Proton Consumption Research Articles

Nucleon consumption and mass-energy conversion induced by dark matter

We propose the nucleon consumption induced by dark matter (DM) as a new scenario to overcome the energy threshold of direct detection. It can be realized with proton (χ+p→χ+ℓ+) or neutron (χ+n→χ+ν) target. Both effective operators and concrete models are provided to illustrate the idea. Since the initial DM and nucleon velocity is only 10−3 and 1/4 of the speed of light, respectively, the cross section and hence event rate are determined by the involved particle masses and not affected by the nucleon Fermi motion. Of the two realizations, the proton consumption has richer phenomena with both charged lepton and the daughter nuclei deexcitation to allow double or even triple coincidence to significantly suppress the background. We also illustrate the projected sensitivities at DM and neutrino experiments such as PandaX-4T, DUNE, JUNO, and Hyper-K. Published by the American Physical Society 2024

(Invited) Intercalation of Copper into Tungsten Oxide Nanostructures: Development of Highly Active Electrocatalytic Systems for CO2-Reduction

There has been growing interest in the electrochemical reduction of carbon dioxide (CO2), a potent greenhouse gas and a contributor to global climate change, and its conversion into useful carbon-based fuels or chemicals. Numerous homogeneous and heterogeneous catalytic systems have been proposed to induce the CO2 reduction and, depending on the reaction conditions various products that include carbon monoxide, oxalate, formate, carboxylic acids, formaldehyde, acetone or methanol, in addition to various hydrocarbons at different ratios. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials. To produce highly efficient and selective electrocatalysts, the transition-metal-based molecular materials are often considered. It is believed that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate.Because reduction of CO2 can effectively occur by hydrogenation, to optimize the conventional copper-based electrocatalytic approach, we explore such a model catalytic matrix as nanostructured tungsten oxide nanowires which are capable to undergo partial reduction to hydrogen-rich nonstoichiometric tungsten oxide bronzes. We demonstrate here that following the ntercalation of copper into tungsten(VI)-oxide-nanowires, the resulting electrocatalytic systems exhibits synergistic properties toward electroreduction of carbon dioxide, in addition to other inert inorganic reactants, such as oxygen, nitrates(V), nitrates(III) or bromates(V). In particular, evidence has been provided that hierarchically deposited films (on glassy carbon) of copper(I) oxide decorated with tungsten(VI) oxide nanowires and, subsequently, subjected to electroreduction and voltammetric conditioning to generate hybrid Cu/WO3 catalyst can be successfully utilized to drive reduction of carbon dioxide (saturated solution, concentration, ca. 0.033 mol dm-3)in a fairly strong acid medium of 0.5 mol dm-3 H2SO4. Here formation of the partially reduced tungsten oxides (HxWO3 and WO3-y) is accompanied by consumption of protons and sorption of hydrogen, and it tends to inhibit hydrogen evolution by shifting the proton discharge toward more negative potentials. Our observations are consistent with the view that copper is irreversibly trapped (i.e., it cannot be reoxidized) within the network of WO3 nanowires. The dispersed metallic copper sites seem to facilitate electron transfers and charge distribution in the catalytic layers. Among important issues are the capacity of copper-containing partially reduced tungsten oxides to induce reductions of nitrates, bromates and oxygen in acid medium. On mechanistic grounds, the existence of hydrogen-rich partially-reduced tungsten oxides, HxWO3, which contain large population of delocalized electrons and monoatomic H, or coexisting protons and electrons, H++ e-, is likely to induce hydrogenation of carbon oxo species, followed by protonation, in the vicinity of Cu to form oxo-hydrocarbon-type products. The hybrid Cu/WO3 system, is also characterized by improved durability, relative to pristine Cu2O-dervied copper, as evident from electroreductions under chronoamperometric conditions. Our research aiming at optimization the material’s activity and selectivity have also concentrated on application of mixed oxides, e.g. WO3-ZrO2. Finally, the present study demonstrates the usefulness of certain diagnostic electroanalytical approaches, such as ultramicroelectrode-based sensing,chronocoulometric probing of the diffusional-type charge propagation dynamics, or voltammetric stripping and monitoring of small organic or inorganic molecules as electroreduction products.

