Hydrophilic Fraction of Dissolved Organic Matter Largely Facilitated Microplastics Photoaging: Insights from Redox Properties and Reactive Oxygen Species.

Dissolved organic matter (DOM) exists widely in natural water, which inevitably influences microplastic (MP) photoaging. Nevertheless, the impacts of DOM fractions with diverse molecular structures on MP photoaging remain to be elucidated. This study explored the photoaging mechanisms of polylactic acid (PLA)-MPs and polystyrene (PS)-MPs in the presence of DOM and its subfractions (hydrophobic acid (HPOA), hydrophobic neutral (HPON), and hydrophilic (HPI)). Across DOM fractions, HPI exhibited the highest electron accepting capacity (23 µmol e- (mg C)-1) due to its abundant tannin-like species (36.8%) with carboxylic groups, which facilitated more reactive oxygen species generation (particularly hydroxyl radical), leading to the strongest photoaging rate of two MPs by HPI. However, the sequences of bond cleavage during photoaging of each MPs were not clearly shifted as revealed by two-dimensional infrared correlation spectra. Inconspicuous effects on the extent of PS- and PLA-MPs photoaging were observed for HPOA and HPON, respectively. This was mainly ascribed to the occurrence of inhibitory mechanisms (e.g., light-shielding and quenching effect) counteracting the reactive oxygen species-promoting effects. The findings identified the HPI fraction of DOM for promoting PS- and PLA-MPs photoaging rate and first constructed a link among DOM molecular structures, redox properties, and effects on MP photoaging.

Mechanism insight into the facet-dependent photoaging of polystyrene microplastics on hematite in freshwater.

Hematite, as an extensive natural mineral with multiple crystal facets, profoundly affects the migration and transformation of pollutants in the natural environment. However, little is known about the photochemical behavior of microplastics on different facets of hematite in the aquatic environment. In this work, the photoaging of polystyrene microplastics (PS-MPs) on different crystal planes ({001}, {100}, and {012} facets) and related mechanisms were studied. Two-dimensional correlation spectroscopy analysis illustrated that the reaction pathways of PS-MPs photoaging on hematite tended to preferential chemical oxidization. The stronger performance of PS-MPs photoaging, expressed by particle size reduction and surface oxidation, was observed on the {012} crystal facet. Under irradiation, {012} facet-dominated hematite with a narrower bandgap (1.93 eV) reinforced the photogenerated charge carrier separation, and the lower activation energy barrier (1.41 eV calculated from density functional theory) led to effective •OH formation from water oxidation. These findings elucidate the underlying photoaging mechanism of MPs on hematite with different mineralogical phases.

Correction: Selective CO2 reduction to HCOOH on a Pt/In2O3/g-C3N4 multifunctional visible-photocatalyst.

[This corrects the article DOI: 10.1039/D0RA03959D.].

Efficient photodegradation of polystyrene microplastics integrated with hydrogen evolution: Uncovering degradation pathways.

Photocatalytic microplastics (MPs) conversion into valuable products is a promising approach to alleviate MPs pollution in aquatic environments. Herein, we developed an amorphous alloy/photocatalyst composite (FeB/TiO2) that can successfully convert polystyrene (PS) MPs to clean H2 fuel and valuable organic compounds (92.3% particle size reduction of PS-MPs and 103.5 µmol H2 production in 12 h). FeB effectively enhanced the light-absorption and carrier separation of TiO2, thereby promoting more reactive oxygen species generation (especially ‧OH) and combination of photoelectrons with protons. The main products (e.g., benzaldehyde, benzoic acid, etc.) were identified. Additionally, the dominant PS-MPs photoconversion pathway was elucidated based on density functional theory calculations, by which the significant role of ‧OH was demonstrated in combination with radical quenching data. This study provides a prospective approach to mitigate MPs pollution in aquatic environments and reveals the synergistic mechanism governing the photocatalytic conversion of MPs and generation of H2 fuel.

Single/co-adsorption and mechanism of methylene blue and lead by ß-cyclodextrin modified magnetic alginate/biochar.

Due to the high biological toxicity, the concurrent elimination of lead (Pb (II)) and methylene blue (MB) has become a challenging problem. Therefore, a newly ß-cyclodextrin (ß-CD) modified magnetic alginate/biochar (ß-CD@MBCP) material was developed. Comprehensive characterizations proved the successful coating of ß-CD onto MBCP surface by microwave-aided fabrication. The ß-CD@MBCP achieved high-efficiency uptake for contaminants under a wide pH scope. In the dual system, Pb (II) elimination was facilitated with the presence of MB, due to the active sites provided by MB. In the presence of Pb (II), MB uptake was inhibited due to the electrostatic repulsion between positively charged MB and Pb (II). Electrostatic attraction and complexation contributed to capturing Pb (II), while π-π interactions, host-guest effect, and H-bonding were important in MB elimination. After four cycles, ß-CD@MBCP maintained comparatively good renewability. Findings demonstrated that ß-CD@MBCP could be an effective remediation material for Pb (II)/MB adsorption from aqueous environments.

Soil structures and immobilization of typical contaminants in soils in response to diverse microplastics.

