Search

[Co.sub.3][O.sub.4] nanomaterials were prepared bydifferent methods. The samples were nominated as[Co.sub.3][O.sub.4] (Pr), [Co.sub.3][O.sub.4] (Co), and [Co.sub.3][O.sub.4] (Hy) due to preparation by precipitation, combustion, and a hydrothermal method, respectively. These nanomaterials were characterized by studying their structural, morphological, and surface properties. The catalytic activity was evaluated by following [H.sub.2][O.sub.2] decomposition through fluorometric and gasometric methods. The obtained results showed that the catalytic efficiency of the catalysts was affected by their preparation methods. The order of catalytic activities of the investigated samples using fluorometric method is compatible with that obtained by gasometric method. [Co.sub.3][O.sub.4] (Hy) exhibited much higher catalytic activity due to the high surface area, small particle size, different oxidation states, different shapes, and the high production of hydroxyl radical. The antimicrobial activity is studied against standard bacterial and fungal strains, and the studies showed that the hydrothermal method enhanced antimicrobial activity more than other preparation methods. Key words: nanostructures, ceramics, kinetics, fluorescence, biological activity. Nous avons prepare des nanomateriaux a base de [Co.sub.3][O.sub.4] par differentes methodes. Les echantillons ont ete designes [Co.sub.3][O.sub.4] (Pr), [Co.sub.3][O.sub.4] (Co) et [Co.sub.3][O.sub.4] (Hy) selon qu'ils ont ete prepares par precipitation, par combustion ou par une methode hydrothermale, respectivement. Nous avons caracterise ces nanomateriaux en etudiant leurs proprietes structurales et morphologiques, ainsi que leurs proprietes de surface. Nous avons evalue leur activite catalytique en suivant la decomposition du [H.sub.2][O.sub.2] par des methodes fluorometriques et gazometriques. Les resultats obtenus ont montre que l'efficacite catalytique de ces catalyseurs etait influencee par leur methode de preparation. L'ordre des activites catalytiques des echantillons a l'etude determine a l'aide d'une methode fluorometrique concorde avec l'ordre obtenu par une methode gazometrique. L'activite catalytique du [Co.sub.3][O.sub.4] (Hy) s'est revelee beaucoup plus elevee en raison de sa grande surface de contact, de la petite taille de ses particules et de leurs differentes formes, de ses differents etats d'oxydation et de sa production elevee de radicaux hydroxyles. Nous avons etudie l'activite antimicrobienne de ces nanomateriaux contre differentes souches bacteriennes et fongiques standards. Les resultats de ces etudes ont montre que la methode hydrothermale donnait lieu a une activite antimicrobienne superieure comparativement aux autres methodes de preparation. [Traduit par la Redaction] Mots-cles : nanostructures, cinetique des ceramiques, fluorescence, activite biologique., Introduction [Co.sub.3][O.sub.4] spinel crystal structure nanoparticles ([AB.sub.2][O.sub.4]) pasture build on a cubic close packing array of oxide atoms (A: divalent cations presented at the tetrahedral 8a sites, B: trivalent cations [...]

Co3O4 nanomaterials were prepared by different methods. The samples were nominated as Co3O4 (Pr), Co3O4 (Co), and Co3O4 (Hy) due to preparation by precipitation, combustion, and a hydrothermal method, respectively. These nanomaterials were characterized by studying their structural, morphological, and surface properties. The catalytic activity was evaluated by following H2O2 decomposition through fluorometric and gasometric methods. The obtained results showed that the catalytic efficiency of the catalysts was affected by their preparation methods. The order of catalytic activities of the investigated samples using fluorometric method is compatible with that obtained by gasometric method. Co3O4 (Hy) exhibited much higher catalytic activity due to the high surface area, small particle size, different oxidation states, different shapes, and the high production of hydroxyl radical. The antimicrobial activity is studied against standard bacterial and fungal strains, and the studies showed that the hydrothermal method enhanced antimicrobial activity more than other preparation methods. [ABSTRACT FROM AUTHOR]

Abstract: The effect of compacting on pure and Ag2O doped Fe2O3/MgO nanoparticles calcined at 500°C and processed at room temperature and high-pressure using a hydraulic press was investigated. The catalysts were characterized by XRD, SBET, EPR, and CO2-TPD techniques and the iso-propanol conversion as the catalytic probe reaction. The results revealed that the crystallite size of compacted catalysts is smaller than that of powder ones. The BET surface area of samples decreases by compression. Electron paramagnetic resonance “EPR” result of the FeMgO nanoparticles revealed the presence of paramagnetic species as a result of Ag-doping. The total basicity of the powder catalyst was higher than that of the compact one. Compression affects the distribution of basic sites of powder catalysts. The catalytic activity and propene selectivity of pure powder catalysts are increased by compression. The compacted catalysts can be used as a reusable active catalyst in the iso-propanol conversion. [Copyright &y& Elsevier]

