Anthropogenic impacts on polycyclic aromatic hydrocarbons in surface water: Evidence from the COVID-19 lockdown.

The lockdown restrictions against coronavirus disease 2019 (COVID-19) have led to unprecedented reductions in global anthropogenic activities. Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic combustion-induced pollutants, but the influence of anthropogenic responses to COVID-19 on PAH contamination remains largely unknown. Here we quantified the impacts of lockdown restrictions on 16PAH pollution based on the data in concentrations dissolved in the water phase and absorbed on the suspended particulate matter (SPM) in the Elbe River from 2015 to 2021 and determined the changes in source contributions classified by individual years and stations. Results show that the annual average PAH concentrations in water and SPM were determined as 0.055 µg·L-1 and 3.77 mg·kg-1 from 2015 to 2021, respectively. Pronounced declines in PAH on SPM (up to -18 %) were observed during the three lockdowns in Germany from 2020 to 2021. However, dramatic rebounds of anthropogenic activities during the removal of the lockdown led to increases (up to 29 %) in ∑16PAH concentrations compared to the same period in previous years. Through the source apportionment method, vehicle and coal emissions were the two most predominant sources of PAHs in the river. Vehicle contribution decreased during the lockdown, while coal emissions increased by 5 %. Health risks for three age groups were assessed as potential low risk and decreased by 18 % from 1.54 × 10-4 in 2015 to 1.27 × 10-4 in 2019, and rebounded to 1.40 × 10-4 in 2020-2021. The findings of this study highlight the strong consistency between PAH concentrations and anthropogenic intensity, implying that source control from improved cleaner production is an effective pathway for mitigating PAH contamination in the aquatic environment.

Evaluation and prediction of anthropogenic impacts on long-term multimedia fate and health risks of PFOS and PFOA in the Elbe River Basin.

Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) have aroused great concern owing to their widespread occurrence and toxic effects. However, their long-term trends and multimedia fate remain largely unknown. Here, we investigate the spatiotemporal characteristics and periodic oscillations of PFOS and PFOA in the Elbe River between 2010 and 2021. Anthropogenic emission inventories and multimedia fugacity model were developed to analyse their historical and future transport fates and quantify related human risks in each medium for the three age groups. The results show that average PFOS and PFOA concentrations in the Elbe River were 4.08 and 3.41 ng/L, declining at the annual rate of 7.36% and 4.98% during the study period, respectively. Periodic oscillations of their concentrations and mass fluxes were most pronounced at 40-60 and 20-40 months. The multimedia fugacity model revealed that higher concentrations occurred in fish (PFOS: 14.29, PFOA: 0.40 ng/g), while the soil was their dominant sink (PFOS: 179, PFOA: 95 tons). The exchange flux between water and sediment was the dominant pathway in multimedia transportation (397 kg/year). Although PFOS and PFOA concentrations are projected to decrease by 22.41% and 50.08%, respectively, from 2021 to 2050, the hazard quotient of PFOS in fish is a low hazard. This study provides information for the assessment of PFOS and PFOA pollution in global watersheds and the development of related mitigation policies, such as banning fish predation in polluted rivers, to mitigate their risks.

Characterizing the long-term occurrence and anthropogenic drivers of per- and polyfluoroalkyl substances in surface water of the Rhine River.

Per- and polyfluoroalkyl substances (PFAS) raise significant concerns due to their persistence, bioaccumulation potential, and toxicity to both ecosystems and human health. However, the long-term trends of PFAS in aquatic environments remain inadequately explored. In this study, we systematically assessed the spatiotemporal distribution, periodic fluctuations, source apportionment, and risk evaluation of 12 PFAS in the Rhine River based on the long-term measuring data collected from 2007 to 2019. The study revealed that the mean concentration and mass flux of total PFAS during this period were 32.83 ng L-1 and 6.36 × 104 µg s-1, declining at an annual rate of 3.70% and 3.82%, respectively. Wavelet analysis demonstrated that the most prominent periodic oscillation of PFAS was 40-60 months. Regarding the sources of PFAS, we employed the self-organizing map (SOM) and the positive matrix factorization (PMF) model for source apportionment. The results indicated that the primary sources of PFAS were agrochemical, pharmaceutical and textile industries, accounting for 38.1% of the total concentration. The contribution from household contamination, tannery industry, and coating materials has increased annually. In contrast, the share of electrochemical fluorination and chemical recycling has shown a continuous decline. The risk quotient (RQ) and hazard quotient (HQ) calculations for three age groups indicated that PFAS exposure did not pose a significant risk to ecological or human health. Implementing source-oriented mitigation strategies is crucial to effectively reduce the ecological and human health risks of PFAS in receiving waters.

