Novel band gap-tunable K–Na co-doped graphitic carbon nitride prepared by molten salt method

K and Na ions co-doped into g-C3N4 crystal lattice can tune the position of CB and VB potentials, influence the structural and optical properties, and thus improve the photocatalytic degradation and mineralization ability. •K, Na co-doped g-C3N4 was prepared in KCl/NaCl molten salt system.•The structural and optical properties of g-C3N4 were greatly influenced by co-doping.•The position of VB and CB can be tuned by controlling the weight ratio of eutectic salts to melamine.•Co-doped g-C3N4 showed outstanding photodegradation ability, mineralization ability, and catalytic stability. Novel band gap-tunable K–Na co-doped graphitic carbon nitride was prepared by molten salt method using melamine, KCl, and NaCl as precursor. X-ray diffraction (XRD), N2 adsorption, Scanning electron microscope (SEM), UV–vis spectroscopy, Photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The CB and VB potentials of graphitic carbon nitride could be tuned from −1.09 and +1.55eV to −0.29 and +2.25eV by controlling the weight ratio of eutectic salts to melamine. Besides, ions doping inhibited the crystal growth of graphitic carbon nitride, enhanced the surface area, and increased the separation rate of photogenerated electrons and holes. The visible-light-driven Rhodamine B (RhB) photodegradation and mineralization performances were significantly improved after K–Na co-doping.