Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

Fouling Release Coatings Based on Acrylate-MQ Silicone Copolymers Incorporated with Non-Reactive Phenylmethylsilicone Oil

Copolymers containing MQ silicone and acrylate were synthesized by controlling the additive amount of compositions. Subsequently, fouling release coatings based on the copolymer with the incorporation of non-reactive phenylmethylsilicone oil were prepared. The surface properties of the coating (CAMQ₄₀) were consistent with that of the polydimethylsiloxane (PDMS) elastomer, which ensured good hydrophobicity. Moreover, the seawater volume swelling rate of all prepared coatings was less than 5%, especially for CAMQ₄₀ with only 1.37%. Copolymers enhanced the mechanical properties of the coatings, while the enhancement was proportional to the molar content of structural units from acrylate in the copolymer. More importantly, the adhesion performance between the prepared coatings and substrates indicated that pull-off strength values were more than 1.6 MPa, meaning a high adhesion strength. The phenylmethylsilicone oil leaching observation determined that the oil leaching efficiency increased with the increase in the structural unit’s molar content from MQ silicone in the copolymer, which was mainly owing to the decrease in compatibility between oil and the cured coating, as well as the decrease in mechanical properties. High oil leaching efficiency could make up for the decrease in the biofouling removal rate due to the enhancement of the elastic modulus. For CAMQ₄₀, it had an excellent antifouling performance at 30 days of exposure time with more than 92% of biofouling removal rate, which was confirmed by biofilm adhesion assay.

Amidoximated wooden solar evaporator for high-efficiency nuclear wastewater treatment

The efficient removal of uranium (VI) (UO₂²⁺) is of great significance to the ecological environment. However, there is still a lack of efficient adsorption materials to remove UO₂²⁺ in wastewater economically. Because natural basswood has high porosity, natural hydrophilicity, and abundant surface functional groups, wood as a support material has a good application prospect in water treatment. In the present work, the amidoxime functional group (AO) is grafted to the hydroxyl group of the wood fiber (AO-wood). A carbon layer is formed on the surface of the basswood by heating, and some Ag nanoparticles with good optothermal effect are added to the wood tunnel (Ag-C-AO-wood). Ag-C-AO-wood is used for efficient wastewater treatment under light conditions. The adsorption kinetic of Ag-C-AO-wood is 4.6 h under one irradiation, which is 7 times faster than AO-wood. It has approached or even surpassed some traditional carbon materials with stirring. This method is expected to break the traditional stirring method. Ag-C-AO-wood can not only remove uranium up to 82% but also have a good removal efficiency (27%) on iodide ions. More importantly, due to basswood characteristics, it is possible to large-scale preparation and explore its potential application value in wastewater.

Sunlight powered degradation of pentoxifylline Cs0.5Li0.5FeO2 as a green reusable photocatalyst: Mechanism, kinetics and toxicity studies

The degradation of Pentoxifylline (PXF) was achieved successfully by green energy in a built-in solar photocatalytic system using hybrid LiCs ferrites (Li_0.5Cs_0.5FeO₂) as magnetically recoverable photocatalysts. Kinetics showed a first-order reaction rate with maximum PXF removal of 94.91% at mildly acidic pH; additionally, the ferromagnetic properties of catalyst allowed recovery and reuse multiple times, reducing costs and time in degradation processes. The degradation products were identified by HPLC-MS and allowed us to propose a thermodynamically feasible mechanism that was validated through DFT calculations. Additionally, toxicity studies have been performed in bacteria and yeast where high loadings of Cs showed to be harmful to Staphylococcus aureus (MIC≥ 4.0 mg/mL); Salmonella typhi (MIC≥ 8.0 mg/mL) and Candida albicans (MIC≥ 10.0 mg/mL). The presented setup shows effectiveness and robustness in a degradation process using alternative energy sources for the elimination of non-biodegradable pollutants.

Fe(II) Redox Chemistry in the Environment

Iron (Fe) is the fourth most abundant element in the earth's crust and plays important roles in both biological and chemical processes. The redox reactivity of various Fe(II) forms has gained increasing attention over recent decades in the areas of (bio) geochemistry, environmental chemistry and engineering, and material sciences. The goal of this paper is to review these recent advances and the current state of knowledge of Fe(II) redox chemistry in the environment. Specifically, this comprehensive review focuses on the redox reactivity of four types of Fe(II) species including aqueous Fe(II), Fe(II) complexed with ligands, minerals bearing structural Fe(II), and sorbed Fe(II) on mineral oxide surfaces. The formation pathways, factors governing the reactivity, insights into potential mechanisms, reactivity comparison, and characterization techniques are discussed with reference to the most recent breakthroughs in this field where possible. We also cover the roles of these Fe(II) species in environmental applications of zerovalent iron, microbial processes, biogeochemical cycling of carbon and nutrients, and their abiotic oxidation related processes in natural and engineered systems.

Role of model organisms and nanocompounds in human health risk assessment

Safeguarding the environment is one of the most serious modern challenges, as increasing amounts of chemical compounds are produced and released into the environment, causing a serious threat to the future health of the Earth as well as organisms and humans on a global scale. Ecotoxicology is an integrative science involving different physical, chemical, biological, and social aspects concerned with the study of toxic effects caused by natural or synthetic pollutants on any constituents of ecosystems, including animals (including humans), plants, or microorganisms, in an integral context. In recent decades, this science has undergone considerable development by addressing environmental risk assessments through the biomonitoring of indicator species using biomarkers, model organisms, and nanocompounds in toxicological assays. Since a single taxon cannot be representative of complex ecotoxicological effects and mechanisms of action of a chemical, the use of test batteries is widely accepted in ecotoxicology. Test batteries include properly chosen organisms that are easy to breed, adapt easily to laboratory conditions, and are representative of the environmental compartment under consideration. One of the main issues of toxicological and ecotoxicological research is to gain a deeper understanding of how data should be obtained through laboratory and field approaches using experimental models and how they could be extrapolated to humans. There is a tendency to replace animal tests with in vitro systems and to perform them according to standardized analytical methods and the rules of the so-called good laboratory practice (GLP). This paper aims to review this topic to stimulate both efforts to understand the toxicological and ecotoxicological properties of natural and synthetic chemicals and the possible use of such data for application to humans.

