Fe-Mn Binary Oxide Research Articles

Adsorption Performance of Fe-Mn Polymer Nanocomposites for Arsenic Removal: Insights from Kinetic and Isotherm Models.

Global concern over arsenic contamination in drinking water necessitates innovative and sustainable remediation technologies. This study evaluates the adsorption performance of Fe-Mn binary oxide (FMBO) nanocomposites developed by coating polyethylene (PE) and polyethylene terephthalate (PET) with FMBO for the removal of As(III) and As(V) from water. Adsorption kinetics were rapid, with equilibrium achieved within 1-4 h depending on the material and pH. PET-FMBO and FMBO exhibited faster rates and higher arsenic removal (up to 96%) than PE-FMBO. Maximum As(III) adsorption capacities ranged from 4.76 to 5.75 mg/g for PE-FMBO, 7.2 to 12.0 mg/g for PET-FMBO, and up to 20.8 mg/g for FMBO, while capacities for As(V) ranged from 5.20 to 5.60 mg/g, 7.63 to 18.4 mg/g, and up to 46.2 mg/g, respectively. The results of the Dubinin-Radushkevich isotherm model, with free energy (Ea) values exceeding 16 kJ/mol, suggest chemisorption is the dominant mechanism, which is supported by the kinetics data. Given the effective removal of As(III), chemisorption likely proceeds through ligand exchange during the Mn oxide-mediated oxidation of As(III) and complexation with hydroxyl groups on the nanocomposite. These findings highlight the strong potential of Fe-Mn polymer nanocomposites, particularly PET-FMBO, for efficient arsenic removal during practical water treatment applications.

Fast and efficient remediation of antimony-contaminated surface water and field soil using alumina supported Fe–Mn binary oxide

Antimony (Sb) pollution in surface water and soil has earned extensive attention. Our previous study synthesized a new class of alumina supported Fe–Mn binary oxide (Fe–Mn@Al2O3) and found that MnO2 in the composite oxidized Sb(III) to Sb(V) and FeOOH and Al2O3 played an indispensable role in adsorption of Sb(III) and Sb(V). This study further explored the removal of Sb in surface water and in situ sequestration of Sb in Sb-contaminated field soil via Fe–Mn@Al2O3. Sb removal from water was pH independent and the removal efficiencies of Sb(III) and total Sb kept constant at 95.4% and 60.5%, respectively, over a pH range of 5.0–10.0. Increasing dissolved organic matter (DOM) from 0 to 22.8 mg/L had negligible effect on Sb(III) removal whereas inhibited the total Sb removal from 60.5% to 51.2%. Dissolved oxygen cannot oxidize aqueous Sb(III), yet, enhanced the Sb(III) removal whereas decreased the total Sb removal. The composite performed well in natural surface water with high DOM and inorganic ligands. In addition, the composite effectively immobilized Sb in field soil. 5% of the composite significantly inhibited the H2SO4 and HNO3 leachable Sb by 93.6% after 30 d. The amendment transformed the Sb speciation from more easily available fractions (i.e., exchangeable, carbonate-bound, and Fe–Mn oxides-bound species) into more stable fractions (i.e., organic material bound and residual species), leading to declined Sb bioaccessibility and reduced environmental risk. The composite facilitated a long-term stability of Sb in soil. The study demonstrated an easy, fast, and effective strategy for efficient immobilization of Sb in water and soil.

Polysulfone membranes decorated with Fe–Mn binary oxide nanoparticles and polydopamine for enhanced arsenate/arsenite adsorptive removal

Arsenic contamination of water is a global environmental concern, and membrane technology combined with nanotechnology contributes to more efficient removal of arsenic. In this study, Fe–Mn oxide (FM), Polydopamine (PDA), and PDA-modified FM (PFM) were incorporated into polysulfone (PSF) to prepare adsorption membranes (PFMP) for arsenic removal. The prepared nanoparticles and membranes were characterized using TEM, SEM, FTIR, TGA, contact angle, and pure water flux. The introduction of particles enhanced the hydrophilicity of the membranes and significantly enhanced the pure water flux of the membranes. Adsorption experiments indicated that the PFMP membrane exhibited the best arsenic removal performance, with maximum adsorption capacities for As(III) and As(V) were 11.57 mg/g and 12.39 mg/g, respectively. The Langmuir model fitted the adsorption isotherms well, and the kinetics followed the pseudo-second-order model. The filtration experiment revealed that the PFMP membrane was capable of reducing As(III) solution (915 L/m2) and As(V) solution (1075 L/m2) from a concentration of 100 μg/L to the safe limit of As (＜10 μg/L). The As-loaded membrane was regenerated using NaOH solution (pH = 11), and the filtration experiment was repeated. FTIR and XPS demonstrated that the mechanism of the reaction between the membrane and arsenic was ligand exchange, where the arsenic ions were bonded to the oxygen ions to form Mn–O–As and Fe–O–As.

