Carbon dots incorporated in hierarchical macro/mesoporous g-C3N4/TiO2 as an all-solid-state Z-scheme heterojunction for enhancement of photocatalytic H2 evolution under visible light

In recent years, coupling TiO2 with other narrow bandgap semiconductors to improve photocatalytic hydrogen generation rate has attracted widespread attention. Herein, carbon dots (C dots) decorated g-C3N4/TiO2 all-solid-state Z-scheme heterojunction photocatalysts with hierarchical macro/mesoporous structure have been fabricated via a facile solvothermal and calcination method. The dosage of C dots greatly influences the microstructure and the visible-light photocatalytic H2 evolution rate (HER). Under the optimal condition, the ternary composites consisting of C dots, g-C3N4 and TiO2 exhibited the highest HER of 580 μmol g−1 h−1, exceed the pure TiO2, pure g-C3N4 and the binary g-C3N4/TiO2 hybrid photocatalyst by a fact of 6.6 times, 2.1 times and 1.6 times, respectively. The excellent photocatalytic performance for hydrogen evolution is ascribed to the stronger light absorption, higher specific surface area and faster charge transportation. An all-solid-state Z-scheme heterojunction mechanism was proposed in which C dots serve as a mediator to improve the separation and transportation of photo-excited charge carriers.