Magnetite Surface Research Articles

CHARACTERIZATION AND SURFACE REACTIVITY OF NATURAL AND SYNTHETIC MAGNETITES: II. ADSORPTION OF Pb(II) AND Zn(II)

Two synthetic and three natural magnetite samples that were obtained from an iron ore deposit located in Central-Western Mexico, were used to investigate the magnetite surface reactivity of different particle sizes towards aqueous Pb(II) and Zn(II). From these, the synthetic samples < 50 nm [specific surface area (SSA)] = 39.3 m 2 /g), 5 µm (SSA = 7.3 m 2 /g), and natural samples 948-fine (SSA = 7.6 m 2 /g), 948 (SSA = 3.0 m 2 /g) and 996 (SSA = 1.4 m 2 /g), successfully removed Pb(II) from aqueous solutions at the investigated pH value of 5.8, but only the three first, finer magnetites removed significant aqueous Zn(II) at pH 7.0. The adsorption kinetics data were fitted using pseudo-second order and intraparticle models. The Pb(II) adsorption capacities were 140.1, 33.3, 65.4, 69.8 and 17.0 µmol/g, for samples < 50 nm, < 5 µm, 948-fine, 948 and 996, respectively, while for Zn(II) they were 159.2, 38.8 and 28.2 µmol/g, for the first three previous samples, respectively. These adsorption capacities suggest that magnetite may play an important role as adsorbents of cationic contaminants in the environment, or that it may be used as efficient remediating agent, but it’s limited to particle sizes with specific surface areas above 3 m 2 /g.

Comparison of methylparaben, ethylparaben and propylparaben adsorption onto magnetic nanoparticles with phenyl group

Parabens (such as methylparaben (MP), ethylparaben (EP) and propylparaben (PP)) are widely used as preservatives in food, medicine and cosmetic products but can destroy the cell membrane of microbes, intracellular protein and the enzyme activity of microbial cells. In this study, the surface of magnetite was modified with styrene (St) as the functional monomer, divinylbenzene (DVB) as the cross-linking agent, polyvinyl pyrrolidone (PVP) as the stabilizer, 2,2-azodiisobutyronitrile (AIBN) as the radical initiator and ethanol as the solvent to prepare magnetic nanoparticles with a phenyl group (PS/Fe3O4) and use this phenyl compound to absorb parabens. The adsorption behaviors of MP, EP and PP on PS/Fe3O4 were almost totally pH-independent because the phenyl ring of PS/Fe3O4 adsorbs MP, EP and PP by π–π electron-donor–acceptor interactions. The Langmuir isotherm indicated that the maximum adsorption capacity of PS/Fe3O4 followed the order of PP (3.5421mgg−1)>EP (3.2862mgg−1)>MP (0.6015mgg−1) possibly owing to the hydrophilic and hydrophobic properties. The mechanism of adsorption confirmed that the adsorption process of MP, EP and PP followed the second-order kinetic model, which suggested that the adsorption process was quite rapid and was probably dominated by a chemical adsorption phenomenon.

Enhancing phosphate adsorption capacity of SDS-based magnetite by surface modification of citric acid

In this study, citric acid (CA) was employed as a low-molecule organic acid to influence the adsorption performance of phosphorus by as-obtained magnetite. The factors including initial phosphate concentrations, dosage of citric acid, pH value, ion strength, contact time and temperature were examined in detail. Results indicated that the dissolution of anion sodium dodecyl sulfate (SDS) covering on surface of magnetite, a slight decrease of Fe level and a superior structure of magnetite after CA modification occurred. The pH-dependence of phosphate adsorption was impeded and the surface potential of magnetite positively increased at pH>5.0 when CA was added. Non-linear regression Langmuir-Freundlich model was fitted well in thermodynamics, and the opposite adsorption process as a function of temperatures with or without CA addition was due to the decrease of active energy and active mobility of phosphate ion. Finally, the declining adsorption efficiency with increasing cycles was observed while phosphate removal was approximately finished and had small change with 0.05 and 0.1M of CA addition. Those improvements of removal efficiency of phosphorus by modified iron oxide were because of the removal of anionic SDS that increased the surface positive charge, and especially the dissolution of element Fe into solution to form precipitate with phosphorus ions. The enhanced stability of magnetite by CA also promoted the high removal efficiency of phosphorus. These implications of CA on phosphate removal can be extended to the field where phosphate pollution is notorious but urgent.

