Related Redox Research Articles

Carbonyl Chemistry for Advanced Electrochemical Energy Storage Systems.

On the basis of the sustainable concept, organic compounds and carbon materials both mainly composed of light C element have been regarded as powerful candidates for advanced electrochemical energy storage (EES) systems, due to theie merits of low cost, eco-friendliness, renewability, and structural versatility. It is investigated that the carbonyl functionality as the most common constituent part serves a crucial role, which manifests respective different mechanisms in the various aspects of EES systems. Notably, a systematical review about the concept and progress for carbonyl chemistry is beneficial for ensuring in-depth comprehending of carbonyl functionality. Hence, a comprehensive review about carbonyl chemistry has been summarized based on state-of-the-art developments. Moreover, the working principles and fundamental properties of the carbonyl unit have been discussed, which has been generalized in three aspects, including redox activity, the interaction effect, and compensation characteristic. Meanwhile, the pivotal characterization technologies have also been illustrated for purposefully studying the related structure, redox mechanism, and electrochemical performance to profitably understand the carbonyl chemistry. Finally, the current challenges and promising directions are concluded, aiming to afford significant guidance for the optimal utilization of carbonyl moiety and propel practicality in EES systems.

Review of soil form and wetness indicators for wetland delineation in South Africa

Wetland delineation in South Africa incorporates soil form and soil wetness indicators, requiring formal soil classification and description of soil redox morphology. The current wetland definition used administratively in South Africa focuses on saturated (hydric) soil signatures within plant root zones. Saturated soil horizons deeper than plant root zones fall outside the 50 cm criterion in the local approach as well as the accepted zone in USA literature. The field of hydropedology accommodates the classification of the various hydrologically active horizons and provides a tool for the handling of horizons with ephemeral wetness. This approach has been variably accepted by mandated authorities in South Africa. The South African soil classification system has evolved through three editions over the past 50 years while retaining the same redox morphology understanding. However, despite the concepts and context of redox morphology having been thoroughly technically adopted by soil scientists, this is not the case within the wetland research and management environment. This especially because the classification system is structured differently from other international systems, and the South African landscape is geologically ancient with mature soils, introducing challenges to resource assessment specialists who rely on international norms and approaches for wetland assessment. This paper reviews the various components of soil classification and redox morphology based on Fe and Mn minerals within the context of the South African soil classification system, the field of hydropedology and wetland delineation indicators. We provide a qualitative correlation between the various diagnostic horizons and materials in the system and their related redox morphology contexts that are relevant to wetland assessment, delineation, and protection in South Africa. This paper therefore aims to serve as a reference point for the description and correlation of various soil hydrological parameters used in formal assessments.

Molecular interaction mechanisms and cellular response of superoxide dismutase and catalase to fluoranthene.

As an important raw material and intermediate product of the petrochemical industry, fluoranthene (Fla) can be emitted with industrial activities and has become a typical polycyclic aromatic hydrocarbon enriched in the Chinese topsoil layer, posing a significant threat to sensitive soil biota. Here, multispectral tools and molecular simulation techniques were integrated to elucidate the molecular mechanism of Fla interaction with key antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) at the molecular level. Meanwhile, we further revealed the cellular responses of SOD and CAT and the associated redox states in earthworm (Eisenia fetida) coelomocytes based on the molecular-level results. Our results showed that the exposure to Fla affected the backbone structure of SOD and CAT molecules and resulted in the formation of Fla-SOD polymers as well as an overall reduction in the size of the Fla-CAT binding system. Fla altered the microenvironment around Tyr residues in the SOD molecule and quenched the endogenous fluorescence of Tyr within the CAT molecule. In earthworm coelomocytes, Fla at 60 and 80 μM resulted in a significant elevation of CAT and SOD activities by 114% (p = 0.032) and 6.09% (p = 0.013), respectively. Molecular simulation results suggested that Fla-induced changes in the structure and conformation of SOD and CAT may be the key reason for their altered activities. The related redox homeostasis detection in earthworm coelomocytes indicated that high concentrations (80 μM) of Fla led to a significant accumulation of intracellular ROS (p = 0.018) and resulted in the development of lipid peroxidation. Our work contributes to an in-depth understanding of the biological effect of Fla to sensitive soil fauna, thus providing new ideas for Fla ecological risk prevention and control.

