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•Polyamide (PA) film with nanofillers was a semi-crystalline cross-linked polymer.•The growth of free volume caused by nanofiller led to enhanced permeability.•Crystallite structures ...of nanofiller affected the dielectric property of PA film.•Structural changes induced by nanofillers governed the performance of NF membrane.
Nanomaterials, added in small quantities as “nanofillers,” have been shown to improve the performance of NF membranes in terms of mechanical properties, anti-fouling characteristics, selectivity, and transport. The goal of this work is to explore the mechanisms of nanofiller improvements on selectivity and transport of NF membranes. Carboxylated cellulose nanocrystals, multi-walled carbon nanotubes, and graphene oxide were selected as nanofillers to be added in the fabrication of free-standing polyamide (PA) films for the characterization of the internal structure of the polymer materials. Investigations of polymer characteristics revealed that the PA film with nanofillers was a semi-crystalline cross-linked polymer that exhibited an increase in chain length and free volume, and a reduction of cross-linkage and crystallite size. Molecular dynamics simulation results showed that the growth of free volume caused by polymeric chain stacking allowed water molecules to readily penetrate the spaces between polymer chains, which was primarily responsible for the enhanced permeability of PA films with nanofillers. The changes in the crystallite structures influenced the dielectric properties of the membrane matrix and the confined water in the pores, leading to the enhancement of dielectric exclusion, which can be harnessed to improve the separation performance. Taken together, our findings elucidated the structural changes of PA polymers induced by nanomaterials governing the properties and performance of NF membranes, which should be considered in the design of high-performance NF membranes.
The level of production of nanoparticles will inevitably lead to their appearance in air, water, soils, and organisms. A theoretical framework that relates properties of nanoparticles to their ...biological effects is needed to identify possible risks to human health and the environment. This paper considers the properties of dispersed metallic nanoparticles and highlights the relationship between the chemical stability of these nanoparticles and their in vitro toxicity. Analysis of published data suggests that chemically stable metallic nanoparticles have no significant cellular toxicity, whereas nanoparticles able to be oxidized, reduced or dissolved are cytotoxic and even genotoxic for cellular organisms.
The ability of metallic nanoparticles to be oxidized, reduced or dissolved in biological media can be used to predict their toxicity in vitro.
Here, we present a model for the prediction of nanoparticle fate in aquatic environments, parametrized using functional assays that take into account conditions of the environmental media and ...nanoparticle properties. The model was used to explore scenarios for five nanomaterials in a freshwater wetland setting and compared with experimental results obtained in mesocosm studies. Material characteristics used in the model were size, density, dissolution rate constants, and surface attachment efficiencies. Model predictions and experimentally measured removal rate constants from the water column were strongly correlated, with Pearson correlation coefficient 0.993. Further, the model predicted removal rate constants quantitively very close to measured rates. Of particular importance for accurate predictions were two key processes beyond the usual heteroaggregation with suspended solids. These were homoaggregation of nanomaterials and nanomaterial attachment to aquatic plant surfaces. These results highlight the importance of including all relevant aggregation and deposition processes over short time scales for nanoparticle transport, while demonstrating the utility of functional assays for surface attachment as model inputs.
Aquatic ecosystems are expected to receive Ag0 and Ag2S nanoparticles (NPs) through anthropogenic waste streams. The speciation of silver in Ag-NPs affects their fate in ecosystems, but its influence ...on interactions with aquatic plants is still unclear. Here, the Ag speciation and distribution was measured in an aquatic plant, duckweed (Landoltia punctata), exposed to Ag0 or Ag2S NPs, or to AgNO3. The silver distribution in duckweed roots was visualized using synchrotron-based micro X-ray fluorescence (XRF) mapping and Ag speciation was determined using extended X-ray absorption fine structure (EXAFS) spectroscopy. Duckweed exposed to Ag2S-NPs or Ag0-NPs accumulated similar Ag concentrations despite an order of magnitude smaller dissolved Ag fraction measured in the exposure medium for Ag2S-NPs compared to Ag0-NPs. By 24 h after exposure, all three forms of silver had accumulated on and partially in the roots regardless of the form of Ag exposed to the plants. Once associated with duckweed tissue, Ag0-NPs had transformed primarily into silver sulfide and silver thiol species. This suggests that plant defenses were active within or at the root surface. The Ag2S-NPs remained as Ag2S, while AgNO3 exposure led to Ag0 and sulfur-associated Ag species in plant tissue. Thus, regardless of initial speciation, Ag was readily available to duckweed.