The influence of surface modification, coating agents and pH value of aqueous solutions on physical properties of magnetite nanoparticles investigated by ESR method

The article presents the results of electron spin resonance (ESR) studies for aqueous solutions of functionalized superparamagnetic iron(II,III) oxide nanoparticles. The samples studied differed in type of organic ligands at the magnetite surface, type of coating agent and pH value of aqueous solutions. The ESR spectra of the samples were obtained at room temperature and at 230K. The field cooling (FC) experiment was performed for selected samples, and the effective anisotropy field (HK2) and the first order magnetocrystalline anisotropy constant (K1) was calculated. The process of the nanoparticles diffusion in different environments (human blood, human serum) forced by an inhomogeneous magnetic field was monitored and their interactions with different solvents have been discussed. It has been shown that ESR method is useful to observe the impact of organic ligands at the magnetite surface, type of coating agent and pH value of aqueous solutions on the properties of iron(II,III) oxide nanoparticles.

Release and cytotoxicity studies of magnetite/Ag/antibiotic nanoparticles: An interdependent relationship

Though the cytotoxic properties of magnetite nanoparticles (NPs) are rather well investigated and known to be dose dependent and rather low, surface functionalization can drastically change their properties. To determine whether the cytotoxicity of magnetite/Ag/antibiotic NPs may be associated, among other things, with iron, silver and antibiotic release, this study investigates the release profiles and cytotoxicity of magnetite/Ag/rifampicin and magnetite/Ag/doxycycline NPs compares it similar profiles from magnetite, magnetite/Ag NPs and antibiotics. It was established that the studied NPs released not only water-soluble substances, such as antibiotics, but also poorly-soluble ones, such as iron and silver. The deposition of silver on the magnetite surface promotes the release of iron by the formation of a galvanic couple. Antibiotic adsorbed on the magnetite/Ag surface plays a dual role in the galvanic corrosion processes: as a corrosion inhibitor for iron oxides and as a corrosion promoter for silver. Magnetite/Ag/rifampicin and magnetite/Ag/doxycycline. NPs were found to have greater cytotoxicity towards the HEK293T cell line than magnetite NPs. These results were attributed to the combined toxic action of the released iron, silver ions and antibiotics. Intensive and simultaneous release of the NP components caused cell stress and suppressed their growth.

Emerging investigator series: As(v) in magnetite: incorporation and redistribution.

Exposure to As in groundwater negatively impacts millions of people around the globe, and As mobility in groundwater is often controlled by Fe mineral dissolution and precipitation. Additionally, trace elements can be released from and incorporated into the structure of Fe oxides in the presence of dissolved Fe(ii). The potential for As to redistribute between sorbed on the magnetite surface and incorporated in the magnetite structure, however, remains unclear. In this study, we use selective chemical extraction and X-ray absorption spectroscopy (XAS) to distinguish magnetite-sorbed and incorporated As(v) and to provide evidence for As(v) incorporation during magnetite precipitation. While As in the As-magnetite coprecipitates did not redistribute between sorbed and incorporated over a 4 month period, a small, but measurable increase in incorporated As(v) of up to 13% was observed for sorbed As(v). We suggest that Fe(ii)-catalyzed recrystallization of magnetite did not significantly influence the redistribution of sorbed As(v) because the extent of Fe atom exchange was small (∼10%). In addition, the extent of As redistribution was the same in the absence and presence of added aqueous Fe(ii), suggesting that aqueous Fe(ii) had, overall, a minor effect on As redistribution for both coprecipitated and sorbed As(v). Our results suggest that coprecipitation of As(v) with magnetite and redistribution of As(v) sorbed on magnetite are potential pathways for irreversible As(v) uptake and sequestration. These pathways are likely to play a significant role in controlling As mobility in natural systems, during human-induced redox cycling of groundwater such as aquifer storage and recovery, as well as in iron oxide-based As removal systems.

