Abstract Microplastics (MPs), act as vectors of heavy metal pollutants in the environment, is of practical significance to study the adsorption process and mechanism on heavy metals. In this study, polystyrene microplastics (PSMPs) were used as model MPs to study the adsorption of Pb 2+ on PSMPs and the effects of humic acid (HA) on the adsorption process. The results showed that HA promoted the adsorption of Pb 2+ on PSMPs, and the higher the concentration of HA, the greater the adsorption of Pb 2+ . With the increase of pH value and decrease of ionic strength, the adsorption capacity of PSMPs for Pb 2+ increased. The scanning electron microscope equipped with the energy dispersive spectroscope (SEM–EDS), fourier transform-infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis showed that Pb 2+ could be adsorbed directly onto PSMPs and also indirectly by HA. The higher K SV values in the PSMPs-HA-Pb 2+ system than PSMPs-HA system by fluorescence analysis of HA suggested that HA acted as a bridging role in the adsorption of Pb 2+ on PSMPs. The site energy distribution analysis further revealed that HA increased the average site energy μ ( E * ) and its standard deviation σ e * of PSMPs by introducing more adsorption sites, thus enhanced the adsorption affinity of PSMPs. This study provided more thoughts and insights into the adsorption behavior and mechanism of MPs for Pb 2+ in aquatic environments.
Ubiquitous dissolved organic matter (DOM), a heterogeneous mixture with various organic components and continuous molecular weight (MW) distribution, can significantly influence the fate, bioavailability and toxicity of microplastics (MPs) in aquatic environments. However, to date, understanding of the MW-dependent adsorption heterogeneities of DOM on MPs in aquatic environments has remained unknown.In this study, the soil humic acid (HA), a representative DOM, was fractionated into >100 kDa HA, 30-100 kDa HA, 10-30 kDa HA, 3-10 kDa HA and <3 kDa HA, whose adsorption behaviors on polystyrene MPs (PSMPs) under different electrolytes at pH6.0 investigated by using total organic carbon, ultraviolet-visible absorption spectroscopy, fourier transform infrared spectroscopy, synchronous fluorescence (SF) spectroscopy coupled with two-dimensional correlation spectroscopy (SF-2D-COS)，as well as site energy distribution analysis. High molecular weight MW-fractionated HAs dominated the soil HA. The adsorption of the MW-fractionated HAs onto PSMPS can be reasonably explained by Langmuir and Freundlich isotherm models. Enhanced aromaticity in residual solutions after adsorption was observed. The heterogeneous/complicated distributions of active adsorption sites in the humic-like materials of the MW-fractionated HAs, and the subsequent subtle changes of these sites to PSMPs were characterized by SF-2D-COS. High molecular weight MW-fractionated HAs provided more active adsorption sites than those in the low molecular weight counterparts, which also possessed stronger adsorption affinities and higher complexation capacities to PSMPs. The adsorption heterogeneities of PSMPs at the experimental conditions were close. This study will help us better understand the biogeochemical behaviors of DOM and MPs in aquatic environments.
Substantial amounts of extracellular polymeric substances (EPS) are present in sludge from wastewater treatment plants (WWTP), and EPS can significantly affect the fate, bioavailability, and toxicity of microplastics (MPs) that coexist in the effluent, however, the mechanism of action between EPS and microplastics remains unclear. In addition, ultraviolet (UV) disinfection is indispensable in the wastewater treatment process in WWTP, which can significantly affect the characteristics of EPS. Therefore, it is of great significance to study the photochemical characteristics of EPS and the effect on binding MPs. In this study, using multispectral technology and two-dimensional correlation spectroscopy analysis, indicates that the molecular weight and aromaticity of EPS after phototransformation were reduced. The results showed that the adsorption of EPS on PSMPs was in the order of TB-EPS > LB-EPS > S-EPS, which was positively correlated with the SUVA254, but negatively correlated with O/C of EPS. This indicates that the main adsorption mechanisms of PSMPs on EPS were π-π and hydrophobicity. The adsorption capacity of S-EPS, LB-EPS and TB-EPS to PSMPs decreased with the increasing of illumination time. After phototransformation, the adsorption sensitivity and reaction sequence of EPS and PSMPs did not change much. This research provides a theoretical basis for understanding the photochemical transformation of extracellular polymers and the morphology and migration of microplastics in sewage treatment, and evaluating the impact of microplastics on ecosystems.
Abstract Electrocatalytic water splitting is a promising route for sustainable hydrogen production. However, the high overpotential of the anodic oxygen evolution reaction poses significant challenge. SrIrO 3 -based perovskite-type catalysts have shown great potential for acidic oxygen evolution reaction, but the origins of their high activity are still unclear. Herein, we develop a Co-doped SrIrO 3 system to enhance oxygen evolution reaction activity and elucidate the origin of catalytic activity. In situ experiments reveal Co activates surface lattice oxygen, rapidly exposing IrO x active sites, while bulk Co doping optimizes the adsorbate binding energy of IrO x . The Co-doped SrIrO 3 demonstrates high oxygen evolution reaction electrocatalytic activity, markedly surpassing the commercial IrO 2 catalysts in both conventional electrolyzer and proton exchange membrane water electrolyzer.
Understanding the interactions between heterogeneous dissolved organic matter (DOM) and nonylphenols (NPs) is essential for predicting their behavior and fate in the environment. Herein, we firstly obtained different MW-fractionated humic acids (HAs) using the ultrafiltration method. Afterward, the molecular weight (MW)-dependent interactions of HAs with 4-nonylphenol (4-NP) were analysed by excitation emission matrix (EEM) fluorescence spectroscopy, fluorescence quenching, UV-vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and principal component analysis (PCA). EEM spectra indicated that the quenching mechanism was static. In the binding process, the higher MW fractions showed stronger interaction with 4-NP than the lower MW counterparts, exhibiting a clear MW-dependent interaction heterogeneity. The interaction constants for the 4-NP-HAs system were suppressed as the ionic strength decreased and pH increased, which was especially obvious in the binding of 4-NP to the lower MW-fractionated HAs. The FTIR spectra revealed that hydroxyl and aromatics were involved in the interaction process of HA fractions with 4-NP. It was also found from 1H NMR that π-π interactions between aromatic rings of 4-NP and MW-fractionated HAs were responsible for the complexation. The correlation analysis and PCA results indicated that aromaticity and MW play important roles in the interaction process and confirmed an obvious interaction heterogeneity among MW-fractionated HAs samples. This work highlighted MW-dependent interaction heterogeneities of HA, which suggested that heterogeneity in MW distribution should be taken into consideration when exploring the fate and biogeochemistry cycling of 4-NP from contaminated environments.
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