Arsenate adsorption, desorption, and re-adsorption on Fe–Mn binary oxides: Impact of co-existing ions

Fe–Mn binary oxides have demonstrated impressive arsenate removal efficiencies as adsorbents. However, their interaction with co-existing ions can lead to arsenate desorption, complicating the remediation process. The dynamics of both desorption and subsequent readsorption of arsenate on these oxides under the influence of various ions remain largely unexplored. This study illuminates these processes through a detailed six-month batch experiment, examining the behavior of arsenate in the presence of both single and multiple competing ions. Our findings demonstrate varied desorption impacts by different ions. Notably, the desorption effects induced by bicarbonate (HCO3−) and phosphate (PO43−) were the most significant, with maximum desorption rates reaching 21.8 % and 20.8 %, respectively. Following desorption, As(V) exhibited varying re-adsorption rates; notably, As(V) desorbed by HCO3− and PO43− achieved nearly complete re-adsorption at rates of 100 % and 97.8 % respectively after 150 days. The dynamics altered substantially in the presence of multiple ions. Specifically, the co-presence of Ca2+ and Mg2+ significantly reduced the desorption of As(V) by HCO3−, with maximum desorption rates decreasing to 0 % and 2.9 %, respectively. Moreover, the inclusion of silicate (SiO32−) in the system markedly enhanced the re-adsorption of As(V), surpassing rates observed in the presence of HCO3− alone. In contrast, when PO43−and HCO3− were present together, almost no re-adsorption of As(V) occurred, leading to a higher final desorption rate of 27.4 %. These results highlight the complex and significant role that specific ions and their combinations play in the desorption and re-adsorption of As(V) on Fe–Mn binary oxide surfaces. The study emphasizes the importance of considering the types and interactions of co-existing ions in environmental settings when utilizing Fe–Mn binary oxides for efficient arsenic removal.

Fe-Mn binary oxides improve the methanogenic performance and reduce the environmental health risks associated with antibiotic resistance genes during anaerobic digestion

Increasing evidence indicates that metal oxides can improve the methanogenic performance during anaerobic digestion (AD) of piggery wastewater. However, the impacts of composite metal oxides on the methanogenic performance and risk of antibiotic resistance gene (ARG) transmission during AD are not fully understood. In this study, different concentrations of Fe-Mn binary oxides (FMBO at 0, 250, 500, and 1000 mg/L) were added to AD to explore the effects of FMBO on the process. The methane yield was 7825.1 mL under FMBO at 250 mg/L, 35.2% higher than that with FMBO at 0 mg/L. PICRUSt2 functional predictions showed that FMBO promoted the oxidation of acetate and propionate, and the production of methane from the substrate, as well as increasing the abundances of most methanogens and genes encoding related enzymes. Furthermore, under FMBO at 250 mg/L, the relative abundances of 14 ARGs (excluding tetC and sul2) and four mobile gene elements (MGEs) decreased by 24.7% and 55.8%, respectively. Most of the changes in the abundances of ARGs were explained by microorganisms, especially Bacteroidetes (51.20%), followed by MGEs (11.98%). Thus, the methanogenic performance of AD improved and the risk of horizontal ARG transfer decreased with FMBO, especially at 250 mg/L.

In-situ utilization of As(III) enhances selective recovery of heavy metals from acid mine drainage by hydroxyl-enriched Fe-Mn binary oxide