Operando Synchrotron X-Ray Scattering Study of (Bi)Carbonate Precipitation in Gas Diffusion Electrodes for CO2 Reduction Using Neutral and Acidic Electrolytes

Electrochemical CO2 reduction (eCO2R) offers a promising pathway to convert CO2 into sustainable fuels and chemicals, moving us closer to a net zero or net negative carbon economy. 1 To compete with established fuel/chemical production routes, electrocatalysts needs to be highly active, selective towards a desired product, and stable. Thanks to the use of gas diffusion electrodes (GDEs) fed by gaseous CO2, high activities (i.e. high current densities) can be achieved. 2 However, under these conditions rapid degradation typically takes place due to (bi)carbonate precipitation caused by excessive CO2 dissolution in the basic local environment around the catalyst. This phenomenon is so severe that is considered a potential showstopper for the eCO2R technology. A proposed strategy to overcome this limitation is to perform the eCO2R in acidic electrolytes, in which (bi)carbonate crystals are unstable.In this work, we investigate in detail (bi)carbonate precipitation using operando synchrotron wide angle X-ray scattering experiments on polymer-based Cu GDEs, which have shown record high selectivity for C≥2 products and are impervious to flooding.3,4 We show that in neutral electrolytes (pH=4.5), (bi)carbonate precipitation takes place within minutes of switching on the eCO2R at technologically relevant current densities (200 mA/cm2). The extent of (bi)carbonate precipitation correlates with the decay of carbon product selectivity (particularly of C≥2 products) and with the increase of H2 production.5 Strikingly, using strongly acidic electrolytes (pH=1) under the same conditions does not lead to any delayed or reduced (bi)carbonate precipitation. Also here, the decay of carbon product selectivity correlates with the amount of precipitated (bi)carbonate and is even faster than in neutral electrolytes.5 Electrochemical studies with electrolytes of different pH corroborate these findings and show that, when lowering pH, an increasingly high current density is required for the eCO2R to be activated, with H2 being the sole product before reaching sufficiently higher currents. These results confirm that a high local pH close to the catalyst is necessary for effective eCO2R, thus requiring the higher proton consumption rates caused by higher current densities when using more acidic electrolytes. Our findings show that, while it is possible to operate Cu GDEs under sufficiently high current densities and achieve good selectivity for carbon products even in strongly acidic electrolytes (FEC2H4 > 45 % and FEC≥2 > 70 %), this takes place alongside substantial (bi)carbonate precipitation and thus at the expense of stability. References 1Senocrate, A.; Battaglia, C.; J. Energy Storage 2021, 36, 102373. 2Verma, S.; Hamasaki, Y.; Kim, C.; Huang, W.; Lu, S.; Jhong, H. R. M.; Gewirth, A. A.; Fujigaya, T.; Nakashima, N.; Kenis, P.; ACS Energy Lett. 2018, 3, 193–198. 3Senocrate, A.; Bernasconi, F.; Rentsch, D.; Kraft, K.; Trottmann, M.; Wichser, A.; Bleiner, D.; Battaglia, C.; ACS Appl. Energy Mater. 2022, 5, 14504. 4Bernasconi, F.; Senocrate, A.; Kraus, P.; Battaglia, C.; EES Catalysis 2023, 1, 1009. 5Bernasconi, Plainpan, Mirolo, Battaglia, Senocrate, under review.

A Straightforward Model for Quantifying Local pH Gradients Governing the Oxygen Evolution Reaction.

