Stirred-flow cell experiments were performed to investigate the kinetics of uranyl [U(VI)] desorption from a contaminated sedimentcollected from the Hanford 300 Area at the U.S. Department of Energy Hanford Site, Washington. Three influent solutions of variable pH, Ca and carbonate concentrations that affected U(VI) aqueous and surface speciation were used under dynamic flow conditions to evaluate the effect of geochemical conditions on the rate of U(Vl) desorption. The measured rate of U(VI) desorption varied with solution chemical composition that evolved as a result of thermodynamic and kinetic interactions between the solutions and sediment The solution chemical composition that led to a larger disequilibrium between adsorbed U(VI) and equilibrium adsorption state yielded a faster desorption rate. The experimental results were used to evaluate a multirate, surface complexation model (SCM) that has been proposed to describe U(VI) desorption kinetics in the Hanford sedimentthat contained complex adsorbed U(VI) in mass transfer limited domains (Lui et al. Water Resour. Res. 2008, 44, W08413). The model was modified and supplemented by including multirate, ion exchange reactions to describe the geochemical interactions between the solutions and sediment With the same setof model parameters, the modified model reasonably well described the evolution of major ions and the rates of U(VI) desorption under variable geochemical and flow conditions, implying that the multirate SCM is an effective way to describe U(VI) desorption kinetics in subsurface sediments.

The fate of nano zerovalent iron (nZVI) during subsurface injection was examined using carboxymethylcellulose (CMC) stabilized nZVI in a very large three-dimensional physical model aquifer with detailed monitoring using multiple, complementary detection methods. A fluorescein tracer test in the aquifer plus laboratory column data suggested that the very-aggressive flow conditions necessary to achieve 2.5 m of nZVI transport could be obtained using a hydraulically constrained flow path between injection and extraction wells. However, total unoxidized nZVI was transported only about 1 m and <2% of the injected nZVI concentration reached that distance. The experimental data also indicated that groundwater flow changed during injection, likely due to hydrogen bubble formation, which diverted the nZVI away from the targeted flow path. The leading edge of the iron plume became fully oxidized during transport. However, within the plume, oxidation of nZVI decreased in a fashion consistent with progressive depletion of aquifer "reductant demand". To directly quantify the extent of nZVI transport, a spectrophotometric method was developed, and the results indicated that deployment of unoxidized nZVI for groundwater remediation will likely be difficult.

It is of fundamental and technological significance to develop dual‐role anode materials for both lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs) with high performance. Here, a composite material based on CoSe2 nanoparticles encapsulated in N‐doped carbon framework intertwined with carbon nanotubes (CoSe2@N‐CF/CNTs) is prepared successfully from cobalt‐based zeolitic imidazolate framework (ZIF‐67). As anode materials for LIBs, CoSe2@N‐CF/CNTs composites deliver a reversible capacity of 428 mAh g−1 even after 500 cycles at a current density of 1 A g−1 with almost 100% Coulombic efficiency. The charge and discharge mechanisms of CoSe2 are characterized using ex situ X‐ray diffraction and Raman analysis, from which the lithiation products of CoSe2 are found to be LixCoSe2 and Li2Se, which are further converted to CoSe2 upon delithiation. The CoSe2@N‐CF/CNTs composites also demonstrate excellent electrochemical performance as anode materials for SIBs with a carbonate‐based electrolyte, with specific capacities of 606 and 501 mAh g−1 at 0.1 and 1 A g−1 in the 100th cycle. The electrochemical performance of the anode materials is further studied by pseudocapacitance and galvanostatic intermittent titration technique (GITT) measurements. This work may be exploited for the rational design and development of dual‐role anode materials for both Li‐ and Na‐ion batteries.

Dissolved organic matter (DOM) plays a key role in many biogeochemical processes, but the drivers controlling the diversity of chemical composition and properties of DOM molecules (chemodiversity) in soils are poorly understood. It has also been debated whether environmental conditions or intrinsic molecular properties control the accumulation and persistence of DOM due to the complexity of both molecular composition of DOM and interactions between DOM and surrounding environments. In this study, soil DOM samples were extracted from 33 soils collected from different regions of China, and we investigated the effects of climate and soil properties on the chemodiversity of DOM across different regions of China, employing a combination of Fourier transform ion cyclotron resonance mass spectrometry, optical spectroscopy, and statistical analyses. Our results indicated that, despite the heterogeneity of soil samples and complex influencing factors, aridity and clay can account for the majority of the variations of DOM chemical composition. The finding implied that DOM chemodiversity is an ecosystem property closely related to the environment, and can be used in developing large-scale soil biogeochemistry models for predicting C cycling in soils.

Oxidation-reduction potential (ORP) measurements have been widely used to assess the results of injection of nano zerovalent iron (nZVI) for groundwater remediation, but the significance of these measurements has never been established. Using rotating disk electrodes (RDE) in suspensions of nZVI, we found the electrode response to be highly complex but also a very sensitive probe for a range of fundamentally significant processes. The time dependence of the electrode response reflects both a primary effect (attachment of nZVI onto the electrode surface) and several secondary effects (esp., oxidation of iron and variations in dissolved H2 concentration). At nZVI concentrations above ∼200 mg/L, attachment of nZVI to the electrode is sufficient to give it the electrochemical characteristics of an Fe(0) electrode, making the electrode relatively insensitive to changes in solution chemistry. Lower nZVI concentrations give a proportional response in ORP, but much of this effect is mediated by the secondary effects noted above. Coating the nZVI with natural organic matter (NOM), or the organic polymers used to make stabile suspensions of nZVI, moderates its effect on ORP measurments. Our results provide the basis for interpretating ORP measurements used to characterize the results of injecting nZVI into groundwater.