New insights on nanostructure of ordered mesoporous FeMn bimetal oxides (OMFMs) by a novel inverse micelle method and their superior arsenic sequestration performance: Effect of calcination temperature and role of Fe/Mn oxides

Calcination-controlled performance optimization of iron-vanadium bimetallic oxide nanoparticles for synergistic tumor therapy

Calcination has been widely demonstrated as a favorable protocol for producing various inorganic nanomaterials for tumor therapy. However, little attention has been paid to its effect on the biotherapeutic efficacy of inorganic nanomaterials. Herein, we compare the effects of different calcination atmospheres on the therapeutic efficacy of Fe-V-O (FVO) nanomaterials. We find that compared with FVO nanomaterials synthesized by calcination in air, those prepared by argon calcination have a lower metallic valence state and a higher near-infrared light absorption capacity, hence resulting in significantly better biosafety and higher chemodynamic therapy (CDT)/photothermal therapy (PTT) efficacy. This study demonstrates that the therapeutic efficacy of inorganic nanomaterials can be optimized by employing different thermal treatment atmospheres, which provides new insights into the development of efficient anti-tumor agents.

A review on multi-synergistic transition metal oxide systems towards arsenic treatment: Near molecular analysis of surface-complexation (synchrotron studies/modeling tools)

The science and interface chemistry between the arsenic (As) anions and the different adsorbent systems have been gaining interest in recent years in environmental remediation applications. Metal-oxides and the corresponding hybrid systems have shown promising performance as novel adsorbents in various treatment technologies. The abundance, surface chemistry, high surface area (active-centres), various synthesis and functionalization methodologies, and good recyclability make these metal oxide-based nanomaterials as potential remediating agents for As oxyanions. This work critically reviews eight different platforms focused on the arsenic contamination issue, where the first classification describes the origin of arsenic contamination and presents geographical and demo-graphical considerations. The following section briefs the state-of-the-art remediation techniques for arsenic treatment with a comparative evaluation. An emphasized discussion has been provided regarding the adsorption and classification of various metal oxide adsorbents. In the next classification, various multi-synergism abilities like Redox activity, Surface functional groups, Surface area/morphology, Heterogeneous catalysis, Reactive oxygen species, Photo-catalytic/electro-catalytic reactions, and Electrosorption are detailed. The classification of various characterization tools for accessing the arsenic remediation qualitatively and quantitatively are given in the fifth chapter. The first-of-its-kind dedicated analysis has been given on the surface complexation aspects of the arsenic speciation onto various metal adsorbent systems using synchrotron results, surface-complexation modeling, and molecular simulation (e.g., DFT) in the sixth chapter. The current sensing applications of these novel nano-material systems for arsenic determination using colorimetric and electrochemical-based analytical tools and a note about the economic parameters, i.e., regeneration aspects of various adsorbent systems/the sustainable applications of the treated sludge materials, are provided in the final sections. This work makes a critical analysis of 'Environmental Nanotechnology' towards 'Arsenic Treatment'.

In situ preparation of a multifunctional adsorbent by optimizing the Fe2+/Fe3+/Mn2+/HA ratio for simultaneous and efficient removal of Cd(II), Pb(II), Cu(II), Zn(II), As(III), Sb(III), As(V) and Sb(V) from aqueous environment: Behaviors and mechanisms

Multiple potentially toxic elements (PTEs) often coexist in practical wastewater environment, which poses serious risks to the ecological environment and human health. However, few of the reported adsorbents are capable of simultaneously and effectively removing multiple PTEs from wastewater due to the unique properties of each element. In this work, a multifunctional adsorbent FMHs was developed by optimizing Fe²⁺/Fe³⁺/Mn²⁺/HA ratio, and applied to remove Cd(II), Pb(II), Cu(II), Zn(II), As(III), Sb(III), As(V) and Sb(V) from aqueous solution. Results revealed that the adsorption data obeyed the Elovich, Sips and Redlich-Peterson models in the mono-component system, and the maximum adsorption capacity of FMHs was superior to most adsorbents reported in the literatures. In addition, FMHs retained considerable removal capacity after four cycles, and maintained excellent adsorption performance under the interference of different environmental factors (including pH, ionic strength, co-existing ions and humic acid). In the multi-component system, FMHs also presented high adsorption capacity for all the selected PTEs, especially for Sb(III/V) and Pb(II). Characterization results confirmed that various removal mechanisms, such as precipitation, surface complexation, ion exchange, electrostatic attraction and redox, were responsible for the capture of PTEs by FMHs.