Preparation of Humic Acid/l-Cysteine-Codecorated Magnetic Fe3O4 Nanoparticles for Selective and Highly Efficient Adsorption of Mercury

Humic acid and l-cysteine-codecorated magnetic Fe3O4 nanoparticles (HA/LC-MNPs) were synthesized using a coprecipitation method. Humic acid fractions abundant with carboxyl and hydroxyl groups can be selectively coated on the surface of MNPs during synthesis. HA/LC-MNPs with abundant heteroatoms (N, S, and O) show excellent removal capacity, great selectivity, and also fast trapping of Hg2+ in a wide pH range. The adsorption capacity of HA/LC-MNPs for Hg2+ can reach 206.5 mg/g, and the chemisorption was attributed to the major adsorption form. In competitive adsorption, HA/LC-MNPs preferentially adsorbed Hg2+ with an affinity order of Hg2+ > > Pb2+ > Cu2+ ≫ Zn2+ > Cd2+. In total, 93.91% of Hg2+ can be quickly captured in the presence of a 6000 times higher concentration of competing metal ions (Pb2+, Cu2+, Cd2+, and Zn2+) within 30 min. The adsorption mechanism was analyzed using X-ray photoelectron spectroscopy (XPS). It suggested that the HA/LC-MNPs enhanced the adsorption capacity of Hg2+ because of the complexing abilities of the multiple thiol, amino, and carboxyl groups in sorbents with Hg2+, the ion exchange ability of the carboxyl group, and the negative charge surface. All in all, HA/LC-MNPs are a potentially useful and economic material for the selective removal of Hg2+ from polluted water.

A review on ex situ mineral carbonation

The increased CO₂ quantities in the environment have led to many harmful effects. Therefore, it is very important to decrease the CO₂ levels in the environment. CO₂ capture along with safe and permanent storage using mineral CO₂ sequestration method can play an important role to reduce carbon emissions into the environment. Mineral sequestration is a stable storage method that provides long-term storage and an appropriate substitute for the more popular geological storage method. The process is most suited for places where there is a lack of underground cavities for underground geological storage. Minerals rich in Ca and Mg are used predominantly in carbonation reactions. In addition, those alkaline wastes that are rich in Mg and Ca such as cement waste, steel slag and many process ashes can also be employed in CO₂ sequestration. Mineral carbonation could be used for the sequestration of billions of tonnes of CO₂ every year. However, various drawbacks related to mineral carbonation still need to be addressed, such as resolving the slow rate of reactions, necessity of large amounts of feedstock, decreasing the high overall cost of CO₂ sequestration and reducing the huge energy requirements to accelerate the carbonation reaction. This study explores a number of carbonation methods, parameters that control the process and future potential applications of carbonated products.

Recovering rare earth elements from contaminated soils: Critical overview of current remediation technologies

Rare earth elements (REE) are essential for sustainable energies such as solar and wind power, with rising demand due to the ambitious goal for a circular society. REE are currently mined from virgin ores while REE-rich contaminated soil is left untreated in the environment. Soil remediation strategies are needed that concomitantly cleanup soil and harvest metals that contribute to process circular economy. In this review we aim to (i) define REE concentrations in contaminated soils as well as (ii) identify soil remediation techniques used in remediating REE from soils, emphasizing the ones that extract REE. Current literature lists REE polluted soils in the vicinities of REE mines, coal mines, high traffic roads and agricultural soils (due to REE association with phosphate fertilizers). We first list the conventional separation methods used in the mining industry and their main strategies in extracting/precipitating REE. Solvent extraction is the most commonly conventional method used followed by electrodeposition of REE at high temperatures. We then highlight soil remediation techniques that are used to treat REE. These techniques can be separated into two types: the ones that (a) stabilize REE in soils, and the ones that (b) extract REE from soils. Bioremediation, soil amendments and others offer stabilization of REE, eventually creating a legacy problem since REE keep accumulating in the soil. Soil remediation techniques that achieve REE extraction are a step closer to resource recovery, contributing to the circularity of REE. Techniques such as phytoremediation, soil washing and electrokinetic treatment show promising extraction results.

A critical review of contaminant removal by conventional and emerging media for urban stormwater treatment in the United States

Stormwater is a major component of the urban water cycle contributing to street flooding and high runoff volumes in urban areas, and elevated contaminant concentrations in receiving waters from contact with impervious surfaces. Engineers and city planners are investing in best management practices to reduce runoff volume and to potentially capture and use urban stormwater. However, these current approaches result in moderate to low contaminant removal efficiencies for certain classes of contaminants (e.g., particles, nutrients, and some metals). This review describes options and opportunities to augment existing stormwater infrastructure with conventional and emerging reactive media to improve contaminant removal. This critical analysis characterizes media physicochemical properties and mechanisms contributing to contaminant removal, describes possible candidates for new engineered media, highlights lab and field studies investigating stormwater media contaminant removal, and identifies possible limitations and knowledge gaps in media implementation. Following this analysis, information is provided regarding factors that may contribute to or adversely impact urban stormwater treatment by media. The review closes with insights into additional research directions and important information necessary for safe and effective urban stormwater treatment using media.

