N-Alkyl substituted triazenide-bridged homoleptic iron(II) dimers with an exceptionally short Fe-Fe bond.

Dinuclear transition metal complexes with direct metal-metal interactions have the potential to generate unique reactivities and properties. Using asymmetric triazine ligands HN3tBuR (R = Et, iPr, nBu) featuring different alkyl substituents at 1,3-N centers, we report here the first rational synthesis of 'tetragonal lantern' type Fe(II) triazenides [Fe2(N3tBuR)4] [R = Et (1), iPr (2), nBu (3)] having an exceptionally short Fe-Fe distance (2.167-2.174 Å). Unlike the previously reported lantern structures with related amidinate or guanidinate ligands, highly air-sensitive 1-3 show a lower spin ground state, as indicated by Mössbauer, 1H NMR and DFT studies.

Improved Visible Emission from ZnO Nanoparticles Synthesized via the Co-Precipitation Method.

Since ZnO nanoparticles (NPs) possess a variety of intrinsic defects, they can provide a wide spectrum of visible emission, without adding any impurity or any doping atoms. They are attracting more and more interest as a material for light sources and energy downshifting systems. However, defect emission with a high luminescence quantum efficiency (PL QY) is difficult to obtain. Here, we present the co-precipitation synthesis parameters permitting to attain ZnO NPs with highly visible PL QYs. We found that the nature of zinc precursors and alkaline hydroxide (KOH or LiOH) used in this method affects the emission spectra and the PL QY of the as-grown ZnO NPs. LiOH is found to have an advantageous effect on the visible emission efficiency when added during the synthesis of the ZnO NPs. More precisely, LiOH permits to increase the emission efficiency in the visible up to 13%. We discuss the effects of the nanoparticle size, the morphology and the surface stabilization on the enhancement of the luminescent emission efficiency. Various spectral contributions to the luminescent emission were also examined, in order to achieve a control of the defect emission to increase its efficiency.

New Carbamoyl Surface-Modified ZrO2 Nanohybrids for Selective Au Extraction from E-Waste.

Efficient and selective extractions of precious and critical metal ions such as Au(III) and Pd(II) were investigated using zirconia nanoparticles surface modified with different organic mono- and di-carbamoyl phosphonic acid ligands. The modification is made on the surface of commercial ZrO2 that is dispersed in aqueous suspension and was achieved by optimizing the Bronsted acid-base reaction in ethanol/H2O solution (1:2), resulting in inorganic-organic systems of ZrO2-Ln (Ln: organic carbamoyl phosphonic acid ligand). The presence, binding, amount, and stability of the organic ligand on the surface of zirconia nanoparticles were confirmed by different characterizations such as TGA, BET, ATR-FTIR, and 31P-NMR. Characterizations showed that all the prepared modified zirconia had a similar specific surface area (50 m2.g-1) and the same amount of ligand on the zirconia surface in a 1:50 molar ratio. ATR-FTIR and 31P-NMR data were used to elucidate the most favorable binding mode. Batch adsorption results showed that (i) ZrO2 surface modified with di-carbamoyl phosphonic acid ligands had the highest adsorption efficiency to extract metals than mono-carbamoyl ligands, and (ii) higher hydrophobicity of the ligand led to better adsorption efficiency. The surface-modified ZrO2 with di-N,N-butyl carbamoyl pentyl phosphonic acid ligand (ZrO2-L6) showed promising stability, efficiency, and reusability in industrial applications for selective gold recovery. In terms of thermodynamic and kinetic adsorption data, ZrO2-L6 fits the Langmuir adsorption model and pseudo-second-order kinetic model for the adsorption of Au(III) with maximum experimental adsorption capacity qmax = 6.4 mg.g-1.

Extreme structural stability of Ti0.5Sn0.5O2 nanoparticles: synergistic effect in the cationic sublattice.

