Rapid fabrication of hollow and yolk–shell α-Fe2O3 particles with applications to enhanced photo-Fenton reactions

α-Fe2O3 microspheres with hollow and yolk–shell (X@Fe2O3) morphologies are fabricated through synthesis in the confined environment of aerosol droplets. The process exploits the competitive carbonization of sucrose and the recrystallization of iron salts concurrently occurring in the droplet, to control the initial placement of iron species on the external surface or within the carbon microspheres. Upon calcination, the iron salts fuse and are oxidized to form a robust α-Fe2O3 shell. A partial burnoff of the carbon during calcination leads to the formation of microspheres with a core of carbon while complete burnoff leads to hollow α-Fe2O3 particles. Integration of ceramic nanoparticles in the precursor solution results in the inclusion of clusters of such nanoparticles in the core. The flexibility of synthesis of either hollow or yolk–shell particles makes the process amenable to the rapid fabrication of functional materials. As an example, α-Fe2O3 hollow microspheres show a 20-fold improvement in photo-Fenton reactivity towards the degradation of methylene blue, in comparison to commercially available materials.