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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.

No MeSH data available.


SEM images of dried ZrO2 gels prepared with various solvent ratios (VH2O/VEtOH): (a) 1.8/3.0 (P11), (b) 2.0/2.8 (P12), (c) 2.2/2.6 (P13), (d) 2.4/2.4 (P14) and (e) 2.6/2.2 (P15).
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Figure 3: SEM images of dried ZrO2 gels prepared with various solvent ratios (VH2O/VEtOH): (a) 1.8/3.0 (P11), (b) 2.0/2.8 (P12), (c) 2.2/2.6 (P13), (d) 2.4/2.4 (P14) and (e) 2.6/2.2 (P15).

Mentions: From the above equations (5) and (6), it can be seen that the increasing χ, which can be caused by the enlarging polarity difference of the gelation phase and mixed solvents, can also alter ΔG from negative to positive. As we have known, the polarity of the gel phase gradually decreases during the poly-condensation because of the consumption of high polarity hydroxy groups, and the polarity of the mixed solvents rises due to the enlarging proportion of water. We also investigate the influence of different solvent proportions on the morphology of dried gels, as presented in figure 3. The morphologies of the dried gels change from nanopores, through co-continuous skeletons, to broken bulky skeletons with the increase of water proportion. When the proportion of water in the mixed solvents is low, the polarity difference between the gel phase and mixed solvents becomes small and leads to a weak phase separation tendency (figure 3(a)). In contrast, the phase separation tendency in the system becomes stronger with a higher proportion of water, and the broken bulky skeletons are obtained (figure 3(e)).


Preparation of macroporous zirconia monoliths from ionic precursors via an epoxide-mediated sol-gel process accompanied by phase separation
SEM images of dried ZrO2 gels prepared with various solvent ratios (VH2O/VEtOH): (a) 1.8/3.0 (P11), (b) 2.0/2.8 (P12), (c) 2.2/2.6 (P13), (d) 2.4/2.4 (P14) and (e) 2.6/2.2 (P15).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: SEM images of dried ZrO2 gels prepared with various solvent ratios (VH2O/VEtOH): (a) 1.8/3.0 (P11), (b) 2.0/2.8 (P12), (c) 2.2/2.6 (P13), (d) 2.4/2.4 (P14) and (e) 2.6/2.2 (P15).
Mentions: From the above equations (5) and (6), it can be seen that the increasing χ, which can be caused by the enlarging polarity difference of the gelation phase and mixed solvents, can also alter ΔG from negative to positive. As we have known, the polarity of the gel phase gradually decreases during the poly-condensation because of the consumption of high polarity hydroxy groups, and the polarity of the mixed solvents rises due to the enlarging proportion of water. We also investigate the influence of different solvent proportions on the morphology of dried gels, as presented in figure 3. The morphologies of the dried gels change from nanopores, through co-continuous skeletons, to broken bulky skeletons with the increase of water proportion. When the proportion of water in the mixed solvents is low, the polarity difference between the gel phase and mixed solvents becomes small and leads to a weak phase separation tendency (figure 3(a)). In contrast, the phase separation tendency in the system becomes stronger with a higher proportion of water, and the broken bulky skeletons are obtained (figure 3(e)).

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.