Franck Tessier

Functionalized silica for heavy metal ions adsorption

Abstract Heavy metals adsorbents were prepared by co-condensation of tetraethoxysilane and functionalized trialkoxysilane RSi(OR′)3. Functionalized porous silicas with aminopropyl (H2N(CH2)3-), [amino-ethylamino]propyl- (H2N-(CH2)2-NH(CH2)3), (2-aminoethylamino)-ethylamino]propyl (H2N-(CH2)2-NH-(CH2)2-NH(CH2)3-), and mercaptopropyl (HS-(CH2)3-) groups were synthesized using dodecylamine as structure directing agent. These materials have been characterized by elemental analysis, powder X-ray diffraction, nitrogen gas sorption, Fourier transform infrared and Raman spectroscopies and thermogravimetric analysis. These organo-silicas were prepared for use in the removal of heavy metal ions from aqueous solutions. Samples synthesized with [amino-ethylamino]propyl- and (2-aminoethylamino)ethylamino]propyl- functions show a high loading capacity for Cu2+, Ni2+, Co2+ and the anion Cr(VI). The sample synthesized with a mercaptopropyl function has a high loading capacity for Cd2+.

Ternary and higher order rare-earth nitride materials: synthesis and characterization of ionic-covalent oxynitride powders

The possibility to introduce nitrogen as a substitute for oxygen within the anionic network of ternary and higher order rare-earth oxides has been examined. The higher anionic formal charge resulting from this N3−/O2− substitution can be compensated either through cross-substitutions or by the creation of anionic vacancies. Resulting oxynitrides belong to different structures types which are well known in the oxide crystal chemistry. A commonly used synthesis method consists of a thermal nitridation in flowing ammonia of corresponding rare-earth oxide compositions. In such a solid–gas process the reactivity of the oxide precursors is an important reaction parameter, and a soft chemistry route involving a complexing method may be advantageously utilized to prepare them. The N3−/O2− anionic substitution induces also a more covalent character illustrated, for example, by strongly colored oxynitride powders that gives the possibility to tune the absorption edge of the UV–visible spectra by suitable adjustment of the N/O ratio.

P-Type Nitrogen-Doped ZnO Nanoparticles Stable under Ambient Conditions

Zinc oxide is considered as a very promising material for optoelectronics. However, to date, the difficulty in producing stable p-type ZnO is a bottleneck, which hinders the advent of ZnO-based devices. In that context, nitrogen-doped zinc oxide receives much attention. However, numerous reviews report the controversial character of p-type conductivity in N-doped ZnO, and recent theoretical contributions explain that N-doping alone cannot lead to p-typeness in Zn-rich ZnO. We report here that the ammonolysis at low temperature of ZnO(2) yields pure wurtzite-type N-doped ZnO nanoparticles with an extraordinarily large amount of Zn vacancies (up to 20%). Electrochemical and transient spectroscopy studies demonstrate that these Zn-poor nanoparticles exhibit a p-type conductivity that is stable over more than 2 years under ambient conditions.

New routes to transition metal nitrides: and characterization of new phases

Transition metal nitrides form a class of materials with unique physical properties which give them varied applications, as high temperature ceramics, magnetic materials, superconductors or catalysts. They are commonly prepared by high temperature conventional processes, but alternative synthetic approaches have also been explored, more recently, which utilize moderate-temperature conditions. For example, high surface area γ-Mo 2 N nitride powders (fcc phase) are prepared from commercial oxide MoO 3 through a topotactic transformation process. Of prime importance is the nature of the precursor, because it may yield new nitride phases unattainable by other synthetic routes. A novel promising method to nitride synthesis has been developed using sulfides as starting materials. The ammonolysis reaction has been applied first to the preparation of two binary molybdenum nitrides: Mo 5 N 6 (filled 2H-MoS 2 structure) and δ-MoN (NiAs-type structure) from MoS 2 , and then extended to other metals such as W, Cr or Ti, as well as molybdenum- and tantalum-based ternary systems. Fine reactive molybdenum sulfide precursor powders (S g ≥200 m 2 g –1 ) have been synthesized in thiocyanate melt. On the other hand, alkali metal ternary oxides offer potential as nitridation precursors. For example, a binary nitride Nb 4 N 5 (defect NaCl-type structure) results from ammonolysis of sodium or potassium niobates whereas LiNb 3 O 8 is transformed into a mixed valent ternary nitride LiNb 3 N 4 (filled 2H-MoS 2 structure). Another illustration of the Li + inductive effect is given in the direct synthesis of LiMN 2 from Li 2 MO 4 (M=Mo, W). The nitrides Mo 5 N 6 , δ-MoN and Nb 4 N 5 show superconducting behavior at T<12 K.

