Humic acid-coated hydrated ferric oxides-polymer nanocomposites for heavy metal removal in water

Water pollution by toxic heavy metals poses a threat to the environment and human bodies. Herein, a novel hydrated ferric oxide nanoparticle (HFO) based hybrid adsorbent was fabricated for the removal of toxic Cu(II), Cd(II) and Pb(II) from water. HFOs were immobilized into a porous resin D-201, and then this nanocomposite HFO-D201 was coated with humic acid (HA) to enhance the binding sites of target metals. Both HFOs and HA contribute to the sequestration of heavy metals. The as-synthesized hybrid adsorbent HA-HFO-D201 exhibited excellent performance on the removal of Cu(II), Cd(II), and Pb(II) in a pH range of 3-9, while no Fe leaching was observed. The presence of natural organic matter (20 mg C/L) has limited influences on the adsorption, and more than 85% of the target metals can be removed after treatment. HA-HFO-D201 showed preferable adsorption toward Cu(II) and Pb(II) (1 mg/L) from the background Ca²⁺ solution at much higher concentrations (100 mg/L), while the retention of Cd(II) (1 mg/L) decreased to some extent. Fixed-bed column experiments exhibited that the treatment capacities of HA-HFO-D201 are 90 bed volumes (BV) for Cd(II), 410 BV for Pb(II) and > 800 BV for Cu(II) of simulated contaminated water to meet the WHO drinking water standard. Meanwhile, depleted HA-HFO-D201 can be readily regenerated by a chelating agent Na₂EDTA for repeated use. The hybrid adsorbent HA-HFO-D201 has excellent potential to remove heavy metals in water treatment systems.

Fabrication, application, optimization and working mechanism of Fe2O3 and its composites for contaminants elimination from wastewater

Fe₂O₃ and its composites have been extensively investigated and employed for the remediation of contaminated water with the characteristics of low cost, outstanding chemical stability, high efficiency of visible light utilization, excellent magnetic ability and abundant active sites for adsorption and degradation. In this review, the potentials of Fe₂O₃ in water remediation were discussed and summarized in detail. Firstly, various synthesis methods of Fe₂O₃ and its composites were reviewed and compared. Based on the structures and characteristics of the obtained materials, their applications and related mechanisms in pollutants removal were surveyed and discussed. Furthermore, several strategies for optimizing the remediation processes, including dispersion, immobilization, nano/micromotor construction and simultaneous decontamination, were also highlighted and discussed. Finally, recommendations for further work in the development of novel Fe₂O₃-related materials and its practical applications were proposed.

Effect of Hematite Doping with Aliovalent Impurities on the Electrochemical Performance of α-Fe2O3@rGO-Based Anodes in Sodium-Ion Batteries

The effect of the type of dopant (titanium and manganese) and of the reduced graphene oxide content (rGO, 30 or 50 wt %) of the α-Fe₂O₃@rGO nanocomposites on their microstructural properties and electrochemical performance was investigated. Nanostructured composites were synthesized by a simple one-step solvothermal method and evaluated as anode materials for sodium ion batteries. The doping does not influence the crystalline phase and morphology of the iron oxide nanoparticles, but remarkably increases stability and Coulombic efficiency with respect to the anode based on the composite α-Fe₂O₃@rGO. For fixed rGO content, Ti-doping improves the rate capability at lower rates, whereas Mn-doping enhances the electrode stability at higher rates, retaining a specific capacity of 56 mAhg^-1 at a rate of 2C. Nanocomposites with higher rGO content exhibit better electrochemical performance.

