Inhibitory effect of nitrate/nitrite on the microbial reductive dissolution of arsenic and iron from soils into pore water

Construction of Fe3O4@Au catalysts via the surface functional group effect of ferric oxide for efficient electrocatalytic nitrite reduction

Surface modification is one of the effective strategies to control the morphology and electrocatalytic performance of noble metal/transition metal oxide matrix composite catalysts. In this work, we successfully introduced modification groups such as -NH2, -COOH, and -SH on the surface of Fe3O4 using the hydrothermal method. It was found that when the modification group -COOH was introduced, the regular spherical morphology of Fe3O4 was still maintained in Fe3O4-COOH, while Fe3O4-COOH had a relatively smaller spherical particle size (≈155.9 nm). Due to its smaller particle size, Fe3O4-COOH has a larger active area than Fe3O4, exposing more active sites. The abundant active sites in Fe3O4-COOH provide more nucleation and growth sites for Au particles, which is beneficial for the recombination between Fe3O4-COOH and Au. In addition, the experimental results of exploring the effect of Au precursor dosage on the synthesis of the Fe3O4-COOH@Au structure and performance show that the synthesized Fe3O4-COOH@Au1.0 catalyst has higher electrocatalytic activity. Due to the larger electrochemically active surface area of the Fe3O4-COOH@Au1.0 catalyst compared to those of Fe3O4-COOH@Au0.5 and Fe3O4-COOH@Au1.5 catalysts, the adsorption and activation of NO2- reactants were accelerated, thereby improving the electrocatalytic performance. Therefore, owing to the morphological and structural characteristics of Fe3O4-COOH combined with the high activity of Au nanoparticles, the synthesized Fe3O4-COOH@Au exhibits effective electrocatalytic activity in the electrocatalytic NO2-RR synthesis of ammonia. At a voltage of -0.8 V (vs. RHE), the ammonia yield reached 2092.8 μg h-1 mgcat-1 and Faraday efficiency reached 81.2%. The findings of this work will enrich our understanding of the construction of efficient Fe3O4@Au catalysts based on surface functionalization and help to design efficient electrocatalytic NO2-RR catalysts for practical applications.

Prediction of As and Cd dissolution in various soils under flooding condition

Although the mobility of arsenic (As) and cadmium (Cd) in soils during the flooding-drainage process has been intensively studied, predicting their dissolution among various soils still remains a challenge. After comprehensively monitoring multiple parameters related to As and Cd dissolution in 8 soils for a 60-day anaerobic incubation, the redundancy analysis (RDA) and structural equation model (SEM) were employed to identify the key factors and influencing pathways controlling the dynamic release of As and Cd. Results showed that pH alone explained 90.5 % Cd dissolution, while the dissolved-Fe(II) and 5 M-HCl extractable Fe(II) jointly only explained 50.6 % As dissolution. After data normalization, the ratio of Fe(II) to 5 M-HCl extracted total Fe (i.e. FetotII/Fetot) significantly improved the correlation to R2 = 0.824 (p < 0.001) with a fixed slope of 0.393 among the 8 soils. Our results highlight the crucial role played by the reduction degree of total iron contents in determining both the reduction and dissolution of As during flooding. In contrast, dissolved-Fe(II) was too vulnerable to soil properties to be a stable indicator of As dissolution. Therefore, we propose to replace the dissolved-Fe(II) with this novel ratio as the key index to quantitatively assess the kinetic change of As solubility potential across various soils under flooding conditions.

Arsenic stress on soil microbial nutrient metabolism interpreted by microbial utilization of dissolved organic carbon

In a 120-day microcosm incubation experiment, we investigated the impact of arsenic contamination on soil microbial nutrient metabolism, focusing on carbon cycling processes. Our study encompassed soil basal respiration, key enzyme activities (particularly, β-1,4-N-acetylglucosaminidase and phosphatases), microbial biomass, and community structure. Results revealed a substantial increase (1.21-2.81 times) in β-1,4-N-acetylglucosaminidase activities under arsenic stress, accompanied by a significant decrease (9.86%-45.20%) in phosphatase activities (sum of acid and alkaline phosphatases). Enzymatic stoichiometry analysis demonstrated the mitigation of microbial C and P requirements in response to arsenic stress. The addition of C-sources alleviated microbial C requirements but exacerbated P requirements, with the interference amplitude increasing with the complexity of the C-source. Network analysis unveiled altered microbial nutrient requirements and an increased resistance process of microbes under arsenic stress. Microbial carbon use efficiency (CUE) and basal respiration significantly increased (1.17-1.59 and 1.18-3.56 times, respectively) under heavy arsenic stress (500 mg kg-1). Arsenic stress influenced the relative abundances of microbial taxa, with Gemmatimonadota increasing (5.5-50.5%) and Bacteroidota/ Nitrospirota decreasing (31.4-47.9% and 31.2-63.7%). Application of C-sources enhanced microbial resistance to arsenic, promoting cohesion among microorganisms. These findings deepen our understanding of microbial nutrient dynamics in arsenic-contaminated areas, which is crucial for developing enzyme-based toxicity assessment systems for soil arsenic contamination.

