Search

We describe here a new process for the synthesis of very high quality 2D Covalent Organic Frameworks (COFs), such a C 2 N and CN carbon nitrides. This process relies on the use of a metallic surface as both a reagent and a support for the coupling of small halogenated building blocks. The conditions of the assembly reaction are chosen so as to leave the inorganic salts by-products on the surface, to further confine the assembly reaction on the surface and increase the quality of the 2D layers. We found that under these conditions, the process directly returns few layers material. The structure/quality of these materials is demonstrated by extensive cross-characterizations at different scales, combining optical microscopy, Scanning Electron Microscopy (SEM)/Transmission Electron Microscopy (TEM) and Energy Dispersive Spectroscopy (EDS). The availability of such very large, high-quality layers of these materials opens interesting perspectives, for example in photochemistry and electronics (intrinsic transport properties, high gap substrate for graphene, etc...)., (© 2023. Springer Nature Limited.)

This paper describes a simple, two-steps chemical pathway to obtain bimetallic carbide nanoparticles (NPs) of general formula MxM″yC, also called η-carbides. This process allows for a control of the chemical composition of metals present in the carbides (M = Co and M″ = Mo or W). The first step involves the synthesis of a precursor consisting of a network of octacyanometalates. The second step consists in a thermal degradation of the previously obtained octacyanometalates networks under neutral atmosphere (Ar or N 2 ). It is shown that this process results in the formation of carbide NPs with diameter of ≈ 5nm, and the stoichiometries Co 3 M' 3 C, Co 6 M' 6 C, Co 2 M' 4 C for the CsCoM' systems., (© 2023 Wiley-VCH GmbH.)

The surfactant used during a colloidal synthesis is known to control the size and shape of metallic nanoparticles. However, its influence on the nanoparticle (NP) structure is still not well understood. In this study, we show that the surfactant can significantly modify the lattice parameter of a crystalline particle. First, our electron diffraction measurements reveals that NiPt nanoparticles around 4 nm in diameter covered by a mixture of oleylamine and oleic acid (50:50) display a lattice parameter expansion around 2% when compared to the same particles without surfactant. Using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX) techniques, we show that this expansion can not be explained by crystal defects, twinning, oxidation, or atoms insertion. Then, using covered NPs in the 4-22 nm size range, we show that the lattice parameter evolves linearly with the inverse of the NP size, as it is expected when a surface stress is present. Finally, the study is extended to pure nickel and pure platinum NPs, with different sizes, coated by different surfactants (oleylamine, trioctylphosphine, polyvinylpyrrolidone). The surfactants induce lattice parameter variations, whose magnitude could be related to the charge transfer between the surfactant and the particle surface.

The development of synthesis methods with enhanced control over the composition, size and atomic structure of High Entropy Nano-Alloys (HENA) could give rise to a new repertoire of nanomaterials with unprecedented functionalities, notably for mechanical, catalytic or hydrogen storage applications. Here, we have developed two original synthesis methods, one by a chemical route and the other by a physical one, to fabricate HENA with a size between 3 and 10 nm and a face centered cubic structure containing three (CoNiPt), four (CoNiPtCu and CoNiPtAu) or five (CoNiPtAuCu) metals close to the equiatomic composition. The key point in the proposed chemical synthesis method is to compensate the difference in reactivity of the different metal precursors by increasing the synthesis temperature using high boiling solvents. Physical syntheses were performed by pulsed laser ablation using a precise alternating deposition of the individual metals on a heated amorphous carbon substrate. Finally, we have exploited aberration-corrected transmission electron microscopy to explore the nanophase diagram of these nanostructures and reveal intrinsic thermodynamic properties of those complex nanosystems. In particular, we have shown (i) that the complete mixing of all elements can only occur close to the equiatomic composition and (ii) how the Ostwald ripening during HENA synthesis can induce size-dependent deviations from the equiatomic composition leading to the formation of large core-shell nanoparticles.

