Templated Mesoporous Silica Outer Shell for Controlled Silver Release of a Magnetically Recoverable and Reusable Nanocomposite for Water Disinfection

In this work, we encapsulated Fe3O4@SiO2@Ag (MS-Ag), a bifunctional magnetic silver core–shell structure, with an outer mesoporous silica (mS) shell to form an Fe3O4@SiO2@Ag@mSiO2 (MS-Ag-mS) nanocomposite using a cationic CTAB (cetyltrimethylammonium bromide) micelle templating strategy. The mS shell acts as protection to slow down the oxidation and detachment of the AgNPs and incorporates channels to control the release of antimicrobial Ag+ ions. Results of TEM, STEM, HRSEM, EDS, BET, and FTIR showed the successful formation of the mS shells on MS-Ag aggregates 50–400 nm in size with highly uniform pores ∼4 nm in diameter that were separated by silica walls ∼2 nm thick. Additionally, the mS shell thickness was tuned to demonstrate controlled Ag+ release; an increase in shell thickness resulted in an increased path length required for Ag+ ions to travel out of the shell, reducing MS-Ag-mS’ ability to inhibit E. coli growth as illustrated by the inhibition zone results. Through a shaking test, the MS-Ag-mS nanocomposite was shown to eradicate 99.99+% of a suspension of E. coli at 1 × 106 CFU/mL with a silver release of less than 0.1 ppb, well under the EPA recommendation of 0.1 ppm. This high biocidal efficiency with minimal silver leach is ascribed to the nanocomposite’s mS shell surface characteristics, including having hydroxyl groups and possessing a high degree of structural periodicity at the nanoscale or “smoothness” that encourages association with bacteria and retains high Ag+ concentration on its surface and in its close proximity. Furthermore, the nanocomposite demonstrated consistent antimicrobial performance and silver release levels over multiple repeated uses (after being recovered magnetically because of the oxidation-resistant silica-coated magnetic Fe3O4 core). It also proved effective at killing all microbes from Long Island Sound surface water. The described MS-Ag-mS nanocomposite is highly synergistic, easy to prepare, and readily recoverable and reusable and offers structural tunability affecting the bioavailability of Ag+, making it excellent for water disinfection that will find wide applications

Lack of Enantioselective Microbial Degradation of Chlordane in Long Island Sound Sediment

Numerous studies have examined the enantiomeric compositions of trans- and cis-chlordane in soils (agricultural, background, and house foundation soils) and in the atmosphere. In contrast, little is known about the enantiomeric compositions of chlordane in sediment. In this work, surficial sediments and sediment cores were collected at various sites in Long Island Sound (LIS) previously surveyed by the National Oceanic and Atmospheric Administration's (NOAA) National Status and Trends (NS&T) Program. Archived surficial sediments at selected sites were acquired from the NS&T Specimen Bank. The chlordanes were racemic or nearly racemic in most archived and recently collected sediments, indicating that the enantiomeric compositions of the sources of chlordane to LIS sediment did not change in the past two decades, and that house foundation soils are likely the major source of chlordanes to LIS. Invariant enantiomeric compositions temporally in surficial sediments and at different depths in sediment cores clearly indicate the lack of enantioselective biodegradation in LIS sediment, in striking contrast to the widely observed enantioselective biodegradation of chlordanes in soils

Persistent Chlordane Concentrations in Long Island Sound Sediment: Implications from Chlordane, ²¹⁰Pb, and ¹³⁷Cs Profiles

Concentrations of chlordane, a banned termiticide and pesticide, were examined in recently collected surficial sediment (10 sites) and sediment cores (4 sites) in Long Island Sound (LIS).The highest chlordane concentrations were observed in western LIS, near highly urbanized areas. Chlordane concentrations did not decrease significantly in the past decade when compared to the data collected in 1996, consistent with the observation of near-constant chlordane levels in blue mussel tissues collected during the same time period. Chlordane concentrations in many of the sites exceeded levels above which harmful effects on sediment-dwelling organisms are expected to frequently occur. Chlordane concentrations in two of the four sediment cores showed a peak below the sediment surface, suggesting reduced chlordane inputs in recent years. The lack of a chlordane concentration maximum below the sediment surface in the other two cores, coupled with the lack of a well-defined 137Cs peak, indicated significant sediment mixing. Simulations of 137Cs and 210Pb profiles in sediment cores with a simple sediment-mixing model were used to constrain both the deposition rate and the bioturbation rate of the sediment. Simulations of the chlordane profiles indicated continued chlordane input to LIS long after chlordane was phased out in the U.S. Continued chlordane input and significant sediment mixing may have contributed to the persistent chlordane concentrations in surficial sediment, which poses long-term threats to benthic organisms in LIS