Resonance Raman spectra and excited state properties of methyl viologen and its radical cation from time-dependent density functional theory.

Time-dependent density functional theory (TDDFT) was applied to gain insights into the electronic and vibrational spectroscopic properties of an important electron transport mediator, methyl viologen (MV2+ ). An organic dication, MV2+ has numerous applications in electrochemistry that include energy conversion and storage, environmental remediation, and chemical sensing and electrosynthesis. MV2+ is easily reduced by a single electron transfer to form a radical cation species (MV•+ ), which has an intense UV-visible absorption near 600 nm. The redox properties of the MV2+ /MV•+ couple and light-sensitivity of MV•+ have made the system appealing for photo-electrochemical energy conversion (e.g., solar hydrogen generation from water) and the study of photo-induced charge transfer processes through electronic absorption and resonance Raman spectroscopic measurements. The reported work applies leading TDDFT approaches to investigate the electronic and vibrational spectroscopic properties of MV2+ and MV•+ . Using a conventional hybrid exchange functional (B3-LYP) and a long-range corrected hybrid exchange functional (ωB97X-D3), including with a conductor-like polarizable continuum model to account for solvation, the electronic absorption and resonance Raman spectra predicted are in good agreement with experiment. Also analyzed are the charge transfer character and natural transition orbitals derived from the TDDFT vertical excitations calculated. The findings and models developed further the understanding of the electronic properties of viologens and related organic redox mediators important in renewable energy applications and serve as a reference for guiding the interpretation of electronic absorption and Raman spectra of the ions.

Tissue-preferential recruitment of electron transfer chains for cytochrome P450-catalyzed phenolic biosynthesis.

Cytochrome P450 system consists of P450 monooxygenase and redox pattern(s). While the importance of monooxygenases in plant metabolism is well documented, the metabolic roles of the related redox components have been largely overlooked. Here, we show that distinct electron transfer chains are recruited in phenylpropanoid-monolignol P450 systems to support the synthesis and distribution of different classes of phenolics in different plant tissues. While Arabidopsis cinnamate 4-hydroxylase adopts conventional NADPH-cytochrome P450 oxidoreductase (CPR) electron transfer chain for its para-hydroxylation reaction, ferulate 5-hydroxylase uses both NADPH-CPR-cytochrome b5 (CB5) and NADH-cytochrome b5 reductase-CB5 chains to support benzene ring 5-hydroxylation, in which the former route is primarily recruited in the stem for syringyl lignin synthesis, while the latter dominates in the syntheses of 5-hydroxylated phenolics in seeds and seed coat suberin. Our study unveils an additional layer of complexity and versatility of P450 system that the plants evolved for diversifying phenolic repertoires.

Fundamentals of energy storage from first principles simulations: Challenges and opportunities

Efficient electrochemical energy storage and conversion require high performance electrodes, electrolyte or catalyst materials. In this contribution we discuss the simulation-based effort made by Institute of Energy and Climate Research at Forschungszentrum Jülich (IEK-13) and partner institutions aimed at improvement of computational methodologies and providing molecular level understanding of energy materials. We focus on discussing correct computation of electronic structure, oxidation states and related redox reactions, phase transformation in doped oxides and challenges in computation of surface chemical reactions on oxides and metal surfaces in presence of electrolyte. Particularly, in the scope of this contribution we present new simulated data on Ni/Co and Am/U-bearing oxides, and Pb, Au and Ag metal surface materials. The computed results are combined with the available experimental data for thoughtful analysis of the computational methods performance.

Hydrogen-Bonded Organic Framework for High-Performance Lithium/Sodium-Iodine Organic Batteries.

