Said Agouram

Nontemplate Synthesis of CH3NH3PbBr3 Perovskite Nanoparticles

To date, there is no example in the literature of free, nanometer-sized, organolead halide CH3NH3PbBr3 perovskites. We report here the preparation of 6 nm-sized nanoparticles of this type by a simple and fast method based on the use of an ammonium bromide with a medium-sized chain that keeps the nanoparticles dispersed in a wide range of organic solvents. These nanoparticles can be maintained stable in the solid state as well as in concentrated solutions for more than three months, without requiring a mesoporous material. This makes it possible to prepare homogeneous thin films of these nanoparticles by spin-coating on a quartz substrate. Both the colloidal solution and the thin film emit light within a narrow bandwidth of the visible spectrum and with a high quantum yield (ca. 20%); this could be advantageous in the design of optoelectronic devices.

Deep oxidation of pollutants using gold deposited on a high surface area cobalt oxide prepared by a nanocasting route

Gold deposited on a cobalt oxide with high surface area (138 m(2)g(-1)), obtained through a nanocasting route using a siliceous KIT-6 mesoporous material as a hard template, has demonstrated high activity for the total oxidation of propane and toluene, and ambient temperature CO oxidation. The addition of gold promotes the activity when compared to a gold-free Co(3)O(4) catalyst prepared using the same nanocasting technique. The enhanced catalytic activity when gold is present has been explained for the deep oxidation of propane and toluene in terms of the improved reducibility of cobalt oxide when gold is added, rather than to the intrinsic activity of metallic gold particles. The improved behaviour for CO oxidation has been linked to the simultaneous presence of Au(δ+) and Au°.

High activity mesoporous copper doped cerium oxide catalysts for the total oxidation of polyaromatic hydrocarbon pollutants

The doping of mesoporous ceria with copper significantly enhances activity for naphthalene total oxidation, the enhanced performance is controlled by the increased concentration of surface oxygen defects.

Determination of limiting factors of photovoltaic efficiency in quantum dot sensitized solar cells: Correlation between cell performance and structural properties

Semiconductor quantum dots (QDs) are important candidates as light absorbing materials in low cost and high efficiency sensitized solar cells (SCs). We present a combination of structural, chemical, electrical, and optical characterization that provides insight to the photovoltaic efficiencies of devices formed by TiO2 electron conducting oxide network sensitized with CdSe. In devices using colloidal QDs the collection efficiency under short circuit conditions (CESCs) for photoinjected electrons is rather high (∼90%) but the photovoltaic performance is limited by the low loading of QDs into the mesoporous TiO2 structure. On the other hand, chemical bath deposited (CBD) QDSCs exhibit a remarkably high optical density, but only slightly higher short circuit current and efficiency. It is observed that CESC is ∼50% due to the high recombination rates of the closed packed QDs structure. Our results indicate routes for improvement of QDSCs performance by the increase in colloidal QDs loading and the reduction i...

Highly dispersed encapsulated AuPd nanoparticles on ordered mesoporous carbons for the direct synthesis of H2O2 from molecular oxygen and hydrogen.

AuPd nanoparticles (<3 nm) have been encapsulated on the pores of a nanostructured CMK-3 carbon prepared by a nanocasting procedure. This material has been shown to be an excellent catalyst for the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen.

The Luminescence of CH3NH3PbBr3 Perovskite Nanoparticles Crests the Summit and Their Photostability under Wet Conditions is Enhanced

CH3 NH3 PbBr3 perovskite nanoparticles (PAD ) are prepared with a photoluminescence quantum yield of ≈100% in air atmosphere by using the quasi-spherical shaped 2-adamantylammonium bromide (ADBr) as the only capping ligand. The photostability under wet conditions of this kind of nanoparticles is enhanced by using cucurbit[7]uril-adamantylammonium (AD@CB) host-guest complexes as the capping ligand.

