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Hetero‐contacts are interfaces between different materials at the nanoscale leading to novel functional properties. In hetero‐aggregates, primary particles of at least two different materials are mixed at primary particle or cluster level. Double flame spray pyrolysis (DFSP) is a versatile technique for the controlled synthesis of such materials. Characterization of hetero‐aggregates by scanning transmission electron microscopy (STEM) requires acquisition and evaluation of many aggregate images in order to derive statistically significant results. Usually, STEM energy dispersive X‐ray spectroscopy (EDXS) is used to acquire elemental maps providing the material distribution of the primary particles within hetero‐aggregates. However, the acquisition of a single EDXS map takes up to several minutes. For this reason, determination of material types of primary particles from the intensity in high‐angle annular dark field STEM images alone is desirable. These images can be acquired within a couple of seconds. In the present work, a method is suggested which allows for achieving this objective. It can be applied to distinguish materials with a significant difference in their atomic number and hence sufficient material contrast in the STEM images. [ABSTRACT FROM AUTHOR]

In hetero-aggregates, different materials form sintered hetero-contacts, which lead to new material properties. In this study, the influence of process parameters on the formation of hetero-contacts in Double Flame Spray Pyrolysis (DFSP) was quantified. The mixing of jets was monitored by Particle Image Velocimetry (PIV) measurements as well as by thermocouples and compared to the single flame setting. Overlap of the jets was evaluated using tracers to visualize the mixing zone. Ten CuO/CeO 2 model material samples were prepared with different flame inclination angles, nozzle distances and different particle volume fractions. Mixing on hetero-aggregate level was quantified using Convolutional Neural Network (CNN) evaluations of STEM images, Temperature-Programmed Reduction (TPR) and Differential Centrifugal Sedimentation (DCS) disk centrifugation to determine cluster sizes and hetero-coordination numbers as mixing quantifiers. Here, good correlations between the differently measured quantifiers were observed. [Display omitted] • Single-step synthesis of hetero-aggregates by gas phase mixing of different materials leading to hetero-contact formation. • Quantification of the mixing process of two aerosol-laden jets with respect to gas velocity, temperature, and tracer mixing. • Quantification of mixing quality on hetero-aggregate level in a CuO/CeO 2 model material • Cluster sizes, hetero-coordination numbers, mobility equivalent diameters, and material reducibility as mixing quantifiers. [ABSTRACT FROM AUTHOR]

In this study, microalgae Chlorella vulgaris (C. vulgaris) were simultaneously exposed to environmental concentrations of amino-functionalized polystyrene nanoplastics (PS-NH 2 ; 0.05, 0.1, 0.2, 0.3 and 0.4 mg/L) and the world's second most used pesticide, the herbicide atrazine (ATZ; 10 μg/L), in the absence and presence of humic acid (HA; 1 mg/L) for 21 days. Due to the low concentrations of PS-NH 2 , the majority of them could not cause a significant difference in the end-points of biomass, chlorophylls a and b , total antioxidant, total protein, and superoxide dismutase and malondialdehyde compared to the control group (p > 0.05). On the other hand, by adding ATZ to the PS-NH 2 , all the mentioned end-point values showed a considerable difference from the control (p < 0.05). The exposure of PS-NH 2 +ATZ treatments to the HA could remarkably reduce their toxicity, additionally, HA was able to decrease the changes in the expression of genes related to oxidative stress (e.g., superoxide dismutase, glutathione reductase, and catalase) in the C. vulgaris in the most toxic treatment group (e.g., PS-NH 2 +ATZ). The synergistic toxicity of the PS-NH 2 +ATZ group could be due to their enhanced bioavailability for algal cells. Nevertheless, the toxicity alleviation in the PS-NH 2 +ATZ treatment group after the addition of HA could be due to the eco-corona formation, and changes in their zeta potential from positive to negative value, which would increase their electrostatic repulsion with the C. vulgaris cells, in such a way that HA also caused a decrease in the formation of C. vulgaris -NPs hetero-aggregates. This research underscores the complex interplay between PS-NH 2 , ATZ, and HA in aquatic environments and their collective impact on microalgal communities. [Display omitted] • First study reports long-term (21 days) joint toxicity of PS-NH 2 +ATZ in the presence of HA on an organism. • Synergistic toxicity of PS-NH 2 +ATZ treatments could be due to their increased bioavailability. • Expression of oxidative stress-related genes showed modulated oxidative stress response by HA. • Extracellular organic matter secreted by C. vulgaris can be the main cause for hetero-aggregates formation. [ABSTRACT FROM AUTHOR]

