Novel synthesis of sulfur-doped Ag3PO4 photocatalyst for efficient degradation of cylindrospermopsin

Abstract

This study introduces a novel synthesis of sulfur (S)-doped Ag₃PO₄ photocatalyst using a simple precipitation method facilitated by ammonium sulfate ((NH₄)₂SO₄). The calcination at 200 °C in air optimized the photocatalytic performance, leading to the complete degradation of cylindrospermopsin (CYN) within only 5 min under visible light irradiation. The degradation rate constant for the calcined S-doped Ag₃PO₄ (A-200) is 1.77 times higher than the pristine sample (A). The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed that air calcination, facilitated by thermal treatments and charge compensation, enhanced the incorporation of S⁶⁺ by replacing P⁵⁺ in the lattice of Ag₃PO₄ and the production of silver vacancies. These changes resulted in a reduced band gap and more efficient separation of photogenerated electron-hole pairs. Photogenerated holes (h⁺) and singlet oxygen (¹O₂) were identified as the main oxidizing agents responsible for the detoxification of CYN. Moreover, the degradation mechanism analysis indicated that the cleavage of hydroxymethyl uracil, tricyclic alkaloids, and sulfate groups in CYN is crucial for its degradation and detoxification.