In Ukrainian

The adsorption capacity of magnetite and Fe3O4/SiO2, Fe3O4/TiO2 и Fe3O4/Al2O3 composites towards Pb2+ cations in human serum was investigated. The effect of the solvent and the stabilizer on the adsorption of lead cations and protein compounds in blood serum medium was studied. The effect of chemical modification of the magnetite surface on adsorption properties of the synthesized composites was showed. The conclusion about prospects of synthesized nanocomposites as a medical-biological sorbents, its technical and environmental purposes was made.

Influence of silver content on rifampicin adsorptivity for magnetite/Ag/rifampicin nanoparticles

Magnetite nanoparticles (NPs) decorated with silver (magnetite/Ag) are intensively investigated due to their application in the biomedical field. We demonstrate that the increase of silver content on the surface of nanoparticles improves the adsorptivity of antibiotic rifampicin as well as antibacterial properties. The use of ginger extract allowed to improve the silver nucleation on the magnetite surface that resulted in an increase of silver content. Physicochemical and functional characterization of magnetite/Ag NPs was performed. Our results show that 5%–10% of silver content in magnetite/Ag NPs is already sufficient for antimicrobial properties against Streptococcus salivarius and Staphylococcus aureus. The rifampicin molecules on the magnetite/Ag NPs surface made the spectrum of antimicrobial activity wider. Cytotoxicity evaluation of the magnetite/Ag/rifampicin NPs showed no harmful action towards normal human fibroblasts, whereas the effect on human embryonic kidney cell viability was time and dose dependent.

Redox reactions of selenium as catalyzed by magnetite: Lessons learned from using electrochemistry and spectroscopic methods

Although previous studies have demonstrated redox transformations of selenium (Se) in the presence of Fe-bearing minerals, the specific mechanism of magnetite-mediated Se electron transfer reactions are poorly understood. In this study, the redox chemistry of Se on magnetite is investigated over an environmentally relevant range of Eh and pH conditions (+0.85 to −1.0V vs. Ag/AgCl; pH 4.0–9.5). Se redox peaks are found via cyclic voltammetry (CV) experiments at pH conditions of 4.0–8.0. A broad reduction peak centered at −0.5V represents a multi-electron transfer process involving the transformation of selenite to Se(0) and Se(−II) and the comproportionation reaction between Se(−II) and Se(IV). Upon anodic scans, the oxidation peak centered at −0.25V is observed and is attributed to the oxidation of Se(−II) to higher oxidation states. Deposited Se(0) may be oxidized at +0.2V when pH is below 7.0. Over a pH range of 4.0–8.0, the pH dependence of peak potentials is less pronounced than predicted from equilibrium redox potentials. This is attributed to pH gradients in the microporous media of the cavity where the rate of proton consumption by the selenite reduction is faster relative to mass transfer from the solution.In chronoamperometry measurements at potentials ⩾−0.6V, the current–time transients show good linearity between the current and time in a log–log scale. In contrast, deviation from the linear trend is observed at more negative potentials. Such a trend is indicative of Se(0) nucleation and growth on the magnetite surface, which can be theoretically explained by the progressive nucleation model. XPS analysis reveals the dominance of elemental selenium at potentials ⩽−0.5V, in good agreement with the peak assignment on the cyclic voltammograms and the nucleation kinetic results.

