and light irradiation effect on the electrocatalytic performance of Hemoglobin modified Co3O4-g-C3N4 nanomaterials for oxygen evolution reaction

The oxygen evolution reaction (OER) plays a key role in the water splitting process and a high energy conversion efficiency is essential for the definitive advance of hydrogen-based technologies. Unfortunately, the green and sustainable development of electrocatalysts for water oxidation is nowadays a real challenge. Herein, a successful mechanochemical method is proposed for the synthesis of a novel hemoglobin (Hb) modified Co3O4/g-C3N4 composite nanomaterial. The controlled incorporation of cobalt entities as well as Hb functionalization, without affecting the g-C3N4 nanoarchitecture, was evaluated using different physicochemical techniques, such as X-ray diffraction, N2-physisorption, scanning electron microscopy, UV-visible spectroscopy and X-ray photoelectron spectroscopy. The beneficial effect of the resulting ternary bioconjugate together with the influence of the temperature and light irradiation was investigated by electrochemical analysis. At 60 °C and under light exposition, this electrocatalyst requires an overpotential of 370 mV to deliver a current density of 10 mA·cm−2, showing a Tafel slope of 66 mV·dec−1 and outstanding long-term stability for 600 OER cycles. This work paves a way for the controlled fabrication of multidimensional and multifunctional bio-electrocatalysts

Mechanochemical Synthesis of Nickel-Modified Metal–Organic Frameworks for Reduction Reactions

In this work, we report the incorporation of nickel oxide nanoparticles into a metal–organic framework (MOF) structure by a solvent-free mechanochemical strategy. In particular, the zirconium-based MOF UiO-66 was modified with different Ni loadings and characterized using complementary techniques including X-ray diffraction (XRD), N2 porosimetry and X-ray photoelectron spectroscopy (XPS). The catalytic potential of the as-prepared Ni/UiO-66 materials in the hydrogenation reaction of methyl levulinate using 2-propanol as hydrogen donor solvent has been investigated under flow conditions. Under optimized conditions, the 5%Ni/UiO-66 led to the best catalytic performance (70% yield, 100% selectivity to gamma-valerolactone), which could be attributed to the higher content of the Ni species within the MOF structure. The obtained results are promising and contribute to highlighting the great potential of MOFs in biomass upgrading processes, opening the path to the sustainable development of the chemical industry