Microplastics (MPs) accumulation in soil ecosystems has become a worldwide issue. The influence of MPs on soil structures and contaminant transport has not been clearly unraveled. This study conducted soil column experiments covering four different treatments: soil without MPs (CK), soil with 0.5 wt% polyethylene (S+PE), soil with 0.5 wt% polyacrylonitrile (S+PAN), and soil with 0.5 wt% polyethylene terephthalate (S+PET). The interconnections between changes in soil structures and shifts in sorption efficiency for typical hydrophobic organic contaminants (e.g., phenanthrene (PHE)) and heavy metal (e.g., lead (Pb (II)) by soils induced by MPs were explored. MPs-added soils contained fewer macro-aggregates and lower aggregate stability compared to CK. Three MPs, particularly PE, promoted PHE sorption by soils but reduced Pb (II) sorption, which occurred in soils with or without dissolved organic carbon. The comparison between experimental and predicted sorption capacity, as well as the one-point sorption data of different aggregate sizes, showed that such variations in PHE and Pb (II) sorption were related to the shifts in soil aggregates besides from the physical mixture of soils with MPs. This finding is perspective to give an in-depth understanding of the effects of different MPs types on soil micro-environments and transport for contaminants.

Loading with micro-nanosized α-MnO2 efficiently promotes the removal of arsenite and arsenate by biochar derived from maize straw waste: Dual role of deep oxidation and adsorption.

The function of biochar (BC) as an eco-friendly adsorbent for environmental remediation is gaining much attention. However, the pristine BC had limited abilities for the removal of As (III, V). Towards this issue, this study synthesized biochar/micro-nanosized α-MnO2 (BM) composites with different mass ratios of biochar to MnO2. Comprehensive characterizations confirmed the successful loading of micro-nanosized α-MnO2 onto the BC surface and the obvious specific surface area enhancement (7.5-13.5 times) of BM relative to BC. BM composites exhibited 5.0-13.0 folds higher removal capacity for As (III, V) than pristine BC since the composites gave full play to the oxidation contributed by micro-nanosized α-MnO2 substrate and adsorption functions provided by the Mn-OH, BC-COOH, and BC-OH functional groups. Moreover, BM was well reused maintaining a relatively high removal efficiency for As (III, V). Regardless of reaction time and initial As (III) concentration (C0), the removal of As (III) by pristine BC was negligibly contributed by the oxidized As (V) remaining in solutions, with the relative contribution <15.0%. For the BM composites, relative contribution of adsorbed As (III, V) dominated over that of oxidation to mobile As (V) remaining in solution, and exhibited the decreasing trend with increasing C0. These findings demonstrated BM as a promising candidate in remediating As (III, V)-polluted water, and provide mechanistic insights into the role of oxidation and adsorption in As (III, V) removal.

Bio-alcohol induced self-assembly of heterojunctioned TiO2/WO3 composites into a hierarchical yolk-shell structure for photocatalysis.

In the fabrication of efficient multicomponent semiconductors for photocatalysis, well-defined hierarchical structures and high-quality heterojunctions are still highly desired. A general preparation method was developed for a series of hierarchical TiO2-based heterojunctions with tailored interior space from solid, core-shell and yolk-shell to fully hollow structures.

Self-Driven Reactive Oxygen Species Generation via Interfacial Oxygen Vacancies on Carbon-Coated TiO2-x with Versatile Applications.

The effective activation and utilization of O2 have always been the focus of scientists because of its wide applications in catalysis, organic synthesis, life and medical science. Here, a novel method for activating O2 spontaneously via interfacial oxygen vacancies on carbon-coated TiO2-x to generate reactive oxygen species (ROS) with versatile applications is reported. The interfacial oxygen vacancies can be stabilized by the carbon layer and hold its intrinsic properties for spontaneous oxygen activation without light irradiation, while common surface oxygen vacancies on TiO2-x are always consumed by the capture of H2O to form the surface hydroxyls. Thus, O2 absorbed at the interface of carbon and TiO2-x can be directly activated into singlet oxygen (1O2) or superoxide radicals (·O2-), confirmed both experimentally and theoretically. These reactive oxygen species exhibit excellent performance in oxidation reactions and inhibition of MCF-7 cancer cells, providing new insight into the effective utilization of O2 via oxygen vacancies on metal oxides.

Selective CO2 reduction to HCOOH on a Pt/In2O3/g-C3N4 multifunctional visible-photocatalyst.

Selective photocatalytic reduction of CO2 has been regarded as one of the most amazing ways for re-using CO2. However, its application is still limited by the low CO2 conversion efficiency. This work developed a novel Pt/In2O3/g-C3N4 multifunctional catalyst, which exhibited high activity and selectivity to HCOOH during photocatalytic CO2 reduction under visible light irradiation owing to the synergistic effect between photocatalyst, thermocatalyst, and heterojunctions. Both In2O3 and g-C3N4 acted as visible photocatalysts, in which porous g-C3N4 facilitated H2 production from water splitting while the In2O3 nanosheets embedded in g-C3N4 pores favored CO2 fixation and H adsorption onto the Lewis acid sites. Besides, the In2O3/g-C3N4 heterojunctions could efficiently inhibit the photoelectron-hole recombination, leading to enhanced quantum efficiency. The Pt could act as a co-catalyst in H2 production from photocatalytic water splitting and also accelerated electron transfer to inhibit electron-hole recombination and generated a plasma effect. More importantly, the Pt could activate H atoms and CO2 molecules toward the formation of HCOOH. At normal pressure and room temperature, the TON of HCOOH in CO2 conversion was 63.1 µmol g-1 h-1 and could reach up to 736.3 µmol g-1 h-1 at 40 atm.