Ti0.5Sn0.5O2 nanoparticles (∼5 nm and ∼10 nm) have been studied under high pressure by Raman spectroscopy. For particles with diameter ∼10 nm, a transformation has been observed at 20-25 GPa while for particles with ∼5 nm diameter no phase transition has been observed up to ∼30 GPa. The Ti0.5Sn0.5O2 solid solution shows an extended stability at the nanoscale, both of its cationic and anionic sublattices. This ultrastability originates from the contribution of Ti and Sn mixing: Sn stabilizes the cationic network at high pressure and Ti ensures a coupling between the cationic and anionic sublattices. This result questions a "traditional" crystallographic description based on polyhedra packing and this synergistic effect reported in this work is similar to the case of metamaterials but at the nanoscale.

Adsorptive removal of Ag/Au quantum dots onto covalent organic frameworks@magnetic zeolite@arabic gum hydrogel and their catalytic microwave-Fenton oxidative degradation of Rifampicin antibiotic.

Recent progress in nanotechnology via incorporation of small particle size as quantum dots (QDs) (1-10 nm) in many industrial activities and commercial products has led to significant undesired environmental impacts. Therefore, QDs removal from wastewater represents an interesting research topic with a lot of challenges for scientists and engineers nowadays. In this work, the coagulative removal of metal quantum dots as silver and gold from industrial water samples is explored. A novel biosorbent was assembled via binding of covalent organic frameworks (COFs) with magnetic zeolite and Arabic gum hydrogel (COFs@MagZ@AGH) as a promising removal material for Ag-QDs and Au-QDs. This was fully characterized by EDX, SEM, TEM, FT-IR, XPS, XRD and surface area and applied in coagulative removal of Au-QDs and Ag-QDs in presence of several experimental factors as pH, presence of other electrolytes, stirring time, initial QDs concentration, coagulant dosage, and temperature in order to optimize the removal processes. At optimum conditions, COFs@MagZ@AGH was able to recover 99.19% and 87.57% of Ag-QDs and Au-QDs QDs, respectively via chemical adsorption mechanism with perfect fitting to pseudo-second order model. Reuse of the recovered Ag/Au-QDs@COFs@MagZ@AGH as efficient catalysts in catalytic degradation of Rifampicin antibiotic (Rf) from water was additionally investigated and optimized via microwave-Fenton catalysts with excellent oxidative degradation efficiency (100%). Reusability and applicability of the biosorbent (COFs@MagZ@AGH) and catalysts (Ag/Au-QDs@COFs@MagZ@AGH) in real industrial water samples were also explored and successfully accomplished.

Design of Hybrid PAH Nanoadsorbents by Surface Functionalization of ZrO2 Nanoparticles with Phosphonic Acids.

This study focuses on the preparation of innovative nanocomposite materials based on surface modification of commercial nano-ZrO2 optimized from Brønsted acid-base surface reactions. This surface modification was carried out by direct grafting of suitable phosphonic acids bearing a vinylic or phenylic substituent in aqueous solution. Different loading quantities of the anchoring organophosphorus compounds were applied for each materials synthesis. The resulting nanohybrids were thoroughly characterized by infrared spectroscopy (DRIFT), solid-state nuclear magnetic resonance (NMR), nitrogen adsorption-desorption (BET), thermogravimetric analysis (TG), and X-ray photoelectron spectroscopy (XPS), demonstrating the reliability and efficient tunability of the surface functionalization based on the starting Zr/P ratio. Our nanocomposite materials exhibited a high specific surface area as well as complex porosity networks with well-defined meso-pore. The as-prepared materials were investigated for the adsorption of a mixture of 16 polycyclic aromatic hydrocarbons (PAHs) at 200 ng·mL-1 in an aqueous solution. Adsorption kinetics experiments of each individual material were carried out on the prepared PAHs standard solution for a contact time of up to 6 h. Pretreatments of the adsorption test samples were performed by solid-phase extraction (SPE), and the resulting samples were analyzed using an ultrasensitive GC-orbitrap-MS system. The pseudo-first-order and the pseudo-second-order models were used to determine the kinetic data. The adsorption kinetics were best described and fitted by the pseudo-second-order kinetic model. The correlation between the nature of the substituent (vinylic or phenylic) and the parameters characterizing the adsorption process were found. In addition, an increase of PAHs adsorption rates with phosphonic acid loading was observed.

Optimum in the thermoelectric efficiency of nanostructured Nb-doped TiO2 ceramics: from polarons to Nb-Nb dimers.

