Quantitation of Atmospheric Suspended Polystyrene Nanoplastics by Active Sampling Prior to Pyrolysis-Gas Chromatography-Mass Spectrometry.

Plastic has been demonstrated to release nanoplastics (NPs) into the atmosphere under sunlight irradiation, posing a continuous health risk to the respiratory system. However, due to lack of reliable quantification methods, the occurrence and distribution of NPs in the atmosphere remain unclear. Polystyrene (PS) micro- and nanoplastics (MNPs) represent a crucial component of atmospheric MNPs. In this study, we proposed a simple and robust method for determining the concentration of atmospheric PS NPs using pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). Following active sampling, the filter membrane is directly ground and introduced into the Py-GC/MS system to quantify PS NPs. The proposed method demonstrates excellent reproducibility and high sensitivity, with a detection limit as low as down to 15 pg/m3 for PS NPs. By using this method, the occurrence of PS NPs in both indoor and outdoor atmospheres has been confirmed. Furthermore, the results showed that the abundance of outdoor PS NPs was significantly higher than that of indoor samples, and there was no significant difference in NP vertical distribution within a height of 28.6 m. This method can be applied for the routine monitoring of atmospheric PS NPs and for evaluating their risk to human health.

Molecular insights into the dissolved organic matter of leather wastewater in leather industrial park wastewater treatment plant.

Leather wastewater (LW) effluent is characterized by complex organic matter, high salinity, and poor biodegradability. To meet the discharge standards, LW effluent is often mixed with municipal wastewater (MW) before being treated at a leather industrial park wastewater treatment plant (LIPWWTP). However, whether this method efficiently removes the dissolved organic matter (DOM) from LW effluent (LWDOM) remains debatable. In this study, the transformation of DOM during full-scale treatment was revealed using spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. LWDOM exhibited higher aromaticity and lower molecular weight than DOM in MW (MWDOM). The DOM properties in mixed wastewater (MixW) were similar to those in LWDOM and MWDOM. The MixW was treated using a flocculation/primary sedimentation tank (FL1/PST), anoxic/oxic (A/O) process, secondary sedimentation tank (SST), flocculation/sedimentation tank, denitrification filter (FL2/ST-DNF), and an ozonation contact reactor (O3). The FL1/PST unit preferentially removed the peptide-like compounds. The A/O-SST units had the highest removal efficiencies for dissolved organic carbon (DOC) (61.34 %) and soluble chemical oxygen demand (SCOD) (52.2 %). The FL2/ST-DNF treatment removed the lignin-like compounds. The final treatment showed poor DOM mineralization efficiency. The correlation between water quality indices, spectral indices, and molecular-level parameters indicated that lignin-like compounds were strongly correlated with spectral indices and CHOS compounds considerably contributed to the SCOD and DOC. Although the effluent SCOD met the discharge standard, some refractory DOM from LW remained in the effluent. This study illustrates the composition and transformation of DOM and provides theoretical guidance for improving the current treatment processes.

Removal of iodide anions in water by silver nanoparticles supported on polystyrene anion exchanger.

The removal of iodide (I-) from source waters is an effective strategy to minimize the formation of iodinated disinfection by-products (DBPs), which are more toxic than their brominated and chlorinated analogues. In this work, a nanocomposite Ag-D201 was synthesized by multiple in situ reduction of Ag-complex in D201 polymer matrix, to achieve highly efficient removal of iodide from water. Scanning electron microscope /energy dispersive spectrometer characterization showed that uniform cubic silver nanoparticles (AgNPs) evenly dispersed in the D201 pores. The equilibrium isotherms data for iodide adsorption onto Ag-D201 was well fitted with Langmuir isotherm with the adsorption capacity of 533 mg/g at neutral pH. The adsorption capacity of Ag-D201 increased with the decrease of pH in acidic aqueous solution, and reached the maximum value of 802 mg/g at pH 2. This was attributed to the oxidization of I-, by dissolved oxygen under the catalysis of AgNPs, to I2 which was finally adsorbed as AgI3. However, the aqueous solutions at pH 7 - 11 could hardly affect the iodide adsorption. The adsorption of I- was barely affected by real water matrixes such as competitive anions (SO42-, NO3-, HCO3-, Cl-) and natural organic matter, of which interference of NOM was offset by the presence of Ca2+. The proposed synergistic mechanism for the excellent performance of iodide adsorption by the absorbent was ascribed to the Donnan membrane effect caused by the D201 resin, the chemisorption of I- by AgNPs, and the catalytic effect of AgNPs.

