Lai Truong-Phuoc

A few-layer graphene–graphene oxide composite containing nanodiamonds as metal-free catalysts

We report a high yield exfoliation of few-layer-graphene (FLG) with up to 17% yield from expanded graphite, under 5 h sonication time in water, using graphene oxide (GO) as a surfactant. The aqueous dispersion of GO attached FLG (FLG–GO), with less than 5 layers, is used as a template for further decoration of nanodiamonds (NDs). The hybrid materials were self-organized into 3D-laminated nanostructures, where spherical NDs with a diameter of 4–8 nm are homogeneously distributed on the surface of the FLG–GO complex (referred to as FLG–GO@NDs). It was found that GO plays a dual role, it (1) mediated exfoliation of expanded graphite in aqueous solution resulting in a FLG–GO colloid system, and (2) incorporated ND particles for the formation of composites. A high catalytic performance in the dehydrogenation of ethyl-benzene on FLG–GO@ND metal-free catalyst is achieved; 35.1% of ethylbenzene conversion and 98.6% styrene selectivity after a 50 h reaction test are observed which correspond to an activity of 896 mmolST gcatalyst−1 h−1, which is 1.7 and 5 times higher than those of the unsupported NDs and traditional catalysts, respectively. The results demonstrate the potential of the FLG–GO@ND composite as a promising catalyst for steam-free industrial dehydrogenation applications.

Few layer graphene decorated with homogeneous magnetic Fe3O4 nanoparticles with tunable covering densities

Magnetic iron oxide nanoparticles (NPs) with narrow size distribution (8 ± 2 nm), well defined chemical composition and crystalline structure are synthesized and homogeneously dispersed onto the surface of few-layer graphene (FLG) via a solvothermal decomposition method. The iron oxide NPs are strongly anchored to the graphene surface and confer a magnetic character to the final composite. The metal oxide/support interaction is high enough to avoid the NPs coalescence and/or agglomeration and thus to preserve the NPs size and dispersion after thermal treatment up to 400 °C. The introduced iron oxide NPs on FLG also play a role of nano-spacers to prevent the re-stacking of the graphene sheets upon the drying process. It is expected that such a composite could find use in several application fields such as catalyst support for liquid-phase reactions with easy magnetic separation, in electrochemical energy storage and in waste water treatment. The ability of the synthesized iron oxide NP/FLG composite to adsorb foreign elements (organic pollutants) is demonstrated in the methylene blue (MB) adsorption and its catalytic properties are evaluated in the selective oxidation of H2S.

Nitrogen-doped carbon nanotubes on silicon carbide as a metal-free catalyst

Abstract A hierarchical metal-free catalyst consisting of nitrogen-doped carbon nanotubes decorated onto a silicon carbide (N-CNTs/SiC) macroscopic host structure was prepared. The influence of N-CNTs incorporation on the physical properties of the support was evaluated using different characterization techniques. The catalyst was tested as a metal-free catalyst in the selective oxidation of H 2 S and steam-free dehydrogenation of ethylbenzene. The N-CNTs/SiC catalyst exhibited extremely good desulfurization performance compared to a Fe 2 O 3 /SiC catalyst under less conducive reaction conditions such as low temperature, high space velocity, and a low O 2 -to-H 2 S molar ratio. For the dehydrogenation of ethylbenzene, a higher dehydrogenation activity was obtained with the N-CNTs/SiC catalyst compared to a commercial K-Fe/Al 2 O 3 catalyst. The N-CNTs/SiC catalyst also displayed good stability as a function of time on stream for both reactions, which was attributed to the strong anchoring of the nitrogen dopant in the carbon matrix. The extrudate shape of the SiC support allowed the direct macroscopic shaping of the catalyst for use in a conventional fixed-bed reactor without the problems of catalyst handling, transportation, and pressure drop across the catalyst bed that are encountered with nanoscopic carbon-based catalysts.

Layer-by-Layer Photocatalytic Assembly for Solar Light-Activated Self-Decontaminating Textiles

Novel photocatalytic nanomaterials that can be used to functionalize textiles, conferring to them efficient solar-light-activated properties for the decontamination of toxic and lethal agents, are described. Textiles functionalized with one-dimensional (1D) SnS2-based nanomaterials were used for photocatalytic applications for the first time. We showed that 1D SnS2/TiO2 nanocomposites can be easily and strongly affixed onto textiles using the layer-by-layer deposition method. Ultrathin SnS2 nanosheets were associated with anatase TiO2 nanofibers to form nano-heterojunctions with a tight interface, considerably increasing the photo-oxidative activity of anatase TiO2 due to the beneficial interfacial transfer of photogenerated charges and increased oxidizing power. Moreover, it is easy to process the material on a larger scale and to regenerate these functionalized textiles. Our findings may aid the development of functionalized clothing with solar light-activated photocatalytic properties that provide a high level of protection against chemical warfare agents.

Activation of few layer graphene by μW-assisted oxidation in water via formation of nanoballs - Support for platinum nanoparticles.

The functionalization of carbon nanomaterials in controlled and selective manner and in order to stabilize small metal nanoparticles is of high interest particularly in the catalysis field. We present the μ-waves assisted few layer graphene (FLG) oxidation in water, which results in a partial sheets exfoliation and formation of oxygen functionalized carbon nanoballs, supported on highly graphitized graphene sheets. This double morphology material allows homogenous anchoring of Pt nanoparticles, while the advantages of planar and highly crystallized FLG are preserved. For comparison, acid treated FLG (conventional heating) exhibits highly hydrophobic and inert surface with carboxylic groups as anchoring sides localized at the FLG edges. Despite similar oxygen content, the performed physicochemical analyses depict different nature and localization of the oxygen/defects functionalities introduced in water (in μ-waves) and acid treated FLGs. Finally, the addition of FLG during the preparation of Pt particles-carried out by μ-wave assisted polyol method yields small nanoparticles with average size of 1nm.

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.

Nitrogen-Doped Carbon Composites as Metal-Free Catalysts

This chapter provides an overview of recent developments of functionalized and doped carbon-based materials as potential metal-free catalysts in several fields of application. The panel of applications of those carbon nanomaterials is wide, such as medicine, advanced materials, and electronics, because of their unique physical and chemical properties. A particular attention is paid in this overview to their utilization in catalysis since they offer an alternative with much higher efficiency than conventional transition metal or oxide-based catalysts due to their architecture, which improves heat and mass transfer phenomena. Their high chemical inertness allows them to withstand operations in aggressive media. Surface functionalization or matrix doping with N and O species can finely tune the surface reactivity. These carbon-based metal-free catalysts also display an exceptionally high resistance toward deactivation due to the strong localization of the active sites within the catalyst matrix. Future challenges are likely related to the selection of appropriate synthesis route to get maximum concentration of N-containing species through the use of nontoxic and abundant raw materials. Today the development of more friendly environmental synthesis routes represents an outstanding outcome for further upscaling. The peculiar catalytic properties of those materials have been illustrated through relevant examples such as hydrogen oxidation, desulfurization, and liquid-phase transesterification reactions. The integration of those materials in the reactor design through controlled macroscopic shaping is also an important issue.