Yann Leconte

In vitro evaluation of SiC nanoparticles impact on A549 pulmonary cells: Cyto-, genotoxicity and oxidative stress

Silicon carbide (SiC) is considered a highly biocompatible material, consequently SiC nanoparticles (NPs) have been proposed for potential applications in diverse areas of technology. Since no toxicological data are available for these NPs, the aim of this study was to draw their global toxicological profile on A549 lung epithelial cells, using a battery of classical in vitro assays. Five SiC-NPs, with varying diameters and Si/C ratios were used, and we show that these SiC-NPs are internalized in cells where they cause a significant, though limited, cytotoxic effect. Cell redox status is deeply disturbed: SiC-NP exposure cause reactive oxygen species production, glutathione depletion and inactivation of some antioxidant enzymes: glutathione reductase, superoxide dismutase, but not catalase. Finally, the alkaline comet assay shows that SiC-NPs are genotoxic. Taken together, these data prove that SiC-NPs biocompatibility should be revisited.

One-Step Synthesis of Si@C Nanoparticles by Laser Pyrolysis: High-Capacity Anode Material for Lithium-Ion Batteries

Carbon-covered silicon nanoparticles (Si@C) were synthesized for the first time by a one-step continuous process in a novel two stages laser pyrolysis reactor. Crystallized silicon cores formed in a first stage were covered in the second stage by a continuous shell mainly consisting in low organized sp(2) carbon. At the Si/C interface silicon carbide is absent. Moreover, the presence of silicon oxide is reduced compared to materials synthesized in several steps, allowing the use of such material as promising anode material in lithium-ion batteries (LIB). Auger Electron Spectroscopy (AES) analysis of the samples at both SiKLL and SiLVV edges proved the uniformity of the carbon coating. Cyclic voltammetry was used to compare the stability of Si and Si@C active materials. In half-cell configuration, Si@C exhibits a high and stable capacity of 2400 mAh g(-1) at C/10 and up to 500 mAh g(-1) over 500 cycles at 2C. The retention of the capacity is attributed to the protective effect of the carbon shell, which avoids direct contact between the silicon surface and the electrolyte.

Novel Preparation of N‐Doped SnO2 Nanoparticles via Laser‐Assisted Pyrolysis: Demonstration of Exceptional Lithium Storage Properties

Laser pyrolyzed SnO2 nanoparticles with an option of nitrogen (N) doping are prepared using a cost-effective method. The electrochemical performance of N-doped samples is tested for the first time in Li-ion batteries where the sample with 3% of N-dopant exhibits optimum performance with a capacity of 522 mAh gactive material-1 that can be obtained at 10 A g-1 (6.7C).

Structural and microstructural characterization of nanocrystalline silicon thin films obtained by radio-frequency magnetron sputtering

Textured silicon thin films are deposited by reactive magnetron sputtering in hydrogen-rich plasma on (100)-Si and amorphous SiO2 substrates. We quantitatively determine, combining x-ray texture analysis, x-ray reflectivity, transmission electron microscopy, atomic force microscopy measurements, and Raman and Fourier transform infrared spectroscopy analyses, the structure (cell parameter and mean electron density) and microstructure (crystalline fraction, preferred orientations, anisotropic crystallite sizes, thicknesses, etc.) of these films. For both kinds of substrates, no perfect ⟨111⟩ orientation is observed whereas a systematic elongation of the anisotropic Si crystallites along one [111] direction is present. A small elongation of the Si cell parameter of the nanocrystals is found without internal stress. With the substrate to target distance, the crystalline fraction and mean electron density show an opposite behavior to that of the film porosity. The former increases and the latter decreases, and...