As(III), a common pollutant in acid mine drainage (AMD), can provide potential active sites for the adsorption of heavy metals on adsorbents. In this study, Pb(II), As(III), and Cu(II) were sequentially recovered from AMD using hydroxyl-enriched Fe-Mn binary oxide (O-FMO) via the in-situ utilization strategy of As(III). The results showed that the prepared O-FMO demonstrated better adsorption performance under acidic conditions than FMO. O-FMO exhibited an outstanding selectivity (＞99.6%) for the removal of Pb(II) and As(III) via the generation of insoluble As-Pb complex in AMD and the immobilized Pb and As could be subsequently separated using respective acid and alkaline solutions. Furthermore, the recovered O-FMO containing residual As could promote the selective removal of Cu(II) (Selectivity ＞98.4 %) from the treated AMD. Mechanism analysis revealed that the oxidized As(V) on the O-FMO played a dominant role in promoting metals adsorption via electrostatic interaction and complexation. Pb(II) can directly form a generally stable complex with H3AsO4 (As(V)) under acidic conditions, thereby replacing the Cu(II) and Cd(II) which only form acid-soluble complexes with H2AsO4-1 (As(V)). Besides, metal electronegativity affects the traits and the formation sequence of As-metal complexes. Hence, the recovery of metal(loid)s (purity > 98.4 %) from AMD following the order: Pb(II), As(III), and Cu(II) could be achieved by reutilizing O-FMO. This work offers a unique approach for AMD remediation by utilizing pollutants to treat pollution.

Critical role of zero-valent iron in the efficient activation of H2O2 for 4-CP degradation by bimetallic peroxidase-like.

Peroxidase-like based on double transition metals have higher catalytic activity and are considered to have great potential for application in the field of pollutant degradation. First, in this paper, a novel Fe0-doped three-dimensional porous Fe0@FeMn-NC-like peroxidase was synthesized by a simple one-step thermal reduction method. The doping of manganese was able to reduce part of the iron in Fe-Mn binary oxides to Fe0 at high temperatures. In addition, Fe0@FeMn-NC has excellent peroxidase-like mimetic activity, and thus, it was used for the rapid degradation of p-chlorophenol (4-CP). During the degradation process, Fe0 was able to rapidly replenish the constantly depleted Fe2+ in the reaction system and brought in a large number of additional electrons. The ineffective decomposition of H2O2 due to the use of H2O2 as an electron donor in the reduction reactions from Fe3+ to Fe2+ and from Mn3+ to Mn2+ was avoided. Finally, based on the experimental results of LC-MS and combined with theoretical calculations, the degradation process of 4-CP was rationally analyzed, in which the intermediates were mainly p-chloro-catechol, p-chloro resorcinol, and p-benzoquinone. Fe0@FeMn-NC nano-enzymes have excellent catalytic activity as well as structural stability and perform well in the treatment of simulated wastewater containing a variety of phenolic pollutants as well as real chemical wastewater. It provides some insights and methods for the application of peroxidase-like enzymes in the degradation of organic pollutants.

Amorphous Fe–Mn binary oxides nanoparticles decorating waste bamboo biomass-based monolith for efficient arsenic removal with column adsorption

The removal of naturally occurring arsenic from aqueous media remains a challenging endeavor for the protection of public health and ecosystems. Herein, we devised a workable fresh-biomass-based monolith adsorbent by in situ generation of amorphous Fe–Mn binary oxides nanoparticles (Fe–Mn–O) on a waste bamboo biomass (MB) via a simple procedure of pre-oxidation plus co-precipitation. In the pre-oxidation process of MB, the surface underwent roughening and the manganese ions permeated deeply inside the biomass, both of which facilitated the loading of Fe–Mn–O (25.06 wt%). As a result, the Fe–Mn–O/MB had outstanding adsorption capacities of 33.41 and 36.88 mg g−1 for As(III) and As(V), respectively. XRD and FTIR analyses show that the amorphous structure of Fe–Mn–O with low-coordinated active centers provides numerous hydroxyl functional groups that enhance arsenic adsorption, moreover, oxidation of As(III) was realized. In different water matrix, the Fe–Mn–O/MB composite exhibited a retention of 87.33 % and 89.53 % of its original adsorption capacity for As(III) and As(V) after five cycles of reuse as well as enabled continuous operation in a fixed-bed system with a bed volume of around 1150. Therefore, this work provides a promising approach for efficient abatement of inorganic arsenic-caused water pollution.

