PhD subjects

Alkanes are essential molecules in the energy sector (fuels), as well as in specialty chemicals (cosmetics, adhesives, etc.) and fine chemicals. Today, they are mainly derived from non-renewable fossil resources, and their use contributes to climate change through the production of carbon dioxide. To achieve carbon neutrality, producing alkanes from renewable carbon sources such as biomass would appear to be an attractive alternative. In biomass, fatty esters of the RCO2R type have long alkyl chains, but the presence of oxygen atoms means they are not a direct substitute for petroleum-based alkanes.

The aim of this thesis is to develop homogeneous catalytic systems for the photocatalytic deoxygenation of esters into the corresponding alkanes, by simple extrusion of a CO2 molecule. The energy required for the reduction reaction will be provided by light. Throughout this thesis project, the focus will be on developing catalytic systems and understanding reaction mechanisms through experimental studies (kinetics, NMR studies, observation of reaction intermediates, etc.) combined with theoretical chemistry (DFT calculations).

The objective of this Phd is to develop an experimental device to perform in situ and real time elemental analysis of nanoparticles during their synthesis (by laser pyrolysis or flame spray pyrolysis). Laser-Induced Breakdown Spectroscopy (LIBS) will be used to identify the different elements present and to determine their stoichiometry.

Preliminary experiments conducted at LEDNA have shown the feasibility of such a project and in particular the acquisition of a LIBS spectrum of a single nanoparticle. Nevertheless, the experimental device must be developed and improved in order to obtain a better signal to noise ratio, to decrease the detection limit, to take into account the different effects on the spectrum (effect of nanoparticle size, complex composition or structure), to automatically identify and quantify the elements present.

In parallel, other information can be sought (via other optical techniques) such as the density of nanoparticles, the size or shape distribution.

Understanding the non-specific or specific interactions between biomolecules and nanomaterials is key to the development of safe nanomedicines and nanoparticles. Indeed, adsorption of biomolecules is the first process occurring after the introduction of biomaterials into the human body, which controls their biological response. In this thesis, we will simulate the interface between nanosystems and biomolecules on a scale of a hundred nanometers, using the new exascale computing resources available at the CEA from 2025 (Jules Verne machine installed at the CCRT).

Graphene as a constituent of graphite was close to us for almost 500 years. However, it is only in 2005 that A. Geim and K. Novoselov (Nobel Prize in 2010) reported for the first time the obtaining of a nanostructure composed by a single layer of carbon atom. The exceptional electronic properties of graphene make it a very promising material for applications in electronic and renewable energies.

For many applications, one should be able to modify and control precisely the electronic properties of graphene. In this context, we propose to synthesize chemically graphene nanoparticles and study their absorption and photoluminescence properties. We will focus on their solubilty in water in order to study potential applications in biology. This project will be developed in collaboration with Physicists so the candidate will work in a multidisciplinary environment.

Glycomics involves identifying oligosaccharides (OS) present in a biological fluid as a source of biomarkers for diagnosing various pathologies (cancers, Alzheimers disease, etc.). To study these OS, sample preparation involves 2 key phases, enzymatic cleavage (breaking the bond between OS and proteins) followed by purification and extraction (separation of OS and proteins). However, the materials currently used in the protocols impose numerous manual and time-consuming steps, incompatible with high-throughput analysis.

In this context, the LEDNA laboratory specialized in materials science has recently developed a sol-gel process for the manufacture of Hierarchical Porosity Monoliths (HPMs) in miniaturized devices. These materials have provided a proof of concept demonstrating their value for the second stage of glycomic analysis, i.e. the purification and extraction of oligosaccharides. The LEDNA is now looking to improve the first step, corresponding to enzymatic cleavage, which has become a limiting factor in the glycomics analysis process. Functionalization of porous materials, in particular HPMs, with enzyme would enable simple sample preparation in just a few hours with a single step.

The aim of this thesis is therefore to show that the use of porous materials with a dual function - catalytic and filtration - applied to the preparation of samples for glycomic analysis is a relevant means of simplifying and accelerating glycomic analysis, as well as employing them in hospital-related studies to identify new biomarkers of pathologies.

