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Two Au/TiO2 samples with different gold loadings (0.7 and 4.0 wt.% Au) were prepared by deposition-precipitation with urea and calcined at 673 K. TEM revealed gold particles of 3.2 and 3.9 nm for the 0.7 and 4.0 wt.% samples, respectively. The samples were subjected to different red-ox treatments and then the state of gold was determined by the FTIR spectra of CO adsorbed at low temperature. Several kinds of gold carbonyl species were detected during the experiments: (i) Au0–CO at around 2107 cm−1; (ii) Au+–CO at ca. 2175 cm−1; (iii) Auδ+–CO in the region of 2140–2137 cm−1 and (iv) Auδ′+–CO (δ′ > δ) at around 2155 cm−1. The 4.0 wt.% sample contained mainly metallic gold after evacuation at 673 K. Subsequent interaction with oxygen at 373 K leads to oxidation of a fraction of the surface metallic gold sites to Auδ+ sites. These sites were considered as cations located on the surface of the metal particles with a partially positive charge δ+ (0 < δ < 1) because of electron transfer from the gold bulk. Evacuation at 673 K leads to back reduction of the Auδ+ sites to metallic gold. The oxidation of gold particles was more efficient when performed with a NO + O2 mixture. It resulted in creation of Auδ′+ sites with a higher positive charge than that of the Auδ+ sites. In this case the oxidation involved a higher number of Au0 sites. A similar treatment of the 0.7 wt.% Au sample, however, resulted in formation of “isolated” Au+ species. The results indicate that small metal particles are more easily oxidized by a NO + O2 mixture. A model of the formation of the different sites, explaining well the experimental results, is proposed. [ABSTRACT FROM AUTHOR]

Wastewater originating in the chemical process industries contain high concentrations of organics that must be treated before discharge. Phenol is one of the most important of these pollutants because it istoxic, even at low concentrations. Recently, hydrogen peroxide treatment has emerged as a viable alternative oxidation technique for treatment. It does not form any harmful or intrusive by-products and it is an ecologically clean and non-toxic chemical. However, the methods for treatment of wastewater with hydrogen peroxide are based mostly on homogeneous catalysis by metal ions inducing additional pollution. From this, it was anticipated that the use of heterogeneous catalysiswould be a good alternative, thus opening up a new field of investigation. Previous studies, based on screening tests, evidenced the catalytic activity of an MFI zeolite Fe-ZSM-5 for phenol elimination by H2O2. The oxidation tests are carried out in a batch mode, using a stirred glass reactor. The influence of pH, temperature and H2O2 stoichiometric ratio on the phenol oxidation rate with Fe-ZSM-5 is studied. The temperature is below 100 deg.C in order to avoid pressurization of the treatment reactor. Using a H2O2 stoichiometric ratio equal to 1.5 avoids accumulation of any quinone-like by-products. Under these conditions, the catalytic system H2O2 /Fe-ZSM-5 allows a total elimination of phenol and a significant TOC removal (50%)without leaching-off more than 1 ppm of Fe(II) ions. At the end of the reaction period, only carboxylic acids (maleic, fumaric, oxalic, acetic) accumulate. These latter should not be considered as a drawback of this process. The chemical oxidation process would be used only as a detoxification step and such compounds could be treated with a biological process, in a second step. [ABSTRACT FROM AUTHOR]

WO 3 is a known photocatalytic metal oxide frequently studied for its depollution properties. However, it suffers from a high recombination rate of the photogenerated electron/holes pair that is detrimental to its performance. In this paper, we present a new chemical method to decorate WO 3 nanoleaves (NLs) with a complementary metal oxide (ZnWO 4 ) in order to improve the photocatalytic performance of the composite material for the abatement of 400 ppb NO 2 under mild UV exposure. Our strategy was to synthesize WO 3 ·2H 2 O nanoleaves, then, to expose them, in water-free organic solution, to an organometallic precursor of Zn(Cy) 2 . A structural water molecule from WO 3 ·2H 2 O spontaneously decomposes Zn(Cy) 2 and induces the formation of the ZnO@WO 3 ·H 2 O nanocomposite. The material was characterized by electronic microscopy (SEM, TEM), TGA, XRD, Raman and solid NMR spectroscopies. A simple thermal treatment under air at 500 °C affords the ZnWO 4 @WO 3 nanocomposite. The resulting material, additionally decorated with 1% wt. Au, presents a remarkable increase (+166%) in the photocatalytic abatement of NO 2 under UV compared to the pristine WO 3 NLs. This synthesis method paves the way to the versatile preparation of a wide range of MOx@WO 3 nanocomposites (MOx = metal oxide).

