Transport of functional group modified polystyrene nanoplastics in binary metal oxide saturated porous media

Dual roles of goethite coating on the transport of plastic nanoparticles in heterogeneous porous media: The significance of collector surface roughness

This study systematically examines the roles of positive goethite on the retention and release of negative plastic nanoparticles (PSNPs) with different surface functional groups (Blank, -COOH, and -NH2). It provides the first evidence for the dual roles of goethite coatings on colloid transport; e.g., increased transport caused by surface morphology modification or decreased transport due to increased surface roughness and charge heterogeneity. Although previous work has shown that goethite-coated sand increases the retention of negative colloids, this work demonstrates that collector surface roughness can also reduce the retention of PSNPs due to increased interaction energy profiles. Nonmonotonic retention of all the different functionalized PSNPs was observed in goethite-coated rough sand, and the magnitude of variations was contingent on the PSNP functionalization, the solution ionic strength (IS), and the goethite coating. The release of PSNPs with IS decrease (phase I) and pH increase (phase II) varied significantly due to differences in energy barriers to detachment, e.g., release in phase I was inhibited in both goethite-coated sands, whereas release in phase II was enhanced in coated smooth sand but completely inhibited in rough sand. The findings of this study provide innovative insight into transport mechanisms for colloidal and colloid-associated contaminants.

Effect of water-soluble polymers on the transport of functional group-modified polystyrene nanoplastics in goethite-coated saturated porous media

The research on the impact of water-soluble polymers (WSPs) on the migration and fate of plastic particles is extremely limited. This article explored the effects of polyacrylic acid (PAA, a common WSP) and physicochemical factors on the transport of polystyrene nanoparticles (PSNPs-NH2/COOH) with different functional groups in QS (quartz sand) and FOS (goethite-modified quartz sand, simulates mineral colloids). Research has shown that PAA can selectively adsorb onto the surface of PSNPs-NH2, forming ecological corona heterogeneous aggregates. This process increased the spatial hindrance and elastic repulsion, resulting in the recovery of PSNPs-NH2 always exceeding that of PSNPs-COOH. Overall, PAA can hinder the migration of PSNPs in QS but can promote their migration in FOS. When multivalent cations coexist with PAA, the transport of PSNPs in the media is primarily affected by cation bridging and CH-cation-π interaction. The presence of oxyanions and PAA prevents PSNPs from following the Hofmeister rule and promotes their migration (PO43-: 82.34 ± 0.16% to 94.63 ± 2.82%>SO42-: 81.38 ± 2.73% to 91.15 ± 0.93%>NO3-: 55.85 ± 0.70%-87.16 ± 3.80%). The findings of this study contribute significantly to a better understanding of the migration of WSPs and group-modified NPs in complex saturated porous media.

Stereoselective transport of 2-aryl propionic acid enantiomers in porous media subjected to chiral organic acids

The study examined the transport behavior of the 2-aryl propionic acid (2-APA) chiral pharmaceutical enantiomers by means of a laboratory-scale saturated quartz sand column experiment. Four typical of 2-APA and their enantiomers were selected for the study under different types of chiral organic acids (COAs)-mediated effects. Differences in the transport of the 2-APA enantiomeric pairs have been identified in response to various pH, types of COAs, and enantiomeric structures of COAs. Redundancy analysis identified the factors responsible for the largest differences in transport of 2-APA enantiomeric pairs, while spectroscopic characterization and density function theory (DFT) studies elucidated the underlying mechanisms contributing to the differences in transport of enantiomeric pairs. Obvious correlations among homochirality or heterochirality between COAs and 2-APA enantiomeric pairs were observed for changes in the mobility of 2-APA. The results indicate widespread COAs significantly affect the transport behavior of chiral man-made chemicals, suggesting more attention is needed to fill the gap in the perception of the transport behavior of chiral compounds.

Statuses, shortcomings, and outlooks in studying the fate of nanoplastics and engineered nanoparticles in porous media respectively and borrowable sections from engineered nanoparticles for nanoplastics

This review discussed the research statuses, shortcomings, and outlooks for the fate of nanoplastics (NPs) and engineered nanoparticles (ENPs) in porous media and borrowable sections from ENPs for NPs. Firstly, the most important section was that we reviewed the research statuses on the fate of NPs in porous media and the main influencing factors, and explained the influencing mechanisms. Secondly, in order to give NPs a reference of research ideas and influence mechanisms, we also reviewed the research statuses on the fate of ENPs in porous media and the factors and mechanisms influencing the fate. The main mechanisms affecting the transport of ENPs were summarized (Retention or transport modes: advection, diffusion, dispersion, deposition, adsorption, blocking, ripening, and straining; Main forces and actions: Brownian motion, gravity, electrostatic forces, van der Waals forces, hydration, filtration, bridging; Affecting elements of the forces and actions: the ENP and media grain surface functional groups, size, shape, zeta potential, density, hydrophobicity, and roughness). Instead of using the findings of ENPs, thorough study on NPs was required because NPs and ENPs differed greatly. Based on the limited existing studies on the NP transport in porous media, we found that although the conclusions of ENPs could not be applied to NPs, most of the influencing mechanisms summarized from ENPs were applicable to NPs. Combining the research thoughts of ENPs, the research statuses of NPs, and some of our experiences and reflections, we reviewed the shortcomings of the current studies on the NP fate in porous media as well as the outlooks of future research. This review is very meaningful for clarifying the research statuses and influence mechanisms for the NP fate in porous media, as well as providing a great deal of inspiration for future research directions about the NP fate in porous media.