Oxygen vacancy induced surface stabilization: (110) terminated magnetite

Scanning tunneling microscopy (STM) measurements of the (110) surface of magnetite showed the coexistence of two reconstructions: the known $(1\ifmmode\times\else\texttimes\fi{}3)$ row reconstruction and a surprising atomic structure of high complexity which occupies a small fraction of the surface. Oxygen vacancies on the ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$(110) B-terminated surface have previously been determined to be the most energetically favorable surface termination of those considered [Li et al., Surf. Sci. 601, 876 (2007)]. However, this study only investigated oxygen vacancies which were threefold coordinated. Here, first principles calculations indicate that twofold coordinated oxygen represents the most energetically stable oxygen vacancy on the B-terminated (110) surface of magnetite. STM simulations reveal that the structure that occupies a small fraction of the surface corresponds to this energetically favorable B-terminated ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$(110) surface. The oxygen vacancies form an ordered array: Along the $[\overline{1}10]$ direction, every second twofold coordinated oxygen atom is vacant, and vacancies are separated by 6 \AA{}. In adjacent twofold coordinated oxygen rows, the vacancies are shifted in the $[\overline{1}10]$ direction by 3 \AA{}. Density functional theory calculations of the spin density distributions indicate that surface and subsurface octahedrally coordinated iron atoms are charge ordered. The charge ordering and existence of oxygen vacancies act to reduce the surface charge. However, other polarity compensation mechanisms may be at play to stabilize the surface.

Core Amino Acid Residues in the Morphology-Regulating Protein, Mms6, for Intracellular Magnetite Biomineralization.

Living organisms produce finely tuned biomineral architectures with the aid of biomineral-associated proteins. The functional amino acid residues in these proteins have been previously identified using in vitro and in silico experimentation in different biomineralization systems. However, the investigation in living organisms is limited owing to the difficulty in establishing appropriate genetic techniques. Mms6 protein, isolated from the surface of magnetite crystals synthesized in magnetotactic bacteria, was shown to play a key role in the regulation of crystal morphology. In this study, we have demonstrated a defect in the specific region or substituted acidic amino acid residues in the Mms6 protein for observing their effect on magnetite biomineralization in vivo. Analysis of the gene deletion mutants and transformants of Magnetospirillum magneticum AMB-1 expressing partially truncated Mms6 protein revealed that deletions in the N-terminal or C-terminal regions disrupted proper protein localization to the magnetite surface, resulting in a change in the crystal morphology. Moreover, single amino acid substitutions at Asp123, Glu124, or Glu125 in the C-terminal region of Mms6 clearly indicated that these amino acid residues had a direct impact on magnetite crystal morphology. Thus, these consecutive acidic amino acid residues were found to be core residues regulating magnetite crystal morphology.

Trivalent Actinide Uptake by Iron (Hydr)oxides.

The retention of Am(III) by coprecipitation with or adsorption onto preformed magnetite was investigated by X-ray diffraction (XRD), solution chemistry, and X-ray absorption spectroscopy (XAS). In the coprecipitation experiment, XAS data indicated the presence of seven O atoms at 2.44(1) Å, and can be explained by an Am incorporation at Fe structural sites at the magnetite surface. Next-nearest Fe were detected at distances suggesting that Am and Fe polyhedra share corners in geometries ranging from bent to close to linear Am-O-Fe bonds. After aging for two years, the coordination number and the distance to the first O shell significantly decreased, and atomic shells were detected at higher distances. These data suggest a structural reorganization and an increase in structural order around sorbed Am. Upon contact with preformed Fe3O4, Am(III) forms surface complexes with cosorbed Fe at the surface of magnetite, a possible consequence of the high concentration of dissolved Fe. In a separate experiment, chloride green rust (GR) was synthesized in the presence of Am(III), and subsequently converted to Fe(OH)2(s) intermixed with magnetite. XAS data indicated that the actinide is successively located first at octahedral brucite-like sites in the GR precursor, then in Fe(OH)2(s), an environment markedly distinct from that of Am(III) in Fe3O4. The findings indicate that the magnetite formation pathway dictates the magnitude of Am(III) incorporation within this solid.