Mitigation of environmentally-related hazardous pollutants from water matrices using nanostructured materials - A review

An unprecedented rise in population growth and rapid worldwide industrial development are associated with the increasing discharge of a range of toxic and baleful compounds. These toxic pollutants including dyes, endocrine-disrupters, heavy metals, personal care products, and pharmaceuticals are destructing nature's balance and intensifying environmental toxicity at a disquieting rate. Therefore, finding better, novel and more environmentally sound approaches for wastewater remediation are of great importance. Nanoscale materials have opened up some new horizons in various fields of science and technology. Among a range of treatment technologies, nanostructured materials have recently received incredible interest as an emerging platform for wastewater remediation owing to their exceptional surface-area-to-volume ratio, unique electrical and chemical properties, quantum size effects, high scalability, and tunable surface functionalities. An array of nanomaterials including noble metal-based nanostructures, transition metal oxide nanomaterials, carbon-based nanomaterials, carbon nanotubes, and graphene/graphene oxide nanomaterials to their novel nanocomposites and nanoconjugates have been attempted as the promising catalysts to overcome environmental dilemmas. In this review, we summarized recent advances in nanostructured materials that are particularly engineered for the remediation of environmental contaminants. The toxicity of various classes of relevant tailored nanomaterials towards human health and the ecosystem along with perspectives is also presented. In our opinion, an overview of the up-to-date advancements on this emerging topic may provide new ideas and thoughts for engineering low-cost and highly-efficient nanostructured materials for the abatement of recalcitrant pollutants for a sustainable environment.

MOF-derived 1D hollow bimetallic iron(iii) oxide nanorods: effects of metal-addition on phase transition, morphology and magnetic properties

It is demonstrated that 1D hollow bimetallic iron oxide nanorods containing Mn, Ru, Ni, La and Ag ions can be obtained regardless of the different values of ionic radius and hardness of metal dopants from NH₄OH-etched MIL-88A MOF particles.

Mn-Doped Maghemite (γ-Fe2O3) from Metal-Organic Framework Accompanying Redox Reaction in a Bimetallic System: The Structural Phase Transitions and Catalytic Activity toward NOx Removal

Mn-doped maghemite (γ-Fe₂O₃) particles were generated from a binary metal (Fe,Mn)-based metal-organic framework (MOF) via thermal decomposition under air. The X-ray photoelectron spectroscopy analysis revealed that the synthesis of Fe/Mn-MOF accompanied the reduction of the metal ions. The existence of Mn ions in this synthetic process leads to thermally stable maghemite particles under air. A temperature-induced structural phase transition from γ-Fe₂O₃ to α-Fe₂O₃ was observed through a mixed phase with another structure. Mn-doped γ-Fe₂O₃ and α-Fe₂O₃ exhibit superparamagnetic behavior. The sample annealed at 600 °C showed a mixed magnetic hysteresis loop indicating the existence of an intermediate structural phase between γ-Fe₂O₃ and α-Fe₂O₃ during the phase conversion from FeMn-MOF. The constructed Mn-doped iron oxides are active toward reducing nitric oxide with NH₃. The NO conversion is 97% over Mn-doped γ-Fe₂O₃ calcined at 320 °C.

Synthesis and Characterization of Mixed Iron-Manganese Oxide Nanoparticles and Their Application for Efficient Nickel Ion Removal from Aqueous Samples

Mixed iron-manganese oxide nanoparticles, synthesized by a simple procedure, were used to remove nickel ion from aqueous solutions. Nanostructures, prepared by using different weight percents of manganese, were characterized by transmission electron microscopy, selected area diffraction, X-ray diffraction, Raman spectroscopy, and vibrating sample magnetometry. Adsorption/desorption isotherm curves demonstrated that manganese inclusions enhance the specific surface area three times and the pores volume ten times. This feature was crucial to decontaminate both aqueous samples and food extracts from nickel ion. Efficient removal of Ni2+ was highlighted by the well-known dimethylglyoxime test and by ICP-MS analysis and the possibility of regenerating the nanostructure was obtained by a washing treatment in disodium ethylenediaminetetraacetate solution.

