Importance of inner-sphere P-O-Fe bonds in natural and synthetic mineral-organic associations.

Sorption of organic molecules on mineral surfaces can occur through several binding mechanisms of varying strength. Here, we investigated the importance of inner-sphere P-O-Fe bonds in synthetic and natural mineral-organic associations. Natural organic matter such as water extracted soil organic matter (WESOM) and extracellular polymeric substances (EPS) from liquid bacterial cultures were adsorbed to goethite and examined by FTIR spectroscopy and P K-edge NEXAFS spectroscopy.

Crystallization Engineering of CuNi S Ultra-Fine Nanocrystals with Optimized Band Structures for Efficient Photocatalytic Pollutant Degradation and Hydrogen Production.

The mono-dispersed cubic siegenite CuNi S ultra-fine (≈5 nm) nanocrystals are fabricated through crystallization engineering under hot injection. The strong hydroxylation on mostly exposed CuNi S (220) surface leads to the formation of multi-valence (Cu , Cu , Ni , Ni ) species with unsaturated hybridization and coordination micro-environments, which can induce rich redox reactions to optimize interfacial kinetics for the adsorbed reaction intermediates. The as-synthesized CuNi S nanocrystals with ultra-small particle size and the characteristics of being highly dispersed can increase specific surface area and hydroxylated active sites, which considerably contribute to the improvement of photocatalytic activities.

Positron-emitting radiotracers spatially resolve unexpected biogeochemical relationships linked with methane oxidation in Arctic soils.

Arctic soils are marked by cryoturbic features, which impact soil-atmosphere methane (CH ) dynamics vital to global climate regulation. Cryoturbic diapirism alters C/N chemistry within frost boils by introducing soluble organic carbon and nutrients, potentially influencing microbial CH oxidation. CH oxidation in soils, however, requires a spatio-temporal convergence of ecological factors to occur.

Atomically Dispersed Fe-Co Bimetallic Catalysts for the Promoted Electroreduction of Carbon Dioxide.

The electroreduction reaction of CO (ECORR) requires high-performance catalysts to convert CO into useful chemicals. Transition metal-based atomically dispersed catalysts are promising for the high selectivity and activity in ECORR. This work presents a series of atomically dispersed Co, Fe bimetallic catalysts by carbonizing the Fe-introduced Co-zeolitic-imidazolate-framework (C-Fe-Co-ZIF) for the syngas generation from ECORR.

Dissolved organic matter concentration, molecular composition, and functional groups in contrasting management practices of peatlands.

About 91,300 ha of peatlands has been rewetted in western Europe since the mid-1990s. Still, it is unknown how long-term rewetting alters the dissolved organic matter (DOM) concentration, molecular composition, and functional groups. We examined these DOM characteristics in three peatland types subjected to 47- to 231-yr drainage and 18- to 24-yr rewetting to address this knowledge gap.

Relative proportions of organic carbon functional groups in biochars as influenced by spectral data collection and processing.

Solid-state C Nuclear Magnetic Resonance (NMR) and synchrotron-based X-ray Absorption Near-Edge Structure (XANES) have applications for determining the relative proportions of organic C functional groups in materials. Spectral data obtained by NMR is typically processed using integration (INTEG) whereas XANES spectral data is typically processed using deconvolution (DECONV). The objective of this study was to examine the impact of spectral data collection and processing on the estimated relative proportions of organic C functional groups in biochars.

Nitrogen speciation and transformations in fire-derived organic matter.

Vegetation fires are known to have broad geochemical effects on carbon (C) cycles in the Earth system, yet limited information is available for nitrogen (N). In this study, we evaluated how charring organic matter (OM) to pyrogenic OM (PyOM) altered the N molecular structure and affected subsequent C and N mineralization. Nitrogen near-edge X-ray absorption fine structure (NEXAFS) of uncharred OM, PyOM, PyOM toluene extract, and PyOM after toluene extraction were used to predict PyOM-C and -N mineralization potentials.

