Carbon Mineralizability Determines Interactive Effects on Mineralization of Pyrogenic Organic Matter and Soil Organic Carbon

Soil organic carbon (SOC) is a critical and active pool in the global C cycle, and the addition of pyrogenic organic matter (PyOM) has been shown to change SOC cycling, increasing or decreasing mineralization rates (often referred to as priming). We adjusted the amount of easily mineralizable C in the soil, through 1-day and 6-month preincubations, and in PyOM made from maple wood at 350 °C, through extraction. We investigated the impact of these adjustments on C mineralization interactions, excluding pH and nutrient effects and minimizing physical effects. We found short-term increases (+20–30%) in SOC mineralization with PyOM additions in the soil preincubated for 6 months. Over the longer term, both the 6-month and 1-day preincubated soils experienced net ∼10% decreases in SOC mineralization with PyOM additions. Additionally, the duration of preincubation affected interactions, indicating that there may be no optimal preincubation time for SOC mineralization studies. We show conclusively that mineralizability of SOC in relation to PyOM-C is an important determinant of the effect of PyOM additions on SOC mineralization

Electrodeposition from Acidic Solutions of Nickel Bis(benzenedithiolate) Produces a Hydrogen-Evolving Ni–S Film on Glassy Carbon

Films electrodeposited onto glassy carbon electrodes from acidic acetonitrile solutions of [Bu₄N]­[Ni­(bdt)₂] (bdt = 1,2-benzenedithiolate) are active toward electrocatalytic hydrogen production at potentials 0.2–0.4 V positive of untreated electrodes. This activity is preserved when the electrode is rinsed and transferred to a fresh acid solution. X-ray photoelectron spectra indicate that the deposited material contains Ni and S, and time-of-flight secondary ion mass spectrometry shows that electrodeposition decomposes the Ni­(bdt)₂ assembly. Correlations between voltammetric and spectroscopic results indicate that the deposited material is active, i.e., that catalysis is heterogeneous rather than homogeneous. Control experiments establish that obtaining the observed catalytic response requires both Ni and the 1,2-benzenedithiolate ligand to be present during deposition

<i>In Situ</i> Molecular Imaging of the Biofilm and Its Matrix

Molecular mapping of live biofilms at submicrometer resolution presents a grand challenge. Here, we present the first chemical mapping results of biofilm extracellular polymeric substance (EPS) in biofilms using correlative imaging between super resolution fluorescence microscopy and liquid time-of-flight secondary ion mass spectrometry (TOF-SIMS). <i>Shewanella oneidensis</i> is used as a model organism. Heavy metal chromate (Cr₂O₇^2–) anions consisting of chromium Cr­(VI) was used as a model environmental stressor to treat the biofilms. Of particular interest, biologically relevant water clusters have been first observed in the biofilms. Characteristic fragments of biofilm matrix components such as proteins, polysaccharides, and lipids can be spatially imaged. Furthermore, characteristic fatty acids (e.g., palmitic acid), quinolone signal, and riboflavin fragments were found to respond after the biofilm is treated with Cr­(VI), leading to biofilm dispersal. Significant changes in water clusters and quorum sensing signals indicative of intercellular communication in the aqueous environment were observed, suggesting that they might result in fatty acid synthesis and inhibition of riboflavin production. The Cr­(VI) reduction seems to follow the Mtr pathway leading to Cr­(III) formation. Our approach potentially opens a new avenue for mechanistic insight of microbial community processes and communications using <i>in situ</i> imaging mass spectrometry and super resolution optical microscopy

Microstructure and Cs Behavior of Ba-Doped Aluminosilicate Pollucite Irradiated with F⁺ Ions

