Maghemite Surface Research Articles

Maghemite surface termination variations: Influence of models and Pt substrate

In spite of the growing interest in maghemite, its structure is not accurately known, and numerous uncertainties remain. The ongoing debate centers on its crystalline structure, whether cubic or tetragonal, and its implications for stable surface terminations. This study explores the crystalline nature of maghemite — cubic versus tetragonal — and its effects on surface stability. Using density functional theory (DFT) with Hubbard corrections, we evaluated the stability and electronic properties of maghemite’s (001) and (111) surfaces under both cubic and tetragonal configurations, while also considering the influence of a Pt substrate and strain arising from lattice mismatch. Our findings indicate that native cubic (001) surfaces are inherently more stable than tetragonal ones. However, the presence of a Pt substrate shifts this stability, favoring the cubic (111) surface presenting a higher adhesion energy. We examined the electronic properties of various cases to provide a rationalization of the observed stability order. Our study provides crucial insights into the impact of crystalline structure and Pt substrate on the stability and favored terminations of maghemite surfaces, emphasizing their prospective utility as water oxidation catalysts.

Influence of Silica Coatings on Magnetite-Catalyzed Selenium Reduction.

The reactivity of iron(II/III) oxide surfaces may be influenced by their interaction with silica, which is ubiquitous in aquatic systems. Understanding the structure-reactivity relationships of Si-coated mineral surfaces is necessary to describe the complex surface behavior of nanoscale iron oxides. Here, we use Si-adsorption isotherms and Fourier transform infrared spectroscopy to analyze the sorption and polymerization of silica on slightly oxidized magnetite nanoparticles (15% maghemite and 85% magnetite, i.e., ∼2 maghemite surface layers), showing that Si adsorption follows a Langmuir isotherm up to 2 mM dissolved Si, where surface polymerization occurs. Furthermore, the effects of silica surface coatings on the redox-catalytic ability of magnetite are analyzed using selenium as a molecular probe. The results show that for partially oxidized nanoparticles and even under different Si surface coverages, electron transfer is still occurring. The results indicate anion exchange between silicate and the sorbed SeIV and SeVI. X-ray absorption near-edge structure analyses of the reacted Se indicate the formation of a mixed selenite/Se0 surface phase. We conclude that neither partial oxidation nor silica surface coatings block the sorption and redox-catalytic properties of magnetite nanoparticles, a result with important implications to assess the reactivity of mixed-valence phases in environmental settings.

The Composition and Magnetic Structure of Fe3O4/γ-Fe2O3 Core-Shell Nanocomposites under External Magnetic Field: Mössbauer Study (Part II)

The composition and the magnetic structure of Fe3O4/γ-Fe2O3 nanoparticles placed into external magnetic field with a strength of 1.8 kOe are studied with Mossbauer spectroscopy. We showed that the thickness of the maghemite (γ-Fe2O3) shell can be changed by the synthesis conditions. We found that there is a layer, in which the magnetic moments are not oriented collinearly to those located in the depth of the shell, on the surface of maghemite (γ-Fe2O3) shell in the Fe3O4/γ-Fe2O3 nanocomposites; in other words, there is a canted spin structure. An intermediate layer in the spin-glass state is formed between the core and the shell. The data on structure of core/shell particles are important to understand the properties of nanocomposites, which are of great interest to apply in various fields, including biomedicine.

Transient coating of γ-Fe2O3 nanoparticles with glutamate for its delivery to and removal from brain nerve terminals.

Glutamate is the main excitatory neurotransmitter in the central nervous system and excessive extracellular glutamate concentration is a characteristic feature of stroke, brain trauma, and epilepsy. Also, glutamate is a potential tumor growth factor. Using radiolabeled ʟ-[14C]glutamate and magnetic fields, we developed an approach for monitoring the biomolecular coating (biocoating) with glutamate of the surface of maghemite (γ-Fe2O3) nanoparticles. The nanoparticles decreased the initial rate of ʟ-[14C]glutamate uptake, and increased the ambient level of ʟ-[14C]glutamate in isolated cortex nerve terminals (synaptosomes). The nanoparticles exhibit a high capability to adsorb glutamate/ʟ-[14C]glutamate in water. Some components of the incubation medium of nerve terminals, that is, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and NaH2PO4, decreased the ability of γ-Fe2O3 nanoparticles to form a glutamate biocoating by about 50% and 90%, respectively. Only 15% of the amount of glutamate biocoating obtained in water was obtained in blood plasma. Albumin did not prevent the formation of a glutamate biocoating. It was shown that the glutamate biocoating is a temporal dynamic structure at the surface of γ-Fe2O3 nanoparticles. Also, components of the nerve terminal incubation medium and physiological fluids responsible for the desorption of glutamate were identified. Glutamate-coated γ-Fe2O3 nanoparticles can be used for glutamate delivery to the nervous system or for glutamate adsorption (but with lower effectiveness) in stroke, brain trauma, epilepsy, and cancer treatment following by its subsequent removal using a magnetic field. γ-Fe2O3 nanoparticles with transient glutamate biocoating can be useful for multifunctional theranostics.