Global trade drives transboundary transfer of the health impacts of polycyclic aromatic hydrocarbon emissions.

International trade leads to a redistribution of pollutant emissions related to the production of goods and services and subsequently affects their severe health impacts. Here, we present a framework of emissions inventories, input-output model, numerical atmospheric chemistry model, and estimates of the global burden of disease. Specifically, we assess emissions and health impacts of polycyclic aromatic hydrocarbons (PAH), a carcinogenic byproduct of production activities, and consider income, production, final sale, and consumption stages of the global supply chain between 2012 and 2015. We find that in 2015, global anthropogenic PAH emissions were 304 Gg (95% CI: 213~421 Gg) and estimated related lifetime lung cancer deaths were 6.9 × 104 (95% CI: 1.8 × 104~1.5 × 105 deaths). The role of trade in driving the PAH-related health risks was greater than that in driving the emissions. Our findings indicate that international cooperation is needed to optimise the global supply chains and mitigate PAH emissions and health impacts.

[Spatiotemporal Distribution and Source Apportionment of Suspended Polycyclic Aromatic Hydrocarbons in Surface Water].

Polycyclic aromatic hydrocarbons (PAHs) are a type of typical environmental pollutant with carcinogenic effects and high ecological risk. With the development of industry, surface water acts as a primary sink for PAHs. Owing to their low solubility, a significant amount of PAHs are adsorbed onto suspended particulate matter in surface water, which presents a serious risk to human health and the ecological environment. To protect human health and aquatic organisms, a systematic assessment of the trends in PAHs exposure risk is essential. Based on long-term monitoring data from 2002 to 2016, this study systematically evaluated the spatiotemporal distribution and source apportionment of PAHs adsorbed on suspended particulate matter in surface water. The results of the Mann-Kendall test indicated that pollution levels of PAHs decreased from 2012 to 2016. The maximum average content was 6239 µg·kg-1, and the minimum was 2760 µg·kg-1. Benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, and benzo(a)anthracene showed significant declines from 2002-2016 (P<0.05). Levels of benzo(a)pyrene, dibenzo(a,h)anthracene, and indeno(1,2,3-cd)pyrene were steady. Wavelet analysis showed that the pollution level of PAHs had significant periodic oscillations for surface water. Midstream and downstream Σ16PAHs showed significant declines from 2002-2016 (P<0.05), whereas upstream Σ16PAHs were steady. ANOVA analysis showed that the spatial difference was significant and occurred in the following order:midstream (6168 µg·kg-1)>upstream (5407 µg·kg-1)>downstream (3412 µg·kg-1). Diagnostic ratio analysis and the positive matrix factorization model suggested that the major sources of PAHs were traffic sources, coal burning sources, and biomass combustion sources, which accounted for 40.9%, 33.7%, and 25.4%, respectively. The contribution of traffic sources decreased by 25.9%. The contributions of coal burning sources and biomass combustion sources increased by 4.8% and 21.1% from 2002-2009 to 2010-2016, respectively. These results provide scientific reference for risk analysis and the control of PAHs pollution in surface water.

Global Trends and Drivers in Consumption- and Income-Based Emissions of Polycyclic Aromatic Hydrocarbons.

