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Stabilization of colloidal Ti, Zr, and Hf oxide nanocrystals by protonated tri-n-octylphosphine oxide (TOPO) and its decomposition products

(2017) CHEMISTRY OF MATERIALS. 29(23). p.10233-10242
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Abstract
Although TiO2, ZrO2, and HfO2 nanocrystals are often synthesized in tri-n-octylphosphine oxide (TOPO), it is unclear whether TOPO also serves as ligand. Using liquid and solid state H-1 and P-31 nuclear magnetic resonance spectroscopy and X-ray fluorescence spectroscopy, we show that the nanocrystal surface is capped by several derivatives of TOPO. In the P-31 NMR spectrum, di-n-octylphosphinate (delta = 57 ppm) and P,P'-(di-n-octyl) pyrophosphonate (delta = 20 ppm) are found coordinated to the nanocrystal. In addition, hydrogen chloride associates with the metal oxide nanocrystal surface and protonates TOPO. The resulting hydroxyl-tri-n-octylphosphonium, [HO-PR3](+), is tightly associated with the nanocrystal surface (delta(P-31) = 73 ppm) due to electrostatic interactions and hydrogen bonding. To simplify the complex surface composition, we exchange the original surface species for carboxylate or phosphonate ligands. The protonation of TOPO is an unexpected example of lyophilic ion pairing between an acidic metal oxide nanocrystal and a weakly basic ligand molecule that is formed in nonpolar solution. Our results contrast with the classically envisaged L-type binding motif of TOPO to surface metal ions. The generality of this stabilization mode and its relevance to catalysis is discussed.
Keywords
SOL-GEL SYNTHESIS, SURFACE-CHEMISTRY, LIGAND-EXCHANGE, NONAQUEOUS SYNTHESIS, BUILDING-MATERIALS, THIN-FILMS, ZIRCONIA NANOCRYSTALS, SCALE SYNTHESIS, ACID PROPERTIES, CO OXIDATION

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Citation

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MLA
De Keukeleere, Katrien et al. “Stabilization of Colloidal Ti, Zr, and Hf Oxide Nanocrystals by Protonated Tri-n-octylphosphine Oxide (TOPO) and Its Decomposition Products.” CHEMISTRY OF MATERIALS 29.23 (2017): 10233–10242. Print.
APA
De Keukeleere, K., Coucke, S., De Canck, E., Van Der Voort, P., Delpech, F., Coppel, Y., Hens, Z., et al. (2017). Stabilization of colloidal Ti, Zr, and Hf oxide nanocrystals by protonated tri-n-octylphosphine oxide (TOPO) and its decomposition products. CHEMISTRY OF MATERIALS, 29(23), 10233–10242.
Chicago author-date
De Keukeleere, Katrien, Sofie Coucke, Els De Canck, Pascal Van Der Voort, Fabien Delpech, Yannick Coppel, Zeger Hens, Isabel Van Driessche, Jonathan S Owen, and Jonathan De Roo. 2017. “Stabilization of Colloidal Ti, Zr, and Hf Oxide Nanocrystals by Protonated Tri-n-octylphosphine Oxide (TOPO) and Its Decomposition Products.” Chemistry of Materials 29 (23): 10233–10242.
Chicago author-date (all authors)
De Keukeleere, Katrien, Sofie Coucke, Els De Canck, Pascal Van Der Voort, Fabien Delpech, Yannick Coppel, Zeger Hens, Isabel Van Driessche, Jonathan S Owen, and Jonathan De Roo. 2017. “Stabilization of Colloidal Ti, Zr, and Hf Oxide Nanocrystals by Protonated Tri-n-octylphosphine Oxide (TOPO) and Its Decomposition Products.” Chemistry of Materials 29 (23): 10233–10242.
Vancouver
1.
De Keukeleere K, Coucke S, De Canck E, Van Der Voort P, Delpech F, Coppel Y, et al. Stabilization of colloidal Ti, Zr, and Hf oxide nanocrystals by protonated tri-n-octylphosphine oxide (TOPO) and its decomposition products. CHEMISTRY OF MATERIALS. 2017;29(23):10233–42.
IEEE
[1]
K. De Keukeleere et al., “Stabilization of colloidal Ti, Zr, and Hf oxide nanocrystals by protonated tri-n-octylphosphine oxide (TOPO) and its decomposition products,” CHEMISTRY OF MATERIALS, vol. 29, no. 23, pp. 10233–10242, 2017.
@article{8537298,
  abstract     = {Although TiO2, ZrO2, and HfO2 nanocrystals are often synthesized in tri-n-octylphosphine oxide (TOPO), it is unclear whether TOPO also serves as ligand. Using liquid and solid state H-1 and P-31 nuclear magnetic resonance spectroscopy and X-ray fluorescence spectroscopy, we show that the nanocrystal surface is capped by several derivatives of TOPO. In the P-31 NMR spectrum, di-n-octylphosphinate (delta = 57 ppm) and P,P'-(di-n-octyl) pyrophosphonate (delta = 20 ppm) are found coordinated to the nanocrystal. In addition, hydrogen chloride associates with the metal oxide nanocrystal surface and protonates TOPO. The resulting hydroxyl-tri-n-octylphosphonium, [HO-PR3](+), is tightly associated with the nanocrystal surface (delta(P-31) = 73 ppm) due to electrostatic interactions and hydrogen bonding. To simplify the complex surface composition, we exchange the original surface species for carboxylate or phosphonate ligands. The protonation of TOPO is an unexpected example of lyophilic ion pairing between an acidic metal oxide nanocrystal and a weakly basic ligand molecule that is formed in nonpolar solution. Our results contrast with the classically envisaged L-type binding motif of TOPO to surface metal ions. The generality of this stabilization mode and its relevance to catalysis is discussed.},
  author       = {De Keukeleere, Katrien and Coucke, Sofie and De Canck, Els and Van Der Voort, Pascal and Delpech, Fabien and Coppel, Yannick and Hens, Zeger and Van Driessche, Isabel and Owen, Jonathan S and De Roo, Jonathan},
  issn         = {0897-4756},
  journal      = {CHEMISTRY OF MATERIALS},
  keywords     = {SOL-GEL SYNTHESIS,SURFACE-CHEMISTRY,LIGAND-EXCHANGE,NONAQUEOUS SYNTHESIS,BUILDING-MATERIALS,THIN-FILMS,ZIRCONIA NANOCRYSTALS,SCALE SYNTHESIS,ACID PROPERTIES,CO OXIDATION},
  language     = {eng},
  number       = {23},
  pages        = {10233--10242},
  title        = {Stabilization of colloidal Ti, Zr, and Hf oxide nanocrystals by protonated tri-n-octylphosphine oxide (TOPO) and its decomposition products},
  url          = {http://dx.doi.org/10.1021/acs.chemmater.7b04580},
  volume       = {29},
  year         = {2017},
}

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