Modified graphitic carbon nitride as the photocatalyst for wastewater treatment under visible light irradiation

Abstract

Monomeric graphitic carbon nitride (g-C3N4) with abundant pores and suitable energy band structure was preparedbycalcining the mixture precursor at high temperature. Meanwhile, Zr/g-C3N4 and g-C3N4/ZnO photocatalysts were fabricated by doping the transition metal and constructing heterojunctions respectively, thereby overcoming the defects of monomeric carbon nitride and improving photocatalytic activity. Sample morphology and structure were characterized by TEM, BET, XRD, XPS, PL, and UV–vis DRS techniques, and the photocatalytic performance was evaluated by degradation of methylene blue (MB) under visible light irradiation. The results indicated that the different energy band structures of g-C3N4 from various precursors promoted the transfer and separation of photogenerated electron-hole pairs, thus improving the photocatalytic performance. Furthermore, Zr/g-C3N4 presented an outstanding photocatalytic activity for MB degradation, which was mainly due to the adjustment of band gap and the rapid movement of charge caused by the introduction of Zr. The g-C3N4/ZnO photocatalyst synthesized by co-melting and recrystallizing the composite precursors of two semiconductors performed well on the aspects of structure and performance, degrading 98.07% MB after 180 min of irradiation, 29% higher than that of g-C3N4-MU. The Z-scheme charge transfer route in g-C3N4/ZnO system integral to improving the separation of photocarriers and enhancing the oxidation of photocatalyst. Based on the radical scavenging experiment, the main oxidation species in the photocatalytic process was determined, and the photocatalytic mechanism was further speculated, which provided a future direction in highly efficient g-C3N4 photocatalyst design.