Magnetic properties of iron oxide-based nanoparticles: Study using Mössbauer spectroscopy with a high velocity resolution and magnetization measurements

We review the results of the study of magnetite, maghemite and nickel ferrite nanoparticles (NPs), applying for magnetic fluids, using Mössbauer spectroscopy with a high velocity resolution and magnetization measurements. The Mössbauer spectra of these NPs were fitted using a large number of magnetic sextets reflecting NPs complicity. The presence of polar molecules at the magnetite surface in magnetic fluid increases the NPs magnetic moment and the median hyperfine magnetic field. However, surface coating of maghemite NPs with dimeracptosuccinic acid decreases the median hyperfine magnetic field. An example of nickel ferrite NPs demonstrated a new physical model based on distribution of Ni2+ in the local microenvironment of Fe3+ which can explain a large number of magnetic sextets in the Mössbauer spectra measured with a high velocity resolution.

Binding effects and mechanisms of the carboxymethyl starch modified with nano-CaCO3 in magnetite concentrate pellets

This study aimed to identify the carboxymethyl starch modified with nano-CaCO3 (CCMS) as an alternative binder in iron ore pelletization. Pelletization results showed that all wet, dry, preheated and fired pellets produced with CCMS met with the required values of strengths. The total Fe content of pellets also had a 1.04% increase by replacing 2% bentonite with 1% CCMS. FTIR and zeta potential tests verified that CMS interacted with the magnetite mainly through ligand exchange, hydrogen bond and electrostatic interaction. Meanwhile, in addition to above three interactions, CCMS reacted with negative sites of the magnetite by its unique positive charge sites (-Ca(OH)+). CCMS had more active sites and the chemical bonding of CCMS on the magnetite surface was stronger. Besides, nano-CaCO3 interacted strongly with CMS and the cross linked structure between nano-CaCO3 and CMS molecules was built, giving CCMS a higher solution viscosity. Therefore, compared with CMS, the increased strength of green pellets with CCMS was mainly caused by the stronger chemical bonding and higher solution viscosity of CCMS. Porosity and FESEM measurements were also carried out to clarify the developed strengths of preheated and fired pellets with CCMS. In comparison with CMS, the nano-CaCO3 in CCMS resulted in the formation of more melt slags and facilitated the bridging, bonding and recrystallization between hematite particles. Thereby, the developed oxide bonding between hematite grains and the formation of more slags jointly decreased the porosity and improved the compressive strength of heat treated pellets.