Zero-valent bimetallic catalyst/absorbent for simultaneous facilitation of MgSO3 oxidation and arsenic uptake

Cobalt (Co)-based catalysts can efficiently reduce the heat waste from sulfate concentration by enhancing sulfite oxidation during wet flue gas desulfurization system. However, arsenic (As) can poison such catalysts and migrate into the sulfate by-products, resulting in severe secondary pollution. In this study, a zero-valent Co/iron (Fe)-based nanoparticle (NZV-Co₂Fe₁) was fabricated and applied as a bifunctional catalyst/adsorbent. The catalytic stability of the Co-based catalyst was enhanced by the introduction of Fe because the poisonous effect of As was substantially suppressed because of the high adsorption capacity of Fe for As. Compared with the noncatalytic benchmark, the presence of 0.5 g/L NZV-Co₂Fe₁ can increase the rate of MgSO₃ oxidation by approximately 12-fold even at a high concentration of As (2.5 mg/L). The Langmuir model was fitted to the As adsorption isotherms, indicating that As uptake is a single-layer adsorption process. The pseudo-second-order kinetic model indicated that As was removed through chemisorption. The oxidation pathway of As(III) involves reactive radicals (mainly OH, SO₄^- and SO₅^-) and ligand-to-metal charge transfer between SO₃^2- and Co²⁺. The availability of MgSO₃ improved the removal efficiency at high concentrations of As(III) (1 mg/L). These results indicate that using NZV-Co₂Fe₁ as a catalyst to purify the by-products of flue gas desulfurization can effectively prevent secondary pollution.

Synthesis and application of starch-stablized Fe-Mn/biochar composites for the removal of lead from water and soil

Starch-stablized and Fe/Mn bimetals modified biochar derived from corn straw (SFM@CBC and SFM@CBC-350) were firstly prepared, characterized (FTIR, XRD, SEM, EDS, BET and XPS), and applied in Pb removal from water and soil. SFM@CBC and SFM@CBC-350 displayed highly effective adsorption performance of Pb²⁺ from wastewater with the maximum adsorption capacity of 170.91 mg g^-1 and 190.17 mg g^-1, respectively, which were much greater than that of FM@CBC (149.25 mg g^-1) and CBC (101.10 mg g^-1). Studies of adsorption kinetics, isotherms and thermodynamics indicated that the absorption of Pb²⁺ by SFM@CBC and SFM@CBC-350 was spontaneous and endothermic reaction, and it was controlled by monolayer chemisorption. The mechanism studies indicated that Pb²⁺ removal involved with multiple mechanism, including complexation (dominant process confirmed by XPS analysis), physical adsorption, electrostatic attraction, and cation exchange. The reusability test demonstrated that SFM@CBC and SFM@CBC-350 had very good stability and reusability. In addition, in order to further explore Pb removal performance of the modified biochar, SFM@CBC-350 was used in soil-ryegrass pot systems. Compared with the controls, the addition of SFM@CBC-350 reduced Pb content in soil and ryegrass, increased the biomass and total chlorophyll content, reduced the activity of antioxidant enzymes (CAT, SOD, MDA and POD) and ROS fluorescence intensity of ryegrass, thus alleviating Pb stress of ryegrass. Besides, the addition of SFM@CBC-350 could increase the richness and diversity of soil microorganisms, which was beneficial to the growth of ryegrass. Hence, SFM@CBC-350 has the potential of being used as a green, efficient and promising adsorbent in Pb removal from wastewater and soil.

Facile preparation of novel magnetic mesoporous FeMn 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 SO₄^2- exhibited marginal influence on the adsorption for both Sb(III) and Sb(V), except the PO₄^3- for Sb(III) and SiO₃^2- or PO₄^3- 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 FeO_x 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.