Rutile is the most common and stable polymorph form of titanium oxide TiO2 at all temperatures. The doping of rutile TiO2 with a small amount of niobium is reknown for being responsible for a large increase of the electrical conductivity by several orders of magnitude, broadening its technological interest towards new emerging fields such as the thermoelectric conversion of waste heat. The electronic conduction has been found to be of a polaronic nature with strongly localized charges around the Ti3+ centers while, on the other side, the relatively high value of the thermal conductivity implies the existence of lattice heat carriers, i.e. phonons, with large mean free paths which makes the nanostructuration relevant for optimizing the thermoelectric efficiency. Here, the use of a high-pressure and high-temperature sintering technique has allowed to vary the grain size in rutile TiO2 pellets from 300 to 170 nm, leading to a significant reduction of the lattice thermal conductivity. The thermoelectric properties (electrical conductivity, Seebeck coefficient and thermal conductivity) of Nb-doped rutile nanostructured ceramics, namely NbxTi1-xO2 with x varying from 1 to 5%, are reported from room temperature to ∼900 K. With the incorporation of Nb, an optimum in the thermoelectric properties together with an anomaly on the tetragonal lattice constant c are observed for a concentration of ∼2.85%, which might be the fingerprint of the formation of short Nb dimers.

Molecular Engineering of Metal Alkoxides for Solution Phase Synthesis of High-Tech Metal Oxide Nanomaterials.

The 'bottom-up' synthesis of inorganic nanomaterials with precision at the atomic/molecular level offers many opportunities for the design and improvement of the nanomaterials for various applications. Molecular engineering during soft chemical processing for the synthesis of functional nanomaterials enables the desired chemical and physical properties of the precursors, such as solubility or volatility, clean decomposition, control of stoichiometry for multimetallic species to name a few, and leads to easy control of uniform particle size distribution, stoichiometry…. This Minireview illustrates some important aspects of the molecular engineering in light of some recent developments from the molecular synthesis of nanomaterials involving non-silicon metal alkoxide systems for high-tech applications.

Heteroleptic Tin(IV) Aminoalkoxides and Aminofluoroalkoxides as MOCVD Precursors for Undoped and F-Doped SnO2 Thin Films.

A series of asymmetric and potentially bidentate amino alcohols and amino fluoro alcohols (RNOH) having a different number of methyl/trifluoromethyl substituents at the α-carbon atom, [HOC(R1)(R2)CH2NMe2] (R1 = R2 = H (dmaeH); R1 = H, R2 = CH3 (dmapH); R1 = R2 = CH3 (dmampH); R1 = H, R2 = CF3 (F-dmapH); R1 = R2 = CF3 (F-dmampH)) have been used to develop new monomeric and heteroleptic tin(IV) amino(fluoro)alkoxides [Sn(OR)2(ORN)2] (R = Et, Pri, But). These new complexes, which were thoroughly characterized by spectroscopy (IR and multinuclei NMR (1H, 13C, 19F, and 119Sn)) as well as single-crystal X-ray studies on representative samples, were investigated for their thermal behavior to determine their suitability as MOCVD precursors for the deposition of metal oxide thin films. The two most suitable compounds, [Sn(OBut)2(dmamp)2] and [Sn(OBut)2(F-dmamp)2], were used in a direct liquid injection chemical vapor deposition (DLI-CVD) process to deposit undoped SnO2 and F-doped SnO2 thin films, respectively, on silicon and quartz substrates. Film growth rates at different temperatures (from 400 to 700 °C), film thickness, crystalline quality, and surface morphology were investigated. The films deposited on quartz showed high transparency (above 80%) in the visible region and low carbon contamination on the surface (11-13% from XPS), which could easily be removed completely with 2 min of Ar+ sputtering.

Nanometric NaYF4 as an Unconventional Support for Gold Catalysts for Oxidation Reactions.