Ru doped NiMoO4 nanoarray as a high-efficiency electrocatalyst for nitrite reduction to ammonia

The electrocatalytic reduction of nitrite to recyclable ammonia (NH3) is essential to maintain nitrogen balance and meet growing energy requirements. Herein, we report that Ru doped honeycomb NiMoO4 nanosheet with copious oxygen vacancies grown on nickel foam substrate has been prepared by a facile hydrothermal synthesis and immersion process, which can act as an efficient electrocatalyst for NH3 synthesis by reduction of nitrite. By optimizing the concentration of RuCl3 solution, 0.01Ru-NiMoO4/NF possesses excellent NO2-RR performance with NH3 yield of 20249.17 ± 637.42 μg h-1 cm-2 at -0.7 V and FE of 95.56 ± 0.72 % at -0.6 V. When assembled into a Zn-NO2- battery, it provides a remarkable level of power density of 13.89 mW cm-2, outperforming the performance of virtually all previous reports. The efficient adsorption and activation of NO2- over Ru-doped NiMoO4 with oxygen vacancy have been verified by density functional theory calculations, as well as the possible reaction pathway.

Biological oxidation of As(III) and Sb(III) by a novel bacterium with Sb(III) oxidase rather than As(III) oxidase under anaerobic and aerobic conditions

Sb and As are chemically similar, but the sequences and structures of Sb(III) and As(III) oxidase are totally distinct. It is thus interesting to explore whether Sb(III) oxidase oxidizes As(III), and if so, how microbial oxidations of Sb(III) and As(III) influence one another. Previous investigations have yielded ambiguous or even erroneous conclusions. This study aimed to clarify this issue. Firstly, we prepared a consortium of Sb(III)-oxidizing prokaryotes (SOPs) by enrichment cultivation. Metagenomic analysis reveals that SOPs with the Sb(III) oxidase gene, but lacking the As(III) oxidase gene are predominant in the SOP community. Despite this, SOPs exhibit comparable Sb(III) and As(III)-oxidizing activities in both aerobic and anaerobic conditions, indicating that at the microbial community level, Sb(III) oxidase can oxidize As(III). Secondly, we isolated a representative cultivable SOP, Ralstonia sp. SbOX with Sb(III) oxidase gene but without As(III) oxidase gene. Genomic analysis of SbOX reveals that this SOP strain has a complete Sb(III) oxidase (AnoA) gene, but lacks As(III) oxidase (AioAB or ArxAB) gene. It is interesting to discover that, besides its Sb(III) oxidation activities, SbOX also exhibits significant capabilities in oxidizing As(III) under both aerobic and anaerobic conditions. Moreover, under aerobic conditions and in the presence of both Sb(III) and As(III), SbOX exhibited a preference for oxidizing Sb(III). Only after the near complete oxidation of Sb(III) did SbOX initiate rapid oxidation of As(III). In contrast, under anaerobic conditions and in the presence of both Sb(III) and As(III), Sb(III) oxidation notably inhibited the As(III) oxidation pathway in SbOX, while As(III) exhibited minimal effects on the Sb(III) oxidation. These findings suggest that SOPs can oxidize As(III) under both aerobic and anaerobic conditions, exhibiting a strong preference for Sb(III) over As(III) oxidation in the presence of both. This study unveils a novel mechanism of interaction within the Sb and As biogeochemical cycles.

