Electro-Assisted Self-Assembly of Cetyltrimethylammonium-Templated Silica Films in Aqueous Media: Critical Effect of Counteranions on the Morphology and Mesostructure Type

The electro-assisted self-assembly (EASA) of tetraethoxysilane (TEOS) and cetyltrimethylammonium bromide (CTABr) in hydro-alcoholic medium is now recognized to be a versatile method to generate highly ordered mesoporous silica films with unique orientation of mesopore channels normal to the underlying surface. In this work, we have evaluated the possibility to extend the method to aqueous media (i.e., without adding a cosolvent) and to determine the parameters affecting the EASA process and the resulting organization/orientation of the mesoporous framework by using electron microscopies and diffraction techniques. Contrary to water/cosolvent-based sols, the nature of the surfactant and supporting electrolyte counteranions (X^–) was found to induce drastic variations on both the morphology and the mesostructural order of the deposits formed by electrochemically induced gelification (by pH increase) of CTAX/NaX-based silica sols. These changes are triggered by different surfactant assemblies arising from lower critical micellar concentration when passing from hydro-alcoholic to aqueous medium, and they are affected by the chaotropic–cosmotropic character of the counteranions. To be brief, cosmotropic anions (such as SO₄^2–) promote the formation of thin films but suffering from poor or no ordering, whereas weakly bonded anions (such as Cl^–) favor the mesostructuration but mainly in the form of particles or aggregates, while chaotropic anions (such as Br^–) lead to rather thick deposits made of poorly organized aggregates. Mixing these anions, to get mixed micelles, enables compromises to be reached between these “extreme” behaviors and mesostructured thin films can be indeed obtained with the CTACl/Na₂SO₄ and CTABr/Na₂SO₄ media, exhibiting, respectively, some vertical or horizontal orientation of mesopore channels. This can be rationalized by taking into account the CTA⁺, X^– binding strength variations (Cl^– < SO₄^2– < Br^–), thus affecting competitive binding of negatively charged silicate species, and sphere-to-rod transition abilities (SO₄^2– ≈ Cl^– < Br^–) of the CTA⁺-based templates. Cyclic voltammetry was also used to characterize mass transport processes through the films. Finally, a preliminary work aiming at getting swelled pores of such electrogenerated films with mesitylene was carried out to evaluate the potential interest of the water-based EASA process for the entrapment of hydrophobic molecules inside the surfactant–silica phases

Local Structure-Driven Localized Surface Plasmon Absorption and Enhanced Photoluminescence in ZnO-Au Thin Films

Nanocomposite films consisting of gold nanoparticles embedded in zinc oxide (ZnO-Au) have been synthesized with different gold loadings by reactive magnetron sputtering at near-room temperature followed by ex situ annealing in air up to 300 °C. Using X-ray diffraction and high resolution transmission microscopy it is shown that during deposition gold substitutes zinc in ZnO as isolated atoms and in nanoparticles still exhibiting the structure of ZnO. Both situations degrade the crystalline quality of the ZnO matrix, but thermal annealing cures it from isolated gold atoms and triggers the formation of gold nanoparticles of size higher than 3 nm, sufficient to observe a strong activation of localized surface plasmon resonance (LSPR). The amplitude of LSPR absorption observed after annealing increases with the gold loading and annealing temperature. Moreover, UV and visible photoluminescence from the ZnO matrix is strongly enhanced upon activation of LSPR showing strong coupling with the gold nanoparticles. Finally, modeling of spectroscopic ellipsometry measurements unambiguously reveals how curing the defects increases the optical bandgap of the ZnO matrix and modifies the optical dielectric functions of the nanocomposite and ZnO matrix

Gd Doping at the Co/Pt Interfaces to Induce Ultrafast All-Optical Switching

Single-pulse all-optical switching has mainly been observed and studied in transition-metal-Gd-based thin films with high potential for enabling new application for energy-efficient and fast magnetic data storage, memory, or logic. For GdCo alloys, ultrafast single-pulse switching has only been observed close to the compensation composition, in agreement with theoretical predictions. Here, we demonstrate that starting with a [Co/Pt] bilayer showing strong perpendicular anisotropy, a small Gd dusting at the interface is sufficient to induce a well-defined single-pulse all-optical switching. A careful analysis of the impact of the Gd–Co interface on all optical switching is presented. The opportunity to perform single-pulse all-optical switching with a very little amount of Gd opens perspectives for its applicability but also questions the theoretical understanding of the toggle switching underlying mechanism

One-Pot Noninjection Route to CdS Quantum Dots via Hydrothermal Synthesis

Water-dispersible CdS quantum dots (QDs) emitting from 510 to 650 nm were synthesized in a simple one-pot noninjection hydrothermal route using cadmium chloride, thiourea, and 3-mercaptopropionic acid (MPA) as starting materials. All these chemicals were loaded at room temperature in a Teflon sealed tube and the reaction mixture heated at 100 °C. The effects of CdCl₂/thiourea/MPA feed molar ratios, pH, and concentrations of precursors affecting the growth of the CdS QDs, was monitored via the temporal evolution of the optical properties of the CdS nanocrystals. High concentration of precursors and high MPA/Cd feed molar ratios were found to lead to an increase in the diameter of the resulting CdS nanocrystals and of the trap state emission of the dots. The combination of moderate pH value, low concentration of precursors and slow growth rate plays the crucial role in the good optical properties of the obtained CdS nanocrystals. The highest photoluminescence achieved for CdS@MPA QDs of average size 3.5 nm was 20%. As prepared colloids show rather narrow particle size distribution, although all reactants were mixed at room temperature. CdS@MPA QDs were characterized by UV–vis and photoluminescence spectroscopy, powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry and MALDI TOF mass spectrometry. This noninjection one-pot approach features easy handling and large-scale production with excellent synthetic reproducibility. Surface passivation of CdS@MPA cores by a wider bandgap material, ZnS, led to enhanced luminescence intensity. CdS@MPA and CdS/ZnS@MPA QDs exhibit high photochemical stability and hold a good potential to be applied in optoelectronic devices and biological applications