Polycyclic aromatic hydrocarbons (PAHs) are a class of the most hazardous substances. As unavoidable byproducts of petrogenic and pyrogenic processes, their emissions are dominantly linked to various economic sectors. In international trade, not only final consumption but also primary input can transfer the emissions among regions. Therefore, a long-term impact assessment of the international trade on PAH global emissions based on the final consumption and primary input could significantly benefit worldwide PAH mitigation strategies. This study investigated the changes in consumption- and income-based PAH emissions and interregional flows of worldwide regions, using the latest available data from 1999 to 2014. Results show that in 2014, 16.8 and 10.1% of global PAH emissions were transferred by consumption and primary input through international trade. Meanwhile, the production-, consumption-, and income-based emissions in most regions were decreasing. Furthermore, from the consumption-based perspective, sub-Saharan Africa surpassed China and became the largest net exporter of consumption-based emissions. From the income-based perspective, the net income-based outflows of India and the rest of Asia increased significantly, indicating the income-based emission leakage in emerging markets. From the socioeconomic perspective, emission intensity dominated the global decline in PAH emissions. As the two main factors driving the increase in emissions, the primary input structure (41%) had a larger effect than the final demand level (28%) from 1999 to 2014. Therefore, global cooperation, through the mitigation strategies of reducing emission factors and improving international trade patterns, is posited as an efficient strategy to reduce PAH pollution and related health risks.

Characterizing the long-term occurrence of polycyclic aromatic hydrocarbons and their driving forces in surface waters.

As carcinogenic and ubiquitous pollutants, an in-depth understanding of the long-term environmental behaviors of polycyclic aromatic hydrocarbons (PAHs) and their driving forces is crucial for reducing human health risks. Based on long-term monitoring data from 2001 to 2016, this study systematically investigated the temporal and seasonal trends, periodic oscillation, source apportionment, and human health risks of PAHs in eight rivers in the Free State of Saxony, Germany. The results showed that the annual average ∑16PAHs (sum of 16 PAH concentrations) ranged from 28.2 ng L-1 to 202 ng L-1. Using the Mann-Kendall test, a trend of decreasing PAH concentrations was determined (slope range: -0.103 to -0.0159). Wavelet analysis indicated that the most significant periodic oscillation of PAHs was 10-30 months, with more pollution in winter. Source apportionment analysis suggested that vehicular emissions and coal combustion contributed the most to PAH concentrations (20.6-40.3% and 21.7-41.4%, respectively) and related health risks (54.1-80.1% and 5.61-37.9%, respectively). Furthermore, the risks (oral lifetime: 4.24×10-7-1.34×10-6; dermal lifetime: 2.86×10-5-9.05×10-5) were determined to be low. The data revealed that the substitution of petroleum and coal with cleaner energy would facilitate the mitigation of PAHs.

Consumption- and Income-Based Sectoral Emissions of Polycyclic Aromatic Hydrocarbons in China from 2002 to 2017.

China is the largest emitter of polycyclic aromatic hydrocarbons (PAHs) in the world. Because of their negative influences on human health, the characteristics and potential driving forces of PAH emissions should be evaluated to establish effective mitigation strategies for different economic sectors. This study is the first to quantify the embodied and enabled PAH emissions of 108 sectors in China in 2002, 2007, 2012, and 2017. The results show that the total sectoral emissions increased by 92% (from 28.0 to 53.7 kt) from 2002 to 2012 and decreased to 53.0 kt in 2017. The eight aggregated sectors had different characteristics according to their production-, consumption-, and income-based emissions. Both the embodied and enabled emission flows increased (from 13.8 to 29.2 kt and from 11.3 to 20.5 kt, respectively) with time. The influences of the major final demands and primary inputs reversed from increasing to decreasing emissions over time. In particular, the primary input structure had a stronger impact on decreasing emissions than the final demand structure. The results revealed that different mitigation policies should be applied to different sectors and that adjusting primary input behaviors might be a relatively efficient method to reduce PAH emissions.

Environmental behavior and potential driving force of bisphenol A in the Elbe River: A long-term trend study.