One-pot synthesis of nZVI-embedded biochar for remediation of two mining arsenic-contaminated soils: Arsenic immobilization associated with iron transformation

Waste biomass derived biochar has been proven as an effective and friendly amendment for remediation of heavy metals-contaminated soil. However, biochar is less effective for soil arsenic (As) immobilization in most cases. To improve the ability of biochar for As immobilization, in this study, the composite of biochar embedded with nano zero valent iron (nZVI/BC) was prepared through simple one-step pyrolysis of biomass sawdust and Fe₂O₃ mixture and then applied for amendment of two mining As-contaminated soils. Pristine sawdust biochar (BC) and nZVI alone or in combination were included for comparison. Results show that the prepared nZVI/BC contained about 40% Fe which was mainly present as Fe°. All treatments except BC reduced As concentration in (NH₄)₂SO₄ extraction and gastrointestinal solution. Particularly, nZVI/BC reduced the labile As in (NH₄)₂SO₄ extraction in two soils by over 93% and bioaccessible As in gastrointestinal solution decreased by over 85%. Fe° on the surface of nZVI/BC was oxidized into amorphous FeOOH which adsorbed or co-precipitated with As. Meanwhile, Ca-Fe-As-O and Al-Fe-As-O co-precipitated at the interface between nZVI/BC and two soils enriched with Ca and Al, respectively. Results indicated that the simply-prepared nZVI/BC was a promising material for remediation of As-contaminated soils.

Improved methods for mass production of magnetosomes and applications: a review

Magnetotactic bacteria have the unique ability to synthesize magnetosomes (nano-sized magnetite or greigite crystals arranged in chain-like structures) in a variety of shapes and sizes. The chain alignment of magnetosomes enables magnetotactic bacteria to sense and orient themselves along geomagnetic fields. There is steadily increasing demand for magnetosomes in the areas of biotechnology, biomedicine, and environmental protection. Practical difficulties in cultivating magnetotactic bacteria and achieving consistent, high-yield magnetosome production under artificial environmental conditions have presented an obstacle to successful development of magnetosome applications in commercial areas. Here, we review information on magnetosome biosynthesis and strategies for enhancement of bacterial cell growth and magnetosome formation, and implications for improvement of magnetosome yield on a laboratory scale and mass-production (commercial or industrial) scale.

Nanotechnology in soil remediation - applications vs. implications

Engineered nanomaterials (ENMs) and nanotechnology have shown great potential in addressing complex problems and creating innovative approaches in soil remediation due to their unique features of high reactivity, selectivity and versatility. Meanwhile, valid concerns exist with regard to their implications towards the terrestrial environment and the ecosystem. This review summarizes: (i) the applications and the corresponding mechanisms of various types of ENMs for soil remediation; (ii) the environmental behavior of ENMs in soils and their interactions with the soil content; (iii) the environmental implications of ENMs during remedial applications. The overall objective is to promote responsible innovations so as to take optimal advantage of ENMs and nanotechnology while minimizing their adverse effects to the ecological system. It is critical to establish sustainable remediation methods that ensure a healthy and safe environment without bringing additional risk.

Comparative developmental toxicity of iron oxide nanoparticles and ferric chloride to zebrafish (Danio rerio) after static and semi-static exposure

Iron oxide nanoparticles (IONPs) are used in several medical and environmental applications, but their mechanism of action and hazardous effects to early developmental stages of fish remain unknown. Thus, the present study aimed to assess the developmental toxicity of citrate-functionalized IONPs (γ-Fe₂O₃ NPs), in comparison with its dissolved counterpart, in zebrafish (Danio rerio) after static and semi-static exposure. Embryos were exposed to environmental concentrations of both iron forms (0.3, 0.6, 1.25, 2.5, 5 and 10 mg L^-1) during 144 h, jointly with negative control group. The interaction and distribution of both Fe forms on the external chorion and larvae surface were measured, following by multiple biomarker assessment (mortality, hatching rate, neurotoxicity, cardiotoxicity, morphological alterations and 12 morphometrics parameters). Results showed that IONPs were mainly accumulated on the zebrafish chorion, and in the digestive system and liver of the larvae. Although the IONPs induced low embryotoxicity compared to iron ions in both exposure conditions, these nanomaterials induced sublethal effects, mainly cardiotoxic effects (reduced heartbeat, blood accumulation in the heart and pericardial edema). The semi-static exposure to both iron forms induced high embryotoxicity compared to static exposure, indicating that the nanotoxicity to early developmental stages of fish depends on the exposure system. This is the first study concerning the role of the exposure condition on the developmental toxicity of IONPs on fish species.

Selective and fast recovery of rare earth elements from industrial wastewater by porous β-cyclodextrin and magnetic β-cyclodextrin polymers

Recovery of rare earth elements (REEs) from industrial wastewater has drawn great attention due to their potential environmental toxicity, as well as their high demand in modern technologies. In this study, we developed a magnetic composite based on the high surface area porous β-cyclodextrin polymer (P-CDP), namely P-CDP@Fe₃O₄. Both P-CDP and P-CDP@Fe₃O₄ rapidly sequester REEs such as Nd, Gd, Eu, and Y, reaching equilibrium in less than 10 min and fitting the Langmuir isotherm model with maximum adsorption capacities ranging from 7.76 to 9.59 mg/g at 25 °C when the highest initial concentration was 100 mg/L. Besides, the recovery of these REEs was not affected by competitive alkali, alkaline earth, and transition metal ions in model studies and industrial wastewater as revealed by the recovery efficiencies, which ranged from 62% to 100% indicating an excellent selectivity on both adsorbents. In addition, both adsorbents can be fully regenerated under mildly acidic conditions for at least five consecutive cycles. Moreover, P-CDP@Fe₃O₄ can be easily isolated by an external magnetic field which simplifies its synthesis and usability. It also overcomes the clogging and high backpressure issues of P-CDP, which facilitates its application for REEs recovery as compared with P-CDP. These characteristics demonstrate the promise of P-CDP and P-CDP@Fe₃O₄ for the pollution control and recovery of REEs.