Rapid and selective removal of trace As(III) from water using Fe[sbnd]Mn binary oxide

The rapid removal of trace arsenic is crucial for ensuring the safety of drinking water. However, achieving the rapid removal of trace arsenic poses a significant challenge. In this study, we aim to enhance the removal efficiency of trace arsenic by increasing the specific surface area of the adsorbent material while maintaining its micrometer size. The material design allowed for the rapid removal of trace amounts of As(III) in groundwater within 10 s, resulting in a concentration as low as 0.281 μg L−1, which meets the WHO drinking water standard (<10 μg L−1). Our experimental results demonstrated that the FeMn binary oxide could partially oxidize As(III) into As(V), achieving a removal efficiency exceeding 99 %. Furthermore, we investigated the influence of common cations and anions, such as K+, Mg2+, Ca2+, Cl−, NO3−, SO42−, and PO43−, which may be present in natural water, on As(III) removal. Our findings indicated that the FeMn binary oxide exhibited remarkably high separation factors (ranging from 10 to 103) for other coexisting ions, indicating its exceptional selectivity for As(III) even in the presence of other ions. The outstanding arsenic uptake capability and selectivity of the FeMn binary oxide make it a highly promising adsorbent for the efficient removal of trace As(III) from aqueous solutions.

Favorably adjusting the oxygen species over Fe-Mn binary oxide sorbent by directional etching for arsenic oxidation and adsorption

In this study, raw and etched Fe-Mn binary oxide sorbents were prepared via the coprecipitation method to explore the catalytic oxidation and adsorption of As2O3. The oxidation and adsorption capacities for As2O3 were investigated at different temperatures, citric acid etching concentrations, and O2 concentrations. Compared with the raw sorbent, the sorbents etched with citric acid show excellent arsenic adsorption and oxidation capacities. As confirmed by scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) studies, etching increased the number of oxygen vacancies and specific surface area. Oxygen temperature programming desorption (O2-TPD) characterization showed that the oxygen vacancy structure enhanced the instability and fluidity of the lattice oxygen, promoting arsenic adsorption and oxidation. Hydrogen temperature programmed reduction (H2-TPR) characterization indicated that citric acid etching facilitated the oxidation of the sorbent. In addition, density functional theory (DFT) calculations also confirmed that etching facilitated arsenic adsorption by altering the adsorption energies of the sorbents.

Simultaneous oxidization-adsorption for arsenic and antimony by biological Fe-Mn binary oxides (BFMO): The efficiencies and mechanism

Here, a novel manganese oxidizing bacterium Morganella Morganii MnOx-1 was applied to synthesize biological iron-manganese oxides (BFMO) to simultaneously oxidize and adsorb As and Sb. The oxidization rates of As(III) and Sb(III) by BFMO were 74.13% and 51.85%, which were 1.43 and 1.30 times of that by biological manganese oxides (BMO), respectively. Moreover, the simultaneous removal rates of As(III), As(V), Sb(III) and Sb(V) (100 mg/L of each) by BFMO with the stain MnOx-1 were 87.05%, 94.23%, 79.65% and 84.33% in 7 days, and 80.26%, 99.32%, 82.97% and 88.50% in 28 days, respectively. In addition, BMO contributed to oxidize As(III) and Sb(III), and FeOOH was mainly responsible for adsorption by complexing with the metalloids in the simultaneous removal of As and Sb. The function groups on the surface of BFMO, such as -OH, C-O, C-O, C-C, etc. were also involved the adsorption processes. Our results have important implications for understanding the transformations of As and Sb intermediating by manganese oxidizing bacteria, and develop an environmental-friendly method for simultaneously removing As and Sb pollutants in water.

Evolution of biogenic Fe-Mn binary oxide physicochemical properties during biofilter start-up for sustainable urban groundwater treatment

The declining freshwater resources due to climate change, population growth, and urbanization evoke the increasing demand for groundwater to replenish drinking water, while excess manganese (Mn) in groundwater poses a critical threat to drinking water safety. Biofiltration enables convenient and facile purifying of Mn-rich groundwater and its start-up process is crucial to efficacy. In this study, biogenic Fe and Mn binary oxides (BioFMBO) effects on the mid and late start-up of biofilter were investigated and compared with the role of bio-oxidation. The results showed that the dominant role of BioFMBO on Mn removal was more pronounced in the late start-up (85%) as compared to the mid-start-up (50%), reaching 2.5–11.2 times of the bio-oxidation effect. Besides, the biofilter regeneration period after BioFMBO disruption was 1.5–2 folds that of bio-inactivation. These phenomena were due to the continuous conversion of Mn and Fe to amorphous BioFMBO during filtration, characterized by mixed Mn(II)/(III)/(IV) species and abundant reactive oxygen vacancies with high catalytic oxidation ability to expedite single electron transfer during Mn oxidation. Additionally, the mixed Mn species ratio and reactive oxygen vacancies content changed with the enhanced catalysis capacity of BioFMBO, improving the Mn removal performance and regeneration ability of the biofilter.