Fire-derived organic matter retains ammonia through covalent bond formation.

Fire-derived organic matter, often referred to as pyrogenic organic matter (PyOM), is present in the Earth's soil, sediment, atmosphere, and water. We investigated interactions of PyOM with ammonia (NH) gas, which makes up much of the Earth's reactive nitrogen (N) pool. Here we show that PyOM's NH retention capacity under ambient conditions can exceed 180 mg N g PyOM-carbon, resulting in a material with a higher N content than any unprocessed plant material and most animal manures.

Manganese-Driven Carbon Oxidation at Oxic-Anoxic Interfaces.

The formation of reactive manganese (Mn) species is emerging as a key regulator of carbon oxidation rates, and thus CO emissions, in soils and sediments. Many subsurface environments are characterized by steep oxygen gradients, forming oxic-anoxic interfaces that enable rapid redox cycling of Mn. Here, we examined the impact of Mn(II) oxidation along oxic-anoxic interfaces on carbon oxidation in soils using laboratory-based diffusion reactors.

Golden single-atomic-site platinum electrocatalysts.

Bimetallic nanoparticles with tailored structures constitute a desirable model system for catalysts, as crucial factors such as geometric and electronic effects can be readily controlled by tailoring the structure and alloy bonding of the catalytic site. Here we report a facile colloidal method to prepare a series of platinum-gold (PtAu) nanoparticles with tailored surface structures and particle diameters on the order of 7 nm. Samples with low Pt content, particularly PtAu, exhibited unprecedented electrocatalytic activity for the oxidation of formic acid.

Theory-driven design of high-valence metal sites for water oxidation confirmed using in situ soft X-ray absorption.

The efficiency with which renewable fuels and feedstocks are synthesized from electrical sources is limited at present by the sluggish oxygen evolution reaction (OER) in pH-neutral media. We took the view that generating transition-metal sites with high valence at low applied bias should improve the activity of neutral OER catalysts. Here, using density functional theory, we find that the formation energy of desired Ni sites is systematically modulated by incorporating judicious combinations of Co, Fe and non-metal P.

Retention Mechanisms of Citric Acid in Ternary Kaolinite-Fe(III)-Citrate Acid Systems Using Fe K-edge EXAFS and L3,2-edge XANES Spectroscopy.

Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling.

Homogeneously dispersed multimetal oxygen-evolving catalysts.

Earth-abundant first-row (3d) transition metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution.

Validating the scalability of soft X-ray spectromicroscopy for quantitative soil ecology and biogeochemistry research.

Synchrotron-based soft-X-ray scanning transmission X-ray microscopy (STXM) has the potential to provide nanoscale resolution of the associations among biological and geological materials. However, standard methods for how samples should be prepared, measured, and analyzed to allow the results from these nanoscale imaging and spectroscopic tools to be scaled to field scale biogeochemical results are not well established. We utilized a simple sample preparation technique that allows one to assess detailed mineral, metal, and microbe spectroscopic information at the nano- and microscale in soil colloids.

Observation of the origin of d0 magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques.

Efforts have been made to elucidate the origin of d(0) magnetism in ZnO nanocactuses (NCs) and nanowires (NWs) using X-ray-based microscopic and spectroscopic techniques. The photoluminescence and O K-edge and Zn L3,2-edge X-ray-excited optical luminescence spectra showed that ZnO NCs contain more defects than NWs do and that in ZnO NCs, more defects are present at the O sites than at the Zn sites. Specifically, the results of O K-edge scanning transmission X-ray microscopy (STXM) and the corresponding X-ray-absorption near-edge structure (XANES) spectroscopy demonstrated that the impurity (non-stoichiometric) region in ZnO NCs contains a greater defect population than the thick region.

Fe-N bonding in a carbon nanotube-graphene complex for oxygen reduction: an XAS study.