The research project will involve developing a device incorporating porous materials with catalytic and filtration functions. Several aspects will be addressed, ranging from the synthesis and shaping of these materials to characterization of their textural and physico-chemical properties. Particular emphasis will be placed on enzyme immobilization. The most promising prototype(s) will be evaluated in a glycomic analysis protocol, verifying the oligosaccharide profiles obtained from human biofluids (plasma, milk). Physico-chemical characterization will involve a variety of techniques (SEM, TEM, etc.), as well as characterization of porosity parameters (nitrogen adsorption, Hg porosimeter). Oligosaccharides will be analyzed by high-resolution mass spectrometry (mainly MALDI-TOF).

For this multidisciplinary thesis project, we are looking for a student chemist or physical chemist, interested in materials chemistry and motivated by the applications of fundamental research in the field of new technologies for health. The thesis will be carried out in two laboratories, LEDNA for the materials part and LI-MS for the use of materials in glycomics analysis. The research activity will be carried out at the Saclay research center (91).

The recycling and chemical recovery of plastics are necessary and crucialsteps to accelerate the transition to a circular economy and reduce the pollution associated with these materials.

The aim of this project is to develop catalytic systems for depolymerizing oxygenated and nitrogenous plastics into their monomers or derivatives (alcohols, amines, halides or even hydrocarbons). These methods, which enable the carbonaceous matter in polymers to be recovered under mild conditions in the form of chemical products useful to the chemical industry, are still underdeveloped and will, in the future, be virtuous processing routes for recycling certain plastics.

The aim of this doctoral project is to develop and use new metal molecular complexes (aluminium, zirconium, rare earths, etc.) and organic catalysts (boron-based), which

- are simple, inexpensive, recyclable and more selective than current catalysts (composed of iridium, ruthenium and boron), to depolymerize different types of plastics (polyesters, polycarbonates, polyurethanes and polyamides),
- allow, in the case of reductive catalysis, the use of hydrosilanes and hydroboranes, as well as the use of new reducing agents acting by transfer hydrogenation routes.

Finally, we will also consider the use of organic anhydrides to transform plastics into reactive organic compounds useful in organic chemistry.

In situ solid-state Nuclear Magnetic Resonance (ssNMR) is a valuable characterization tool to decipher the electrochemical phenomena during battery operation. However, the broad signal lineshapes acquired from the sample static condition often retrain from the full potential of ssNMR characterization. Ex situ ssNMR experiments, using Magic-Angle sample Spinning (MAS), are often necessary to interpret the in situ data. As in any ex situ characterizations, the analyses do not always represent the real electrochemistry because of unwanted artifacts from the ex situ sample preparation, i.e., cell dismantling and electrode separations. Consequently, in situ ssNMR applications have been limited. The PhD student will address this limitation by developing a spinning battery cell for acquiring high-resolution ssNMR data under MAS for in situ study, including a new method of spatially-resolved ssNMR spectroscopy. Combining in situ, MAS, and localized spectroscopy would lead to an unprecedented in situ ssNMR tool for deciphering fundamental insights into battery chemistry, which the student will emphasize by studying phenomena such as interfaces and dendrite formation in operating Li-ion batteries.

The major public health problem of sepsis requires breakthrough technologies for ultra-fast diagnosis. Dense, fluidized granular beds are ideal systems for liquid-solid or gas-solid exchange processes. They are widely used in industry thanks to their high surface-to-volume ratio. Over the past decade, microfluidics and lab-on-a-chip have enabled numerous advances, particularly in biological sample preparation. We propose to develop a versatile microfluidic platform that will enable the creation of such dense, fluidized beds. We will first work on the incorporation of membranes into microchannels, drawing on the patented know-how developed in the laboratory. We will then study and characterize the granular beds, and finally test them for the detection of bacteria in biological samples. This work will be carried out in collaboration with our physicists (LEDNA) and biologist (LERI) partners at CEA Saclay.