The production and consumption of protons by an electrocatalyst will, under certain conditions, generate localized microenvironments with properties distinct from those of the bulk solution. These local properties are particularly impactful for reactions involving proton-coupled electron transfer, where the generation of locally basic or acidic environments may significantly influence the energy efficiency and reaction selectivity of the electrocatalyst. Whereas local pH environments have been observed and characterized in reductive half-reactions, including the CO2 reduction and hydrogen evolution reactions, the incompatibility of conventional techniques and materials has limited studies in oxidative half-reactions, including the oxygen evolution reaction (OER), which provides the reducing equivalents for solar-to-fuels electrolysis. With the straightforward parameters bulk pH, buffer composition and pKa, and mass transport, we develop a model for describing local pH as a function of current density regardless of the microscopic details of the mechanism. Using an acid-stable PbOx OER catalyst, we observe the formation and dissipation of pH gradients during the OER and validate the model with voltammetric and potentiometric studies. The model predicts how local acidic environments can develop over a narrow OER current density window, thus providing further motivation for the development of OER catalysts that are stable to acid, even when operating in basic aqueous conditions. More generally, the model is not restricted to the OER and is useful for determining the onset of local pH gradients for other electrocatalytic reactions that involve the consumption or generation of protons in energy conversion reactions.

Electrochemical CO2 Reduction in Acidic Electrolytes: Spectroscopic Evidence for Local pH Gradients.

Inspired by recent advances in electrochemical CO2 reduction (CO2R) under acidic conditions, herein we leverage in situ spectroscopy to inform the optimization of CO2R at low pH. Using attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and fluorescent confocal laser scanning microscopy, we investigate the role that alkali cations (M+) play on electrochemical CO2R. This study hence provides important information related to the local electrode surface pH under bulk acidic conditions for CO2R, both in the presence and absence of an organic film layer, at variable [M+]. We show that in an acidic electrolyte, an appropriate current density can enable CO2R in the absence of metal cations. In situ local pH measurements suggest the local [H+] must be sufficiently depleted to promote H2O reduction as the competing reaction with CO2R. Incrementally incorporating [K+] leads to increases in the local pH that promotes CO2R but only at proton consumption rates sufficient to drive the pH up dramatically. Stark tuning measurements and analysis of surface water structure reveal no change in the electric field with [M+] and a desorption of interfacial water, indicating that improved CO2R performance is driven by suppression of H+ mass transport and modification of the interfacial solvation structure. In situ pH measurements confirm increasing local pH, and therefore decreased local [CO2], with [M+], motivating alternate means of modulating proton transport. We show that an organic film formed via in situ electrodeposition of an organic additive provides a means to achieve selective CO2R (FECO2R ∼ 65%) over hydrogen evolution reaction in the presence of strong acid (pH 1) and low cation concentrations (≤0.1 M) at both low and high current densities.

Alteration of soil pH induced by submerging/drainage and application of peanut straw biochar and its impact on Cd(II) availability in an acidic soil to indica-japonica rice varieties

The effects of soil pH variations induced by submergence/drainage and biochar application on soil cadmium (Cd) availability to different rice (Oryza sativa L.) varieties are not well understood. This study aims to investigate the possible reasons for available Cd(II) reduction in paddy soil as influenced by biochar and to determine Cd(II) absorption and translocation rates in different parts of various rice varieties. A pot experiment in a greenhouse using four japonica and four indica rice varieties was conducted in Cd(II) contaminated paddy soil with peanut straw biochar. The results indicated that the submerging led to an increase in soil pH due to the consumption of protons (H+) by the reduction reactions of iron/manganese (Fe/Mn) oxides and sulfate (SO42−) and thus the decrease in soil available Cd(II) contents. However, the drainage decreased soil pH due to the release of protons during the oxidation of Fe2+, Mn2+, and S2− and thus the increase in soil available Cd(II) contents. Application of the biochar increased soil pH during soil submerging and inhibited the decline in soil pH during soil drainage, and thus decreased soil available Cd(II) contents under both submerging and drainage conditions. The indica rice varieties absorbed more Cd(II) in their roots and accumulated higher amounts of Cd(II) in their shoots and grains than the japonica rice varieties. The Cd(II) sensitive varieties exhibited a greater absorption and translocation rate of Cd(II) compared to the tolerant varieties of both indica and japonica rice. Biochar inhibited the absorption and accumulation of Cd(II) in the rice varieties, which ultimately lowered the Cd(II) contents in rice grains below the national food safety limit (0.2 mg kg−1). Overall, planting japonica rice varieties in Cd(II) polluted paddy soils combined with the use of biochar can effectively reduce Cd(II) content in rice grains which protects human health against Cd(II) toxicity.

