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A batch process is developed to generate sulphur functionalized graphene nanoflakes (S-GNFs), corresponding to nanoparticles of stacked graphene. The growth and functionalization of the catalysts are done in a single thermal plasma reactor. The GNFs are first grown through the decomposition of methane in the thermal plasma volume followed by homogeneous nucleation of the nanoparticles in the well-controlled recombining plasma stream allowing the 2-dimensional evolution of the nanoparticle morphology. The precursor feeding conditions are then changed to liquid carbon disulphide in order to generate sulphur-based functional groups on the nanoparticles. The plasma conditions and carbon disulphide injection are varied, and samples with tuneable amount of sulphur between 4 and 28 at% are obtained. The functional groups generated include polythiophene polymer partly covering the GNFs, sulphur functionalities implemented directly on the graphitic structure, and traces of orthorhombic sulphur. The S-GNFs exhibit higher electrocatalytic activity toward the oxygen reduction reaction in alkaline medium for the samples containing the highest amounts of sulphur.

In the current study, it was found that the physiochemical properties of TiO2 are effected with formic acid as a chelating agent in a sol–gel process. From XRD studies it was revealed that due to the chelation of formate group with titanium precursor, anatase/brookite mixture of 86:14 is obtained while the control sample which has been prepared without formic acid showed pure anatase at 400 °C. FTIR studies indicated that, the formate group favored a monodentate mode of coordination with titanium precursor under the effect of addition of increasing amount of formic acid, while under the effect of increasing titanium precursor content the formate group is chelated with titanium atoms in a bidentate bridging mode. In addition, from the FTIR study it was demonstrated that increasing the amount of water in the hydrolysis step, a reduction in the intensity of the carboxylate (COO−) stretches was observed indicating that the titania formate bridging complex becomes weaker, resulting in a weakened titanium gel network structure which could readily collapse during calcination favoring early rutile formation. Raman spectroscopy showed that as a result of sample composite nature and presence of oxygen vacancies as demonstrated by PL analysis causes the broadening and frequency shifting of the Raman bands. Photocatalytic studies demonstrated that the formic acid modified sample composed of anatase/rutile mixture of 94:6 calcined at 600 °C show significantly higher catalytic activity compared to the control sample prepared under similar conditions. Kinetic analysis show first order kinetics for the decomposition of methylene blue, a rate constant (kapp) of 0.074 min−1 was obtained with anatase/rutile (94:6) mixture which is even higher than the Degussa P25 (0.067 min−1).

The control of nanoparticle synthesis using thermal plasmas is difficult and often leads to problems of chemical and structural purity, and poor process robustness in terms of consistency of product from run to run. Good reactor design allowed to overcome these issues and to develop a new material based on graphene with a flake-like structure (labeled graphene nanoflakes, GNF) supporting nitrogen for catalytic applications, for example as platinum replacement in fuel cells. These structures showed not only to be active, but also stable in polymer electrolyte fuel cell operation. Characterization of these structures, in situ fuel cell studies and modeling analysis all indicate that achievement of stability relates on the crystalline two-dimensional graphene structure. This paper first reviews the basic aspects behind the structural objectives, describes the synthesis process design leading to this crystalline structure, and provides a two-dimensional analysis on the graphitic growth based on fundamental theory and CFD calculations. These calculations indicate that an independent control of the graphene structure thickness (number of atomic planes) and sheet lengths is possible in a thermal plasma reactor.

In this work, we use an inorganic titanium precursor (titanium oxysulfate, TiOSO4) for the preparation of doped TiO2 by the sol–gel method. Molybdenum (Mo), iron (Fe) and vanadium (V) in the concentration range of 0.0312–2.0 mol% are added as dopants. The prepared samples were characterized by XRD, FTIR, N2 isotherms, SEM–EDX, TEM, UV–Vis DRS and PL techniques. X-ray diffraction revealed that an increase in the concentration of Mo causes the transformation of brookite into anatase phase. In contrast, Fe and V favor the formation of brookite phase. A decrease in crystallite size was observed on the addition of dopant ions compared to that of pure TiO2 (7 nm), for 0.0312 mol% concentration of dopant in TiO2, a crystallite size of 6.3 nm (Mo), 6.2 nm (Fe) and 6.4 nm (V) was calculated. A noticeable change in anatase lattice parameter along the “c” direction was observed with increasing dopant concentration, this is evidence that the dopant ions have entered the TiO2 crystal lattice by substitutional doping, which induces local distortion of the crystal structure and variation in interatomic distances. An increase in BET surface area and a decrease in pore size were observed with increasing dopant concentration, this may be due to their substitutional doping in crystal lattice and or their presence in the grain boundaries hindering the crystal growth. Diffuse reflectance studies indicate that doped TiO2 showed visible light absorption compared to that of pure TiO2 (3.1 eV). For 0.25 mol% concentration of dopant in TiO2, energy values of 2.6 eV (Mo), 2.95 eV (Fe) and 2.92 eV (V) were obtained. PL analysis clearly shows that the dopant ions have the capability to alter the oxygen vacancies and to produce Ti+3 surface species which trap the photogenerated electron and transfer the electron to surface absorbed oxygen and results in the decrease of electron hole pair recombination rate. Visible light photoactivity tests for the discoloration of methylene blue demonstrated that the doped samples showed enhanced photoactivity compared to undoped TiO2 and commercially available Degussa P25, because of composite nature, surface hydroxyl groups, narrowed band gap and decreased recombination rate of photogenerated electron–hole pairs. The highest photocatalytic activity was observed with 0.25 mol% dopant concentration, the calculated reaction rate constant (kobs) was 0.97 min−1 (Mo), 1.18 min−1 (Fe) and 1.17 min−1 (V) compared to 0.18 min−1 (undoped TiO2) and 0.17 min−1 (Degussa P25).

