High catalytic hydrolysis of microcystins on pyrite surface

Abstract

Eutrophication of water bodies is a phenomenon during which toxic microcystins from cyanobacteria are released into water. Natural minerals in soils and sediments are able to catalyze the degradation of microcystins. Here we studied the hydrolytic removal of microcystins on the surface of pyrite (FeS2). The surface structure of pyrite was analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and Fourier transformed infrared. The surface acidity of pyrite was measured by in situ diffuse reflectance infrared Fourier transform spectroscopy during pyridine adsorption/desorption. The concentration of d-alanine, d-glutamic acid, l-arginine and l-leucine were determined in pyrite/microcystin aqueous solution by high-performance liquid chromatography. Hydrolysis at the pyrite–microcystin interface was monitored by attenuated total reflection Fourier transformed infrared spectroscopy. Results show that sulfion and iron are layered, wherein the sulfion is above the surface, which provides active sites for the hydrolysis of microcystins. The hydrolysis rate of microcystins was up to 100% at 60 °C after 24 h in the presence of pyrite, based on the yield of l-arginine. Surface Lewis (≡Fe) and Bronsted acid (≡SH) sites of pyrite possibly bond to the carbonyl oxygen of peptide bonds, leading to highly efficient hydrolysis of microcystins.