Microplastic hetero-aggregates are stable forms of microplastics in the aqueous environment. However, when disinfecting water containing microplastic hetero-aggregates, the response of them in water to different oxidizing agents and the effect on water quality have not been reported. Our results showed that Ca(ClO) 2 , K 2 S 2 O 8 , and sodium percarbonate (SPC) treatment could lead to the disaggregation of microplastic hetero-aggregates as well as a rise in cell membrane permeability, which caused a large amount of organic matter to be released. When the amount of oxidant dosing is insufficient, the oxidant cannot completely degrade the released organic matter, resulting in DOC, DTN, DTP and other indicators being higher than before oxidation, thus causing secondary pollution of the water body. In comparison, K 2 FeO 4 can purify the water body stably without destroying the microplastic hetero-aggregates, but it only weakly inhibits the toxic cyanobacteria Microcystis and Pseudanabaena , which may cause cyanobacterial bloom as well as algal toxin and odorant contamination in practical application. Compared with the other oxidizers, K 2 S 2 O 8 provides better inhibition of toxic cyanobacteria and has better ecological safety. Therefore, when treating microplastic-containing water bodies, we should consider both water purification and ecological safety, and select appropriate oxidant types and dosages to optimize the water treatment. [Display omitted] • Microplastics adsorb organics and microorganisms to raise water quality. • Ca(ClO) 2 , K 2 S 2 O 8 and SPC destroy hetero-aggregates, leading to secondary pollution. • K 2 FeO 4 does not cause the release of organics adsorbed by hetero-aggregates. • K 2 FeO 4 is not effective in controlling the proliferation of toxic cyanobacteria. [ABSTRACT FROM AUTHOR]

Microalgae can excrete exopolymer substances (EPS) with a potential to form hetero-aggregates with microplastic particles. In this work, two freshwater (Microcystis panniformis and Scenedesmus sp.) and two marine (Tetraselmis sp. and Gloeocapsa sp.) EPS producing microalgae were exposed to different microplastics. In this study, the influence of the microplastic particles type, size and density in the production of EPS and hetero-aggregates potential was studied. Most microalgae contaminated with microplastics displayed a cell abundance decrease (of up to 42%) in the cultures. The results showed that the formed aggregates were composed of microalgae and EPS (homo-aggregates) or a combination of microalgae, EPS and microplastics (hetero-aggregates). The hetero-aggregation was dependent on the size and yield production of EPS, which was species specific. Microcystis panniformis and Scenedesmus sp. exhibited small EPS, with a higher propension to disaggregate, and consequently lower capabilities to aggregate microplastics. Tetraselmis sp. displayed a higher ability to aggregate both low and high-density microplastics, being partially limited by the size of the microplastics. Gloeocapsa sp. had an outstanding EPS production and presented excellent microplastic aggregation capabilities (adhered onto the surface and also incorporated into the EPS). The results highlight the potential of microalgae to produce EPS and flocculate microplastics, contributing to their vertical transport and consequent deposition. Thus, this work shows the potential of microalgae as biocompatible solutions to water microplastics treatment. Image 1 • Specific microalgae can excrete EPS with favourable characteristics to aggregate microplastics and form hetero-aggregates. • Microalgae can colonize microplastics and use the EPS to adhere and incorporate the particles. • Microplastics colonization and hetero-aggregation contribute to its vertical transport and deposition. Microalgae extracellular polymeric substances have the potential to aggregate microplastics, contributing to their vertical transport and deposition. [ABSTRACT FROM AUTHOR]

Mixing nanoparticles is critical in various industries, including pharmaceuticals, solar, and nanotechnology. When different nanopowders are mixed, hetero-aggregates consisting of hetero-contacts are formed, facilitating the exchange of charge, mass and moments between particles of different materials. This research paper presents a novel approach for mixing nanoparticles using special spouted bed equipment to produce hetero-aggregates. The paper explores the potential of special spouted bed equipment for mixing nanoparticles. High-velocity opposed inlet air streams in this equipment result in high gas-solid contact efficiency and enhanced particle circulation, which contribute to the breakage of aggregates and promote the mixing process. The study investigates the aggregate breakage and mixing quality in produced hetero-aggregates. Experimental results demonstrate that the special spouted bed equipment enables efficient mixing of nanoparticles, leading to higher dispersion in hetero-aggregates with many hetero-contacts. The modified homogeneity of mixing method is utilized to quantify the mixing inside the single hetero-aggregates. Visual confirmation of the assessed values of mixing quality is provided by EDX spectral mapping. [Display omitted] • Utilizing high velocity jets in a ProCell type spouted bed to produce hertero-aggregates of nanoparticles. • Modified homogeneity of mixing method is used to quantify mixing inside a single hetero-aggregate of nanoparticles. • EDX is used to quantify mixing at a scale of 200 nm. [ABSTRACT FROM AUTHOR]