Abstract: Three types of Fe2O3/MgO (FeMgOIM, FeMgOCo and FeMgOHY) nanomaterials were prepared by impregnation, co-precipitation and hydrothermal methods, respectively. The microporous FeMgO adsorbents were successfully used to remove synthetic textile dye (Remazol Red RB-133) by adsorption from aqueous solution. The as-prepared adsorbents were characterized by XRD, FT-IR, N2 adsorption/desorption isotherms and TEM techniques. The results showed that a nanorod-like shape with high surface area and porous structure was obtained by hydrothermal treatment. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The equilibrium adsorption data were best fitted by Langmuir isothermal model. The removal efficiencies of dye of 50mgL−1 within 19min can be ranked as: FeMgOHY >FeMgOIM >FeMgOCo. Also, the results indicated that pseudo-first-order and intra-particle diffusion models can better describe the adsorption kinetics. The microporous FeMgOHY and FeMgOIM were found to be effective adsorbent for the removal of dye from aqueous solution due to their increase in the microporosity as well as modified surface morphologies. The highly active FeMgOHY nanomaterial was evaluated for chemical oxygen demand (COD) and color reduction of a real industrial wastewater. A reduction in color and COD of 87% and 40%, respectively was achieved after 3h from adsorption. [Copyright &y& Elsevier]

Highlights: [•] Preparation and characterization nano-sized Fe2O3/MgO system. [•] Impregnation, coprecipitation and hydrothermal methods are used for preparation. [•] H2O2 decomposition is sensitive to surface concentration of active species. [•] Methanol conversion is sensitive to solid–solid interactions. [•] All catalysts are highly selective to formaldehyde at 300°C. [•] The catalysts are active and stable even after their recycling two times. [ABSTRACT FROM AUTHOR]

Abstract: Fe2O3/MgO system was prepared by wet impregnation method followed by treatment with different amounts of Zr-dopant salt then heating at 500 and 700°C. The dopant concentrations were 0.48, 0.95 and 1.4mol% ZrO2. Pure and variously doped solids were characterized using XRD, N2-adsorption isotherms carried out at −196°C and catalytic decomposition of H2O2 in aqueous solution at 25–35°C. The results revealed that the nanosized MgO phase was only detected in the diffractograms of pure and doped solids calcined at 500°C. Heating pure and doped solids at 700°C produced nanosized MgFe2O4 phase together with MgO phase. Pure and ZrO2-doped solids calcined at 500 and 700°C are mesoporous adsorbents. The doping process brought about a measurable decrease in the S BET of Fe2O3/MgO system with subsequent increase in its catalytic activity. The catalytic activity of the investigated system toward H2O2 decomposition, expressed as reaction rate constant per unit surface area was found to increase as a function of dopant concentration. The maximum increase in the reaction rate constant per unit surface area measured for the reaction carried out at 30°C attained 125% for the heavily doped samples. This significant increase was based on the catalytic activity of pure catalyst sample measured under the same conditions. [Copyright &y& Elsevier]

Abstract: The effects of Li2O and ZrO2-doping on the surface and catalytic properties of CuO/MgO system have been investigated. The dopant concentration was changed between 0.6 and 3.6mol% Li2O and that of ZrO2 between 2.4–7.7mol%. Pure and variously doped solids were calcined at 673 and 773K. The techniques employed for characterization of different solids were XRD, nitrogen adsorption at 77K and catalytic conversion of iso-propanol at different reaction temperatures ranged between 423 and 573K. The results revealed that the addition increasing amounts of dopant (Li2O and ZrO2) to CuO/MgO solid led to an increase in the degree of dispersion of CuO phase and a decrease in the specific surface areas of the investigated solids. Li2O and ZrO2-doping increases the catalytic conversion of iso-propanol, which proceeds mainly via dehydrogenation to give acetone and aldol condensation of the produced acetone to give methyl isobutyl ketone (MIBK). Doping with 1.2mol% Li2O for the solids calcined at 673K increases both of total conversion and selectivity to MIBK at reaction temperature 473K with 24% and 25%, respectively. Doping with 7.7mol% ZrO2 for the investigated solids calcined at 673K increases both of total conversion and selectivity to MIBK at reaction temperature 473K with 32% and 99%, respectively. [Copyright &y& Elsevier]

Abstract: The effects of cobalt and manganese oxides-doping on surface and catalytic properties of Cr2O3/MgO system have been investigated. The dopant concentration was changed between 1 and 5mol% cobalt and manganese oxides. Pure and variously doped solids were subjected to heat treatment at 400 and 700°C. The techniques employed were X-ray diffraction (XRD), nitrogen adsorption at –196°C, catalytic conversion of iso-propanol at 200–400°C using flow technique and catalytic decomposition of H2O2 at 20–40°C. The results revealed that the doping process of the system investigated followed by calcinations at 400 or 700°C, enhanced the solid–solid interactions between catalyst constituents yielding (α-MgCrO4, β-MgCrO4) and MgCr2O4, respectively. Furthermore, manganese and cobalt oxide-doping for Cr2O3/MgO system increased its catalytic activity much towards H2O2-decomposition. The increase was, however, more pronounced in the case of manganese-doping. Opposite results have been observed in the case of iso-propanol conversion, which proceeds via dehydrogenation and dehydration reaction. The SBET of the investigated system was found to decrease by increasing the dopant concentration. The doping process did not modify the activation energy of the catalyzed reaction, but rather changed the concentration of the catalytically active constituents without changing their energetic nature. [Copyright &y& Elsevier]