Functionalisation of carbon nanostructures towards hybrid materials for different applications

During the last three decades, great scientific efforts led to the discovery and development of new carbon nanomaterials (e.g. carbon nanotubes or CNTs, carbon nanohorns or CNHs, and graphene or G). In the first chapter of this thesis, a general introduction on carbon nanostructures (CNS) and relevant characterisation techniques is provided (Chapter 1). Despite their superior electrical, thermal, and mechanical properties, CNS inherent tendency to aggregate initially limited their applications. This issue can be addressed by various chemical functionalisation routes to improve their dispersibility in water and in polar solvents, thus allowing their handling in liquid phase, and their combination with other chemical entities. Assembly of such multicomponent nanomaterials considerably expands CNS use in fields ranging from biology to energy. In this work, CNS were functionalised to be combined with components of different nature into hybrids or composites for diverse applications. In particular, Chapter 2 discusses the modification of CNTs and G via acid-mediated oxidation or diazo coupling routes to add hydrophilic appendages that favour in situ growth of metal oxide nanostructures (e.g. TiO2). The resulting nanohybrids were tested for photocatalytic hydrogen production. Oxidation of CNT fibres (CNF) was also achieved, first through wet methods, and then by treatment with UV-generated ozone, with only the latter allowing preservation of their macroscopic integrity. The resulting hydrophilic CNF displayed enhanced performance for supercapacitors. Chapter 3 focusses on in situ polymerisation of dopamine on the surface of CNTs and CNHs. The synthetic protocol was optimised to achieve homogeneous coatings that, after graphitisation through high temperature treatment under argon, became conductive. This two-step sequence resulted in the isolation of N-doped CNHs that catalysed the electrochemical reduction of O2 into H2O2 with superior performance relative to current state-of-the-art catalysts. Finally, hydrogel composites were prepared from either CNTs, CNHs, or G and a self-assembling tripeptide (Chapter 4). After an oxidative pre-treatment, each CNS was combined with the peptide and formed supramolecular hydrogels of improved rheological properties (i.e. increased stiffness and resistance to applied stress). Interestingly, hydrogels containing CNTs showed self-healing capacity, thus opening a new window of application for these material

Interfacial charge transfer in functionalized multi-walled carbon nanotube@TiO2 nanofibres

A new insight into photoinduced charge transfer processes across carbon nanotube@TiO2 interfaces has been gained based on experimental details from transient absorption spectroscopy. We show that photoinduced, interfacial hole transfer to carboxylic acid-functionalized multiwalled carbon nanotubes (oxMWCNTs) from TiO2 results in hole-doped oxMWCNTs and reduced TiO2. The latter is inferred from femto- and nanosecond transient absorption spectroscopy performed with oxMWCNT@TiO2 dispersions and complemented with investigations using methyl viologen and N,N,N\u2032,N\u2032-tetramethyl-p-phenylenediamine as an electron scavenger and a hole scavenger, respectively. The results of ultraviolet photoemission spectroscopy (UPS) of the compounds corroborate the findings, highlighting the strong coupling between oxMWCNTs and TiO2 in these hybrids

