The potential of vermiculites as environmentally friendly photocatalysts for hydrogen production and pollutant degradation was demonstrated by a photocatalytic test in an aqueous 50 % methanol solution (MeOH50). After 4 h of irradiation with the commercial TiO2 Evonik P25 catalyst, the H2 yield was of 656.9 ± 4.2 μmol/gcat. For vermiculites Vm1, Vm3, and Vm4, hydrogen yields were comparable (H₂ = 420.6 ± 5.8 μmol/gcat; H₂ = 414.2 ± 1.8 μmol/gcat, and 449.3 ± 1.8 μmol/gcat, respectively) but were lower in the presence of vermiculite-chlorite intermediate Vm2 (H₂ = 385.1 ± 6.6 μmol/gcat). After the extended 24-h irradiation, hydrogen yield was promoted by the negative tetrahedral charge, while the positive octahedral charge inhibited the photocatalytic decomposition of the MeOH50 into hydrogen in favor of the formation of CO and CH4 byproducts. The decrease in methanol yield in the MeOH50 was effectively assessed by the red shift of the C-O and C-H bands in the Raman spectrum, corresponding to the photocatalytic production of H2.

• Keywords
• Methanol water solution, Photocatalytic hydrogen production, Raman spectra, Vermiculite,
• Publication type
• Journal Article MeSH

Hematite (α-Fe2O3) catalysts prepared using the precipitation methods was found to be highly effective, and therefore, it was studied with methane (CH4), showing an excellent stable performance below 500 °C. This study investigates hematite nanoparticles (NPs) obtained by precipitation in water from the precursor of ferric chloride hexahydrate using precipitating agents NaOH or NH4OH at maintained pH 11 and calcined up to 500 °C for the catalytic oxidation of low concentrations of CH4 (5% by volume in air) at 500 °C to compare their structural state in a CH4 reducing environment. The conversion (%) of CH4 values decreasing with time was discussed according to the course of different transformation of goethite and hydrohematites NPs precursors to magnetite and the structural state of the calcined hydrohematites. The phase composition, the size and morphology of nanocrystallites, thermal transformation of precipitates and the specific surface area of the NPs were characterized in detail by X-ray powder diffraction, transmission electron microscopy, infrared spectroscopy, thermal TG/DTA analysis and nitrogen physisorption measurements. The results support the finding that after goethite dehydration, transformation to hydrohematite due to structurally incorporated water and vacancies is different from hydrohematite α-Fe2O3. The surface area SBET of Fe2O3_NH-70 precipitate composed of protohematite was larger by about 53 m2/g in comparison with Fe2O3_Na-70 precipitate composed of goethite. The oxidation of methane was positively influenced by the hydrohematites of the smaller particle size and the largest lattice volume containing structurally incorporated water and vacancies.

• Keywords
• alkaline precipitators, hematite nanoparticles, hydrohematites, methane oxidation, oxygen carrier,
• MeSH
• Methane * MeSH
• Oxidation-Reduction MeSH
• Particle Size MeSH
• Water chemistry   MeSH
• Ferric Compounds * chemistry   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• ferric oxide MeSH Browser
• Methane * MeSH
• Water MeSH
• Ferric Compounds * MeSH