Sahar A. El-Molla

Catalytic Promotion of Activated carbon by Treatment with Some Transition Metal Cations

A commercial activated carbon sample was treated with 1% dilute nitric acid followed by impregnation with 5 wt% and 10 wt% cobalt, nickel, or copper nitrates, which were dissolved in the minimum amounts of distilled water sufficient to cover the surfaces of activated carbon granules followed by drying at 100°C till weights became constant. The transition metal ions-treated samples were heated at 400°C in a flow of argon for 3 h. The analytical tools for characterization of different solids were X-ray diffraction, nitrogen adsorption at −196°C, infrared spectroscopy, catalytic conversion of isopropanol, and catalytic decomposition of H2O2 at 25–45°C. The results revealed that the activated carbon treated with 5 wt% and 10 wt% transition metal oxides heated at 400°C in a argon flow consisted of a mixture of very poor crystalline CoO, Co3O4, NiO, Cu2O, and CuO phases of nano-crystalline nature. The treatment of activated carbon with cobalt, copper, or nickel oxide led to a small increase in its BET surface area. All solids investigated acted mainly as dehydrogenation catalysts with selectivities above 90%. The percentage increase in the catalytic activity, measured at 225°C, due to the treatment with 5% transition metal oxide attained 6%, 24.6%, and 40.6% for cobalt, nickel, and copper oxides, respectively. The observed measurable increase in the catalytic activity of the commercial activated carbon system treated with small amounts of CoO in the catalysis of H2O2 decomposition can be considered as a consequence of the significant increase in the concentration of catalytically active sites taking part in the catalysis of H2O2 decomposition, but it did not modify the mechanism of the catalytic decomposition.

Decomposition of H2O2 on Pure and ZnO-Treated Co3O4/Al2O3 Solids

The effects of Co3O4 loading, precalcination temperature and ZnO treatment on the catalytic properties of the Co3O4/Al2O3 system were investigated. The amounts of Co3O4 were varied between 5.57 wt% and 32.0 wt% and the resulting solids subjected to heat treatment at temperatures in the range 400–600°C. The amounts of ZnO were varied between 0.36 wt% and 2.12 wt%. The results obtained indicated that ZnO treatment of Co3O4/Al2O3 solids followed by precalcination at 400°C resulted in a progressive decrease in the particle size of the Co3O4 crystallites in the resulting samples. The catalytic activity of such solids towards H2O2 decomposition decreased progressively as the precalcination temperature employed was increased in the range 400–600°C. The relationship between the catalytic activity expressed as a plot of the reaction rate constant, k, versus the amount of Co3O4 in the samples showed a progressive increase in the range 5.6–17.7 wt% followed by an abrupt increase when the extent of loading exceeded this limit. Treatment with ZnO effected a measurable increase (42%) in the specific surface area (SBET) of the treated solids. However, such treatment also resulted in a considerable increase in the value of the reaction rate constant for the catalyzed reaction. Thus, the maximum increase in the value of k20°C due to doping with 2.12 wt% ZnO attained a value of 543% while the corresponding increase in the value of the reaction rate constant per unit surface area, k̄20°C, was 331%. Precalcination at 400–600°C of Co3O4/Al2O3 solids subjected to ZnO treatment did not modify the mechanism whereby the catalytically active constituents (surface cobalt species) were involved in the reaction although their concentration was altered without affecting their energetic nature.

Synthesis of highly active thin film based on TiO2 nanomaterial for self-cleaning application

Highly active self-cleaning surfaces were prepared from hydrothermally treated TiO2 nanomaterials for different times (0, 12, 24 and 36 h) under acidic condition. TiO2 thin films were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). TiO2 thin film (hydrothermal 24h) exhibited hybrid morphology from accumulated plates, clusters, rods and spheres. The photo self-cleaning activity in term of quantitative determination of the active oxidative species (OH) produced on the thin film surfaces was evaluated using fluorescent probe method. The results show that, the highly active thin film is the hydrothermally treated for 24 h at 200 °C. The structural, morphology and photoactivity properties of nano-TiO2 thin films make it promising surfaces for self-cleaning application. Mineralization of commercial textile dye (Remazol Red RB-133, RR) from highly active TiO2 thin film surface was applied. Moreover, the durability of this nano-TiO2 thin film (hydrothermal 24h) was studied.