Improved Removal Capacity and Equilibrium Time of Maghemite Nanoparticles Growth in Zeolite Type 5A for Pb(II) Adsorption.

Novel magnetic zeolite type 5A nanocomposites were synthesized by the co-precipitation method and applied to lead removal from aqueous ambient. Maghemite nanoparticles were mixed with zeolite and, by controlling its content, transmission electron microscopy results gave sizes of 5 to 15 nm and selected area electron diffraction patterns confirmed the presence of zeolite. The nanocomposites have high specific surface area with values up to 194 m2/g. Magnetization measurements proved superparamagnetic behavior with saturation values of ~35 emu/gFe. Kinetic adsorption experiments showed removal efficiencies of 99.9% and an enhanced equilibrium time of 5 min. The lead concentrations after adsorption experiments lay under the permissible levels of 10 μg L−1, according to the World Health Organization. The maximum adsorption capacity, estimated by Sips model, was 265 mg L−1 at 300 K. The removal efficiency was significantly improved in the range of pH > 6, as well as in the presence of cation interferents such as Ca(II), Cu(II), and Cd(II). The adsorption mechanism was explained with cation exchange between Pb(II), the zeolite framework, and the protonated maghemite surface. Besides, our system revealed recyclability even after seven regeneration cycles. Thus, our synthesized materials have remarkable adsorption properties for lead water remediation processes.

Surface reducibility, reactivity, and stability induced by noble metal modifications on the γ-Fe2O3 maghemite (001) surfaces

In these last years large research efforts have been devoted to the synthesis and investigation of reducible metal oxide surfaces modified with metal atoms and nanoparticles for improving their performance in a number of advanced applications. Among reducible metal oxides, iron oxides have the advantage to be made up from two of the most common elements on Earth. In this paper we analyze the structural, electronic, and magnetic consequences of the insertion of isolated noble metal atoms (Cu, Ag, Au) on the γ-Fe2O3 (001) surface. We have considered many different configurations for the single atoms: adsorbed, substitutional to iron atoms, or to oxygen atoms, and, using first principles calculations, we have studied how the presence of the noble metal atoms on the surface influences the surface stability, its reducibility, and, therefore, its catalytic activity, and how these properties depend on the kind of noble metal atom and its position. Our results show that noble metal atoms adsorbed on the surface facilitate the adsorption of CO molecules, and, among them, Cu atoms are those that bind best to the surface also providing the strongest adsorption energy for the CO molecule. At ambient temperature and pressure the noble metal atoms prefer to substitute the iron atoms than to just adsorb on the surface, but for Ag atoms the adsorption and substitutional energies are very close. The surfaces with Ag in place of Fe are the most reducible and reactive for exchange of oxygen atoms. Finally, Au is the best noble metal for oxygen substitution. Our results provide useful insights for the researchers designing and synthesizing new noble metal—iron oxides nanostructures for applications in biology, medicine, catalysis, and chemical analysis.

A study on the mechanism of Ca2+ adsorption on TiO2 and Fe2O3 with the usage of calcium ion-selective electrode.

