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The zirconia powders were characterized

What is ZrO2?

was prepared from various zirconium carboxylate complexes that were synthesized
by the reaction of zirconium oxychloride with carboxylic acids or carboxylate
salts in aqueous media. The carboxylates used in this study included aliphatic
and α-hydroxyl carboxylic acids. It was determined that the aliphatic zirconium
carboxylate complexes coordinate with the zirconium ions in a bridging
bidentate mode. In contrast, a bridging chelating bonding with the
incorporation of the OH in the bonding was observed with the α-hydroxyl
carboxylate complexes. A vibrational-frequency calculation with a simplified
structure of propanoic acid on m-ZrO2 supports that a cis bidentate
configuration is a more plausible structure. Notably, it was found that the
nature of the zirconium carboxylate plays a profound role in the crystallinity,
surface area, and other properties of the zirconia produced by their
decomposition. ZrO2 obtained from the aliphatic carboxylates showed a
dependence on the carboxylate ligands: the longer the carboxylate ligand chain,
the higher the surface area of the resulting zirconia. For example, ZrO2
obtained from zirconium ethyl hexanoate (Zr-7) showed a relatively higher
surface area than that prepared from the other aliphatic zirconium carboxylate
complexes. Also, scanning electron microscopy was performed to examine the
influence of the zirconium carboxylate precursor on the morphology of the final
oxide. Figure 8 shows the SEM images of ZrO2 derived from the thermal treatment
of the zirconium pivalate complex (Zr-5) at 400°C, demonstrating the formation
of agglomerates containing spherical nanosize particles with an approximate
average diameter of about 100–200 nm.


The interaction between stable m-ZrO2 and acetic acid and propanoic acid

chose the two acids since acetic acid is the smallest carboxyl acid, while
propanoic acid is the smallest used in the experiment. A stable (2 × 2) ()
plane was used as a surface for the zirconia surface. In this study, the cis
configuration was examined, by a previous study, since the cis configuration is
more stable than the trans configuration. The gas-phase acetic and propanoic
acids. In addition, it was found that both acetic and propanoic acids are
dissociatively adsorbed on the surface, and their adsorption energies are −1.39
eV and −1.43 eV, respectively. Both cis structures have similar Zr-O distances
(~2.2 Å), while those of the H from the OH group are 2.51 Å and 2.46 Å,
indicating total dissociation. Based on the structure of propanoic acid (a
vibrational-frequency calculation was executed to compare with the experimental
results). Its surface OH stretching mode is calculated to be 3,605 cm−1, which
is close to the typical OH stretching of Zr-1 (Figure 3(a); 3,643 cm−1). In
particular, the calculated asymmetric mode for COO is 1,497 cm−1, which aligns
with the experimental finding of 1,564 cm−1. The vibrational-frequency
simulations and geometry optimization support the result that the cis bidentate
structure is preferred to the trans configuration. It is highly difficult to
construct a more plausible model to simulate the zirconium carboxylates as
proposed ([Zr4O2(OH)5(OAP)5Cl2]·8H2O). However, more accurate results could be
produced if one considers the hydrogen bond.


The zirconia powders were

precursors and zirconia powders were characterized by the
Brunauer-Emmett-Teller (BET) multilayer nitrogen adsorption method
(Quantachrome Nova 1200), thermogravimetric analyses (Seiko EXSTAR 6000 TG/DTA
6200), scanning electron micrograph (SEM) (JEOL JXM 6400), diffuse reflectance
infrared spectroscopy (Nicolet Magna-IR 750), and X-ray powder diffraction (XRD)
patterns using copper Kα radiation with a wavelength of 1.5418 Å (Bruker AXS
D8). The volume fraction of the tetragonal and monoclinic phases (t-ZrO2 and
m-ZrO2, resp.) and the relative ratio of t-ZrO2 to m-ZrO2 were determined using
the method proposed by Toraya and coworkers (see supporting information). To
examine the interaction between zirconia and carboxylic acid, periodic DFT
calculations were performed using the Vienna ab initio simulation package
(VASP). The projector augmented wave method (PAW) [22] with the generalized
gradient approximation (GGA) using the Perdew-Burke-Ernzerhof (PBE) functional
was used. In keeping with previous studies, a stable () plane with a (2 × 2)
surface was utilized. Similar to the previous study, a supercell with 16 Zr and
32 O atoms was constructed. A vacuum space of 15 Å and a 415 eV kinetic energy
cut-off for a plane wave basis set were applied. The Monkhorst-Pack=meshes with
(3 × 3 × 3) and (3 × 3 × 1) k-points were used for bulk and surface
calculations, respectively. For 2D surface calculations, half of the atomic
layers were fixed to the bulk structure, and the remaining layers and the
adsorbate were fully relaxed. Adsorption energies (Eads) were defined as Eads =
E(adsorbate/ZrO2) − E(ZrO2) − E(adsorbate), where E(adsorbate/ZrO2), E(ZrO2),
and E(adsorbate) are the calculated energies of a carboxylic acid on zirconia,
bare zirconia, and gas-phase carboxylic acid. The surface coverage was 25%. To
support the infrared spectroscopic measurements, frequencies were also calculated
based on the optimized structures. In this study, we applied the same k-point
for geometry optimization since our previous study showed a minor difference
between prediction and experiment.


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