At the nanoscale, the synthesis of a random alloy ( i.e. without phase segregation, whatever the composition) by chemical synthesis remains a difficult task, even for simple binary type systems. In this context, a unique approach based on the colloidal route is proposed enabling the synthesis of face-centred cubic and monodisperse bimetallic, trimetallic, tetrametallic and pentametallic nanoparticles with diameters around 5 nm as solid solutions. The Fe-Co-Ni-Pt-Ru alloy (and its subsets) is considered a challenging task as each element has fairly different physico-chemical properties. Particles are prepared by temperature-assisted co-reduction of metal acetylacetonate precursors in the presence of surfactants. It is highlighted how the correlation between precursors' degradation temperatures and reduction potential values of the metal cations is the driving force to achieve a homogeneous distribution of all elements within the nanoparticles.

We report a new and versatile colloidal route towards the synthesis of nanoalloys with controlled size and chemical composition in the solid solution phase (without phase segregation such as core-shell structure or Janus structure) or chemical ordering. The principle of the procedure is based on the correlation between the oxidation-reduction potential of metal cations present in the precursors and the required synthesis temperature to nucleate particles without phase segregation. The procedure is demonstrated via the synthesis of Face Centered Cubic (FCC) Ni x Pt 1- x nanoparticles, which was elaborated by the co-reduction of nickel(ii) acetylacetonate and platinum(ii) acetylacetonate with 1,2-hexadecanediol in benzyl ether, using oleylamine and oleic acid as surfactants. The chemical composition and solid solution FCC structure of the nanoalloy are demonstrated by crosslinking imaging and chemical analysis using transmission electron microscopy and X-ray diffraction techniques. Whatever the chemical composition inspected, a systematic expansion of the lattice parameters is measured in relation to the respective bulk counterpart., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this paper, we report the first synthesis and characterisations of bimetallic gold(i)-silver(i) calix[8]arene complexes. We show that the radiolytic reduction of these complexes leads to the formation of small bimetallic nanoparticles with an alloyed structure, as evidenced by XPS, HR-TEM and STEM/HAADF-EDX measurements., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Nanoformulated calix[8]arenes functionalized with N -heterocyclic carbene (NHC)-palladium complexes were found to be efficient nano-reactors for Suzuki-Miyaura cross-coupling reactions of water soluble iodo- and bromoaryl compounds with cyclic triol arylborates at low temperature in water without any organic co-solvent. Combined with an improved one-step synthesis of triol arylborates from boronic acid, this remarkably efficient new tool provided a variety of 4'-arylated phenylalanines and tyrosines in good yields at low catalyst loading with a wide functional group tolerance.

Recent advances in structural control during the synthesis of SWCNTs have in common the use of bimetallic nanoparticles as catalysts, despite the fact that their exact role is not fully understood. We therefore analyze the effect of the catalyst's chemical composition on the structure of the resulting SWCNTs by comparing three bimetallic catalysts (FeRu, CoRu and NiRu). A specific synthesis protocol is designed to impede the catalyst nanoparticle coalescence mechanisms and stabilize their diameter distributions throughout the growth. Owing to the ruthenium component which has a limited carbon solubility, tubes grow in tangential mode and their diameter is close to that of their seeding nanoparticles. By using the as-synthesized SWCNTs as a channel material infield effect transistors, we show how the chemical composition of the catalysts and temperature can be used as parameters to tune the diameter distribution and semiconducting-to-metallic ratio of SWCNT samples. Finally, a phenomenological model, based on the dependence of the carbon solubility as a function of catalyst nanoparticle size and nature of the alloying elements, is proposed to interpret the results.

