Luc Boussekey

Synthesis and photocatalytic activity of iodine-doped ZnO nanoflowers

The paper reports on the preparation and photocatalytic activity of thin films of iodine-doped ZnO nanoflowers deposited on glass substrate using a simple growth process based on hydrothermal synthesis. Addition of iodic acid (5–20 vol%) in the reaction mixture allows the introduction of iodine ions in the form of I− or IO3− in the ZnO lattice, as suggested by X-ray photoelectron spectroscopy. Doping ZnO nanostructured films with iodine did not impact their morphology, while it has a significant influence on their optical properties. Indeed, the nanostructured ZnO films, prepared in the presence of iodic acid, display a large increase of the visible luminescence, which reaches a maximum at a concentration of 10 vol%. Finally, the photocatalytic activity of the ZnO nanostructured films for the photodegradation of a model pollutant, rhodamine B, was evaluated under UV and visible light irradiation. While under UV light irradiation, both undoped and iodine-doped ZnO films show a similar behavior, the photocatalytic performance of iodine-doped under visible light irradiation is significantly enhanced in comparison to that of undoped ZnO.

Hydrothermal synthesis, phase structure, optical and photocatalytic properties of Zn2SnO4 nanoparticles.

Zinc stannate (Zn2SnO4 or ZTO) nanoparticles were synthesized via hydrothermal method using NaOH as a mineralizer. X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) of the synthesized ZTO nanoparticles revealed the formation of highly pure ZTO phase with the spinel-like structure. The nanoparticles have spherical shape with an average size of about 25 nm. The Raman spectrum of the sample was dominated by the A(1g) vibration mode of pure ZTO phase. From UV-Vis measurement, a band gap E(g) of 3.465 eV was determined. The photocatalytic activity of the ZTO nanoparticles was evaluated for the photodegradation of rhodamine B (RhB) under visible light irradiation. The influence of catalyst concentration and irradiation time on the photocatalytic process was investigated. The ZTO catalyst showed the best photocatalytic performance at a concentration of 0.2 g/L, and the photodecomposition of RhB followed first-order kinetics with a rate constant k=0.0249 min(-1). The ZTO-assisted photocatalytic degradation of RhB occurred via two competitive processes: a photocatalytic process and a photosensitized process. The detection of hydroxyl radicals by fluorescence measurements suggests that these species play an important role in the photocatalytic process.

Silica Cross-linked Micelles Loading with Silicon Nanoparticles: Preparation and Characterization

A new family of luminescent and stable silicon-based nanoparticles (NPs), silica cross-linked pluronic F127 (PF127) micelles loaded with decyl capped silicon nanoparticles (decyl-SiNPs), were synthesized in aqueous media. The decyl-SiNPs were prepared by first liberating hydride terminated SiNPs (H-SiNPs) from a porous silicon matrix followed by their functionalization via hydrosilylation with 1-decene under photochemical activation. The silicon-based NPs exhibit bright photoluminescence (PL) with a quantum yield of ∼3.8% and peaking at ∼2.0 eV, which lies within the transmission window that is useful for biological imaging. They display a hydrodynamic size of ∼25 nm with exterior polyethylene oxide (PEO) blocks stretching out in aqueous media. Chloroform was found to quench the excitation at energy above 4.9 eV by shielding the incident light or relaxing the charge carriers, which highlights that caution against solvent interference should be taken when performing the studies on PL origin and luminescence efficiency of SiNPs. For PF127, the blocks of hydrophilic PEO participate in the PL quenching, while poly(propylene oxide) (PPO) does not. The colloidal solution displays excellent PL stability against salt (NaCl) and temperature but is susceptible to basic solution at pH above 9.