Functional features of a novel Sb(III)- and As(III)-oxidizing bacterium: Implications for the interactions between bacterial Sb(III) and As(III) oxidation pathways

Antimony (Sb) and arsenic (As) share similar chemical characteristics and commonly coexist in contaminated environments. It has been reported that the biogeochemical cycles of antimony and arsenic affect each other. However, there is limited understanding regarding microbial coupling between the biogeochemical processes of antimony and arsenic. Here, we aimed to solve this issue. We successfully isolated a novel bacterium, Shinella sp. SbAsOP1, which possesses both Sb(III) and As(III) oxidase, and can effectively oxidize both Sb(III) and As(III) under aerobic and anaerobic conditions. SbAsOP1 exhibits greater aerobic oxidation activity for the oxidation of As(III) or Sb(III) compared to its anaerobic activity. SbAsOP1 also significantly catalyzes the oxidative mobilization of solid-phase Sb(III) under aerobic conditions. The activity of SbAsOP1 in oxidizing solid Sb(III) is 3 times lower than its activity in oxidizing soluble form. It is noteworthy that, in the presence of both Sb(III) and As(III) under aerobic conditions, either As(III) or Sb(III) significantly inhibits the oxidation of Sb(III) or As(III), respectively. In comparison, under anaerobic conditions and in the coexistence of Sb(III) and As(III), As(III) significantly inhibits Sb(III) oxidation, whereas Sb(III) almost completely inhibits As(III) oxidation. These findings suggest that under both aerobic and anaerobic conditions, SbAsOP1 demonstrates a partial preference for Sb(III) oxidation. Additionally, bacterial oxidations of Sb(III) and As(III) mutually inhibit each other to varying degrees. These observations gain a novel understanding of the interplay between the biogeochemical processes of antimony and arsenic.

Pot experimental trial for assessing the role of different composts on decontamination and reclamation of a polluted soil from an illegal dump site in Southern Italy using Brassica juncea and Sorghum bicolor

A pot experiment was carried out to evaluate the remediation potential of Brassica juncea and Sorghum bicolor in the decontamination of soil polluted with heavy metals such as copper, lead, tin, and zinc along with polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and heavy hydrocarbons. Two composts obtained from different composting processes were tested as biostimulating agents. At the end of the trial, the effect of plant/compost combinations on soil microbial composition, contaminant removal, biochemical indicators, and plant biomass production was determined. The results highlighted that compost addition improved plant biomass despite slowing down plants' removal of organic and inorganic contaminants. In addition, compost partially enhanced the soil biochemical indicators and modified the relative abundance of the rhizosphere microorganisms. Sorghum showed better mitigation performance than Brassica due to its higher growth. The soil fertility level, the choice of plant species, and microbial richness were found fundamental to perform soil remediation. In contrast, compost was relevant for a higher crop biomass yield.

Self-supported P-doped NiFe2O4 micro-sheet arrays for the efficient conversion of nitrite to ammonia

The nitrite reduction reaction (NO2-RR) is an important process for eliminating toxic nitrites from water while simultaneously producing high-value ammonia under ambient conditions. For the aim to improve the NO2-RR efficiency, we designed a new synthetic strategy to prepare a phosphorus-doped three-dimensional NiFe2O4 catalyst loaded onto a nickel foam in-situ and evaluated its performance for the reduction of NO2- to NH3. The catalyst achieved a high Faradaic efficiency (FE) of 95.39%, and an ammonia (NH3) yield rate of 34788.51 µg h-1 cm-2 at - 0.45 V vs. RHE. A high NH3 yield rate and FE were maintained after 16 cycles at - 0.35 V vs. RHE in an alkaline electrolyte. This study provides a new direction for the rational design of highly stable electrocatalysts for the conversion of NO2- to NH3.

Key process for reducing grains arsenic by applying sulfate varies with irrigation mode: Dual effects of microbe-mediated arsenic transformation and iron plaque

Sulfate affects the transformation of arsenic (As) in soil and its absorption by plant roots. However, the influence of sulfate and irrigation interactions on the mobility of As in the soil-rice system remains poorly understood. To address this gap, we conducted a pot experiment with varying sulfate levels and irrigation modes to examine their effects on rice As translocation, soil As forms, iron plaque formation, and microorganisms involved in As transformation. The addition of exogenous sulfate significantly reduced grain As levels by a maximum of 60.1%, 46.7%, and 70.5% under flooding (F), flooding-moist alternate (FM), moist (M) conditions, respectively. However, the changes in soil available As did not fully correspond to grains As content. Soil available As was only reduced by sulfate under the FM treatment, which limited grains As accumulation under this condition. The reduction in grains As content under F and M conditions was mainly attributed to sulfate-induced increases in soil pH, which in turn inhibited As translocation and promoted iron plaque formation. Additionally, both irrigation mode and sulfate fertilization independently or interactively influenced the abundance of Sulfuritalea, Koribacter, Geobacter, and Sulfuriferula, thereby affecting the As forms in soil through the Fe/S redox process. Specifically, under F and FM conditions, SO42--S inhibited Geobacter but stimulated Fe-oxidizing bacteria, possibly resulting in increased As bound to Fe/Mn oxides (As-F3). Under M condition, SO42--S levels regulated As adsorption and release through the participation of Fe/S cycle bacteria, specifically influencing the adsorbed As fraction (As-F2). Therefore, the addition of SO42--S hindered As translocation to grains by promoting As sequestration in the iron plaque and facilitating microbe-mediated As immobilization through the Fe/S cycle, which was dependent on soil moisture. These results can be used as a guide for sulfur fertilizer application under different soil moisture with the goal of minimizing rice grain As.

