The Chemistry of Phase Separation in Aqueous Hydrolyzing Metal Systems: Aluminium(III) and Iron(III)

HydrolysisHydrolysis of aqueous metal ion systems is fundamental to the phase separation of (oxy)(hydr)oxides(Oxy)(hydr)oxides, the understanding of which can help controlling, e.g., the formation of specific crystal structures, and advance various applications. Unlike the predominant, simplified physical notions implemented in the framework of classical nucleationNucleation theory, recent advances in the understanding of nucleationNucleation processes have highlighted the role of subtle chemical changes in precursors species and of the solvent, water. All of this has demonstrated the importance of “non-classical” concepts when discussing phase separation in hydrolyzing metal systems, beyond the classical ideas of the size of critical nuclei and the interpretation of supersaturation. Keeping in mind the vital importance of the chemistries of aluminium(III)Aluminium(III) andIron(III) iron(III)Iron(III) ions in geochemical, physiological, and engineering processes, but also in the medical and renewable energy fields, herein, we summarize recent findings on the mechanisms of (oxy)(hydr)oxide formation from homogeneous aqueous solutions. Specific attention is paid to the role of water in understanding the nucleationNucleation behavior, an area where significant further advances are expected in the future. Also, we review the role of organic additives in controlling the nucleationNucleation of aluminium(III)Aluminium(III) and iron(III)Iron(III) (oxy)(hydr)oxides(Oxy)(hydr)oxides, including biomineralization processes.