Photo-Fenton assisted AgCl and P-doped g-C3N4 Z-scheme photocatalyst coupled with Fe3O4/H2O2 system for 2, 4-dimethylphenol degradation

Abstract

In this study graphitic carbon nitride (g-C3N4 or GCN) and phosphorus doped graphitic carbon nitride (p-g-C3N4 or PCN) were prepared using facile thermal polycondensation method. Phosphorus doping was employed to preserve the non-metallic nature of GCN. The AgCl/PCN/Fe3O4 heterojunction was synthesized using a simple in-situ route. The photocatalytic performance of the GCN, PCN, Fe3O4 and AgCl/PCN/Fe3O4 was tested towards 2, 4-dimethylphenol (DMP) pollutant. The work explored improvement in physiochemical properties and reduction of band gap of GCN after P doping (through Tauc's plot method). Coupling with AgCl (silver halide) also enhanced photoinduced charge carriers' separation and migration ability due to apt band alignment among both AgCl and PCN photocatalysts which resulted in formation of direct Z-scheme charge transfer mechanism. Similarly, the incorporation of ferrimagnetic material i.e. Fe3O4 enhanced the generation of hydroxyl (•OH) radicals via photo-Fenton process and facilitated photocatalysts easy separation from the aqueous medium. Through PL and EIS analysis the enhanced charge separation and migration ability in AgCl/PCN/Fe3O4 nanocomposite was validated. The attained DMP degradation efficiency of photo-Fenton assisted AgCl/PCN/Fe3O4/H2O2 Z-scheme nanocomposite was much higher i.e. 99% compared to other photocatalysts within 60 min of visible light irradiation following pseudo-first-order kinetics. Electron paramagnetic resonance (EPR) and scavenging tests confirmed the substantial role of •OH and •O2− radicals in the photo-Fenton reaction. Furthermore, liquid chromatography-mass spectrometry (LC-MS) analysis detected the generated oxidative products and mineralization pathways associated with DMP degradation. The proposed direct Z-scheme charge transfer route presented efficient charge separation and migration ability in AgCl/PCN/Fe3O4 nanocomposite. Recycle ability of the fabricated AgCl/PCN/Fe3O4 photocatalyst was tested up to 5 cycles with 90% removal efficacy, confirming the excellent reusability and stability of AgCl/PCN/Fe3O4 photocatalyst.