Control of TiO₂ Structures from Robust Hollow Microspheres to Highly Dispersible Nanoparticles in a Tetrabutylammonium Hydroxide Solution

Abstract

A new process for controlling the structure of TiO2 from hollow microspheres to highly dispersible nanoparticles has been developed by altering the concentration of tetrabutylammonium hydroxide (TBAH) in the solvothermal reaction of titanium isopropoxide. Robust and size-controllable hollow TiO2 microspheres, constructed by the assembly of 18 nm TiO2 nanoparticles, were synthesized at relatively high TBAH concentration. The diameters of hollow spheres, with a shell thickness of approximately 250 nm, were controlled to 1.5-4 microm by varying the concentration of TBAH in the range of 0.1-0.5 M. After calcination at 450 degrees C, the hollow microspheres were not appreciably deformed and were still floating on the surface of the water. However, highly dispersible TiO2 nanoparticles with an average diameter of 13 nm were obtained at a low TBAH concentration such as 9.2 mM. The colloidal particle size of TiO2 in an aqueous suspension at pH 2 was 12.5-13.5 nm, which indicates that the each nanoparticle is completely separated. The overall procedure is simple and highly reproducible, and large-scale synthesis is available at low cost.

Hollow Micro‐/Nanostructures: Synthesis and Applications

“…Recently, chains of Co hollow sub-microspheres have been synthesized via aggregation of PVP-stabilized primary nanoparticles presumably assisted by the gas bubbles liberated from the reaction. [255] Gas bubble templating has also been suggested as a means for preparing hollow spheres of sulfides (ZnS, [256] CuS [257] ), oxides (SnO 2 , [258] TiO 2 , [259] Fe 3 O 4 [260] ). It should be pointed out that the gas bubble templating mechanism remains highly speculative, especially in systems involving highly soluble gases (CO 2 , NH 3 ) resulting from decomposition of organic molecules such as urea and thiourea.…”

Photocatalytic Activity and Electronic Structure Analysis of N‐doped Anatase TiO2: A Combined Experimental and Theoretical Study

“…The synthesis of N-doped TiO 2 nanophotocatalyst can be achieved by sol-gel method [12], hydrothermal method [13], solvothermal method [14], chemical vapor deposition [15], emulsion precipitation [16], electrical oxidation [17], etc. Among these methods, the hydrothermal method is the most adopted for the synthesis of N-doped TiO 2 nanoparticles at low temperature, because doping, as well as the size of nanoparticles, can be easily controlled depending on the reaction conditions, such as solvents, pH, temperature, hydrolysis rate, etc.…”

Control of Particle Characteristics in the Preparation of TiO2Nano Particles Assisted by Microwave

“…As described above, reaction times can be reduced considerably but the shape of the product was found to be TiO 2 of spherical microtube shown in Figure 1(d) instead of hollow microsphere. 7 Since there is wider space in spherical microtube (1 µm × over 3µm) than that in hollow sphere (1-3 µm diameter), some applications for micro reactor and gas storage can be visualized. Easy recycle induced by easy separation of these materials projected from over mm sizes of particles that are consisted with nano particles of 25-30 nm will be additional merits.…”

“…Lee reported that addition of small amount of TBAH resulted in the formation of nano particles but a hollow microsphere by gathering of nano TiO 2 particles was formed with addition of more TBAH. 7 In the mechanism given by Lee, it is proposed that gas phase C 4 H 8 formed by the decomposition of TBAH acts as an aggregation center of TiO 2 particles. This proposal was supported by the evolution of microbubbles during the solvothermal reaction.…”