Recent advances in application of iron-manganese oxide nanomaterials for removal of heavy metals in the aquatic environment

Heavy metal pollution has a serious negative impact on the ecological environment and human health due to its toxicity, persistence, and non-biodegradable properties. Among the technologies applied in heavy metals removal, adsorption has been widely used as the most promising method because of its simple operation, high removal efficiency, strong applicability, and low cost. Iron-manganese oxide nanomaterials, as an effective absorbent, have attracted wide attention due to their simple preparation, wide material sources, and lower ecological impact. So far, no quantitative investigation has been conducted on the preparation and application of iron-manganese oxide nanomaterials in heavy metals removal. This review discussed the preparation methods and characteristics of iron‑manganese oxide nanomaterials over the past decade and provided some basic information for the improvement of preparation methods. The physicochemical properties of iron‑manganese oxide nanomaterials and environmental conditions are regarded as important factors that affect the removal efficiency of heavy metals. In addition, the removal mechanisms of heavy metals in aqueous solution with iron‑manganese oxide nanomaterials were mainly included redox, complex precipitation, electrostatic attraction, and ion exchange. The reusability and practicability in actual wastewater treatment of 3nganese oxide nanomaterials were further discussed. Several key problems still need to be solved in the existing progress, such as improving the ability and stability of the iron‑manganese oxide nanomaterials to remove heavy metals from actual wastewater. In conclusion, this review provides a future direction for the application of iron‑manganese oxide nanomaterials for heavy metals removal and even in the large-scale treatment of actual wastewater.

Arsenic removal by manganese-doped mesoporous iron oxides from groundwater: Performance and mechanism

FeMn bimetallic oxides have been widely used in catalytic adsorption due to their large pore size, large specific surface area and mesoporous structure, which have great potential for high As groundwater remediation. In this study, FeMn composite oxide was synthesized by template-free route and forming mesopores through high temperature calcination, and its efficiency and mechanism for As removal were subsequently investigated. The results showed that the different Fe/Mn molar ratios and calcination temperatures have important effect on FeMn composite oxides performance. For all synthesized materials, the largest specific surface area is 388.6 m²/g of Fe₁Mn₁-300. The maximum As absorption capacity was also reached by Fe₁Mn₁-300, which is 59.44 mg/g for As(III) and 31.68 mg/g for As(V), respectively. As removal efficiency was further evaluated through batch adsorption experiments conducted with five variables, initial As concentration, adsorption equilibrium time, pH, solid-to-liquid ratio, and competitive ions. The adsorption capacity of the material reaches to the maximum when the initial As concentration is 40 mg/L, and that for As(III) and As(V) is 74.05 and 38.09 mg/g, respectively. When the pH rises, the adsorption capacity generally shows a decreasing trend, thus acidic conditions are more conducive to the adsorption reaction. The optimum solid-to-liquid ratios for removal 10 mg/L of As(III) and As(V) are 0.3 mg/L and 1 mg/L, respectively. The order of competitive ions effects on As removal is: PO₄^3- > HCO₃^- > SO₄^2- ≈ NO₃^- ≈ Cl^-. The adsorption mechanisms for As by FeMn composite oxides included adsorption, co-precipitation and oxidative chelation, which was a combination of physical and chemical process.

Sorption of arsenate(Ⅴ) to naturally occurring secondary iron minerals formed at different conditions: The relationship between sorption behavior and surface structure

Arsenic (As) is a problematic pollutant that can cause cancer and other chronic diseases due to its potential toxicity. Iron (oxyhydr)oxides can readily sorb As and play important roles in the geochemical cycle of As. Attention has mainly been given to the affinity and mechanism of As sorption by synthetic pure iron (oxyhydr)oxides, and little is known about the relationship between As behavior and multicomponent secondary iron minerals (SIMs) naturally formed in acid mine drainage (AMD). To investigate this relationship, we performed sorption kinetics, isotherm and competitive sorption experiments to investigate As(V) sorption behaviors on naturally formed SIMs harvested from different runoff zones of an abandoned coal mine. Several spectroscopic analyses were used to evaluate the structural and component changes and phase transformation. Three environmental SIMs formed at nascent (n-SIM), transient (t-SIM) and mature (m-SIM) stages were determined to be similar in the element components of Fe, S and O but different in structure. As(V) sorption behaviors on these environmental SIMs followed a pseudo-second-order kinetic model, and the sorption extent followed the sequence of n-SIM > t-SIM > m-SIM. As(V) sorption is not significantly influenced by Na⁺/Ca²⁺ concentration or ionic strength except for that of PO₄^3-, and it slightly decreases as the Cr(Ⅲ) concentration increases but increases with increasing Sb(Ⅲ)/(V) concentration. The results of spectral analyses indicate that As(V) immobilization mainly depends on exchange with SO₄^2- and surface complexation, along with the phase transformation of schwertmannite/jarosite to goethite and other phases. These findings are helpful for better understanding the geochemical behaviors of As(V) associated with environmental SIMs.