Regulating the reaction pathway of nZVI to improve the decontamination performance through magnetic spatial confinement effect.

Nanoscale zero-valent iron (nZVI) shows high effectiveness in the catalyzed removal of contaminants in wastewater treatment. However, the uncontrolled interfacial electron transfer behavior and formation of surface iron oxide (FeOx) layer led to severe electron wasting and occasionally form highly toxic intermediates. Here, we constructed magnetic mesoporous SiO2 shell on surface of nZVI to stimulate a magnetic spatial confinement effect and regulate the electron transfer pattern. Therein, Fe atom facilely spread out from the nZVI core, orderly release electron to surface adsorbed H2O molecule, which is efficiently transformed into active hydrogen (H*). Meanwhile, in-situ Raman revealed that Fe atoms were involved in the formation of penetrable γ-FeOOH rather than FeOx layer, enabling the continuous inward diffusion of H2O and outward diffusion of H* . Employing the catalyzed removal of halogenated phenols as demo reaction, the presence of magnetic mesoporous SiO2 shell utilized the reaction between electrons and H2O to switch the reaction pathway from the reduction/oxidation hybrid process to hydrodehalogantion, and increased the conversion of halogenated phenols-to-phenols by 5.53 times. This study shows the forehand of improving the decontamination performance of nZVI through sophisticated designed surface coating, as well as fine regulating the environmental behavior of magnetic material via micro-magnetic field.

Gaseous Arsenic Capture in Flue Gas by CuCl2-Modified Halloysite Nanotube Composites with High-Temperature NOx and SOx Resistance.

Gaseous arsenic emitted from coal combustion flue gas (CCFG) causes not only severe contamination of the environment but also the failure of selective catalytic reduction (SCR) catalysts in power plants. Development of inexpensive and effective adsorbents or techniques for the removal of arsenic from high-temperature CCFG is crucial. In this study, halloysite nanotubes (HNTs) at low price were modified with CuCl2 (CuCl2-HNTs) through ultrasound assistance and applied for capturing As2O3(g) in simulated flue gas (SFG). Experiments on arsenic adsorption performance, adsorption mechanism, and adsorption energy based on density functional theory were performed. Modification with CuCl2 clearly enhanced the arsenic uptake capacity (approximately 12.3 mg/g) at 600 °C for SFG. The adsorbent exhibited favorable tolerance to high concentrations of NOx and SOx. The As2O3(III) was oxidized and transformed into As2O5(V) on the CuCl2-HNTs. The Al-O bridge had the highest adsorption energy for the O end of the As-O group (-2.986 eV), and the combination formed between arsenic-containing groups and aluminum was stable. In addition, the captured arsenic could be stabilized in the sorbent at high temperature, making it possible to use the sorbent before the SCR system. This demonstrates that CuCl2-HNTs is a promising sorbent for arsenic oxidation and removal from CCFG.

Distribution and chemical speciation of arsenic in different sized atmospheric particulate matters.

The distribution and chemical speciation of arsenic (As) in different sized atmospheric particulate matters (PMs), including total suspended particles (TSP), PM10, and PM2.5, collected from Baoding, China were analyzed. The average total mass concentrations of As in TSP, PM10, and PM2.5 were 31.5, 35.3, and 54.1 µg/g, respectively, with an order of PM2.5 >PM 10 > TSP, revealing that As is prone to accumulate on fine particles. Due to the divergent toxicities of different As species, speciation analysis of As in PMs is further conducted. Most of previous studies mainly focused on inorganic arsenite (iAsIII), inorganic arsenate (iAsV), monomethylarsonate (MMA), and dimethylarsinate (DMA) in PMs, while the identification and sensitive quantification of trimethylarsine oxide (TMAO) were rarely reported. In this study, a high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry system was optimized for As speciation including TMAO in PMs. An anion exchange column was used to separate MMA, DMA and iAsV, while a cation exchange column to separate TMAO and iAsIII. Results showed that iAsV was the dominate component in all the samples, corresponding to a portion of 79.2% ± 9.3% of the total extractable species, while iAsIII, TMAO and DMA made up the remaining 21%. Our study demonstrated that iAsIII accounted for about 14.4% ± 11.4% of the total extracted species, with an average concentration of 1.7 ± 1.6 ng/m3. It is worth noting that TMAO was widely present in the samples (84 out of 97 samples), which supported the assumption that TMAO was ubiquitous in atmospheric particles.

