Tuning Crystal Phase of Palladium-Selenium Nanowires for Enhanced Ethylene Glycol Electrocatalytic Oxidation.

Alcohol electrooxidation is pivotal for a sustainable energy economy. However, designing efficient electrocatalysts for this process is still a formidable challenge. Herein, palladium-selenium nanowires featuring distinct crystal phases: monoclinic Pd7Se2 and tetragonal Pd4.5Se for ethylene glycol electrooxidation reaction (EGOR) are synthesized. Notably, the supported monoclinic Pd7Se2 nanowires (m-Pd7Se2 NWs/C) exhibit superior EGOR activity, achieving a mass activity (MA) and specific activity (SA) of 10.4 A mgPd -1 (18.7 mA cm-2), which are 8.0 (6.7) and 10.4 (8.2) times versus the tetragonal Pd4.5Se and commercial Pd/C and surpass those reported in the literature. Furthermore, m-Pd7Se2 NWs/C displays robust catalytic activity for other alcohol electrooxidation. Comprehensive characterization and density functional theory (DFT) calculations reveal that the enhanced electrocatalytic performance is attributed to the increased formation of Pd0 on the high-index facets of the m-Pd7Se2 NWs, which lowers the energy barriers for the C─C bond dissociation in CHOHCHOH* and the CO* oxidation to CO2*. This study provides palladium-based alloy electrocatalysts exhibiting the highest mass activity reported to date for the electrooxidation of ethylene glycol, achieved through the crystalline phase engineering strategy.

Elemental Sulfur and Organic Matter Amendment Drive Alkaline pH Neutralization and Mineral Weathering in Iron Ore Tailings Through Inducing Sulfur Oxidizing Bacteria.

Mineral weathering and alkaline pH neutralization are prerequisites to the ecoengineering of alkaline Fe-ore tailings into soil-like growth media (i.e., Technosols). These processes can be accelerated by the growth and physiological functions of tolerant sulfur oxidizing bacteria (SOB) in tailings. The present study characterized an indigenous SOB community enriched in the tailings, in response to the addition of elemental sulfur (S0) and organic matter (OM), as well as resultant S0oxidation, pH neutralization, and mineral weathering in a glasshouse experiment. The addition of S0 was found to have stimulated the growth of indigenous SOB, such as acidophilic Alicyclobacillaceae, Bacillaceae, and Hydrogenophilaceae in tailings. The OM amendment favored the growth of heterotrophic/mixotrophic SOB (e.g., class Alphaproteobacteria and Gammaproteobacteria). The resultant S0 oxidation neutralized the alkaline pH and enhanced the weathering of biotite-like minerals and formation of secondary minerals, such as ferrihydrite- and jarosite-like minerals. The improved physicochemical properties and secondary mineral formation facilitated organo-mineral associations that are critical to soil aggregate formation. From these findings, co-amendments of S0 and plant biomass (OM) can be applied to enhance the abundance of the indigenous SOB community in tailings and accelerate mineral weathering and geochemical changes for eco-engineered soil formation, as a sustainable option for rehabilitation of Fe ore tailings.

Arbuscular Mycorrhizal Fungi Drive Organo-Mineral Association in Iron Ore Tailings: Unravelling Microstructure at the Submicron Scale by Synchrotron-Based FTIR and STXM-NEXAFS.

Arbuscular mycorrhizal (AM) fungi play an important role in organic matter (OM) stabilization in Fe ore tailings for eco-engineered soil formation. However, little has been understood about the AM fungi-derived organic signature and organo-mineral interactions in situ at the submicron scale. In this study, a compartmentalized cultivation system was used to investigate the role of AM fungi in OM formation and stabilization in tailings. Particularly, microspectroscopic analyses including synchrotron-based transmission Fourier transform infrared (FTIR) and scanning transmission X-ray microspectroscopy combined with near-edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS) were employed to characterize the chemical signatures at the AM fungal-mineral and mineral-OM interfaces at the submicron scale. The results indicated that AM fungal mycelia developed well in the tailings and entangled mineral particles for aggregation. AM fungal colonization enhanced N-rich OM stabilization through organo-mineral association. Bulk spectroscopic analysis together with FTIR mapping revealed that fungi-derived lipids, proteins, and carbohydrates were associated with Fe/Si minerals. Furthermore, STXM-NEXAFS analysis revealed that AM fungi-derived aromatic, aliphatic, and carboxylic/amide compounds were heterogeneously distributed and trapped by Fe(II)/Fe(III)-bearing minerals originating from biotite-like minerals weathering. These findings imply that AM fungi can stimulate mineral weathering and provide organic substances to associate with minerals, contributing to OM stabilization and aggregate formation as key processes for eco-engineered soil formation in tailings.

