Oligomeric and polymeric surfactants for the transfer of luminescent ZnO nanocrystals to water

International audienceThe water dispersion of luminescent nanocrystals (NCs) synthesized in organic solvent by encapsulation in a surfactant bilayer is a promising strategy for preserving the optical properties of NCs. The phase transfer of highly monodispersed ZnO NCs using the monomer, dimer, trimer and polymer of a series of alkyl ammonium surfactants is compared. Transfer yields over 60% could be obtained with the oligomers and the polymer. In contrast, we observed no measurable transfer using the single chain surfactant. NMR spectroscopy, including DOSY and NOESY, demonstrated that increasing the oligomerization number ameliorates the stability within the coating bilayer. The NCs exhibit a strong luminescence in water and show long term chemical and photo-chemical stability

Lithium ion as growth-controlling agent of ZnO nanoparticles prepared by organometallic synthesis

ZnO nanoparticles were synthesized by adding solid Zn(c-C6H11)2 to a THF solution of the lithium (sodium) precursor and octylamine (OA) as stabilizer. The proportion of Li (Na) was varied from 1 to 10 mol% compared to Zn. Two different lithium precursors namely Li[N(CH3)2] (series 1) and Li[N(Si(CH3)3)2] (series 2) and one sodium precursor namely Na[N(Si(CH3)3)2] (series 3) were used. Interestingly, Li precursors induce a modification of the growth of the particles while, no effect is observed when Na precursors is used. Indeed, isotropic nanoparticles were obtained when Li precursors were used while nanorods were formed with Na precursor as already observed in the same experimental conditions without alkali-metal precursor. Observations by TEM show that as the Li/Zn molar ratio increases, the mean diameters of the nanoparticles vary from 3.7 ± 0.7 nm to 2.5 ± 0.4 nm, and from 4.3 ± 1.0 nm to 3.1 ± 0.8 nm for series 1 and series 2, respectively, while the length and the diameter of the nanorods are ca. 11 × 4 nm, for series 3. Interestingly, the consequence of the lithium induced size variation leads to a shift of the emission band in the visible range, from yellow to blue through white as a function of increasing concentration of lithium precursor. The intensity of this emission is strong enough to be clearly seen by the human eye

QTAIM and ELF topological analyses of zinc-amido complexes

International audienceThe structures of three dinuclear zinc-amido complexes, involved in the very first step of the preparation of zinc oxide nanoparticles via an organometallic route, have been investigated by density functional theory computational studies. The various zinc–nitrogen and zinc–cyclohexyl bonds are finely characterized using quantum theory of atoms in molecules and electron localization function (ELF) topological analyses. The results are compared to the topological analyses of parent zinc-amido or zinc-alkyl complexes, for which an experimental structure has been already reported. The original two-component dative zinc-amido bond is unravelled by ELF topological analysis. Fukui indices condensed on the ELF basins allow for the comparison of the chemical reactivity of the three dinuclear zinc-amido complexes. The larger sensitivity to electrophilic attack of the terminal zinc-amido bonds with respect to the bridging intracyclic zinc-amido bonds or with respect to the terminal zinc–cyclohexyl bonds is evidenced

From Organometallic Chemistry to Multifunctional Nanoparticle-Based Devices for Gas Detection and Degradation of Air Pollutants

This article was presented at the International Conference EcoBalt 2023 “Chemicals & Environment”, Tallinn, Estonia, 9–11 October 2023, and belongs to the Proceedings of International Conference EcoBalt 2023 "Chemicals & Environment")

Modification of the magnetic properties of SmCo5 particles depending on the grinding atmosphere

Particles of SmCo5 were synthesized and ground mechanically under two different gaseous atmospheres (Ar or H2). The influence of the gaseous atmosphere on the crystallinity, the morphology of the particles and their magneticproperties has been studied. The major differences in terms of crystallinity and morphology are reached after 20 min of grinding. The sample ground under H2 is still well crystallized whereas the homologous sample ground under Ar is almost amorphous. For longer grinding times, both the crystallinity and morphology are very close whatever the gaseous atmosphere. The sample is amorphous and consists of aggregates. However, for the sample ground under H2 during 2 h, formation of SmH2+δ and Co is observed. Values of the coercivity and saturation magnetization are discussed in regard to these characteristics

Electrical and optical characterization of a capacitively-coupled RF plasma with a pulsed argon gas injection

International audienceNanocomposite thin film deposition using a reactor-injector of nanoparticles implies a pulsed gas injection. In a plasma, this can affect the behavior of the downstream process. Here, the case of an asymmetric low-pressure RF plasma with a pulsed argon gas injection is analyzed by electrical and optical emission spectroscopy measurements. It is found that this injection mode can highly affect the plasma stability: both the electron temperature and density are modified during the rise and the decrease of the gas pressure. A new injection mode combining continuous and pulsed injections is proposed to obtain more stable conditions

Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial

International audienceShaping ability of hybrid nanomaterials is a key point for their further use in devices. It is therefore crucial to control it. To this end, it is necessary that the macroscopic properties of the material remain constant over time. Here, we evidence by multinuclear Magic‐Angle Spinning Nuclear Magnetic Resonance spectroscopic study including 17O isotope exchange that for a ZnO‐alkylamine hybrid material, the partial carbonation of amine into ammonium carbamate molecules is behind the conversion from highly viscous liquid to a powdery solid when exposed to air. This carbonation induces modification and reorganization of the organic shell around the nanocrystals and affects significantly the macroscopic properties of the material such as it physical state, its solubility and colloidal stability. This study, straightforwardly extendable, highlights that the nature of the functional chemical group allowing connecting the stabilizing agent (SA) to the surface of the nanoparticles is of tremendous importance especially if the SA is reactive with molecules present in the environment

Nanocrystal-ligand interactions deciphered: the influence of HSAB and pK(a) in the case of luminescent ZnO

International audienceDespite all the efforts made by the scientific community to rationalize the interaction of organic molecules with nanocrystals (Ncs), we are still at the level of the empirical recipe when the material behavior in solution is concerned. In an effort to address this issue, the analysis of the luminescence measurements of ZnO Ncs in the presence of various organic substrates using a Langmuir adsorption model was carried out to determine for the first time the affinity constants and the number of binding sites as well as to rank the interaction strengths of these substrates with regard to ZnO Ncs. The results were confirmed by NMR spectroscopic studies, which, besides, provided a deep understanding of the substrate-ZnO Nc interactions. Analysis of the results using pK(a) and HSAB theory demonstrates that the interaction of a given substrate can be determined by its pK(a)versus the pK(a) of the organic molecules present at the surface of pristine Ncs and that the hard or soft character of the substrates can govern the emission intensity of the ZnO Ncs

Evidence for Core Oxygen Dynamics and Exchange in Metal Oxide Nanocrystals from In Situ ¹⁷O MAS NMR

Long-term stability of the properties of nanocrystals (NCs) is of paramount importance for any applicative development. However, these are jeopardized by chemical and structural alterations of the NCs induced by the environment and the working conditions. Among the species that alter the NCs properties, water molecules are of tremendous importance. We used ¹⁷O solid-state NMR spectroscopy to follow this process and the dynamics of O atoms in metal oxide NCs. Using ZnO as reference material, different chemical environments for the O atoms are characterized and a dynamic exchange process between the NCs and the O atoms from water is evidenced. The exchange does not involve only surface atoms but also ones located deeper inside the ZnO core of the NCs. Finally, a postsynthesis process based on watering/drying cycles is proposed that may greatly improve the long-term stability of metal oxide NCs