Microwave-Assisted Synthesis of Water-Dispersible Humate-Coated Magnetite Nanoparticles: Relation of Coating Process Parameters to the Properties of Nanoparticles

Nowadays, there is a demand in the production of nontoxic multifunctional magnetic materials possessing both high colloidal stability in water solutions and high magnetization. In this work, a series of water-dispersible natural humate-polyanion coated superparamagnetic magnetite nanoparticles has been synthesized via microwave-assisted synthesis without the use of inert atmosphere. An impact of a biocompatible humate-anion as a coating agent on the structural and physical properties of nanoparticles has been established. The injection of humate-polyanion at various synthesis stages leads to differences in the physical properties of the obtained nanomaterials. Depending on the synthesis protocol, nanoparticles are characterized by improved monodispersity, smaller crystallite and grain size (up to 8.2 nm), a shift in the point of zero charge (6.4 pH), enhanced colloidal stability in model solutions, and enhanced magnetization (80 emu g⁻¹).

Nanoconfinement-Mediated Water Treatment: From Fundamental to Application

Safe and clean water is of pivotal importance to all living species and the ecosystem on earth. However, the accelerating economy and industrialization of mankind generate water pollutants with much larger quantity and higher complexity than ever before, challenging the efficacy of traditional water treatment technologies. The flourishing researches on nanomaterials and nanotechnologies in the past decade have generated new understandings on many fundamental processes and brought revolutionary upgrades to various traditional technologies in almost all areas, including water treatment. An indispensable step toward the real application of nanomaterials in water treatment is to confine them in large processable substrate to address various inherent issues, such as spontaneous aggregation, difficult operation and potential environmental risks. Strikingly, when the size of the spatial restriction provided by the substrate is on the order of only one or several nanometers, referred to as nanoconfinement, the phase behavior of matter and the energy diagram of a chemical reaction could be utterly changed. Nevertheless, the relationship between such changes under nanoconfinement and their implications for water treatment is rarely elucidated systematically. In this Critical Review, we will briefly summarize the current state-of-the-art of the nanomaterials, as well as the nanoconfined analogues (i.e., nanocomposites) developed for water treatment. Afterward, we will put emphasis on the effects of nanoconfinement from three aspects, that is, on the structure and behavior of water molecules, on the formation (e.g., crystallization) of confined nanomaterials, and on the nanoenabled chemical reactions. For each aspect, we will build the correlation between the nanoconfinement effects and the current studies for water treatment. More importantly, we will make proposals for future studies based on the missing links between some of the nanoconfinement effects and the water treatment technologies. Through this Critical Review, we aim to raise the research attention on using nanoconfinement as a fundamental guide or even tool to advance water treatment technologies.

The facile synthesis of zoledronate functionalized hydroxyapatite amorphous hybrid nanobiomaterial and its excellent removal performance on Pb2+ and Cu2

In this paper, a simple chemical precipitation method was proposed to obtain zoledronate functionalized hydroxyapatite (zole-HAP) hybrid nano- biomaterials (zole-HAP-HNBM) which were firstly applied to adsorption. The characterizations of materials verified that the addition of zoledronate declined the crystallinity and transformed the morphology of HAP from short rod shape to microsphere, changed micro structure of the hybrid nanobiomaterial. Adsorption experiments carried out under different conditions showed that adsorption capacity of the nanobiomaterial, enhanced by the addition of zoledronate in preparation, which is equal to 1460.14 mg/g on Pb²⁺ and 226.33 mg/g on Cu²⁺ in optimum qualifications, was elevated more than the reported values in many literatures. At last, the sorption mechanisms of HAP and zole-HAP for Pb²⁺and Cu²⁺ were probed by experiments and Multifwn program calculation in details. It suggested that the dominant sorption mechanisms of HAP for Pb²⁺ were ion exchange and dissolution-precipitation rather than surface complexation, while besides the dissolution-precipitation mechanism, surface complexation may contribute more in the adsorption process of 10zole-HAP for Pb²⁺. Once considering HAP and 10zole-HAP, removal mechanisms of Cu²⁺ could involve surface complexation and ion exchange.

Corrosion Resistance of Modified Hexagonal Boron Nitride (h-BN) Nanosheets Doped Acrylic Acid Coating on Hot-Dip Galvanized Steel

The hexagonal boron nitride (h-BN) nanosheets modified by silane coupling agent (KH560) were doped into acrylic acid coating on the surface of galvanized steel to improve its corrosion resistance. H-BN nanosheets modified by KH560 were prepared and characterised by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The corrosion resistance of the acrylic acid coatings was measured by electrochemical testing. The results show that the corrosion current density of the coating with modified h-BN nanosheets was reduced from 2.2 × 10⁻⁵ A/cm² to 2.3 × 10⁻⁷ A/cm² compared with the acrylic acid coating. The impedance of the composite coating with modified h-BN is 4435 Ω·cm², higher than the BNNS coating (2500 Ω·cm²) and the acrylic acid coating (1500 Ω·cm²). This is due to the physical barrier and electrical insulation properties of the hexagonal boron nitride (h-BN) nanosheets.

Trend of the research on rare earth elements in environmental science

Rare earth elements (REEs) consist of 17 transition metals which are the 15 lanthanides and yttrium and scandium. These elements have great utility in the production of modern technology, especially electronics. However, these materials may pose a serious threat to the environment if handled or disposed of incorrectly; the effects of which are being studied by the field of environmental toxicology. A multitude of studies have indicated that rare earth elements have harmful impacts on biological life, making a reform to the disposal of rare earth elements increasingly pressing. Scientific interest in REEs is constantly rising due to the increased use of REEs due to their utility. In this paper, we display our meta-analysis of a scientific literature database, PubMed, to quantitatively map the temporal flux of research and interest pertaining to REEs, especially in the field of environmental science. Our findings may prove useful for planning research on REEs or predicting the future of REE usage.

