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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.


XRD patterns of ZrO2 monoliths after solvothermal treatment with various ammonia concentrations.
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Figure 9: XRD patterns of ZrO2 monoliths after solvothermal treatment with various ammonia concentrations.

Mentions: The solvothermal treatment of gels is introduced to study the effects on the crystallization and modification of ZrO2 skeletons. The choice of appropriate organic solvents plays a key role in the solvothermal synthesis, such as redox, polarity, complexation, viscosity, and so forth, and strongly influences the heterogeneous liquid–solid reactions [36]. In this study, an ethanol solution of ammonia was chosen as the solvent, and ZrO2 monoliths were solvothermally treated with various ammonia concentrations at 180 °C for 12 h. The XRD patterns shown in figure 9 demonstrates that the peaks of tetragonal ZrO2 crystallite become increasingly sharp when the ammonia concentration increases from 0.5 to 2.0 mol L−1. This is on account of the higher solubility of ZrO2 gel particles in the solvent with a higher concentration of ammonia and with the reaction of dissolution-precipitation, which will lead to the formation of the products with higher crystallinity at a rapid rate [26]. Figure 10 shows the macroporous morphology of ZrO2 monoliths before and after being solvothermally treated with different ammonia concentrations. It is observed that ammonia concentration does not much affect the tailoring on the skeletons of gels. The scale of the co-continuous skeleton slightly increases, and the surface of the skeletons just become smooth.


Preparation of macroporous zirconia monoliths from ionic precursors via an epoxide-mediated sol-gel process accompanied by phase separation
XRD patterns of ZrO2 monoliths after solvothermal treatment with various ammonia concentrations.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 9: XRD patterns of ZrO2 monoliths after solvothermal treatment with various ammonia concentrations.
Mentions: The solvothermal treatment of gels is introduced to study the effects on the crystallization and modification of ZrO2 skeletons. The choice of appropriate organic solvents plays a key role in the solvothermal synthesis, such as redox, polarity, complexation, viscosity, and so forth, and strongly influences the heterogeneous liquid–solid reactions [36]. In this study, an ethanol solution of ammonia was chosen as the solvent, and ZrO2 monoliths were solvothermally treated with various ammonia concentrations at 180 °C for 12 h. The XRD patterns shown in figure 9 demonstrates that the peaks of tetragonal ZrO2 crystallite become increasingly sharp when the ammonia concentration increases from 0.5 to 2.0 mol L−1. This is on account of the higher solubility of ZrO2 gel particles in the solvent with a higher concentration of ammonia and with the reaction of dissolution-precipitation, which will lead to the formation of the products with higher crystallinity at a rapid rate [26]. Figure 10 shows the macroporous morphology of ZrO2 monoliths before and after being solvothermally treated with different ammonia concentrations. It is observed that ammonia concentration does not much affect the tailoring on the skeletons of gels. The scale of the co-continuous skeleton slightly increases, and the surface of the skeletons just become smooth.

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.