Fabrication of MgAl2O4 spinel with exposed (400) crystal planes for enhanced Congo red adsorption

Magnesium aluminate (MgAl 2 O 4 ) spinel with dominant (400) plane exposure was synthesized by tailoring the precursor structure using a nonhydrolytic sol-gel method (NHSG). The effects of magnesium source and aluminum source on the preferential growth and morphology of MgAl 2 O 4 were systematically investigated. Rietveld refinement was used to analyze the structural variations of the prepared MgAl 2 O 4 . Furthermore, Density Functional Theory (DFT) calculation was performed to determine the adsorption energies of Congo red on the (311) plane and (400) plane. Results demonstrate that uniform MgAl 2 O 4 petals with a length of 240–280 nm were prepared using Mg and Al respectively as magnesium source and aluminum source, exhibiting a significantly enhanced I 400 /I 311 ratio of 2.459. This higher I 400 /I 311 ratio indicates a greater proportion of well-defined petals and corresponds to enhanced adsorption capacity. The MgAl 2 O 4 precursor, synthesized through polycondensation of MgAl 2 (OC 2 H 5 ) 8 prepared from metallic Mg and Al, exhibits an atomic arrangement analogous to the (400) plane of MgAl 2 O 4 spinel, facilitating its crystallization into (400)-dominant MgAl 2 O 4 petals. DFT calculations further reveal that the (400) plane of MgAl 2 O 4 exhibits a stronger adsorption energy to Congo red (CR) (-3.86 eV) than the (311) plane (-0.88 eV), consistent with the experimental results. This work provides a novel method for special crystal plane exposure.