Nowadays, there is a strong interest in the development of nanostructured ceramics in order to develop materials with special or improved properties with respect to those of classical bulk ceramics. Thermoelectric nanostructures are very attractive because they can provide a practical way to scavenge energy from the environment to power microsystems and thus be used in novel self-powered sensing devices. Thermoelectric generators can be used in automobiles to convert the wasted heat from an engine's coolant or exhaust into electricity. It is accepted that such systems can lead to a fuel consumption decrease of around 10%. Heat from the sun is also a source of energy that can be converted into electricity by thermoelectric systems. A lot of thermoelectric materials have been extensively studied during the last decade. Recently, spectacular results have been obtained for various systems through the introduction of nanostructures in the materials. Nanoscale heterostructures can be achieved by decreasing the grain size and/or by introducing dispersed nanoparticles or continuous secondary phase. These systems are usually referenced as nanocomposites. Among the materials having good thermoelectric properties, some have a highly anisotropic structure. In those cases, it could be of great interest to align the grains along one crystallographic direction. Such materials are called textured ceramics and can be obtained through different ways. Nevertheless, all the existing texturing methods require long sintering time at high temperature, in order to allow the texturing process to take place. Consequently, it is rather difficult to obtain nanotextured ceramics. NanoCerTex project deals with the development of thermoelectric nanotextured materials and nanocomposites for energy harvesting, by using an original combination of a soft chemistry route nanofibers fabrication technique (electrospinning) and flash sintering technique (spark plasma sintering techniques). The key issue to overcome is maintaining the nanometric dimension during the texturing process. Two axes will be explored: - Development of bulk dense nanotextured thermoelectric ceramics. The objective will be to sinter by flash technique, a stack of aligned fibers to produce dense and bulk-textured ceramics with submicrometric grains. It is expected that for compounds with highly anisotropic crystal structure, texturing develops spontaneously during the uniaxial pressure sintering. For materials with isotropic structure, texturing can be induced by introducing some anisotropic seeds into the fibers during electrospinning. Texturing will be developped during subsequent sintering step. This method is an implementation of the well-known Templated Grain Growth method used for bulk micrometric ceramics to nanofibers. - Development of textured thermoelectric nanocomposites, which will consist on inorganic multiphase systems. The objective is to increase the Figure of Merit ZT by decreasing the thermal conductivity of the material while maintaining a high electrical conductivity. The use of aligned core-shell nanofibers should lead to nanocomposite thermoelectric ceramics with enhanced properties. NanoCerTex aims at understanding the mechanisms of fiber formation during electrospinning and texture development during the subsequent thermal treatment. In depth ex situ analysis (XRD, SE-MEB, MET, EBSD…) of the crystallization within the fiber and in situ characterization by synchrotron radiation (SAXS, WAXS…) will be performed in order to get more insight on how to improve the process. To our knowledge, developing textured nanocomposite thermoelectric ceramics by using the electrospinning technique has not been reported. This project aims at demonstrating the interest of electrospinning coupled with spark plasma sintering process for the design of new functional anisotropic materials with enhanced properties, by creating a texturing at a submicron scale. Although this work will be done on the

This TREMPLIN project aims at supporting a future application to the ERC Consolidator call of a proposal which was evaluated favorably in 2016. The goal is to provide a proof-of-concept validating the feasability of the innovative approach sumitted to the ERC. The summary of the ERC project, called MOLTEN, is the following: MOLTEN targets the emergence of a synthesis process to strongly widen the range of compounds reachable as nanoparticles, scarce compared to bulk phases known from usual approaches. It focuses on boron-based inorganic phases, as transport and surface properties of reported bulk compounds suggest that nanoparticles will open novel avenues in energy conversion. Their synthesis performed at temperatures (T) above 1000°C yields large crystal growth. Hence these phases are uncharted at the nanoscale. To reach nanoparticles, metastable states not accessible by solid state chemistry and known processes must be obtained. MOLTEN draws on liquid-phase syntheses and proposes 3 breakthroughs based on liquid ionic mixtures, made of inorganic molten salts at 300-1000°C, and inorganic and organic salts below 300°C: 1) Exploration of the T range up to 1000°C in liquids as a virgin field for colloidal syntheses. T lower than standard solid state processes provides conditions favorable to the discovery of novel metastable compounds; 2) Discovery of a parameter in liquid-phase syntheses enabled by ionic mixtures: adjusting the liquid mixture composition allows using biphasic media and tuning the solvating ability for enhanced precursor solubility; 3) Development of new strategies to ensure increased nucleation rates and limited crystal growth: high T microwave heating and quenching. The first part (WP1) addresses boron carbon phosphides with dense structures, as the few known bulk compounds hint at a tremendous variety of unreported materials. WP2 deals with boron and silicon-based inorganic clathrates and open frameworks, including compositions and structures never reported. WP3 focuses on advanced characterization of the crystal structure and morphology, and of novel properties in thermoelectric conversion of waste heat and photocatalytic water splitting. WP4 explores reaction mechanisms at play within this novel platform of nanomaterials synthesis through phase diagrams and in situ investigations. The TREMPLIN strategy is to focus synthesis efforts on a single type of materials and a specific high impact application: silicon-based clathrate compounds for applications in thermal-to-electrical energy conversion, for the recovery of waste heat and impact on energy harnessing and environmental issues. This approach should provide a proof-of-concept of the novel synthetic strategy I want to develop in MOLTEN It will also build and establish my expertise on the chemistry of silicon-based nanomaterials.

