A novel Z-scheme Ag6Si2O7/AgI nanocomposite photocatalyst: Study on the degradation of various refractory compounds and reduction of vanadium (V)

Abstract

The Z-scheme photocatalyst system, with independent reduction and oxidation reaction processes and efficient separation of carriers, has been widely concerned in the field of wastewater treatment. Herein, a Z-scheme Ag6Si2O7/AgI heterojunction nanocomposite was successfully constructed through co-precipitation method and subsequently investigated as a novel photocatalyst for the first time. The macroscopic physical structure, microscopic chemical element composition and optical properties of samples as-prepared samples were adequately detected by various characterization techniques. The photocatalytic properties of Ag6Si2O7/AgI heterostructure with different composite ratios were investigated by degrading methyl orange (MO) under visible light irradiation (λ > 420 nm), and the degradation efficiency of optimal sample (1/3 Ag6Si2O7/AgI) can achieve 99.7% within 8 min, which was about 15.3 and 124.6 folds higher than that of individual Ag6Si2O7 (6.5%) and AgI (0.8%), respectively. Meanwhile, Ag6Si2O7/AgI showed an excellent capability of phenol degradation and V reduction, which might be ascribed to the strong visible light absorption, rapid separation efficiency of photo-induced charge carriers and direct Z-scheme charge transfer mechanism verified by the results of UV–vis diffuse reflection spectra, transient photocurrent response spectra and XPS measurements, respectively. Moreover, Ag6Si2O7/AgI nanocomposite presented a good stability and reusability after four runs. Finally, a possible Z-scheme mechanism is proposed to illustrate the enhanced photocatalytic performance of the Ag6Si2O7/AgI nanocomposite.