The paper presents the quantitative characterization of the solid/water interface applying both experimental and theoretical approaches for the system of TiO2 (mixture of anatase and rutile) and Fe2O3 (maghemite) with calcium ions in the pH function. The aim of the study was also to find a bonding mechanism between Ca2+ and metal oxides surface based on the calculations from the surface complexation modeling code (GEOSURF by Sahai and Sverjensky, 1998). In order to obtain adsorption edges, a calcium ion-selective electrode (Ca-ISE) was applied for determination of Ca2+ concentration in the suspensions. The results of both the Ca-ISE and parallel spectrophotometric determination were similar. The adsorption data showed that TiO2 exhibited stronger calcium binding than Fe2O3 at pH > 8. Using 2-pK TLM (triple-layer model) it was demonstrated that mechanism of the calcium adsorption onto the metal oxides surface involved different reactions. In the case of TiO2 it involved formation of >SO-_CaOH+ predominately on the β-plane and at pH > 9 also on the 0-plane. In the case of Fe2O3 one could observe the existence of (>SO-)2_Ca2+ on the β-plane in the whole studied pH range. At pH above 7 the tetranuclear complexes (>SOH)2(>SO-)2_Ca(OH)+ were found, and at pH > 9 also >SO-_CaOH+ could be observed. On the other hand, the analysis of the ζ-potential data suggested the absence of the tetra-species on the maghemite surface. The study indicated that the properly validated calcium ion-selective electrode can be an attractive instrument for monitoring Ca2+ adsorption on metal oxides in the environment.

Reduction and Oxidation of Maghemite (001) Surfaces: The Role of Iron Vacancies

The knowledge of surface reduction and oxidation energetics in reducible oxides is essential for the design of improved catalysts for oxidation reactions. This is particularly true for iron oxides, a very attractive material system, because of the availability and biocompatibility of its constituents. In this work, by means of the density functional theory, we have thoroughly studied the γ-Fe2O3(001) maghemite surfaces, taking full account of iron vacancies beyond a mean field approach. Despite the structural similarity with the more studied magnetite Fe3O4 surfaces from which maghemite differs only for the presence of iron vacancies in the octahedral sites and for the absence of reduced Fe2+ cations, the surface properties are quite different. Our investigation shows that the presence of Fe vacancies is responsible for an increase in the surface reducibility. Also, it favors surface oxidation. The main reason is that the Fe vacancies cause a decrease of electronic charge of the surface oxygen atoms, whic...

Organophosphonate-functionalized nanosized magnetic iron oxides as sorbents for heavy metal cations

The surface of synthetic magnetite (Fe3O4) and maghemite (γ-Fe2O3) nanoparticles was modified with phosphonic chelating compounds, 1-hydroxyethane-1,1-di(phosphonic acid) and nitrilotris(methylenephosphonic acid). The sorption affinity of functionalized magnetic iron oxides towards Niii under acidic conditions was increased by one order of magnitude.

Reduction and transformation of nanomagnetite and nanomaghemite by a sulfate-reducing bacterium

Abstract Magnetite and maghemite are important components of iron oxides that determine the magnetic properties of rocks, soils, and sediments, and are also materials with broad industrial applications. We investigated the reduction and transformation of both phases with a strain of sulfate-reducing bacteria (SRB). SRB growth resulted in 28.1% and 7.1% sulfate to acid volatile sulfur conversion in magnetite and maghemite, respectively. Transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) analyses indicate that monosulfides (mackinawite and greigite) and polysulfides are the main secondary sulfides in the magnetite experiment, while the maghemite experiment also contained a high proportion of pyrite. XPS analyses indicate the reduction of Fe(III) to Fe(II) on the surface of magnetite and maghemite both by dissolved sulfides and SRB. Mossbauer spectroscopy measurements reveal the formation of superparamagnetic phases in microbial experiments, which indicates the dissolution and particle size decrease of the two minerals both by dissolved sulfides and SRB. X-ray diffraction and Mossbauer spectroscopy analyses suggest a complete transformation of nanomaghemite to nanomagnetite under the mediation of SRB through solid phase Fe(III) reduction. This transformation controls the changing and different patterns of both magnetic susceptibility and magnetic hysteresis for the two minerals. It is suggested that the structural similarity between magnetite and maghemite, and the conductivity of magnetite, constrain the unique solid phase transformation. Our findings indicate that the maghemite–magnetite solid solution is a potential natural battery for the growth of anaerobic microbes in sulfidic environments.