As an endocrine disruptor, a deep understanding of the environmental behavior and potential driving force of bisphenol A (BPA) is helpful for developing a mitigation strategy and reducing the exposure risk to the public. Based on long-term monitoring data from 2004 to 2016, this study systematically evaluated the long-term trend, periodic characteristics, and potential risks of BPA in the Elbe River in the state of Saxony, Germany. Multiple advanced statistical approaches were employed for data mining. Pettitt's test was used to determine the main change points of BPA that occurred from 2008 to 2011. The Mann-Kendall test showed a decreasing trend in BPA concentrations (slope: -0.087 to -0.112, P < 0.05) over the past 13 years, particularly in the wet seasons (slope: -0.730 to -0.038, P < 0.05). Wavelet analysis revealed similar periodicities of BPA among stations (which experienced 4-5 oscillations in the first major period). The ARIMA model forecasted the mean BPA concentration as ranging from 9 to 41 ng L-1 in the subsequent 3 months, which was similar to that in the last 3 months (20-42 ng L-1). Besides, the highest hazard quotients (>0.3) were documented for Chironomus riparius, Oryzias latipes, Potamopyrgus antipodarum, and Hydra vulgar, which indicates that BPA may threaten their growth and development. The hazard index values for non-cancer risk of BPA no greater than 6.47 × 10-9 (HQ far below 1), which suggests that BPA did not pose a significant threat to human health. Because BPA pollution is closely related to industrial activities, a long-term decline in BPA concentrations could be attributed to the reduced number of factories, limited discharge, and improved decontamination efficiency. However, the minimal change in the BPA concentration in the near future could reflect periodic fluctuations.

Characterizing the anthropogenic-induced trace elements in an urban aquatic environment: A source apportionment and risk assessment with uncertainty consideration.

The spatial distribution of water quality status, especially in water bodies near intensively urbanized areas, is tightly associated with patterns of human activities. For establishing a robust assessment of the sediment quality in an urban aquatic environment, the source apportionment and risk assessment of Cr, Mn, Ni, Cu, Zn, As, Cd, Hg, and Pb in sediments from an anthropogenic-influenced lake were carried out with considering uncertainties from the analysis methods, random errors in the sample population and the spatial sediment heterogeneity. The distribution analysis of the trace metals with inverse distance weighting-determined method showed that the pollutants were concentrated in the middle and southern areas of the lake. According to the self-organizing map and constrained positive matrix factorization receptor model, agricultural sources (24.8%), industrial and vehicular sources (42.5%), and geogenic natural sources (32.7%) were the primary contributors to the given metals. The geogenic natural had the largest random errors, but the overall result was reliable according to the uncertainty analysis. Furthermore, the stochastic contamination and ecological risk models identified a moderate/considerable contamination level and a moderate ecological risk to the urban aquatic ecosystem. With consideration of uncertainties from the spatial heterogeneity, the contamination level of Hg, and the ecological risk of Cd in had a 20-30% probability of the increase.

Yolk-Shell Fe3 O4 @Void@N-Carbon Nanostructures Based on One-Step Deposition of SiO2 and Resorcinol-3-Aminophenol-Formaldehyde (R-APF) Cocondensed Resin Dual Layers onto Fe3 O4 Nanoclusters.

Yolk-shell magnetic nanoparticles@nitrogen-enriched Carbon nanostructures with a magnetic core and a hollow nitrogen-enriched carbon shell exhibit considerable promise in various applications, such as drug delivery, heterogenous catalysts, removal of metal ions and organic pollutants, and screening of biomolecules, due to their strong magnetic response, unique cavities, and the selective absorption ability of nitrogen-enriched groups. However, their complicated synthesis always involves possible surface modification, layer-by-layer deposition of a sacrificial middle layer and an outer nitrogen-enriched layer on magnetic nanoparticles, subsequent carbonization, and final removal of the sacrificial middle layer. Herein, yolk-shell Fe3 O4 @nitrogen-enriched carbon nanostructures are constructed based on NH4 + ion-induced one-step deposition of SiO2 and Resorcinol-3-aminophenol-formaldehyde cocondensed resin (R-APF) dual layers onto poly acrylic acid-modified Fe3 O4 nanoclusters without any extra surface modification. The N-Carbon shell thickness of the yolk-shell Fe3 O4 @Void@N-Carbon nanostructure can be finely tailored though tailoring the feeding amount of aminophenol and resorcinol to tune the thickness of the outer R-APF resin shell onto Fe3 O4 @SiO2 intermediate particles. This NH4 + ion-induced one-pot deposition of double layers can effectively promote synthesis efficiency of this kind of yolk-shell nanostructure.

