Shape-Controlled Anatase Titanium(IV) Oxide Particles Prepared by Hydrothermal Treatment of Peroxo Titanic Acid in the Presence of Polyvinyl Alcohol

Abstract

Anatase titanium(IV) oxide (TiO2) particles with specific exposed crystal faces were prepared by hydrothermal treatment of peroxo titanic acid (PTA) solution with polyvinyl alcohol as a shape-control reagent. Crystal phase, shape, and size of TiO2 particles were found to be greatly dependent on pH value of PTA solution and time of hydrothermal treatment. TiO2 particles prepared from PTA solution of pH 7 had {101} and {001} exposed crystal faces, and the shape of TiO2 particles changed with the time of hydrothermal treatment. The prepared TiO2 particles with specific exposed crystal faces showed higher photocatalytic activity for acetaldehyde decomposition than commercial spherical TiO2 particles. This result implies that back reaction was prevented by spatial separation of redox sites in the particles because of selective migration of electrons and positive holes to specific exposed crystal faces and/or different reactivity of electrons and positive holes on the specific exposed crystal face. Furthermore, the shape evolution of TiO2 particles showed a relationship with photocatalytic activity, and a stacked structure of octahedral anatase showed the highest photocatalytic activity due to both oxidation and reduction sites with large surface area.

Specific Facets-Dominated Anatase TiO2: Fluorine-Mediated Synthesis and Photoactivity

“…This finding may be helpful to interpret some important photocatalytic processes. For example, a large surface area of {101} facets was suitable for acetaldehyde decomposition, while anatase TiO 2 samples with dominant {001} facets had excellent ability to remove NO and toluene through photocatalytic reactions [94,107].…”

“…Therefore, an ideal spatial separation of red-ox sites on the anatase particles, with a consequent reduction of electron-hole pairs recombination rate and a parallel photocatalytic efficiency enhancement, may occur [106,107]. This is another crucial aspect concerning potential positive effects induced in photocatalysis by specific TiO 2 crystal engineering.…”

Decahedral-shaped anatase titania photocatalyst particles: Synthesis in a newly developed coaxial-flow gas-phase reactor

“…This approach involves the application of fluorinecontaining species (e.g., hydrogen fluoride, ammonium fluoride, titanium(IV) fluoride and tetrafluoroborate ion) as morphology-controlling agents to prevent the formation of more thermodynamically stable octahedral anatase titania particles (OAPs) exposing only {101} facets [22][23][24][25][26][27][28][29][30][31][32][33]. Other compounds including polyvinyl alcohol [34,35] and carbonate ions generated during decomposition of urea have also been used to control the shape [20].…”

“…However, the disadvantage of this approach is strong adsorption of shape-control reagents (e.g., fluoride ions) on the crystal surface or their doping into the lattice, which may result in a decrease in photocatalytic activity [34]. Furthermore, at high temperatures, fluorine compounds generate toxic and corrosive products, making scaling-up of the preparation process difficult.…”

Spatial separation of photogenerated electrons and holes among {010} and {110} crystal facets of BiVO4

“…Similar phenomena were also reported in other references [27][28][29] . However, some references observed higher photocatalytic oxidation activity of organics on anatase nanocrystals with well-faceted {101} surfaces than that of the above-mentioned {001} facet [30][31][32] . Farneth et al 21 concluded that the fine Ag particles are mostly deposited by reduction of Ag þ on the {110} face of TiO 2 , while Hotsenpiller et al 22 reached the conclusion that the Ag particles were photocatalytically deposited at higher velocities on the {001} and {011} facets than on the {110} and {010} facets.…”