Metal Oxysulfide Nanoparticles

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There are only so many elements that the chemist may use for building new forms of matter: oxygen, carbon, some metals... One could think that all simple combinations were explored already. But certain forms of matter still resist! Here, we explore combination of oxygen, sulfur and one or two metals. We also do our best to limit the size of the grains to a few nanometer... taking to our advantages the many exciting properties that the chemists expect at this scale!

Metal oxysulfides are compounds of metal, oxygen and sulfur. Moreover, the sulfur is not forming sulfate ions in these structures: one can find metal-sulfur bonds. Metal oxysulfides can typically be formed by treating a metal oxide with H2S. However, this requires high temperatures (800 °C or more), which lead to large crystals... not what we want to obtain nanoparticles! This is why we are looking for alternative chemical routes, at lower temperatures, to form a range of metal oxysulfide nanoparticles. In collaboration with colleagues from solid-state physics and biology, we are also studying the electronic and magnetic properties of the nanoparticles that we prepare as well as their behavior towards cells.

Review:

Metal Oxysulfides: From Bulk Compounds to Nanomaterials

This review summarizes the syntheses and applications of metal oxysulfides. Bulk compounds of rare earth and transition metals are discussed in the section Introduction. After a presentation of their main properties and applications, their structures are presented and their syntheses are discussed. The section Bulk Materials and Their Main Applications is dedicated to the growing field of nanoscaled metal oxysulfides. Lanthanide-based nanoparticles are discussed first, followed by transition-metal based nanoparticles.

Frontiers2020

C. Larquet, S. Carenco, Frontiers in Chem. 2020, doi:10.3389/fchem.2020.00179

Related papers:

Unraveling the Role of Alkali Cations in the Growth Mechanism of Gd2O2S Nanoparticles

Alkali cations are required for the colloidal synthesis of Ln2O2S nanoplates in organic solvent. We challenge the commonly accepted scenario of partial lanthanide substitution by the alkali. We demonstrate the formation of an alkali-stabilized oleate mesophase acting as a template for nanoparticle nucleation and growth.

ChemMater2020

C. Larquet, D. Carriere, A.-M. Nguyen, T. K.-C. Le, X. Frogneux-Plé, I. Génois, P. Le Griel, A. Gauzzi, C. Sanchez, S. Carenco, Chem. Mater. 2020, doi:10.1021/acs.chemmater.9b04059

Band Gap Engineering from Cation Balance: The Case of Lanthanide Oxysulfide Nanoparticles

(Gd,Ce)2O2S anisotropic nanoparticles with hexagonal structure exhibit colors varying from white to brown with increasing Ce concentration. Bandgap engineering is thus possible, from 4.7 eV to 2.1 eV. Surprisingly, due to the limited thickness of the lamellar nanoparticles, the bandgap of the nanoparticles is direct as validated by density functional theory on slabs. The fine control of the bandgap over a wide range, solely triggered by the cation ratio, is rarely described in the literature and highly promising for further development of this class of compounds.

ChemMater2019

C. Larquet, A.-M. Nguyen, E. Glais, L. Paulatto, C. Sassoye, M. Selmane, P. Lecante, C. Maheu, C. Geantet, L. Cardenas, C. Chanéac, A.Gauzzi, C. Sanchez, S. Carenco, Chem. Mater. 2019, 31, 5014-23.

Thermal Stability of Oleate-Stabilized Gd2O2S Nanoplates in Inert and Oxidizing Atmospheres

Capping ligands play an important role in the chemistry of nanoparticles. Ultrathin monodisperse Ln2O2Sx oxysulfide nanoparticles (Ln = lanthanide) show promising luminescence and light absorption properties. Here, we show that the thermal stability of Gd2O2Sx nanocrystals is limited because of their non‐stoichiometric composition and strongly depends on the annealing atmosphere. Annealing the nanoparticles in air enables removing the ligands without altering the nanocrystals structure.

ChemNanoMat2019

C. Larquet, D. Hourlier, A.-M. Nguyen, A. Torres-Pardo, A. Gauzzi, C. Sanchez, S. Carenco, ChemNanoMat 2019, 5, 539-46.

Tunable Magnetic Properties of (Gd,Ce)2O2S Oxysulfide Nanoparticles

Gadolinium oxysulfide nanoparticles are suitable candidates for bimodal imaging Here, we synthesized and characterized bimetallic (Gd,Ce)2O2S nanoparticles and demonstrated that they are paramagnetic over a wide temperature range including the body one. The mixture of Gd and Ce magnetic centers enables a fine control of the magnetic properties up to high Ce concentrations (80%) and over a large range of magnetic moments, while photoemission properties are guaranteed up to 20% of Ce owing to a regular dispersion of the Ce centers.

EurJIc2019

C. Larquet, Y. Klein, D. Hrabovsky, A. Gauzzi, C. Sanchez, S. Carenco, EurJIc. 2019, 6, 762-765 | EurJIc Cover.

Synthesis of Ce2O2S and Gd2(1– y)Ce2yO2S Nanoparticles and Reactivity from in Situ X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy

This article describes the synthesis of bimetallic oxysulftide nanoplatelets. They could be obtained over the whole (Gd,Ce) composition range with good control of size and cristallinity.

We observed that cerium-rich nanoparticles are less stable in air than Gd-rich nanoparticles. With in situ X-ray absorption and X-ray photoelectron spectroscopy, we could demonstrate that (i) all these nanoparticles actually exhibit surface sulfate, (ii) sulfate form as a consequence of exposure to water and/or oxygen, (iii) there is a threshold of 50% Ce above which the structure is not stable anymore in air, due to the formation of Ce(IV) species.

InorgChem2017-2

C. Larquet, A.-M. Nguyen, M. Ávila-Gutiérrez, L. Tinat, B. Lassalle-Kaiser, J.-J. Gallet, F. Bournel, A. Gauzzi, C. Sanchez, S. Carenco, Inorg. Chem. 2017, 22, 14227-14236

Outreach article:

[Article] Les oxysulfures de lanthanides : Un terrain de jeu pour la nanochimie

Les oxysulfures de métaux contiennent du soufre à un état d’oxydation négatif. Les oxysulfures de lanthanides cristallins sont utilisés depuis plus de cinquante ans mais les premières synthèses de nanoparticules datent du début du siècle. Cet article discute de la stratégie à adopter pour préparer de telles nanoparticules avec l’exemple de l’oxysulfure de gadolinium. Ces nanoparticules présentent une surface réactive, comme le montre la formation spontanée de sulfates à l’air libre.

AC2019

C. Larquet, A.-M. Nguyen, T. K.-C. Le, M. Avila-Gutierrez, S. Carenco, L'Actualité Chimique. 2019, 436, 28-31.

 

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