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Particle size of nanomaterials has significant impact on their photocatalyst properties. In this paper, TiO 2 nanoparticles with different crystalline sizes were prepared by adjusting the alkali-hydrothermal time (0-48 h). An annealing in N 2 atmosphere after hydrothermal treatment caused TiO 2 reduction and created defects, resulting in the visible light photocatalytic activity. The evolution of physicochemical properties along with the increase of hydrothermal time at a low alkali concentration has been revealed. Compared with other TiO 2 samples, TiO 2 -24 showed higher photocatalytic activity toward degrading Rhodamine B and Sulfadiazine under visible light. The radical trapping and ESR experiments revealed that O 2•is the main reactive specie in TiO 2 -24.Large specific surface areas and rapid transfer of photogenerated electrons are responsible for enhancing photocatalytic activity. The above findings clearly demonstrate that particle size and surface oxygen defects can be regulated by alkali-hydrothermal method. This research will deepen the understanding of particle size on the nanomaterials performance and provide new ideas for designing efficient photocatalysts.

Layered Ruddlesden-Popper (RP) hybrid perovskite semiconductors have recently emerged as promising materials for photovoltaics application. However, the strong quantum and dielectric confinement of RP perovskite compounds increases their optical bandgap and binding energy of exciton, which limit their application in solar cells. Herein, the doping of RP-based (BA) 2 (MA) 3 Pb 4 I 13 perovskite materials by means of Li + is reported for the first time, which can significantly help to reduce dielectric confinement and thus the exciton-binding energy via reducing the dielectric constant difference between organic spacer cation and inorganic framework. Furthermore, the Li + doping boosts the carrier mobility, reduces the trap density states, and thus allows to achieve power conversion efficiency of ≈15% via Li + -(BA) 2 (MA) 3 Pb 4 I 13 -based perovskite solar cell, which is the highest efficiency for layered perovskites (n = 4) so far. This work highlights the promising ionic doping engineering for further improvement of the layered perovskite materials.