The metal-support interaction plays an important role in gold catalysis. We employ here crystalline cubic (α-) and hexagonal (ß-) phases of heterometallic fluoride NaYF4 nanoparticles (NPs), obtained by the decomposition of a single source precursor [NaY(TFA)4(diglyme)] (TFA = trifluoroacetate), as nonoxide supports for gold catalysts. Using an isostructural gadolinium analogue, we also obtained doped α-NaYF4:Gd3+ and ß-NaYF4:Gd3+ NPs. A successful deposition of ∼1% by weight gold NPs of average size 5-6.5 nm on these doped and undoped metal fluorides using HAuCl4·3H2O afforded Au/NaYF4 catalysts which were thoroughly characterized by using several physicochemical techniques such as X-ray diffraction, Brunauer-Emmett-Teller analysis, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. A comparative study of the above catalysts for different oxidation reactions show that while for the aerobic oxidation of trans-stilbene in solution phase, they are either better (in terms of stilbene conversion) or at par (in terms of trans-stilbene oxide yield) in comparison to the reference catalyst Au/TiO2 of the World Gold Council, their activity toward CO oxidation reactions in gas phase remains much less than that of gold catalysts supported on metal oxides.

TiO2-Based Hybrid Nanocomposites Modified by Phosphonate Molecules as Selective PAH Adsorbents.

A robust sol-gel process was developed for the synthesis of surface-functionalized titania nanocrystallites bearing unsaturated groups starting from molecular heteroleptic single-source precursors. Molecules and nanomaterials were thoroughly characterized by multinuclear liquid and solid-state nuclear magnetic resonance (NMR), infra-red (FT-IR, DRIFT) spectroscopies. Nitrogen adsorption-desorption (BET), thermogravimetric (TG) and elemental analyses demonstrated the reliability and the fine tuning of the surface functionalization in terms of ratio TiO2:ligand. The as-prepared materials were used as nano-adsorbents to remove mixture of 16 polycyclic aromatic hydrocarbon (PAHs) from aqueous solutions. Adsorption kinetic experiments were carried out for 24 h in solutions of one PAH [benzo(a)pyrene, 220 ppb] and of a mixture of sixteen ones [220 ppb for each PAH]. Most kinetic data best fitted the pseudo-second order model. However, in PAHs mixture, a competition process took place during the first hours leading to a remarkable high selectivity between light and heavy PAHs. This selectivity could be fine-tuned depending on the nature of the unsaturated group of the phosphonate framework and on the nanomaterial textures.

Asymmetrically substituted triazenes as poor electron donor ligands in the precursor chemistry of iron(ii) for iron-based metallic and intermetallic nanocrystals.

Triazene ligands are introduced, for the first time, in the precursor chemistry for their ability to afford oxygen-free molecular precursors of Fe0 nanoparticles. For this purpose, we synthesized new asymmetric triazene ligands t-BuN[double bond, length as m-dash]N-NHR (R = Et, i-Pr, n-Bu) featuring different alkyl substituents at 1,3-N centers, as well as a symmetric ligand t-BuN[double bond, length as m-dash]N-NHt-Bu and used them to develop novel heteroleptic monomeric FeII triazenide derivatives [Fe(t-BuN3R)2(TMEDA)] (where TMEDA = tetramethylethylenediamine). A range of physico-chemical studies such as FT-IR, TG-DTA, 1H & 13C NMR, mass spectrometry, single crystal X-ray structure analysis, cyclic voltammetry and Mössbauer spectroscopy were used to characterize these newly synthesized ligands and FeII derivatives. One representative derivative [Fe(t-BuN3Et)2(TMEDA)] was evaluated as a precursor for the synthesis of metallic Fe0 and intermetallic Al13Fe4 nanoparticles by the chemical solution deposition method.

Reduced {001}-TiO2-x photocatalysts: noble-metal-free CO2 photoreduction for selective CH4 evolution.

