In situ S-doped ultrathin gC3N4 nanosheets coupled with mixed-dimensional (3D/1D) nanostructures of silver vanadates for enhanced photocatalytic degradation of organic pollutants

Abstract

A novel plasmonic Z-scheme sulphur doped gC₃N₄/Ag₃VO₄/β-AgVO₃/Ag (SGA-x) hybrid quaternary photocatalyst was successfully fabricated via the ultrasonic assisted Kirkendall effect and diffusion processes followed by low temperature phase conversion. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis diffuse-reflectance spectroscopy (UV-vis DRS) and X-ray photoelectron spectroscopy. The photocatalytic activities of the obtained photocatalysts were measured by degradation of methylene blue (MB), methyl orange (MO) and 2,4-dichlorophenoxy acetic acid (2,4-D) under visible-light irradiation. Among the composites with various levels of β-AgVO₃, SGA-7 exhibited the highest degradation efficiency with 95.45% MB degradation for 30 min, which was about 1.47 times higher than that of S-gC₃N₄/Ag₃VO₄ (SGA). The inter-particle electronic coupling in hollow nanoflower leads to self-narrowing of the band gap of Ag₃VO₄. Moreover, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) spectral analysis indicate that the introduction of a minute amount of β-AgVO₃ by low temperature phase conversion of Ag₃VO₄ could efficiently promote the separation efficiency of photogenerated charge carriers. This enhanced photocatalytic activity is attributed to the synergistic effects of heterostructured semiconductor photocatalysis, increased surface area, improved utilization of solar light due to a hollow structure, decreased photocorrosion and the surface plasmon resonance (SPR) of Ag nanoparticles (NPs). Besides, trapping experiments implied that holes and ˙O²⁻ were the predominant active species during the degradation process. A possible combination of conventional and Z scheme mechanisms of enhanced photocatalytic activity of SGA-7 is proposed.