Heteroaggregation of different surface-modified polystyrene nanoparticles with model natural colloids.

This study investigated heteroaggregation of three surface-functionalized polystyrene nanoparticles (PSNPs), i.e. negatively charged unfunctionalized nanoparticles (Bare-PS) and carboxylated nanoparticles (COOH-PS), and positively charged amino-functionalized nanoparticles (NH2-PS), with two model natural colloids, positively charged hematite and negatively charged kaolin, respectively. Heteroaggregation was conducted at a constant natural colloid concentration and variable NP/colloid concentration ratios. Electrostatic interaction was the main mechanism driving the formation of heteroaggregates. In binary systems containing hematite and Bare-PS/COOH-PS, a charge neutralization - charge inverse mechanism was observed with the increase of PSNP concentration. At NP/hemetite concentration ratios much smaller or larger than the full charge neutralization point, the primary heteroaggregates were stable, while full charge neutralization induced the formation of large secondary heteroaggregates. Large aggregates were not observed in suspensions containing kaolin and NH2-PS, as highly positively charged NH2-PS reversed surface charges of kaolin at extremely low concentrations. Heteroaggregation between PSNPs and natural colloids with the same charge is unfavorable due to strong electrostatic repulsion. In the presence of electrolytes, homoaggregation and heteroaggregation both occurred, and homoaggregation of hematite played a key role when the concentration of PSNPs was low. The presence of Suwannee River natural organic matter (SRNOM) could modify surface charges of nanoparticles, and thus affect heteroaggregation behaviors of the binary suspension. When SRNOM and electrolytes were both present, whether SRNOM inducing or hindering the stability of the binary system was a combined effect of NP/colloid concentration ratios, SRNOM concentrations, electrolyte types and ionic strength. Mechanisms extensively reported in homoaggregation such as steric hindrance and cation bridging effects between SRNOM and Ca2+ also stand for heteroaggregation. These results highlight the critical role of surface modification on the environmental behaviors of NPs, and will underpin our understanding of the fate and transport of NPs in the aquatic environment.

Sequential Isolation of Microplastics and Nanoplastics in Environmental Waters by Membrane Filtration, Followed by Cloud-Point Extraction.

Respective detection of microplastics (MPs) and nanoplastics (NPs) is of great importance for their different environmental behaviors and toxicities. Using spherical polystyrene (PS) and poly(methyl methacrylate) (PMMA) plastics as models, the efficiency for sequential isolation of MPs and NPs by membrane filtration and cloud-point extraction was evaluated. After filtering through a glass membrane (1 µm pore size), over 90.7% of MPs were trapped on the membrane, whereas above 93.0% of NPs remained in the filtrate. The collected MPs together with the glass membrane were frozen in liquid nitrogen, ground, and suspended in water (1 mL) and subjected to pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) determination. The NPs in the filtrate were concentrated by cloud-point extraction, heated at 190 °C to degrade the extractant, and then determined by Py-GC/MS. For MPs and NPs spiked in pure water, the method detection limits are in the range of 0.05-1.9 µg/L. The proposed method is applied to analyze four real water samples, with the detection of 1.6-7.6 µg/L PS MPs and 0.6 µg/L PMMA MPs in three samples, and spiked recoveries of 75.0-102% for MPs and 67.8-87.2% for NPs. Our method offers a novel sample pretreatment approach for the respective determination of MPs and NPs.

Identification of polystyrene nanoplastics using surface enhanced Raman spectroscopy.