Insights into sulfur cycling contribution to nitrogen removal in sulfur autotrophic denitrification combined microbial electrochemical denitrification

In the face of increasing discharge standards, sulfur autotrophic denitrification (SAD) is gradually applied for deep nitrogen removal of electron-donor-deficient waters. However, the product sulfate induces secondary pollution in the effluent, and the proton consumption from alkalinity is detrimental to the stable operation of the system. In this study, a sulfur autotrophic denitrification coupled with microbial electrochemical denitrification system (S-MED) is proposed to reduce the addition of inorganic sulfur, alleviating nitrite accumulation, while enabling the system to self-sustain at a neutral pH. The S-MED system that was operated under the applied potential of −0.5 V achieved a nitrate removal of 97.5 ± 1.57 % and a total nitrogen removal of 90.3 ± 4.27 %, which were 14.6 % and 68.0 % higher than the SAD systems in control under the S/N molar ratio of 0.8. The nitrite accumulation rate was reduced by 69.1 % compared to SAD. The effluent sulfate concentration was also reduced to 5.8 mg/mg-N TN removal. The electrochemically active denitrifying bacterium Thiobacillus was enriched in the coupled system, and the copy numbers of functional genes of narGHI, napAB, and nirK involved in denitrification were increased. According to the microbial analysis and electrochemical characteristics, it suggested that S2- might be generated from sulfate with the presence of electrodes, enabling the cycling of sulfur, providing mobile electron carriers for denitrification, thus allowing bacteria to conduct denitrification by indirectly obtaining electrons from the electrode.

Voltammetric approach to measuring free acid in anhydride and ester based on benzoquinone electrochemical reduction

AbstractFree acids commonly exist in anhydride and esters because they are unstable and tend to break down into free acids, which affect the quality of subsequent products in industrial production. Phthalic anhydride and ethyl acetate undergo hydrolysis reactions to form phthalic acid and acetic acid. A differential pulse voltammetry method for the determination of phthalic acid and acetic acid was developed with a bare glassy carbon electrode. Phthalic acid and acetic acid caused a new cathodic peak at more positive potential during the reduction of 1,4‐benzoquinone in acetonitrile or aqueous solution. The new peaks are attributed to the drastic increase in pH at the electrode surface caused by the consumption of protons in the benzoquinone reduction reaction. The peak current of the new cathodic peak was dependent on the concentration of phthalic acid and acetic acid but independent of BQ, phthalic anhydride, and ethyl acetate. This method does not cause hydrolysis of anhydride and ester because no external base is introduced. Furthermore, the method is sensitive, rapid, and does not require pretreatment.

Power Generation Characteristics of Metal–Fueled Redox Flow Polymer Electrolyte Fuel Cells Employing Heteropolyanions as Anode Redox Mediators

In this study, the heteropolyanion of [PW12O40]3– is applied as an anode redox mediator in the redox flow polymer electrolyte fuel cells (PEFCs). This system enables continuous power generation by the electrochemical oxidation of the heteropolyanions over the carbon anode and subsequent re–reduction of the oxidized heteropolyanions in the anode tank. Currently, effective reduction methods alternative to biomass are required to achieve both high performance and long–term stability. In this study, a novel reduction method of heteropolyanions utilizing the corrosion reaction of metals (aluminum, iron, nickel, cobalt) in strong acid aqueous solutions is investigated. Current passage tests reveal that the hydrogen evolution reaction, which competes with the re–reduction of the oxidized heteropolyanions, affects the fuel efficiency. Among metals studied, aluminum is able to effectively re–reduce oxidized heteropolyanions while suppressing the consumption of protons and metals associated with the hydrogen evolution reaction. On the other hand, cobalt consumes a large amount of metal in the hydrogen evolution reaction and is found to be inferior to aluminum in fuel efficiency. This study provides an innovative approach to the reduction method of the anode redox mediator in the redox flow PEFCs.

