Photon-induced redox chemistry on pyrite promotes photoaging of polystyrene microplastics.

The mineral particles in sediment could affect polystyrene microplastics (PS-MPs) prosperity through physical and chemical interactions. Pyrite with semiconducting properties is the most abundant metal sulfide mineral in the sediments of lake and river mouths. The widespread sunlight and the coexistence of PS-MPs and pyrite in lake or river water due to frequently water fluctuation is a typical photoaging environment for PS-MPs. The oxidation of reactive oxygen species (ROS) generated from pyrite would degrade the PS-MPs in theory. However, researches about photoaging of PS-MPs mediated by pyrite are paucity. Here, we investigated the photoaging process of PS-MPs affected by pyrite under simulated light condition. Remarkably, surface morphology of PS-MPs mediated by pyrite was broken. And the oxygen-containing functional group of PS-MPs increased, as revealed by Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle test. 2D-COS analysis showed photoaging of PS-MPs with pyrite happened in the following order: C-H > C=C > C=O > C-O > OH. The photoaging of PS-MPs and transformation of intermediate were accelerated by ROS (O2·-, ·OH and 1O2) generated from pyrite. The free ·OH may play a major role in the promotion. Because the interfacial ROS reactions on pyrite surface were limited due to the electrostatic repulsion between pyrite and PS-MPs. The study explored photoaging behavior of PS-MPs accelerated by pyrite, which could be helpful for understanding photon-induced redox chemistry on PS-MPs via widespread sulfide metal minerals on earth's surface and providing further information to assess potential risks of PS-MPs.

Stabilization and Utilization of Pyrite under Light Irradiation: Discussion of Photocorrosion Resistance.

The control of pyrite (FeS2) oxidation from a source is a problem of great concern on treatment of acid mine drainage (AMD). Compared with air and water, the effect of light on pyrite oxidation has not attracted enough attention. However, we found that pyrite photocorrosion in the light promoted the oxidation of pyrite. Herein, we introduce a method of coating pyrite with graphene oxide (GO), which can inhibit the oxidation and photocorrosion of pyrite while it can also degrade organic pollutants. The characterization results show that a covalent bond forms between the GO and pyrite. The stable and uniform GO coating prevents the permeation of O2 and H2O and promotes the transfer of photogenerated electrons. Moreover, it changes the conduction band (CB) and valence band (VB) levels of GO-pyrite. All of these are vital for preventing the corrosion of pyrite and promoting its photocatalytic ability. More importantly, the effect of CB and VB levels on the oxidized species was discussed. The inhibition of photocorrosion is achieved by the reaction of GO with the photoinduced h+, •OH, and •O2 -. The study provides insights for source treatment of AMD under light and the reuse of massive abandoned pyrite.