TinCn−1Tx2D-sheets are functionalized using a new etching environment allowing the modification of their surface chemistry and production of rationalized TiO2@MXene nanocomposites.

MXenes are a new, and growing, family of 2D materials with very promising properties for a wide variety of applications. Obtained from the etching of MAX phases, numerous properties can be targeted thanks to the chemical richness of the precursors. Herein, we highlight how etching agents govern surface chemistries of Ti 3 C 2 T x , the most widely studied MXene to date. By combining characterization tools such as X-ray diffraction, X-ray photoelectron, Raman and electron energy loss spectroscopies, scanning and transmission electron microscopies and a surface sensitive electrochemical reactionthe hydrogen evolution reaction, HERwe clearly demonstrate that the etching agent (HF, LiF/HCl or FeF 3 /HCl) strongly modifies the nature of surface terminal groups (F, OH and/or O), oxidation sensitivity, delamination ability, nature of the inserted species, interstratification, concentration of defects and size of flakes. Beyond showing how using these different characterization tools to analyze MXenes, this work highlights that the MXene synthesis routes can influence targeted applications.

Understanding the formation mechanism of colloidal nanocrystals is of paramount importance in order to design new nanostructures and synthesize them in a predictive fashion. However, reliable data on the pathways leading from molecular precursors to nanocrystals are not available yet. We used synchrotron-based time-resolved in situ small and wide-angle X-ray scattering to experimentally monitor the formation of CdSe quantum dots synthesized in solution through the heating up of precursors in octadecene at 240 °C. Our experiment yields a complete movie of the structure of the solution from the self-assembly of the precursors to the formation of the quantum dots. We show that the initial cadmium precursor lamellar structure melts into small micelles at 100 °C and that the first CdSe nuclei appear at 218.7 °C. The size distributions and concentration in nanocrystals are measured in a quantitative fashion as a function of time. We show that a short nucleation burst lasting 30 s is followed by a slow decrease of nanoparticle concentration. The rate-limiting process of the quantum dot formation is found to be the thermal activation of selenium.

The MXenes, among which Ti 3 C 2 T x is the most studied, are a large family of 2D materials with proven potential in a variety of application fields (e.g., energy storage and conversion, water purification, electromagnetic interference shielding, humidity sensor, etc). For most of these applications, MXenes properties depend, at least partly, on their water sorption ability and on the induced structural swelling, which is commonly considered a stepwise process, like in clay-like materials. In the present study, we rather evidence the systematic coexistence of different hydrates in MXene interstratified crystals. Hydration heterogeneity and related structure disorder are described from the quantitative analysis of X-ray diffraction data. This specific methodological approach allows disentangling the complex interstratification and rationalizing the prediction of MXene electrical properties. The widespread use of this approach paves the way for a systematic and thorough determination of MXene structure, including order-disorder, and thus for grasping the influence of structural disorder (hydration heterogeneity) on a large number of MXene physical properties (e. g. optical transparency, capacitance). Deciphering this complex structural disorder is also essential in the design of new MXene-based materials for a variety of applications (supercapacitors, batteries, water treatment…).

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Single crystalline FeCo nanoparticles with tunable size and shape were prepared by co-decomposing two metal-amide precursors under mild conditions. The nature of the ligands introduced in this organometallic synthesis drastically affects the reactivity of the precursors and thus the chemical distribution within the nanoparticles. The presence of the B2 short-range order was evidenced in FeCo nanoparticles prepared in presence of HDAHCl ligands, combining 57 Fe Mössbauer, zero field 59 Co Ferromagnetic Nuclear Resonance (FNR) and X-ray diffraction studies. This is the first time that the B2 structure is directly formed during synthesis without the need of any annealing step. The as-prepared nanoparticles exhibit magnetic properties comparable with the ones of the bulk (Ms = 226 Am².kg-1). Composite magnetic materials prepared from these FeCo nanoparticles led to a successful

Single crystalline magnetic FeCo nanostars were prepared using an organometallic approach under mild conditions. The fine tuning of the experimental conditions allowed the direct synthesis of these nano-octopods with body-centered cubic (bcc) structure through a one-pot reaction, contrarily to the seed-mediated growth classically used. The FeCo nanostars consist of 8 tetrahedrons exposing {311} facets, as revealed by high resolution transmission electron Microscope (HRTEM) imaging and electron tomography (ET), and exhibit a high magnetization comparable with the bulk one (Ms = 235 A.m².kg -1 ). Complex 3D spin configurations resulting from the competition between dipolar and exchange interactions are revealed by electron holography. This spin structures are stabilized by the high aspect ratio tetrahedral branches of the nanostars, as confirmed by micromagnetic simulations. This illustrates how magnetic properties can be significantly tuned by nanoscale shape control.

This paper deals with the synthesis of high-magnetization porous silicon-based nanocomposites. Using well-controlled organometallic synthesis of ferromagnetic FeCo nanoparticles, the impregnation of mesoporous silicon has been performed by immersion of porous silicon in a colloidal solution. The technique was optimized by controlling the temperature, the immersion duration, and the solvent nature. The characterization of the nanocomposites showed a homogeneous filling of the pores and a high magnetization of 135 emu/cm3. Such composites present a great interest for many applications including data storage, medical instrumentations, catalysis, or electronics.