Contradictory Impacts of Nitrate on the Dissimilatory Arsenate-Respiring Prokaryotes-Induced Reductive Mobilization of Arsenic from Contaminated Sediments: Mechanism Insight from Metagenomic and Functional Analyses

Dissimilatory arsenate-respiring prokaryotes (DARPs) are considered to be a key impetus of the reductive dissolution of solid-phase arsenic. However, little is known about the interaction between nitrate and DARPs so far. In this study, we showed that nitrate either inhibited or promoted the DARP population-catalyzed reductive mobilization of As in sediments. Metagenomic analysis of the microbial communities in the microcosms after seven days of As release assays suggested that microbes mainly consisted of: Type-I DARPs having potential to reduce NO3- into NO2- and Type-II DARPs having potential to reduce NO3- to NH4+. We further isolated two cultivable DARPs, Neobacillus sp. A01 and Paenibacillus sp. A02, which represent Type-I and -II DARPs, respectively. We observed that nitrate suppressed A01-mediated release of As(III) but promoted A02-mediated release of As(III). Furthermore, we demonstrated that this observation was due to the fact that nitrite, the end product of incomplete denitrification by Type-I DARPs, suppressed the arrA gene expression per cell and growth of all DARPs, whereas ammonium, the end product of dissimilatory nitrate reduction to ammonium (DNRA) by Type-II DARPs, enhanced the arrA gene expression per cell and significantly promoted the growth of all DARPs. These findings suggest that the actual effects of nitrate on DARP population-catalyzed reductive mobilization of arsenic, largely depend on the ratio of Type-I to Type-II DARPs in sediments.

3D cauliflower-like Ni foam: a high-efficiency electrocatalyst for ammonia production via nitrite reduction

A 3D cauliflower-like Ni foam on titanium plate (Ni foam/TP) shows high electrocatalytic performance for ambient ammonia (NH3) synthesis via nitrite (NO2-) reduction. In 0.1 M phosphate-buffered saline solution with 0.1 M NO2-, such Ni foam/TP attains a high NH3 Faradaic efficiency (FE) of 95.9% and a large NH3 yield of 742.7 μmol h-1 cm-2 at -0.8 V. Its Zn-NO2- battery offers a high power density of 6.2 mW cm-2 and an NH3 FE of 90.1%.

Ruthenium doping: An effective strategy for boosting nitrite electroreduction to ammonia over titanium dioxide nanoribbon array

Electrochemical reduction of nitrite (NO₂^-) not only removes NO₂^- contaminant but also produces high-added value ammonia (NH₃). This process, however, needs efficient and selective catalysts for NO₂^--to-NH₃ conversion. In this study, Ruthenium doped titanium dioxide nanoribbon array supported on Ti plate (Ru-TiO₂/TP) is proposed as an efficient electrocatalyst for the reduction of NO₂^- to NH₃. When operated in 0.1 M NaOH containing NO₂^-, such Ru-TiO₂/TP achieves an ultra-large NH₃ yield of 1.56 mmol h^-1 cm^-2 and a super-high Faradaic efficiency of 98.9%, superior to its TiO₂/TP counterpart (0.46 mmol h^-1 cm^-2, 74.1%). Furthermore, the reaction mechanism is studied by theoretical calculation.