Evaluation of the photocatalytic activity of Ln3+–TiO2 nanomaterial using fluorescence technique for real wastewater treatment

Evaluation the photocatalytic activity of different Ln(3+) modified TiO2 nanomaterials using fluorescence based technique has rarely been reported. In the present work, xmol Ln(3+) modified TiO2 nanomaterials (Ln = Nd(3+), Sm(3+), Eu(3+), Gd(3+), Dy(3+) and Er(3+) ions; x = 0.005, 0.008, 0.01, 0.02 and 0.03) were synthesized by sol-gel method and characterized using different advanced techniques. The photocatalytic efficiency of the modified TiO2 expressed in the charge carrier separation and OH radicals formation were assigned using TiO2 fluorescence quenching and fluorescence probe methods, respectively. The obtained fluorescence measurements confirm that doping treatment significantly decreases the electron-hole recombination probability in the obtained Ln(3+)/TiO2. Moreover, the rate of OH radicals formation is increased by doping. The highly active nanoparticles (0.02Gd(3+)/TiO2 and 0.01Eu(3+)/TiO2) were applied for industrial wastewater treatment using solar radiation as a renewable energy source.

Effect of calcination temperature and MoO3-doping of Co3O4/Al2O3 system on its surface and catalytic properties

Abstract The effect of MoO 3 -doping (0.5–7.5 mol%) of Co 3 O 4 /Al 2 O 3 system on its surface and catalytic properties were investigated. The extent of cobalt oxide was fixed at about 16.6 mol%, and the pure and doped solids were heated at 400 and 600 °C. The techniques employed were XRD, N 2 adsorption at −196 °C and catalytic decomposition of H 2 O 2 at 20–50 °C. The results revealed that most of the dopant added was retained on the uppermost surface layers on the treated samples precalcined at 600 °C. The doping process resulted in a limited modification in the surface characteristics for the treated solids. The addition of 2 mol% MoO 3 to the investigated system led to a considerable increase in the catalytic activity by three- and five fold for the solids calcined at 400 and 600 °C, respectively. However, the addition of further amounts of dopant resulted in a progressive measurable decrease in the catalytic activity due to an effective conversion of some of surface Co 3 O 4 into cobalt molybdate. The considerable increase in the catalytic activity due to treatment with 2 mol% MoO 3 could result from creation of new ion pairs and also to an effective increase in the surface concentration of cobalt species. The doping process did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active sites without changing their energetic nature.

Effect of Ag-doping of nanosized FeMgO system on its structural, surface, spectral, and catalytic properties

The effects of Ag-doping on the physico-chemical, spectral, surface, and catalytic properties of the FeMgO system with various Fe2O3 loadings were investigated. The dopant (Ag) molar ratio varied between 0.01 % and 0.05 %. The techniques employed for characterisation of catalysts were TG/DTG, XRD, ESR, N2 adsorption at −196°C, and catalytic decomposition of H2O2 at 25–35°C. The results obtained revealed that the investigated catalysts consisted of nanosized MgO as the major phase, apart from the MgFe2O4 and/or Fe3O4 phases. ESR result of the FeMgO system revealed the presence of paramagnetic species as a result of Ag-doping. The textural properties including SBET, porosity and St were modified by Ag-doping. The doping process with Ag-species improved the catalytic activity of the FeMgO system. Increasing the calcination temperature from 400°C to 800°C increased the catalytic activity (k*30 °C) of 0.05 AgFeMgO in H2O2 decomposition by 21.2 times.

