Sol–gel preparation of hierarchically porous magnesium aluminate (MgAl2O4) spinel monoliths for dye adsorption
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Hierarchically porous spinel-type binary metal oxide MgAl2O4 with cocontinuous skeletons and interconnected macropores has been synthesized by a facile sol–gel method accompanied by phase separation, in which poly (ethylene oxide) (PEO) works as phase separation inducer to form micrometer-scale phase-separated macrochannels at the same time of sol–gel transition. The obtained xerogels exhibit in the form of a monolith with well-defined macropores and cocontinuous dense skeletons by adjusting the amount of PEO. The xerogel and those heat-treated at or below 600 °C are amorphous, and heat-treatment at or above 700 °C allows the precipitation of complete crystalline MgAl2O4 spinel with a macropore size of 0.7–0.9 μm, a porosity of 60–70%, and a BET surface area of 40–80 m2 g−1, without spoiling the macrostructure of monoliths. Three anionic dyes and two cationic dyes are selected as targeted adsorbates to investigate the selective adsorption ability of a hierarchically porous MgAl2O4 spinel. The resultant MgAl2O4 spinel shows a high affinity and adsorption rate toward anionic dyes Congo Red, Methyl Orange, and Methyl Blue. The maximum adsorption capacity of MgAl2O4 spinel toward these three anionic dyes are 2721.6 mg g−1 for Congo Red, 2469.7 mg g−1 for Methyl Orange, and 6771.9 mg g−1 for Methyl Blue, respectively.
Hierarchically porous spinel-type binary metal oxide MgAl2O4 has facilely been synthesized by a sol–gel method accompanied by phase separation.
The resultant MgAl2O4 spinel has high adsorption capacity toward anionic dyes Congo Red, Methyl Orange, and Methyl Blue.
A probable adsorption mechanism based on the strong electrostatic attraction and hydrogen bonding is discussed.
KeywordsHierarchically porous monolith Sol–gel Phase separation Magnesium aluminate spinel Dye adsorption
This work is supported by the High Science & Technique Brainstorm Project of Zhejiang Province of China (No. 2017C01002) and National Natural Science Foundation of China (51372225).
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Conflict of interest
The authors declare that they have no conflict of interest.
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