Transport of polystyrene nanoplastics with different functional groups in goethite-coated saturated porous media: Effects of low molecular weight organic acids and physicochemical properties

The influence of low molecular weight organic acids (LMWOAs) and goethite on the migration of nanoplastics in the soil environment remains poorly understood. To elucidate the mechanism of influence, the study investigated the impact of LMWOAs on the migration ability of functionalized polystyrene nanoplastics (PSNPs-NH2/COOH) in quartz sand (QS) and goethite (α-FeOOH)-coated quartz sand (FOS). We investigated the effect of changes in iron valence induced by LMWOAs on the migration of PSNPs. The results revealed that the migration ability of polystyrene nanoplastics (PSNPs) declined as the ionic strength (IS) increased and the pH decreased, primarily due to the compression of the double layer and protonation reactions. The migration of PSNPs is facilitated by LMWOAs through distinct mechanisms in the two media. Specifically, LMWOAs were adsorbed on the FOS and QS surfaces through complexation and hydrogen bonding, respectively. At pH 4.0, LMWOAs exhibit redox activity, resulting in the generation of additional Fe(III). This redox process enhances the electrostatic attraction between the media and PSNPs, thereby reducing the competition at specific points and spatial resistance associated with LMWOAs. In contrast to FOS, LMWOAs at pH 4.0 reduced the migration ability of PSNPs in QS, following the trend of MA > TA > CA. This difference was attributed to the pKa of LMWOAs and the weak hydrogen bonding on the QS surface. The relevant mathematical models effectively validate the migration results. The above conclusions suggest that LMWOAs can alter the valence state of iron on the surface of goethite, thereby influencing the migration of plastic particles in environmental media.

Quantification of two-site kinetic transport parameters of polystyrene nanoplastics in porous media

In this study, a combination of column experiments, interface chemistry theory and transport model with two-site kinetics was used to systematically investigate the effect of pH on the transport of polystyrene nanoparticles (PSNPs) in porous media. The porous media containing quartz sand (QS) and three kinds of clay minerals (CMs)-kaolinite (KL), illite (IL) and montmorillonite (MT), was used in column experiments to simulate the porous media in the soil-groundwater systems. Experimental results showed that the inhibitory effect of CMs on the transport of PSNPs is weakened as pH increases. The two-dimensional (2D) surface of the DLVO interaction energy (2D-pH-DLVO) was built to calculate the interactions between PSNPs and CMs under different conditions of pH. Results suggested the inflection point of PSNP-QS, PSNP-KL, PSNP-IL and PSNP-MT are 2.42, 3.30, 2.84 and 3.69, respectively. Most importantly, there was a significant correlation between the two-site kinetic parameters related to PSNPs transport and the DLVO energy barrier (DB). The contributions of the interactions of PSNPs-PSNPs and PSNPs-minerals were determined for PSNPs transport in porous media. The critical values of pH related to the migration ability of PSNPs in porous media could be determined by a combination of column experiments, 2D-pH-DLVO and PSNPs transport model. The critical values of pH were 2.95-3.01, 3.22-3.51, 2.98-3.02, 3.31-3.33 for the migration ability of PSNPs in QS, QS + KL, QS + IL and QS + MT porous media, respectively. The stronger migration ability of PSNPs under high pH conditions is attributed to the enhanced deprotonation of the media surface and increased negative surface charge, which increases the electrostatic repulsion between PSNPs and porous media (QS, CMs). Moreover, the agglomeration of PSNPs usually is weaker and the average particle size of agglomerates is smaller under the condition of high pH, thus leading to the stronger migration ability of PSNPs under high pH conditions.

Co-transport of degradable microplastics with Cd(Ⅱ) in saturated porous media: Synergistic effects of strong adsorption affinity and high mobility

With the utilization of degradable plastics in the agricultural film and packaging industries, degradable microplastics (MPs) with strong mobility distributed in the underground environment may serve as carriers for heavy metals. It is essential to explore the interaction of (aged) degradable MPs with Cd(Ⅱ). The adsorption and co-transport behavior of different types of (aged) MPs (polylactic acid (PLA), polyvinyl chloride (PVC)) with Cd(Ⅱ) were investigated through batch adsorption experiments and column experiments under different conditions, respectively. The adsorption results showed that the adsorptive capacity of (aged) PLA with O-functional groups, polarity, and more negative charges was stronger than that of PVC and aged PVC, which was attributed to the binding of (aged) PLA to Cd(Ⅱ) through complexation and electrostatic attraction. The co-transport results indicated that the promotion of Cd(Ⅱ) transport by MPs followed the order of aged PLA > PLA > aged PVC > PVC. This facilitation was more pronounced under conditions of stronger transport of MPs and favorable attachment of Cd(Ⅱ) to MPs. Overall, the combination of strong adsorption affinity and high mobility helped (aged) PLA act as effective carriers for Cd(Ⅱ). The DLVO theory well explains the transport behavior of Cd(Ⅱ)-MPs. These findings provide new insights into the co-transport of degradable MPs and heavy metals in the subsurface environment.