What Factors Determine the Retention Behavior of Engineered Nanomaterials in Saturated Porous Media?

Transport of polystyrene microplastics in bare and iron oxide-coated quartz sand: Effects of ionic strength, humic acid, and co-existing graphene oxide

This research explored the effects of widely utilized nanomaterial graphene oxide (GO) and organic matter humic acid (HA) on the transport of microplastics under different ionic solution strengths in bare sand and iron oxide-coated sand. The results found transport of polystyrene microplastics (PS) did not respond to the presence of HA in sand that contains large amounts of iron oxide. Compared to bare quartz sand, ionic strength had little effect: <20 % of PS passed through Fe sand columns. There was a significant promotion of PS transport in the presence of GO, however, which can be attributed to the increased surface electronegativity of PS and steric hindrance. Moreover, GO combined with HA significantly promoted the transport of PS in the Fe sand, and transport further increased when the concentration of HA increased from 5 to 10 mg/L. Interestingly, the degree of this increase exactly corresponded to the change in the surface charge of the microplastics, demonstrating that electrostatic interaction dominated the PS transport. Further results indicated that co-existing pollutants had significant impacts on the transport of microplastics under various conditions by altering the surface characteristics of the plastic particles and the spatial steric hindrance within porous media. This research will offer insights into predicting the transport and fate of microplastics in complex environments.

Using Machine Learning to make nanomaterials sustainable

Sustainable development is a key challenge for contemporary human societies; failure to achieve sustainability could threaten human survival. In this review article, we illustrate how Machine Learning (ML) could support more sustainable development, covering the basics of data gathering through each step of the Environmental Risk Assessment (ERA). The literature provides several examples showing how ML can be employed in most steps of a typical ERA.A key observation is that there are currently no clear guidance for using such autonomous technologies in ERAs or which standards/checks are required. Steering thus seems to be the most important task for supporting the use of ML in the ERA of nano- and smart-materials. Resources should be devoted to developing a strategy for implementing ML in ERA with a strong emphasis on data foundations, methodologies, and the related sensitivities/uncertainties. We should recognise historical errors and biases (e.g., in data) to avoid embedding them during ML programming.

Insight into the Crucial Role of Secondary Mineral Phases in the Transfer of Gold Nanoparticles through a Sand Column Using Online ICP-MS/spICP-MS Monitoring

Investigating the transport of engineered nanoparticles through representative soils is an important issue in assessing their mobility and fate in the environment. In this study, successive injections of gold nanoparticles (AuNPs) were performed in a quartz sand column with an eluent composed of 10^-2 M NaCl at a pH of 7.5. After this series of injections, remobilization of the AuNPs was examined by raising the eluent pH to 10. ¹⁹⁷Au and the conservative ionic tracer ⁷⁹Br were monitored simultaneously by online inductively coupled plasma mass spectrometry (ICP-MS), and the particulate nature of gold eluting from the column was confirmed by setting the ICP-MS in the "single particle" mode. The extent of AuNP attachment was greater than predicted by DLVO theory considering quartz as the sole collector, decreased with the number of injections and with particle size. In contrast with the repulsive interaction energy between the particles and the quartz surface, kaolinite, a secondary mineral of the sand, provided favorable conditions for particle attachment. The superimposed signals of ¹⁹⁷Au and ²⁷Al in the column effluent after pH increase suggest that gold nanoparticles were essentially remobilized as heteroaggregates with the kaolinite colloids they were attached to when favorable conditions for clay detachment from the sand grains were encountered.

Next-Generation Multifunctional Carbon-Metal Nanohybrids for Energy and Environmental Applications

Nanotechnology has unprecedentedly revolutionized human societies over the past decades and will continue to advance our broad societal goals in the coming decades. The research, development, and particularly the application of engineered nanomaterials have shifted the focus from "less efficient" single-component nanomaterials toward "superior-performance", next-generation multifunctional nanohybrids. Carbon nanomaterials (e.g., carbon nanotubes, graphene family nanomaterials, carbon dots, and graphitic carbon nitride) and metal/metal oxide nanoparticles (e.g., Ag, Au, CdS, Cu₂O, MoS₂, TiO₂, and ZnO) combinations are the most commonly pursued nanohybrids (carbon-metal nanohybrids; CMNHs), which exhibit appealing properties and promising multifunctionalities for addressing multiple complex challenges faced by humanity at the critical energy-water-environment (EWE) nexus. In this frontier review, we first highlight the altered and newly emerging properties (e.g., electronic and optical attributes, particle size, shape, morphology, crystallinity, dimensionality, carbon/metal ratio, and hybridization mode) of CMNHs that are distinct from those of their parent component materials. We then illustrate how these important newly emerging properties and functions of CMNHs direct their performances at the EWE nexus including energy harvesting (e.g., H₂O splitting and CO₂ conversion), water treatment (e.g., contaminant removal and membrane technology), and environmental sensing and in situ nanoremediation. This review concludes with identifications of critical knowledge gaps and future research directions for maximizing the benefits of next-generation multifunctional CMNHs at the EWE nexus and beyond.

