Effects of Annealing on the Morphology and Porosity of Porous TiO₂ Films Fabricated by Deposition of Aerosol Nanoparticles

Abstract

The present study investigates the impact of post annealing of TiO 2 nanoparticulate lms on their crystallinity, mechanical strength, and morphology. Non-agglomerated and amorphous TiO 2 nanoparticles of 46 nm diameter were synthesized in a plasma eld, and were subsequently deposited on substrates to form nanoparticulate lms. The lms were annealed at various temperatures in the range of 100-1,200°C. Phase transformations from amorphous-to-anatase and from anatase-to-rutile were observed at 400°C and at 1,000°C, respectively. The high rutile transformation temperature was considered to be due to a tensile eld induced by shrinkage of the lm. The as-deposited lm and the lms annealed at below 400°C had poor mechanical strength. Conversely, the lms annealed at over 500°C were strengthened by necking of the nanoparticles. The size of nanoparticles changed with increasing temperature. Annealing at 100-300°C caused the nanoparticles to shrink to approximately 30 nm. The nanoparticle diameters changed only slightly when annealed at 400-600°C because the annealing time was insu cient for changes to manifest. Annealing at 700-900°C caused the nanoparticle diameter to increase to approximately 50 nm because of sintering and coalescence of the nanoparticles. The diameter of the nanoparticles annealed at over 1,000°C became approximately 200 nm because of densi cation during the anatase-to-rutile transformation. The porosities of the lms annealed at below 900°C were over 80%. However, the porosities of the lms annealed at over 1,000°C decreased signi cantly due to densi cation.

Effect of Heating Rate on the Photocatalytic Activity of Ag–TiO2 Nanocomposites by One-Step Process via Aerosol Routes

“…These results show that the relative thickness decreases with the applied heat treatment. The densification of the film after annealing was closely related to the release or dehydration of residual hydroxyl group by the heat [16]. The relative thickness was obtained from the measured thickness of the annealed film divided by the thickness of the as-deposited film.…”

“…Briefly, TTIP vapor was flown and fed continuously to a radio frequency plasma reactor (AX-1000IIP, Adtec Plasma Technology Co. Ltd., Fukuyama, Japan) and dissociated, forming negatively charged TiO 2 nanoparticles [16,26]. Simultaneously, in the evaporationcondensation PVD system, vaporized Ag granules in the tubular furnace (TMF-300N, As One, Tokyo, Japan) were flown by the carrier gas and quickly condensed in the cooling system.…”

“…The synthesized Ag and TiO 2 nanoparticles were continuously deposited onto a Si substrate with an applied +300 voltage. The voltage was given to uniformly collect the nanoparticles and control the deposition of the nanocomposite [16,26]. To obtain similar 0.35 mg weight s(±5%), the thin film deposition time was varied from 25-30 min.…”

“…The surface morphology and film thickness of the nanocomposites with different heating rates were observed by scanning electron microscopy (SEM, S-5200, Hitachi High Technologies, Tokyo, Japan). Furthermore, the geometric mean diameter (GMD) of the nanoparticles can be obtained from the SEM images by measurement of the nanoparticles with Equation (2) [16]:…”

JCEJ Outstanding Paper Award of 2015

“…Aerosol Nanoparticles" by Masaru Kubo, Yuki Mantani, and Manabu Shimada, Hiroshima University (Kubo et al, 2015) Citation: In this paper, the authors investigated the effects of post annealing of the TiO 2 nanoparticulate films at various temperatures on their crystallinity, mechanical strength, and morphology. The details of the sintering process of TiO 2 nanoparticles were also provided.…”