Multifunctional magnetic MgMn-oxide composite for efficient purification of Cd2+ and paracetamol pollution: Synergetic effect and stability

A multifunctional magnetic composite (0.3Ma-MgMnLDO-a) with the function of Cd²⁺ adsorption and paracetamol (PAM) degradation was successfully fabricated. Surface morphology showed that Fe₃O₄ agglomeration was overcome on composite. The composite had high specific surface area of 105.32 m² g^-1 and saturation magnetization of 40 emu∙g^-1. 0.3Ma-MgMnLDO-a could reach Cd²⁺ adsorption equilibrium within 5 min with 99 % removal rate. The maximum adsorption capacity was 3.76 mmol·g^-1 (422.62 mg g^-1), which apparently higher than that of Fe₃O₄-a and MgMnLDO-a, indicating that the Fe/Mn synergism results in excellent ability for Cd²⁺ adsorption. Moreover, the composite could efficiently activate peroxymonosulfate (PMS) to rapid degrade PAM with the highest first-order rate constants (k_obs = 0.116 min^-1) and total organic carbon (TOC) removal rate (67.7 %), which also due to the contribution of Fe/Mn synergism in PMS activation. The cycling of Mn^III/Mn^IV and Fe^II/Fe^III played an important role in activating PMS to generateO₂^-•, ¹O₂ and OH for degradation. The composite exhibited both stable adsorption and catalytic performance on wide pH (3-9) and five reuse cycles. Notably, there was mutual promotion between Cd²⁺ and PAM adsorption, while the coexistence of Cd²⁺ had slight inhibition on PAM degradation. Overall, the magnetic composite had promising application for purifying heavy metals and pharmaceuticals.

Effect of Microbial Biomass and Humic Acids on Abiotic and Biotic Magnetite Formation

Magnetite (Fe₃O₄) is an environmentally ubiquitous mixed-valent iron (Fe) mineral, which can form via biotic or abiotic transformation of Fe(III) (oxyhydr)oxides such as ferrihydrite (Fh). It is currently unclear whether environmentally relevant biogenic Fh from Fe(II)-oxidizing bacteria, containing cell-derived organic matter, can transform to magnetite. We compared abiotic and biotic transformation: (1) abiogenic Fh (aFh); (2) abiogenic Fh coprecipitated with humic acids (aFh-HA); (3) biogenic Fh produced by phototrophic Fe(II)-oxidizer Rhodobacter ferrooxidans SW2 (bFh); and (4) biogenic Fh treated with bleach to remove biogenic organic matter (bFh-bleach). Abiotic or biotic transformation of Fh was promoted by Fe_aq²⁺ or Fe(III)-reducing bacteria. Fe_aq²⁺-catalyzed abiotic reaction with aFh and bFh-bleach led to complete transformation to magnetite. In contrast, aFh-HA only partially (68%) transformed to magnetite, and bFh (17%) transformed to goethite. We hypothesize that microbial biomass stabilized bFh against reaction with Fe_aq²⁺. All four Fh substrates were transformed into magnetite during biotic reduction, suggesting that Fh remains bioavailable even when associated with microbial biomass. Additionally, there were poorly ordered magnetic components detected in the biogenic end products for aFh and aFh-HA. Nevertheless, abiotic transformation was much faster than biotic transformation, implying that initial Fe_aq²⁺ concentration, passivation of Fh, and/or sequestration of Fe(II) by bacterial cells and associated biomass play major roles in the rate of magnetite formation from Fh. These results improve our understanding of factors influencing secondary mineralization of Fh in the environment.

Biofunctionalized nanomaterials for in situ clean-up of hydrocarbon contamination: A quantum jump in global bioremediation research

Interfacing organic or inorganic nanoparticles with biological entities or molecules or systems with the aim of developing functionalized nano-scale materials or composites for remediation of persistent organic hydrocarbon pollutants (such as monocyclic and polycyclic aromatic hydrocarbons, MAH/PAH) has generated great interest and continues to grow almost unabated. However, the usefulness and potency of these materials or conjugates hinges over several key barriers, including structural assembly with fine-tuned control over nanoparticle/biomolecule ratio, spatial orientation and activity of biomolecules, the nano/bio-interface strategy and hierarchical architecture, water-dispersibility and long term colloidal stability in environmental media, and non-specific toxicity. The present review thus critically analyses, discusses and interprets recently reported attempts and approaches to functionalize nanoparticles with biomolecules. Since there is no comprehensive and critical reviews on the applications of nanotechnology in bioremediation of MAHs/PAHs, this overview essentially captures the current global scenario and vision on the use and future prospects of biofunctionalized nanomaterials with respect to their strategic interactions involved at the nano/bio-interface essential to understand and decipher the structural and functional relationships and their impact on persistent hydrocarbon remediation.

Mechanistic and Thermodynamic Insights into Anion Exchange by Green Rust

Fougerite is a naturally occurring green rust, that is, a layered double hydroxide (LDH) containing iron (Fe). Fougerite was identified in natural settings such as hydromorphic soils. It is one of the few inorganic materials with large anion adsorption capacity that stems from the presence of isomorphic substitutions of Fe²⁺ by Fe³⁺ in its layers. The importance of anion adsorption in the interlayer of LDH has often been highlighted, but we are still missing a mechanistic understanding and a thermodynamic framework to predict the anion uptake by green rust. We combined laboratory and in operando synchrotron X-ray diffraction and scattering experiments with geochemical modeling to contribute to filling this gap. We showed that the overall exchange process in green rusts having nanometer and micrometer sizes can be seen as a simple anion exchange mechanism without dissolution-recrystallization or interstratification processes. A thermodynamic model of ion exchange, based on the Rothmund and Kornfeld convention, made it possible to predict the interlayer composition in a large range of conditions. This multiscale characterization can serve as a starting point for the building of robust and mechanistic geochemical models that will allow predicting the role of green rust on the geochemical cycle of ions, including nutrients, in soils.

