To predict the fate of aqueous pollutants, a better understanding of heterogeneous Fe(III) (hydr)oxide nucleation and growth on abundant mineral surfaces is needed. In this study, we measured in situ heterogeneous Fe(III) (hydr)oxide nucleation and growth on quartz, muscovite, and corundum (Al2O3) in 10–4 M Fe(III) solution (in 10 mM NaNO3 at pH = 3.7 ± 0.2) using grazing incidence small-angle X-ray scattering (GISAXS). Interestingly, both the fastest heterogeneous nucleation and slowest growth occurred on corundum. To elucidate the mechanisms, zeta potential and water contact angle measurements were conducted. Electrostatic forces between the charged Fe(III) (hydr)oxide polymeric embryos and substrate surfaces—which affect local saturations near the substrate surfaces—controlled heterogeneous growth rates. Water contact angles (7.5° ± 0.7, 22.8° ± 1.7, and 44.8° ± 3.7 for quartz, muscovite, and corundum, respectively) indicate that corundum has the highest substrate–water interfacial energy. Furthermore, a comparison of structural mismatches between the substrates and precipitates indicates a lowest precipitate–substrate interfacial energy for corundum. The fastest nucleation on corundum suggests that interfacial energies in the solution–substrate–precipitate system controlled heterogeneous nucleation rates. The unique information provided here bolsters our understanding of nanoparticle–mineral surface interactions, mineral surface modification by iron oxide coating, and pollutant transport.
In this letter, we discuss the increase in the average cluster size by lowering the stagnation temperature of the methane (CH4) gas. The Coulomb explosion experiments are conducted to estimate the cluster size and the size distribution. The average CH4 cluster sizes Nav of 6 230 and 6 580 are acquired with the source conditions of 30 bars at 240 K and 60 bars at 296 K, respectively. Empirical estimation suggests a five-fold increase in the average size of the CH4 clusters at 240 K compared with that at room temperature under a backing pressure of 30 bars. A strong nonlinear Hagena parameter relation (\Gamma *\propto T^{-3.3}) for the CH4 clusters is revealed. The results may be favorable for the production of large-sized clusters by using gases at low temperature and high back pressures.
This study investigated the cotransport of titanium dioxide nanoparticles (nTiO(2)) and fullerene nanoparticles (nC(60)), two of the most widely utilized nanoparticles, in saturated quartz sand under a series of ionic strengths in NaCl solutions (0.1-10 mM) at both pH 5 and 7. Under all examined ionic strengths at pH 5, both breakthrough h curves and retained profiles of nTiO(2) in the copresence of nC(60) were similar to those without nC(60), indicating that nC(60) nanoparticles copresent in suspensions did not significantly affect the transport and retention of nTiO(2) in quartz sand at pH 5. In contrast, under all examined ionic strengths at pH 7, the breakthrough curves of nTiO(2) in the copresence of nC(60) in suspensions were higher and the retained profiles were lower than those without nC(60), which demonstrated that the presence of nC(60) in suspensions increased the rate of transport (decreased retention) of nTiO(2) in quartz sand at pH 7 Competition of deposition sites on quartz sand surfaces by the copresence of nC(60) was found to contribute to the increased nTiO(2) transport at pH 7. Under all examined ionic strength conditions at both pH 5 and 7, the breakthrough curves of nC(60) were reduced in the copresence of nTiO(2), and the corresponding retained profiles were higher than those without nTiO(2), indicating that the presence of nTiO(2) decreased the transport of nC(60) in quartz sand. Co-deposition of nC(60) with nTiO(2) in the form of nTiO(2)-nC(60) clusters as well as the deposition of nC(60) onto previously deposited nTiO(2) were responsible for the increased nC(60) deposition in the presence of nTiO(2) at pH 5, whereas deposition of nC(60) onto surfaces of predeposited nTiO(2) was found to be responsible for the increased nC(60) deposition at pH 7.
Fano resonances are numerically predicted in an ultracompact plasmonic structure, comprising a metal-isolator-metal (MIM) waveguide side-coupled with two identical stub resonators. This phenomenon can be well explained by the analytic model and the relative phase analysis based on the scattering matrix theory. In sensing applications, the sensitivity of the proposed structure is about 1.1 x 10(3) nm/RIU and its figure of merit is as high as 2 x 10(5) at lambda=980 nm, which is due to the sharp asymmetric Fano line-shape with an ultra-low transmittance at this wavelength. This plasmonic structure with such high figure of merits and footprints of only about 0.2 mu m(2) may find important applications in the on-chip nano-sensors.
The paper estimates the household labor earning process using the March Current Population Survey 1968–2011. GMM estimates confirm that the results in Storesletten et al. (2004) still hold in a much larger data set over a longer period. The persistent idiosyncratic risk is strongly countercyclical, with an annual auto-correlation equal to .973 and an standard deviation that increases by 72.5% (from .090 to .156) as the macroeconomy moves from peak to trough.