Boosting hydrogen evolution of nickel phosphide by expanding built-in electric field with tungsten oxide

Manipulating the built-in electric field (BIEF) in the catalyst to regulate the electronic structure and improve the carrier transport is a promising approach, but it is rarely applied in the design of hydrogen evolution reaction (HER) catalysts. In this study, the electrochemical microenvironment of nickel phosphide supported on nickel foam (Ni2P/NF) has been modified by introducing tungsten oxide (WO3) through simple ion group exchange strategy, thereby expanding the BIEF and enhancing the electron transport property. As a direct outcome, the target catalyst (20-WO3/Ni2P/NF) exhibits ultralow overpotential of 301 mV at high current density of − 1000 mA cm−2. Additional characterization and density functional theory calculations demonstrate that the WO3 can not only serve as a new hydrogen adsorption active site, but also effectively decrease the dissociation energy of water molecules at the nickel site, which results in rapid production and consumption of protons and enhancing the overall catalytic activity.

A role for fermentation in aerobic conditions as revealed by computational analysis of maize root metabolism during growth by cell elongation.

The root is a well-studied example of cell specialisation, yet little is known about the metabolism that supports the transport functions and growth of different root cell types. To address this, we used computational modelling to study metabolism in the elongation zone of a maize lateral root. A functional-structural model captured the cell-anatomical features of the root and modelled how they changed as the root elongated. From these data, we derived constraints for a flux balance analysis model that predicted metabolic fluxes of the 11 concentric rings of cells in the root. We discovered a distinct metabolic flux pattern in the cortical cell rings, endodermis and pericycle (but absent in the epidermis) that involved a high rate of glycolysis and production of the fermentation end-products lactate and ethanol. This aerobic fermentation was confirmed experimentally by metabolite analysis. The use of fermentation in the model was not obligatory but was the most efficient way to meet the specific demands for energy, reducing power and carbon skeletons of expanding cells. Cytosolic acidification was avoided in the fermentative mode due to the substantial consumption of protons by lipid synthesis. These results expand our understanding of fermentative metabolism beyond that of hypoxic niches and suggest that fermentation could play an important role in the metabolism of aerobic tissues.

Biochar-Acid Soil Interactions—A Review

Soil acidity is a major problem of agriculture in many parts of the world. Soil acidity causes multiple problems such as nutrient deficiency, elemental toxicity and adverse effects on biological characteristics of soil, resulting in decreased crop yields and productivity. Although a number of conventional strategies including liming and use of organic and inorganic fertilizers are suggested for managing soil acidity but cost-effective and sustainable amendments are not available to address this problem. Currently, there is increasing interest in using biochar, a form of biomass derived pyrogenic carbon, for managing acidity while improving soil health and fertility. However, biochar varies in properties due to the use of wide diversity of biomass, variable production conditions and, therefore, its application to different soils can result in positive, neutral and or negative effects requiring an in-depth understanding of biochar-acid soil interactions to achieve the best possible outcomes. Here, we present a comprehensive synthesis of the current literature on soil acidity management using biochar. Synthesis of literature showed that biochars, enriched with minerals (i.e., usually produced at higher temperatures), are the most effective at increasing soil pH, basic cation retention and promoting plant growth and yield. Moreover, the mechanism of soil acidity amelioration with biochar amendments varies biochar types, i.e., high temperature biochars with liming effects and low temperature biochars with proton consumption on their functional groups. We also provide the mechanistic interactions between biochar, plant and soils. Altogether, this comprehensive review will provide guidelines to agricultural practitioners on the selection of suitable biochar for the reclamation of soil acidity.