Radionuclide ¹³⁷Cs is one of the major fission products that dominate heat generation in spent fuels over the first 300 years. A durable waste form for ¹³⁷Cs that decays to ¹³⁷Ba is needed to minimize its environmental impact. Aluminosilicate pollucite CsAlSi₂O₆ is selected as a model waste form to study the decay-induced structural effects. Whereas Ba-containing precipitates are not present in charge-balanced Cs_0.9Ba_0.05AlSi₂O₆, they are found in Cs_0.9Ba_0.1AlSi₂O₆ and identified as monoclinic Ba₂Si₃O₈. Pollucite is susceptible to electron-irradiation-induced amorphization. The threshold density of electronic energy deposition for amorphization was determined to be ∼235 keV/nm³. Pollucite can be readily amorphized under F⁺ ion irradiation at 673 K. A significant amount of Cs diffusion and release from the amorphized pollucite occurs during the irradiation. However, cesium is immobile in the crystalline structure under He⁺ ion irradiation at room temperature. The critical temperature for amorphization is not higher than 873 K under F⁺ ion irradiation. If kept at or above 873 K all the time, the pollucite structure is unlikely to be amorphized; Cs diffusion and release are improbable. A general discussion regarding pollucite as a potential waste form is provided in this report

In Situ Mass Spectrometric Determination of Molecular Structural Evolution at the Solid Electrolyte Interphase in Lithium-Ion Batteries

Dynamic structural and chemical evolution at solid–liquid electrolyte interface is always a mystery for a rechargeable battery due to the challenge to directly probe a solid–liquid interface under reaction conditions. We describe the creation and usage of in situ liquid secondary ion mass spectroscopy (SIMS) for the first time to directly observe the molecular structural evolution at the solid–liquid electrolyte interface for a lithium (Li)-ion battery under dynamic operating conditions. We have discovered that the deposition of Li metal on copper electrode leads to the condensation of solvent molecules around the electrode. Chemically, this layer of solvent condensate tends to be depleted of the salt anions and with reduced concentration of Li⁺ ions, essentially leading to the formation of a lean electrolyte layer adjacent to the electrode and therefore contributing to the overpotential of the cell. This observation provides unprecedented molecular level dynamic information on the initial formation of the solid electrolyte interphase (SEI) layer. The present work also ultimately opens new avenues for implanting the in situ liquid SIMS concept to probe the chemical reaction process that intimately involves solid–liquid interface, such as electrocatalysis, electrodeposition, biofuel conversion, biofilm, and biomineralization

In Situ Mass Spectrometric Determination of Molecular Structural Evolution at the Solid Electrolyte Interphase in Lithium-Ion Batteries

Dynamic structural and chemical evolution at solid–liquid electrolyte interface is always a mystery for a rechargeable battery due to the challenge to directly probe a solid–liquid interface under reaction conditions. We describe the creation and usage of in situ liquid secondary ion mass spectroscopy (SIMS) for the first time to directly observe the molecular structural evolution at the solid–liquid electrolyte interface for a lithium (Li)-ion battery under dynamic operating conditions. We have discovered that the deposition of Li metal on copper electrode leads to the condensation of solvent molecules around the electrode. Chemically, this layer of solvent condensate tends to be depleted of the salt anions and with reduced concentration of Li⁺ ions, essentially leading to the formation of a lean electrolyte layer adjacent to the electrode and therefore contributing to the overpotential of the cell. This observation provides unprecedented molecular level dynamic information on the initial formation of the solid electrolyte interphase (SEI) layer. The present work also ultimately opens new avenues for implanting the in situ liquid SIMS concept to probe the chemical reaction process that intimately involves solid–liquid interface, such as electrocatalysis, electrodeposition, biofuel conversion, biofilm, and biomineralization

Mitigating Voltage Fade in Cathode Materials by Improving the Atomic Level Uniformity of Elemental Distribution

Lithium- and manganese-rich (LMR) layered-structure materials are very promising cathodes for high energy density lithium-ion batteries. However, their voltage fading mechanism and its relationships with fundamental structural changes are far from being well understood. Here we report for the first time the mitigation of voltage and energy fade of LMR cathodes by improving the atomic level spatial uniformity of the chemical species. The results reveal that LMR cathodes (Li­[Li_0.2Ni_0.2M_0.6]­O₂) prepared by coprecipitation and sol–gel methods, which are dominated by a LiMO₂ type <i>R</i>3̅<i>m</i> structure, show significant nonuniform Ni distribution at particle surfaces. In contrast, the LMR cathode prepared by a hydrothermal assisted method is dominated by a Li₂MO₃ type <i>C</i>2/<i>m</i> structure with minimal Ni-rich surfaces. The samples with uniform atomic level spatial distribution demonstrate much better capacity retention and much smaller voltage fade as compared to those with significant nonuniform Ni distribution. The fundamental findings on the direct correlation between the atomic level spatial distribution of the chemical species and the functional stability of the materials may also guide the design of other energy storage materials with enhanced stabilities

