Size-dependent electronic, optical and photocatalytic properties of Ti3C2O2 quantum dots studied by first-principles calculations

Abstract Due to quantum confinement effect, quantum dots (QDs) would show totally different electronic and optical properties from two-dimensional (2D) nanosheets. For the first time, we have systemically investigated the optical, electronic and photocatalytic properties of Ti3C2O2 QDs based on the first-principles calculations. Our results show that the most stable structures of Ti3C2O2 QDs have features of hexagonal unit centered by O atom. The energy gaps of QDs with H passivation vary from 2.76 to 1.14 eV with the increase of lateral size. The lowest unoccupied molecular orbital (LUMO) is mainly contributed by Ti:3d, while the highest occupied molecular orbital (HOMO) is mainly contributed by C:2p and Ti:3d. The corresponding partial charge density at HOMO or LUMO is distributed around Ti and C atoms in the outside surface of QDs. The QDs show large absorption coefficient with the order of 105 cm−1 at visible light range, while the first absorption peaks vary from 2.8 to 1.4 eV (443–886 nm). Most importantly, the Ti3C2O2 QDs present size-dependent photocatalytic selectivity for CO2 reduction and photocatalytic activity for water splitting, caused by the shift of energy level positions of HOMO and LUMO. Our study reveal the potential of Ti3C2O2 QD in electronic and photocatalytic applications and provide new ideals into the design of photocatalysis based on QD materials.