Combined application of strong alkaline materials and specific organic fertilizer accelerates nitrification process of a rare earth mining soil

The extensive usage of ammonium sulfate as the leaching agent to extract rare earth elements led to widespread ammonia nitrogen (NH4+-N) pollution in the tailing soils of ion-adsorbed rare earth deposits in southern China. However, the cost-effective technologies to tackle with the long-term retention of NH4+-N in the rare earth mining soil have been largely unresolved. In this study, we developed a cost-effective approach to activate soil nitrification by the co-application of alkaline materials and organic fertilizer. The co-application of 0.3 % of organic fertilizer and 0.1 % ∼ 0.2 % of CaO or MgO or Mg(OH)2 stimulated a soil NH4+-N decrease rate of 2.01–7.58 mg kg−1 d−1 and a soil NO3−-N accumulation rate of 1.56–7.09 mg kg−1 d−1. Noting that only if the soil pH was elevated to 7.81–9.00, the NH4+-N decrease rate and NO3−-N accumulation rate were dependent on the proton consumption capacity of the alkaline materials. The application of CaCO3 could not stimulate soil nitrification possibly due to the soil pH was uncapable to be elevated to above 7.68. The qPCR, amplicon sequencing, and nitrification inhibitor batch incubation results demonstrated that organic fertilizer supplied active ammonia-oxidizing bacteria Nitrosomonas europaea. The proliferation of Nitrosomonas europaea in the alkaline materials and organic fertilizer co-applied soil was responsible for the soil nitrification. Furthermore, the application of commercial denitrifying bacteria inoculum promoted the removal of accumulated NO3−-N. The findings of this study provide a lost-cost technology to remove NH4+-N from the rare earth mining soil.

The role of crystallinity of palladium nanocrystals in ROS generation and cytotoxicity induction.

Palladium (Pd) nanocrystals with different crystalline forms exhibit distinct enzyme-like activities in generating reactive oxygen species (ROS). How such crystallinity-dependent catalytic activity regulates potential cytotoxicity remains to be elucidated. In the present work, Pd nanocrystals with four different crystalline forms were synthesized, and the underlying mechanisms involved in ROS-mediated cytotoxicity were systematically revealed. Pd nanocrystals with the {100} (nanocubes) and {111} (nanooctahedrons and nanotetrahedrons) facets triggered cytotoxicity by generating singlet oxygen (1O2) and hydroxyl radicals (OH˙), respectively. Meanwhile, Pd nanoconcave-tetrahedrons, which had both the {110} and {111} facets, induced ROS-mediated cytotoxicity via activating the superoxide (O2˙-) pathway. Consumption of protons and generation of hydroxide during intracellular ROS conversion resulted in pH alkalization, eventually leading to cell death. Our findings emphasize the importance of facet-dependent ROS generation promoted by Pd nanocrystals. Furthermore, alkalization is identified as a new biomarker for analyzing ROS-mediated cytotoxicity.

Direct Air Capture of CO2 through Carbonate Alkalinity Generated by Phytoplankton Nitrate Assimilation.

Despite the consensus that keeping global temperature rise within 1.5 °C above pre-industrial level by 2100 reduces the chance for climate change to reach the point of no return, the newest Intergovernmental Panel on Climate Change (IPCC) report warns that the existing commitment of greenhouse gas emission reduction is only enough to contain the warming to 3-4 °C by 2100. The harsh reality not only calls for speedier deployment of existing CO2 reduction technologies but demands development of more cost-efficient carbon removal strategies. Here we report an ocean alkalinity-based CO2 sequestration scheme, taking advantage of proton consumption during nitrate assimilation by marine photosynthetic microbes, and the ensuing enhancement of seawater CO2 absorption. Benchtop experiments using a native marine phytoplankton community confirmed pH elevation from ~8.2 to ~10.2 in seawater, within 3-5 days of microbial culture in nitrate-containing media. The alkaline condition was able to sustain at continued nutrient supply but reverted to normalcy (pH ~8.2-8.4) once the biomass was removed. Measurements of δ13C in the dissolved inorganic carbon revealed a significant atmospheric CO2 contribution to the carbonate alkalinity in the experimental seawater, confirming the occurrence of direct carbon dioxide capture from the air. Thermodynamic calculation shows a theoretical carbon removal rate of ~0.13 mol CO2/L seawater, if the seawater pH is allowed to decrease from 10.2 to 8.2. A cost analysis (using a standard bioreactor wastewater treatment plant as a template for CO2 trapping, and a modified moving-bed biofilm reactor for nitrate recycling) indicated that a 1 Mt CO2/year operation is able to perform at a cost of ~$40/tCO2, 2.5-5.5 times cheaper than that offered by any of the currently available direct air capture technologies, and more in line with the price of $25-30/tCO2 suggested for rapid deployment of large-scale CCS systems.