Synthesis and energetics of yellow TaON

From the standard enthalpy of formation of tantalum oxynitride TaON, determined by oxidative drop solution calorimetry, it is possible to explain its particular synthesis conditions from Ta 2O5 and NH3, i.e. the use of wet ammonia which prevents the formation of tantalum nitride Ta3N5. Thermogravimetric analyses were performed to study both the ammonolysis of Ta2O5 and the oxidation in air of Ta3N5 and TaON. TaON powder was prepared, which bright yellow color agrees well with its electronic structure.  2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Energetics of binary iron nitrides

Abstract High-temperature solution calorimetry in molten sodium molybdate 3Na 2 O·4MoO 3 was used to determine the energetics of formation of a series of binary iron nitrides: γ′-Fe 4 N, e-Fe 3 N 1+ y ( y =0, 0.10, 0.22, 0.30, 0.33), ζ-Fe 2 N and γ′′-FeN 0.91 . The linear relation Δ H ° f (FeN x )=−65.23 x +13.48 kJ mol −1 was found between the enthalpies of formation from the elements at 298 K of iron nitrides FeN x and their nitrogen content x . Using this linear approximation, the enthalpy of formation of α′′-Fe 16 N 2 has been estimated to Δ H ° f (Fe 16 N 2 )=85.2±46.8 kJ mol −1 .

Calorimetric determination of the enthalpy of formation of InN and comparison with AlN and GaN

The standard enthalpy of formation of InN at 298 K has been determined usinghigh-temperature oxidative drop solution calorimetry in a molten sodium molybdatesolvent at 975 K. Calorimetric measurements were performed on six InN samples withvarying nitrogen contents. The samples were characterized using x-ray diffraction,chemical analysis, electron microprobe analysis, and Brunauer–Emmett–Teller surfacearea measurement. The variation of the enthalpy of drop solution (kJ/g) with nitrogencontent is approximately linear. The data, when extrapolated to stoichiometric InN,yield a standard enthalpy of formation from the elements of −28.6 ± 9.2 kJ/mol. Therelatively large error results from the deviation of individual points from the straightline rather than uncertainties in each set of data for a given sample. This new directlymeasured enthalpy of formation is in good agreement with the old combustioncalorimetric result by Hahn and Juza (1940). However, this calorimetric enthalpy offormation is significantly different from the enthalpy of formation values derived fromthe temperature dependence of the apparent decomposition pressure of nitrogen overInN. A literature survey of the enthalpies of formation of III–N nitride compounds ispresented.I. INTRODUCTIONNitrides of composition AN (A 4 Al, Ga, and In),III–N, represent important optoelectronic materials withsemiconductor applications such as quantum wells, la-sers, display devices, and storage devices.

Typical features of nitrogen in nitride-type compounds

Nitride and oxynitride materials have attractive properties directly related to the role played by nitrogen. In particular, a comparison between oxynitrides and oxides highlights the characteristics of a nitrogen N3−/oxygen O2− substitution: an increase in the anionic formal charge, a greater covalent character, a higher cross-linking density in glasses, a reducing character due to the N3−/N0 redox couple, and modified acid–base properties. Each specific character is illustrated by appropriate examples.

Eu 2+ and Mn 2+ codoped Ba 2 Mg(BO 3 ) 2 —new red phosphor for white LEDs

A new red phosphor, Ba2Mg(BO3)2:Eu,Mn, was synthesized by the solid-state reaction method and its photoluminescence properties were investigated by excitation and emission spectra and decay curves. Its excitation band is extending from 250-450 nm, which is adaptable to the emission band of near-ultraviolet LED chips (350-420 nm). Upon the excitation of 365 nm light, the phosphor exhibits strong red emission centered at 615 nm. The relationship between Eu2+ and Mn2+ dopants was studied from the viewpoint of a crystal structure and by photoluminescence spectra and decay curves. The results show that the characteristic Eu2+ emission predominate in the emission band and Mn2+ promote the redistribution of Eu2+ at the cation sites of the host crystal.

Mixed valent niobium nitrides and oxynitrides resulting from ammonolysis of alkaline niobates

Abstract Nitridation of alkaline niobates MNbO 3 and MNb 3 O 8 (M = Li, Na, K) in flowing ammonia leads to different reaction products depending on the temperature and the considered niobate. Two series of mixed valent NaCl-type oxynitrides are formed in the LiNbON system. A complete nitrogen/oxygen substitution can be obtained since the ternary oxide LiNb 3 O 8 is transformed, without lithium evaporation, into a ternary nitride LiNb 3 N 4 which has a filled up MoS 2 -type structure. Reaction of sodium or potassium niobates with NH 3 results in a total evaporation of sodium or potassium and formation of the binary nitride Nb 4 N 5 closely related to the NaCl structure.