Ligand Control of Dinitrosyl Iron Complexes for Selective Superoxide-Mediated Nitric Oxide Monooxygenation and Superoxide-Dioxygen Interconversion.

Through nitrosylation of [Fe-S] proteins, or the chelatable iron pool, a dinitrosyl iron unit (DNIU) [Fe(NO)2] embedded in the form of low-molecular-weight/protein-bound dinitrosyl iron complexes (DNICs) was discovered as a metallocofactor assembled under inflammatory conditions with elevated levels of nitric oxide (NO) and superoxide (O2-). In an attempt to gain biomimetic insights into the unexplored transformations of the DNIU under inflammation, we investigated the reactivity toward O2- by a series of DNICs [(NO)2Fe(µ-MePyr)2Fe(NO)2] (1) and [(NO)2Fe(µ-SEt)2Fe(NO)2] (3). During the superoxide-induced conversion of DNIC 1 into DNIC [(K-18-crown-6-ether)2(NO2)][Fe(µ-MePyr)4(µ-O)2(Fe(NO)2)4] (2-K-crown) and a [Fe3+(MePyr)x(NO2)y(O)z]n adduct, stoichiometric NO monooxygenation yielding NO2- occurs without the transient formation of peroxynitrite-derived •OH/•NO2 species. To study the isoelectronic reaction of O2(g) and one-electron-reduced DNIC 1, a DNIC featuring an electronically localized {Fe(NO)2}9-{Fe(NO)2}10 electronic structure, [K-18-crown-6-ether][(NO)2Fe(µ-MePyr)2Fe(NO)2] (1-red), was successfully synthesized and characterized. Oxygenation of DNIC 1-red leads to the similar assembly of DNIC 2-K-crown, of which the electronic structure is best described as paramagnetic with weak antiferromagnetic coupling among the four S = 1/2 {FeIII(NO-)2}9 units and S = 5/2 Fe3+ center. In contrast to DNICs 1 and 1-red, DNICs 3 and [K-18-crown-6-ether][(NO)2Fe(µ-SEt)2Fe(NO)2] (3-red) display a reversible equilibrium of "3 + O2- ⇋ 3-red + O2(g)", which is ascribed to the covalent [Fe(µ-SEt)2Fe] core and redox-active [Fe(NO)2] unit. Based on this study, the supporting/bridging ligands in dinuclear DNIC 1/3 (or 1-red/3-red) control the selective monooxygenation of NO and redox interconversion between O2- and O2 during reaction with O2- (or O2).

Nitrogen-Rich Organic Matter Formation and Stabilization in Iron Ore Tailings: A Submicrometer Investigation.

Organic matter (OM) formation and stabilization are critical processes in the eco-engineered pedogenesis of Fe ore tailings, but the underlying mechanisms are unclear. The present 12 month microcosm study has adopted nanoscale secondary ion mass spectrometry (NanoSIMS) and synchrotron-based scanning transmission X-ray microscopy (STXM) techniques to investigate OM formation, molecular signature, and stabilization in tailings at micro- and nanometer scales. In this system, microbial processing of exogenous isotopically labeled OM demonstrated that 13C labeled glucose and 13C/15N labeled plant biomass were decomposed, regenerated, and associated with Fe-rich minerals in a heterogeneous pattern in tailings. Particularly, when tailings were amended with plant biomass, the 15N-rich microbially derived OM was generated and bound to minerals to form an internal organo-mineral association, facilitating further OM stabilization. The organo-mineral associations were primarily underpinned by interactions of carboxyl, amide, aromatic, and/or aliphatic groups with weathered mineral products derived from biotite-like minerals in fresh tailings (i.e., with Fe2+ and Fe3+) or with Fe3+ oxyhydroxides in aged tailings. The study revealed microbial OM generation and subsequent organo-mineral association in Fe ore tailings at the submicrometer scale during early stages of eco-engineered pedogenesis, providing a basis for the development of microbial based technologies toward tailings' ecological rehabilitation.

Ecological engineering of iron ore tailings into useable soils for sustainable rehabilitation.