Probing the interaction effects of metal ions in Mn x Fe(3-x)O4 on arsenite oxidation and adsorption

Wastewater treatment is still a global concern and materials capable of pollutant sequestration continue to be improved in a bid to ensure water reusability and curb water shortages. Some of the most promising materials so far are nanosized materials because of their unique properties and the ease of manipulation to improve their properties. In this work we investigated the effects of varying Fe3+ : Fe2+ ratios in magnetite nanoparticles and the influence of manganese doping. Diffraction measurements indicated that the manganese introduced into the magnetite matrix displaced some Fe atoms resulting in the formation of a uniform phase matching the card data for magnetite with no additional manganese phases being formed. XPS confirmed the presence of manganese on the surface of the doped nanomaterials and that both As(iii) and As(v) were bound on the adsorbent surface. The central composite design (CCD) of response surface methodology (RSM) was used to determine the effects the nanoparticle compositions had on As(iii) adsorption and oxidation. A quadratic equation was used to model the experimental data with a correlation coefficient close to unity indicating that the model was a good fit for the data. The interaction between Fe3+ and Mn had a positive influence in the reduction of As(iii) in solution while Fe3+/Fe2+ interactions had antagonistic effects and the Fe2+/Mn interactions were found to be insignificant. Increasing the amounts of Fe3+ and manganese therefore resulted in the highest reduction in As(iii) concentration.

Gold, Silver and Iron Oxide Nanoparticles: Synthesis and Bionanoconjugation Strategies Aimed at Electrochemical Applications

Nanomaterials have revolutionized the sensing and biosensing fields, with the development of more sensitive and selective devices for multiple applications. Gold, silver and iron oxide nanoparticles have played a particularly major role in this development. In this review, we provide a general overview of the synthesis and characteristics of gold, silver and iron oxide nanoparticles, along with the main strategies for their surface functionalization with ligands and biomolecules. Finally, different architectures suitable for electrochemical applications are reviewed, as well as their main fabrication procedures. We conclude with some considerations from the authors' perspective regarding the promising use of these materials and the challenges to be faced in the near future.

Synthesis, physical characterization, and antifungal and antibacterial activities of oleic acid capped nanomagnetite and cobalt-doped nanomagnetite

Nanoparticles, 10–14 nm, consisting of either Fe3O4 or Co0.2Fe2.8O4 stabilized with oleic acid, were prepared using solution combustion. Their structural and magnetic properties were examined using X-ray diffractometry, scanning electron microscopy, vibrating sample magnetometry, and Fourier-transform infrared spectroscopy. The properties of both sets of materials are similar, except that the cobalt-doped particles are considerably less magnetic. The in vitro inhibitory activities of the nanoparticles were assessed against pathogenic bacteria Shigella dysenteriae, Klebsiella pneumoniae, Acinetobacter baumannii, Streptococcus pyogenes, and pathogenic fungi and molds Candida albicans, Fusarium oxysporum, and Aspergillus fumigatus. The magnetite nanoparticles were moderately effective against all tested pathogens, but the activity of the cobalt-doped nanoparticles was significantly lower, possibly due to an interruption of the Fenton reaction at the bacterial membrane. This work suggests that potentially doping magnetite with stronger metal oxidants may instead enhance their antimicrobial effects.

N-doped carbon coated Mn3O4/PdCu nanocomposite as a high-performance catalyst for 4-nitrophenol reduction

This paper reports the chemical synthesis of highly-active Mn₃O₄/PdCu nanocomposites coated with N-doped carbon (NC) shell using polydopamine (PDA) as the carbon source, which provides high specific surface area and pore volume. The structure and morphology of Mn₃O₄/PdCu@NC nanocomposites were systematically studied. Taking advantage of the synergistic effects of PdCu alloy and Mn₃O₄ support, the Mn₃O₄/PdCu@NC catalyst exhibited an outstanding activity toward the reduction of 4-nitrophenol (4-NP), in comparison to Mn₃O₄/PdM@NC (M = Ni, Au, Ag), Mn₃O₄/PdCu@PDA, and commercial Pd/C catalyst. Owing to the protection by NC shell, the as-prepared catalyst showed stable conversion efficiency of up to 90% over ten successive cycles. Considering 4-NP as one of the important organic pollutants from industrial production, the effects of various inorganic and organic species on the catalytic efficiency were further tested and most of them had negligible impact. This strategy of utilizing an N-doped carbon shell could be extended to obtain PdCu alloys supported on other metal oxides, making it applicable for applications in treatment of environmental pollutants.

Enhanced removal of As(Ⅲ) and As(Ⅴ) from aqueous solution using ionic liquid-modified magnetic graphene oxide

In this study, ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆])-modified magnetic graphene oxide (MGO-IL) was prepared for the first time, and was used to adsorb and remove arsenic (As(Ⅲ) and As(V)) ions from aqueous solution. MGO-IL was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and magnetization curves. Effects of ionic liquid type, solution pH, initial arsenic concentration and contact time on the adsorption performance of MGO-IL for As(Ⅲ) and As(V) were studied. The experimental results showed that the adsorption equilibrium was achieved within 30 min, with maximum adsorption capacities of 160.65 mg g^-1 for As(Ⅲ) and 104.13 mg g^-1 for As(V), respectively, and MGO-IL could be rapidly isolated from solution by applying a magnetic field. MGO-IL was reused for 5 times, without marked decrease in its adsorption capacities. Moreover, common coexisting anions did not interfere with the absorption of As(Ⅲ) and As(V). Compared with MGO, the sorption quantities of MGO-IL for As(Ⅲ) and As(V) were greatly enhanced, and the equilibrium time was significantly reduced. Therefore, MGO-IL can potentially serve as an excellent adsorbent for the simultaneous separation and removal of As(Ⅲ) and As(V) from water.