The preparation of reduced TiO2 photocatalysts with high Ti3+ concentration is a great challenge due to their instability in air. Here we report a new approach for the synthesis of reduced TiO2 with {001} facets exposed via a hydrothermal process. By the introduction of fluoride atoms, {001} and {101} facets are formed, which act as hole and electron collectors, respectively, for charge separation. By adjusting the volume of HF added, a rutile-anatase transition is observed for the first time. EPR spectra confirm the generation of Ti3+ species in the bulk of TiO2, and Ti3+ signals are studied in the anatase and rutile phases separately. The quantified EPR shows that reduced TiO2 samples present 14 000-fold more spins compared to the pristine TiO2, and the intensity can reach as high as 24.6 × 1019 spins per g. The obtained samples also have a unique disordered layer with a thickness of 1-2 nm on their surfaces, which contributes to the stabilization of the formed Ti3+ species by preventing their oxidation in air. In addition, the synthesized reduced TiO2 samples also exhibit wide-spectrum solar light absorption, especially in the near-infrared region. Owing to their enhanced solar light absorption, improved electron-hole separation and special facet exposure, these samples exhibit enhanced photocatalytic CO2 reduction performance and high CH4 selectivity under solar light irradiation, in the absence of a noble metal Pt as a co-catalyst.

A Facile Molecular Precursor-based Synthesis of Ag2 Se Nanoparticles and Its Composites with TiO2 for Enhanced Photocatalytic Activity.

The reactions of different silver(I) reagents AgX (X(-) =iodide, trifluoroacetate, triflate) with selenoethers R2 Se (R=Me, tBu) in a variety of solvents were investigated in relation with their use as precursors for Ag2 Se nanomaterials. Different reaction conditions led to different reactivities and afforded either molecular complexes or metal selenide nanoparticles. The reactions leading to in situ formation of the metal selenide nanoparticles were then extended in the presence of commercial TiO2 (P25) to prepare silver selenide-titania nanocomposites with different Ag/Ti ratios. These nanocomposites, well characterized by elemental analysis (Ag, Se), PXRD, TEM, BET, XPS and UV/Vis studies, were investigated as photocatalysts for the degradation of formic acid (FA) solution. The xAg2 Se-TiO2 nanocomposites (x=0.01, 0.13 and 0.25 mol %) exhibited a much higher catalytic activity as compared to P25, which is an established benchmark for the photocatalysis under UV light, and retained a good photocatalytic stability after recycling for several times.

A convenient and quantitative route to Sn(IV)-M [M = Ti(IV), Nb(V), Ta(V)] heterobimetallic precursors for dense mixed-metal oxide ceramics.

The strategy of reacting SnCl4 with M(OR)x provided a convenient and quantitative approach to new heterobimetallics with a simple addition formula, [SnCl4M(OR)x(HOR)y] (M = Ti, Nb, Ta; R = Et, Pr(i), x = 4, 5; y = 0-2) or sometimes an oxo complex [SnCl3(O)Ti2(OPr(i))7(HOPr(i))2]. The alcoholysis reactions of these heterometallics afforded mixed alkoxo complexes [SnCl4(µ-OEt)2M(Pr(i)O)x(Pr(i)OH)y] [M = Ti (x = y = 2), Nb, Ta (x = 3, y = 1)] under mild conditions, or a planar rectangular oxo product [SnCl3(µ-OEt)2Nb(OEt)2(EtOH)(µ-O)]2 at refluxing/extended stirring time. DFT calculations shed light on the stability and reactivity of these complexes. The use of these thoroughly characterized heterometallics as sol-gel precursors suppresses the formation of the undesired SnO2 grains, which are difficult to be sintered to a high density. The combined approach of using bottom-up synthesis of mixed Ti0.5Sn0.5O2 nanoparticles and Spark Plasma Sintering allowed the successful densification of chloride-free mixed-metal oxide ceramics. The influence of thermal treatment before sintering on the density and spinodal decomposition of the TiO2-SnO2 pellets is reported.

Novel barium-organic incorporated iodometalates: do they have template properties for constructing rare heterotrimetallic hybrids?

New barium-organic derivatives are introduced as countercations in the iodocuprates and -argentates to yield novel hybrids with unique structural motifs and bonding modes, many of them also showing vivid fluorescence on exposure to UV light. The tetrahedral MX4/trigonal-coplanar MX3 unit in these hybrids [Ba2(DMSO)12Cu8I12] (1) and [Ba(tetraglyme)2]2[Ag8I12]·EtOH (7) can be replaced by the M'I4/M'I3 unit without compromising their basic structural motifs, thus leading to the formation of the rare mixed Cu-Ag iodometalates [Ba2(DMSO)12Cu4Ag4I12] (9) and [Ba(tetraglyme)2]2[CuAg7I12]·EtOH (10), respectively. In contrast, a breakdown in the structure-directing properties of these iodometalates was observed in the mixed Ag-Pb iodometalate [Ba(tetraglyme)2]2[Pb2Ag2I10]·2Me2CO (11), where the basic structure of the synthon [Ba(tetraglyme)2]2[Ag4I8] (8) was not retained due to the compulsory molecular rearrangement required as a result of replacing AgI4/AgI3 units with octahedral PbI6 units.