Ecological engineering of soil formation in tailings is an emerging technology toward sustainable rehabilitation of iron (Fe) ore tailings landscapes worldwide, which requires the formation of well-organized and stable soil aggregates in finely textured tailings. Here, we demonstrate an approach using microbial and rhizosphere processes to progressively drive aggregate formation and development in Fe ore tailings. The aggregates were initially formed through the agglomeration of mineral particles by organic cements derived from microbial decomposition of exogenous organic matter. The aggregate stability was consolidated by colloidal nanosized Fe(III)-Si minerals formed during Fe-bearing primary mineral weathering driven by rhizosphere biogeochemical processes of pioneer plants. From these findings, we proposed a conceptual model for progressive aggregate structure development in the tailings with Fe(III)-Si rich cements as core nuclei. This renewable resource dependent eco-engineering approach opens a sustainable pathway to achieve resilient tailings rehabilitation without resorting to excavating natural soil resources.

Mineral weathering of iron ore tailings primed by Acidithiobacillus ferrooxidans and elemental sulfur under contrasting pH conditions.

The acidophilic sulfur oxidizing bacterium (SOB), Acidithiobacillus ferrooxidans, has been found to stimulate elemental sulfur (S0) oxidation and mineral weathering in alkaline Fe ore tailings. However, A. ferrooxidans growth and activities depend on the pH conditions surrounding their interfaces with minerals. The present study aimed to investigate how pH influences bacterial growth and functions in Fe ore tailings. A simulated aquatic 'homogeneous' incubation system was initially adjusted into acidic (pH 4), neutral (pH 7) and alkaline (pH 9) conditions, which mimicked the microenvironmental conditions of the water-cell-mineral interfaces in the tailings. It was found that A. ferrooxidans grew well and oxidised S0 under the prevailing and initially acidic conditions (pH < 6). These stimulated the weathering of biotite and amphibole-like minerals and the formation of nanosized jarosite and ferrihydrite-like minerals mediated by extracellular polymer substrate (EPS). In contrast, the initially neutral/alkaline pH conditions (i.e., pH > 7) with the presence of the alkaline tailings restricted SOB growth and functions in S0-oxidation and mineral weathering. These findings suggest that it is essential to prime acidic conditions in microenvironments to support SOB growth, activities, and functions toward mineral weathering in tailings, providing critical basis for involving SOB in eco-engineered pedogenesis in tailings.

The synergetic effect of a gold nanocluster-calcium phosphate composite: enhanced photoluminescence intensity and superior bioactivity.

Gold nanoclusters (AuNCs) are a unique class of materials that exhibit visible luminescence. Amorphous calcium phosphate (ACP) is a widely used biomaterial for a variety of purposes, such as drug delivery, bone cementing, and implant coatings. In this study, a nanocomposite of AuNCs and ACP is prepared by biomimetic mineralization in a Dulbecco's modified Eagle's medium (DMEM). The strong interaction between AuNCs and Ca2+ ions effectively induces aggregation of AuNCs. The as-formed nanocomposite, AuNCs@ACP, emits significantly enhanced luminescence compared to AuNCs alone. The luminescence enhancement mechanism is investigated using synchrotron X-ray absorption fine structure spectroscopy. In addition, the presence of AuNCs stabilizes ACP and also enhances the biocompatibility of ACP in promoting cell proliferation, and the nanocomposites are promising as nanoprobes for cancer therapy and/or bone tissue engineering.

Attenuating metal-substrate conjugation in atomically dispersed nickel catalysts for electroreduction of CO2 to CO.

Atomically dispersed transition metals on carbon-based aromatic substrates are an emerging class of electrocatalysts for the electroreduction of CO2. However, electron delocalization of the metal site with the carbon support via d-π conjugation strongly hinders CO2 activation at the active metal centers. Herein, we introduce a strategy to attenuate the d-π conjugation at single Ni atomic sites by functionalizing the support with cyano moieties. In situ attenuated total reflection infrared spectroscopy and theoretical calculations demonstrate that this strategy increases the electron density around the metal centers and facilitates CO2 activation. As a result, for the electroreduction of CO2 to CO in aqueous KHCO3 electrolyte, the cyano-modified catalyst exhibits a turnover frequency of ~22,000 per hour at -1.178 V versus the reversible hydrogen electrode (RHE) and maintains a Faradaic efficiency (FE) above 90% even with a CO2 concentration of only 30% in an H-type cell. In a flow cell under pure CO2 at -0.93 V versus RHE the cyano-modified catalyst enables a current density of -300 mA/cm2 with a FE above 90%.

Anionic Redox Activities Boosted by Aluminum Doping in Layered Sodium-Ion Battery Electrode.