Performance and mechanism of simultaneous Sb(III) and Cd(II) removal from water by Fe-Mn binary oxide/bone char.

A novel Fe-Mn binary oxide (FMBO)/bone char composite (FMBC) was synthesized and utilized to simultaneously adsorb Sb(III) and Cd(II) from aqueous phase in this study. The successful loading of Fe-Mn binary oxide on the bone char surface was revealed by the results of scanning electron microscope, X-ray diffraction patterns, and energy dispersive spectroscopy of FMBC. The FMBC exhibited remarkable ability of simultaneous removing Sb(III) and Cd(II) from aqueous, and the presence of Cd(II) enhanced Langmuir theoretical maximum adsorption capacity for Sb(III) significantly from 67.8 to 209.0mg/g. Besides, FMBC could efficiently remove Sb(III) and Cd(II) in the wide initial pH range of 2-7. The influences of ionic strength, co-existing anions, humic acid, and temperature on the adsorption of Sb(III) and Cd(II), and the application potential of FMBC in actual groundwater were investigated. The main mechanisms of Sb(III) and Cd(II) adsorption onto FMBC involved redox, electrostatic interaction, surface complexation, ion exchange, and precipitation. The result of X-ray photoelectron spectroscopy and mapping spectrum analysis revealed that Mn(III) on FMBC played the key role in the Sb(III) oxidation, while FeOOH worked as the adsorption sites of FMBC. Meanwhile, the hydroxyapatite on FMBC also contributed to the removal of Cd(II). The presence of Cd(II) not only increased the positive charge on the surface of FMBC but also formed the Fe-Sb-Cd ternary complex, promoting the removal of Sb. This work provides valuable information for the application of FMBO/bone char as a cost-effective adsorbent to remediate co-pollution of Sb(III) and Cd(II) in aqueous environment.

Co-adsorption mechanisms of Cd(II) and As(III) by an Fe-Mn binary oxide biochar in aqueous solution

Biochar can remove oppositely charged ionic species of Cd(II) and As(III)/As(V) from water but the co-adsorption mechanisms of the metal(loid)s are poorly understood. This study aims to unravel the co-absorption mechanisms of Cd(II) and As(III) by a Pennisetum sp. straw biochar (BC) modified with Fe-Mn oxide (FMBC). The maximum adsorption capacity of Cd(II) and As(III) by FMBC was 141.1 and 31.8 mg/g, respectively, which was 2.71 and 3.89 times higher than that of BC. The adsorption of Cd(II) by FMBC demonstrated a homogeneous monolayer chemical process, while the As(III) adsorption presented a heterogeneous multilayer process. In the dual-adsorbate system, Cd(II) increased the adsorption of As(III) on FMBC by 5.1–123.9%, while As(III) reduced the adsorption of Cd(II) by 0.7–24.8%, indicating respective synergism and competition effect. Systematic co-adsorption experiments and adsorbent characterization results suggested that the synergistic mechanism occurred via electrostatic attraction and ternary surface complexation, whereas the competitive effect emerged due to complexing reaction with oxygen-containing functional groups of FMBC. The FMBC could be a potential adsorbent to adsorb Cd(II) and As(III) simultaneously.

As(III) removal by a recyclable granular adsorbent through dopping Fe-Mn binary oxides into graphene oxide chitosan

