Graphitic carbon nitride co-modified by zinc phthalocyanine and graphene quantum dots for the efficient photocatalytic degradation of refractory contaminants

Broad solar light absorption and rapid photogenerated electron-hole pair separation are two critical factors for the efficient enhancement of catalytic performance in a g-C3N4-based photocatalytic system. This study developed a facile method to construct a ternary graphitic carbon nitride/zinc tetracarboxyphthalocyanine/graphene quantum dots (g-C3N4/ZnTcPc/GQDs) composite photocatalyst. Graphene quantum dots (GQDs) were used to modify g-C3N4/ZnTcPc through hydrothermal method, where g-C3N4/ZnTcPc was fabricated by immobilizing zinc tetracarboxyphthalocyanine (ZnTcPc) onto g-C3N4 covalently via amido bonds. The photocatalyst was characterized by transmission electron microscopy, ultraviolet-visible diffuse reflectance spectrum, and X-ray photoelectron spectroscopy. The g-C3N4/ZnTcPc/0.1GQDs composites presented an increased photocatalytic activity by using Rhodamine B, sulfaquinoxaline sodium and carbamazepine as the model pollutants under solar light irradiation. ZnTcPc bonding on the g-C3N4 broadens its visible-light spectral response, and GQDs promotes the photogenerated electron-hole-pair separation efficiency because of its efficient electrons-transfer property. Experiments confirmed that superoxide radicals, photogenerated holes and singlet oxygen are the primary active species. The photocatalytic degradation pathway of Rhodamine B, sulfaquinoxaline sodium and carbamazepine was proposed on the basis of ultra-performance liquid chromatography and high-definition mass spectrometry.