Coincident Biogenic Nitrite and pH Maxima Arise in the Upper Anoxic Layer in the Eastern Tropical North Pacific

AbstractThe Eastern Tropical North Pacific (ETNP), like the other marine oxygen deficient zones (ODZs), is characterized by an anoxic water column, nitrite accumulation at the anoxic core, and fixed nitrogen loss via nitrite reduction to N2O and N2 gases. Here, we constrain the relative contribution of biogeochemical processes to observable features such as the secondary nitrite maximum (SNM) and local pH maximum by simultaneous measurement of inorganic nitrogen and carbon species. High‐resolution sampling within the top 1 km of the water column reveals consistent chemical features previously unobserved in the region, including a tertiary nitrite maximum. Dissolved inorganic carbon measurements show that pH increases with depth at the top of the ODZ, peaking at the potential density of the SNM at σθ = 26.15 ± 0.06 (1 s.d.). We developed a novel method to determine the relative contributions of anaerobic ammonium oxidation (anammox), denitrification, nitrite oxidation, dissimilatory nitrate reduction to nitrite, and calcium carbonate dissolution to the nitrite cycling in the anoxic ODZ core. The calculated relative contributions of each reaction are slightly sensitive to the assumed C:N:P ratio and the carbon oxidation state of the organic matter sinking through the ODZ. Furthermore, we identify the source of the pH increase at the top of ODZ as the net consumption of protons via nitrite reduction to N2 by the denitrification process. The increase in pH due to denitrification impacts the buffering effect of calcite and aragonite dissolving in the ETNP.

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Carbonate Minerals and Dissimilatory Iron-Reducing Organisms Trigger Synergistic Abiotic and Biotic Chain Reactions under Elevated CO2 Concentration.

Increasing CO2 emission has resulted in pressing climate and environmental issues. While abiotic and biotic processes mediating the fate of CO2 have been studied separately, their interactions and combined effects have been poorly understood. To explore this knowledge gap, an iron-reducing organism, Orenia metallireducens, was cultured under 18 conditions that systematically varied in headspace CO2 concentrations, ferric oxide loading, and dolomite (CaMg(CO3)2) availability. The results showed that abiotic and biotic processes interactively mediate CO2 acidification and sequestration through "chain reactions", with pH being the dominant variable. Specifically, dolomite alleviated CO2 stress on microbial activity, possibly via pH control that transforms the inhibitory CO2 to the more benign bicarbonate species. The microbial iron reduction further impacted pH via the competition between proton (H+) consumption during iron reduction and H+ generation from oxidization of the organic substrate. Under Fe(III)-rich conditions, microbial iron reduction increased pH, driving dissolved CO2 to form bicarbonate. Spectroscopic and microscopic analyses showed enhanced formation of siderite (FeCO3) under elevated CO2, supporting its incorporation into solids. The results of these CO2-microbe-mineral experiments provide insights into the synergistic abiotic and biotic processes that alleviate CO2 acidification and favor its sequestration, which can be instructive for practical applications (e.g., acidification remediation, CO2 sequestration, and modeling of carbon flux).