Zinc Speciation in the Suspended Particulate Matter of an Urban River (Orge, France): Influence of Seasonality and Urbanization Gradient

Among trace metal pollutants, zinc is the major one in the rivers from the Paris urban area, such as the Orge River, where Zn concentration in the suspended particulate matter (SPM) can reach 2000 mg/kg in the most urbanized areas. In order to better understand Zn cycling in such urban rivers, we have determined Zn speciation in SPM as a function of both the seasonal water flow variations and the urbanization gradient along the Orge River. Using TEM/SEM-EDX and linear combination fitting (LCF) of EXAFS data at the Zn K-edge, we show that Zn mainly occurs as tetrahedrally coordinated Zn²⁺ sorbed to ferrihydrite (37–46%), calcite (0–37%), amorphous SiO₂ (0–21%), and organic-P (0–30%) and as octahedrally coordinated Zn²⁺ in the octahedral layer of phyllosilicates (18–25%). Moreover, the Zn speciation pattern depends on the river flow rate. At low water flow, Zn speciation changes along the urbanization gradient: geogenic forms of Zn inherited from soil erosion decrease relative to Zn bound to organic–phosphates and amorphous SiO₂. At high water flow, Zn speciation is dominated by soil-borne forms of Zn regardless the degree of urbanization, indicating that erosion of Zn-bearing minerals dominates the Zn contribution to SPM under such conditions

Additive-Free Assemblies of Ramified Single-Walled Carbon Nanotubes

Carbon nanotubes (CNTs) are difficult to process, and their assembly in macroscopic materials that allow us to benefit from the exceptional properties of the nanotubes is of crucial interest for applications. The developed CNT processing procedures usually involve additives that remain in the final product and are known to diminish the properties of the CNT-based material. Here, we propose a multistep approach to process single-walled carbon nanotubes (SWNTs) and obtain macroscopic additive-free SWNT materials. High-quality dispersion of purified SWNTs is first induced in polar solvent due to their preceding reduction reaction with an alkali metal. The partial debundling process occurring at this stage leads to ramified SWNTs. They can then be self-assembled by attractive intermolecular forces through a controlled destabilization of the dispersions by a simple oxidation. Swollen gels of SWNTs are formed at an air/solvent interface. After freeze-drying, the additive-free SWNT material shows a hierarchical structure with highly interconnected SWNTs. Thanks to the obtained ramification of the SWNTs, these latter are able to well entangle what guarantees the robustness of the obtained additive-free SWNT material. Moreover, this integrated process offers an increase of the accessible surface compared to that of the raw bundled SWNTs. The obtained assembled SWNTs show an improved adsorption capacity

A Facile Approach for Doxorubicine Delivery in Cancer Cells by Responsive and Fluorescent Core/Shell Quantum Dots

Biocompatible thermoresponsive copolymers based on 2-(2-methoxyethoxy) ethyl methacrylate (MEO₂MA) and oligo (ethylene glycol) methacrylate (OEGMA) were grown from the surface of ZnO quantum dots (QDs) by surface initiated atom transfer radical polymerization with activators regenerated by electron transfer (SI-ARGET ATRP) in order to design smart and fluorescent core/shell nanosystems to be used toward cancer cells. Tunable lower critical solution temperature (LCST) values were obtained and studied in water and in culture medium. The complete efficiency of the process was demonstrated by the combination of spectroscopic and microscopic studies. The colloidal behavior of the ZnO/copolymer core/shell QDs in water and in physiological media with temperature was assessed. Finally, the cytotoxicity toward human colon cancer HT29 cells of the core/shell QDs was tested. The results showed that the polymer-capped QDs exhibited almost no toxicity at concentrations up to 12.5 μg.mL^–1, while when loaded with doxorubicin hydrochloride (DOX), a higher cytotoxicity and a decreased HT29 cancer cell viability in a short time were observed

Thermal behavior of Mg-Ni-phyllosilicate nanoscrolls and performance of the resulting composites in hexene-1 and acetone hydrogenation

Here we report on the thermal properties of Mg−Ni‐phyllosilicate nanoscrolls as a promising precursor for production of Ni/silicate composite catalysts. Spontaneous scrolling of the phyllosilicate layer originating from size difference between metal‐oxygen and silica sheets provides high surface area of the catalyst. Metal nanoparticles can be obtained directly from the matrix by H2 reduction. The phyllosilicate structure passed through a number of transformations including partial dehydroxylation with formation of sepiolite‐like phase followed by silicate or oxide crystallization. Temperature ranges of these transitions overlapped with the reduction process sophisticating the H2 consumption profiles. In particular, some amount of Ni2+ got sealed up by the sepiolite structural features, that opened a path for the tuning of Ni0 : Ni2+ ratio of the catalyst. An increase of Ni content in the system yielded a decrease in the metal nanoparticles sizes due to both high intensity of nucleation and type of residual matrix. Ni nanoparticles size distribution and specific surface area of the composite catalysts governed conversion rate of hexene‐1 and acetone hydrogenation. In the view of the turnover frequency MgNi2Si2O5(OH)4 precursors were slightly more preferable than pure Ni3Si2O5(OH)4