Although silver nanoparticles are being exploited widely in antimicrobial applications, the mechanisms underlying silver nanoparticle antimicrobial properties in environmentally relevant media are not fully understood. The latter point is critical for understanding potential environmental impacts of silver nanoparticles. The aim of this study was to elucidate the influence of inorganic aquatic chemistry on silver nanoparticle stability (aggregation, dissolution, reprecipitation) and bacterial viability. A synthetic "fresh water" matrix was prepared comprising various combinations of cations and anions while maintaining a fixed ionic strength. Aggregation and dissolution of silver nanoparticles was influenced by electrolyte composition; experimentally determined ionic silver concentrations were about half that predicted from a thermodynamic model and about 1000 times lower than the maximum dispersed silver nanoparticle concentration. Antibacterial activity of silver nanoparticles was much lower than Ag(+) ions when compared on the basis of total mass added; however, the actual concentrations of dissolved silver were the same regardless of how silver was introduced. Bacterial inactivation also depended on bacteria cell type (Gram-positive/negative) as well as the hardness and alkalinity of the suspending media. These simple, but systematic studies--enabled by high-throughput screening--reveal the inherent complexity associated with understanding silver nanoparticle antibacterial efficacy as well as potential environmental impacts of silver nanoparticles.

Hydrophilic modification of ultrafiltration membranes was achieved through blending of Pluronic F127 with poly(ether sulfone) (PES). The chemical composition and morphology changes of the membrane surface were confirmed by water contact angle, X-ray photoelectron spectroscopy, scanning electron microscopy, and protein adsorption measurements. The decreased static water contact angle with an increase in the Pluronic F127 content indicated an increase of surface hydrophilicity. XPS analysis revealed enrichment of PEO segments of Pluronic F127 at the membrane surface. The apparent protein adsorption amount decreased significantly from 56.2 to 0 microg/cm(2) when the Pluronic F127 content varied from 0% to 10.5%, which indicated that the blend membrane had an excellent ability to resist protein adsorption. The ultrafiltration experiments revealed that the Pluronic F127 content had little influence on the protein rejection ratio and pure water flux. Most importantly, at a high Pluronic F127 content membrane fouling, especially irreversible fouling, has been remarkably reduced. The flux recoveries of blend membranes reached as high as 90% after periodic cleaning in three cycles.

To solve the tradeoff between permeability and selectivity of polymeric membranes, organic−inorganic hybrid membranes composed of poly(vinyl alcohol) (PVA) and γ-glycidyloxypropyltrimethoxysilane (GPTMS) were prepared by an in situ sol−gel approach for pervaporative separation of benzene/ cyclohexane mixtures. The structure of PVA-GPTMS hybrid membranes was characterized with FTIR, 29Si NMR, SEM, TEM, and XRD. Energy-dispersive X-ray Si-mapping analysis demonstrated homogeneous dispersion of silica in the PVA matrix. Compared with pure PVA membranes, the hybrid membranes exhibited high thermal stability and lower T g, and in particular improved pervaporation properties. Permeation flux increased from 20.3 g/(m2 h) for pure PVA membrane to 137.1 g/(m2 h) for PVA-GPTMS hybrid membrane with 28 wt % GPTMS content, and separation factor increased from 9.6 to 46.9 correspondingly. The pervaporation results of PVA-GPTMS hybrid membranes are all above the upper bound tradeoff curve (Lue, S. J.; Peng, S. H. J. Membr. Sci. 2003, 222, 203), while that of pure PVA membrane is obviously below the curve. Positron annihilation lifetime spectroscopy (PALS) was employed to elucidate the enhancement of permeation flux in polymer-based pervaporation membranes, and a size-selective mechanism was proposed to explain the enhancement of the separation factor.

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