A relevant but yet unconsidered subset of particles that may alter the fate of extracellular antibiotic resistance genes (eARGs) are nano-scale particles (NPs), which are ubiquitous in natural ...environments and have unique properties. In this study, sorption isotherms were developed describing the association of linear DNA fragments isolated from widespread eARGs (blaI and nptII) with either micon-sized kaolinite or silica nanoparticles (SNPs), to determine if sorption capacity was enhanced at the nanoscale. For each isotherm, eARG fragments were added at five starting concentrations (5–40 μg/mL) to mixed batch systems with 0.25 g of particles and nuclease-free water. Sorption was quantified by the removal of DNA from solution, as detected by a Qubit fluorimeter. Isotherms were developed for eARGs of various fragment lengths (508, 680 and 861 bp), guanine-cytosine (GC) contents (34%, 47% and 54%) and both double and single stranded eARGs, to assess the impact of DNA properties on particle association. Sorption isotherms were also developed in systems with added humic acid and/or CaCl2, to assess the impact of these environmental parameters on sorption. FTIR analysis was performed to analyze the conformation of sorbed eARGs. Desorption of eARGs was studied by quantifying the removal of eDNA from washed and vortexed post-sorption particles. Statistically significant irreversible sorption of eARGs to environmentally relevant NPs (humic acid functionalized silica nanoparticles) was demonstrated for the first time. Nano-emergent properties did not increase sorption capacity of eARGs, but led to a unique compressed conformation of sorbed eARGs. The addition of humic acid, increased CaCl2 concentration and small DNA fragment size favored sorption. NPs showed a slight preference for the sorption of single-stranded DNA over double-stranded DNA. These findings suggest that NP association with eARGs may be a significant and unique environmental phenomenon that could influence the spread of antibiotic resistance.
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•Extracellular DNA sorbs significantly to environmentally relevant nanoparticles.•DNA sorption to nanoparticles was favored in systems with humic acid and calcium.•Sorption of single stranded DNA was favored over double stranded DNA.•Sorption to nanoparticles lead to a uniquely compressed DNA conformation.•Nanoparticles may be reservoirs of antibiotic resistance genes for microbial uptake.
Transformations and long-term fate of engineered nanomaterials must be measured in realistic complex natural systems to accurately assess the risks that they may pose. Here, we determine the ...long-term behavior of poly(vinylpyrrolidone)-coated silver nanoparticles (AgNPs) in freshwater mesocosms simulating an emergent wetland environment. AgNPs were either applied to the water column or to the terrestrial soils. The distribution of silver among water, solids, and biota, and Ag speciation in soils and sediment was determined 18 months after dosing. Most (70 wt %) of the added Ag resided in the soils and sediments, and largely remained in the compartment in which they were dosed. However, some movement between soil and sediment was observed. Movement of AgNPs from terrestrial soils to sediments was more facile than from sediments to soils, suggesting that erosion and runoff is a potential pathway for AgNPs to enter waterways. The AgNPs in terrestrial soils were transformed to Ag2S (∼52%), whereas AgNPs in the subaquatic sediment were present as Ag2S (55%) and Ag-sulfhydryl compounds (27%). Despite significant sulfidation of the AgNPs, a fraction of the added Ag resided in the terrestrial plant biomass (∼3 wt % for the terrestrially dosed mesocosm), and relatively high body burdens of Ag (0.5–3.3 μg Ag/g wet weight) were found in mosquito fish and chironomids in both mesocosms. Thus, Ag from the NPs remained bioavailable even after partial sulfidation and when water column total Ag concentrations are low (<0.002 mg/L).
Silver nanoparticles (AgNPs)-alginate composite beads were synthesized using three different approaches as filler materials of packed columns for simultaneous filtration-disinfection as an ...alternative portable water treatment process. The prepared composite beads were packed into a column through which Escherichia coli containing water was filtered to evaluate the disinfection efficacy. Excellent disinfection performance (no detectable viable colony) was achieved with a hydraulic retention time (HRT) as short as 1 min (the shortest tested) with the SGR (Simultaneous-Gelation-Reduction) and AR (Adsorption–Reduction) beads that were prepared using in situ reduction of Ag+. Comparatively, the SGR beads released significantly less Ag+/AgNPs than the AR beads did within the same HRT. From the results of this study it was identified that SGR may be the best choice among all three different synthesis approaches in that the SGR beads can achieve satisfactory bactericidal performance with a relatively low material consumption rate.