Our ability to manufacture metal oxide nanoparticles (NPs) with well-defined composition, morphology and properties is a key to accessing new materials that can have a revolutionary technological impact, for example for photocatalysis or storage of energy. Among the different nanopowders production technologies, Flame Spray Pyrolysis (FSP) constitutes a promising option for the industrial synthesis of NPs. This synthesis route is based on the rapid evaporation of a solution - solvent plus precursors - atomized in the form of droplets in a pilot flame to obtain nanoparticles. Unfortunately, mastery of the FSP process is currently limited due to too much variability in operating conditions to explore for the multitude of target nanoparticles. In this context, the objective of this thesis is to develop the experimental and numerical framework required by the future deployment of artificial intelligence for the control of FSP systems. To do this, the different phenomena taking place in the synthesis flames during the formation of the nanoparticles will be simulated, in particular by means of fluid dynamics calculations. Ultimately, the creation of a digital twin of the process is expected, which will provide a predictive approach for the choice of the synthesis parameters to be used to arrive at the desired material. This will drastically reduce the number of experiments to be carried out and in consequence the time to develop new grades of materials

To meet the increasing energy demand and diversify energy resources, fuel cells emerge as a promising solution. This Ph.D work aims to contribute to the development of Proton Exchange Membrane Fuel Cells (PEMFCs), with a specific focus on bipolar plates (BPs) which ensure gas distribution and current collection. The first objectives are to design and manufacture stainless steel BPs using 3D printing (SLM - Selective Laser Melting) and to develop organic and inorganic anticorrosion coatings. Multiple channel architectures will be designed and characterized, including in-situ assessments with membrane-electrode assemblies (MEAs). Coatings will also be characterized, particularly in terms of their corrosion resistance through polarization methods. In the second phase, the aim is to integrate the optimized BPs with MEAs and thoroughly study the performance of PEMFCs using electrochemical techniques to gain fundamental insights into the mechanisms that limit PEMFCs performance.

Catalysis is today at the core of chemical industrial applications. For example, the conversion of nitrile to amide, which is relevant in pharmaceuticals, agrochemicals, synthetic chemistry and polymer chemistry, by hydration requires an efficient catalyst due to its slow kinetics. For environmental reasons, it is crucial to discover catalysts without transition metals, neither toxic nor corrosive, and cheap. One example of such catalyst is hydroxide choline.

During this thesis, the student will learn how to perform ab initio molecular dynamics simulations coupled with a method which can reconstruct the free-energy landscape of the hydration reaction for different aromatic nitriles in different in silico experimental conditions. He or she will also have to perform quantum chemistry calculations at a level that can describe all the required intra and intermolecular interactions. This theoretical approach has already been successfully used within our team to describe other chemical reactions in aqueous solution and will be applied to the innovative field of green chemistry.

Among nanoscale semiconductors, nanodiamonds (ND) have not been really considered yet for photoelectrocatalytic reactions in the energy-related field. This originates from the confusion with ideal monocrystalline diamond featuring a wide bandgap (5.5 eV) that requires a deep UV illumination to initiate photoreactivity. At the nanoscale, ND enclose native defects (sp2 carbon, chemical impurities such as nitrogen) that can create energetic states in the diamond’s bandgap decreasing the light energy needed to initiate the charge separation. In addition, the diamond electronic structure can be strongly modified (over several eV) playing on its surface terminations (oxidized, hydrogenated, aminated) which can open the door to optimized band alignments with the species to be reduced or oxidized. Combining these assets, ND becomes competitive with other semiconductors toward photoreactions. The aim of this PhD is to investigate the ability of nanodiamonds in reducing CO2 through photoelectrocatalysis. To achieve this goal, electrodes will be made from nanodiamonds with different surface chemistries (oxidized, hydrogenated and aminated), either using a conventional ink-type approach or a more innovative one that results in a porous material including nanodiamonds and a PVD-deposited matrix. Then, the (photo)electrocatalytic performances under visible illumination of these nanodiamond-based electrodes toward CO2 reduction will be investigated in terms of production rate and selectivity, in presence or not of a transition metal macrocyclic molecular co-catalyst.