Cellular Delivery of Nanoparticles Revealed with Combined Optical and Isotopic Nanoscopy

Direct polymerization of an oxaliplatin analogue was used to reproducibly generate amphiphiles in one pot, which consistently and spontaneously self-assemble into well-defined nanoparticles (NPs). Despite inefficient drug leakage in cell-free assays, the NPs were observed to be as cytotoxic as free oxaliplatin in cell culture experiments. We investigated this phenomenon by super-resolution fluorescence structured illumination microscopy (SIM) and nanoscale secondary ion mass spectrometry (NanoSIMS). In combination, these techniques revealed NPs are taken up <i>via</i> endocytic pathways before intracellular release of their cytotoxic cargo. As with other drug-carrying nanomaterials, these systems have potential as cellular delivery vehicles. However, high-resolution methods to track nanocarriers and their cargo at the micro- and nanoscale have been underutilized in general, limiting our understanding of their interactions with cells and tissues. We contend this type of combined optical and isotopic imaging strategy represents a powerful and potentially generalizable methodology for cellular tracking of nanocarriers and their cargo

The Role of Cesium Cation in Controlling Interphasial Chemistry on Graphite Anode in Propylene Carbonate-Rich Electrolytes

Despite the potential advantages it brings, such as wider liquid range and lower cost, propylene carbonate (PC) is seldom used in lithium-ion batteries because of its sustained cointercalation into the graphene structure and the eventual graphite exfoliation. Here, we report that cesium cation (Cs⁺) directs the formation of solid electrolyte interphase on graphite anode in PC-rich electrolytes through its preferential solvation by ethylene carbonate (EC) and the subsequent higher reduction potential of the complex cation. Effective suppression of PC-decomposition and graphite-exfoliation is achieved by adjusting the EC/PC ratio in electrolytes to allow a reductive decomposition of Cs⁺-(EC)_<i>m</i> (1 ≤ <i>m</i> ≤ 2) complex preceding that of Li⁺-(PC)_<i>n</i> (3 ≤ <i>n</i> ≤ 5). Such Cs⁺-directed interphase is stable, ultrathin, and compact, leading to significant improvement in battery performances. In a broader context, the accurate tailoring of interphasial chemistry by introducing a new solvation center represents a fundamental breakthrough in manipulating interfacial reactions that once were elusive to control

Investigation of Ion–Solvent Interactions in Nonaqueous Electrolytes Using in Situ Liquid SIMS

Ion–solvent interactions in nonaqueous electrolytes are of fundamental interest and practical importance, yet debates regarding ion preferential solvation and coordination numbers persist. In this work, in situ liquid SIMS was used to examine ion–solvent interactions in three representative electrolytes, i.e., lithium hexafluorophosphate (LiPF₆) at 1.0 M in ethylene carbonate (EC)–dimethyl carbonate (DMC) and lithium bis­(fluorosulfonyl)­imide (LiFSI) at both low (1.0 M) and high (4.0 M) concentrations in 1,2-dimethoxyethane (DME). In the positive ion mode, solid molecular evidence strongly supports the preferential solvation of Li⁺ by EC. Besides, from the negative spectra, we also found that PF₆^– forms association with EC, which has been neglected by previous studies due to the relatively weak interaction. In both LiFSI in DME electrolytes, however, no evidence shows that FSI^– is associated with DME. Furthermore, strong salt ion cluster signals were observed in the 1.0 M LiPF₆ in EC–DMC electrolyte, suggesting that a significant amount of Li⁺ ions stay in the vicinity of anions. In sharp comparison, weak ion cluster signals were detected in dilute LiFSI in DME electrolyte, suggesting most ions are well separated, in agreement with our molecular dynamics simulation results. These findings indicate that with virtues of little bias on detecting positive and negative ions and the capability of directly analyzing concentrated electrolytes, in situ liquid SIMS is a powerful tool that can provide key evidence for improved understanding on the ion–solvent interactions in nonaqueous electrolytes. Therefore, we anticipate wide applications of in situ liquid SIMS on investigations of various ion–solvent interactions in the near future