Aqueous growth of titania subnanoparticles: an understanding of the ultrasmall visible-light-absorbing unit of (TiO 2 ) 8 (H 2 O) 16 .

An atomistic understanding of the initial hydrothermal growth of titania remains crucial for the development of nanosized materials, where the presence of water strongly affects the particle growth in comparison to the vapor-phase growth. Herein, we explore the structural evolution of aqueous titania from its salt precursors and determine the nanoparticle configurations in the practical environment by invoking ab initio molecular dynamic simulations and a machine-learning accelerated structural search. Thermodynamically, Ti(OH) 4 ·2H 2 O serving as the hydrated monomer undergoes planar-to-tubular-to-spherical multistage growth in the Ti(OH) 4 /H 2 O hydrothermal system, in which large-sized (TiO 2 ) n (H 2 O) m particles ( n = 1-20) are generated via the olation/oxolation reaction. Importantly, in a mixture of particles of different sizes, we identify that (TiO 2 ) 8 (H 2 O) 16 is one of the most abundant species in solution with peculiar metastability and exhibits extraordinary visible-light absorption ability, which may be the smallest aqueous titania subnanoparticle in the form of suspension and worth exploring for photocatalytic applications.