Tarek T. Ali

Influence of crystal structure of nanosized ZrO2 on photocatalytic degradation of methyl orange.

Nanosized ZrO2 powders with near pure monoclinic, tetragonal, and cubic structures synthesized by various methods were used as catalysts for photocatalytic degradation of methyl orange. The structural and textural properties of the samples were analyzed by X-ray diffraction, Raman spectroscopy, TEM, UV-vis, X-ray photoelectron spectroscopy (XPS), and N2 adsorption measurements. The performance of synthesized ZrO2 nanoparticles in the photocatalytic degradation of methyl orange under UV light irradiation was evaluated. The photocatalytic activity of the pure monoclinic ZrO2 sample is higher than that of the tetragonal and cubic ZrO2 samples under optimum identical conditions. The characterization results revealed that monoclinic ZrO2 nanoparticles possessed high crystallinity and mesopores with diameter of 100 Å. The higher activity of the monoclinic ZrO2 sample for the photocatalytic degradation of methyl orange can be attributed to the combining effects of factors including the presence of small amount of oxygen-deficient zirconium oxide phase, high crystallinity, large pores, and high density of surface hydroxyl groups.

Direct formation of thermally stabilized amorphous mesoporous Fe2O3/SiO2 nanocomposites by hydrolysis of aqueous iron III nitrate in sols of spherical silica particles.

Nanocomposite materials containing 10% and 20% iron oxide/silica, Fe2O3/SiO2 (w/w), were prepared by direct hydrolysis of aqueous iron III nitrate solution in sols of freshly prepared spherical silica particles (Stöber particles) present in their mother liquors. This was followed by aging, drying, calcination up to 600 degrees C through two different ramp rates, and then isothermal calcinations at 600 degrees C for 3 h. The calcined and the uncalcined (dried at 120 degrees C) composites were characterized by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), N2 adsorption/desorption techniques, and scanning electron microscopy as required. XRD patterns of the calcined composites showed no line broadening at any d-spacing positions of iron oxide phases, thereby reflecting the amorphous nature of Fe2O3 in the composite. The calcined composites showed nitrogen adsorption isotherms characterizing type IV isotherms with high surface area. Moreover, surface area increased with the increasing of the iron oxide ratio and lowering of the calcination ramp rate. Results indicated that iron oxide particles were dispersed on the exterior of silica particles as isolated and/or aggregated nanoparticles. The formation of the title composite was discussed in terms of the hydrolysis and condensation mechanisms of the inorganic FeIII precursor in the silica sols. Thereby, fast nucleation and limited growth of hydrous iron oxide led to the formation of nanoparticles that spread interactively on the hydroxylated surface of spherical silica particles. Therefore, a nanostructured composite of amorphous nanoparticles of iron oxide (as a shell) spreading on the surface of silica particles (as a core) was formed. This morphology limited the aggregation of Fe2O3 nanoparticles, prevented silica particle coalescence at high temperatures, and enhanced thermal stability.

Photocatalytic Activity of Doped and Undoped Titanium Dioxide 32 Nanoparticles Synthesised by Flame Spray Pyrolysis

*Email: felicity.sartain@bio-nano-consulting.com The photocatalytic activities of a series of titanium dioxide (TiO2) based nanoparticles, synthesised via flame spray pyrolysis (FSP), have been investigated and compared with the commercially available Evonik Aeroxide TiO2 P 25 (P 25). The effects of metal ions aluminium, tin and platinum, respectively, on the physical and chemical properties of the TiO2 nanoparticles are reported. The set of six samples were characterised by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma-mass spectrometry (ICP-MS) and ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy. Specific surface areas were determined using nitrogen adsorption and desorption measurements. Subsequent photocatalytic studies of the degradation of methyl orange (MO) dye under UV irradiation demonstrated that addition of Al and Sn had a negative effect on catalytic performance, whereas the addition of ≤0.7 at% Pt to each sample enhanced photocatalytic activity. Most interestingly, the Pt-doped composite samples (TiO2-Sn/Pt and TiO2-Al/Pt) both showed a significantly higher rate of degradation of MO, when compared to P 25. All Pt-doped samples show an increased visible photon absorption capacity. The relationships between the physical and chemical characteristics are discussed in relation to photocatalytic performance.

Effect of pretreatment temperature on the photocatalytic activity of microwave irradiated porous nanocrystalline ZnO

Porous nanocrystalline ZnO photocatalysts were successfully synthesized by microwave irradiation and then thermally treated at different temperatures (150 °C, 200 °C, 250 °C and 300 °C). The physico-chemical properties of synthesized samples were determined by using different characterization techniques. The characterization results indicated that the as-synthesized sample was comprised of both ZnO and Zn(OH)2 phases with a particle size of approximately 50 nm. Thermal treatment of the as-synthesized sample at 150 °C resulted in a pure ZnO phase with a particle size of 40 nm. The results also demonstrated that the surface area, pore diameter and bandgap energy reach a maximum value for the ZnO sample treated at 200 °C. The ZnO nanoparticles pretreated at 200 °C showed the highest photocatalytic activity (99% of degradation) in a short reaction time (90 min), which can be attributed to the combined effects of several factors including low crystallite size, relatively high surface area, pore diameter, pore volume and bandgap energy. Reusability results show that the catalysts can be readily separated from the reaction mixture by filtration after the photocatalytic reaction and reused at least five times without any loss of activity.