Extraordinary Enhancement of UV Absorption in TiO2 Nanoparticles Enabled by Low-Oxidized Graphene Nanodots

Titanium oxide (TiO2) exhibits intrinsically strong absorption of ultraviolet (UV) light, which has been utilized in a variety of applications, such as environmental purification/sterilization, health care, and energies. Accordingly, it is greatly demanded to precisely tune and further improve the UV absorption of TiO2 to significantly broaden its versatility. Herein, we report an extraordinary enhancement of UV absorption in TiO2 nanoparticles (NPs) incorporated with graphene nanodots (GNDs) of low oxygen concentration. Chemically bonded TiO2 NP/GND composites exhibit highly tunable UV absorption, achieving over 243% enhancement of molar extinction coefficient at 336 nm. We found that the drastic improvement is a result of the direct charge transfer from the lowest unoccupied molecular orbitals of GNDs to the conduction bands of TiO2, enabled by wide/direct band gaps in GNDs with a small amount of oxygen. Also, the significantly improved power conversion efficiency (PCE ∼ 16.74%) and UV stability of the TiO2 NP/GND composites reveal their high promise for applications benefiting from TiO2 NP/GND composites, such as solar cells and photolysis.