The rechargeable lithium/sodium-iodine battery (Li/Na-I2 ) is a promising candidate for meeting the growing energy demand. Herein, a flexible hydrogen-bonded organic framework (HOF) linked to the Ti3 C2 Tx MXene complex (HOF@Ti3 C2 Tx ) has been presented for iodine loading. HOF is self-assembled by organic monomers through hydrogen bonding interactions between each monomer. It leads to numerous cavities in HOF structure, which can encapsulate iodine through various adsorptive sites and intermolecular interactions. The unique structure of complex can accelerate the nucleation of iodine, achieve fast reaction kinetics, stabilize iodide and retard the shuttle effect, thus improving the cycling stability of I2 -based batteries. The I2 /HOF@Ti3 C2 Tx exhibits large reversible capacities of 260.2 and 207.6 mAh g-1 at 0.2 C after repeated cycling for Li-I2 and Na-I2 batteries, respectively. This work can gain insights into the HOF-related energy storage application with reversible iodine encapsulation and its related redox reaction mechanisms with Li and Na metal ions.

Hydrogen‐Bonded Organic Framework for High‐Performance Lithium/Sodium‐Iodine Organic Batteries

AbstractThe rechargeable lithium/sodium‐iodine battery (Li/Na‐I2) is a promising candidate for meeting the growing energy demand. Herein, a flexible hydrogen‐bonded organic framework (HOF) linked to the Ti3C2TxMXene complex (HOF@Ti3C2Tx) has been presented for iodine loading. HOF is self‐assembled by organic monomers through hydrogen bonding interactions between each monomer. It leads to numerous cavities in HOF structure, which can encapsulate iodine through various adsorptive sites and intermolecular interactions. The unique structure of complex can accelerate the nucleation of iodine, achieve fast reaction kinetics, stabilize iodide and retard the shuttle effect, thus improving the cycling stability of I2‐based batteries. The I2/HOF@Ti3C2Txexhibits large reversible capacities of 260.2 and 207.6 mAh g−1at 0.2 C after repeated cycling for Li‐I2and Na‐I2batteries, respectively. This work can gain insights into the HOF‐related energy storage application with reversible iodine encapsulation and its related redox reaction mechanisms with Li and Na metal ions.

High-Energy-Density 3.5 V Carbon Supercapacitor Fabricated with Ionic-Liquid-Incorporated Redox-Active Gel Polymer Electrolyte

Introducing redox-active species in the electrolyte component is an effective approach to improving the energy density of carbon supercapacitors via additional pseudocapacitive redox activities at the electrode–electrolyte interfaces. Herein, we report a quasisolid-state supercapacitor fabricated with symmetrical activated carbon electrodes and an ionic liquid (IL, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, BMPTFSI)-incorporated nonaqueous, redox-active gel polymer electrolyte (R-GPE) added with a redox-additive IL (BMPBr), entrapped in a polymer matrix of poly(vinylidene fluoride-co-hexafluoropropylene). The R-GPE film with an optimum composition of an additive (BMPBr) showing a high mechanical stability (tensile strength ∼0.32 MPa and elongation at break ∼154%), a wide thermal stability range (up to ∼385 °C), and excellent electrochemical properties (an ionic conductivity of ∼1.2 × 10–3 S cm–1 at room temperature and an electrochemical stability window of ∼6.5 V) is found as an excellent substitute of liquid electrolytes in supercapacitors. The quasisolid-state supercapacitor is fabricated from biomass (pollen-cone)-derived activated carbon electrodes separated by the R-GPE film and characterized via electrochemical techniques, namely, electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge tests. The Br–-related redox activities at the interfaces lead to a significant improvement in specific capacitance (from ∼164 to ∼248 F g–1), specific energy (from ∼65 to ∼105 W h kg–1), and maximum power (from ∼15 to 31 kW kg–1). With a moderate rate capability, the supercapacitor demonstrates a good cycling performance with an initial ∼23% fading in the specific capacitance and a ∼100% Coulombic efficiency for ∼10 000 charge–discharge cycles.

Close correlation between thiolate basicity and certain NMR parameters in cysteine and cystine microspecies.

