A Z-scheme g-C3N4/Ag3PO4 nanocomposite: Its photocatalytic activity and capability for water splitting

Photodegradation of Rifampin (Rf) was evaluated by g-C3N4/Ag3PO4 nanocomposite (NC) under the visible-light irradiation. The samples were characterized by XRD, SEM-EDX, and X-Ray mapping, FTIR, and DRS. The XRD patterns showed the body-centered cubic phase for Ag3PO4 with an average size of 21.4 ± 3.8 nm and 20 nm for the NC by the Scherrer and Williamson-Hall equations, respectively. The pHpzc values about 10.7, 9.7, and 6.9 and the bandgap energies of 2.39, 2.97, and 2.90 eV were respectively for the as-synthesized Ag3PO4, g-C3N4, and g-C3N4/Ag3PO4 samples. The absorbencies of Rf solutions at maximum wavelengths of 330 and 470 nm were used to estimate the Rf photodegradation extent. Greater degradation extents were obtained by the absorbencies recorded at 470 nm. The percentage of the composite components varied the photodegradation efficiency, and the composite containing 60% g-C3N4 (G60) showed the highest activity. The best photodegradation results obtained at CRf: 2 ppm, solution pH: 5.5, catalyst dose: 1 g/L, irradiation time: 10 min. The solutions with degradation extents of 96 and 97% showed the mineralization extents of 96.4 and 98.2%, calculated from the COD results. The photodegradation pathway obeyed the direct Z-Scheme mechanism. This mechanism pathway was theoretically evaluated for the probable ability of the composite for the hydrogen production and water splitting. The potential of the CB positions (Ag3PO4: −1.08 V, g-C3N4: 0.21 V) confirms that the accumulated electrons in CB-Ag3PO4 position are stronger reducing agent than that of g-C3N4 for the reduction of dissolved oxygen to the superoxide radicals and they are also capable of reducing water molecules or protons to hydrogen molecules.