Ag3PO4 immobilized on hydroxy-metal pillared montmorillonite for the visible light driven degradation of acid red 18

Abstract

This work reports the facile fabrication of Ag₃PO₄/Fe–Al/Mt and Ag₃PO₄/Al/Mt by loading Ag₃PO₄ on hydroxy-iron–aluminum pillared montmorillonite (Fe–Al/Mt) and hydroxy-aluminum pillared montmorillonite (Al/Mt). The structural characteristics of the resulting materials were studied with XRD, SEM-EDS, XPS, ICP, nitrogen adsorption–desorption isotherms, and UV-vis diffuse reflectance spectra; the photocatalytic activity of the obtained catalysts was tested using acid red 18 (AR18) as a model contaminant under visible light irradiation. The obtained results illustrate that Ag₃PO₄ of a high dispersity and smaller size was successfully loaded on hydroxy-metal pillared montmorillonite. The photocatalytic activity and structural stability of the three synthesized catalysts were in the order Ag₃PO₄/Fe–Al/Mt > Ag₃PO₄/Al/Mt > Ag₃PO₄. An efficiency of 98.5% was achieved for AR18 degradation by Ag₃PO₄/Fe–Al/Mt after recycling seven times, while only 54.9% was achieved for Ag₃PO₄. The superoxide radical anion (O₂˙⁻) was confirmed to be the dominant reactive species in all the three degradation systems, and the Ag₃PO₄/Fe–Al/Mt system formed the largest amount of O₂˙⁻. Except for the larger specific surface area and smaller particle size, the high removal efficiency of AR18, remarkable O₂˙⁻ generation performance, and good stability of Ag₃PO₄/Fe–Al/Mt could be attributed to the presence of Fe³⁺ as well, which can act as an electron acceptor for photo-induced electrons from Ag₃PO₄ during the photocatalytic process and then inhibit the transformation of Ag⁺ into metallic Ag.