Environment segregation of Er3+ emission in bulk sol–gel-derived SiO2–SnO2 glass ceramics

Er-doped (100-x) SiO2–x SnO2 glass–ceramic monoliths were prepared using a sol–gel method. Raman spectroscopic measurements showed the structural evolution of the silica matrix caused by the formation and the growth of SnO2 nanocrystals. Analysis of the photoluminescence properties shows that the quantity of Er3+ ions embedded in the vicinity of SnO2 nanocrystals could be controlled by the SnO2 concentration. We give spectroscopic evidence of energy transfer to erbium ions provided by SnO2 nanocrystals in the silica matrix. The 4I13/2 level decay curves present a double-exponential profile with two lifetimes associated to rare-earth ions in two different environments.

Direct-writing of PbS nanoparticles inside transparent porous silica monoliths using pulsed femtosecond laser irradiation

Pulsed femtosecond laser irradiation at low repetition rate, without any annealing, has been used to localize the growth of PbS nanoparticles, for the first time, inside a transparent porous silica matrix prepared by a sol-gel route. Before the irradiation, the porous silica host has been soaked within a solution containing PbS precursors. The effect of the incident laser power on the particle size was studied. X-ray diffraction was used to identify the PbS crystallites inside the irradiated areas and to estimate the average particle size. The localized laser irradiation led to PbS crystallite size ranging between 4 and 8 nm, depending on the incident femtosecond laser power. The optical properties of the obtained PbS-silica nanocomposites have been investigated using absorption and photoluminescence spectroscopies. Finally, the stability of PbS nanoparticles embedded inside the host matrices has been followed as a function of time, and it has been shown that this stability depends on the nanoparticle mean size.

Preparation and Characterization of Decyl-Terminated Silicon Nanoparticles Encapsulated in Lipid Nanocapsules

In this Article, we report on the encapsulation of decyl-modified silicon nanoparticles (decyl-SiNPs) into ∼80 nm lipid nanocapsules (LNCs). The decyl-SiNPs were produced by thermal hydrosilylation of hydride-terminated SiNPs (H-SiNPs) liberated from porous silicon. Various techniques, including Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV-vis absorption, dynamic light scattering (DLS), and photoluminescence (PL), were used to characterize their size, shape, colloidal, and optical properties. The results indicate that these nanocapsules feature controllable size, good dispersity, high loading rate of SiNPs, colloidal stability in various media, and bright PL. The PL of decyl-SiNPs loaded LNCs was stable upon heating to 80 °C, but was sensitive to basic solutions due to proton-gated emission of the SiNPs arranged at the LNCs interface between the oil phase and the hydrophilic polyethylene glycol moieties of the surfactant. These luminescent nanocapsules are therefore promising candidates as cellular probes for fluorescence imaging. In addition, it was found that TEM imaging of small-sized decyl-SiNPs could be greatly improved by preliminary negative staining of TEM grids with phosphotungstic acid.

Hydrothermal synthesis of ZTO/graphene nanocomposite with excellent photocatalytic activity under visible light irradiation.

A facile and efficient one-step hydrothermal approach for the synthesis of Zn2SnO4 nanoparticles/reduced graphene oxide (ZTO/rGO) nanocomposites using zinc acetate, tin chloride and graphene oxide (GO) as precursors, and sodium hydroxide as reducing agent has been developed. This approach allows simultaneous reduction of GO and growth of spinel ZTO nanoparticles (NPs) on the rGO sheets. The morphology and microstructure characterizations of ZTO/rGO nanocomposites revealed that this method leads to close interfacial contact of ZTO NPs and rGO and efficient dispersion of ZTO NPs on the surface of rGO sheets. The photocatalytic activity of the ZTO/rGO nanocomposite was investigated for the reduction of rhodamine B under visible light irradiation. Compared to pure ZTO NPs, ZTO/rGO nanocomposite exhibited superior photocatalytic activity with a full degradation of rhodamine B within 15min. The enhanced photocatalytic performance of ZTO/rGO was mainly attributed to excellent electron trapping and effective adsorption properties of rGO.