In Ukrainian

The aim of the work is investigation of cytotoxic influence of the magnetocarried polyfunctional nanocomposites based on single-domain magnetite (Fe 3 O 4 ) and anthracycline antibiotic doxorubicin (DOX) on yeast cells Saccharomyces cerevisiae. Magnetite was synthesized according to the Elmor reaction. For investigations we used a fraction of particles with sizes of 6-23 nm. Specific surface area of the samples studied was S = 105–180 m 2 /g. Magnetosensitive nanocomposites Fe 3 O 4 /DOX, Fe 3 O 4 /SiO 2 /DOX, Fe 3 O 4 /TiO 2 /DOX, Fe 3 O 4 / hydroxyapatite (HA)/DOX were synthesized. To obtain Fe 3 O 4 /SiO 2 nanocomposites, we used tetraethoxysilane (TEOS) as a modifying agent. The technique for synthesis of nanocomposites consisting of magnetite modified with silica dioxide involves hydrolysis of TEOS. The coating was 0.2 g of SiO 2 on 1 g of magnetite. Specific surface area of the nanocomposite increases from 105 m 2 /g (for unmodified magnetite) to 130 m 2 /g. To obtain Fe 3 O 4 /TiO 2 nanocomposites, we used n-butylorthotitanate as a modifying agent. The technique based on the reaction of conversion of n-butylorthotitanate on the magnetite surface into ТіО 2 . This conversion consists in hydrolysis of n-butylorthotitanate followed by condensation of hydrolysis products with formation of amorphous ТіО 2 . Modification of the surface of nanosized magnetite with hydroxyapatite (obtaining of Fe 3 O 4 /H А composites) was carried out by the reaction: 10 Са (NO 3 ) 2 + 6 (NH 4 )2HPO 4 + 8 NH 4 ОН → Са 10 (PO 4 ) 6 ( ОН ) 2 + 20 NH 4 NO 3 . We realized immobilization of DOX on the surfaces of magnetite Fe 3 O 4 and nanostructures Fe 3 O 4 /SiO 2 , Fe 3 O 4 /TiO 2 , Fe 3 O 4 /HA by adsorption method from saline environment. Bioactivity of the nanocomposites was determined in the study of viability of cells by a cytochemical method using optical microscopy and Goryaev chamber with registration of concentration change for cells in suspensions containing nanocomposites, yeast cells, minimal synthetic nutrient medium and saline. Fe3O4/DOX, Fe 3 O 4 /SiO 2 /DOX, Fe 3 O 4 /TiO 2 /DOX, Fe 3 O 4 /HA/DOX nanocomposites had cytotoxic and antiproliferative activity with respect to Saccharomyces cerevisiae cells, which were characteristic for a free form of doxorubicin. Using the chosen objects, we worked out rather effective, reliable, safe and relatively inexpensive technique for control of cytotoxic activity of nanocomposites, which could be actual for use in development of new medical magnetocarried remedies of targeted delivery, in particular, for oncology.

Influence of Surface Treatment on Magnetic Properties of Fe3O4 Nanoparticles Synthesized by Electrochemical Method.

The changes of magnetic properties in magnetite nanoparticles during two different stabilization processes were investigated. Magnetic nanoparticles (MNPs) were obtained by electrochemical synthesis from two kinds of salts: (CH3)4NCl and NaCl. After that, two methods-steric and electrostatic-were used to stabilize MNPs with oleic acid (OA) and sodium hydroxide (NaOH), respectively. As a consequence, aqueous and organic dispersions were obtained after surface modification. The coated nanoparticles were characterized by TEM, zeta potential, thermogravimetry analysis (TGA), cyclic voltammetry (CV), magnetization measurements, and infrared and Mössbauer spectroscopy. The results showed that the particles were between 8 and 13 nm in size. In addition, the MNPs were coated with negative charge layers from NaOH by physisorption and coated with carboxylate groups from OA by the chemisorption process, and hence, they exhibited different reactivity and behavior depending on the nature of the electrolyte used in the electrochemical synthesis. Furthermore, the uncoated and coated MNPs had a narrow size distribution. Additionally, the saturation magnetization values showed dependence on the magnetite synthesis conditions and surface modifiers.

Adsorption of alkenyl succinic anhydride from solutions in carbon tetrachloride on a fine magnetite surface

The adsorption of alkenyl succinic anhydride from a solution in carbon tetrachloride on a fine magnetite surface at a temperature of 298.15 K is studied using fine magnetite, which forms the basis of magnetic fluids, as the adsorbent. An adsorption isotherm is recorded and interpreted in terms of the theory of the volume filling of micropores (TVFM). Adsorption process parameters are calculated on the basis of the isotherm. It is shown that at low equilibrium concentrations, the experimental adsorption isotherm is linear in the TVFM equation coordinates.

Effects of common groundwater ions on chromate removal by magnetite: importance of chromate adsorption.