Graphene oxide chitosan composite (GOCS) is recognized as an environmentally friendly composite adsorbent because of its stability and abundant functional groups to adsorb heavy metals, and Fe-Mn binary oxides (FMBO) have attracted increasing interest due to their high removal capacity of As(III). However, GOCS is often inefficient for heavy metal adsorption and FMBO suffers poor regeneration for As(III) removal. In this study, we have proposed a method of dopping FMBO into GOCS to obtain a recyclable granular adsorbent (Fe/MnGOCS) for achieving As(III) removal from aqueous solutions. Characterization of BET, SEM-EDS, XRD, FTIR, and XPS are carried out to confirm the formation of Fe/MnGOCS and As(III) removal mechanism. Batch experiments are conducted to investigate the effects of operational factors (pH, dosage, coexisting ions, etc.), as well as kinetic, isothermal, and thermodynamic processes. Results show that the removal efficiency (Re) of As(III) by Fe/MnGOCS is about 96 %, which is much higher than those of FeGOCS (66 %), MnGOCS (42 %), and GOCS (8 %), and it increases slightly with the increasing molar ratio of Mn and Fe. This is because amorphous Fe (hydro)oxides (mainly in the form of ferrihydrite) complexation with As(III) is the major mechanism to remove As(III) from aqueous solutions, and it is accompanied by As(III) oxidation mediated by Mn oxides and the complexation of As(III) with oxygen-containing functional groups of GOCS. Charge interaction plays a weaker role in As(III) adsorption, therefore Re is persistently high over a wide range of pH values of 3–10. But the coexisting PO43− can greatly decrease Re by 24.11 %. As(III) adsorption on Fe/MnGOCS is endothermic and its kinetic process is controlled by pseudo-second-order with a determination coefficient of 0.95. Fitted by the Langmuir isotherm, the maximum adsorption capacity is 108.89 mg/g at 25 °C. After four times regeneration, there is only a slight decrease of <10 % for the Re value. Column adsorption experiments show that Fe/MnGOCS can effectively reduce As(III) concentration from 10 mg/L to <10 μg/L. This study provides new insights into binary polymer composite modified by binary metal oxides to efficiently remove heavy metals from aquatic environments.

Reduced Fe, Mn-based catalyst with dual reaction sites for rapid decolorization treatment via Fenton-like reactions

Ferromanganese oxides are promising efficient catalysts for peroxymonosulfate (PMS) activation. In this study, a novel porous ferromanganese oxides (FeMnOx) nanocubes derived from prussian blue analogues was prepared via a successive codeposition-calcination method, and the reduced Fe, Mn-based catalysts were further synthesized by a hydrogenation process. Their catalytic performance was evaluated in a Fenton-like degradation of Rhodamine B (RhB) and other dyes in the presence of PMS. It was found that FeMnOx showed outstanding catalytic activity in dyes elimination, which benefited by the synergetic effect of dual reaction sites, reductive Fe-Mn binary oxides and oxygen vacancies (OVs) for PMS activation. The optimized sample (H2 annealed at 260 °C, FMO-260) exhibited high degradation efficiency to RhB within 5 cycles and after regeneration, implying the strong stability and reusability. Moreover, the influences of PMS and FMO-260 dosages, pH values, coexist anions for the degradation efficiency to RhB were also carried out. According to inhibitor experiments and EPR (electron paramagnetic resonance) tests, a possible catalytic mechanism and degradation pathway of RhB was proposed. This study provides a novel fabrication strategy to design Fe, Mn-based catalysts and demonstrates more potential in the decolorization field.

Integrated As2O3/SeO2 capture mechanism by Mn–Fe binary oxide in coal-fired flue gas

The integrated capture of multiple pollutants is a prospective approach to achieve the economical pollution reduction. In this work, the integrated capture of As2O3 and SeO2 in coal-fired flue gas by Mn–Fe binary oxide was investigated combined the experiments and density functional theory (DFT) calculations. Results showed that Mn–Fe binary oxide has a significant performance for As2O3 and SeO2 removal. When the Mn/Fe ratio was 1:1, Mn–Fe binary oxide presented the optimum capture ability for As2O3 (SeO2) at 600 °C (750 °C). For the integrated adsorption progress, As2O3 exhibited a better adsorption selectivity than SeO2, which made it easier to adsorb onto sorbent surface, prior to SeO2, and it was negative to SeO2 capture. On the other hand, the presence of SeO2 facilitated the As2O3 capture, for that the pre-adsorption product of SeO2 was favorable to As2O3 retention. Aiming to the phenomenon, DFT calculations were conducted to reveal the integrated adsorption mechanism. Mn and Fe sites were active sites on Fe/Mn3O4 surface for As2O3 and SeO2 adsorption. The presence of SeO2 increased the As2O3 adsorption energy on Fe/Mn3O4 surface, while the adsorption energy of SeO2 decreased with As2O3 introduction. In addition, the adsorption energy of As2O3 on Fe/Mn3O4 surface with pre-adsorbed selenium was higher than that on the clean surface, and it might be reason for the positive effect of pre-adsorbed selenium on As2O3 capture. The results from this work would help to provide an insight on the integrated removal of trace element (TEs) from coal-fired power plant.

