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Title: Understanding solvothermal crystallization of mesoporous anatase beads by in situ synchrotron PXRD and SAXS
Authors: Xia, F
Chen, DH
Scarlett, NVY
Madsen, IC
Lau, D
Leoni, M
Ilavsky, J
Brand, HEA
Caruso, RA
Keywords: X-ray diffraction
Delayed neutron precursors
Issue Date: 7-Jul-2014
Publisher: American Chemical Society
Citation: Xia, F., Chen, D., Scarlett, N. V., Madsen, I. C., Lau, D., Leoni, M., Ilavsky, J., Brand, H. E. A. & Caruso, R. A. (2014). Understanding solvothermal crystallization of mesoporous anatase beads by in situ synchrotron PXRD and SAXS. Chemistry of Materials, 26(15), 4563-4571. doi:10.1021/cm501810x
Abstract: Submicrometer-sized mesoporous anatase (TiO2) beads have shown high efficiency as electrodes for dye-sensitized solar cells and are recoverable photocatalysts for the degradation of organic pollutants. The detailed mechanism for crystallization of the amorphous TiO2/hexadecylamine (HDA) hybrid beads occurring during the solvothermal process needs to be understood so that reaction parameters can be rationally refined for optimizing the synthesis. In this work, the solvothermal crystallization was monitored by in situ synchrotron powder X-ray diffraction (PXRD) and synchrotron small-angle X-ray scattering (SAXS) techniques. In situ PXRD provided crystallization curves, as well as the time evolution of anatase crystallite mean size and size distribution, and in situ SAXS provided complementary information regarding the evolution of the internal bead structure and the formation of pores during the course of the solvothermal process. By exploring the effects of temperature (140-180 °C), bead diameter (300 and 1150 nm), bead internal structure, and solvent composition (ethanol and ammonia concentrations) on this process, the crystallization was observed to progress 3-dimensionally throughout the entire bead due to solvent entrance after an initial fast partial dissolution of HDA from the nonporous precursor bead. On the basis of the kinetic and size evolution results, a 4-step crystallization process was proposed: (1) an induction period for precursor partial dissolution and anatase nucleation; (2) continued precursor dissolution accompanied by anatase nucleation and crystal growth; (3) continued precursor dissolution accompanied by only anatase crystal growth; and (4) complete crystallization with no significant Ostwald ripening. © 2014 American Chemical Society.
ISSN: 0897-4756
Appears in Collections:Journal Articles

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