The imbalance between prooxidants and antioxidants in biological systems, known as oxidative stress, can lead to a disruption of redox signaling by the reactive oxygen/nitrogen species and is related to severe diseases. The most vulnerable moiety targeted by oxidant species in the redox signaling pathways is the thiol (SH) group in the cysteine residues, especially in its deprotonated (S−) form. Cysteine, along with its oxidized, disulfide-containing form, cystine, constitute one of the most abundant low molecular weight biological redox couples, providing a significant contribution to the redox homeostasis in living systems. In this work, NMR spectra from cysteine, cystine, and cysteine-containing small peptides were thoroughly studied at the submolecular level, and through the chemical shift data set of their certain atoms it is possible to estimate either thiolate basicity or the also related standard redox potential. Regression analysis demonstrated a strong linear relationship for chemical shift vs thiolate logK of the cysteine microspecies data. The αCH 13C chemical shift is the most promising estimator of the acid-base and redox character.

Formation of iron oxyhydroxides as a result of glauconite weathering in soils of temperate climate

The aim of this study was to investigate glauconite weathering in soils of temperate climate, with special attention paid to formation of iron oxyhydroxides at the expense of the glauconite. Five soil profiles developed on parent material in which glauconite was the main (if not the only) phyllosilicate and source of Fe were selected for the study. Basic physical and chemical properties of bulk (<2 mm) soil samples (color, texture, pH, and carbonate and soil organic carbon content) were determined. Clay fractions (<2 µm and <0.2 µm) and green pellets were separated from the studied soils and analyzed using X-ray diffractometry, Fourier-transform infrared spectroscopy, Mössbauer spectroscopy, and inductively coupled plasma - optical emission spectrometry. Thin sections prepared from selected undisturbed soil materials were observed under optical microscope. Three of the soils were acidic with pH ranging from 4.3 to 5.5 and the remaining two were alkaline with pH from 6.8 to 8.6. Parent glauconites from each profile showed quite similar chemical composition, except that in one case Fe(II) was much more abundant than in the others. In both acidic and alkaline soils, glauconite weathering products included Al-smectite-rich glauconite-smectite mixed-layered minerals (G-S), kaolinite, and Fe oxyhydroxides. G-S were likely formed by transformation of glauconite, whereas kaolinite and iron oxyhydroxides (i.e. goethite, lepidocrocite, and perhaps ferrihydrite) crystallized in the studied soils from substances dissolved from parent glauconites. Leaching of Fe and Mg from the glauconite structure and loss of K were indicated. In acidic soils the weathering products concentrated in the clay fractions, whereas in alkaline soils they occurred both in clays and in the glaucony pellets. Mössbauer spectroscopy indicated that fine crystalline and especially nanocrystalline iron oxyhydroxides are substantial products of glauconite weathering in all the studied clays. Formation of the Fe oxyhydroxides was controlled by hydrological conditions (and related redox activity) and by soil pH. Alkaline conditions seemed to favor goethite crystallization, whereas redox activity led to formation of lepidocrocite and likely ferrihydrite. Soil color was mostly controlled by the presence of glauconite. Only the relatively significant lepidocrocite content in a few of the studied soil horizons was marked by brown or rusty colors indicating high redox activity.

Advances in the regulation of kinetics of cathodic H+/Zn2+ interfacial transport in aqueous Zn/MnO2 electrochemistry.

Rechargeable aqueous Zn-MnO2 energy storage systems have attracted extensive attention owing to their high theoretical capacity and non-flammable mild aqueous electrolytes. Nevertheless, the complicated reaction mechanism of a MnO2-based cathode severely restricts its further development. Therefore, it is crucial to clarify the kinetics of H+/Zn2+ interfacial transport in the MnO2 cathode for realizing controllable regulation of interfacial ion transport and then realizing high capacity and long lifespan. Recently, based on different reaction mechanisms, various strategies have been employed to improve the performance of aqueous Zn/MnO2 cells, such as surface modifications and structural engineering. Herein, we systematically summarize the recent advances in the modulation of interfacial H+/Zn2+ transport and related redox kinetics to effectively improve the electrochemical responses. Furthermore, the challenges of designing novel MnO2 cathodes have also been prospected in detail to provide possible guidelines for the development of Zn/MnO2 batteries.

