Thierry Romero

Synthesis of porous carbon nanotubes foam composites with a high accessible surface area and tunable porosity

The macroscopic shaping of carbon nanostructure materials with tunable porosity, morphologies, and functions, such as carbon nanotubes (CNT) or carbon nanofibers (CNF), into integrated structures is of great interest, as it allows the development of novel nanosystems with high performances in filter applications and catalysis. In the present work, we report on a low temperature chemical fusion (LTCF) method to synthesize a self-macronized carbon nanotubes foam (CNT-foam) with controlled size and shape by using CNT as a skeleton, dextrose as a carbon source, and citric acid as a carboxyl group donor reacting with the hydroxyl group present in dextrose. The obtained composite has a 3D pore structure with a high accessible surface area (>350 m2 g−1) and tunable meso- and macro-porosity formed by the addition of a variable amount of ammonium carbonate into the starting mixture followed by a direct thermal decomposition. The as-synthesized CNT-foam also exhibits a relatively high mechanical strength which facilitates its handling and transport, while the nanoscopic morphology of the CNT significantly reduces the problem of diffusion and contributes to an improvement of the effective surface area for subsequent applications. These CNT-foams are successfully employed as selective and recyclable organic absorbers with high efficiency in the field of waste water treatment.

Hierarchical porous carbon fibers/carbon nanofibers monolith from electrospinning/CVD processes as a high effective surface area support platform

Nanocarbons with unique physicochemical properties have been considered typical sustainable materials for use as catalyst supports and directly as catalysts. Unfortunately, the powder form of nanocarbons renders them difficult to use in industrial processes due to the high pressure drop, their difficulty of handling as well as health injuries caused to human beings. Herein, hierarchical carbon fibers/carbon nanofibers (CF/CNF) composites, with high effective surface areas and controlled macroscopic shapes, were successfully synthesized through a combination of electrospinning (ES) and chemical vapour deposition (CVD). A web of poly(acrylonitrile)/poly(vinyl pyrrolidone) (PAN/PVP) composite fibers embedding a nickel salt was firstly produced by electrospinning. After a carbonization step, the polymeric material was converted into porous carbon embedding nickel nanoparticles, available on the fiber surface. Then, the catalytic growth of the CNFs was carried out from the nickel nanoparticles by CVD leading finally to the formation of a hierarchical carbon web of hairy fibers with a high effective surface area. The density, diameters and lengths of the CNFs attached on the surface of the CFs could be finely tuned by adjusting the CVD conditions. The specific surface area of the CF/CNF monolith amounted to more than 200 m2 g−1 along with high accessibility due to the small dimensions. The hierarchical CF/CNF composite has been used as a metal-free catalyst for the steam- and oxygen-free catalytic dehydrogenation of ethylbenzene to styrene. The catalytic results have pointed out that such a monolith can be efficiently used as a material platform for different applications , going from catalysis to wastewater treatment, thanks to the high effective surface area and reactivity of the CNF with prismatic planes.

Colloid Approach to the Sustainable Top-Down Synthesis of Layered Materials

The successful future of 2D materials, which are crucial for accelerating technology development and societal requirements, depends on their efficient preparation in an economical and ecological way. Herein, we present a significant advance in the top-down exfoliation and dispersion method via an aqua colloid approach. We demonstrate that a broad family of natural oil-in-water emulsification agents with an elevated hydrophilic/lipophilic balance acts in the exfoliation of layered materials and the formation of their concentrated colloids. The concentration exceeds 45 g/L for exfoliated few-layered graphene sheets possessing a micrometer size. The exfoliation of carbon nanofibers provides one of the best known unsupported and N-undoped metal-free catalysts to date in the selective dehydrogenation of ethylbenzene to styrene. Other examples include aqua colloids of exfoliated/dispersed nitrides, carbides, or nanodiamonds.