Sol-gel preparation of hierarchically porous magnesium aluminate (MgAl2O4) spinel monoliths for dye adsorption

摘要

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 degrees C are amorphous, and heat-treatment at or above 700 degrees C allows the precipitation of complete crystalline MgAl2O4 spinel with a macropore size of 0.7-0.9m, a porosity of 60-70%, and a BET surface area of 40-80m(2)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 2721.6mgg(-1) for Congo Red, 2469.7mgg(-1) for Methyl Orange, and 6771.9mgg(-1) for Methyl Blue, respectively.