Highly efficient photocatalytic performance and mechanism of α-ZnTcPc/gC3N4 composites for methylene blue and tetracycline degradation under visible light irradiation

In this study, zinc (II) 1, 8(11), 15(18), 22(25)-tetrakis(4-carboxylphenoxy) phthalocyanine (alpha-ZnTcPc) was synthesized as sensitizer to construct a novel photocatalyst alpha-ZnTcPc/g-C3N4 by a polycondensation strategy. The FT-IR and XPS spectra demonstrated that the a-ZnTcPc molecules were covalently coupled on g-C3N4. The 10% alpha-ZnTcPc/g-C3N4 composites exhibit excellent extended spectral response with intense broad near-infrared absorption at 695 nm and with significantly fascinated charge carrier separation. As expected, the 10% alpha-ZnTcPc/g-C3N4 displayed a remarkable improved photocatalytic performance in decomposition of methylene blue (MB) and antibiotic tetracycline with degradation rates of 94.49% and 91.43% under visible light irradiation, respectively. The hydroxyl radicals (center dot OH) were observed as the main reactive oxidizing species in tetracycline decomposition. Moreover, the possible mechanism for enhanced visible light photocatalytic capability might be ascribed to the synergetic effect between alpha-ZnTcPc and g-C3N4, which creates large surface areas, decreases the recombination rate of photogenerated charge carries, as well as improves the visible light harvesting significantly. This work not only presents a practical method to conquer the drawback of pure g-C3N4, but also provides useful insights to construct other g-C3N4-based composites to take full advantage of solar light towards practical applications for eliminating recalcitrant organic pollutants.