Sodium-ion batteries (SIBs) have attracted widespread attention for large-scale energy storage, but one major drawback, i.e., the limited capacity of cathode materials, impedes their practical applications. Oxygen redox reactions in layered oxide cathodes are proven to contribute additionally high specific capacity, while such cathodes often suffer from irreversible structural transitions, causing serious capacity fading and voltage decay upon cycling, and the formation process of the oxidized oxygen species remains elusive. Herein, a series of Al-doped P2-type Na0.6 Ni0.3 Mn0.7 O2 cathode materials for SIBs are reported and the corresponding charge compensation mechanisms are investigated qualitatively and quantitatively. The combined analyses reveal that Al doping boosts the reversible oxygen redox reactions through the reductive coupling reactions between orphaned O 2p states in NaOAl local configurations and Ni4+ ions, as directly evidenced by X-ray absorption fine structure results. Additionally, Al doping also induces an increased interlayer spacing and inhibits the unfavorable P2 to O2 phase transition upon desodiation/sodiation, which is common in P2-type Mn-based cathode materials, leading to the great improvement in capacity retention and rate capability. This work provides deeper insights into the development of structurally stable and high-capacity layered cathode materials for SIBs with anion-cation synergetic contributions.

Endogenous Conjugation of Biomimetic Dinitrosyl Iron Complex with Protein Vehicles for Oral Delivery of Nitric Oxide to Brain and Activation of Hippocampal Neurogenesis.

Nitric oxide (NO), a pro-neurogenic and antineuroinflammatory gasotransmitter, features the potential to develop a translational medicine against neuropathological conditions. Despite the extensive efforts made on the controlled delivery of therapeutic NO, however, an orally active NO prodrug for a treatment of chronic neuropathy was not reported yet. Inspired by the natural dinitrosyl iron unit (DNIU) [Fe(NO)2], in this study, a reversible and dynamic interaction between the biomimetic [(NO)2Fe(µ-SCH2CH2OH)2Fe(NO)2] (DNIC-1) and serum albumin (or gastrointestinal mucin) was explored to discover endogenous proteins as a vehicle for an oral delivery of NO to the brain after an oral administration of DNIC-1. On the basis of the in vitro and in vivo study, a rapid binding of DNIC-1 toward gastrointestinal mucin yielding the mucin-bound dinitrosyl iron complex (DNIC) discovers the mucoadhesive nature of DNIC-1. A reversible interconversion between mucin-bound DNIC and DNIC-1 facilitates the mucus-penetrating migration of DNIC-1 shielded in the gastrointestinal tract of the stomach and small intestine. Moreover, the NO-release reactivity of DNIC-1 induces the transient opening of the cellular tight junction and enhances its paracellular permeability across the intestinal epithelial barrier. During circulation in the bloodstream, a stoichiometric binding of DNIC-1 to the serum albumin, as another endogenous protein vehicle, stabilizes the DNIU [Fe(NO)2] for a subsequent transfer into the brain. With aging mice under a Western diet as a disease model for metabolic syndrome and cognitive impairment, an oral administration of DNIC-1 in a daily manner for 16 weeks activates the hippocampal neurogenesis and ameliorates the impaired cognitive ability. Taken together, these findings disclose the synergy between biomimetic DNIC-1 and endogenous protein vehicles for an oral delivery of therapeutic NO to the brain against chronic neuropathy.

Acidophilic Iron- and Sulfur-Oxidizing Bacteria, Acidithiobacillus ferrooxidans, Drives Alkaline pH Neutralization and Mineral Weathering in Fe Ore Tailings.

The neutralization of strongly alkaline pH conditions and acceleration of mineral weathering in alkaline Fe ore tailings have been identified as key prerequisites for eco-engineering tailings-soil formation for sustainable mine site rehabilitation. Acidithiobacillus ferrooxidans has great potential in neutralizing alkaline pH and accelerating primary mineral weathering in the tailings but little information is available. This study aimed to investigate the colonization of A. ferrooxidans in alkaline Fe ore tailings and its role in elemental sulfur (S0) oxidation, tailings neutralization, and Fe-bearing mineral weathering through a microcosm experiment. The effects of biological S0 oxidation on the weathering of alkaline Fe ore tailings were examined via various microspectroscopic analyses. It is found that (1) the A. ferrooxidans inoculum combined with the S0 amendment rapidly neutralized the alkaline Fe ore tailings; (2) A. ferrooxidans activities induced Fe-bearing primary mineral (e.g., biotite) weathering and secondary mineral (e.g., ferrihydrite and jarosite) formation; and (3) the association between bacterial cells and tailings minerals were likely facilitated by extracellular polymeric substances (EPS). The behavior and biogeochemical functionality of A. ferrooxidans in the tailings provide a fundamental basis for developing microbial-based technologies toward eco-engineering soil formation in Fe ore tailings.

Iron phthalocyanine with coordination induced electronic localization to boost oxygen reduction reaction.