Rational Construction of Heterostructured Cu3 P@TiO2 Nanoarray for High-Efficiency Electrochemical Nitrite Reduction to Ammonia

Electroreduction of nitrite (NO₂ ^- ) to valuable ammonia (NH₃ ) offers a sustainable and green approach for NH₃ synthesis. Here, a Cu₃ P@TiO₂ heterostructure is rationally constructed as an active catalyst for selective NO₂ ^- -to-NH₃ electroreduction, with rich nanosized Cu₃ P anchored on a TiO₂ nanoribbon array on Ti plate (Cu₃ P@TiO₂ /TP). When performed in the 0.1 m NaOH with 0.1 m NaNO₂ , the Cu₃ P@TiO₂ /TP electrode obtains a large NH₃ yield of 1583.4 µmol h^-1  cm^-2 and a high Faradaic efficiency of 97.1%. More importantly, Cu₃ P@TiO₂ /TP also delivers remarkable long-term stability for 50 h electrolysis. Theoretical calculations indicate that intermediate adsorption/conversion processes on Cu₃ P@TiO₂ interfaces are synergistically optimized, substantially facilitating the conversion of NO₂ ^- -to-NH₃ .

Ambient ammonia synthesis via nitrite electroreduction over NiS2 nanoparticles-decorated TiO2 nanoribbon array

Nitrite (NO₂^-), as a N-containing pollutant, widely exists in aqueous solution, causing a series of environmental and health problems. Electrocatalytic NO₂^- reduction is a promising and sustainable strategy to remove NO₂^-, meanwhile, producing high value-added ammonia (NH₃). But the NO₂^- reduction reaction (NO₂^-RR) involves complex 6-electron transfer process that requires high-efficiency electrocatalysts to accomplish NO₂^--to-NH₃ conversion. Herein, we report NiS₂ nanoparticles decorated TiO₂ nanoribbon array on titanium mesh (NiS₂@TiO₂/TM) as a fantastic NO₂^-RR electrocatalyst for ambient NH₃ synthesis. When tested in NO₂^--containing solution, NiS₂@TiO₂/TM achieves a satisfactory NH₃ yield of 591.9 µmol h^-1 cm^-2 and a high Faradaic efficiency of 92.1 %. Besides, it shows remarkable stability during 12-h electrolysis test.

Environmental Mn(II) enhances the activity of dissimilatory arsenate-respiring prokaryotes from arsenic-contaminated soils

Many investigations suggest that dissimilatory arsenate-respiring prokaryotes (DARPs) play a key role in stimulating reductive mobilization of As from solid phase into groundwater, but it is not clear how environmental Mn(II) affects the DARPs-mediated reductive mobilization of arsenic. To resolve this issue, we collected soil samples from a realgar tailings-affected area. We found that there were diverse arsenate-respiratory reductase (arr) genes in the soils. The microbial communities had high arsenate-respiring activity, and were able to efficiently stimulate the reductive mobilization of As. Compared to the microcosms without Mn(II), addition of 10 mmol/L Mn(II) to the microcosms led to 23.99%-251.79% increases in the microbial mobilization of As, and led to 133.3%-239.2% increases in the abundances of arr genes. We further isolated a new cultivable DARP, Bacillus sp. F11, from the arsenic-contaminated soils. It completely reduced 1 mmol/L As(V) in 5 days under the optimal reaction conditions. We further found that it was able to efficiently catalyze the reductive mobilization and release of As from the solid phase; the addition of 2 mmol/L Mn(II) led to 98.49%-248.78% increases in the F11 cells-mediated reductive mobilization of As, and 70.6%-104.4% increases in the arr gene abundances. These data suggest that environmental Mn(II) markedly increased the DARPs-mediated reductive mobilization of As in arsenic-contaminated soils. This work provided a new insight into the close association between the biogeochemical cycles of arsenic and manganese.

Selective NOx- Electroreduction to Ammonia on Isolated Ru Sites

Nitrate and nitrite (NO_x^-) are widespread contaminants in industrial wastewater and groundwater. Sustainable ammonia (NH₃) production via NO_x^- electroreduction provides a prospective alternative to the energy-intensive industrialized Haber-Bosch process. However, selectively regulating the reaction pathway, which involves complicated electron/proton transfer, toward NH₃ generation relies on the robust catalyst. A specific consideration in designing selective NO_x^--to-NH₃ catalysts should meet the criteria to suppress competing hydrogen evolution and avoid the presence of neighboring active sites that are in favor of adverse N-N coupling. Nevertheless, efforts in this regard are still inadequate. Herein, we demonstrate that isolated ruthenium sites can selectively reduce NO_x^- into NH₃, with maximal Faradaic efficiencies of 97.8% (NO₂^- reduction) and 72.8% (NO₃^- reduction) at -0.6 and -0.4 V, respectively. Density functional theory calculations simulated the reaction mechanisms and identified the *NO → *NOH as the potential rate-limiting step for NO_x^--to-NH₃ conversion on single-atom Ru sites.