In vitro cellular responses to silicon carbide nanoparticles: impact of physico-chemical features on pro-inflammatory and pro-oxidative effects

Silicon carbide is an extremely hard, wear resistant, and thermally stable material with particular photoluminescence and interesting biocompatibility properties. For this reason, it is largely employed for industrial applications such as ceramics. More recently, nano-sized SiC particles were expected to enlarge their use in several fields such as composite supports, power electronics, biomaterials, etc. However, their large-scaled development is restricted by the potential toxicity of nanoparticles related to their manipulation and inhalation. This study aimed at synthesizing (by laser pyrolysis or sol–gel methods), characterizing physico-chemical properties of six samples of SiC nanopowders, then determining their in vitro biological impact(s). Using a macrophage cell line, toxicity was assessed in terms of cell membrane damage (LDH release), inflammatory effect (TNF-α production), and oxidative stress (reactive oxygen species generation). None of the six samples showed cytotoxicity while remarkable pro-oxidative reactions and inflammatory response were recorded, whose intensity appears related to the physico-chemical features of nano-sized SiC particles. In vitro data clearly showed an impact of the extent of nanoparticle surface area and the nature of crystalline phases (α-SiC vs. β-SiC) on the TNF-α production, a role of surface iron on free radical release, and of the oxidation state of the surface on cellular H2O2 production.

Pronounced crystallization of silicon layers deposited with high deposition rates at temperatures ⩽200 °C

Abstract Silicon layers were grown at 200 °C by reactive magnetron sputtering in a hydrogen-rich plasma (80% dilution). The samples were examined by Raman and infrared spectroscopies, as well as by transmission electron microscopy and optical transmission. In addition to the pronounced crystallization induced by the interactions with the H-based radicals, the incremental crystallization observed on the sample deposited in the region close to the cathode, where the radical density is high, appears due to the contribution of the incorporated Si nanopowders created in the surrounding plasma. The formation of these particles appeared, therefore, spatially limited because of its dependence on the radical density that is inhomogeneously distributed in the cathode-substrate separating area. To some extent, this allows one to control their insertion, the growth rate and layer compactness, through variation of electrodes spacing, r.f. power and plasma pressure. The occurrence of both particle creation in the plasma and columnar growth in the bulk attests of the key role played by the highly sticking and reactive SiH2.

Evaluation of electrochemical performances of ZnFe2O4/γ-Fe2O3 nanoparticles prepared by laser pyrolysis

A ZnFe2O4/γ-Fe2O3 nanocomposite (theoretical specific capacity: 1002 mA h g−1) was successfully synthesized by laser pyrolysis, a very attractive nanosynthesis technique characterized by high versatility and flexibility. The obtained nanopowder was thoroughly characterized by XRD, XPS, Mossbauer spectroscopy and HRTEM, which confirmed the presence of two phases. A bimodal size distribution with small particles (tens of nanometers) and large ones (above 500 nm) was revealed by SEM and TEM. The ZnFe2O4/Fe2O3 nanocomposite was tested as a negative electrode material for lithium-ion batteries, showing significantly improved lithium storage properties with a high reversible capacity and rate capability compared to a pure ZnFe2O4 electrode. A capacity exceeding 1200 mA h g−1 is sustained after 100 cycles at 100 mA g−1, with a gradual increase of the capacity during cycling. At 500 mA g−1 current rate, a reversible and stable capacity of 360 mA h g−1 is observed after 300 cycles. Electrochemical measurements with several electrolytes and electrode formulations were also conducted in order to explore the origin of the extra capacity and its increase with cycling.

SiC nanoparticles cyto- and genotoxicity to Hep-G2 cells

While emerging nanotechnologies have seen significant development in recent years, knowledge on exposure levels as well as data on toxicity of nanoparticles are still quite limited. Indeed, there is a general agreement that development of nanotechnologies may lead to considerable dissemination of nanoparticles in the environment. Nevertheless, questions relative to toxicity versus innocuousness of such materials still remain. Our present study has thus been carried out with the purpose of assessing some aspects of toxicological capacities of three kinds of nano-sized particles: TiO2 and SiC nanoparticles, as well as multi-walled carbon nanotubes (CNT). In order to address the question of their potential toxicity toward living cells, we chose several cellular models. Assuming inhalation as the most probable exposure scenario, we used A549 alveolar epithelial cells as a model for mammalian primary target organ (lung). Furthermore, we considered that nanoparticles that would deposit into the pulmonary system may be translocated to the circulatory system. Thus, we decided to study the effect of nanoparticles on potentially secondary target organs: liver (WIF-B9, Can-10, HepG2) and kidneys (NRK-52E, LLC-PK1). Herein, we will focus our attention on results obtained on the HepG2 cell line exposed to SiC nanoparticles. Scarce literature exists on SiC nanotoxicology. According to the authors that have already carried out studies on this particular nanoparticle, it would seem that SiC nanoparticles do not induce cytotoxicity. That is one of the reasons of the potential use of these nanoparticles as biological labels [1]. We thus were interested in acquiring more data on biological effects induced by SiC nanoparticles. Furthermore, one of the particular aspects of the present study lies in the fact that we tried to specify the influence of physico-chemical characteristics of nanoparticles on toxicological endpoints (cytotoxicity and genotoxicity).