The fabrication of miniaturized electronic, chemical and photonic components on flexible, stretchable, non-planar, and biocompatible substrates as opposed to conventional rigid substrates can open doors for the next generation of advanced devices with new functionalities. In this context, one great challenge consists in the development of new technologies to generate, localized and stabilize metallic nano-objects on flexible surfaces by industrially viable processes. The existing protocols to fabricate metallic nanostructures could be demonstrated only on limited resolution and/or small surfaces. These techniques usually involve multiple steps such as pattern transfer that are difficult to perform on polymeric substrates at the nanoscale without degradation and delamination of the nanostructures. The MetaFleSS project aims to develop of a simple, environmental-friendly and scalable nanofabrication technique to in-situ generate, localize and anchor metal nano-objects on flexible substrates. The approach is based on metal reduction induced by mechanical homolysis of the surface, recently demonstrated in the literature and by our preliminary results. During mechanical pulling-off, local homolytic bond breaking induces formation of “mechanoradicals” on the surface that act as reducing sites; the metal reduction takes place after immersion in metal precursors aqueous solutions leading to the formation of metal nanoparticles patterns on the surface. In order to better control the radical formations, the contact interface will be rationally designed. In the first part of the project, the homolysis-assisted reduction process will be investigated. The first objective is thus to access the mechanoreactivity of the hybrid interface on flat surfaces in order to understand the mechanism of formation of metallic nanoparticle, with optimized size and density. The second objective of the project will be to explore the potentiality of this simple approach for nanopatterning. In order to optimize the radicals formation and spatially localized the reduction process, the hybrid interface will be rationally designed by using topographic and chemical heterogeneities. Patterned ceramic masters obtained by nanoimprinting lithography or/and micelles self-assembly will be used to explore the limit of the approach in term of geometry and resolution. Finally the properties of the flexible/stretchable nanopatterned metallic components will be tested in order to develop functional devices such as stretchable plasmonic sensors.

CellsInFoams uses an ice-templating technique (freeze casting) to develop bacteria-containing materials able to outperform the current solutions in soil bioremediation. The project aims at developing macroporous materials with precisely controlled morphology to encapsulate environmental relevant bacteria. These materials will be hybridized by coating with an inorganic layer to control the exchanges between the bioremediation platforms and the contaminated soils. The project will explore the interdependence between the materials processing conditions and cellular viability. Finally the biodegradation activity of the proposed remediation platforms will be assessed in aqueous and soil media. In parallel to such activity we will focus on the ice structuring mechanisms and its impact on bacterial encapsulation and viability. In summary, CellsInFoams addresses the problem of soil bioremediation by proposing a completely new strategy that combines elements from cell cryopreservation and materials processing into one, unique process.

Nowadays, if synthetic colorants still present a wider range of colors and are cheaper than natural colorants, they remain highly polluting. Their production based on petrochemicals and their use in the coloring industry have a huge impact on the environment and our health. Therefore, replacing polluting synthetic colorants by bio-based colorants is today the main priority of various industries e.g. coating, painting, textile, cosmetic and construction. However, many issues, including color range, stability, tinting strength and costs need to be solved before setting a competitive and sustainable alternative to synthetic colorants. Inspired by the biomineralization and pigmentation mechanisms occurring in sea urchin spines the ColMhyBio project proposes to produce a large color panel of bio-based hybrid colorants having chemically- and photo-stable colors. The skeletal elements of sea urchins, in particular their spines exhibit a wide range of intense, homogeneous and long-lasting colors ranging from purple to green. These remarkable color properties are likely due to the occlusion of a mixture of different polyhydroxylated-naphthoquinones (PHNQ) molecules, the pigment of the spines, within the inorganic CaCO3 host. In this project, we will first develop eco-friendly protocols for the extraction of the PHNQ molecules from recycled colored spines and from red-spherule cells in which they are biosynthesized. Different bio-inspired syntheses will be then developed to encapsulate the PHNQ molecules within a crystalline CaCO3 inorganic host during the crystallization of an amorphous CaCO3 phase (ACC). The PHNQ’s incorporation during ACC crystallization is expected to lead to strong inorganic-organic interactions likely responsible for the color variations and stability. Thus, a chart of new bio-based hybrid colorants exhibiting a large palette of chemically- and photo-stable colors devoted to a sustainable biocoloring industry will be produced.