fig3

Figure 3. Structural information of distinctive hollow structures. TEM images of the Fe-IPA with hollow structure obtained after reaction for (A1) 1 h, (A2) 2 h, (A3) 4 h, and (A4) 12 h. The scale bars are 300 nm; (A5) Schematic illustration of the formation process of Fe-glycerate hollow spheres: (I) formation of Fe-glycerate nanosheets on the surface of the initially formed Fe-IPA solid spheres; (II) further growth of Fe-glycerate nanosheets and consumption of Fe-IPA spheres; (III) formation of hierarchical Fe-glycerate hollow spheres. Reproduced with the permission of Ref.^[71] Copyright 2015, John Wiley & Sons. (B) Schematic illustration of the formation process of yolk-shell MoO₂ microspheres. Reproduced with the permission of Ref.^[77] Copyright 2013, Royal Society of Chemistry. (C) Schematic illustration of the formation process of NiCo₂O₄ core-in-double-shell hollow spheres. Reproduced with the permission of Ref.^[87] Copyright 2014, John Wiley & Sons.