Nanostructured titanium dioxide average size from alternative analysis of Scherrer's Equation

ABSTRACT The materials sizing in nano-scale is a challenge to be overcome, because the size determined by various methods differ. In order to shed light about the nanomaterials sizing, a modified Scherrer's equation was applied to estimate more accurately the nanostructured titanium dioxide crystal size. The manufactured titanium dioxide-nanostructured powder with nominal average size about 21nm was used as the reference standard to determine the accurate of modified equation. From X-ray diffraction data, an average crystal size about 20.63 nm was achieved for unheated sample. To establish a relation between the result obtained with modified Scherrer's equation and the nominal average crystal size, a statistical treatment and a comparative assessment were performed. The average absolute divergence does not exceed 0.70 nm. The value of crystal size determined from X-ray data was in good agreement with that informed by the supplier. Additionally, the behavior of sample was studied as a function of temperature.

Crystal structure of quenched and in-field electroluminescent phosphors

Electroluminescent zinc sulfide doped with copper and chloride (ZnS:Cu, Cl) powder was heated to 400°C and rapidly quenched to room temperature. Comparison between the quenched and non-quenched phosphors using synchrotron radiation X-ray powder diffraction (XRPD) (λ = 0.828692 Å) and X-ray absorption spectroscopy (XAS) was made. XRPD shows that the expected highly faulted structure is observed with excellent resolution out to 150° 2θ (or to (12 2 2) of the sphalerite phase). The quenched sample compared to the unheated sample shows a large change in peak ratios between 46.7° and 46.9°, which is thought to correspond to the wurtzite (0 0 6), (0 3 2) and sphalerite (3 3 3)/(5 1 1) peaks. Hence, a large proportion of this sphalerite diffraction is lost from the material upon rapid quenching, but not when the material is allowed to cool slowly. The Zn K-edge XAS data indicate that the crystalline structures are indistinguishable using this technique, but do give an indication that the electronic structure has altered due to changing intensity of the white line. It is noted that the blue electroluminescence (EL) emission bands are lost upon quenching: however, a large amount of total EL emission intensity is also removed, which is consistent with our findings. We report the XRPD of a working alternating-current electroluminescence device in the synchrotron X-ray beam, which exhibits a new diffraction pattern when the device is powered in an AC field even though the phosphor is fixed in the binder. Significantly, only a few crystals are required to yield the diffraction data because of the high flux X-ray source. These in panel data show multiple sharp diffraction lines spread out under the region, where capillary data show broad diffraction intensity indicating that the phosphor powder is comprised of unique crystals, each having different structures.

Effect of Thermal Treatment on the Photocatalytic Activity of TiO2 Coatings for Photocatalytic Oxidation of Benzoic Acid

The effects of thermal treatment on the properties and photoactivities of TiO2 catalysts supported on 316 stainless steel plates were examined. Degussa P-25 was immobilized on 316 stainless steel plates by electrophoretic deposition. These TiO2-coated plates were heated at 473, 673, and 873 K for 1 h. The photoactivities of these TiO2 coatings were determined based on the removal of benzoic acid as the model pollutant. In particular, the photoactivity decreased by 52% in the sample heated at 873 K compared with the unheated sample. The results of x-ray diffraction showed that the crystallinity and the crystallite sizes of the catalysts supported on the plates did not significantly vary with increasing temperature over the range examined. Negligible change in the catalyst phase (the anatase-to-rutile ratio) was indicated from x-ray diffraction and micro-Raman spectroscopy. However, it was found that the Brunauer–Emmett–Teller surface area of the scraped catalysts heated at 873 K decreased by nearly 13% compared with the unheated sample. In addition, scanning electron microscopy/energy dispersive x-ray and x-ray photoelectron spectroscopy analyses also detected the presence of Fe3+ ions at the surface of the supported catalysts heated at 873 K. The drop in surface area and the presence of Fe3+ ions at the catalyst surface, which were considered to function as electron–hole recombination centers, were possible factors leading to the drop in the photoactivity exhibited by the sample. A lower temperature for thermal treatment such as 473 K was proposed to ensure the coating stability and the catalyst photoactivity.