Effect of g-C3N4 precursors on the morphological structures of g-C3N4/ZnO composite photocatalysts

In this study, g-C3N4/ZnO (CNZ) composite materials were synthesized through a one-step facile method with diverse precursors to investigate the interaction between g-C3N4 precursors and ZnO and the resultant morphological structures. Thiourea (Thio), urea, and dicyandiamide (DCDA) were used as g-C3N4 precursors. Several characterization methods were employed to understand the structural and optical properties affected by the interaction variation between g-C3N4 and ZnO nanoparticles during the thermal polycondensation process to the g-C3N4 structure. Consequently, each composite material resulted in different morphological composite structures. DCDA-CNZ formed a core–shell structure covered with thin g-C3N4 layers due to an efficient interaction between DCDA and ZnO nanoparticles. Meanwhile, Thio and Urea-CNZ showed a segregated morphology of porous g-C3N4 and ZnO nanoparticles in the composites, which was ascribed to a weak interaction between them and gas generation from thiourea and urea during the thermal polymerization. The core–shell morphology of DCDA–CNZ led to a unique behavior, such as the deficient electron density of Zn and g-C3N4-responded photoluminescence emission. Furthermore, DCDA–CNZ exhibited the highest efficiency for the photocatalytic degradation of methylene blue under visible-light irradiation, implying the strong influence of the morphological structure on the photocatalytic performance.