Gas Diffusion Electrodes on the Electrosynthesis of Controllable Iron Oxide Nanoparticles

The electrosynthesis of iron oxide nanoparticles offers a green route, with significant energy and environmental advantages. Yet, this is mostly restricted by the oxygen solubility in the electrolyte. Gas-diffusion electrodes (GDEs) can be used to overcome that limitation, but so far they not been explored for nanoparticle synthesis. Here, we develop a fast, environmentally-friendly, room temperature electrosynthesis route for iron oxide nanocrystals, which we term gas-diffusion electrocrystallization (GDEx). A GDE is used to generate oxidants and hydroxide in-situ, enabling the oxidative synthesis of a single iron salt (e.g., FeCl₂) into nanoparticles. Oxygen is reduced to reactive oxygen species, triggering the controlled oxidation of Fe²⁺ to Fe³⁺, forming Fe_3−xO_4−x (0 ≤ x ≤ 1). The stoichiometry and lattice parameter of the resulting oxides can be controlled and predictively modelled, resulting in highly-defective, strain-heavy nanoparticles. The size of the nanocrystals can be tuned from 5 nm to 20 nm, with a large saturation magnetization range (23 to 73 A m² kg⁻¹), as well as minimal coercivity (~1 kA m⁻¹). Using only air, NaCl, and FeCl₂, a biocompatible approach is achieved, besides a remarkable level of control over key parameters, with a view on minimizing the addition of chemicals for enhanced production and applications.

Novel Enzyme-Free Multifunctional Bentonite/Polypyrrole/Silver Nanocomposite Sensor for Hydrogen Peroxide Detection over a Wide pH Range

Precise designs of low-cost and efficient catalysts for the detection of hydrogen peroxide (H₂O₂) over wide ranges of pH are important in various environmental applications. Herein, a versatile and ecofriendly approach is presented for the rational design of ternary bentonite-silylpropyl-polypyrrole/silver nanoarchitectures (denoted as BP-PS-PPy/Ag) via the in-situ photo polymerization of pyrrole with salinized bentonite (BP-PS) in the presence of silver nitrate. The Pyrrolyl-functionalized silane (PS) is used as a coupling agent for tailoring the formation of highly exfoliated BP-PS-PPy sheet-like nanostructures ornamented with monodispersed Ag nanoparticles (NPs). Taking advantage of the combination between the unique physicochemical properties of BP-PS-PPy and the outstanding catalytic merits of Ag nanoparticles (NPs), the as-synthesized BP-PS-PPy/Ag shows a superior electrocatalytic reduction and high-detection activity towards H₂O₂ under different pH conditions (from 3 to 10). Intriguingly, the UV-light irradiation significantly enhances the electroreduction activity of H₂O₂ substantially, compared with the dark conditions, due to the high photoelectric response properties of Ag NPs. Moreover, BP-PS-PPy/Ag achived a quick current response with a detection limit at 1 μM within only 1 s. Our present approach is green, facile, scalable and renewable.

Removal of heavy crude oil from water surfaces using a magnetic inorganic-organic hybrid powder and membrane system

Oil spills are among the most significant threats to aquatic ecosystems. The present work describes the synthesis of different organic-inorganic hybrid matrices with magnetic properties, obtained in the forms of powders and membranes. The powders were synthesized using the following biomass wastes to form the organic phase: coconut mesocarp, sugarcane bagasse, sawdust, and water hyacinth. The resulting powders were denoted HMG-CO, HMG-CN, HMG-SE, and HMG-AP, respectively. Membranes (denoted MHMG-PES) were prepared using polyethersulfone polymer. In both cases, the inorganic phase was cobalt ferrite. The materials were evaluated in terms of their efficiencies in removing crude oil from water surfaces. The presence of organic matter, polyethersulfone, and cobalt ferrite in the structures of the materials was confirmed by XRD and FTIR analyses. The efficiencies of the materials were determined using the Standard Test Method for Sorbent Performance of Adsorbents (ASTM F726-99). Among the hybrids in powder form, the HMG-CN material presented the highest oil removal efficiency (85%, adsorptive capacity of 17 g g^-1), which could be attributed to the fibrous nature of the sugarcane bagasse. The MHMG-PES membrane was able to remove 35 times its own mass of oil (adsorptive capacity of 35 g g^-1). In addition to this high removal efficiency, an important advantage of MHMG-PES, compared to the HMG-CN hybrid powder, was that the oil could be mechanically removed from the membrane surface, eliminating the need for subsequent time-consuming extraction steps requiring large volumes of organic solvents and additional energy expenditure. When the two materials were used simultaneously, it was possible to remove 45 times their own mass of oil (adsorptive capacity of 45 g g^-1), with the adsorptive capacity of HMG-CN increasing by 23%. This high adsorptive capacity was due to the retaining barrier formed by the HMG-CN hybrid powder, which prevented the oil patch from spreading and enabled its homogeneous removal, which was not possible using MHMG-PES alone. It could be concluded that use of the magnetic hybrids synthesized using biomass wastes, together with the hybrid magnetic membrane, provided an effective and inexpensive technological alternative for the removal of oil from water surfaces.

Preparation of Activated Biochar-Supported Magnetite Composite for Adsorption of Polychlorinated Phenols from Aqueous Solutions

For this study, we applied activated biochar (AB) and its composition with magnetite (AB-Fe3O4) as adsorbents for the removal of polychlorophenols in model wastewater. We comprehensively characterized these adsorbents and performed adsorption tests under several experimental parameters. Using FTIR, we confirmed successful synthesis of AB-Fe3O4 composite through cetrimonium bromide surfactant. We conducted adsorption tests using AB and AB-Fe3O4 to treat model wastewater containing polychlorophenols, such as 2,3,4,6-Tetrachlorophenol (TeCP), 2,4,6-Trichlorophenol (TCP), and 2,4-Dichlorophenol (DCP). Results of the isotherm and the kinetic experiments were well adapted to Freundlich’s isotherm model and the pseudo-second-order kinetic model, respectively. Main adsorption mechanisms in this study were attributed to non-covalent, π-electron acceptor–donor interactions and hydrophobic interactions judging from the number of chloride elements in each chlorophenol and its hydrophobic characteristics. We also considered the electrostatic repulsion effect between TeCP and AB, because adsorption performance of TeCP at basic condition was slightly worse than at weak acidic condition. Lastly, AB-Fe3O4 showed high adsorption selectivity of TeCP compared to other persistent organic pollutants (i.e., bisphenol A and sulfamethoxazole) due to hydrophobic interactions. We concluded that AB-Fe3O4 may be used as novel adsorbent for wastewater treatment including toxic and hydrophobic organic pollutants (e.g., TeCP).