There is clear evidence that micro- and nanoplastics are accumulating in the environment, and their increasing concern of potential harm to wildlife has been identified as a major global issue. However, identification of nanoplastics in environmental samples remains a great challenge, and thus highlighting the great need for new approach. Herein, for the first time, we show that surface enhanced Raman spectroscopy (SERS) offered a feasible approach to identify trace polystyrene (PS) nanoplastics, which is the most produced nanoplastics and also widely presented in the natural environment. We found that when PS nanoplastics were surrounded by SERS-active silver nanoparticles (AgNPs), a set of Raman spectra with chemical information could be obtained via SERS mapping. This map showed the potential PS distribution of the nanoplastics on a silicon wafer, allowing a quick and detailed analysis of the nanoplastics. Moreover, the proposed method was able to identify previously undetectable plastic particles as small as ~50 nm spiked in real water, demonstrating the power of SERS to probe nanoplastics. Our work is thus an important step in nanoplastic research, and we believe that this approach can be further developed to study the occurrence, formation, and transports of nanoplastics in the natural environment.

Nano-selenium functionalized zinc oxide nanorods: A superadsorbent for mercury (II) removal from waters.

In this study, nano selenium functionalized zinc oxide nanorods, NanoSe@ZnO-NR, was prepared, characterized and investigated for Hg(II) removal from waters of different types. The study results revealed that the material showed a superior adsorption capacity (qm, 1110 mg g-1) and excellent distribution coefficient (Kd, 9.11 × 108 mL g-1) which is two or more orders above most of the adsorbents reported in the literature. It should be also known that, 30 mg of the adsorbent can quickly reduce 10 mg L-1 Hg(II) to undetectable level from 10 mL of sample solution. The adsorption data were well explained with the pseudo-second order kinetic model and Langmuir adsorption isotherm model. Besides, the capturing capability of the material is independent on the pH change (2-12), selective against interfering cations, and exhibited fast kinetics (equilibrium time, ∼1 min). The NanoSe@ZnO-NR performance was also tested on real samples from different origin, surface waters (tap, lake and river) and wastewaters (effluent and influent), and complete removal and ≥99.2% removal efficiency was observed at 0.01 and 10 mg L-1 spiking levels, respectively. Therefore, NanoSe@ZnO-NR can be considered as a potential adsorbent in advancing the wastewater treatment technology.

Speciation Analysis of the Uptake and Biodistribution of Nanoparticulate and Ionic Silver in Escherichia coli.

A new method was developed to determine the nanoparticulate and ionic silver (Ag) species in bacteria (Escherichia coli, E. coli). By removal of the cell wall with lysozyme, the cell surface-adsorbed Ag species were separated from the intracellular Ag species, which were extracted by tetramethylammonium hydroxide and determined by size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry (SEC-ICP-MS). The detection limit is 3 ng/107 CFU/mL (where CFU is colony-forming unit) for both silver nanoparticles (AgNPs) and ionic Ag(I) species. The cell wall-adsorbed Ag was calculated by subtracting the contents of the intra- and extracellular Ag from the total exposure dose of Ag, and therefore the biodistribution of Ag species was profiled. We then applied this strategy to quantitatively analyze extra- and intracellular Ag species in E. coli after respective exposure to Ag+ and 10 and 30 nm AgNPs at different effective concentrations (EC10, EC50, and EC90). Results showed that the intracellular and cell wall-bound Ag account for 5.98-15.21% and 25.13-64.43% of the exposed dose, respectively, and AgNPs could transform into complexed or free Ag+. Our method opens new avenues for the quantitative analysis of the uptake and biodistribution of nanoparticles and their transformation species in bacteria.

Intracellular Dissolution of Silver Nanoparticles: Evidence from Double Stable Isotope Tracing.

To track transformations of silver nanoparticles (AgNPs) in vivo, HepG2 and A549 cells were cocultured with two enriched stable Ag isotopes (107AgNPs and 109AgNO3) at nontoxic doses. After enzymatic digestion, 107AgNPs, ionic 107Ag+ and 109Ag+ in exposed cells could be separated and quantified by liquid chromatography combined with ICP-MS. We found that ratios of 107Ag+ to total 107Ag and proportions of 107Ag+/ 109Ag+ in cells increased gradually after exposure, proving that the Trojan-horse mechanism occurred, i.e., AgNPs released high contents of Ag+ after internalization. While the presence of 109Ag+ (5 and 100 µg/L) has little influence on the uptake of 107AgNPs (0.1 and 2 mg/L), the presence of 107AgNPs at a high dose (2 mg/L) dramatically increases the ingestion of 109Ag+, even though 107AgNPs at a low dose (100 µg/L) showed negligible effects on the internalization of 109Ag+. Cellular homeostasis may be perturbed under sublethal exposure of 107AgNPs, and thus enhanced uptake of 109Ag+. Our findings suggest that the widely adopted control experiments in toxicology studies, culturing organisms with AgNO3 at the same concentration of Ag+ in the AgNP exposure medium, may underestimate uptake of Ag+ and thus cannot exclude suspected toxic effects of Ag+ at high AgNP exposure doses.

