Self-acclimation mechanism of pyrite to sulfamethoxazole concentration in terms of degradation behavior and toxicity effects caused by reactive oxygen species.

Pyrite has been extensively tested for oxidizing contaminants via the activation of water molecule or dissolved oxygen, while the changing of oxidation species induced by contaminant's concentration has been largely underestimated. In this study, we revealed a self-acclimation mechanism of pyrite in terms of •OH conversion to 1O2 during the sulfamethoxazole (SMX) degradation process under oxic conditions. Two reaction stages of SMX degradation by pyrite were observed. The SMX concentration decreased by 70% rapidly in the first 12 h after the reaction was initiated, then, the removal rate began to decrease as the SMX concentration decreased. Importantly, •OH and O2•- were the dominant oxidizing species in stage one, while 1O2 was responsible for the further degradation of SMX in stage two. The self-acclimated mechanism of pyrite was proven to be caused by the conversion of oxidative species at the surface of pyrite. This process can overcome the shortages of •OH such as ultrashort lifetime and limited effective diffusion in the decontamination of micropollutant. Moreover, different reactive oxygen species will lead to different degradation pathways and environmental toxicity while degrading pollutants. This finding of oxidizing species' self-acclimation mechanism should be of concern when using pyrite for water treatment.

Ultrasmall Ru Nanoparticles Highly Dispersed on Sulfur-Doped Graphene for HER with High Electrocatalytic Performance.

Nanostructuring and metal-support interactions have been explored as effective methods to improve the electrocatalytic activity in heterogeneous catalysis. In this study, we have fabricated ultrasmall Ru nanoparticles (NPs) dispersed on S-doped graphene (denoted as Ru/S-rGO) by a facile "one-pot" procedure. The experimental results indicated that both the S doping and moderate degree of oxidization of GO can induce the formation and high dispersion of the ultrasmall Ru NPs with larger electrochemically active surface areas for exposing more active sites. Metal-support interaction between S-doped graphene and Ru NPs was observed from the X-ray photoelectron spectroscopy and electronic charge-difference studies. It resulted in the decrease in the electron density of Ru, which facilitated electron release from H2O and H-OH bond breakage. The results of density functional theory calculation confirmed that the S-dopants could reduce the energy barrier for breaking the H-OH bond to accelerate water dissociation during the alkaline hydrogen evolution reaction (HER). At a current density 20 mA cm-2, the lowest overpotential of 14 mV, superior to that of Pt/C in alkaline solution, was observed for Ru/S-rGO-24. The observed lowest value of overpotential was because of the ultrasmall size, high dispersion, and metal-support interaction. This work provides a simple and effective method in designing advanced electrocatalysts for the HER in an alkaline electrolyte.