The electronic structure study of carbon nanotube-graphene complexes has been performed using comprehensive X-ray absorption spectroscopy (XAS) at Fe L- and K-edges, along with C, N and O K-edges. The results obtained from the study of an iron-containing carbon nanotube-graphene complex (NT-G) have been compared in great detail with those of an iron-free carbon nanotube-graphene complex (pNT-G) and iron phthalocyanine (FePc). It has been confirmed that complex-like Fe(3+) in a high spin state is the major iron component in NT-G.

Aqueous Cu(II)-organic complexation studied in situ using soft X-ray and vibrational spectroscopies.

In situ aqueous solutions containing copper-ligand mixtures were measured at the Cu L-edge using X-ray absorption near edge structure (XANES) and with attenuated total reflectance infrared (ATR-FTIR) spectroscopies. Copper complexation with environmentally relevant ligands such as EDTA, citrate, and malate provided a bridge between spectroscopic studies and general environmental behavior and will allow for future study of complex environmental samples. XANES results show that the lowest unoccupied molecular orbital (LUMO) energy is governed by the ligand field strength and is related to Lewis acid/base properties of the ligand functional groups.

Speciation and distribution of copper in a mining soil using multiple synchrotron-based bulk and microscopic techniques.

Molecular-level understanding of soil Cu speciation and distribution assists in management of Cu contamination in mining sites. In this study, one soil sample, collected from a mining site contaminated since 1950s, was characterized complementarily by multiple synchrotron-based bulk and spatially resolved techniques for the speciation and distribution of Cu as well as other related elements (Fe, Ca, Mn, K, Al, and Si). Bulk X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that soil Cu was predominantly associated with Fe oxides instead of soil organic matter.

An advanced Ni-Fe layered double hydroxide electrocatalyst for water oxidation.

Highly active, durable, and cost-effective electrocatalysts for water oxidation to evolve oxygen gas hold a key to a range of renewable energy solutions, including water-splitting and rechargeable metal-air batteries. Here, we report the synthesis of ultrathin nickel-iron layered double hydroxide (NiFe-LDH) nanoplates on mildly oxidized multiwalled carbon nanotubes (CNTs). Incorporation of Fe into the nickel hydroxide induced the formation of NiFe-LDH.

Imaging state of charge and its correlation to interaction variation in an LiMn(0.75)Fe(0.25)PO(4) nanorods-graphene hybrid.

Visualization of the state of charge (SOC) in an LiMn(0.75)Fe(0.25)PO(4) nanorods-graphene hybrid nanostructure (LMFP-C) is realized by chemical mapping of the Fe valance state using scanning transmission X-ray microscopy (STXM).

Oxygen reduction electrocatalyst based on strongly coupled cobalt oxide nanocrystals and carbon nanotubes.

Electrocatalyst for oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and energy-intensive industries. The design and synthesis of highly active ORR catalysts with strong durability at low cost is extremely desirable but remains challenging. Here, we used a simple two-step method to synthesize cobalt oxide/carbon nanotube (CNT) strongly coupled hybrid as efficient ORR catalyst by directly growing nanocrystals on oxidized multiwalled CNTs.

An ultrafast nickel-iron battery from strongly coupled inorganic nanoparticle/nanocarbon hybrid materials.

Ultrafast rechargeable batteries made from low-cost and abundant electrode materials operating in safe aqueous electrolytes could be attractive for electrochemical energy storage. If both high specific power and energy are achieved, such batteries would be useful for power quality applications such as to assist propelling electric vehicles that require fast acceleration and intense braking. Here we develop a new type of Ni-Fe battery by employing novel inorganic nanoparticle/graphitic nanocarbon (carbon nanotubes and graphene) hybrid materials as electrode materials.

Spectroscopic understanding of ultra-high rate performance for LiMn(0.75)Fe(0.25)PO4 nanorods-graphene hybrid in lithium ion battery.

Comprehensive X-ray absorption near-edge structure spectroscopy at the C, O and Li K-edges and the Mn, Fe, and P L-edges of LiMn(0.75)Fe(0.25)PO(4) nanorods-graphene has been reported in great detail.