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This work describes the synthesis and catalytic applications of magnetic composites based on carbon nanotubes and nanofibers prepared by CVD (chemical vapor deposition) using two natural materials with special morphology, i.e. layered vermiculite clay and fibrous chrysotile. Extensive characterization by XRD, Mossbauer, Raman, SEM, TEM, TG/DTA, contact angle showed that the composites are made mainly of carbon nanotubes and nanofibers fixed on the surface of the layered or fibrous matrix containing also carbon coated iron or cobalt cores responsible for the magnetic properties of the composites. The combination of hydrophilic Si and Al oxides surface with the hydrophobic carbon nanostructure produced amphiphilic materials with remarkable effect on the interaction and separation of two phases system, e.g. oil and water. For example, immiscible oil/water mixtures can be easily emulsified in the presence of the amphiphilic composites producing a much more efficient interface. It is demonstrated that this emulsification is very important for the biodiesel synthesis and hydrolysis of soybean oil. After reaction, the emulsion can be easily broken by a simple magnetic separation process. This emulsion–demulsification process can be also used for biodiesel purification and wastewater treatment. The composites are also used to prepare a magnetically recoverable supported Pd catalyst for the hydrogenation of the model molecule 1,5-COD.

In this work, new magnetic amphiphilic composites were prepared by chemical vapor deposition with ethanol on the surface of hydrophilic natural chrysotile matrix containing Fe catalyst. XRD, Raman, Mossbauer and SEM analyses suggest the formation of a complex nanostructured material composed of hydrophobic carbon nanotubes/nanofibers grown on the hydrophilic surface of the MgSi fiber mineral and the presence of Fe metallic nanoparticles coated by carbon. These nanostructured particles show amphiphilic properties and interact very well with both oil and aqueous phases. When added to emulsions the amphiphilic particles locate on the oil/water interface and, under a magnetic field, the oil droplets collapsed leading to the separation of the aqueous and oil phases. Preliminary work showed excellent results on the use of these particles to break wastewater emulsions in the biodiesel process.

The oxidation of aqueous sulfide promoted by activated carbon (AC) was investigated. Raman, infrared, X-ray diffraction, ultraviolet–visible spectroscopy and electron paramagnetic resonance analyses show that AC oxidizes aqueous sulfide to form a complex mixture of polysulfides and sulfur oxide species. This oxidation is strongly promoted by the presence of oxygen surface groups introduced by oxidation of the AC as shown by kinetic measurements. These results are discussed in terms of the similarities the AC have with enzymatic systems, i.e. redox surface groups (e.g. quinone) combined with an efficient electron conduction system.

In this work, it is demonstrated how a novel technique based on temperature-programmed chemical vapor deposition (TPCVD) can be used to investigate the synthesis of carbon nanotubes (CNTs) from methane on a classic catalyst FeMo(x)/MgO (x = 0.07, 0.35 and 1.00). TPCVD monitors carbon deposition by measuring H2 formed during CH4 decomposition and affords information on the different catalytic species, deactivation process, reaction kinetics and carbon yields. The obtained results showed for FeMgO catalyst a simple TPCVD peak related to the production of carbon beginning at 760 degrees C with maximum at 800 degrees C followed by a rapid deactivation resulting in a low carbon yield. The addition of Mo to Fe/MgO catalyst completely changes the TPCVD profile with the formation of a new catalytic species active at temperatures higher than 900 degrees C, which is stable and continuously decomposes CH4 to produce high carbon yields. Raman, TG/DTG, Mössbauer, SEM, TEM, XRD and TPR analyses suggested that this active catalytic phase is likely related to Fe-Mo and Fe-Mo-C phases active to produce single wall and mainly multiwall carbon nanotubes.

This work reports that the cyclohexane oxidation by iodosylbenzene and iodobenzene diacetate yields cyclohexanol as the sole product if catalyzed by the simple Mn(III) aminophenylporphyrins 5,10,15,20-tetrakis(2-aminophenyl)porphyrinatomanganese(III) chloride (Mn(III)(T2APP)Cl) and 5,10,15,20-tetrakis(4-aminophenyl)porphyrinatomanganese(III) chloride (Mn(III)(T4APP)Cl). This high selectivity was unmatched by other simple phenyl-substituted Mn(III) meso -tetraphenylporphyin-based catalysts (Mn(III)(T- X -PP)Cl, where X = H, 4-OMe, 4-Me, 4-CO 2 Me, 2-Me), which led to a mixture of both cyclohexanol and cyclohexanone. The absence of cyclohexanone in the Mn(III)(T2APP)Cl and Mn(III)(T4APP)Cl as well as the possibility of re-use of the catalysts was investigated. An intermolecular coordination of the amino moieties in Mn(III)(T2APP)Cl and Mn(III)(T4APP)Cl is suggested to play a role in the high selectivity of these systems.

Amphiphilic magnetic composites were produced based on chrysotile mineral and carbon structures by chemical vapor deposition at different temperatures (600–900 °C) and cobalt as catalyst. The materials were characterized by elemental analysis, X-ray diffraction, vibrating sample magnetometry, adsorption and desorption of N 2 , Raman spectroscopy, scanning electronic microscopy, and thermal analysis showed an effective growth of carbon structures in all temperatures. It was observed that at 800 and 900 °C, a large amount of carbon structures are formed with fewer defects than at 600 and 700 °C, what contributes to their stability. In addition, the materials present magnetic phases that are important for their application as catalysts and adsorbents. The materials have shown to be very active to remove the oil dispersed in a real sample of emulsified wastewater from biodiesel production and to remove methylene blue by adsorption and oxidation via heterogeneous Fenton mechanism.

International audience; Few layer graphene and natural graphite were chemically modified by oxidation with HNO3 at 80 and 140 °C and used to promote the oxidation of sulfide ions in aqueous solutions. TEM, potentiometric titration, XRD, BET and Raman spectroscopy show that HNO3 treatment even at 140 °C did not modify the graphene and graphite morphologies but produced significant amounts of different oxygen surface groups. The presence of these groups on few layer graphene and graphite strongly increased the Saq2− oxidation, showing activities comparable to a high surface area activated carbon with a similar amount of oxygen surface groups. The obtained results suggest that the sulfide oxidation efficiency requires a balance between two important effects, i.e. the presence of oxygen functionalities to initiate the Saq2− oxidation and the electrical conductivity that is important to further transfer the electrons removed from sulfide.