Vanadium doped titanium dioxide (V–TiO2) photocatalyst was synthesized by the sol–gel method using ammonium vanadate as vanadium source. The prepared samples were characterized by XRD, N2 adsorption–desorption method, UV–Vis DRS, Fourier transform infrared (FTIR), scanning electron microscope–energy dispersive X-ray and photoluminescence (PL) analysis. The results show that V5+ ions were successfully incorporated into the crystal lattice of TiO2 as a consequence, not only an obvious decrease in the band gap and a red shift of the absorption threshold into the visible light region was recorded for the V modified TiO2, but, also a decrease in photogenerated electrons and holes recombination rate was observed as demonstrated by PL analysis. FTIR study indicated that in undoped TiO2 sample the acetate group favored a bidentate bridging mode of binding with titanium atoms, whereas a bidentate chelating mode of linkage was observed in V–TiO2 powders. The crystallite size of the samples calcined at 300 and 500 °C were decreased beyond the molar ratio of 200:1 (V:Ti), this may be due to dopant presence in the grain boundaries hindering the crystal growth. The photocatalytic activities for both pure and vanadium doped TiO2 powders were tested in the discoloration of a reactive dyestuff, methylene blue, under visible light. The 100:1 (V:Ti) doped photocatalyst, calcined at 300 °C showed enhanced photocatalytic activity under visible light with a rate constant (kobs) of 5.024 × 10−3 min−1 which is nearly five times higher than that of pure TiO2, as result of low band gap value, high specific surface area and a decrease in recombination rate.

Carbon black nanopowders were produced using two thermal plasma processes based on DC, respectively ICP plasma torches. Although the produced particles were in the nanometer size range, the values obtained for the surface area of the particles using a Brunauer Emmett Teller technique were very small. This indicated the presence of contaminants in the experimental powders, as confirmed by Raman spectroscopy and thermogravimetric Analysis. A thermal treatment process was developed in order to extract these volatile compounds, which were then identified using a Gas Chromatography–Mass Spectrometry method. The experimental powders were analyzed using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy before and after the thermal treatment in order to determine the effect of the heat treatment on the powder structural properties.

Carbon material was produced using an inductively coupled thermal plasma torch system of 35 kW and a conical shape reactor. The carbon nanopowders were obtained by plasma decomposition of methane at various flow rates and show a uniform microstructure throughout the reactor. The product has a crystalline graphitic structure, with a stacking of between 6 and 16 planes and a nano-flake morphology with particles dimensions of approximately 100 nm long, 50 nm wide and 5 nm thick. Nitrogen was also introduced in some synthesis experiments along with the methane precursor using flow rates of 0.1 and 0.2 slpm. The resulting product has the same structural properties and the nitrogen is incorporated into the graphitic structure through pyridinic type bonds.

Carbon black (CB) nanopowders were obtained by plasma decomposition of methane at various flow rates using inductively coupled thermal plasma torch system of 35 kW. Nitrogen was also introduced in some experiments along with the methane. Using a cylindrical shape reactor the obtained powders were composed mainly of spherical particles, non-uniform in terms of particles size with diameters between 30 and 150 nm. The shape and size of this reactor resulted in the presence of recirculation areas enabling the formation of large CB particles and other secondary volatile compounds. Changing the reactor to a conical geometry resulted in the production of CB powders showing a crystalline and flake-like morphology made of sheets having 6–16 graphitic planes. The conical shape avoids the presence of recirculation areas and promotes the formation of a uniform powder morphology throughout the reactor.