Cloud-Point Extraction Combined with Thermal Degradation for Nanoplastic Analysis Using Pyrolysis Gas Chromatography-Mass Spectrometry.

The contamination of micro- and nanoplastics in marine systems and freshwater is a global issue. Determination of micro- and nanoplastics in the aqueous environment is of high priority to fully assess the risk that plastic particles will pose. Although microplastics have been detected in a variety of aquatic ecosystems, the analysis of nanoplastics remains an unsolved challenge. Herein, for the first time, a Triton X-45 (TX-45)-based cloud-point extraction (CPE) was proposed to preconcentrate trace nanoplastics in environmental waters. Under the optimum extraction conditions, an enrichment factor of 500 was obtained for two types of nanoplastics with different compositions, polystyrene (PS) and poly(methyl methacrylate) (PMMA), without disturbing their original morphology and sizes. Additionally, following thermal treatment at 190 °C for 3 h, the CPE-obtained extract could be submitted to pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) analysis for mass quantification of nanoplastics. Taking 66.2 nm PS nanoplastics and 86.2 nm PMMA nanoplastics as examples, the proposed method showed excellent reproducibility, and high sensitivity with respective detection limits of 11.5 and 2.5 fM. Feasibility of the proposed approach was verified by application of the optimized procedure to four real water samples. Recoveries of 84.6-96.6% at a spiked level of 88.6 fM for PS nanoplastics and 76.5-96.6% at a spiked level of 50.4 fM for PMMA nanoplastics were obtained. Consequently, this work provides an efficient approach for nanoplastic analysis in environmental waters.

Facile fabrication of silver nanoparticle decorated α-Fe2O3 nanoflakes as ultrasensitive surface-enhanced Raman spectroscopy substrates.

Although great progress has been made on designing noble metal nanoparticle aggregates/assemblies as surface-enhanced Raman spectroscopy (SERS) substrates, an ever increasing research interest has focused on fabrication of hierarchical nanostructures for superior SERS performance. Here, we report effective decoration of silver nanoparticles (AgNPs) onto vertically and densely grown α-Fe2O3 nanoflakes (NFs) as SERS active substrates. The SERS substrate was prepared by thermally annealing Fe foil at 450 °C to grow α-Fe2O3 NFs and electroless deposition of AgNPs onto α-Fe2O3 NFs, with excellent ability to control the particle size and density. The AgNP-decorated α-Fe2O3 NFs offer high density hot spots and exhibited high SERS performance with enhancement factor of 8.1 × 106. Integration of α-Fe2O3 nanostructure functions as intrinsic internal standard and selective binder for specific analytes like the toxic arsenic. The substrate was successfully used for quantitative detection of arsenic with spatial uniformity (relative standard deviation, RSD, 8.8%) and good reproducibility (RSD, 9.7%). The Raman signal of α-Fe2O3 integrated to the SERS substrate was utilized as internal standard which significantly improves reproducibility. The substrate exhibited a high sensitivity for arsenic detection with a limit of detection down to 1.5 µg L-1, which is much lower than permissible limit (10 µg L-1) set by the WHO. Moreover, the SERS substrates showed excellent practicability and selectivity for determination of arsenic in environmental waters which is valuable for environmental and human health protection.

Au@Pd Bimetallic Nanocatalyst for Carbon-Halogen Bond Cleavage: An Old Story with New Insight into How the Activity of Pd is Influenced by Au.