OPTIMIZATION OF LIPASE IMMOBILIZATION ON MAGHEMITE AND ITS PHYSICO-CHEMICAL PROPERTIES

ABSTRACT Nanomaterial-based biocatalysts have emerged as current carriers suitable for enzyme immobilization. The nano-sized materials provide large surface area for enzyme attachment, thus increasing the probability for its efficient catalyst activity. By using magnetized nanomaterials, enhancement of the downstream processing is evident as it eases the immobilized enzyme separation from the reaction mixture further. Lipase / maghemite composites were prepared by initial maghemite surface modification to cater to the needs for biocatalyst attachment. Surface modification using chitosan and subsequent cross-linking with glutaraldehyde provide a suitable environment for the enzyme to be immobilized. Optimization of the conditions for lipase immobilization was carried out using a response surface methodology (RSM) experimental design to obtain the precise optimized conditions for the process. Selected process variables involved were chosen and optimized conditions for lipase immobilization were 9 hour incubation time, 55°C incubation temperature and 12 % (v/v) glutaraldehyde content. The optimized immobilized lipase activity was 1.8 U. Characterizations of the on synthesized materials were also performed. The size distribution of maghemite nanomaterials was mainly within the range of 2-3 nm. Thermal properties of the synthesized maghemite was investigated using DSC and TGA analyses and we found that maghemite changes to hematite at 456.3°C. Magnetic properties of both untreated and lipase immobilized maghemite were studied using VSM and both were superparamagnetic nanomaterials with saturation magnetizations of 34.3 and 80.3, respectively.

Cr(III) and Fe(II) recovery from the polymetallic leach solution of electroplating sludge by Cr(III)-Fe(III) coprecipitation on maghemite

The separation of Cr(III) from the polymetallic leaching solution is a typical problem encountered during the recycling of electroplating sludge. In this paper, a novel method was proposed to recover Cr(III) and Fe(II) synchronously by forming the Cr(III)-Fe(III) coprecipitates on the surface of maghemite (γ-Fe2O3) fine particles with Fe2(SO4)3 solution as the supplemental Fe source. The results showed that high Fe(III) to Cr(III) ratio in solution promoted the hydrolysis and precipitation of Cr(III). In addition, the maghemite particles, served as the crystal nuclei, could induce the formation of the core-shell structured Cr(III)-Fe(III) coprecipitates on its surface and accelerate the sedimentation of the coprecipitates in the magnetic field. By using a two-stage Cr(III)-Fe(III) coprecipitation process, the recoveries of Cr and Fe reached 96.17% and 99.39%, and the grades of Ni, Cu, and Zn in the coprecipitates were at 0.41%, 0.38%, and 0.22%, respectively. The obtained coprecipitates can be recycled as the feed material of chromium smelting after heat treatment. This method is simple and efficient for high-concentration Cr3+ solution treatment, which is beneficial for the sustainable development of resources and environment.

Periodic density functional theory study of maghemite (001) surface. Structure and electronic properties

ABSTRACT The structure of the iron oxide γ-Fe2O3 surfaces along (001) direction has been modeled for the first time using periodic DFT. Four different types of surfaces were analyzed depending on the upper layer composition (presence of tetrahedral or octahedral Fe) and the presence of iron vacancy locations. The inclusion of a Hubbard (DFT + U) correction allows a good agreement between calculated and experimental bulk properties. Relaxation of surface layers results in important surface reconstructions, electronic charge transfer with respect to the bulk, and a decrease in the dipole moment. Surfaces with tetrahedral Fe atoms on the top layer resulted to be the most stable ones. An almost linear correlation between the work function and the electronic charge transfer to O atoms was found. An analysis of the density of states shows that the Fermi level in tetrahedral Fe-terminated surfaces is far from the valence band whereas the reverse occurs with octahedral Fe-terminated atoms. The tetrahedral Fe-terminated surface has a more basic character than the octahedral ones. In addition, the presence of a subsurface Fe vacancy stabilizes the system and seems to be adequate for bond activation by electron transfer from the surface to the adsorbate, such as H2.

Maghemite nanosorbcats for methylene blue adsorption and subsequent catalytic thermo-oxidative decomposition: Computational modeling and thermodynamics studies

In this study methylene blue (MB) has been investigated for its adsorption and subsequent catalytic thermo-oxidative decomposition on surface of maghemite (γ-Fe2O3) nanoparticles. The experimental adsorption isotherm fit well to the Freundlich model, indicating multi-sites adsorption. Computational modeling of the interaction between the MB molecule and γ-Fe2O3 nanoparticle surface was carried out to get more insights into its adsorption behavior. Adsorption energies of MB molecules on the surface indicated that there are different adsorption sites on the surface of γ-Fe2O3 confirming the findings regarding the adsorption isotherm. The catalytic activity of the γ-Fe2O3 nanoparticles toward MB thermo-oxidative decomposition has been confirmed by subjecting the adsorbed MB to a thermo oxidation process up to 600°C in a thermogravimetric analyzer. The experimental results showed a catalytic activity for post adsorption oxidation. The oxidation kinetics were studied using the Ozawa–Flyn–Wall (OFW) corrected method. The most probable mechanism functions were fifth and third orders for virgin MB and MB adsorbed onto γ-Fe2O3 nanoparticles, respectively. Moreover, the results of thermodynamic transition state parameters, namely changes in Gibbs free energy of activation (ΔG‡), enthalpy of activation (ΔH‡), and entropy of activation (ΔS‡), emphasized the catalytic activity of γ-Fe2O3 nanoparticles toward MB oxidation.