Aqueous aggregation and stability of graphene nanoplatelets, graphene oxide, and reduced graphene oxide in simulated natural environmental conditions: complex roles of surface and solution chemistry

Graphene-family nanomaterials (GFNs) exhibit universal applications and consequently will inevitably enter aquatic systems. However, both the fate and behavior of GFNs in aquatic environments have not been completely explored at field relevant conditions. Herein, we have systematically investigated the aqueous aggregation and stability of graphene nanoplatelets (GNPs), graphene oxide (GO), and reduced graphene oxide (RGO) under varied solution chemistry parameters (pH, divalent cations, and dissolved organic carbon (DOC)) during 21 days of incubation in simulated natural environmental conditions. Results indicate that pH values from 6 to 9 had a notable impact on the aqueous behaviors of the three GFNs. Divalent cations (Ca²⁺ and Mg²⁺) at the concentrations of 2.5 and 10 mM remarkably increased the extent of aggregation of the three GFNs and resulted in severe sedimentation, independently of surface chemical functionalization. The presence of only DOC ranging from 0.5 to 2 mg C/L significantly elevated the dispersion stability of GNPs and RGO in a dose-dependent manner, whereas no effects were observed on GO. Furthermore, DOC at the studied concentrations and surface functionality were insufficient to counterbalance the impact of the divalent cations. Direct visual and in situ observations further supported the conclusions on the effects of divalent cations or/and DOC. These findings further underline that the environmental behaviors of GFNs are controlled by the complex interplay between water chemistry parameters and GFN surface properties.

Uptake and transformations of engineered nanomaterials: Critical responses observed in terrestrial plants and the model plant Arabidopsis thaliana

With the applications of engineered nanomaterials (ENMs) continually expanding and production quickly growing, residues of ENMs will end up in the environment at levels that may be harmful to non-target organisms. Many of the tunable properties that have made them desirable, such as type, size, charge, or coating, also contribute to the current difficulties in understanding the fate of ENMs in the environment. This review article focuses on studies that investigate plant-ENM interactions, including techniques used to study these interactions and documented plant responses due to the phytotoxic effects of ENMs. The many variables which can be altered for an experiment, such as type, size, and concentration of ENMs, make it difficult to formulate generalizations about the uptake mechanism involved, or to make an inference on the subcellular localization and distribution of the internalized ENMs in plant tissue. In order to avoid these challenges, studies can utilize a model organism such as Arabidopsis thaliana, and a combination of analytical techniques that can reveal complementary information in order to assess how the different experimental conditions influence the uptake and phytotoxicity of ENMs. This review presents recent studies regarding plant-ENM interactions employing Arabidopsis to demonstrate how the use of this model plant can advance our understanding of plant-ENM interactions and guide additional studies using other plant species. Overarching results suggest that more sensitive tests and consistency in experimental designs are needed to fully assess and understand the phytotoxic effects of ENMs in the environment.

Carboxymethylcellulose Mediates the Transport of Carbon Nanotube-Magnetite Nanohybrid Aggregates in Water-Saturated Porous Media

Carbon-metal oxide nanohybrids (NHs) are increasingly recognized as the next-generation, promising group of nanomaterials for solving emerging environmental issues and challenges. This research, for the first time, systematically explored the transport and retention of carbon nanotube-magnetite (CNT-Fe3O4) NH aggregates in water-saturated porous media under environmentally relevant conditions. A macromolecule modifier, carboxymethylcellulose (CMC), was employed to stabilize the NHs. Our results show that transport of the magnetic CNT-Fe3O4 NHs was lower than that of nonmagnetic CNT due to larger hydrodynamic sizes of NHs (induced by magnetic attraction) and size-dependent retention in porous media. Classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory can explain the mobility of NHs under varying experimental conditions. However, in contrast with colloid filtration theory, a novel transport feature-an initial lower and a following sharp-higher peaks occurred frequently in the NHs' breakthrough curves. The magnitude and location of both transport peaks varied with different experimental conditions, due to the interplay between variability of fluid viscosity and size-selective retention of the NHs. Promisingly, the estimated maximum transport distance of NHs ranged between ∼0.38 and 46 m, supporting the feasibility of employing the magnetically recyclable CNT-Fe3O4 NHs for in situ nanoremediation of contaminated soil, aquifer, and groundwater.