AuPd bimetallic nanocatalysts exhibit superior catalytic performance in the cleavage of carbon-halogen bonds (C-X) in the hazardous halogenated pollutants. A better understanding of how Au atoms promote the reactivity of Pd sites rather than vaguely interpreting as bimetallic effect and determining which type of Pd sites are necessary for these reactions are crucial factors for the design of atomically precise nanocatalysts that make full use of both the Pd and Au atoms. Herein, we systematically manipulated the coordination number of Pd-Pd, d-orbital occupation state, and the Au-Pd interface of the Pd reactive centers and studied the structure-activity relationship of Au-Pd in the catalyzed cleavage of C-X bonds. It is revealed that Au enhanced the activity of Pd atoms primarily by increasing the occupation state of Pd d-orbitals. Meanwhile, among the Pd sites formed on the Au surface, five to seven contiguous Pd atoms, three or four adjacent Pd atoms, and isolated Pd atoms were found to be the most active in the cleavage of C-Cl, C-Br, and C-I bonds, respectively. Besides, neighboring Au atoms directly contribute to the weakening of the C-Br/C-I bond. This work provides new insight into the rational design of bimetallic metal catalysts with specific catalytic properties.

Hydride generation coupled with thioglycolic acid coated gold nanoparticles as simple and sensitive headspace colorimetric assay for visual detection of Sb(III).

Antimony (Sb) is a toxic element which causes different health problems including cardiac problems and lung cancer in humans, and its levels in surface water can be noticeably increased to 100 µg/L typically in the proximity of anthropogenic sources. Thus, besides instrumental techniques, it is of great significance to develop a simple, sensitive and selective analytical method for direct analysis of Sb(III) at trace level without the need of any expensive and/or complicated instrumentations and sample preparation processes. Herein, a simple and sensitive headspace colorimetric assay was developed for the detection of Sb(III) by hydride generation coupled with thioglycolic acid functionalized gold nanoparticles (TGA-AuNPs). Sb(III) in the 30 mL sample solution was converted into its volatile form (SbH3) through hydride generation reaction and headspace extracted into 100 µL chromogenic reagent, which contains methanol as extractant and TGA-AuNPs as nanosensors, leading to aggregation of TGA-AuNPs and therefore a red-to-blue color change. Parameters influencing the chromogenic and hydride generation reactions were optimized. Addition of 300 µM ethylenediamine tetraacetic acid (EDTA) as masking agent largely suppressed the inferences from mercury and arsenic. The proposed method can tolerate at least 10-fold As(III) and 100-fold other metal ions including Hg(II). The detection limits were 6.0 and 1.2 µg/L Sb(III) by naked-eye and UV-Vis spectrometer, respectively, which meet the maximum admissible level in drinking water (6 µg/L) set by the United States Environmental Protection Agency. The feasibility of the proposed method was demonstrated by rapid detection of Sb(III) in river water, lake water, ground water and sea water samples by naked-eye at a spiking level of 6 µg/L Sb(III).

Single-drop gold nanoparticles for headspace microextraction and colorimetric assay of mercury (II) in environmental waters.

A novel headspace colorimetric nanosensor strategy for specific detection of Hg(II) was developed based upon analyte induced etching and amalgamation of gold nanoparticles (AuNPs). The Hg(II) was first selectively reduced to its volatile form, Hg(0), by stannous chloride (SnCl2) through chemical cold vapor generation (CVG) reaction. Then, the Hg(0) was headspace extracted into 37µL thioglycolic acid functionalized AuNP aqueous suspension containing 10% methanol as extractant and simultaneously reacted with AuNPs through the strong metallophilic Hg-Au interaction, resulting in a red-to-blue color change. Parameters influencing the chromogenic and chemical vapor generation reactions were optimized. The limit of detections were determined as 5nM through inspection by naked-eye and 1nM based on measurements by UV-Vis spectrometer, which are below the safe limit of Hg(II) in drinking water set by the US Environmental Protection Agency, showing excellent potential for monitoring ultralow levels of Hg(II) in environmental water samples. The assay was not interfered by the presence of other common metal ions even at 1000-fold excess over Hg(II) concentration. The outstanding selectivity results from the combined effect of selective reduction of Hg(II) by SnCl2, efficient separation of sample matrix through headspace extraction, and amalgamation process that occurs specifically between Hg and AuNPs. The method was successfully applied to the visual detection of Hg(II) in environmental water samples at a 10nM spiking level, with recoveries in the range of 86.8-99.8%. More importantly, compared to classical colorimetric assays for detection of Hg(II), this method is featured with simplicity, quite high sensitivity and excellent selectivity. The method is also superior to most colorimetric methods for detection of Hg(II) in terms of its applicability to matrix-rich real samples including wastewater.