Effect of anthropogenic activities on the occurrence of polycyclic aromatic hydrocarbons in aquatic suspended particulate matter: Evidence from Rhine and Elbe Rivers.

As carcinogenic and pervasive pollutants, polycyclic aromatic hydrocarbons (PAHs) in surface water are crucial to environmental policies, and the understanding of their trends and influencing factors is critical for achieving a good chemical and ecological status of water bodies. Based on long-term monitoring data from 1998 to 2017, this study systematically evaluated the spatiotemporal distribution, multimedia transport, fate, and source apportionment of PAHs adsorbed on suspended particulate matter (SPM) in Rhine and Elbe Rivers. The results of the Mann-Kendall test indicated that pollution levels of PAHs decreased from 2.81×105µg⋅s-1 to 9.80×104µg⋅s-1 on average in the Rhine and from 1.60×105 µg⋅s-1 to 5.21×104 µg⋅s-1 in the Elbe in the last 20 years. Spatially, SPM near urban areas had higher PAH mass fluxes (Rhine:3.07×105µg⋅s-1, Elbe: 1.73×105µg⋅s-1) and greater rates of decrease (slopes for Rhine and Elbe: -409, -323) than those near rural areas (Rhine:1.41×105 µg⋅s-1, Elbe: 9.35×104µg⋅s-1; slopes for Rhine and Elbe: -128, -89), indicating the significant influence of anthropogenic activities. Wavelet analysis showed that the pollution level of PAH had significant periodic oscillations for the Rhine and Elbe, and revealed several abrupt change points for the two rivers. A multimedia fugacity model demonstrated that impervious surfaces had the highest concentration (Rhine: 1.84g⋅m-3, Elbe: 0.15g⋅m-3), while soil (Rhine: 8.33×107g, Elbe: 2.53×106g) and sediments (Rhine: 4.85×106g, Elbe: 1.31×106g) had higher masses of PAHs. Furthermore, source apportionment computed using a self-organizing map and positive matrix factorization model suggested that the major sources of PAHs were vehicular emissions and coal combustion, which accounted for 51.86% of the total mass in the Rhine and 62.92% in the Elbe. The data revealed that the long-term trends of PAH variation were associated with changes in energy consumption and the implementation of vehicular emission standards. Therefore, the substitution of coal and petroleum with renewable energies could assist strategies of PAH mitigation in the environment and gradual reduction of pollution levels.

Concentration decline in response to source shift of trace metals in Elbe River, Germany: A long-term trend analysis during 1998-2016.

Monitoring spatial and temporal chemical status of water bodies is crucial to assist environmental policy, identify the chemical fingerprints, and further reduce the source orientated pollutants. Elbe River is one of the major rivers affected by anthropogenic activities in vicinity countries. This study assessed the spatiotemporal changes in response to source shift of Cd, Cu, Ni, Pb, and Zn in the suspended particulate matter (SPM) at upstream, midstream, and downstream of the Elbe River reach in Saxony state, Germany. The average contents of trace metals in SPM was found in the order of Zn (676 mg/kg) ¼ Pb (79 mg/kg) > Cu (74 mg/kg) > Ni (48 mg/kg) ¼ Cd (3.2 mg/kg). According to the Mann-Kendall trend test, Cd, Cu, Pb, and Zn showed significant declines over 1998-2016. The results of source apportionment indicate industrial, urban, natural, and historical mining sources influencing the metal contents in the Elbe River of Saxony. The contributions of industrial and urban pollution decreased by 58.2% from 1998 to 2007 to 2008-2016. The contribution of the natural source was steady over the last two decades.

A decline in the concentration of PAHs in Elbe River suspended sediments in response to a source change.