Chirality Effects on Peptide Self-Assembly Unraveled from Molecules to Materials

Self-assembling short peptides are attractive minimal systems for mimicking the constituents of living systems and building (bio)materials. The combination of both D- and L-amino acids into heterochiral sequences is a versatile strategy for building durable supramolecular architectures, especially when their homochiral analogs do not self-assemble. The reasons for this divergent behavior have remained obscure until now. Here, we elucidate how and why homochiral and heterochiral peptides behave differently. We identify a key spectroscopy signature and its corresponding molecular conformation, whereby an amphiphilic structure is uniquely enabled by the peptide stereochemistry. Importantly, we unravel the self-assembly process as a continuum from the conformation of single molecules to their organization into nano- and microstructures and through to macroscopic hydrogels, which are probed for cytotoxicity in fibroblast cell culture. In this way, (bio)material properties at the macro-scale can be linked to the chemical structure of their building blocks at the angstrom scale. Nature makes pervasive use of homochirality (e.g., D-sugars and L-peptides) to assemble biomolecules, whose interactions determine life processes. D-amino acids rarely occur, and their effects are not yet completely understood. For a long time, structural complexity (e.g., polypeptides and constrained molecules) was considered a requirement for achieving defined conformations that ultimately allow biomolecule recognition and function. Here, we detail how minimalist building blocks can adopt conformations with a characteristic spectroscopic signature, whereby substitution of just one L-amino acid for its D mirror image leads to a divergent path for assembly in water. Subtle molecular variations are amplified through increasing size scale all the way to macroscopic differences that are visible to the eye. Ultimately, the design of heterochiral (bio)molecules thus provides an alternative approach to shed new light on the supramolecular interactions that define life as we know it. This work explains why and how heterochiral and homochiral tripeptides differ in their assembly in water. A characteristic spectroscopic signature is assigned to molecular conformation. We monitor the process as a continuum from the molecular scale to the macroscopic biomaterials so that the final properties are linked to chemical structure of the building blocks. This work lays the foundation for the design of supramolecular hydrogel biomaterials based on short sequences of hydrophobic D- and L-amino acids

Graphene: A Disruptive Opportunity for COVID‐19 and Future Pandemics?

International audienceThe graphene revolution, which has taken place during the last 15 years, has represented a paradigm shift for science. The extraordinary properties possessed by this unique material have paved the road to a number of applications in materials science, optoelectronics, energy, and sensing. Graphene‐related materials (GRMs) are now produced in large scale and have found niche applications also in the biomedical technologies, defining new standards for drug delivery and biosensing. Such advances position GRMs as novel tools to fight against the current COVID‐19 and future pandemics. In this regard, GRMs can play a major role in sensing, as an active component in antiviral surfaces or in virucidal formulations. Herein, the most promising strategies reported in the literature on the use of GRM‐based materials against the COVID‐19 pandemic and other types of viruses are showcased, with a strong focus on the impact of functionalization, deposition techniques, and integration into devices and surface coatings

Light-Programmable Logic-in-Memory in 2D Semiconductors Enabled by Supramolecular Functionalization: Photoresponsive Collective Effect of Aligned Molecular Dipoles

International audienceNowadays, the unrelenting growth of the digital universe calls for radically novel strategies for data processing and storage. An extremely promising and powerful approach relies on the development of logic-in-memory (LiM) devices through the use of floating gate and ferroelectric technologies to write and erase data in a memory operating as a logic gate driven by electrical bias. In this work, we report an alternative approach to realize the logic-in-memory based on two-dimensional (2D) transition metal dichalcogenides (TMDs) where multiple memorized logic output states have been established via the interface with responsive molecular dipoles arranged in supramolecular arrays. The collective dynamic molecular dipole changes of the axial ligand coordinated onto self-assembled metal phthalocyanine nanostructures on the surface of 2D TMD enables large reversible modulation of the Fermi level of both n-type molybdenum disulfide (MoS2) and p-type tungsten diselenide (WSe2) field-effect transistors (FETs), to achieve multiple memory states by programming and erasing with ultraviolet (UV) and with visible light, respectively. As a result, logic-in-memory devices were built up with our supramolecular layer/2D TMD architecture where the output logic is encoded by the motion of the molecular dipoles. Our strategy relying on the dynamic control of the 2D electronics by harnessing the functions of molecular-dipole-induced memory in a supramolecular hybrid layer represents a versatile way to integrate the functional programmability of molecular science into the next generation nanoelectronics

Supramolecular engineering of charge transfer in wide bandgap organic semiconductors with enhanced visible-to-NIR photoresponse

Despite advances in designed supramolecular organic nanowires for optoelectronics, realizing near infrared phototransistors with wide bandgap materials remains a challenge. Here, the authors report high-performance vertical phototransistors featuring supramolecularly engineered organic nanowires