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► Silver–alginate composite beads were prepared using three different approaches. ► The efficacy of the composite beads for disinfection was tested using column test. ► Excellent disinfection performance was achieved with two types of composite beads. ► These composite beads provide alternative for portable water disinfection.
Theoretical and experimental approaches were employed to study the effect of aggregation on the affinity between nanoparticles (NPs) and a flat surface that is quantified by the attachment ...efficiency. Computer simulations were used to generate virtual aggregates formed via either diffusion limited cluster aggregation or reaction limited cluster aggregation. The colloidal interactions between the simulated aggregates and a flat surface were evaluated based on the surface element integration approach. It was found that the strength of colloidal interaction for the aggregated NPs was on the same order of magnitude as those for the primary particles and was significantly weaker than that for an equivalent sphere defined by the gyration radius of the aggregate. The results from the deposition experiments using quartz crystal microbalance suggested that the attachment efficiencies (unfavorable deposition) for aggregated NPs were higher at the initial stage but later became similar to that of the primary NPs when equilibrium deposition was reached. The high initial affinity was postulated to be attributable to secondary minimum deposition. These results suggest that it is the size of the primary particles, not that of the aggregates, that determines the strength of the colloidal interaction between the aggregate and an environmental surface.
Crop disease control is crucial for the sustainable development of agriculture, with recent advances in nanotechnology offering a promising solution to this pressing problem. However, the efficacy of ...nanoparticle (NP) delivery methods has not been fully explored, and knowledge regarding the fate and mobility of NPs within trees is still largely unknown. In this study, we evaluate the efficiency of NP delivery methods and investigate the mobility and distribution of NPs with different surface coatings (citrate (Ct), polyvinylpyrrolidone (PVP), and gum Arabic (GA)) within Mexican lime citrus trees. In contrast to the limited delivery efficiency reported for foliar and root delivery methods, petiole feeding and trunk injection are able to deliver a large amount of NPs into trees, although petiole feeding takes much longer time than trunk injection (7 days vs 2 h in citrus trees). Once NPs enter plants, steric repulsive interactions between NPs and conducting tube surfaces are predicted to facilitate NP transport throughout the plant. Compared to PVP and Ct, GA is highly effective in inhibiting the aggregation of NPs in synthetic sap and enhancing the mobility of NPs in trees. Over a 7 day experimental period, the majority of the Ag recovered from trees (10 mL, 10 ppm GA-AgNP suspension) remain throughout the trunk (81.0% on average), with a considerable amount in the roots (11.7% on average), some in branches (4.4% on average), and a limited amount in leaves (2.9% on average). Furthermore, NP concentrations during injection and tree incubation time postinjection are found to impact the distribution of Ag in tree. We also present evidence for a transport pathway that allows NPs to move from the xylem to the phloem, which disperses the NPs throughout the plant architecture, including to the roots.
Wastewater effluent and sewage sludge are predicted to be important release pathways for nanomaterials used in many consumer products. The uncertainty and variability of potential nanomaterial ...inputs, nanomaterial properties, and the operation of the wastewater treatment plant contribute to the difficulty of predicting sludge and effluent nanomaterial concentration. With a model parsimony approach, we developed a mass-balance representation of engineered nanomaterial (ENM) behavior based on a minimal number of input variables to describe release quantities to the environment. Our simulations show that significant differences in the removal of silver nanoparticles (nano-Ag) can be expected based on the type of engineered coatings used to stabilize these materials in suspension. At current production estimates, 95% of the estimated effluent concentrations of the nano-Ag considered to be least well-removed by the average wastewater treatment plant are calculated to fall below 0.12μg/L, while 95% of the estimated sludge concentrations of nano-Ag with coatings that increase their likelihood of being present in biosolids, fall below 0.35μg/L.
► We derive a mass balance model for nano-Ag behavior in WWTP. ► We estimate nano-Ag concentrations in effluent and sludge for 4 surface chemistries. ► We highlight relative uncertainties of inputs and identify future research needs.
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