Ambient Ammonia Synthesis via Nitrate Electroreduction in Neutral Media on Fe3O4 Nanoparticles-decorated TiO2 Nanoribbon Array

Electrochemical nitrate (NO₃^-) reduction is a potential approach to produce high-value ammonia (NH₃) while removing NO₃^- pollution, but it requires electrocatalysts with high efficiency and selectivity. Herein, we report the development of Fe₃O₄ nanoparticles decorated TiO₂ nanoribbon array on titanium plate (Fe₃O₄@TiO₂/TP) as an efficient electrocatalyst for NO₃^--to-NH₃ conversion. When operated in 0.1 M phosphate-buffered saline and 0.1 M NO₃^-, such Fe₃O₄@TiO₂/TP achieves a prominent NH₃ yield of 12394.3 μg h^-1 cm^-2 and a high Faradaic efficiency of 88.4%. In addition, it exhibits excellent stability during long-time electrolysis.

Cu nanoparticles decorated juncus-derived carbon for efficient electrocatalytic nitrite-to-ammonia conversion

Electrocatalytic nitrite reduction to value-added NH₃ can simultaneously achieve sustainable ammonia production and N-contaminant removal in natural environments, which has attracted widespread attention but still lacks efficient catalysts. In this work, Cu nanoparticles decorated juncus-derived carbon can be proposed as a high-active electrocatalyst for NO₂^--to-NH₃ conversion, obtaining a high Faradaic efficiency of 93.2% and a satisfactory NH₃ yield of 523.5 μmol h^-1 mg_cat.^-1. Density functional theory calculations were applied to uncover insightful understanding of internal catalytic mechanism.

Biological effect of phosphate on the dissimilatory arsenate-respiring bacteria-catalyzed reductive mobilization of arsenic from contaminated soils

Dissimilatory arsenate-respiring prokaryotes (DARPs) are considered to be the major drive of the reductive mobilization of arsenic from solid phases. However, it is not fully understood how phosphate, a structural analog of arsenate, affects the DARPs-mediated arsenic mobilization. This work aimed to address this issue. As-contaminated soils were collected from a Shimen Realgar Mine-affected area. We identified a unique diversity of DARPs from the soils, which possess high As(V)-respiring activities using one of multiple small organic acids as the electron donor. After elimination of the desorption effect of phosphate on the As mobilization, the supplement of additional 10 mM phosphate to the active slurries markedly increased the microbial community-mediated reductive mobilization of arsenic as revealed by microcosm tests; this observation was associated to the fact that phosphate significantly increased the As(V)-respiratory reductase (Arr) gene abundances in the slurries. To confirm this finding, we further obtained a new DARP strain, Priestia sp. F01, from the samples. We found that after elimination of the chemical effect of phosphate, the supplement of 10 mM phosphate to the active slurries resulted in an 82.2% increase of the released As(III) in the solutions, which could be contributed to that excessive phosphate greatly increased the Arr gene abundance, and enhanced the transcriptional level of arrA gene and the bacterial As(V)-respiring activity of F01 cells. Considering that phosphate commonly coexists with As in the environment, and is a frequently-used fertilizer, these findings are helpful for deeply understanding why As concentrations in contaminated groundwater are dynamically fluctuated, and also provided new knowledge on the interactions between the biogeochemical processes of P and As.

High-Efficiency Ammonia Electrosynthesis on Anatase TiO2-x Nanobelt Arrays with Oxygen Vacancies by Selective Reduction of Nitrite

Electrocatalytic reduction of nitrite to NH₃ provides a new route for the treatment of nitrite in wastewater, as well as an attractive alternative to NH₃ synthesis. Here, we report that an oxygen vacancy-rich TiO_2-x nanoarray with different crystal structures self-supported on the Ti plate can be prepared by hydrothermal synthesis and by subsequently annealing it in an Ar/H₂ atmosphere. Anatase TiO_2-x (A-TiO_2-x) can be a superb catalyst for the efficient conversion of NO₂^- to NH₃; a high NH₃ yield of 12,230.1 ± 406.9 μg h^-1 cm^-2 along with a Faradaic efficiency of 91.1 ± 5.5% can be achieved in a 0.1 M NaOH solution containing 0.1 M NaNO₂ at -0.8 V, which also exhibits preferable durability with almost no decay of catalytic performances after cycling tests and long-term electrolysis. Furthermore, a Zn-NO₂^- battery with such A-TiO_2-x as a cathode delivers a power density of 2.38 mW cm^-2 as well as a NH₃ yield of 885 μg h^-1 cm^-2.

