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Preparation of macroporous zirconia monoliths from ionic precursors via an epoxide-mediated sol-gel process accompanied by phase separation

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ABSTRACT

Monolithic macroporous zirconia (ZrO2) derived from ionic precursors has been successfully fabricated via the epoxide-mediated sol-gel route accompanied by phase separation in the presence of propylene oxide (PO) and poly(ethylene oxide) (PEO). The addition of PO used as an acid scavenger mediates the gelation, whereas PEO enhances the polymerization-induced phase separation. The appropriate choice of the starting compositions allows the production of a macroporous zirconia monolith with a porosity of 52.9% and a Brunauer–Emmett–Teller (BET) surface area of 171.9 m2 · g−1. The resultant dried gel is amorphous, whereas tetragonal ZrO2 and monoclinic ZrO2 are precipitated at 400 and 600 °C, respectively, without spoiling the macroporous morphology. After solvothermal treatment with an ethanol solution of ammonia, tetragonal ZrO2 monoliths with smooth skeletons and well-defined mesopores can be obtained, and the BET surface area is enhanced to 583.8 m2 · g−1.

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SEM image of ZrO2 monoliths after heat treatment at 700 °C
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Figure 7: SEM image of ZrO2 monoliths after heat treatment at 700 °C

Mentions: Figure 6 displays the XRD patterns of the gels heat-treated at various temperatures. No peaks are observed for the gels heat-treated at 300 °C, which manifests an amorphous state. After calcination at 400 °C, broad diffraction peaks appear due to the precipitation of tetragonal ZrO2, and all tetragonal ZrO2 turn to monoclinic ZrO2 after calcination at 900 °C. From the Scherrer’s equation the crystallite size of tetragonal ZrO2 obtained at 400 °C is 7.6 nm, and the monoclinic crystallite size acquired at 900 °C is 35.4 nm. This means that increasing the heat-treated temperature can enlarge the tetragonal ZrO2 crystallite and finally transform it into monoclinic ZrO2 crystallite, which is more stable at a low temperature. The result is consistent with Garvie’s theory [49], which believes that tetragonal ZrO2 can exist in low temperatures when the nanoparticle size is less than 30 nm. Figure 7 presents the SEM image of gels heat-treated at 700 °C. It can be seen that the well-defined macroporous morphology is basically retained, signifying that the heat treatment does not destroy the macropore structure of ZrO2 monoliths.


Preparation of macroporous zirconia monoliths from ionic precursors via an epoxide-mediated sol-gel process accompanied by phase separation
SEM image of ZrO2 monoliths after heat treatment at 700 °C
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036470&req=5

Figure 7: SEM image of ZrO2 monoliths after heat treatment at 700 °C
Mentions: Figure 6 displays the XRD patterns of the gels heat-treated at various temperatures. No peaks are observed for the gels heat-treated at 300 °C, which manifests an amorphous state. After calcination at 400 °C, broad diffraction peaks appear due to the precipitation of tetragonal ZrO2, and all tetragonal ZrO2 turn to monoclinic ZrO2 after calcination at 900 °C. From the Scherrer’s equation the crystallite size of tetragonal ZrO2 obtained at 400 °C is 7.6 nm, and the monoclinic crystallite size acquired at 900 °C is 35.4 nm. This means that increasing the heat-treated temperature can enlarge the tetragonal ZrO2 crystallite and finally transform it into monoclinic ZrO2 crystallite, which is more stable at a low temperature. The result is consistent with Garvie’s theory [49], which believes that tetragonal ZrO2 can exist in low temperatures when the nanoparticle size is less than 30 nm. Figure 7 presents the SEM image of gels heat-treated at 700 °C. It can be seen that the well-defined macroporous morphology is basically retained, signifying that the heat treatment does not destroy the macropore structure of ZrO2 monoliths.

View Article: PubMed Central - PubMed

ABSTRACT

Monolithic macroporous zirconia (ZrO2) derived from ionic precursors has been successfully fabricated via the epoxide-mediated sol-gel route accompanied by phase separation in the presence of propylene oxide (PO) and poly(ethylene oxide) (PEO). The addition of PO used as an acid scavenger mediates the gelation, whereas PEO enhances the polymerization-induced phase separation. The appropriate choice of the starting compositions allows the production of a macroporous zirconia monolith with a porosity of 52.9% and a Brunauer–Emmett–Teller (BET) surface area of 171.9 m2 · g−1. The resultant dried gel is amorphous, whereas tetragonal ZrO2 and monoclinic ZrO2 are precipitated at 400 and 600 °C, respectively, without spoiling the macroporous morphology. After solvothermal treatment with an ethanol solution of ammonia, tetragonal ZrO2 monoliths with smooth skeletons and well-defined mesopores can be obtained, and the BET surface area is enhanced to 583.8 m2 · g−1.

No MeSH data available.


Related in: MedlinePlus