High photocatalytic activity of plasmonic Ag@AgCl/Zn2SnO4 nanocomposites synthesized using hydrothermal method

Ag@AgCl/Zn2SnO4 (ZTO) nanocomposites were successfully prepared by a hydrothermal method. The morphology, structure, composition, and optical properties of the developed composites were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, UV-visible (UV-vis) spectrophotometry, X-ray photoelectron spectroscopy (XPS), and photoluminescence techniques. All analysis confirmed the anchoring of Ag@AgCl on ZTO. The photocatalytic activity of the Ag@AgCl/ZTO nanocomposites was evaluated for the photodegradation of rhodamine B (RhB) dye, phenol and bisphenol A (BPA) in aqueous solution, under visible light irradiation. An important improvement of the catalytic activity was observed using the nanocomposites as compared to ZTO solely. The photocatalytic enhancement can be attributed to a plasmonic effect at the interface between Ag@AgCl and ZTO. Thus, the good catalytic performance of the nanocomposites combined with their simple synthesis could provide a facile way to achieve highly efficient photocatalysts.

Alkyl passivation and SiO2 encapsulation of silicon nanoparticles: preparation, surface modification and luminescence properties

In this paper, we report on the preparation of decyl-modified silicon nanoparticles (decyl-SiNPs) and their encapsulation into silica nanoparticles (NPs). The decyl-SiNPs were obtained by the photoinduced hydrosilylation of hydride-terminated SiNPs (H-SiNPs), liberated from porous silicon (pSi), followed by encapsulation into silica NPs (SiNPs@SiO2) via the Stober process. Two different sized SiNPs@SiO2 were synthesized, ∼15 and 25 nm in diameter. Their composition, size, shape, luminescence properties, colloidal and spectral stability in different environments and under ultraviolet (UV) light irradiation were studied by various techniques, including Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV-vis absorption, dynamic light scattering (DLS) and photoluminescence (PL) spectroscopy. The results indicate that the SiO2 coating renders the hydrophobic alkylated SiNPs dispersible in water, but leads to some loss of their PL intensity. The SiNPs@SiO2 NPs exhibit a wide pH stability, but show a pronounced PL degradation due to a blinking behavior. The photobleaching process could be partially suppressed by increasing the SiO2 outer shell thickness. Some investigations were made on the luminescence quenching, spectral shift and photobleaching. For potential bioapplications, the SiNPs@SiO2 NPs were modified with aminopropyl groups under acidic conditions without obvious luminescence loss and further conjugated with folic acid (FA). Considering the features of red-emission, versatile SiO2 surface chemistry and controlled size, the present SiNPs@SiO2 nanocomposites may find wide applications in cellular fluorescence labeling and the preparation of light-emitting devices.

Ferromagnetism induced in ZnO nanorods by morphology changes under a nitrogen–carbon atmosphere

We use thermal carbonization with acetylene and nitrogen to treat hydrothermally grown ZnO nanorods on silicon substrates. The method is found to be strongly temperature dependent. Treatment temperatures below 800 °C do not induce any morphological changes of the rods, while temperatures above 800 °C cause significant erosion of the rods leading to hollow- and tubular-like structures. The temperature dependent weight decrease confirms the observation of erosion and X-ray photoelectron spectroscopy (XPS) measurements indicate significant decrease in Zn content. Raman spectra evidence the presence of a diamond-like carbon layer around the rods. The coupling of resonant and non-resonant Raman results with photoluminescence measurements allow us to suggest that both nitrogen and carbon are present within the ZnO lattice. The samples treated above 800 °C are also found to be ferromagnetic and the magnetization increases as the treatment temperature increases (up to 1.45 emu cm−3 at 5 K). Thermal annealing in nitrogen atmosphere does not cause either morphological changes or ferromagnetism, suggesting that the erosion results from the additional carbon source (acetylene) of the treatment. Complexes formed by carbon and nitrogen atoms at the surface of the treated and eroded samples are believed to be at the origin of the ferromagnetism.