This study focuses on the analysis of the long-term trends and source apportionment of PAHs in the suspended sediments of the Elbe River in Saxony, Germany, from 2001 to 2016. The results of the Mann-Kendall trend test indicated that the concentrations of total and individual PAHs exhibited decreasing trends during the 16-year study period. According to the positive matrix factorization (PMF) receptor model, primary sources for every four-year period were identified as oil burning, biomass burning, and vehicular emissions from gasoline and diesel-powered engines. The changes in the sources were consistent with the trends in vehicle numbers and energy consumption during the last 16 years. Furthermore, the results of total toxic benzo[a]pyrene equivalent (TEQ) values indicated potential cancer risks. The results of the mean hazard quotient (MHQ) suggested that PAHs exhibited a 21% probability of being toxic to benthic organisms and to the aquatic environment.

Traffic contribution to polycyclic aromatic hydrocarbons in road dust: A source apportionment analysis under different antecedent dry-weather periods.

Road dust (RD) and its adsorbed pollutants have been regarded as a leading source of diffuse stormwater pollution. Therefore, a source-oriented mitigation strategy of pollutants in RD is important for an integrated stormwater management. In this study, a total of 66 RD samples were collected from 22 asphalt roads with five traffic load categories under different antecedent dry-weather periods (ADPs) in the city of Dresden, Germany. The surface loads (0.1-30.91 µg m-2) and solid-phase concentrations (0.95-27.83 µg g-1) of polycyclic aromatic hydrocarbons (PAHs) in RD were determined. The results show that the Σ16PAHs contents decreased with increasing distance from the city center to the city border. One-way ANOVA indicated that surface load was significantly dominated by ADPs and solid-phase concentration was statistically traffic-load dependent. According to the positive matrix factorization (PMF) receptor model, gasoline- and diesel-powered engine emissions always accounted for the highest proportions of total PAH contents. However, with an increasing ADP, the PAHs contents attributed to the incineration and tire debris became evident. The source-specific risks posed by PAHs were further estimated by the incremental lifetime cancer risk (ILCR) analysis. Traffic contributed to the majority of the carcinogenic substances. Moreover, the hazard quotient (HQ) and mean hazard quotient (MHQ) for the ecological risk assessment suggest that PAHs in RD had a 21% probability of being toxic to benthic organisms and aquatic environments. CAPSULE: Σ16PAH content decreased with an increasing distance from the city center to border, and an increasing number of PAH sources was identified with an increasing residual time.

Vehicular contribution of PAHs in size dependent road dust: A source apportionment by PCA-MLR, PMF, and Unmix receptor models.

This study focuses on the source apportionments of polycyclic aromatic hydrocarbons (PAHs) in road dust (RD) with four size fractions through three receptor models of principal component analysis with multiple linear regression (PCA-MLR), positive matrix factorization (PMF) and Unmix. The concentrations of total PAHs range from 0.45 to 2.03µgg-1. Results show that the concentrations of PAHs increased with a decreasing size fraction. Similar potential sources to PAHs in RD were extracted by three models with a little difference in numbers and percent load contributions of each identified sources. The overall proportion of the identified sources were ranked as vehicular emission>coke oven>surface pavement>others in each size fractions. In terms of risk assessment, the mean values of incremental lifetime cancer risk (ILCR) of the total cancer risk of PAHs in RD were lower than the baseline value of an acceptable risk. However, PAHs in smaller size fraction prone to have a higher adverse effect on children via ingestion. Furthermore, the ecological risk assessment of hazard quotients and mean hazard quotients indicated that PAHs in RD had a 9% probability of being toxic to the benthic organisms and aquatic environment.

Monomer Protonation-Dependent Surface Polymerization to Achieve One-Step Grafting Cross-Linked Poly(4-Vinylpyridine) Onto Core-Shell Fe3 O4 @SiO2 Nanoparticles.

