Insight into the formation and biological effects of natural organic matter corona on silver nanoparticles in water environment using biased cyclical electrical field-flow fractionation

Species selective concentration and determination of nano-selenium and inorganic selenium species in environmental waters by micropore membrane filtration and ICP-MS

Accurate quantification of nano-selenium (nSe) and other ionic Se species in aquatic environments is a prerequisite for reliable estimation of their potential hazards. In this study, a micropore membrane filtration-based method followed by ICP-MS analysis was proposed for the selective concentration and determination of nSe in the water column. Polyvinylidene fluoride (PVDF) and nylon micropore filtration membranes were proven to efficiently capture nSe under optimal conditions (retention > 91.0 ± 0.87%). At the same time, ionic selenite and selenate could escape from the membranes, realizing the isolation of nSe and ionic Se species. The interference of dissolved organic matter (DOM) during separation can be resolved by adding Ca(II) ions, which can induce the formation of DOM aggregates by cation bridging effects. nSe retained on PVDF membranes could be effectively eluted with FL-70 (a powerful alkaline surfactant) aqueous solutions (0.5%, m/v) while maintaining the original size and morphology. Although nSe trapped on nylon membranes could not be easily eluted, quantification can also be achieved after membrane digestion. Speciation of ionic selenite and selenate in the filtrate was further conducted with an anion exchange column by using HPLC coupled with ICP-MS. The developed method was used to analyze Se species in six real water samples. Spiking experiments showed that the recoveries of nSe ranged from 70.2 ± 2.7% to 85.8 ± 1.3% at a spike level of 0.2 µg/L, and the recoveries of Se(IV) and Se(VI) ranged from 83.6 ± 0.5% to 101 ± 1% at a spike level of 0.55 µg/L, verifying the feasibility for the analysis of environmental water samples. This work provides possibilities to investigate the transformation and potential risks of nSe in the environment.

Nanoenabled Enhancement of Plant Tolerance to Heat and Drought Stress on Molecular Response

Global warming has posed significant pressure on agricultural productivity. The resulting abiotic stresses from high temperatures and drought have become serious threats to plants and subsequent global food security. Applying nanomaterials in agriculture can balance the plant's oxidant level and can also regulate phytohormone levels and thus maintain normal plant growth under heat and drought stresses. Nanomaterials can activate and regulate specific stress-related genes, which in turn increase the activity of heat shock protein and aquaporin to enable plants' resistance against abiotic stresses. This review aims to provide a current understanding of nanotechnology-enhanced plant tolerance to heat and drought stress. Molecular mechanisms are explored to see how nanomaterials can alleviate abiotic stresses on plants. In comparison with organic molecules, nanomaterials offer the advantages of targeted transportation and slow release. These advantages help the nanomaterials in mitigating drought and heat stress in plants.

Novel insights into the multistep chlorination of silver nanoparticles in aquatic environments

Due to the increasing applications, silver nanoparticles (AgNPs) are inevitably released into the environments and are subjected to various transformations. Chloride ion (Cl^-) is a common and abundant anion with a wide range of concentration in aquatic environments and exhibits a strong affinity for silver. The results indicate that AgNPs experienced multistep chlorination, which was dependent on the concentration of Cl^- in a non-linear manner. The dissolution of AgNPs was accelerated at Cl/Ag ratio of 1 and the intensive etching effect of Cl^- contributed to the significant morphology changes of AgNPs. The dissolved Ag⁺ quickly precipitated with Cl^- to form an amorphous and passivating AgCl(s) layer on the surface of AgNPs, thus the dissolution rate of AgNPs decreased at higher Cl/Ag ratios (100 and 1000). As the Cl/Ag ratio further increased to 10,000, the overall transformation rate increased remarkably due to the complexation of Cl^- with AgCl(s) to form soluble AgCl_x^(x-1)- species, which was verified by the reaction of AgCl nanoparticles with Cl^-. Besides, several environmental factors (electrolytes, surfactants and natural organic matter) affected AgNPs dissolution and the following chlorination. These results will expand the understanding of the environmental fate and potential risks of AgNPs in natural chloride-rich waters.