Amine ligands are expected to drive the organization of metallic centers as well as the chemical reactivity of silver clusters early growing during the very first steps of the synthesis of silver nanoparticles via an organometallic route. Density functional theory (DFT) computational studies have been performed to characterize the structure, the atomic charge distribution, and the planar two-dimensional (2D)/three-dimensional (3D) relative stability of small-size silver clusters (Ag n , 2 ≤ n ≤ 7), with or without an ethylamine (EA) ligand coordinated to the Ag clusters. The transition from 2D to 3D structures is shifted from n = 7 to 6 in the presence of one EA coordinating ligand, and it is explained from the analysis of the Ag-N and Ag-Ag bond energies. For fully EA saturated silver clusters (Ag n -EA n ), the effect on the 2D/3D transition is even more pronounced with a shift between n = 4 and 5. Subsequent electron localization function (ELF) and quantum theory of atoms in molecules (QTAIM) topological analyses allow for the fine characterization of the dative Ag-N and metallic Ag-Ag bonds, both in nature and in strength. Electron transfer from ethylamine to the coordinated silver atoms induces an increase of the polarization of the metallic core.

Dihydrogen is one of the sustainable energy vectors envisioned for the future. However, the rapidly reversible and secure storage of large quantities of hydrogen is still a technological and scientific challenge. In this context, this review proposes a recent state-of-the-art on H 2 production capacities from the dehydrogenation reaction of ammonia borane (and selected related amine-boranes) as a safer solid source of H 2 by hydrolysis (or solvolysis), catalyzed by nanoparticle-based systems. The review groups the results according to the transition metals constituting the catalyst with a mention to their current cost and availability. This includes the noble metals Rh, Pd, Pt, Ru, Ag, as well as cheaper Co, Ni, Cu, and Fe. For each element, the monometallic and polymetallic structures are presented and the performances are described in terms of turnover frequency and recyclability. The structure-property links are highlighted whenever possible. It appears from all these works that the mastery of the preparation of catalysts remains a crucial point both in terms of process, and control and understanding of the electronic structures of the elaborated nanomaterials. A particular effort of the scientific community remains to be made in this multidisciplinary field with major societal stakes., (© 2021 Wiley-VCH GmbH.)

A series of silver amidinate complexes has been studied both experimentally and theoretically, in order to investigate the role of the precursor complex in the control of the synthesis of silver nanoparticles via an organometallic route. The replacement of the methyl substituent of the central carbon atom of the amidinate anion by a n -butyl group allows for the crystallization of the tetranuclear silver amidinate complex 3 instead of a mixture of di- and trinuclear silver amidinate complexes 1 and 2 , as obtained with a methyl substituent. The relative stabilities and dissociation schemes of various isomeric arrangements of silver atoms in 3 are investigated at the computational DFT level of calculation, depending on the substituents of the amidinate ligand. The tetranuclear silver amidinate complex 4 , exhibiting a diamondlike arrangement of the four silver atoms, is also considered. Ag-N bonds and argentophilic Ag-Ag interactions are finely characterized using ELF and QTAIM topological analyses and compared over the series of the related di-, tri-, and tetranuclear silver amidinate complexes 1 - 4 . In contrast to the Ag-N dative bonds very similar over the series, argentophilic Ag-Ag interactions of various strengths and covalence degree are characterized for complexes 1 - 4 . This gives insight into the role of the amidinate substituents on the nuclearity and intramolecular chemical bonding of the silver amidinate precursors, required for the synthesis of dedicated AgNPs with chemically well defined surfaces.

Access to removable nanocomposite electrodes for electrosensing of pollutants is of great importance. However, the preparation of reproducible and reliable carbon electrodes decorated with metallic nanoparticles, a prerequisite for trustworthy devices, remains a challenge. Here we describe an innovative and easy method to prepare such electrodes. These latter are silicon-coated with a thin carbon film on which controlled silver nanostructures are grafted. Different silver nanostructures and surface coverage of the carbon electrode (16, 36, 51, and 67%) can be obtained through a careful control of the time of the hydrogenolysis of the N-N' isopropyl butylamidinate silver organometallic precursor ( t = 1, 5, 15, and 60 min, respectively). Importantly, all nanocomposite surfaces are efficient for the electrodetection of 4-nitrophenol with a remarkable decrease of the overpotential of the reduction of such molecule up to 330 mV. The surfaces are characterized by atomic force microscopy, grazing incidence X-ray diffraction, scanning electronic microscopy, and Raman spectroscopy. Furthermore, surface-enhanced Raman scattering effect is also observed. The exaltation of the Raman intensity is proportional to the surface coverage of the electrode; the number of hot spots increases with the surface coverage.