Calixarenes are cyclic oligomers obtained by condensation of suitable p-functionalised phenols with formaldehyde, usually allowing for the synthesis of the well known small calixarenes (including up to eight phenolic subunits). We report here the discovery of much larger members of this family, exhibiting sizes up to 90 phenolic subunits: the giant calixarenes. These macrocycles are obtained according to simple, easily scalable processes, in yields up to 65%. We show that the formation of these giant macrocycles is favored by an oxygen-containing-group at the para-position of the starting phenol, high concentrations of heavy alkaline bases (rubidium or cesium hydroxides) and long reaction times. A mechanism is proposed to rationalize these observations. These giant macrocycles can also be obtained in the quasi-solid state, opening interesting perspectives in the field of calixarenes chemistry. Along with their intrinsic fundamental interest, these objects are also opening interesting applicative potentialities.

Benzyloxycalix[8]arene supported catalysts bearing N-heterocyclic carbene palladium complexes on each subunit were readily synthesized. Intermediates and catalysts were fully characterized, allowing for a fine control of their structure. X-ray diffraction analysis confirmed the formation of a calix[8]arene bearing eight well-defined NHC palladium complexes. The macrocyclic structure of calix[8]arenes allowed for a scalable and chromatography-free catalyst synthesis under homogeneous conditions, while the catalytic reaction proceeded under heterogeneous conditions, just by changing the nature of the solvent. Indeed, when used as a suspension in ethanol, a high TON and TOF were obtained through a large panel of functionalized brominated substrates in C-C Suzuki-Miyaura couplings, with low metal contamination after simple filtration.

Short segments of zigzag single-walled carbon nanotubes (SWCNTs) were obtained from a calixarene scaffold by using a completely new, simple and expedited strategy that allowed fine-tuning of their diameters. This new approach also allows for functionalised short segments of zigzag SWCNTs to be obtained; a prerequisite towards their lengthening. These new SWCNT short segments/calixarene composites show interesting behaviour in solution. DFT analysis of these new compounds also suggests interesting photophysical behaviour. Along with the synthesis of various SWCNTs segments, this approach also constitutes a powerful tool for the construction of new, radially oriented π systems., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The application of a negative gate voltage on a carbon nanotube field effect transistor decorated by a binuclear Tb(III) complex leads to the generation of a negatively charged mononuclear one, presenting an electron density transfer to the nanotube and ambipolar behaviour.

A new simple and cost-effective method has been developed for the fabrication of both plano-convex and plano-concave lens arrays with potentially important sag heights. The process is based on the use of potassium bromide (KBr) powder. At ambient temperature and under pressure, KBr powder is compressed on a molding die with the desired shape to form a solid lens array. The quality of the lens arrays has been assessed, and we present the first image produced by a converging KBr lens array.

Assembly of paramagnetic Cu(2) complexes with a Schiff base scaffold possessing extended electron delocalization together with a quasi-planar structure onto carbon nanotubes induces a diameter-selective charge transfer from the complex to the nanotubes leading to an interestingly large and tunable ambipolar effect. We used complementary techniques such as electron paramagnetic resonance, absorption spectroscopy, and photoluminescence to ensure the success of the assembly process and the integrity of the complex in the nanohybrid. We carried out density functional theory type calculations to rationalize the experimental results, evidencing the selective enhanced interaction of the metal complexes with one type of nanotube.

Sequential growth in solution (SGS) was performed for the magnetic cyanide-bridged network obtained from the reaction of Ni(H(2)O)(2+) and Cr(CN)(6)(3-) (referred to as NiCr) on a Si(100) wafer already functionalized by a Ni(II) complex. The growth process led to isolated dots and a low coverage of the surface. We used the NiFe network as a template to improve the growth of the magnetic network. We elaborated alternate NiFe (paramagnetic)-NiCr (ferromagnetic) ultrathin films around 6 nm thick. The magnetic behaviour confirmed the alternate structure with the ferromagnetic zones isolated between the paramagnetic ones since the evolution of the blocking temperature is consistent with the evolution of the layers' thickness expected from the SGS process.

