Preparation of porous titania particles by partial dissolution and heat treatment of hydrous titania

Abstract

Porous titania particles were prepared by partial dissolution of hydrous titania and subsequent heat treatment. Uniform and spherical particles of hydrous titania were prepared by hydrolysis of titanium alkoxide at different hydrolysis conditions. The asprepared hydrous titania particles were soaked in ethanol to dissolve the weakly polycondensed part of the particles. As a result, meso-and macroporous structures were formed on the surface of the hydrous titania particles that were prepared by mild hydrolysis. The porous structure was retained even after heat treatment at 400°C while the particles crystallized into the anatase phase. The specific surface area of the porous titania particles prepared by heat treatment of hydrous titania at 400°C for 15 min was 121 m 2 /g. ©2016The Ceramic Society of Japan. All rights reserved.Key-words : Particle, Porous, Alkoxide, Titania, Hydrolysis [Received September 22, 2016; Accepted October 12, 2016] Recently, titania (TiO 2 ) has been extensively studied because of its wide range of applications in pigments, photocatalysts, and photovoltaics. One of the important factors which affect the functionality of titania, such as the photocatalytic activity, is its specific surface area. Therefore, titania nanoparticles with high specific surface areas are being increasingly investigated. 1),2)However, nanosized particles tend to aggregate which leads to difficulties in practical applications.3) In addition, there are growing concerns about the toxicity of nanomaterials. 4) Thus, methods for synthesizing convenient and non-toxic submicronor micron-sized porous titania particles such as, burning out organic beads, utilizing templates, self-organizing, and etching, have been explored for practical applications.3),5) Hydrolysis of titanium alkoxide has been widely used for the synthesis of spherical hydrous titania (TiO 2 ·nH 2 O) particles. 6)9) We have also reported the mechanism for the formation of uniform, spherical hydrous titania particles by hydrolysis of titanium butoxide in acetonitrile/butanol solution in the presence of ammonia. 10)12)It was found that hydrous titania particles prepared under a very short reaction time became highly porous after washing with ethanol.10) However, most of the obtained porous particles disintegrated and the spherical shape could not be maintained. In addition, the reaction time-range in which porous hydrous titania could be obtained was very narrow and it was difficult to obtain uniform porous particles. The time-range which can obtain porous particles seems to be too short to form uniform outer shape and condensation state of the particles. In this study, we established a method to develop a uniform porous structure on the surface of hydrous titania particles. The hydrous titania particles were prepared at a moderately low polycondensation state and the porous structure was obtained by partial dissolution of the titanium species, followed by washing with an appropriate eluate. Additionally, heat treatment of the prepared porous hydrous t...

Preparation of porous titania particles by partial dissolution and hot-water or hydrothermal treatment of hydrous titania

“…The as-prepared particles obtained only by hydrolysis of titanium alkoxide were amorphous hydrous titania, irrespective of whether the hydrolysis conditions for the spherical or porous HTPs were used (Figure 1(a) and Figure 2(a)) [16]. Under hot-water treatment at 80°C, no obvious change was observed in the XRD patterns of either the spherical or porous particles when compared with those of the as-prepared particles (Figure 1(b) and Figure 2(b)).…”

“…The porous particles were prepared with lower concentrations of ammonia (0.03 M) and water (0.33 M). Their porous structure was formed by the dissolution of the weakly polycondensed parts of the particles [16]. Although the remaining part of the porous particles after the dissolution process must be more stable than the dissolved part, the degree of polycondensation might be lower than that of the spherical particles prepared with higher concentrations of ammonia (0.10 M) and water (0.50 M).…”

“…The porous particles treated at 80°C for a prolonged time exhibited a similar appearance as those treated at higher temperatures for 6 h (Figures 4 and 6). Figure 7 shows the TEM images of the surface of the as-prepared porous HTPs, porous HTPs subjected to the hot-water treatment at 80°C for 24 h, and porous HTPs heat-treated at 400°C for 15 min using an electric furnace, which crystallised into anatase [16]. The as-prepared HTPs were composed of fine primary particles [26], and their surface was relatively smooth (Figure 7(a)).…”

“…Various excellent preparation methods for porous titania with well-defined porous structures were reported, including burning out or etching of organic or inorganic templates [5,9], spray-drying [10], hydrothermal or solvothermal treatment [5,[11][12][13] and nanoparticle assembly [14,15]. We also reported on a method for preparing porous titania particles via the partial dissolution of particle surfaces [16]. In this method, hydrous titania (TiO 2 •nH 2 O) particles (HTPs) were first prepared via a metal alkoxide method.…”

“…The porous particles obtained using the aforementioned method were a water-containing amorphous phase. Thus, in our previous study, they were crystallised to anatase via heat treatment at 400°C [16]. After this heat treatment, the Brunauer–Emmett–Teller (BET) SSA ( S BET ) of the as-prepared porous HTPs was substantially lowered due to the disappearance of microspores in the as-prepared hydrous titania.…”