We report on a new strategy to synthesize Al/CuO nanothermites from commercial Al and ultra-small chemically synthesized CuO nanoparticles coated with alkylamine ligands. These usual ligands stabilize the CuO nanoparticles and prevent them from aggregating, with the goal to enhance the interfacial contact between Al and CuO particles. Using a variety of characterization techniques, including microscopy, spectroscopy, mass spectrometry and calorimetry (ATG/DSC), the structural and chemical evolution of CuO nanoparticles stabilized with alkylamine ligands is analyzed upon heating. This enables us to describe the main decomposition processes taking place on the CuO surface at low temperature (<500 °C): the ligands fragment into organic species accompanied with H2O and CO2 release, which promotes CuO reduction into Cu2O and further Cu. We quantitatively discuss these chemical processes highlighting for the first time the crucial importance of the synthesis conditions that control the chemical purity of the organic ligands (octylamine molecules and derivatives such as carbamate and ammonium ions) in the nanothermite performance. From these findings, an effective method to overcome the ligand-induced CuO degradation at low temperature is proposed and the Al/CuO nanothermite reaction is analyzed, in terms of onset temperature and energy released. We produce original structures composed of aluminium nanoparticles embedded in CuO grainy matrices exhibiting an onset temperature ∼200 °C below the usual Al/CuO onset temperatures, having specific combustion profiles depending on the synthesis conditions, while preserving the total amount of energy released.

Nickel is capable of discharging electric and magnetic shocks in aerospace materials thanks to its conductivity and magnetism. Nickel nanowires are especially desirable for such an application as electronic percolation can be achieved without significantly increasing the weight of the composite material. In this work, single-crystal nickel nanowires possessing a homogeneous magnetic field are produced via a metal-organic precursor decomposition synthesis in solution. The nickel wires are 20 nm in width and 1-2 μm in length. The high anisotropy is attained through a combination of preferential crystal growth in the ⟨100⟩ direction and surfactant templating using hexadecylamine and stearic acid. The organic template ligands protect the nickel from oxidation, even after months of exposure to ambient conditions. These materials were studied using electron holography to characterize their magnetic properties. These thin nanowires display homogeneous ferromagnetism with a magnetic saturation (517 ± 80 emu cm -3 ), which is nearly equivalent to that of bulk nickel (557 emu cm -3 ). Nickel nanowires were incorporated into carbon composite test pieces and were shown to dramatically improve the electric discharge properties of the composite material.

The integration of high-purity nano-objects on substrates remains a great challenge for addressing scaling-up issues in nanotechnology. For instance, grafting gold nanoparticles (NPs) on zinc oxide films, a major step process for catalysis or photovoltaic applications, still remains difficult to master. We report a modified photodeposition (P-D) approach that achieves tight control of the NPs size (7.5 ± 3 nm), shape (spherical), purity, and high areal density (3500 ± 10 NPs/μm 2 ) on ZnO films. This deposition method is also compatible with large ZnO surface areas. Combining electronic microscopy and X-ray photoelectron spectroscopy measurements, we demonstrate that growth occurs primarily in confined spaces (between the grains of the ZnO film), resulting in gold NPs embedded within the ZnO surface grains thus establishing a unique NPs/surface arrangement. This modified P-D process offers a powerful method to control nanoparticle morphology and areal density and to achieve strong Au interaction with the metal oxide substrate. This work also highlights the key role of ZnO surface morphology to control the NPs density and their size distribution. Furthermore, we experimentally demonstrate an increase of the ZnO photocatalytic activity due to high densities of Au NPs, opening applications for the decontamination of water or the photoreduction of water for hydrogen production.

A metal-organic approach has been employed for the preparation of anisotropic CuO nanoparticles. These nanostructures have been characterized by transmission and high resolution transmission electron microscopy, field-emission scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The CuO nanoparticles have been deposited as gas-sensitive layers on miniaturized silicon devices. At an operating temperature of 210 °C, the sensors present an optimum response toward carbon monoxide correlated with a fast response (Rn) and short recovery time. A high sensitivity to CO (Rn≈150 %, 100 ppm CO, RH 50 %) is achieved. These CuO nanoparticles serve as a very promising sensing layer for the fabrication of selective CO gas sensors working at a low temperature., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Micrometer-sized hierarchical Sn3 O2 (OH)2 octahedra, which are self-assembled one inside the other, resembling "Russian doll" organization, have been obtained by a metalorganic approach. This synthesis is based on the controlled hydrolysis of [Sn(NMe2 )2 ]2 in the presence of an alkylamine ligand in an organic solvent (THF). The water content of the medium proved to be a key parameter for the formation of these multi-walled octahedra. The resultant structures have been used as gas-sensitive layers on micromachined silicon devices. During in situ heating, Sn3 O2 (OH)2 is oxidized to SnO2 while retaining the initial morphology. The sensors present outstanding dynamic responses at very low CO concentrations (7 % and 67 % resistance variation to 0.25 and 20 ppm CO, respectively, at an operating temperature of 500 °C). This superior gas-sensing performance is closely related to the unique microstructure of the SnO2 multi-walled octahedra., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The preparation of Ru(0) nanoclusters stabilized by 3-aminopropyltriethoxysilane and their characterization by a combination of complementary techniques are described. These new Ru(0) nanoclusters provide high activity and unprecedented reusability as a heterogeneous catalyst in the dehydrogenation of dimethylamine-borane.