Titanium Oxide Microspheres with Tunable Size and Phase Composition.

Anton S Poluboyarinov,Kristina M Khazova,Vasily A Lebedev,Dmitry S Volkov,Daniil A Kozlov,Irina V Kolesnik,Alexey V Garshev,Vitaly I Chelpanov

doi:10.3390/ma12091472

Anton S Poluboyarinov, Kristina M Khazova + Show 6 more

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https://doi.org/10.3390/ma12091472

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Abstract

Due to their unique physical and chemical properties, monodisperse titanium oxide microspheres can be used in dye-sensitized solar cells, as cosmetic pigments, and for other applications. However, the synthesis of microspheres with narrow size distribution, desired phase composition, and porosity is still a challenge. In this work, spherical titania particles with controllable size, crystallinity, and pore size were obtained by Ti(OnBu)4 hydrolysis in ethanol. The influence of NaOH addition on the particles’ size and morphology was investigated for the first time. Particle diameter can be tailored from 300 nm to 1.5 μm by changing water and NaOH concentrations. Particle size was analyzed by the statistical processing of scanning electron microscopy (SEM) images and differential centrifugal sedimentation (DCS) measurements. Optical properties of the microspheres were studied by diffuse reflectance UV-Vis spectroscopy. Thermal and hydrothermal treatment allowed transforming amorphous phase in as-prepared particles into nanocrystalline anatase and/or rutile. Transmission electron microscopy (TEM) study of the lamellae, cut out from spherical particles using focused ion beam (FIB), revealed that as-synthesized microspheres are non-hollow, homogeneous, and crystallize throughout the whole volume of the particle. The spherical particles possess photoprotective properties; the highest sun protection factor (SPF) was observed for amorphous microspheres.

Highlights

TiO2 particles can be used as cosmetic pigment [1,2,3], a component of dye-sensitized solar cells [4,5,6,7], sorbent material for high-performance liquid chromatography (HPLC) [8,9,10,11], and other applications
After the solution became cloudy, synthesis was continued for two more hours; cooling was stopped, and the solution was left to dry in a propylene beaker in air at room temperature for a week
In our previous work [12], we found out that partially amorphous titania without residual organics, such as Hombikat UV100, demonstrates no narrow exothermic peaks on Differential scanning calorimetry (DSC) during crystallization

Summary

Introduction

TiO2 particles can be used as cosmetic pigment [1,2,3], a component of dye-sensitized solar cells [4,5,6,7], sorbent material for high-performance liquid chromatography (HPLC) [8,9,10,11], and other applications. The spherical morphology of the particles is preferable for all mentioned applications, while the requirements for other properties including the crystallinity, pore size, and particle size can differ. Cosmetic pigments require particles of micrometer-scale size and low crystallinity, because amorphous titanium oxide does not possess high photocatalytic activity [12], and does not serve as a source of free radicals, and does not cause oxidative stress. Spherical particles provide high scattering, which is important for the soft focus effect [13]. Particles for Materials 2019, 12, 1472; doi:10.3390/ma12091472 www.mdpi.com/journal/materials

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