[Simultaneous Immobilization of Cadmium and Arsenic in Paddy Soils with Novel Fe-Mn Combined Graphene Oxide]

Novel Fe-Mn combined graphene oxide （GO-FM） material was produced and tested for its efficacy in remediating agricultural soil co-contaminated by Cd and As. In a 60-day soil incubation experiment， the remediation mechanism and immobilization effects of GO and GO-FM at different addition ratios （0.1%， 0.2%， and 0.3%） were investigated in Shangyu and Foshan soils， which had varying physicochemical properties and contamination degrees. The dynamic changes in pH， DOC concentration， bioavailable Cd and As content， and morphology of Cd and As were explored to determine the remediation efficacy of the materials. The results demonstrated that compared with that in the blank control， GO-FM increased the pH in Shangyu soil but decreased the pH in Foshan soil. After culture， both GO and GO-FM increased the soil DOC content. GO-FM decreased the soluble Cd concentration by 5.08%-19.19% and the bioavailability of Cd by 36.57%-42.8% in Foshan soil， and the main immobilization mechanism was electrostatic adsorption， complexation， and hydroxylated metal ion formation. The immobilization ability of GO-FM on Cd was lower than that of Foshan soil due to the influence of electrostatic repulsion in Shangyu acidic soil. However， with the increase in the amount of GO-FM， the trend of increasing the bioavailability of Cd by graphene oxide was inhibited. The addition of 0.2% and 0.3% GO-FM decreased the bioavailability of Cd by 6.45%-13.56% in Shangyu soil. Additionally， GO-FM decreased the bioavailability of As in Shangyu soil and Foshan soil by 4.34%-9.15% and 0.87%-5.71%， respectively. This was due to the immobilization mechanism of oxidation of As by manganese oxides and inner surface chelate between As and the surface hydroxyl group of iron oxides. In summary， the immobilization effect of GO-FM on Cd in Foshan soil was better than that in Shangyu soil， and the immobilization effect of GO-FM on As in Shangyu soil was better than that in Foshan soil， which can provide a theoretical basis and reference for the prevention and control of Cd and As co-contamination in different types of soil.

Iron and manganese availability drives primary production and carbon export in the Weddell Sea

Next to iron (Fe), recent phytoplankton-enrichment experiments identified manganese (Mn) to (co-)limit Southern Ocean phytoplankton biomass and species composition. Since taxonomic diversity affects aggregation time and sinking rate, the efficiency of the biological carbon pump is directly affected by community structure. However, the impact of FeMn co-limitation on Antarctic primary production, community composition, and the subsequent export of carbon to depth requires more investigation. In situ samplings of 6 stations in the understudied southern Weddell Sea revealed that surface Fe and Mn concentrations, primary production, and carbon export rates were all low, suggesting a FeMn co-limited phytoplankton community. An Fe and Mn addition experiment examined how changes in the species composition drive the aggregation capability of a natural phytoplankton community. Primary production rates were highest when Fe and Mn were added together, due to an increased abundance of the colonial prymnesiophyte Phaeocystis antarctica. Although the community remained diatom dominated, the increase in Phaeocystis abundance led to highly carbon-enriched aggregates and a 4-fold increase in the carbon export potential compared to the control, whereas it only doubled in the Fe treatment. Based on the outcome of the FeMn-enrichment experiment, this region may suffer from FeMn co-limitation. As the Weddell Sea represents one of the most productive Antarctic marginal ice zones, our findings highlight that in response to greater Fe and Mn supply, changes in plankton community composition and primary production can have a disproportionally larger effect on the carbon export potential.

Enhancement of plasma-catalytic oxidation of ethylene oxide (EO) over FeMn catalysts in a dielectric barrier discharge reactor