Synchronous reduction and removal of hexavalent chromium from wastewater by modified magnetic chitosan beads

As one of the highly toxic heavy metal contaminants, hexavalent chromium (Cr(VI)) poses a serious hazard to the environment and public health due to its excellent solubility in aqueous environment. To synchronously reduce and remove Cr(VI) from wastewater efficiently, a class of functionalized magnetic chitosan (CS) beads (MCB-ECH-SH/SO3H) was synthesized with CS as the substrate material and in situ assembling Fe3O4 nanoparticles as the incorporated magnetic material, followed by epichlorohydrin (ECH) cross-linking and l-cysteine grafting. Results showed that Cr(VI) in aqueous solution could be rapidly adsorbed onto MCB-ECH-SH/SO3H via electrostatic attraction, meanwhile -SH groups introduced by l-cysteine grafting could not only significantly facilitate the reduction of Cr(VI) to less toxic trivalent chromium (Cr(III)), but also promote the resultant Cr(III) chelating onto adsorbent due to the proton consumption caused by Cr(VI) reduction, resulting in the synergistic enhancement of Cr(VI) detoxification and total chromium (Cr(Total)) removal. The batch adsorption experiments revealed that the well designed MCB-ECH-SH/SO3H could be applied over a wide pH range (initial pH of 1.0–7.0), and showed much higher remove efficiency (99.6 ± 0.2 %) of Cr(VI) than MCB and MCB-ECH at initial pH 5.0 (60 °C) due to the improvement of stability and reducing capacity. The Cr(Total) sorption behaviors were well according with the pseudo-second-order kinetic and Langmuir models, indicating a single-layer, exothermal, and chemical sorption process, while the maximum Cr(Total) removal capacity of MCB-ECH-SH/SO3H was estimated to be 293.46 mg∙g−1, exceeding most of previously reported related adsorbents. Moreover, MCB-ECH-SH/SO3H could still maintained strong adsorption performance after five cycles and exhibited excellent ability to remove 95 % Cr(VI) within 1 h for low concentration Cr(VI)-containing wastewater. The combination of synchronous reduction and adsorption property, high removal capacity, convenient magnetic separation and good recycling performance makes MCB-ECH-SH/SO3H an ideal candidate for chromium-containing wastewater treatment.

Glycerol amendment enhances biosulfidogenesis in acid mine drainage-affected areas: An incubation column experiment.

Microbial sulfate (SO4 2−) reduction in Acid Mine Drainage (AMD) environments can ameliorate the acidity and extreme metal concentrations by consumption of protons via the reduction of SO4 2− to hydrogen sulfide (H2S) and the concomitant precipitation of metals as metal sulfides. The activity of sulfate-reducing bacteria can be stimulated by the amendment of suitable organic carbon sources in these generally oligotrophic environments. Here, we used incubation columns (IC) as model systems to investigate the effect of glycerol amendment on the microbial community composition and its effect on the geochemistry of sediment and waters in AMD environments. The ICs were built with natural water and sediments from four distinct AMD-affected sites with different nutrient regimes: the oligotrophic Filón Centro and Guadiana acidic pit lakes, the Tintillo river (Huelva, Spain) and the eutrophic Brunita pit lake (Murcia, Spain). Physicochemical parameters were monitored during 18 months, and the microbial community composition was determined at the end of incubation through 16S rRNA gene amplicon sequencing. SEM-EDX analysis of sediments and suspended particulate matter was performed to investigate the microbially-induced mineral (neo)formation. Glycerol amendment strongly triggered biosulfidogenesis in all ICs, with pH increase and metal sulfide formation, but the effect was much more pronounced in the ICs from oligotrophic systems. Analysis of the microbial community composition at the end of the incubations showed that the SRB Desulfosporosinus was among the dominant taxa observed in all sulfidogenic columns, whereas the SRB Desulfurispora, Desulfovibrio and Acididesulfobacillus appeared to be more site-specific. Formation of Fe3+ and Al3+ (oxy)hydroxysulfates was observed during the initial phase of incubation together with increasing pH while formation of metal sulfides (predominantly, Zn, Fe and Cu sulfides) was observed after 1–5 months of incubation. Chemical analysis of the aqueous phase at the end of incubation showed almost complete removal of dissolved metals (Cu, Zn, Cd) in the amended ICs, while Fe and SO4 2− increased towards the water-sediment interface, likely as a result of the reductive dissolution of Fe(III) minerals enhanced by Fe-reducing bacteria. The combined geochemical and microbiological analyses further establish the link between biosulfidogenesis and natural attenuation through metal sulfide formation and proton consumption.