BackgroundReductive precipitation of hexavalent chromium (Cr(VI)) with magnetite is a well-known Cr(VI) remediation method to improve water quality. The rapid (<a few hr) reduction of soluble Cr(VI) to insoluble Cr(III) species by Fe(II) in magnetite has been the primary focus of the Cr(VI) removal process in the past. However, the contribution of simultaneous Cr(VI) adsorption processes in aged magnetite has been largely ignored, leaving uncertainties in evaluating the application of in situ Cr remediation technologies for aqueous systems. In this study, effects of common groundwater ions (i.e., nitrate and sulfate) on Cr(VI) sorption to magnetite were investigated using batch geochemical experiments in conjunction with X-ray absorption spectroscopy.ResultsIn both nitrate and sulfate electrolytes, batch sorption experiments showed that Cr(VI) sorption decreases with increasing pH from 4 to 8. In this pH range, Cr(VI) sorption decreased with increasing ionic strength of sulfate from 0.01 to 0.1 M whereas nitrate concentrations did not alter the Cr(VI) sorption behavior. This indicates the background electrolyte specific Cr(VI) sorption process in magnetite. Under the same ionic strength, Cr(VI) removal in sulfate containing solutions was greater than that in nitrate solutions. This is because the oxidation of Fe(II) by nitrate is more thermodynamically favorable than by sulfate, leaving less reduction capacity of magnetite to reduce Cr(VI) in the nitrate media. X-ray absorption spectroscopy analysis supports the macroscopic evidence that more than 75 % of total Cr on the magnetite surfaces was adsorbed Cr(VI) species after 48 h.ConclusionThis experimental geochemical study showed that the adsorption process of Cr(VI) anions was as important as the reductive precipitation of Cr(III) in describing the removal of Cr(VI) by magnetite, and these interfacial adsorption processes could be impacted by common groundwater ions like sulfate and nitrate. The results of this study highlight new information about the large quantity of adsorbed Cr(VI) surface complexes at the magnetite-water interface. It has implications for predicting the long-term stability of Cr at the magnetite-water interface.Graphical abstractEffects of background anions (sulfate and nitrate) on the Cr(VI) surface coverage at the magnetite-water interface at pH 4 and 9

Functionalized magnetite particles for adsorption of colloidal noble metal nanoparticles

Magnetite (inverse spinel type) particles have been surface-modified with siliceous shells enriched in dithiocarbamate groups. The deposition of colloidal noble metal nanoparticles (Au, Ag, Pt, Pd) onto the modified magnetites can be performed by treating the respective hydrosols with the magnetic sorbents, thus allowing their uptake from water under a magnetic gradient. In particular, for Au colloids, these magnetic particles are very efficient sorbents that we ascribe to the strong affinity of sulfur-containing groups at the magnetite surfaces for this metal. Considering the extensive use of Au colloids in laboratorial and industrial contexts, the approach described here might have an impact on the development of nanotechnologies to recover this precious metal. En route to these findings, we varied several operational parameters in order to investigate this strategy as a new bottom-up assembly method for producing plasmonic-magnetic nanoassemblies.

Calculations of optical properties of some molecules suitable for coating of nanoparticles for biological applications

Coating of nanoparticles by various molecules is promising way to modify their surfaces and extend their bio-functionality, and infrared (IR), and spectroscopy of electronic transitions at ultraviolet and visible (UV/VIS) wavelengths are suitable techniques to investigate details of their attachment at nanoparticle surface. In the present work structure and optical properties of dextran, chitosan, oleic acid and poly(ethylene glycol) have been investigated by semi-empirical quantum mechanics, and ab initio Hartree–Fock calculations using the HyperChem® software package (http://www.hyper.com). The equilibrium conformations, IR, and UV/VIS spectra of molecules of various lengths, before and after their attachment to the magnetite (111) surface are determined, and IR modes and UV/VIS transitions that change the most upon the molecules attachment identified. The results are compared to the existing experimental data and the results of similar calculations, and possible implications for biological applications of nanoparticles coated with the investigated molecules have been discussed.