Simultaneously achieving fast sulfur redox kinetics and high-loading in lithium–sulfur batteries

For lithium-sulfur batteries (LSBs), searching for highly efficient host that allows for high sulfur loading and excellent lithium polysulfides (LiPSs) trapping capability is extremely important. Herein, a systematical study with regard to both experimental and theoretical of N/S heteroatoms co-doped polar surface (denoted as NSHC) is conducted to demonstrate the significance of rational structure design as well as rapid sulfur related redox kinetics for high loading cathode. With prominent merits in both heteroatoms doping and hierarchical structure, the as-fabricated NSHC/S cathode guarantees extraordinary sulfur storage, which enables fast sulfur electrochemistry under the conditions of high sulfur loading (6.72 mg cm−2), high sulfur content (80 wt%) and lean electrolyte usage (electrolyte/sulfur ratio: 7.5 μL mg−1). Of particular emphasis is the compact and high utilization of the host structure that ensures the assembled LSB with long and stable durability (606 mAh·g−1 after 100 cycles at 0.1 C and sulfur loading of 6.72 mg cm−2) and superior rate performance (689 mAh·g−1 at 5.0 C and sulfur loading of 2 mg cm−2).

Possible response of N2O emission to marine redox fluctuation during the Ediacaran-Cambrian transition in Nanhua Basin, South China

The redox state of the ocean and atmosphere during the Ediacaran-Cambrian (E-C) transition is characterized by significant revolutions and perturbations, which had a major effect on the biogeochemical nitrogen cycle. Nitrous oxide (N2O), a powerful greenhouse gas that drives global warming, is primarily produced in the oxygen minimum zones of modern ocean through incomplete denitrification at low oxygen concentration, and its emission to the atmosphere has been closely tied to the redox state of the ocean. To better understand the relationship between the possible variation of N2O emission and its related marine redox fluctuation, a multi geochemical proxy approach was conducted on the upper Ediacaran to lower Cambrian marine successions spanning from platform to slope facies of the Yangtze Block. The results show that δ15N features during the late Ediacaran to Fortunian interval from platform facies displayed high values (up to 8.8‰), indicating a higher degree of denitrification. The Fe speciation data along with elevated Cu/Al ratios in contemporaneous sediments suggests that the gradual depletion of dissolved Cu in water column due to expanded euxinic conditions. Because Cu is the essential element in the terminal step of denitrification pathway, the Cu deficiency in water column could result in incomplete denitrification. We infer that the possible increase of N2O discharge in this interval could contribute to a greenhouse climate and intense the anoxic degree of water column. However, during the Cambrian Stage 2 continuous consumption of NO3– and NO2– in seawater by denitrification would limit denitrification rate and reduce N2O production, and finally N2 fixation dominated the nitrogen cycle in photic zone as evidenced by low δ15N value. Both progressive oxygenation of deep water during the Cambrian Stage 3, and habitable environment temperature caused by less N2O emission could stimulate subsequent biosphere revolution. Our study highlights that N2O emission due to marine redox fluctuations possibly played an important role in regulating environmental and metazoan diversification during the E-C transition.

Design and Catalytic Behaviour of Hosted in Activated Carbon Foam CoxZn1−xFe2O4 Ferrites

Carbon foams with different surface functionality and tailored texture characteristics were prepared from mixtures containing coal tar pitch and furfural in different proportions. The obtained materials were used as a host matrix for the preparation of zinc- and cobalt-mixed ferrite nanoparticles. The texture, morphology, phase composition, and the related redox and catalytic properties of the obtained composites were characterized by low-temperature nitrogen physisorption, XRD, SEM, HRTEM, FTIR, Mössbauer spectroscopy, TPR and catalytic decomposition of methanol to syngas. The impact of the carbon support on the formation of Co- and Zn-mixed ferrites was discussed in detail using KIT-6 silica-based modifications as reference samples. The catalytic behavior of the ferrites was considered in a complex relation to their composition, morphology, location in the porous matrix and metal ions distribution in the spinel sub-lattices. The higher amount of furfural in the carbon foam precursor promoted the formation of cobalt-rich, more accessible and highly active methanol decomposition to syngas spinel particles.

