Sulfate Enhances the Adsorption and Retention of Cu(II) and Zn(II) to Dispersed and Aggregated Iron Oxyhydroxide Nanoparticles

The adsorption and retention of metal ions to nanoscale iron (hydr)oxides in aqueous systems is significantly influenced by prevailing environmental conditions. We examined the influence of sulfate, the second most common anion in seawater that is present in many other natural aquatic systems, on the adsorption and retention of Cu(II) and Zn(II) to synthetic iron oxyhydroxide nanoparticles (NPs) and their aggregates. Batch uptake experiments with monodisperse NPs and NPs aggregated by changes in pH, ionic strength, and temperature were conducted over sulfate concentrations ranging from 0 to 0.30 M. The introduction of 0.03 M sulfate significantly increased the initial adsorption and retention of Zn(II) and Cu(II) compared to sulfate-free conditions; with increasing sulfate \u3e0.03 M, Zn(II) retention continuously increased, while Cu(II) retention was considerably more variable but increased slightly. NP aggregation, when induced by pH and ionic strength, was positively correlated with metal ion retention, while aggregation temperature was negatively correlated with both adsorption and retention. Aqueous geochemical modeling indicated that Zn(II) readily complexes with sulfate to form ZnSO4 (aq), but that stable aqueous CuSO4 species are uncommon. EXAFS spectroscopic analysis suggests structural incorporation of Zn(II) and Zn(II)-sulfate ternary surface complexation, while Cu(II) primarily forms inner-sphere bidentate surface complexes. Collectively, the effects of sulfate in both reducing surface charge repulsion, initiating ternary surface complexation, and enabling structural incorporation aid to enhance both metal adsorption and retention to iron oxyhydroxide NPs and their aggregates

Fluorescent lifetimes of oils and oil distillates in artificial seawater

Supporting data associated with a study of the fluorescent lifetimes of eleven oil and oil distillates in artificial seawater are given. The table is a list of the oil and oil distillate names along with the associated sample numbers used in this study and their API densities. The excel data file contains lifetimes as a function of emission wavelength for different oils and oil products shown by sample number. The lifetimes were measured with a Horiba DeltaFlex Lifetime System that uses pulsed diode light sources. There is a separate sheet for each excitation source: 268, 285 and 348 nm. Lifetimes were well fit to a tri-exponential model with 3 lifetime components: an intermediate T1, a long-lived T2 and a short-lived T3. These data tables also include the fractional population B for each lifetime component and the chi squared values for the fit. Average values and standard deviations are reported. The figure shows the excitation-emission matrix spectra of oils and oil products in artificial seawater acquired with a Horiba Aqualog fluorometer. Excitation wavelength is on the x-axis and emission wavelength is on the y-axis. The color scale is fluorescence intensity in microvolts ranging from low (blue) to high (red). The wavelength range used here is that typically used in studies of dissolved organic matter (DOM). The oils show peaks in what is typically assigned to protein peaks in DOM spectra (excitation = 270-280 nm; emission 300-380 nm). A table with the oil sample names and numbers is available through the blue download button at the top of the page. More files are available below