Molten salt assisted in-situ synthesis of TiO2/g-C3N4 composites with enhanced visible-light-driven photocatalytic activity and adsorption ability

In this work, zero-dimensional (OD)/ two-dimensional (2D) TiO2/g-C3N4 composite photocatalysts with homogeneous well-developed heterostructures were successfully prepared from LiCl-KCl flux using a facile molten salt assisted in-situ route. The phase composition, morphology, surface area, chemical structure, thermal stability as well as optical property of the heterostructured composites were systematically characterized. Benefiting from the exfoliation effect of molten salt flux, the flux-grown g-C3N4 products exhibit a rough surface with porous structures and many co-existed secondary products including nanosheets, nanrods and nanotubes, which also lead to an obvious increase in the surface area of the flux-grown g-C3N4 and composites. The photocatalytic performance of the TiO2/g-C3N4 heterostructure composites was evaluated by photodegradation of methyl orange (MO) and rhodamine B (RhB) under the visible light irradiation (lambda > 420 nm), and proved to be greatly improved compared to individual TiO2 and g-C3N4. Moreover, the enhanced photocatalytic activity of TiO2/g-C3N4 composites can be attributed to the higher surface area and the synergistic effects between TiO2 and g-C3N4 including the increased light harvesting ability and more efficient separation of the photogenerated charge carriers, which originates from the construction of TiO2/g-C3N4 heterostructures at the interface between the two components. Furthermore, a possible mechanism responsible for the enhanced photocatalytic performance was also proposed. Additionally, the TiO2/g-C3N4 composites showed a superior adsorption ability for the removal of cationic dye methylene blue (MB) from aqueous solutions, due to their high surface area and strong electrostatic interactions between catalysts and dye molecules.