Magnetic and dendritic catalysts.

The recovery and reuse of catalysts is a major challenge in the development of sustainable chemical processes. Two methods at the frontier between homogeneous and heterogeneous catalysis have recently emerged for addressing this problem: loading the catalyst onto a dendrimer or onto a magnetic nanoparticle. In this Account, we describe representative examples of these two methods, primarily from our research group, and compare them. We then describe new chemistry that combines the benefits of these two methods of catalysis. Classic dendritic catalysis has involved either attaching the catalyst covalently at the branch termini or within the dendrimer core. We have used chelating pyridyltriazole ligands to insolubilize catalysts at the termini of dendrimers, providing an efficient, recyclable heterogeneous catalysts. With the addition of dendritic unimolecular micelles olefin metathesis reactions catalyzed by commercial Grubbs-type ruthenium-benzylidene complexes in water required unusually low amounts of catalyst. When such dendritic micelles include intradendritic ligands, both the micellar effect and ligand acceleration promote faster catalysis in water. With these types of catalysts, we could carry out azide alkyne cycloaddition ("click") chemistry with only ppm amounts of CuSO4·5H2O and sodium ascorbate under ambient conditions. Alternatively we can attach catalysts to the surface of superparamagnetic iron oxide nanoparticles (SPIONs), essentially magnetite (Fe3O4) or maghemite (γ-Fe2O3), offering the opportunity to recover the catalysts using magnets. Taking advantage of the merits of both of these strategies, we and others have developed a new generation of recyclable catalysts: dendritic magnetically recoverable catalysts. In particular, some of our catalysts with a γ-Fe2O3@SiO2 core and 1,2,3-triazole tethers and loaded with Pd nanoparticles generate strong positive dendritic effects with respect to ligand loading, catalyst loading, catalytic activity and recyclability. In other words, the dendritic catalysts were more efficient and more stable than their nondendritic γ-Fe2O3@SiO2 analogues. The bulk at the dendritic periphery helps to localize the metal nanoparticles at the SPION core surface, which confers these advantages. We could also use sonification as a remarkably simple and efficient method to impregnate the SPIONs with dendrimer-encapsulated PdNPs. Catalysis within the hydrophobic dendrimer pockets that include ligands leads to rapid turnover with or without a γ-Fe2O3@SiO2 core. In addition, catalytically active metal nanoparticles are more robust when they are loaded onto the surface of a γ-Fe2O3@SiO2 dendritic core. Herein, we illustrate this chemistry with examples including olefin metathesis, click chemistry, cross carbon-carbon bond forming reactions, and selective alcohol oxidation.

Efficient synthesis of a maghemite/gold hybrid nanoparticle system as a magnetic carrier for the transport of platinum-based metallotherapeutics.

The preparation and thorough characterization of a hybrid magnetic carrier system for the possible transport of activated platinum-based anticancer drugs, as demonstrated for cisplatin (cis-[Pt(NH3)2Cl2], CDDP), are described. The final functionalized mag/Au–LA–CDDP* system consists of maghemite/gold nanoparticles (mag/Au) coated by lipoic acid (HLA; LA stands for deprotonated form of lipoic acid) and functionalized by activated cisplatin in the form of cis-[Pt(NH3)2(H2O)2]2+ (CDDP*). The relevant techniques (XPS, EDS, ICP-MS) proved the incorporation of the platinum-containing species on the surface of the studied hybrid system. HRTEM, TEM and SEM images showed the nanoparticles as spherical with an average size of 12 nm, while their superparamagnetic feature was proven by 57Fe Mössbauer spectroscopy. In the case of mag/Au, mag/Au–HLA and mag/Au–LA–CDDP*, weaker magnetic interactions among the Fe3+ centers of maghemite, as compared to maghemite nanoparticles (mag), were detected, which can be associated with the non-covalent coating of the maghemite surface by gold. The pH and time-dependent stability of the mag/Au–LA–CDDP* system in different media, represented by acetate (pH 5.0), phosphate (pH 7.0) and carbonate (pH 9.0) buffers and connected with the release of the platinum-containing species, showed the ability of CDDP* to be released from the functionalized nanosystem.

