From Gel to Crystal: Mechanism of HfO2 and ZrO2 Nanocrystal Synthesis in Benzyl Alcohol
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From Gel to Crystal : Mechanism of HfO2 and ZrO2 Nanocrystal Synthesis in Benzyl Alcohol. / Goossens, Eline; Aalling-Frederiksen, Olivia; Tack, Pieter; Van den Eynden, Dietger; Walsh-Korb, Zarah; Jensen, Kirsten M.Ø.; De Buysser, Klaartje; De Roo, Jonathan.
In: Journal of the American Chemical Society, Vol. 146, No. 15, 2024, p. 10723-10734.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - From Gel to Crystal
T2 - Mechanism of HfO2 and ZrO2 Nanocrystal Synthesis in Benzyl Alcohol
AU - Goossens, Eline
AU - Aalling-Frederiksen, Olivia
AU - Tack, Pieter
AU - Van den Eynden, Dietger
AU - Walsh-Korb, Zarah
AU - Jensen, Kirsten M.Ø.
AU - De Buysser, Klaartje
AU - De Roo, Jonathan
N1 - Publisher Copyright: © 2024 The Authors. Published by American Chemical Society.
PY - 2024
Y1 - 2024
N2 - Nonaqueous sol-gel syntheses have been used to make many types of metal oxide nanocrystals. According to the current paradigm, nonaqueous syntheses have slow kinetics, thus favoring the thermodynamic (crystalline) product. Here we investigate the synthesis of hafnium (and zirconium) oxide nanocrystals from the metal chloride in benzyl alcohol. We follow the transition from precursor to nanocrystal through a combination of rheology, EXAFS, NMR, TEM, and X-ray total scattering (PDF analysis). Upon dissolving the metal chloride precursor, the exchange of chloride ligands for benzylalkoxide liberates HCl. The latter catalyzes the etherification of benzyl alcohol, eliminating water. During the temperature ramp to the reaction temperature (220 °C), sufficient water is produced to turn the reaction mixture into a macroscopic gel. Rheological analysis shows a network consisting of strong interactions with temperature-dependent restructuring. After a few minutes at the reaction temperature, crystalline particles emerge from the gel, and nucleation and growth are complete after 30 min. In contrast, 4 h are required to obtain the highest isolated yield, which we attribute to the slow in situ formation of water (the extraction solvent). We used our mechanistic insights to optimize the synthesis, achieving high isolated yields with a reduced reaction time. Our results oppose the idea that nonaqueous sol-gel syntheses necessarily form crystalline products in one step, without a transient, amorphous gel state.
AB - Nonaqueous sol-gel syntheses have been used to make many types of metal oxide nanocrystals. According to the current paradigm, nonaqueous syntheses have slow kinetics, thus favoring the thermodynamic (crystalline) product. Here we investigate the synthesis of hafnium (and zirconium) oxide nanocrystals from the metal chloride in benzyl alcohol. We follow the transition from precursor to nanocrystal through a combination of rheology, EXAFS, NMR, TEM, and X-ray total scattering (PDF analysis). Upon dissolving the metal chloride precursor, the exchange of chloride ligands for benzylalkoxide liberates HCl. The latter catalyzes the etherification of benzyl alcohol, eliminating water. During the temperature ramp to the reaction temperature (220 °C), sufficient water is produced to turn the reaction mixture into a macroscopic gel. Rheological analysis shows a network consisting of strong interactions with temperature-dependent restructuring. After a few minutes at the reaction temperature, crystalline particles emerge from the gel, and nucleation and growth are complete after 30 min. In contrast, 4 h are required to obtain the highest isolated yield, which we attribute to the slow in situ formation of water (the extraction solvent). We used our mechanistic insights to optimize the synthesis, achieving high isolated yields with a reduced reaction time. Our results oppose the idea that nonaqueous sol-gel syntheses necessarily form crystalline products in one step, without a transient, amorphous gel state.
U2 - 10.1021/jacs.4c00678
DO - 10.1021/jacs.4c00678
M3 - Journal article
C2 - 38588404
AN - SCOPUS:85189879902
VL - 146
SP - 10723
EP - 10734
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 15
ER -
ID: 390289262