An efficient and robust exfoliated bentonite/Ag3PO4/AgBr plasmonic photocatalyst for degradation of parabens

Abstract

Efficient visible-light-driven heterojunction photocatalysts have attracted broad interest owing to their promising adsorption and degradation performances in the removal of organic pollutants. In this study, a mesoporous exfoliated bentonite (EB)/Ag₃PO₄/AgBr (30%) photocatalyst was obtained by stripping and exfoliating bentonite as the support for loading Ag₃PO₄ and AgBr. The particle size ranges of Ag₃PO₄ and AgBr were about 10–30 nm and 5–10 nm, respectively. The exfoliated bentonite could greatly improve the dispersion and adsorption of Ag₃PO₄ and AgBr, and significantly enhance the stability of the material during paraben photodegradation. 0.2 g L⁻¹ methylparaben (MPB) was completely decomposed over the EB/Ag₃PO₄/AgBr (30%) in 40 min under visible light irradiation. In addition, the photocatalytic activity of EB/Ag₃PO₄/AgBr (30%) remained at about 91% after five recycling runs manifesting that EB/Ag₃PO₄/AgBr (30%) possessed excellent stability. Radical quenching tests revealed that holes (h⁺) and hydroxyl radicals (·OH) were the major radicals. They attacked the side chain on the benzene ring of parabens, which were gradually oxidized to the intermediates, such as benzoic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, azelaic acid, and eventually became CO₂ and H₂O. The enhancement of photocatalytic activity and photo-stability could be ascribed to the stable structural characteristics, enlarged surface area, high absorption ability, and improved light absorption ability from loading Ag₃PO₄ onto EB. Meanwhile, the matched energy levels of Ag₃PO₄ and AgBr made the photoelectron–hole pairs separate and transfer effectively at the interfaces. As a result, the photocatalytic properties of EB/Ag₃PO₄/AgBr (30%) composites were enhanced.