The combined demands of increasing energy production and the need to reduce fossil fuels to limit global warming have paved the way for an urgent need for clean energy harvesting technologies. One interesting solution is to use solar energy to produce fuels. Thus, low-cost materials such as semiconductors have been intensively studied for photocatalytic reactions. Among them, 1D nanostructures hold promise due to their interesting properties (high specific and accessible surfaces, confined environments, better charge separation). Imogolite, a natural hollow nanotube clay belongs to this category. Although it is not directly photoactive in the visible light range (high band gap), it exhibits a permanent wall polarization due to its intrinsic curvature. This property makes it a potentially useful co-photocatalyst for charge separation. Moreover, this nanotube belongs to a family sharing the same local structure with different curved morphologies (nanosphere and nanotile). In addition, several modifications of these materials are possible (wall doping with metals, coupling with metal nanoparticles, functionalization of the internal cavity) allowing tuning band gap. The proof of concept (i.e., photocatalytic nanoreactor) was only obtained for the nanotube form.

This phD project aims to study the whole family (nanotube, nanosphere, and nanotile, with various functionalizations) as nanoreactors for reduction reactions of protons and CO2 triggered under irradiation.

Raw earth materials, which have found multiple uses for millennia, now offer considerable potential for helping to adapt to the changing climate, thanks to their natural ability to regulate heat and water, as well as their low-CO2 production and shaping. However, scientific advances are still needed to get a more precise understanding of these materials, up to the nanometric scale.

This thesis focuses on the link between the mechanical properties of raw earth soil materials and their nanostructure, emphasizing the roles of confined water, ions and organic substances. Two approaches, based on the expertise on nanoporous media developed at CEA, Saclay and Marcoule, will be followed: the analysis of old materials using spectroscopic and radiation scattering methods, and the development of a screening protocol to identify physicochemical parameters important for durability. This research, which ultimately aims to optimize the formulation of raw earth materials, will be carried out in collaboration with architects specialists in the field.

In the context of the search for processes that are less polluting and more energy-efficient than current processes, it is interesting to produce high-stake molecules such as C2H4 by developing alternative synthesis routes to steam cracking, which is used in the majority of cases, but is energy-intensive and based on fossil resources. Processes such as photocatalysis, which relies on the use of light energy, seem an attractive way of generating these molecules of interest. In this context, we have already shown that the use of TiO2-based photocatalysts decorated with copper particles enables the production of ethylene from an aqueous solution of propionic acid, with a selectivity (C2H4/other carbonaceous products) of up to 85%.

However, photocatalysis kinetics can be slow, and it can take a long time to identify the best catalysts or catalyst/reagent pairs for a given reaction. So, in order to determine whether radiolysis, which relies on the use of radiation to ionize matter, can be an effective method of screening catalysts, initial experiments have already been carried out on catalyst (TiO2 or Cu TiO2)/reagent (propionic acid more or less concentrated) pairs, previously studied in photocatalysis. Initial results obtained by radiolysis are encouraging. In these experiments, only dihydrogen production was measured. A significant difference was observed in this production depending on the system: it was high during radiolysis of propionic acid with TiO2 nanoparticles, and significantly lower in the presence of Cu TiO2 nanoparticles, suggesting a different reaction path in the latter case, in line with observations made during photocatalysis experiments.

The aim of this thesis work will be to extend these initial results by synthesizing nanoparticles (catalysts), preparing reagent/catalyst mixtures, then irradiating them and measuring the various gases produced by gas-phase micro-chromatography, with special attention on ethylene. Particular attention will be paid to determining the species formed, especially transient ones, in order to ultimately propose reaction mechanisms accounting for the differences observed for the different reagent/catalyst pairs. Comparisons will also be made with results obtained by photocatalysis.

Our recent results show that nanodiamond can also act as a photocatalyst, enabling the production of hydrogen under solar illumination [1]. Despite its wide band gap, its band structure is adaptable according to its nature and surface chemistry [2]. Moreover, the controlled incorporation of dopants or sp2 carbon leads to the generation of additional bandgap states that enhance the absorption of visible light, as shown in a recent study involving our group [3]. The photocatalytic performance of nanodiamonds is therefore highly dependent on their size, shape and concentration of chemical impurities. It is therefore essential to develop a tailor-made nanodiamond synthesis method, in which these different parameters can be finely controlled, in order to provide a supply of controlled nanodiamonds, which is currently lacking.