Hydrous ferric oxides (HFO's) precipitated from contaminated waters at several abandoned Sb deposits - Interdisciplinary assessment

The presented paper represents a comprehensive analysis of ochre sediments precipitated from Fe rich drainage waters contaminated by arsenic and antimony. Ochre samples from three abandoned Sb deposits were collected in three different seasons and were characterized from the mineralogical, geochemical, and microbiological point of view. They were formed mainly by poorly crystallized 2-line ferrihydrite, with the content of arsenic in samples ranging from 7 g·kg^-1 to 130 g·kg^-1 and content of antimony ranging from 0.25 g·kg^-1 up to 12 g·kg^-1. Next-generation sequencing approach with 16S RNA, 18S RNA and ITS markers was used to characterize bacterial, fungal, algal, metazoal and protozoal communities occurring in the HFOs. In the 16S RNA, the analysis dominated bacteria (96.2%) were mainly Proteobacteria (68.8%) and Bacteroidetes (10.2%) and to less extent also Acidobacteria, Actinobacteria, Cyanobacteria, Firmicutes, Nitrosprae and Chloroflexi. Alpha and beta diversity analysis revealed that the bacterial communities of individual sites do not differ significantly, and only subtle seasonal changes were observed. In this As and Sb rich, circumneutral microenvironment, rich in iron, sulfates and carbonates, methylotrophic bacteria (Methylobacter, Methylotenera), metal/reducing bacteria (Geobacter, Rhodoferax), metal-oxidizing and denitrifying bacteria (Gallionella, Azospira, Sphingopyxis, Leptothrix and Dechloromonas), sulfur-oxidizing bacteria (Sulfuricurvum, Desulphobulbaceae) and nitrifying bacteria (Nitrospira, Nitrosospira) accounted for the most dominant ecological groups and their impact over Fe, As, Sb, sulfur and nitrogen geocycles is discussed. This study provides evidence of diverse microbial communities that exist in drainage waters and are highly important in the process of mobilization or immobilization of the potentially toxic elements.

Amorphous CoB nanoarray as a high-efficiency electrocatalyst for nitrite reduction to ammonia

Amorphous CoB nanoarray is a high-efficiency catalyst for electrocatalytic NO2−-to-NH3 conversion, capable of attaining a large NH3 yield of 233.1 μmol h−1 cm−2 and a high faradaic efficiency of 95.2% at −0.7 V in 0.1 M Na2SO4 with 400 ppm NO2−.

A novel biofilm bioreactor derived from a consortium of acidophilic arsenite-oxidizing bacteria for the cleaning up of arsenite from acid mine drainage

Arsenite (As(III)) was considered to be of great concern in acid mine drainage (AMD). A promising approach for cleaning up of arsenite from AMD is microbial oxidation of As(III) followed by adsorptions. However, there is virtually no research about the acidophilic bioreactor for As(III) oxidation so far. In this study, we formed a new biofilm bioreactor with a consortium of acidophilic As(III) oxidation bacteria. It is totally chemoautotrophic, with no need to add any carbon or other materials during the operations. It works well under pH 3.0-4.0, capable of oxidizing 1.0-20.0 mg/L As(III) in 3.0-4.5 h, respectively. A continuous operation of the bioreactor suggests that it is very stable and sustainable. Functional gene detection indicated that the biofilms possessed a unique diversity of As(III) oxidase genes. Taken together, this acidophilic bioreactor has great potential for industrial applications in the cleaning up of As(III) from AMD solution.