Microplastic contamination in clean water sources and household wastewater is a significant environmental issue that requires sustainable remediation solutions. This study aims to evaluate the effectiveness of extracellular polymeric substances (EPS) produced by different microalgae strains in removing microplastics from aquatic environments. Four microalgae strains, namely Spirulina sp. Tetraselmis chuii, Chlorella vulgaris, and Dunaliella salina, were cultivated under stress conditions, including the application of polypropylene microplastics, increased light intensity, and enhanced nutrient levels, to stimulate EPS production. The EPS produced was then interacted with microplastics to form hetero-aggregates. Spirulina sp. produced the highest amount of EPS (4.59 g), followed by Tetraselmis chuii (3.27 g), Chlorella vulgaris (3.03 g), and Dunaliella salina (2.86 g). The carbohydrate content in dry EPS was also highest in Spirulina sp. (0.21%), with Tetraselmis chuii (0.19%), Chlorella vulgaris (0.16%), and Dunaliella salina (0.11%) following. The microplastic flocculation efficiency mirrored these results, with Spirulina sp. flocculating 1.397 g of microplastics, outperforming the other strains. These findings suggest that Spirulina sp. and Tetraselmis chuii are particularly effective in producing EPS that can be utilized to remove microplastics from aquatic environments, offering a promising eco-friendly solution.

In urban waters, microplastics (MPs) usually form hetero-aggregates through adsorption of organics and microbes. However, the effects of hetero-aggregates on water quality are rarely reported. In this study we found that the hetero-aggregates, which accumulated contaminants, were like a "time bomb". Chlorination was able to trigger the "time bomb" through destruction of hetero-aggregates, lysis of microbial cells and elevation of the concentration of low-molecular-mass organics. Thereupon previously adhered organics desorbed from MPs, intracellular metabolites were released from lysed cells, and re-formation of hetero-aggregates was limited. This process rapidly increased the concentration of organics but prevented the re-adsorption of organics, which leads to secondary pollution. Thus, to alleviate the risks of secondary pollution caused by hetero-aggregates, the choice of oxidant species and dose should be optimized based on the characteristics of existent hetero-aggregates when purifying urban waters containing MPs. [Display omitted] • Chlorination can result in the destruction of hetero-aggregates. • Lysed microbial cells and detached organics deteriorated water quality. • Levels of low-molecular-mass organics and MPs' hydrophilicity were increased. • Re-formation of hetero-aggregates and re-adsorption of organics were limited. [ABSTRACT FROM AUTHOR]

In this study, the interactions between microplastics, chosen among the most widely used in industry such as polypropylene (PP) and high-density polyethylene (HDPE), and a model freshwater microalgae, Chlamydomas reinhardtii , were investigated. It was shown that the presence of high concentrations of microplastics with size >400 μm did not directly impact the growth of microalgae in the first days of contact and that the expression of three genes involved in the stress response was not modified after 78 days. In parallel, a similar colonization was observed for the two polymers. However, after 20 days of contact, in the case of PP only, hetero-aggregates constituted of microalgae, microplastics and exopolysaccharides were formed. An estimation of the hetero-aggregates composition was approximately 50% of PP fragments and 50% of microalgae, which led to a final density close to 1.2. Such hetero-aggregates appear as an important pathway for the vertical transport of PP microplastics from the water surface to sediment. Moreover, after more than 70 days of contact with microplastics, the microalgae genes involved in the sugar biosynthesis pathways were strongly over-expressed compared to control conditions. The levels of over-expression were higher in the case of HDPE than in PP condition. This work presents the first evidence that depending on their chemical nature, microplastics will follow different fates in the environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Distribution of minerals in microaggregates revealed by SEM-EDS. • Coaction of EPS and mineral size on forming the complexes of microaggregates. • EPS is a dispersant in the mineral mixture containing nano-sized goethite. • EPS is an agglomerant in the system containing micro-sized goethite. • No effect in the goethite size on the complexes forming without EPS. Soil microaggregates composed of mineral–mineral and organo-mineral complexes are crucial for controlling many soil ecosystem functions such as soil stability and persistence of organic matter. However, mechanisms of how microbial-derived organic matter (e.g., extracellular polymeric substances, EPS) and particle size of the mineral shape mineral–mineral and organo-mineral complexes in multiphase system are unclear. Here, batch experiments (i.e., mineral mixtures of quartz, kaolinite, and three different sizes of goethite) were used to determine the effect of goethite size and EPS on the formation of mineral–mineral and organo-mineral complexes. Our results revealed that the multiphase system containing micro-sized goethite had a higher proportion of 50–250 μm aggregates than these containing nano-sized goethite in the presence of EPS. When EPS was absent, the particle distribution was not related to goethite size, and the mineral suspension was homogeneous. The mechanisms of mineral–mineral and organo-mineral complexes formation were further investigated by measuring zeta potential. Negatively charged EPS adsorbed onto positively charged goethite surface through electrostatic interactions, resulting in stable organo-mineral complexes and inhibition of mineral–mineral complexes. EPS-goethite interaction resulted in a marked decrease of phosphorus in the suspension, suggesting preferred adsorption of EPS-P compounds to goethite. This interaction led to EPS fractionation which was affected by goethite size due to the particle size-dependent surface interactions. The information obtained in this study is of fundamental significance for understanding the initial formation of microaggregates in the edaphic microenvironment. [ABSTRACT FROM AUTHOR]