Surface and Catalytic Properties of the CuO/Al2O3 System Treated with Different Proportions of ZnO

The effects of ZnO treatment on the surface and catalytic properties of CuO/Al2O3 were investigated. All the samples studied contained a fixed amount of CuO (13.5 wt%) while the amount of ZnO dopant was varied in the range 0.68–6.46 wt%. The pure and variously doped solids were subjected to heat treatment (precalcination) in the temperature range 400–600°C. The samples obtained were investigated by XRD methods, nitrogen adsorption at −196°C and studies of their catalytic influence on the decomposition of H2O2 at 20–40°C. The results obtained indicated that ZnO treatment of CuO/Al2O3 followed by precalcination at 500°C led to a progressive decrease in the degree of crystallinity of the CuO phase to an extent proportional to the amount of ZnO present in the system. This suggests that such treatment led to a significant decrease in the particle size of the CuO crystallites produced. The BET surface areas of the treated solids increased on increasing the amount of ZnO present in the system. Similarly, the catalytic activity, as expressed in terms of the reaction rate constant for the decomposition of H2O2, increased on increasing the amount of dopant added to reach a maximum value (ca. 67%) when 1.7 wt% ZnO had been added to the system, and then subsequently decreased on further addition of dopant. It was found that ZnO treatment of CuO/Al2O3 did not modify the activation energy of the catalyzed reaction but rather changed the concentration of catalytically active constituents without changing their energetic nature.

Effects of γ-Irradiation on the Surface and Catalytic Properties of Co3O4/MgO Systems Aged for One Year

The effects of γ-rays (20–160 Mrad) on the surface and catalytic properties of two Co3O4/MgO systems were investigated. The formulae of the investigated solids were 0.05Co3O4/MgO and 0.2Co3O4/MgO, respectively, both prepared by the impregnation method and calcined at 500°C. The irradiated samples were left for one year in sealed tubes before any measurements were undertaken. γ-Irradiation of the investigated solids resulted in a progressive decrease in the particle size of the Co3O4 and MgO phases. This treatment also led to a measurable increase in the specific surface area of the treated solids to an extent proportional to the γ-ray dosage. Treatment of the Co3O4/MgO system with different doses of γ-rays brought about a significant increase in the catalytic activity expressed both as the reaction rate constant and as the reaction rate constant per unit surface area. However, the curve relating to the catalytic activity and dosage of γ-rays showed maxima located at 40 and 80 Mrad for samples having the formula 0.05Co3O4/MgO and 0.2Co3O4/MgO, respectively. Furthermore, samples exposed to 160 Mrad showed a larger catalytic activity than the unirradiated samples. The results demonstrate the role of γ-rays in inhibiting the deterioration of the catalytic activity of the investigated systems as a function of aging time. The irradiation process did not modify the activation energy of the catalyzed reaction but altered the concentration of active centres on the surfaces of the solids without changing their energetic nature.

Effect of Ag-doping of Nanosized FeAlO System on its Structural, Surface and Catalytic Properties

The effects of Ag2O-doping on the physicochemical, surface and catalytic properties FeAlO system with various extent of Fe2O3 loading have been investigated. The dopant concentration was changed between 1.5 and 4.0 mol % Ag2O. Pure and variously doped solids were subjected to heat treatment at 400-800?C. The techniques employed for characterization of catalysts were TG/DTG, XRD, N2-adsorption at ?196?C and the catalytic decomposition of H2O2 at 25-40?C. The obtained results revealed that, the investigated catalysts consisted of nanosized ?-Al2O3 phase. The textural properties including SBET, porosity and St were modified by Ag2O-doping. The doping process with Ag-species improved the catalytic activity of FeAlO system. Increasing the precalcination temperature from 400 to 800?C increased the catalytic activity (k30°C) of 3.5 % AgFeAlO with 1.9 fold towards H2O2 decomposition. Furthermore, the maximum increase in the k30°C value due to doping with 3.5 mol% Ag2O attained about 15.1 fold for the solids calcined at 800°C.