Differential responses of photosynthetic parameters and its influence on carbohydrate metabolism in some contrasting rice (Oryza sativa L.) genotypes under arsenate stress

Influence of arsenic (As) in As tolerant and sensitive rice genotypes based chloroplastic pigments, leaf gas exchange attributes and their influence on carbohydrate metabolism were investigated in the present study. As retards growth of crop plants and increase several health ailments by contaminating food chain. Photosynthetic inhibition is known to be the prime target of As toxicity due to over-production of ROS. Hydroponically grown rice seedlings of twelve cultivars were exposed to 25, 50, and 75 μM arsenate (AsV) that exerted negative impact on plastidial pigments content and resulted into inhibition of Hill activity. Internal CO₂ concentration lowered gradually due to interference of As with stomatal conductance and transpiration rate that subsequently led to drop in net photosynthesis. Twelve contrasting rice genotypes responded differentially to As(V) stress. Present study evaluated As tolerant and sensitive rice cultivars with respect to As(V) imposed alterations in pigments content, photosynthetic attributes along with sugar metabolism. Starch contents, the principle carbohydrate storage declined differentially among As(V) stressed test cultivars, being more pronounced in cvs. Swarnadhan, Tulaipanji, Pusa basmati, Badshabhog, Tulsibhog and IR-20 compared to cvs. Bhutmuri, Kumargore, Binni, Vijaya, TN-1 and IR-64. Therefore, the six former cultivars tried to adapt defensive mechanisms by accumulating higher levels of reducing and non-reducing sugars to carry out basal metabolism to withstand As(V) induced alterations in photosynthesis. This study could help to screen As tolerant and sensitive rice genotypes based on their photosynthetic efficiency in As polluted agricultural fields to reduce As contamination assisted ecotoxicological risk.

Microbial reactions and environmental factors affecting the dissolution and release of arsenic in the severely contaminated soils under anaerobic or aerobic conditions

The soils near the abandoned Shimen Realgar Mine are characterized by containing extremely high contents of total and soluble arsenic. To determine the microbial reactions and environmental factors affecting the mobilization and release of arsenic from soils phase into pore water, we collected 24 soil samples from the representative points around the abandoned Shimen Realgar Mine. They contained 8310.84 mg/kg total arsenic and 703.21 mg/kg soluble arsenic in average. The soluble arsenic in the soils shows significant positive and negative correlations with environmental SO₄^2-/TOC/pH/PO₄^3-, and Fe/Mn, respectively. We found that diverse dissimilatory As(V)-respiring prokaryotes (DARPs) and As(III)-oxidizing bacteria (AOB) exist in all the examined soil samples. The activities of DARPs led to 65-1275% increase of soluble As(III) in the examined soils after 21.0 days of anaerobic incubation, and the microbial dissolution and releases of arsenic show significant positive and negative correlations with the environmental pH/TN and NH₄⁺/PO₄^3-, respectively. In comparison, the activities of AOB led to 24-346% inhibition of the dissolved oxygen-mediated dissolution of arsenic in the soils, and the AOB-mediated releases of As(V) show significant positive and negative correlations with the environmental SO₄^2- and pH/NH₄⁺, respectively. The microbial communities of 24 samples contain 54 phyla of bacteria that show extremely high diversities. Total arsenic, TOC, NO₃^- and pH are the key environmental factors that indirectly controlled the mobilization and release of arsenic via influencing the structures of the microbial communities in the soils. This work gained new insights into the mechanism for how microbial communities catalyze the dissolution and releases of arsenic from the soils with extremely high contents of arsenic.

Unique diversity and functions of the arsenic-methylating microorganisms from the tailings of Shimen Realgar Mine

Microbial arsenic (As) methylation plays important roles in the As biogeochemical cycle. However, little is known about the diversity and functions of As-methylating microorganisms from the tailings of a Realgar Mine, which is characterized as containing extremely high concentrations of As. To address this issue, we collected five samples (T1-T5) from the tailings of Shimen Realgar Mine. Microcosm assays without addition of exogenous As and carbon indicated that all the five samples possess significant As-methylating activities, producing 0.8-5.7 μg/L DMAs^V, and 1.1-10.7 μg/L MMAs^V with an exception of T3, from which MMAs^V was not detectable after 14.0 days of incubation. In comparison, addition of 20.0 mM lactate to the microcosms significantly enhanced the activities of these samples; the produced DMAs^V and MMAs^V are 8.0-39.7 μg/L and 5.8-38.3 μg/L, respectively. The biogenic DMAs^V shows significant positive correlations with the Fe concentrations and negative correlations with the total nitrogen concentrations in the environment. A total of 63 different arsM genes were identified from the five samples, which code for new or new-type ArsM proteins, suggesting that a unique diversity of As-methylating microbes are present in the environment. The microbial community structures of the samples were significantly shaped by the environmental total organic carbon, total As contents and NO₃^- contents. These data help to better understand the microorganisms-catalyzed As methylation occurred in the environment with extremely high contents of As.