Controlled UV−C Light-Induced Fusion of Thiol-Passivated Gold Nanoparticles⊥

Thiol-passivated gold nanoparticles (AuNPs) of a relatively small size, either decorated with chromophoric groups, such as a phthalimide (Au@PH) and benzophenone (Au@BP), or capped with octadecanethiol (Au@ODCN) have been synthesized and characterized by NMR and UV-vis spectroscopy as well as transmission electron microscopy (TEM). These NPs were irradiated in chloroform at different UV-wavelengths using either a nanosecond laser (266 and 355 nm, ca. 12 mJ/pulse, 10 ns pulse) or conventional lamps (300 nm < λ < 400 nm and ca. 240 nm < λ < 280 nm) and the new AuNPs were characterized by X-ray and UV-vis spectroscopy, as well as by TEM. Laser irradiation at 355 nm led to NP aggregation and precipitation, while the NPs were photostable under UV-A lamp illumination. Remarkably, laser excitation at 266 nm induced a fast (minutes time-scale) increase in the size of the NPs, producing huge spherical nanocrystals, while lamp-irradiation at UV-C wavelengths brought about nanonetworks of partially fused NPs with a larger diameter than the native NPs.

Nickel oxide supported on porous clay heterostructures as selective catalysts for the oxidative dehydrogenation of ethane

Porous clay heterostructures (PCH) have shown to be highly efficient supports for nickel oxide in the oxidative dehydrogenation of ethane. Thus NiO supported on silica with a PCH structure shows productivity towards ethylene three times higher than if NiO is supported on a conventional silica. This enhanced productivity is due to the increase in the catalytic activity and especially to the drastic increase in the selectivity to ethylene. Additionally, PCH silica partially modified with titanium in the columns (PCH-Ti) have also been synthesized and used as supports for NiO. An enhanced activity and selectivity to ethylene was found over NiO supported over PCH-Ti compared to the corresponding catalysts supported over the Ti-free PCH. The enhanced catalytic performance has been related to the high dispersion of nickel oxide particles on the support, which leads to a lower reducibility of the nickel oxide, hindering the oxidation of ethane into carbon oxides. More interestingly, the particle morphology plays an important role on the catalyst selectivity since a higher distortion of the NiO crystal lattice parameter meant an enhanced selectivity to ethylene.

Self-assembled MgxZn1−xO quantum dots (0 ≤ x ≤ 1) on different substrates using spray pyrolysis methodology

By using the spray pyrolysis methodology in its classical configuration we have grown self-assembled MgxZn1−xO quantum dots (size ∼4–6 nm) in the overall range of compositions 0 ≤ x ≤ 1 on c-sapphire, Si (100) and quartz substrates. Composition of the quantum dots was determined by means of transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy. Selected area electron diffraction reveals the growth of single phase hexagonal MgxZn1−xO quantum dots with composition 0 ≤ x ≤ 0.32 by using a nominal concentration of Mg in the range 0 to 45%. Onset of Mg concentration about 50% (nominal) forces the hexagonal lattice to undergo a phase transition from hexagonal to a cubic structure which resulted in the growth of hexagonal and cubic phases of MgxZn1−xO in the intermediate range of Mg concentrations 50 to 85% (0.39 ≤ x ≤ 0.77), whereas higher nominal concentration of Mg ≥ 90% (0.81 ≤ x ≤ 1) leads to the growth of single phase cubic MgxZn1−xO quantum dots. High resolution transmission electron microscopy and fast Fourier transform confirm the results and show clearly distinguishable hexagonal and cubic crystal structures of the respective quantum dots. A difference of 0.24 eV was detected between the core levels (Zn 2p and Mg 1s) measured in quantum dots with hexagonal and cubic structures by X-ray photoemission. The shift of these core levels can be explained in the frame of the different coordination of cations in the hexagonal and cubic configurations. Finally, the optical absorption measurements performed on single phase hexagonal MgxZn1−xO QDs exhibited a clear shift in optical energy gap on increasing the Mg concentration from 0 to 40%, which is explained as an effect of substitution of Zn2+ by Mg2+ in the ZnO lattice.

Low temperature total oxidation of toluene by bimetallic Au–Ir catalysts

Bimetallic gold–iridium catalysts present a synergetic activity effect on the total oxidation of volatile organic compounds (e.g. toluene) with respect to their monometallic counterparts, leading to catalytic activity at lower temperatures. The enhancement of activity is facilitated by the intimate contact of the iridium and gold species, which modifies the electronic environment of the active sites, assisting in the oxygen activation at lower temperatures. In addition, the bimetallic system shows a considerably stronger metal–support interaction capable of diminishing the detrimental loss of activity associated with metal sintering at high reaction temperatures, in contrast to the monometallic cases whose activities are greatly lost. This paper contributes to the understanding of the key factors behind high activity and good stability of catalysts to achieve the low temperature activity of VOC compounds in air pollution remediation applications.