Facile phyto-mediated synthesis of silver nanoparticles using Chinese winter jujube (Ziziphus jujuba Mill. cv. Dongzao) extract and their antibacterial/catalytic properties.

The aqueous extract of Chinese winter jujube (Ziziphus jujuba Mill. cv. Dongzao) was used as reducing and capping agents for the synthesis of silver nanoparticles (AgNPs) for the first time. The resulting AgNPs were characterised by UV/Visible (UV-Vis) spectroscopy, atomic force microscope, transmission electron microscopy, selected area electron diffraction, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray and Fourier transform infrared spectroscopy (FTIR). The colloidal solution of AgNPs gave a maximum UV-Vis absorbance at 446 nm. The synthesised nanoparticles were almost in the spherical shapes with an average size of 11.5 ± 4. 8 nm. FTIR spectra were applied to identify the functional groups which were possibly responsible for the conversion of metal ions into nanoparticles. The results showed that the prepared AgNPs were coated with the biomolecules in the extract. The biosynthesised AgNPs showed a remarkable catalytic activity at room temperature, and they also showed good antibacterial properties against Escherichia coli and Staphylococcus aureus.

Polyvinylidene Fluoride Micropore Membranes as Solid-Phase Extraction Disk for Preconcentration of Nanoparticulate Silver in Environmental Waters.

Efficient separation and preconcentration of trace nanoparticulate silver (NAg) from large-volume environmental waters is a prerequisite for reliable analysis and therefore understanding the environmental processes of silver nanoparticles (AgNPs). Herein, we report the novel use of polyvinylidene fluoride (PVDF) filter membrane for disk-based solid phase extraction (SPE) of NAg in 1 L of water samples with the disk-based SPE system, which consists of a syringe pump and a syringe filter holder to embed the filter membrane. While the PVDF membrane can selectively adsorb NAg in the presence of Ag+, aqueous solution of 2% (m/v) FL-70 is found to efficiently elute NAg. Analysis of NAg is performed following optimization of filter membrane and elution conditions with an enrichment factor of 1000. Additionally, transmission electron microscopy (TEM), UV-vis spectroscopy, and size-exclusion chromatography coupled with ICP-MS (SEC-ICP-MS) analysis showed that the extraction gives rise to no change in NAg size or shape, making this method attractive for practical applications. Furthermore, feasibility of the protocol is verified by applying it to extract NAg in four real waters with recoveries of 62.2-80.2% at 0.056-0.58 µg/L spiked levels. This work will facilitate robust studies of trace NAg transformation and their hazard assessments in the environment.

Tracking the Transformation of Nanoparticulate and Ionic Silver at Environmentally Relevant Concentration Levels by Hollow Fiber Flow Field-Flow Fractionation Coupled to ICPMS.

It is a great challenge to monitor the physical and chemical transformation of nanoparticles at environmentally relevant concentration levels, mainly because the commonly used techniques like dynamic light scattering and transmission electron microscopy are unable to characterize and quantify trace level nanoparticles in complex matrices. Herein, we demonstrate the on-line coupled system of hollow fiber flow field-flow fractionation (HF5), minicolumn concentration, and inductively coupled plasma mass spectrometry (ICPMS) detection as an efficient approach to study the aggregation and chemical transformation of silver nanoparticles (AgNPs) and ionic Ag species in the aqueous environment at ng/mL levels. Taking advantage of the in-line dialysis of HF5, the selective capture of Ag(I) species by the resin in minicolumn, and the high selectivity and sensitivity of ICPMS detection, we recorded the aggregation of 10 ng/mL AgNPs in complex matrices (e.g., NOM, Na+/Ca2+), revealing an interesting tiny AgNPs formation process of photoreduction of trace level Ag(I) that is different from larger AgNPs generated at high concentration of Ag(I) by accurate characterization and respectively identifying and quantifying new thiol-complexed Ag(I) and residual Ag(I) in the intertransformation of Ag(I) and AgNPs in domestic wastewater by simultaneously detecting the S and Ag signals via ICPMS.