Generalized Two-Dimensional Perturbation Correlation Infrared Spectroscopy Reveals Mechanisms for the Development of Surface Charge and Recalcitrance in Plant-Derived Biochars

Fundamental knowledge of how biochars develop surface-charge and resistance to environmental degradation is crucial to their production for customized applications or understanding their functions in the environment. Two-dimensional perturbation-based correlation infrared spectroscopy (2D-PCIS) was used to study the biochar formation process in three taxonomically different plant biomass, under oxygen-limited conditions along a heat-treatment-temperature gradient (HTT; 200–650 °C). Results from 2D-PCIS pointed to the systematic, HTT-induced defragmenting of lignocellulose H-bonding network and demethylenation/demethylation, oxidation, or dehydroxylation/dehydrogenation of lignocellulose fragments as the primary reactions controlling biochar properties along the HTT gradient. The cleavage of OH^...O-type H-bonds, oxidation of free primary hydroxyls to carboxyls (carboxylation; HTT ≤ 500 °C), and their subsequent dehydrogenation/dehydroxylation (HTT > 500 °C) controlled surface charge on the biochars; while the dehydrogenation of methylene groups, which yielded increasingly condensed structures (R–CH₂–R →RCH–R →RCR), controlled biochar recalcitrance. Variations in biochar properties across plant biomass type were attributable to taxa-specific transformations. For example, apparent inefficiencies in the cleavage of wood-specific H-bonds, and their subsequent oxidation to carboxyls, lead to lower surface charge in wood biochars (compared to grass biochars). Both nontaxa and taxa-specific transformations highlighted by 2D-PCIS could have significant implications for biochar functioning in fire-impacted or biochar-amended systems

Discrimination in Degradability of Soil Pyrogenic Organic Matter Follows a Return-On-Energy-Investment Principle

A fundamental understanding of biodegradability is central to elucidating the role(s) of pyrogenic organic matter (PyOM) in biogeochemical cycles. Since microbial community and ecosystem dynamics are driven by net energy flows, then a quantitative assessment of energy value versus energy requirement for oxidation of PyOM should yield important insights into their biodegradability. We used bomb calorimetry, stepwise isothermal thermogravimetric analysis (<i>iso</i>TGA), and 5-year in situ bidegradation data to develop energy-biodegradability relationships for a suite of plant- and manure-derived PyOM (<i>n</i> = 10). The net energy value (Δ<i><i>E</i></i>) for PyOM was between 4.0 and 175 kJ mol^–1; with manure-derived PyOM having the highest Δ<i><i>E</i></i>. Thermal-oxidation activation energy (<i>E</i>_a) requirements ranged from 51 to 125 kJ mol^–1, with wood-derived PyOM having the highest <i>E</i>_a requirements. We propose a return-on-investment (ROI) parameter (Δ<i><i>E</i>/E</i>_a) for differentiating short-to-medium term biodegradability of PyOM and deciphering if biodegradation will most likely proceed via cometabolism (ROI < 1) or direct metabolism (ROI ≥ 1). The ROI-biodegradability relationship was sigmoidal with higher biodegradability associated with PyOM of higher ROI; indicating that microbes exhibit a higher preference for “high investment value” PyOM

An Index-Based Approach to Assessing Recalcitrance and Soil Carbon Sequestration Potential of Engineered Black Carbons (Biochars)

The ability of engineered black carbons (or biochars) to resist abiotic and, or biotic degradation (herein referred to as recalcitrance) is crucial to their successful deployment as a soil carbon sequestration strategy. A new recalcitrance index, the <i>R</i>₅₀, for assessing biochar quality for carbon sequestration is proposed. The <i>R</i>₅₀ is based on the relative thermal stability of a given biochar to that of graphite and was developed and evaluated with a variety of biochars (<i>n</i> = 59), and soot-like black carbons. Comparison of <i>R</i>₅₀, with biochar physicochemical properties and biochar-C mineralization revealed the existence of a quantifiable relationship between <i>R</i>₅₀ and biochar recalcitrance. As presented here, the <i>R</i>₅₀ is immediately applicable to pre-land application screening of biochars into Class A (<i>R</i>₅₀ ≥ 0.70), Class B (0.50 ≤ <i>R</i>₅₀ < 0.70) or Class C (<i>R</i>₅₀ < 0.50) recalcitrance/carbon sequestration classes. Class A and Class C biochars would have carbon sequestration potential comparable to soot/graphite and uncharred plant biomass, respectively, whereas Class B biochars would have intermediate carbon sequestration potential. We believe that the coupling of the <i>R</i>_<i>50</i>, to an index-based degradation, and an economic model could provide a suitable framework in which to comprehensively assess soil carbon sequestration in biochars

