An improvement of photocatalytic activity of TiO2 Degussa P25 powder

Abstract

a b s t r a c tThe photocatalytic activities of Degussa P25 powders annealed at various temperatures in vacuum and air were studied together with investigations of their compositions by XPS, of their crystal structures by XRD and of their specific surface areas by BET. It is shown that the photocatalytic activity of P25 powders was remarkably enhanced after vacuum annealing; the kinetic coefficient can be raised by 75% during annealing at 400 • C. It is obvious that this enhancement is not related to the adhesion ability of the P25 powders.

Marginally Hydrogenated Triphasic Titania Nanotubes for Effective Visible‐Light Photocatalytic Hydrogen Generation

“…The triphase nature with well‐resolved lattice features is retained in the H‐250 and H‐450 samples, as is evident from HRTEM analysis of their surfaces (Figure e and f). The disorder layer at the lattice surface resulting from hydrogenation is not observed in our case, as the samples are marginally hydrogenated. An important observation is the heterojunctions observed between various phases of titania in any of the nanotubes.…”

“…Thet ubularm orphology is clearly visible in the SEM images ( Figure 3a and b), which show the surfaces of the T-ARB and H-450 samples.T he tubulard iameters are in the range of 30 to 120 nm in both samples.T he bright-field image of T-ARB given in Figure 3c also confirms the tubularm orphology of the sample.F romh igh-resolution TEM (HRTEM) analysis of as ingle nanotube of T-ARB (Figure 3d), it is evident that the three phases,n amely,a natase, rutile,a nd brookite,a re present in the single nanotube.T he triphase nature with well-resolved lattice features is retained in the H-250 and H-450 samples,a si se vident from HRTEM analysis of their surfaces (Figure3ea nd f). Thed isorder layer at the lattice surface resulting from hydrogenation [16,42] is not observed in our case,a st he samples are marginally hydrogenated. An importanto bservation is the heterojunctions observed between various phaseso ft itania in any of the nanotubes.T hey demonstrate physical connectivityb etween the three phases at the nanoscopic level, and the junctions are expected to act as charge-separation centers.T he selected area electron diffraction( SAED) patterns in Figure 3g andhfurther prove that H-450 is more crystalline than T-ARB,w hich thus leads to the conclusion that hydrogenation does not induced isorder on the surface of the TiO 2 nanotubes.…”

“…Although this has been successful in tailoring the optical properties to the visible region, the dopants often act as recombination centers that affect the photocatalytic efficiency . Recently, extensive research interest has been devoted to dopant‐free defective TiO 2 for efficient engineering of the band gap towards visible‐light‐to‐infrared absorption . Hydrogenation of TiO 2 is one such attempt that has produced black titania, the band offsets of which have been shifted to match equivalently with the redox potential of water 19–21]…”

“…[1,14] Recently,e xtensive research interest has been devoted to dopant-free defective TiO 2 for efficient engineering of the band gap towards visible-light-to-infrareda bsorption. [15][16][17][18] Hydrogenation of TiO 2 is one such attempt that has produced black titania,t he band offsets of which have been shifted to match equivalently with the redox potential of water [19][20][21] Moreover, the titania surface has been modified by various meanss uch as coupling with an arrow band gap semiconductor, [22][23][24][25] plasmonic metals, [26,27] and so on [28] to reduce the recombination of photogenerated charge carriers.A mong the modifications adopted, introducing phase junctions was provent ob ea ne ffective strategyt oi nhibit the fast recombination of excited charge carriers. [29] This is because the photocatalytic activity of TiO 2 is not only attributed to the energy-band characteristics but also to the phase composition.…”

The influence of X-ray diffraction pattern angular range on Rietveld refinement results used for quantitative analysis, crystallite size calculation and unit-cell parameter refinement

“…Tamer (2013) recorded XRD patterns of calcite in the 2-70 2 angular interval when studying carbonate rocks. For the characterization of well known titanium dioxides (rutile and anatase), some researchers (Bezerra et al, 2017) have acquired XRD data in the 10-70 2 range, while others (Bessergenev et al, 2015;Al-Dhahir, 2013) used much wider data ranges of 10-90 and 20-120 2, respectively. Braccini et al (2013) and Anupama et al (2017) used the Rietveld method when studying magnetite-and hematite-containing samples.…”