Suppressing the Photocatalytic Activity of Titania by Precisely Controlled Silica Coating

Abstract

A homogeneous thin silica layer with the thickness of a few nanometers was successfully deposited on an anatase particle by the hydrolysis and condensation of tetraethyl orthosilicate. The heat treatment of the titania/silica hybrid at 1000 °C led to the densification of the silica layer on the anatase particles. The anatase particle after the silica coating did not transform to rutile, and no change in the crystallite size was seen by the heat treatment at 1000 °C. The coating and subsequent heating were repeated to vary the thickness of the silica layer to obtain each coating with similar thickness by each coating procedure (ca. 3 and 2 nm, before and after the heat treatment). The samples were evaluated for the photocatalytic decomposition of methylene blue by the UV irradiation to find that the decomposition became slower after the coating and subsequent heat treatment, and the repeated procedures led to further suppression of the photocatalytic decomposition of methylene blue. The quite small decomposition rate constant (0.01 h −1 ) was successfully achieved by the coating and subsequent heating for three times (the thickness of the dense silica layer was ca. 7 nm).

Controlled Phase Transformation and Crystal Growth of Titanium Dioxide from Anatase/Silica Core/Shell Particles

“…The suppression of the phase transformation of TiO 2 has been reported by coating with silica. ,− The transformation has been examined by varying the silica content in the TiO 2 -silica hybrid, ,− while the effect of the silica shell thickness has not been reported. Recently, it was found that the heat treatment of ST-21/silica at 1000 °C led the silica layer to shrink, while the anatase core did not transform to rutile and the crystallite size of the anatase (22 nm) did not change . Therefore, ST-21/silica core/shell particles with varied silica layer thicknesses were heated above 1000 °C to follow the transformation behavior of anatase to rutile more extensively.…”

“…32 Suppression of the photocatalytic activity of anatase particles by coating with silica was reported for UV-shielding pigment application. 33 During the study, it was found that the phase transformation of anatase to rutile upon heating was different for the silica-coated particles from the pristine anatase particles. These observations suggest that the heat treatment of silica-coated titania is a way to control the crystallinity and shape/size of anatase and rutile particles for versatile application.…”

“…The core/shell particle, a type of hybrid, has been investigated as a functional material. − Silica and porous silica shells have been deposited on TiO 2 particles to modify the photocatalytic activity through the reactants’ affinity, − to impart the molecular selectivity of TiO 2 by the molecular sieving effects of porous silica, , and to improve the dispersion stability of TiO 2 . Suppression of the photocatalytic activity of anatase particles by coating with silica was reported for UV-shielding pigment application . During the study, it was found that the phase transformation of anatase to rutile upon heating was different for the silica-coated particles from the pristine anatase particles.…”

Highly Dispersed Ni over a YSZ Anode Anchored by SiO2 at High Temperature through Low-Temperature Chemical Vapor Deposition

“…YSZ-SiO 2 and Ni/YSZ-SiO 2 powders were synthesized by low-temperature pulsed CVD as discussed in the literature . The YSZ or Ni/YSZ powder was evenly spread on Petri dishes with a mass density of 0.25 g/cm 2 , which were kept in an oven at 120 °C for 2 h before deposition.…”

“…The structure and property of Ni/YSZ-SiO 2 during the deposition and sintering are characterized to discuss the relationships between the structure and electrochemical activity. 17 The YSZ or Ni/YSZ powder was evenly spread on Petri dishes with a mass density of 0.25 g/cm 2 , which were kept in an oven at 120 °C for 2 h before deposition. Subsequently, the dishes were placed in a vacuum desiccator, which was purged with N 2 .…”