Effect of doping and chemical ordering on the optoelectronic properties of complex oxides: Fe2O3-V2O3 solid solutions and hetero-structures

The electronic and optical properties of α-(Fe_1-xV_x)₂O₃ at low (x = 0.04) and high (x = 0.5) doping levels are investigated using a combination of periodic and embedded cluster approaches, and time-dependent density functional theory. At low V concentrations the onset of the optical absorption is ∼0.5 eV (i.e., nearly 1.6 eV lower than that in pure α-Fe₂O₃) and corresponds to the electron transitions from V 3d to Fe 3d* orbitals. At high V concentrations, optical absorption energies and intensities are sensitive to specific arrangements of Fe and V atoms and their spin configuration that determine Fe-V hybridization. The onset of the lowest inter-vanadium absorption band in the case of Fe₂O₃/V₂O₃ hetero-structures is as low as ∼0.3 eV and the corresponding peak is at ∼0.7 eV. In contrast, in the case of solid solutions this peak has lower intensity and is shifted to higher energy (∼1.2 eV). Analysis of the orbital character of electronic excitation suggests that Fe₂O₃/V₂O₃ hetero-structures absorb light much more effectively than random alloys, thus promoting efficient photo-induced carrier generation. These predictions can be tested in α-(Fe_1-xV_x)₂O₃ thin films synthesized with well-controlled spatial distribution of Fe and V species.

Designed synthesis and surface engineering strategies of magnetic iron oxide nanoparticles for biomedical applications

Iron oxide nanoparticles (NPs) hold great promise for future biomedical applications because of their magnetic properties as well as other intrinsic properties such as low toxicity, colloidal stability, and surface engineering capability. Numerous related studies on iron oxide NPs have been conducted. Recent progress in nanochemistry has enabled fine control over the size, crystallinity, uniformity, and surface properties of iron oxide NPs. This review examines various synthetic approaches and surface engineering strategies for preparing naked and functional iron oxide NPs with different physicochemical properties. Growing interest in designed and surface-engineered iron oxide NPs with multifunctionalities was explored in in vitro/in vivo biomedical applications, focusing on their combined roles in bioseparation, as a biosensor, targeted-drug delivery, MR contrast agents, and magnetic fluid hyperthermia. This review outlines the limitations of extant surface engineering strategies and several developing strategies that may overcome these limitations. This study also details the promising future directions of this active research field.

Facile synthesis of mesoporous hierarchical ZnS@β-Ni(OH)2 microspheres for flexible solid state hybrid supercapacitors

Mesoporous hierarchical ZnS@β-Ni(OH)₂ microspheres have been successfully synthesized via a facile route and exhibited good performance as electrode materials for supercapacitors.

Eco-friendly synthesis and photodegradation of hierarchical nanostructures of β-FeOOH and α-Fe2O3

β-FeOOH and α-Fe₂O₃ with different morphologies were synthesized via a facile method using urea or saccharide as the organic matrix.

The influence of aluminum chloride on biosynthetic schwertmannite and Cu(ii)/Cr(vi) adsorption

In this study, aluminium chloride modified schwertmannite was biosynthesized using Acidithiobacillus ferrooxidans. Heavy metals can be efficiently removed by the modified biosynthetic schwertmannite.

Electrocatalytic activity of Mn/Cu doped Fe2O3–PANI–rGO composites for fuel cell applications

Low cost catalysts for the oxygen reduction reaction synthesized from a Mn/Cu doped Fe₂O₃–polyaniline (PANI) composite supported on reduced graphene oxide.

Facile synthesis of magnetic nanocomposites of cellulose@ultrasmall iron oxide nanoparticles for water treatment

We report a facile in situ approach to synthesize magnetic nanocomposites of cellulose@ultrasmall iron oxide nanoparticles by co-precipitation using ionic liquid as co-solvent for cellulose and iron salt.

Synthesis of core–shell structured Fe3O4@α-MnO2microspheres for efficient catalytic degradation of ciprofloxacin

Three-dimensional core–shell structured Fe₃O₄@α-MnO₂microspheres were successfully fabricated to activate persulfate for catalytic degradation of ciprofloxacin in wastewater.

Water-soluble Fe3O4superparamagnetic nanocomposites for the removal of low concentration mercury(ii) ions from water

We have developed an easy approach to obtain hydrophilic modified MSPNPs (M-MSPNPs) by simply coating monodispersed hydrophobic magnetite (Fe₃O₄) superparamagnetic nanoparticles (MSPNPs) with functional amphiphilic oligomers. The resulting M-MSPNPs have abundant chelation groups on their surfaces, which could bond with Hg²⁺and exhibit excellent ability in the fast, efficient and selective removal of Hg²⁺from water samples by low-field magnetic separation.