Quantification and biodegradability assessment of meso-2,3-dimercaptosuccinic acid adsorbed on iron oxide nanoparticles

Many interesting applications of magnetic iron oxide nanoparticles (IONPs) have recently been developed based on their magnetic properties and promising catalytic activity. Depending on their intended use, such nanoparticles (NPs) are frequently functionalized with proteins, polymers, or other organic molecules such as meso-2,3-dimercaptosuccinic acid (DMSA) to improve their colloidal stability or biocompatibility. Although the coating strongly affects the colloidal properties and environmental behaviour of NPs, quantitative analysis of the coating is often neglected. To address this issue, we established an ion chromatographic method for the quantitative analysis of surface-bound sulfur-containing molecules such as DMSA. The method determines the amount of sulfate generated by complete oxidation of sulfur present in the molecule. Quantification of the DMSA content of DMSA-coated IONPs showed that reproducibly approximately 38% of the DMSA used in the synthesis was adsorbed on the IONPs. Tests for the biodegradability of free and NP-bound DMSA using a microbial community from a wastewater treatment plant showed that both free and NP-bound DMSA was degraded to negligible extent, suggesting long-term environmental stability of DMSA-coated IONPs.

Adsorption of bovine serum albumin (BSA) by bare magnetite nanoparticles with surface oxidative impurities that prevent aggregation

Bare, uncoated magnetite nanoparticles, synthesized using an electrochemical surfactant-free synthesis, have highly oxidized surfaces that prevent aggregation. These particles have demonstrated highly intriguing biological activity showing extremely potent antibiotic activity against both gram-positive and gram-negative bacteria with little toxicity to rats. This difference in activity could be ascribed to the nature of the protein corona. The kinetics and thermodynamics of the binding of bovine serum albumin (BSA), used as a model serum protein, to these magnetite nanoparticles were analyzed. There is no significant change in particle diameter by dynamic light scattering following adsorption, indicating corona formation does not induce aggregation. The maximum adsorption capacity of the particles was determined to be 300 mg of BSA per gram of magnetite. The particles are able to adsorb 90% of the BSA at protein concentrations as high as 500 mg/L. The adsorption is best described using a pseudo second order model and a Langmuir Type III isotherm model. Thermodynamic analysis showed that the process is entropically driven and is spontaneous at all tested temperatures and conditions. However, it appears to be a weak to moderate physical adsorption. This moderate binding affinity could indicate the differential biological activity of these particles towards bacteria and mammalian cells and further support the contention that these are potentially useful new tools for targeting antibiotic-resistant bacteria.

Effect of multiple iron-based nanoparticles on availability of lead and iron, and micro-ecology in lead contaminated soil

Although iron nanoparticles (NPs) have been used for environmental remediation of heavy metal, their potential to remediate lead (Pb) contaminated soil and effect on soil micro-ecology is unclear. The purpose of this study was to investigate the potential of nanoscale zerovalent iron (nZVI), nanoscale zerovalent iron supported by biochar (nZVI@BC), ferrous sulfide (FeS-NPs), ferrous sulfide supported by biochar (FeS-NPs@BC), ferriferrous oxide (Fe₃O₄-NPs) and ferriferrous oxide supported by biochar (Fe₃O₄-NPs@BC) to remediate Pb contaminated soil and the influences for soil micro-ecology. The results showed that biochar (BC) could improve the crystal shape and superficial area of iron-based nanoparticles. Soil pH values was significantly decreased by FeS-NPs and FeS-NPs@BC, but increased by other iron-nanoparticles. The ability to reduce available Pb concentration showed significant difference among these iron-nanoparticles, that is, the immobilized rate were nZVI by 45.80%, nZVI@BC by 54.68%, FeS-NPs by 2.70%, FeS-NPs@BC by 5.13%, Fe₃O₄-NPs by 47.47%, Fe₃O₄-NPs@BC by 30.51% at day 90. Almost all soil enzyme activities in Fe₃O₄-NPs and Fe₃O₄-NPs@BC groups were increased, but the majority of the enzyme activities were inhibited in other iron-based nanoparticles groups, while the maximum bacterial number was determined in FeS-NPs group. Furthermore, microbial diversity analysis showed that FeS-NPs has significantly changed microbial community richness and diversity, followed by nZVI and Fe₃O₄-NPs. Accordingly, our results suggested that nZVI@BC had the best immobilization effect on Pb in high-concentration Pb-contaminated alkaline soil, but the toxic effect of Fe₃O₄-NPs on soil micro-ecology was relatively minimal.

Enhanced arsenite removal from water by radially porous Fe-chitosan beads: Adsorption and H2O2 catalytic oxidation

Although Fe-chitosan adsorbents are attractive for removing arsenite from water, the practical applications of these granular adsorbents are mainly limited by slow adsorption kinetics. In this study, radially porous Fe-chitosan beads (P/Fe-CB) were prepared using freeze-casting technique. The P/Fe-CB particles possess radially aligned micron-sized tunnels from the surface to the inside as well as excellent acid resistance. Kinetic studies show that the adsorption equilibrium time of P/Fe-CB to 0.975 mg/L As(III) (within 240 min) is considerably shorter than that of compact Fe-chitosan beads (over 600 min). The maximal adsorption capacity of P/Fe-CB for As(III) is 52.7 mg/g. It can work effectively in a wide pH range from 3 to 9, and the coexisting sulfate, carbonate, silicate and humic acid have no significant effect on As(III) removal. The addition of H₂O₂ can further accelerate and promote the As(III) removal except at high pH (11) and phosphate concentration (50 mg/L). The fixed-bed experiments demonstrate that the P/Fe-CB column can effectively treat about 3000 bed volume (BV) of simulated As(III)-containing groundwater to meet the drinking water standard (<10 μg As/L). This study would extend the potential applicability of porous Fe based chitosan adsorbent and millimeter-sized adsorbent combined with H₂O₂ to a great extent.