In this work, an integrated system combining non-thermal plasma (NTP) and FeMn catalysts was developed for ethylene oxide (EO) oxidation. The effect of Fe/Mn molar ratio on the oxidation rate of EO and energy yield of the plasma-catalytic process has been investigated as a function of specific energy density (SED). Compared with the case of using plasma alone, the combination of plasma and FeMn catalysts greatly enhanced the reaction performance by the factor of 25.2% to 97.6%. The maximum oxidation rate of 98.8% was achieved when Fe₁Mn₁ catalyst was placed in the dielectric barrier discharge (DBD) reactor at the SED of 656.1 J·L^-1. The highest energy yield of 2.82 g·kWh^-1 was obtained at the SED of 323.2 J·L^-1 over the Fe₁Mn₁ catalyst. The interactions between Fe and Mn species resulted in larger specific surface area of the catalyst. Moreover, the reducibility of the catalysts was improved, while more surface adsorbed oxygen (O_ads) was detected on the catalyst surfaces. Moreover, the redox cycles between Fe and Mn species facilitated consumption and supplementation of reactive oxygen species, which contributed to the plasma-catalytic oxidation reactions. The major reaction products of plasma-induced EO oxidation over the FeMn catalysts, including CH₃COOH, CH₃CHO, CH₄, C₂H₆ and C₂H₄, were observed using the FT-IR analyzer and GC-MS instrument. The reaction mechanisms of EO oxidation were discussed in terms of both gas-phase reaction and catalyst surface reaction. The redox cycles between Fe and Mn species facilitated the plasma reaction and accelerated the deep oxidation of by-products.

Removal of lead ions by two FeMn oxide substrate adsorbents

Lead pollution has become a global concern due to its ubiquity and persistence. This study describes two FeMn oxide substrate adsorbents, namely, FeMn binary oxides (FMBO) and mesoporous FeMn binary oxide (MFMBO) covered with tannic acid film (FMBO@TA-Fe³⁺ and MFMBO@TA-Fe³⁺), for the treatment of Pb²⁺ in water. The characterization results showed that TA was successfully coated onto the surfaces of FMBO and MFMBO. The maximum capacities of Pb²⁺ on FMBO@TA-Fe³⁺ and MFMBO@TA-Fe³⁺ were 322.08 and 357.14 mg g^-1, respectively, which were twice those of FMBO and MFMBO. The adsorption of Pb²⁺ on the adsorbents was a spontaneous, endothermic process with increasing disorder through thermodynamics studies. An overall mechanism was proposed for Pb²⁺ adsorption, the improved adsorption performance of FMBO@TA-Fe³⁺ and MFMBO@TA-Fe³⁺ is ascribed to the mesoporous characteristics and the introduction of hydroxyl groups. Further investigation indicated the adsorption of Pb²⁺ could be attributed to electrostatic interactions on FMBO@TA-Fe³⁺ and MFMBO@TA-Fe³⁺, and cation exchange existed through the formation of these internal surface complexes. The Pb²⁺-loaded adsorbents could be effectively desorbed in a dilute hydrochloric acid solution, promoting recycling and reuse of the regenerated adsorbents. These results warrant the promising application of FMBO@TA-Fe³⁺ and MFMBO@TA-Fe³⁺ for the removal of Pb²⁺, and this work first proposed TA film-modified FMBO and MFMBO to improve its adsorption capacity in the application of environmental remediation.

Arsenite removal from groundwater by iron-manganese oxides filter media: Behavior and mechanism

Arsenic, a common contaminant in groundwater environments, usually coexists with other contaminants, for example, ammonium, iron, and manganese. In our previous studies, an iron-manganese (Fe-Mn) oxides filter media was developed for catalytic oxidation removal of ammonium, iron, and manganese. In this study, batch oxidation/adsorption kinetic experiments revealed that the filter media could easily oxidize arsenite (As(III)) to arsenate (As(V)). And the sorption kinetics was found to follow the pseudo-second-order kinetic model. X-ray powder diffraction (XRD) and Fourier transform infrared spectra (FTIR) along with X-ray photoelectron spectroscopy (XPS) were used to analyze the surface change in the Fe-Mn oxides. Based on sorption and spectroscopic measurements, the mechanism of As(III) removal by the Fe-Mn oxides filter media was found to be an oxidation coupled with sorption approach. As(III) in the aqueous solution was firstly oxidized to As(V) on the surfaces of the Fe-Mn oxides filter media. Then the converted As(V) was attracted to the Fe-Mn oxides filter media surfaces and bounded with the active sites (-OH groups), through weak intermolecular H-bondings. Our results indicated that the novel Fe-Mn oxides filter media could be applied for the simultaneous removal of ammonium, iron, manganese, and As(III) in drinking water treatment and environmental remediation. PRACTITIONER POINTS: A novel iron-manganese oxides filter for efficient As(III) removal was established. The exhausted filter media could be easily regenerated by NaHCO₃ solution. Mn(III) related to surface lattice oxygen species was responsible for As(III) oxidation. The oxidation and adsorption processes were involved in As(III) removal. The filter media could be successfully applied to simultaneous removal of ammonium, manganese, iron, and arsenic.