Host size effects on optical properties of Y2O3:Eu3+ and Gd2O3:EU3+ nanoparticles synthesized by laser pyrolysis.

Rare earth doped materials have many familiar applications (TV screens, solid lasers, scintillators…) thanks to their efficient and robust luminescence properties. In recent years, growing interest has been focused on the changes in their optical properties with the size of the host particles. In this work, nanomaterials were produced for the first time by using laser pyrolysis. Y, Gd, and Eu nitrates were dissolved in water and used as precursors. Cubic phases of Y2O3:Eu3+ and Gd2O3:Eu3+ were obtained with sizes ranging from 3 to 40 nm. The spectroscopic properties revealed a new and nanostructure-specific broad band in the excitation spectrum. The emission spectrum was found to be characteristic of nanostructured sesquioxides only when excited in this new band, which was finally assumed to be a new charge transfer band for the smallest nanoparticles in the sample.

SiC, TiC and ZrC Nanostructured Ceramics: Elaboration and Potentialities for Nuclear Applications

Carbide ceramics as SiC, TiC or ZrC are potential candidates for high temperature applications such as fourth generation nuclear plants because of their refractory or low activation under neutron irradiation properties. Nevertheless, the typical drawbacks of hard ceramics (brittleness) could limit their use in these applications. In order to overcome these problems, one possibility is to decrease the grain size down to the nanometric scale. Enhancement of the mechanical properties is actually expected in such nanostructured ceramics (ductility) and moreover, these nanomaterials could also take advantage of their strong grain boundaries density to withstand severe irradiation conditions. If one wants to quantify the expected enhancement of the properties, the first challenge that has to be faced is the elaboration of the nanostructured ceramics samples. That means being able to synthesize the pre-ceramics nanopowders in weighable amounts, and then finding an efficient way to sinter them aiming at the maximum densification together with avoiding grain growth. In this contribution, we present SiC, TiC and ZrC nanopowders synthesis by laser pyrolysis and inductively coupled plasma, together with their densification by different techniques (Hot Isostatic Pressing, Spark Plasma Sintering, High Pressure Flash Sintering). We also report the latest findings obtained on the behavior of SiC nanostructured ceramics under low energy ion irradiation. Raw micrometric SiC and ZrC powders were used as precursors in the inductively coupled plasma experiment. The production was as high as 1 kg.h-1, with nanograins ranging from 10 to 100 nm in size depending on the synthesis conditions. For the laser pyrolysis method, gaseous precursors (SiH 4 , C 2 H 2 ) were used for SiC while liquid alkoxides precursors were used for TiC and ZrC respectively. For SiC, the production rate can reach 100 g.h-1 (laboratory scale) with grain sizes ranging from 10 to 50 nm with narrow size distribution. For TiC and ZrC nanopowders, the production rate is lower than for SiC because of the use of liquid precursors that leads to a worse yield. In this latter case, the carbide phase is obtained after carburization of the laser pyrolyzed TiO2 (or ZrO 2 ) / free carbon nanocomposites. The final carbide nanograins size is in the 50 – 80 nm range. After sintering, the obtained pellets show different characteristics depending on the starting powder and the sintering technique. With the right sintering conditions, the densification reaches 95 % without any sintering additives, with no (or limited) grain growth and no modification of the crystalline structure. Concerning the properties of the obtained nanostructured ceramics, the SiC pellets, together with the as-synthesized nanopowders, were submitted to low energy ion irradiation in order to compare their behavior to conventional SiC materials.