Plastic pollution is a global issue posing a threat to marine biota with ecological implications on ecosystem functioning. Micro and nanoplastic impact on phytoplankton autotrophic species (e.g., cell growth inhibition, decrease in chlorophyll a and photosynthetic efficiency and hetero-aggregates formation) have been largely documented. However, the heterogeneity of data makes rather difficult a comparison based on size (i.e. micro vs nano). In addition, knowledge gaps on the ecological impact on phytoplankton assemblage structure and functioning are evident. A new virtual meta-analysis on cause-effect relationships of micro and nanoplastics on phytoplankton species revealed the significant effect posed by polymer type on reducing cell density for tested PVC, PS and PE plastics. Linked with autotrophic phytoplankton role in atmospheric CO 2 fixation, a potential impact of plastics on marine carbon pump is discussed. The understanding of the effects of microplastics and nanoplastics on the phytoplankton functioning is fundamental to raise awareness on the overall impact on the first level of marine food web. Interactions between micro and nanoplastics and phytoplankton assemblages have been quite documented by in vitro examinations; but, further studies considering natural plankton assemblages and/or large mesocosm experiments should be performed to evaluate and try predicting ecological impacts on primary producers. [Display omitted] • Micro and nanoplastic impact on microalgal reproduction. • Micro and nanoplastics are substrates for phytoplankton adhesion and colonization. • Plastic debris forms hetero-aggregates with phytoplankton assemblages. • Carbon cycle can be affected through POC sequestration by micro and nanoplastic. • Micro and nanoplastics can alter the first levels of marine food web. [ABSTRACT FROM AUTHOR]

The graphene oxide (GO) due to its exceptional structure, physicochemical and mechanical properties is a very attractive material for industry application. Even though, the unique properties of GO (e.g. structure, size, shape, etc.) make the risk assessment of this nanomaterial very challenging in comparison with conventional ecotoxicology studies required by regulators. Thus, there is a need for standardized characterization techniques and methodology to secure a high quality/reliable data on the ecotoxicology of GO, and to establish environmentally acceptable levels. Herein, authors address the crucial quality criteria when evaluating the ecotoxicology of GO using an algae (Raphidocelis subcapitata) and a shrimp (Paratya australiensis). This study provides a detail characterization and modification of the used GO, robust quantification and a suspension stability in different media for ecotoxicology studies. It was observed that under the same exposure conditions the behavior of GO and the estimated outcomes (IC 50 values) in modified algae media differed in comparison to the referent media. Further to that, the adverse effects of GO on the algae cell structure and the potential uptake of GO by the algae cells were examined using the TEM with different staining techniques to avoid artefacts. Shrimps which were exposed to GO-algae aggregates via the food intake did not indicate stress or accumulation of GO. Our work presents an important insight to necessity of establishing a benchmark ecotoxicology assays for GO (e.g. characterization techniques, choice of media, etc.) and providing a reliable data to be used by regulators in risk assessment of two-dimensional (2D) nanomaterials. • Ecotoxicology of modified graphene-oxide (GO) was assessed using an algae. • The adverse effects of GO-algae aggregates were estimated using a shrimp. • Characterization, quantification and suspension stability of GO were addressed. • Specific surface area and the shape of GO were affected by the composition of media. • Osmium helped to avoid bias and gave a reasonably good images of algae sections. [ABSTRACT FROM AUTHOR]