Functional polymer-grafting silica nanoparticles hold great promise in diverse applications such as molecule recognition, drug delivery, and heterogeneous catalysis due to high density and uniform distribution of functional groups and their tunable spatial distance. However, conventional grafting methods from monomers mainly consist of one or more extra surface modification steps and a subsequent surface polymerization step. A monomer protonation-dependent surface polymerization strategy is proposed to achieve one-step uniform surface grafting of cross-linked poly(4-vinylpyridine) (P4VP) onto core-shell Fe3 O4 @SiO2 nanostructures. At an approximate pH, partially protonated 4VP sites in aqueous solution can be strongly adsorbed onto deprotonated silanol groups (SiO- ) onto Fe3 O4 @SiO2 nanospheres to ensure prior polymerization of these protonated 4VP sites exclusively onto Fe3 O4 @SiO2 nanoparticles and subsequent polymerization of other 4VP and divinylbenzene monomers harvested by these protonated 4VP monomers onto Fe3 O4 @SiO2 nanoparticles, thereby achieving direct grafting of cross-linked P4VP macromolecules onto Fe3 O4 @SiO2 nanoparticles.

In Situ Confined Growth Based on a Self-Templating Reduction Strategy of Highly Dispersed Ni Nanoparticles in Hierarchical Yolk-Shell Fe@SiO2 Structures as Efficient Catalysts.

Ni-based magnetic catalysts exhibit moderate activity, low cost, and magnetic reusability in hydrogenation reactions. However, Ni nanoparticles anchored on magnetic supports commonly suffer from undesirable agglomeration during catalytic reactions due to the relatively weak affinity of the magnetic support for the Ni nanoparticles. A hierarchical yolk-shell Fe@SiO2 /Ni catalyst, with an inner movable Fe core and an ultrathin SiO2 /Ni shell composed of nanosheets, was synthesized in a self-templating reduction strategy with a hierarchical yolk-shell Fe3 O4 @nickel silicate nanocomposite as the precursor. The spatial confinement of highly dispersed Ni nanoparticles with a mean size of 4 nm within ultrathin SiO2 nanosheets with a thickness of 2.6 nm not only prevented their agglomeration during catalytic transformations but also exposed the abundant active Ni sites to reactants. Moreover, the large inner cavities and interlayer spaces between the assembled ultrathin SiO2 /Ni nanosheets provided suitable mesoporous channels for diffusion of the reactants towards the active sites. As expected, the Fe@SiO2 /Ni catalyst displayed high activity, high stability, and magnetic recoverability for the reduction of nitroaromatic compounds. In particular, the Ni-based catalyst in the conversion of 4-nitroamine maintained a rate of over 98 % and preserved the initial yolk-shell structure without any obvious aggregation of Ni nanoparticles after ten catalytic cycles, which confirmed the high structural stability of the Ni-based catalyst.

UV-Triggered Self-Healing of a Single Robust SiO2 Microcapsule Based on Cationic Polymerization for Potential Application in Aerospace Coatings.

UV-triggered self-healing of single microcapsules has been a good candidate to enhance the life of polymer-based aerospace coatings because of its rapid healing process and healing chemistry based on an accurate stoichiometric ratio. However, free radical photoinitiators used in single microcapsules commonly suffer from possible deactivation due to the presence of oxygen in the space environment. Moreover, entrapment of polymeric microcapsules into coatings often involves elevated temperature or a strong solvent, probably leading to swelling or degradation of polymer shell, and ultimately the loss of active healing species into the host matrix. We herein describe the first single robust SiO2 microcapsule self-healing system based on UV-triggered cationic polymerization for potential application in aerospace coatings. On the basis of the similarity of solubility parameters of the active healing species and the SiO2 precursor, the epoxy resin and cationic photoinitiator are successfully encapsulated into a single SiO2 microcapsule via a combined interfacial/in situ polymerization. The single SiO2 microcapsule shows solvent resistance and thermal stability, especially a strong resistance for thermal cycling in a simulated space environment. In addition, the up to 89% curing efficiency of the epoxy resin in 30 min, and the obvious filling of scratches in the epoxy matrix demonstrate the excellent UV-induced healing performance of SiO2 microcapsules, attributed to a high load of healing species within the capsule (up to 87 wt %) and healing chemistry based on an accurate stoichiometric ratio of the photoinitiator and epoxy resin at 9/100. More importantly, healing chemistry based on a UV-triggered cationic polymerization mechanism is not sensitive to oxygen, extremely facilitating future embedment of this single SiO2 microcapsule in spacecraft coatings to achieve self-healing in a space environment with abundant UV radiation and oxygen.