Pyrogenic Inputs of Anthropogenic Pb and Hg to Sediments of the Hood Canal, Washington, in the 20th Century: Source Evidence from Stable Pb Isotopes and PAH Signatures

Combustion-derived PAHs and stable Pb isotopic signatures (²⁰⁶Pb/²⁰⁷Pb) in sedimentary records assisted in reconstructing the sources of atmospheric inputs of anthropogenic Pb and Hg to the Hood Canal, Washington. The sediment-focusing corrected peak fluxes of total Pb and Hg (1960–70s) demonstrate that the watershed of Hood Canal has received greater atmospheric inputs of these metals than its mostly rural land use would predict. The tight relationships between the Pb, Hg, and organic markers in the cores indicate that these metals are derived from industrial combustion emissions. Multiple lines of evidence point to the Asarco smelter, located in the Main Basin of Puget Sound, as the major emission source of these metals to the watershed of the Hood Canal. The evidence includes (1) similar PAH isomer ratios in sediment cores from the two basins, (2) the correlations between Pb, Hg, and Cu in sediments and previously studied environmental samples including particulate matter emitted from the Asarco smelter’s main stack at the peak of production, and (3) Pb isotope ratios. The natural rate of recovery in Hood Canal since the 1970s, back to preindustrial metal concentrations, was linear and contrasts with recovery rates reported for the Main Basin which slowed post late 1980s

Uranium Adsorbent Fibers Prepared by Atom-Transfer Radical Polymerization (ATRP) from Poly(vinyl chloride)-<i>co</i>-chlorinated Poly(vinyl chloride) (PVC-<i>co</i>-CPVC) Fiber

The need to secure future supplies of energy attracts researchers in several countries to a vast resource of nuclear energy fuel: uranium in seawater (estimated at 4.5 billion tons in seawater). In this study, we developed effective adsorbent fibers for the recovery of uranium from seawater via atom-transfer radical polymerization (ATRP) from a poly­(vinyl chloride)-<i>co</i>-chlorinated poly­(vinyl chloride) (PVC-<i>co</i>-CPVC) fiber. ATRP was employed in the surface graft polymerization of acrylonitrile (AN) and <i>tert</i>-butyl acrylate (<i>t</i>BA), precursors for uranium-interacting functional groups, from PVC-<i>co</i>-CPVC fiber. The [<i>t</i>BA]/[AN] was systematically varied to identify the optimal ratio between hydrophilic groups (from <i>t</i>BA) and uranyl-binding ligands (from AN). The best performing adsorbent fiber, the one with the optimal [<i>t</i>BA]/[AN] ratio and a high degree of grafting (1390%), demonstrated uranium adsorption capacities that are significantly greater than those of the Japan Atomic Energy Agency (JAEA) reference fiber in natural seawater tests (2.42–3.24 g/kg in 42 days of seawater exposure and 5.22 g/kg in 49 days of seawater exposure, versus 1.66 g/kg in 42 days of seawater exposure and 1.71 g/kg in 49 days of seawater exposure for JAEA). Adsorption of other metal ions from seawater and their corresponding kinetics were also studied. The grafting of alternative monomers for the recovery of uranium from seawater is now under development by this versatile technique of ATRP

Formularity: Software for Automated Formula Assignment of Natural and Other Organic Matter from Ultrahigh-Resolution Mass Spectra

