SEM micrographs show that α-Fe2O3, Fe(OH)3, γ-MnO2, and kaolinite all had irregular morphology, while α-FeOOH and α-Al2O3 were in needle and globular shapes, respectively (Fig. S3). The apparent particle sizes of α-Al2O3 and α-Fe2O3 were much larger than those of the other minerals (Fig. S3), which is consistent with the results of specific surface area measurements (Table 1). The BET surface areas of α-Fe2O3, α-FeOOH, Fe(OH)3, α-Al2O3, γ-MnO2, and kaolinite were determined to be 4.4, 25.9,
