Molten-salt synthesis of g-C3N4-Cu2O heterojunctions with highly enhanced photocatalytic performance

A novel heterojunction composite photocatalyst, g-C3N4-Cu2O, was fabricated via a high-temperature solid-phase molten salt method, hydrothermal method, and high-temperature calcination method. The structures and properties of as-synthesized samples were characterized using a range of techniques, such as X-ray photoelectron spectroscopy, scanning electron microscopy, UV-vis diffuse reflectance spectra and the Brunauer Emmet Teller (BET) theory. Their photocatalytic activity was evaluated based on the degradation of methyl orange (MO) under visible light irradiation. Based on the results obtained via TEM, XPS, EPR, and the other techniques, we verified that a heterojunction had formed. The g-C3N4-Cu2O heterojunction had the largest specific surface area, which provided plentiful activated sites for photocatalytic reaction. Moreover, g-C3N4-Cu2O showed the highest photocurrent effect and the minimum charge-transfer resistance. Furthermore, the g-C3N4-Cu2O heterojunction exhibited the highest MO photodegradation rate. After a series of radical trapping experiments and EPR analysis, we demonstrated that the holes and center dot O-2(-) radicals could be the main active species involved in MO photodegradation. The molten-salt process can improve the BET surface area to form abundant heterojunction interfaces, which serve as channels for photogenerated carrier separation and thereby enhance its light utilization and quantum efficiency.