Ultrahigh resolution mass spectrometry, such as Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS), can resolve thousands of molecular ions in complex organic matrices. A Compound Identification Algorithm (CIA) was previously developed for automated elemental formula assignment for natural organic matter (NOM). In this work, we describe software Formularity with a user-friendly interface for CIA function and newly developed search function Isotopic Pattern Algorithm (IPA). While CIA assigns elemental formulas for compounds containing C, H, O, N, S, and P, IPA is capable of assigning formulas for compounds containing other elements. We used halogenated organic compounds (HOC), a chemical class that is ubiquitous in nature as well as anthropogenic systems, as an example to demonstrate the capability of Formularity with IPA. A HOC standard mix was used to evaluate the identification confidence of IPA. Tap water and HOC spike in Suwannee River NOM were used to assess HOC identification in complex environmental samples. Strategies for reconciliation of CIA and IPA assignments were discussed. Software and sample databases with documentation are freely available

Elution of Uranium and Transition Metals from Amidoxime-Based Polymer Adsorbents for Sequestering Uranium from Seawater

High-surface-area amidoxime and carboxylic acid grafted polymer adsorbents developed at Oak Ridge National Laboratory were tested for sequestering uranium in a flowing seawater flume system at the PNNL-Marine Sciences Laboratory. FTIR spectra indicate that a KOH conditioning process is necessary to remove the proton from the carboxylic acid and make the sorbent effective for sequestering uranium from seawater. The alkaline conditioning process also converts the amidoxime groups to carboxylate groups in the adsorbent. Both Na₂CO₃–H₂O₂ and hydrochloric acid elution methods can remove ∼95% of the uranium sequestered by the adsorbent after 42 days of exposure in real seawater. The Na₂CO₃–H₂O₂ elution method is more selective for uranium than conventional acid elution. Iron and vanadium are the two major transition metals competing with uranium for adsorption to the amidoxime-based adsorbents in real seawater. Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt, 1 M) can remove iron from the adsorbent very effectively at pH around 7. The coordination between vanadium­(V) and amidoxime is also discussed based on our ⁵¹V NMR data

Investigations into the Reusability of Amidoxime-Based Polymeric Adsorbents for Seawater Uranium Extraction

The ability to reuse amidoxime-based polymeric adsorbents is a critical component in reducing the overall cost of the technology to extract uranium from seawater. This report describes an evaluation of adsorbent reusability in multiple reuse (adsorption/stripping) cycles in real seawater exposures with potassium bicarbonate (KHCO₃) elution using several amidoxime-based polymeric adsorbents. The KHCO₃ elution technique achieved ∼100% recovery of uranium adsorption capacity in the first reuse. Subsequent reuses showed significant drops in adsorption capacity. After the fourth reuse with the ORNL AI8 adsorbent, the 56-day adsorption capacity dropped to 28% of its original capacity. FTIR spectra revealed that there was a conversion of the amidoxime ligands to carboxylate groups during extended seawater exposure, becoming more significant with longer exposure times. Ca and Mg adsorption capacities also increased with each reuse cycle supporting the hypothesis that long-term exposure resulted in converting amidoxime to carboxylate, enhancing the adsorption of Ca and Mg. Shorter seawater exposure (adsorption/stripping) cycles (28 vs 42 days) had higher adsorption capacities after reuse, but the shorter exposure cycle time did not produce an overall better performance in terms of cumulative exposure time. Recovery of uranium capacity in reuses may also vary across different adsorbent formulations. Through multiple reuses, the AI8 adsorbent can harvest 10 g uranium/kg adsorbent in ∼140 days, using a 28-day adsorption/stripping cycle, a performance much better than would be achieved with a single use of the adsorbent through a very long-term exposure (saturation capacity of 7.4 g U/kg adsorbent). A time dependent seawater exposure model to evaluate the cost associated with reusing amidoxime-based adsorbents in real seawater exposures was developed. The predicted cost to extract uranium from seawater ranged from $610/kg U to$830/kg U. Model simulation suggests that a short seawater exposure cycle (<15 days) is the optimal deployment period for lower uranium production cost in seawater uranium mining