Direct Insight into the Confinement Effect of WS2 Nanostructures in an Ordered Carbon Matrix

Significance 

Transition metal dichalcogenide semiconductors formed by monolayers of composition TX₂, with T and X being a transition metal element and a chalcogen element respectively. In particular, transition metal sulfides, such as MoS2 and WS2 have become research hotspots in recent times. Among the different metal disulfide nanostructures, WS2 inorganic fullerenes are usually obtained via a solid−gas reaction at a relatively high temperature from an oxide nanoparticles powder (WO3) exposed to a H2/H2S gas mixture. The formation mechanism involved here has been widely studied as it represents a way of producing highly sought-after nanoparticles directly related to the shape and size of the oxide nanoparticles. Previous publications have revealed that confinement can limit and/or orient nanoparticles growth. Therefore, composite materials made of nanostructured dichalcogenides located in a porous matrix have been also prepared; resulting in interesting properties for various applications. However, a thorough review of published literature reveals that very few studies have explored the possibility of metal dichalcogenide synthesis in a confined environment with formation of inorganic nanotubes and fullerenes.

To bridge this deficiency, researchers from the Institute of Materials Science of Mulhouse at Upper-Alsace University (UHA) and Institute of Physics and Chemistry of Materials Strasbourg at University of Strasbourg in France: Dr. Julien Kiener, Dr. Maria Girleanu, Professor Ovidiu Ersen and Dr. Julien Parmentier investigated a novel growth mechanism for WS2 nanostructures with well-defined shapes (nanocages or nanotubes), induced by a confinement effect in a mesoporous structure. Their work is currently published in the research journal, Crystal Growth & Design.

In their approach, the research team synthesized WS2/ C Nanocomposites where the carbon matrix has a honey-comb mesoporous structure. This synthesis was based on the soft-template route mixing an amphiphilic surfactant as a pore template, a phenolic resin as a carbon precursor and a W-based salt as a WS2 precursor. Samples were obtained in a single step (one-pot procedure) thanks to the evaporation induced self-assembly technique followed by heat-treatment in H2S atmosphere as depicted in related literature. The researchers then characterized the resulting samples via XRD, Thermogravimetric analysis and TEM analyses – among other techniques.

Interestingly, at the difference of former mechanisms described in literature, the unidirectional mesoporosity associated by the specificity of the one-pot synthesis method was reported to lead to original WS2 curved nanostructures (nanocages, nanotubes) within the porosity. The proposed gas-solid growth mechanism is based on successive reactions of H2S and W-based gaseous species on the dangling bond of the existing WS2 layers formed during the previous nucleation step. Further, carbon was also reported to contribute to the reduction of the oxidation state of W, thus simplifying the process of the formation of WS2 nanometric phases.

In summary, the study presented a unique preparation of original nanostructures such as nanometric slabs, nanoribbons, as well as WS2 individual inorganic nanocages and nanotubes, through a mechanism involving the confinement of reactive species within mesopores of a carbon matrix. Remarkably, it was revealed that lamellar growth occurred for nano-slab well oriented along the longitudinal axis of the mesopores (e.g., nanoribbons in cylindrical pores), whereas for the others, owing to their low curvature energy, their growth occurred by their rolling along the mesopore surface with formation of curved nanolayers, which subsequently lead to inorganic nanocages (with ellipsoidal shape) or nanotubes.

About the author

Dr. Kiener Julien obtained his PhD in Materials Chemistry from Upper-Alsace University, Mulhouse (France), in 2015. His thesis focuses on synthesis and characterization of nanocomposite materials combining a mesoporous carbon matrix with transition metal nanoparticles.

This research work were done trough the framework of a collaboration between Institute of Materials Science of Mulhouse (IS2M, France) and Institute of Materials Physics and Chemistry of Strasbourg (IPCMS, France). He completed a postdoctoral contract through the collaboration between IS2M and private group ONET, working on the same type of materials.

About the author

Dr. Maria Girleanu studied Materials Science at Polytechnic University of Bucharest, Romania and received her PhD in 2010 form the Upper- Alsace University (Mulhouse, France). During the PhD, her work was focused on the mechanical and structural characterization of Ti1-xAlxN thin coatings. As a postdoctoral fellow at IPCMS-CNRS Strasbourg, she specialized in material characterization by transmission electron microscopy, in particular high-resolution STEM-HAADF and electron tomography.

Her main research interests included transition metal chalcogenides for catalytic applications like WS2 and MoS2 and hybrid devices composed by organic semiconductor and metallic nanostructures. Since 2015, she integrated the French Armed Forces at the Biomedical Research Institute on Bretigny-sur-Orge as a TEM specialist. Presently her work focuses on the implementation of cryo-TEM techniques in a level-three-biosafety laboratory.

Unité Imagerie, Département des Plateformes et Recherche Technologique, Institut de Recherche Biomédicale des Armées, Brétigny-sur-Orge, France

About the author

Ovidiu ERSEN, 46 years old, is a Full Professor at the University of Strasbourg and Institute of Physics and Chemistry of Materials of Strasbourg (IPCMS) and is affiliated to IUF (Institut Universitaire de France). He received the award « Fondation University of Strasbourg – Cercle Gutenberg » in 2012 and became USIAS fellow at the University of Strasbourg. In 2019, he received the award “Le grand Prix Raymond Castaing” in Materials Science from the French Society of Microscopy. His research topics consist in the development of new concepts and analysis methods in electron microscopy for solving the dynamical changes in materials at the nanometre scale and in three dimensions.

By combining electron tomography with electron energy loss spectroscopy he pioneered chemical 3D analysis at the nanoscale. Through collaborations with various partners, he acquired a strong knowledge in the field of nanomaterials and nanostructures. By using new generation TEM cells, the implementation of in situ TEM methodologies has become one of his priorities, in particular for performing analysis in gas atmospheres and high temperatures/pressures conditions and under electrochemical conditions. He is involved in several National and International Research programs with both academic partners and private companies.

About the author

Julien Parmentier, 51 years old, is currently Senior Associate Professor at the University of Upper-Alsace (UHA, Mulhouse, France) and at the Institute of Material Science of Mulhouse (IS2M). He earned his PhD in Chemistry of Solids from the University of Strasbourg (France) in 1996. After post-doctoral positions, he accepted in 1999 an Associate Professor position at Upper-Alsace University.

His research deals with the development of synthesis routes for the preparation of original inorganic non-oxide materials (carbon, carbide, nitride, sulfide) with controlled properties for applications in the field of adsorption, energy storage and catalysis. Investigations about tailored- characteristics of materials concern fields such as (hierarchal) porosity, composition, nano- and meso-structurations, and macroscopic shape. Formation mechanism and potential applications of these materials are investigated thanks to academic and industrial partnerships.

Reference

Julien Kiener, Maria Girleanu, Ovidiu Ersen, Julien Parmentier. Direct Insight into the Confinement Effect of WS2 Nanostructures in an Ordered Carbon Matrix. Crystal Growth Design 2020, volume 20, page 2004−2013.

Go To Crystal Growth Design

Check Also

Numerical simulation on electrostatic alignment control of cellulose nano-fibrils in flow - Advances in Engineering

Numerical simulation on electrostatic alignment control of cellulose nano-fibrils in flow