Iron phthalocyanine (FePc) is a promising non-precious catalyst for the oxygen reduction reaction (ORR). Unfortunately, FePc with plane-symmetric FeN4 site usually exhibits an unsatisfactory ORR activity due to its poor O2 adsorption and activation. Here, we report an axial Fe-O coordination induced electronic localization strategy to improve its O2 adsorption, activation and thus the ORR performance. Theoretical calculations indicate that the Fe-O coordination evokes the electronic localization among the axial direction of O-FeN4 sites to enhance O2 adsorption and activation. To realize this speculation, FePc is coordinated with an oxidized carbon. Synchrotron X-ray absorption and Mössbauer spectra validate Fe-O coordination between FePc and carbon. The obtained catalyst exhibits fast kinetics for O2 adsorption and activation with an ultralow Tafel slope of 27.5 mV dec-1 and a remarkable half-wave potential of 0.90 V. This work offers a new strategy to regulate catalytic sites for better performance.

Rhizosphere modifications of iron-rich minerals and forms of heavy metals encapsulated in sulfidic tailings hardpan.

Hardpan caps formed after extensive weathering of the top layer of sulfidic tailings have been advocated to serve as physical barriers separating reactive tailings in depth and root zones above. However, in a hardpan-based root zone reconstructed with the soil cover, roots growing into contact with hardpan surfaces may induce the transformation of Fe-rich minerals and release potentially toxic elements for plant uptake. For evaluating this potential risk, two representative native species, Turpentine bush (Acacia chisholmii, AC) and Red Flinders grass (Iseilema vaginiflorum, RF), of which pre-cultured root mats were interfaced with thin discs of crushed hardpan minerals in the rhizosphere (RHIZO) test. After 35 days, the surface dissolution of hardpan minerals occurred and Fe-rich cement minerals were transformed from ferrihydrite-like minerals to goethite-like and Fe(III)-carboxylic complexes, as revealed by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and synchrotron-based X-ray absorption fine structure spectroscopy (XAFS) analysis. This transformation may result from the functions of root exudates. The transformation of hardpan cement minerals caused the co-dissolution of Cu and Zn initially encapsulated in the cements and their uptake by plants. Nevertheless, only was the minority of the plant Cu and Zn transported into shoots.

Geochemical and mineralogical constraints in iron ore tailings limit soil formation for direct phytostabilization.

The present study aimed to characterize key physico-chemical and mineralogical attributes of magnetite iron (Fe) ore tailings to identify potential constraints limiting in situ soil formation and direct phytostabilization. Tailings of different age, together with undisturbed local native soils, were sampled from a magnetite mine in Western Australia. Tailings were extremely alkaline (pH > 9.0), with a lack of water stable aggregate and organic matter, and contained abundant primary minerals including mica (e.g., biotite), with low specific surface area (N2-BET around 1.2 m2 g-1). These conditions remained relatively unchanged after four years' aging under field conditions. Chemical extraction and spectroscopic analysis [e.g., X-ray diffraction (XRD) and synchrotron-based Fe K edge X-ray absorption fine structure spectroscopy (XAFS) analysis] revealed that the aging process decreased biotite-like minerals, but increased hematite and magnetite in the tailings. However, the aged tailings lacked goethite, a compound abundant in natural soils. Examination using backscattered-scanning electron microscope - energy dispersive X-ray spectrometry (BSE-SEM-EDS) revealed that aged tailings contained discrete sharp edged Fe-bearing minerals that did not physically integrate with other minerals (e.g., Si/Al bearing minerals). In contrast, Fe minerals in native soils appeared randomly distributed and closely amassed with Si/Al rich phyllosilicates, with highly eroded edges. The lack of labile organic matter and the persistence of alkaline-saline conditions may have significantly hindered the bioweathering of Fe-minerals and the biogenic formation of secondary Fe-minerals in tailings. However, there is signature that a native pioneer plant, Maireana brevifolia can facilitate the bioweathering of Fe-bearing minerals in tailings. We propose that eco-engineering inputs like organic carbon accumulation, together with the introduction of functional microbes and pioneer plants, should be adopted to accelerate bioweathering of Fe-bearing minerals as a priority for initiating in situ soil formation in the Fe ore tailings.

Ruthenium-functionalized nickel hydroxide catalyst for highly efficient alcohol oxidations in the presence of molecular oxygen.

Ru/Ni(OH)(2) composite, prepared by simple wetness impregnation method, has demonstrated highly efficient alcohol oxidation reaction in the presence of molecular oxygen at T = 363 K with good selectivity (>99%) and excellent reaction yield (TOF approximately 132 h(-1)).