Selenium mobility in a major Chalk aquifer (Lille metropolis, northern France): Contaminants cycles driven by geology, redox processes and pumping

Chalk groundwater in northern France presents selenium (Se) concentrations from <10 to 70 μg L−1, partly exceeding the latest European Framework Directive's drinking-water limit value of 20 μg L−1. Better to understand the heterogeneous dynamics of Se, we used a combination of geochemical, isotopic and geophysical tools on a study site belonging to the Metropolis of Lille, France. This approach provided a fine understanding of the Se fate in a dynamic redox system constrained by geology, related redox processes and pumping, illustrating how local versus global controls affect the Se cycling. A remarkable redox sequence controls element transfers in groundwater with a progressive creation of reductive conditions. Highlighted by geophysical tools, a wide fracture corridor in the Chalk formation disrupts the geological setting of this redox sequence. Under pumping, this corridor allows the mixing of oxygenated groundwater with groundwater under reducing conditions. The evolution of isotopic compositions of sulphate molecules confirms the global reduction trend of sulphates, while pyrite oxidation occurs very locally, together with high Se concentrations. Pyrite is expected to play a predominant role in Se mobility in the Chalk aquifer. Se and other redox sensitive elements (Fe, Mn, N and S) undergo multiple redox cycles, resulting in a Se-rich redox front that migrates downward over time within the water-level fluctuation zone of the porous Chalk. With the decreasing trend of water levels caused by global changes, a Se stock could be immobilized in the unsaturated zone, but nitrate content and redox conditions in the saturated zone will be major drivers for Se mobility.

Competitive Coordination of Chloride and Fluoride Anions Towards Trivalent Lanthanide Cations (La3+ and Nd3+ ) in Molten Salts.

Molten salt electrolysis is a vital technique to produce high-purity lanthanide metals and alloys. However, the coordination environments of lanthanides in molten salts, which heavily affect the related redox potential and electrochemical properties, have not been well elucidated. Here, the competitive coordination of chloride and fluoride anions towards lanthanide cations (La3+ and Nd3+ ) is explored in molten LiCl-KCl-LiF-LnCl3 salts using electrochemical, spectroscopic, and computational approaches. Electrochemical analyses show that significant negative shifts in the reduction potential of Ln3+ occur when F- concentration increases, indicating that the F- anions interact with Ln3+ via substituting the coordinated Cl- anions, and confirm [LnClx Fy ]3-x-y (ymax =3) complexes are prevailing in molten salts. Spectroscopic and computational results on solution structures further reveal the competition between Cl- and F- anions, which leads to the formation of four distinct Ln(III) species: [LnCl6 ]3- , [LnCl5 F]3- , [LnCl4 F2 ]3- and [LnCl4 F3 ]4- . Among them, the seven-coordinated [LnCl4 F3 ]4- complex possesses a low-symmetry structure evidenced by the pattern change of Raman spectra. After comparing the polarizing power (Z/r) among different metal cations, it was concluded that Ln-F interaction is weaker than that between transition metal and F- ions.

(Spectro)electrochemical Properties of Anthracene Containing Triarylamine Platinum(II) Acetylides

AbstractThe synthesis of [Pt{2}2(PPh3)2] (5) (10‐ethinyl‐9‐di(p‐anisyl)aminoanthracene=alkyne 2H) in a cis and trans configuration was achieved. Adsorption of cis‐5 on AlOx as well as electrochemical oxidation led to a reductive elimination of 10,10′‐(buta‐1,3‐diyne‐1,4‐diyl)bis(9‐di(p‐anisyl)amino‐anthracene) (6). The molecular structures of the alkyne intermediate 2H, [Pt{2}Cl(PPh3)2] (4) and butadiyne 6 have been determined by single crystal X‐ray diffraction. Cyclic voltammetry measurements of the platinum‐acetylides trans‐4, and cis‐ and trans‐5 demonstrated, that the back donation from platinum towards the π‐system results in a shift of the triarylamine and anthracene related redox processes towards lower E°′ values, when compared to the SiMe3‐protected alkyne of 2 (=2SiMe3). Both platinum complex trans‐5 and butadiyne 6 demonstrated that the individual arylamine and the respective anthracenyl buildings blocks can be oxidized in four one electron processes. Spectroelectrochemical studies revealed several intense intra‐ligand absorptions in the NIR, demonstrating a high degree of delocalization in the ligand. However, a direct IVCT through the platinum was not observed.