Controlling the elaboration of Coordination Networks (CoNet) on surfaces at the nanoscale remains a challenge. One suitable technique is the Sequential Growth in Solution (SGS), which has the advantage to be simple, cheap and fast. We addressed two issues in this article: i) the controlled synthesis of ultra thin films of CoNet (thickness lower than 10 nm), and ii) the investigation of the influence of the precursors' concentration on the growth process. Si(100) was used because it is possible to prepare atomically flat Si-H surfaces, which is necessary for the growth of ultrathin films. We used, as a model system, the sequential reactions of K(4)[Fe(II)(CN)(6)] and [Ni(II)(H(2)O)(6)]Cl(2) that occur by the substitution of the water molecules in the coordination sphere of Ni(II) by the nitrogen atoms of ferrocyanide. We demonstrated that the nature of the deposited film depends mainly on the relative concentration of the anchoring sites versus the precursors' solution. Attenuated Total Reflection Fourier Transformed Infra Red (ATR-FTIR), X-ray reflectivity, X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) were used to characterize the steps of the growth process.

Anisotropic nanoparticles of the Fe(pyrazine)Pt(CN)(4) network were prepared embedded in various matrices that revealed to have a dramatic effect on the cooperative spin crossover phenomena. By a judicious choice of the nature of the matrix and the control of interparticle distances, a hysteresis of 15 K was achieved close to room temperature for such nano-objects., (This journal is © The Royal Society of Chemistry 2011)

Isolated nanometric objects of the nickel-iron cyanide-bridged coordination network are obtained by a sequential growth on "molecular seeds" anchored on Si(100) surfaces. Control of the density and the size of the nano-objects is achieved by imposing a growth process without side nucleation.

Recently, the organisation of magnetic molecules on carbon nanotubes has raised much interest due to their possible interesting contribution to molecular spintronics. In this paper, we describe the assembly on SWNTs of a magnetic polyoxometalate encompassing a single cobalt ion (CoPOM) and its isostructural diamagnetic zinc analogue (ZnPOM). The simple magnetic behaviour of CoPOM and the availability of its diamagnetic counterpart render these POM@NTs systems interesting model compounds for the study of molecular electronics devices based on carbon nanotubes and magnetic molecules. The success and rate of the grafting have been investigated by electron microscopy, electron energy loss spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, Raman scattering and magnetisation measurements. These characterisations altogether demonstrate the preservation of the structural and magnetic properties of the molecules upon functionalisation and the existence of an electronic communication between the molecules and the nanotubes.

We present a fabrication method producing large and flat graphene flakes that have a few layers down to a single layer based on substrate bonding of a thick sample of highly oriented pyrolytic graphite (HOPG), followed by its controlled exfoliation down to the few to single graphene atomic layers. As the graphite underlayer is intimately bonded to the substrate during the exfoliation process, the obtained graphene flakes are remarkably large and flat and present very few folds and pleats. The high occurrence of single-layered graphene sheets being tens of microns wide in lateral dimensions is assessed by complementary probes including spatially resolved micro-Raman spectroscopy, atomic force microscopy and electrostatic force microscopy. This versatile method opens the way for deposition of graphene on any substrates, including flexible ones.

The grafting of a monolayer of 6 nm superparamagnetic cyanide-bridged CsNiCr nanoparticles was achieved on a Ni(II)-functionalized Si(100) substrate; magnetic studies reveals that the grafted nanoparticles are nearly magnetically isolated within the monolayer.

A new thioester functionalized calix[8]arene derivative is used for the synthesis of metallic Pd, Pt and Ru nanoparticles, exhibiting several interesting features such as stability and remarkable surface functionalization. Crystalline particles of very small dimensions and good dispersion have been obtained.

An uncommon synergism in the concerted action of OH- and PR3 toward the simple Ru(II) complex Ru(CO)3Cl2(thf) allows a highly efficient reduction of the metal in ethanol or acetonitrile solution at 0 degrees C, with selective production of the corresponding Roper's-type Ru(0) complexes Ru(CO)2(PR3)3 in high yields within 10 min.

The functionalisation of a Si(100) silicon wafer allows for the oriented grafting of a monolayer of Mn12 nanomagnets using a two-step procedure.