Fabrication of α-MnO2/Fe-Mn binary oxide nanocomposite as an efficient adsorbent for the removal of methylene blue from wastewater

The development of the safe and cost-effective technologies for treating the dye-polluted wastewater has been a significant focus of researchers. In the light of this, α-MnO2/Fe-Mn binary oxide (α-MnO2/Fe-Mn BO) nanocomposite has been synthesized by a co-precipitation method. It was characterized by the FT-IR, XRD, BET, SEM, EDX, and TEM. The results indicated that the nanocomposite has a spheroid-like surface, a surface area of 92.954 m2/g and an average pore diameter of 2.39 nm. It was used as an adsorbent for the removal of methylene blue (MB) dye from an aqueous medium. The batch experiment revealed that 0.013 g of the nanocomposite can remove 98 % of MB (12.71 mg/L) in 30 min. The pH of the medium was the dominant factor in MB adsorption, where the highest removal efficiency was obtained at pH 4. Incorporation of sodium dodecyl sulfate (SDS) and NaCl decreased the MB adsorption. The adsorption process followed the pseudo-second-order and Elovich kinetic models. The results also fitted well with the Langmuir and Dubinin-Radushkevich (D-R) adsorption models. The maximum adsorption capacity was 89.63 mg/g at 30 °C and the nanocomposite showed good separation and regeneration properties. The removal efficiency decreased by about 20 % through five cycles. The α-MnO2/Fe-Mn BO is therefore considered a promising adsorbent for dyes owing to its high adsorption capacity, high chemical stability, good reusability, and simple synthesis procedure.

Adsorption performance and its mechanism of aqueous As(III) on polyporous calcined oyster shell-supported Fe-Mn binary oxide.

Fe-Mn binary oxide (FMBO) is a promising adsorbent for As(III) removal through combined adsorption and oxidation. The calcined oyster shell-supported Fe-Mn binary oxide (FMBO/OS) adsorbent was synthesized by the co-precipitation method. Results indicated that the calcined oyster shell, as a carrier, improved the stability of FMBO and its adsorption capacity for As(III). The maximum adsorption capacity of FMBO/OS on As(III) reached 140.5mg·g-1 . Under pH5.0 and 25°C, the removal efficiency of FMBO/OS to As(III) solution (C0 = 10mg·L-1 ) reached 87% within 12 h. Moreover, based on the characterization analyses, the removal mechanisms of As(III) were deduced to include the combined adsorption and oxidation process of FMBO and the synergistic effect of oyster shells. This work provides new insights into synthesizing efficient and green adsorbents to remove aqueous As(III). Meanwhile, it provides technical support for reusing waste biomass materials such as the oyster shell. PRACTITIONER POINTS: FMBO/OS was prepared by a simple hydrothermal co-precipitation method. The carrier alleviates the agglomeration of Fe-Mn oxides. The adsorbent shows a strong adsorption capacity of As(III) and good selectivity. The good results benefit from the synergistic effect of calcium arsenate generation. The prepared adsorbent can adsorb arsenic in real samples.

Facile preparation of novel magnetic mesoporous Fe[sbnd]Mn binary oxides from Mn encapsulated carboxymethyl cellulose-Fe(III) hydrogel for antimony removal from water

Effective removal of Sb(III) and Sb(V) has long been an urgent task for protecting human health and environment. In this study, novel magnetic mesoporous FeMn binary oxides (MMFMs) were fabricated via calcinating the Mn encapsulated carboxymethyl cellulose-Fe(III) hydrogel, and the structure of MMFMs were closely related to the Fe:Mn ratio. Owing to the mesoporous structure together with synergistic effect of FeMn binary component, the MMFMs exhibited excellent mass transfer and adsorption ability to Sb(III) and Sb(V). MMFM3 achieved a maximum Sb(III) and Sb(V) adsorption capacity of 281.5 and 204.6 mg/g, respectively. Co-existing anions of Cl−, NO3− and SO42− exhibited marginal influence on the adsorption for both Sb(III) and Sb(V), except the PO43− for Sb(III) and SiO32− or PO43− for Sb(V). X-ray photoelectron spectroscopic investigation revealed that high valence Mn(IV) was mainly responsible for the oxidation transformation of the highly toxic Sb(III) into less toxic Sb(V), while the FeOx content played major role for the adsorption of Sb(V). The generated inner-sphere FeOSb complex between Fe-OH groups and Sb(III/V) dominantly contributed to the removal of Sb(III/V). Overall, mesoporous structure, magnetic separation ability, excellent adsorption performance together with exceptional regeneration properties demonstrated the great potential of MMFMs for Sb(III/V) remediation.