Single-atom Bi-anchored Au hydrogels with specifically boosted peroxidase-like activity for cascade catalysis and sensing

The complex structure of nanomaterial causes great difficulty in identifying active sites of nanozymes and getting to the bottom of the catalytic mechanism. In this report, single-atom Bi-anchored Au (BiSA@Au) hydrogels were synthesized through a one-step reduction strategy, which enables the precise regulation of the nanozyme activity and specificity at the atomic scale and the in-depth understanding of their catalytic nature. Due to the single-atom Bi doping, the BiSA@Au hydrogels showed previously unachieved peroxidase (POD)-like activity, while the doped single Bi atoms had negligible effects on the enhancements of the other closely related redox enzyme-like activities. Density functional theory verified that the introduction of single Bi atoms not only enhances the adsorption of H2O2 but also decreases the potential barriers for *OOH generation, leading to the boosted POD-like activity. Taking advantage of the unique porous nanowire networks of BiSA@Au hydrogels, a nanozyme/natural enzyme hybrid cascade reaction system was fabricated to achieve the sensitive colorimetric biosensor for glucose. This work paved a new route to rationally design functional nanozymes at the atomic scale, achieving the significant enhancement of POD-like activity with exceptional specificity.

Small-Scale Geochemical Heterogeneities and Seasonal Variation of Iron and Sulfide in Salt Marshes Revealed by Two-Dimensional Sensors

Loss of tidal wetlands is a world-wide phenomenon. Many factors may contribute to such loss, but among them are geochemical stressors such as exposure of the marsh plants to elevated levels on hydrogen sulfide in the pore water of the marsh peat. Here we report the results of a study of the geochemistry of iron and sulfide at different seasons in unrestored (JoCo) and partially restored (Big Egg) salt marshes in Jamaica Bay, a highly urbanized estuary in New York City where the loss of salt marsh area has accelerated in recent years. The spatial and temporal 2-dimensional distribution patterns of dissolved Fe2+ and H2S in salt marshes were in situ mapped with high resolution planar sensors for the first time. The vertical profiles of Fe2+ and hydrogen sulfide, as well as related solutes and redox potentials in marsh were also evaluated by sampling the pore water at discrete depths. Sediment cores were collected at various seasons and the solid phase Fe, S, N, C, and chromium reducible sulfide in marsh peat at discrete depths were further investigated in order to study Fe and S cycles, and their relationship to the organic matter cycling at different seasons. Our results revealed that the redox sensitive elements Fe2+ and S2– showed significantly heterogeneous and complex three dimensional distribution patterns in salt marsh, over mm to cm scales, directly associated with the plant roots due to the oxygen leakage from roots and redox diagenetic reactions. We hypothesize that the oxic layers with low/undetected H2S and Fe2+ formed around roots help marsh plants to survive in the high levels of H2S by reducing sulfide absorption. The overall concentrations of Fe2+ and H2S and distribution patterns also seasonally varied with temperature change. H2S level in JoCo sampling site could change from &amp;lt;0.02 mM in spring to &amp;gt;5 mM in fall season, reflecting significantly seasonal variation in the rates of bacterial oxidation of organic matter at this marsh site. Solid phase Fe and S showed that very high fractions of the diagenetically reactive iron at JoCo and Big Egg were associated with pyrite that can persist for long periods in anoxic sediments. This implies that there is insufficient diagenetically reactive iron to buffer the pore water hydrogen sulfide through formation of iron sulfides at JoCo and Big Egg.