Magnetically Recoverable Palladium(0) Nanocomposite Catalyst for Hydrogenation Reactions in Water

AbstractAn easy and straightforward strategy has been used for loading palladium(0) nanoparticles onto the magnetic surface of maghemite (γ‐Fe2O3), without the use of organic modifiers. The nanocomposite was fully characterized by TEM, XRD, 57Fe Mössbauer spectroscopy, X‐ray photoelectron spectroscopy, and superconducting quantum interference device measurements. The Pd0@γ‐Fe2O3 nanocatalyst has been investigated in various catalytic reactions, under mild conditions (100 kPa H2, RT), and in neat water. Relevant catalytic activities were achieved in the hydrogenation of olefinic substrates, as well as in hydrodehalogenation reactions of halogenoarenes, that constitutes a promising process for wastewater treatment. These nanocatalysts proved also pertinent for the reduction of nitroarene derivatives into the corresponding anilines, which are promising substrates for fine chemistry. Finally, these catalysts proved to be easily recoverable through the use of an external magnet, without significant loss of activity.

Structural characterization, thermal properties, and density functional theory studies of PMMA‐maghemite hybrid material

Maghemite (γ‐Fe2O3)‐poly(methyl methacrylate) (PMMA) nanocomposites were prepared by grafting 3‐(trimethoxy‐silyl) propyl methacrylate on the surface of maghemite nanoparticles, this process being followed by methyl methacrylate radical polymerization. Three different hybrids with 0.1, 0.5, and 2.5 wt% of maghemite nanoparticles were studied. The results indicate that these nanocomposites consist of a homogeneous PMMA matrix in which maghemite nanoparticles with a bimodal size distribution are embedded. The existence of covalent bonding between silane monomers and atoms on the maghemite surface was evidenced. AFM images showed a clear increase in surface roughness for increasing maghemite content. The thermal stability of PMMA‐maghemite nanocomposites is higher than that of pure PMMA and increases for increasing maghemite content. The results of our theoretical studies indicate that the electron density in the maghemite nanoparticle is not homogenous, the low electron density volumes being supposed to be radical trappers during PMMA decomposition, thus acting as a thermal stabilizer. POLYM. COMPOS., 51–60, 2016. © 2014 Society of Plastics Engineers

Degradation of Microcystin-LR in water: Hydrolysis of peptide bonds catalyzed by maghemite under visible light

Maghemite, an abundant iron-oxide mineral, was investigated as a visible light catalyst for decomposing and mineralizing Microcystin-LR (MC-LR) in water using hydrogen peroxide (H2O2) as the initial oxidant. Interestingly, of the twelve intermediates identified by LC–MS, half were products of MC-LR peptide bond hydrolysis rather than the oxidation products typical of photocatalytic oxidation (PCO). The catalytic hydrolysis of MC-LR by maghemite and visible light has not been previously reported. Detailed examination of intermediates provided insight into the catalytic pathway. Electron spin resonance (ESR) spectra revealed that visible light irradiation does not increase hydroxyl radical (OH) production from H2O2 decomposition. Visible light appears to play a new role in this unique PCO system, generating Brønsted sites on the maghemite surface via a metal ligand charge transfer (MLCT), rather than producing OH from H2O2. Because opening the cyclic peptide structure detoxifies MC-LR, this catalytic system could be uniquely efficient in detoxifying MC-LR in the presence of relatively high levels of natural organic matter (NOM). This work introduces a new means of selectively and effectively detoxifying MCs in water using an inexpensive, environmentally friendly and bio-compatible mineral.

Synthesis of silanized maghemite nanoparticles onto reduced graphene sheets composites

Novel γ-Fe2O3@APTES@rGO composites are successfully synthesized by using graphene oxide and silanized maghemite nanoparticles. Graphene oxide and maghemite were obtained by Hummers and Massart methods, respectively. The silanization process was done to functionalize maghemite surface with a controllable quantity of amino groups. Then, by adding aqueous graphene oxide suspension, the bonding between graphene oxide and silanized maghemite nanoparticles was done in refluxing conditions. Afterwards, chemical reduced graphene oxide reaction was realized by addition of hydrazine solution. The characterization of γ-Fe2O3@APTES@rGO composites was studied by X-ray Diffraction, Fourier Transformed Infrared Spectroscopy, thermogravimetric analysis and scanning electron microscopy.