There is a need to develop highly selective and efficient materials for capturing uranium (normally as UO2(2+)) from nuclear waste and from seawater. We demonstrate the promising adsorption performance of S(x)-LDH composites (LDH is Mg/Al layered double hydroxide, [S(x)](2-) is polysulfide with x = 2, 4) for uranyl ions from a variety of aqueous solutions including seawater. We report high removal capacities (q(m) = 330 mg/g), large K(d)(U) values (10(4)-10(6) mL/g at 1-300 ppm U concentration), and high % removals (>95% at 1-100 ppm, or ∼80% for ppb level seawater) for UO2(2+) species. The S(x)-LDHs are exceptionally efficient for selectively and rapidly capturing UO2(2+) both at high (ppm) and trace (ppb) quantities from the U-containing water including seawater. The maximum adsorption coeffcient value K(d)(U) of 3.4 × 10(6) mL/g (using a V/m ratio of 1000 mL/g) observed is among the highest reported for U adsorbents. In the presence of very high concentrations of competitive ions such as Ca(2+)/Na(+), S(x)-LDH exhibits superior selectivity for UO2(2+), over previously reported sorbents. Under low U concentrations, (S4)(2-) coordinates to UO2(2+) forming anionic complexes retaining in the LDH gallery. At high U concentrations, (S4)(2-) binds to UO2(2+) to generate neutral UO2S4 salts outside the gallery, with NO3(-) entering the interlayer to form NO3-LDH. In the presence of high Cl(-) concentration, Cl(-) preferentially replaces [S4](2-) and intercalates into LDH. Detailed comparison of U removal efficiency of S(x)-LDH with various known sorbents is reported. The excellent uranium adsorption ability along with the environmentally safe, low-cost constituents points to the high potential of S(x)-LDH materials for selective uranium capture.
Efficient charge separation and transportation are key factors that determine the photoelectrochemical (PEC) water-splitting efficiency. Here, a simultaneous enhancement of charge separation and hole transportation on the basis of ferroelectric polarization in TiO -SrTiO core-shell nanowires (NWs) is reported. The SrTiO shell with controllable thicknesses generates a considerable spontaneous polarization, which effectively tunes the electrical band bending of TiO . Combined with its intrinsically high charge mobility, the ferroelectric SrTiO thin shell significantly improves the charge-separation efficiency (η ) with minimized influence on the hole-migration property of TiO photoelectrodes, leading to a drastically increased photocurrent density ( J ). Specifically, the 10 nm-thick SrTiO shell yields the highest J and η of 1.43 mA cm and 87.7% at 1.23 V versus reversible hydrogen electrode, respectively, corresponding to 83% and 79% improvements compared with those of pristine TiO NWs. The PEC performance can be further manipulated by thermal treatment, and the control of SrTiO film thicknesses and electric poling directions. This work suggests a material with combined ferroelectric and semiconducting features could be a promising solution for advancing PEC systems by concurrently promoting the charge-separation and hole-transportation properties.
Science" and "Technologies" ("NESTs") have tremendous innovation potential. However this must be weighed against enormous uncertainties caused by many unknowns. The authors of this paper offer a framework to analyze NESTs to help ascertain likely innovation pathways. We have devised a 10-step framework based on extensive Future-oriented Technology Analyses ("FTA") experience, enriched by in-depth case analyses. In the paper, we describe our analytical activities in two case studies. The nanobiosensor experience is contrasted with that of deep brain stimulation in relative quantitative and qualitative emphases. We close the paper by reflecting on this systematic FTA framework for emerging science and technologies, for its intended goal, that is to support decision making.
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