Direct synthesis of hexagonal NaGdF4 nanocrystals from a single-source precursor: upconverting NaGdF4 :Yb³âº ,Tm³âº and its composites with TiO2 for near-IR-driven photocatalysis.

A novel single-source precursor NaGd(TFA)4 (diglyme) (TFA=trifluoroacetate) was synthesized, characterized thoroughly, and used to obtain the hexagonal phase of NaGdF4 nanoparticles as an efficient matrix for lanthanide-doped upconverting nanocrystals (NCs) that convert near-infrared radiation into shorter-wavelength UV/visible light. These NCs were then used to prepare well-characterized TiO2@NaGdF4:Yb(3+),Tm(3+) nanocomposites to extend the absorption range of the TiO2 photocatalyst from the UV to the IR region. While the visible/near IR part of the photoluminescent spectra remains almost unaffected by the presence of TiO2, the UV part is strongly quenched due to the absorption of TiO2 above its gap at approximately 380 nm by energy transfer or FRET. Preliminary results on the photocatalytic activity of the above obtained nanocomposites are presented.

Thermodynamics of nanoparticles: experimental protocol based on a comprehensive Ginzburg-Landau interpretation.

The effects of surface and interface on the thermodynamics of small particles require a deeper understanding. This step is crucial for the development of models that can be used for decision-making support to design nanomaterials with original properties. On the basis of experimental results for phase transitions in compressed ZnO nanoparticles, we show the limitations of classical thermodynamics approaches (Gibbs and Landau). We develop a new model based on the Ginzburg-Landau theory that requires the consideration of several terms, such as the interaction between nanoparticles, pressure gradients, defect density, and so on. This phenomenological approach sheds light on the discrepancies in the literature as it identifies several possible parameters that should be taken into account to properly describe the transformations. For the sake of clarity and standardization, we propose an experimental protocol that must be followed during high-pressure investigations of nanoparticles in order to obtain coherent, reliable data that can be used by the scientific community.

A molecular precursor approach to monodisperse scintillating CeF3 nanocrystals.

A series of anhydrous cerium(III) trifluoroacetate complexes with neutral O-donor ligands, namely Ce2(OAc)(TFA)5(DMF)3 (1), Ce(TFA)3(L)x [x = 2, L = THF (2), DMF (3), DMSO (4); x = 1, L = diglyme (5)] and Ce2(TFA)6(DMSO)x(DMF)y [x = 6, y = 0 (6); x = 4, y = 2 (7)] (where OAc = acetate, TFA = trifluoroacetate, THF = tetrahydrofuran, DMF = dimethylformamide, DMSO = dimethylsulphoxide, and diglyme = MeO(C2H4O)2Me] were synthesized and completely characterized by elemental analysis, FT-IR spectroscopy and TG-DTA-MS studies. A partially hydrated complex [Ce(TFA)3(diglyme)(H2O)] (8) was obtained by slow evaporation of the THF solution of anhydrous 5 in the air. The single crystal X-ray diffraction analysis of 1, 3, 4, and 6­8 showed the versatile bonding mode of the TFA ligand (terminal, chelating and bridging). These complexes, on decomposition in 1-octadecene in inert atmosphere, gave CeF3 nanoparticles of 8­11 nm size. The complex 5 proved to be the best precursor in the series because of the ability of the diglyme ligand to act as capping reagent during decomposition to render the CeF3 particles monodisperse in organic solvents. The obtained CeF3 nanoparticles were characterized by FT-IR, EDX analysis and TEM studies and their luminescence and scintillation responses under UV and X-ray excitation were studied and compared with that of CeF3 single crystal.