The aim of this PhD is to develop a bottom-up approach to nanodiamond synthesis using a sacrificial template (silica beads or fibers) to which diamond seeds 10 nm are attached by electrostatic interaction. The growth of diamond nanoparticles from these seeds will be achieved by exposing these objects to a microwave-enhanced chemical vapor deposition (MPCVD) growth plasma, allowing very fine control of (i) the incorporation of impurities into the material (ii) its crystalline quality (sp2/sp3 ratio) (iii) its size. This growth facility, which exists at the CEA NIMBE, is used for the synthesis of boron-doped diamond core-shells [4]. In the second part of the thesis, an innovative process (patent pending) is implemented to achieve MPCVD growth of diamond nanoparticles by circulating the sacrificial templates in a gas stream. During this work, different types of nanodiamonds will be synthesized: intrinsic nanoparticles (without intentional doping) and nanoparticles doped with boron or nitrogen.

After growth, the nanoparticles will be collected after dissolution of the template. Their crystal structure, morphology and surface chemistry will be studied at CEA NIMBE by scanning electron microscopy, X-ray diffraction and Raman, infrared and photoelectron spectroscopy. A detailed analysis of the crystallographic structure and structural defects will be carried out by high-resolution transmission electron microscopy.

Nanodiamonds will then be surface-modified to give them colloidal stability in water. Their photocatalytic performance for hydrogen production will be evaluated in collaboration with ICPEES (Strasbourg University).


References
[1] Patent, Procédé de production de dihydrogène utilisant des nanodiamants comme photocatalyseurs, CEA/CNRS, N° FR/40698, juillet 2022.
[2] Miliaieva et al., Nanoscale Adv. 2023.
[3] Buchner et al., Nanoscale (2022)
[4] Henni et al., Diam. Relat. mater. (under review)

Reducing the density of materials is one of the best ways to diminish our energy footprint. One solution is to replace massive materials by microlattices. Among these, random architecture structures inspired by bird bone structure offer the best advantages, with isotropic mechanical behavior and increased mechanical resistance, while meeting the challenges of the circular economy. These material-saving metamaterials are manufactured by 3D printing and can be compacted at the end of their life cycle. Among manufacturing technologies, UV polymerization of liquid organic resin or composite is the most promising. It produces mechanically resistant materials without generating manufacturing waste. It is also possible to include large quantities of bio-sourced fillers, reducing even further their environmental impact.

The PhD-thesis proposed here focuses on the development of polymeric nanocomposite microlattice structures from resin formulation to mechanical properties study (viscoelasticity, yield stress, fracture resistance) through printing and post-processing stages. From a more fundamental point of view, the aim is to study the link between the composition, shape and surface properties of the fillers on one hand, and the imprimability of the composite resine and the mechanical properties of the resulting metamaterial on the other hand. The thesis will focus on the study of cellulose-type fillers in nanoparticle, microparticle or fiber form. This multidisciplinary study bridges technology to science while producing data for a digital twin.

As part of the energy transition, the production of hydrogen from solar energy appears to be an extremely promising means of storing and then producing energy. To develop on a large scale, water photoelectrolysis requires materials with high catalytic efficiency. Among the candidates considered, materials derived from barium titanates appear promising because their ferro- and piezoelectric properties could increase their photocatalytic effect. Therefore, we propose to synthesize BaTiO3 nanoparticles by flame spray pyrolysis and to make substitutions on Ba and O in order to study the effect of these modifications on the ferroelectric properties of the material. The addition of noble metal inclusions to the surface of the particles, likely to improve catalysis, will also be addressed. Finally, photocatalysis and piezocatalysis tests will make it possible to establish the links between ferroelectric and catalytic phenomena in this family of materials. This subject will be carried out in collaboration between the LEEL of the CEA and the SPMS of Centrale – Supelec.