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Magnetic iron nanoparticles (MNPs) encapsulated in a carbon shells and containing sulfo groups on the surface (Fe@C-SO3H) were synthesized. The aggregative stability of aqueous suspensions of the Fe@C-SO3H nanoparticles was studied in solutions of bovine serum albumin and calcium chloride and in phosphate-buffered saline, which simulate blood plasma. It is shown that the Fe@C-SO3H particles practically do not aggregate in the phosphate buffer saline for a long time (several days). On the contrary, MNPs encapsulated in a protein shells using ultrasonic treatment form aggregates up to 110–120 nm in size under these conditions. Suspensions of the Fe@C-SO3H particles are stable in aqueous solutions of calcium chloride in the range of the solid phase concentration between 0.05 and 0.10 g L−1. The results obtained indicate the possibility of using the functionalized Fe@C-SO3H nanoparticles in vitro experiments in biological media.

The possibility of using the transverse relaxation time T2 of protons in aqueous media for quantitative measurement of the capture of magnetic nanoparticles by cells has been studied and demonstrated. The measurement of T2 was performed on a portable original NMR relaxometer with a measuring cell for a standard well of a biological plate. The novelty of the approach is that quantitative measurements of the capture kinetics were carried out using measurements of the proton relaxation time of the nutrient medium, which is determined by the remaining number of magnetic particles (not captured by the cells) in the medium. To study the kinetics of capture, two types of magnetic nanoparticles were synthesized: magnetite particles Fe3O4 and composite particles Fe@C with an iron-carbon shell structure. The surface of the particles was functionalized with amine-and carboxyl groups. The capture of aminated particles of Fe@C cells is established by microscopy and NMR-relaxometry by measuring the time T2. It is shown that the proposed method makes it possible to register very small concentrations of trapped magnetic nanoparticles equal to tens of pg/cell.

A comparative analysis of the structure and magnetic properties of nanoparticles of Fe-Ni and Fe-Co alloys without carbon and encapsulated in carbon obtained by gas-condensation synthesis is carried out. Particular attention is paid to the study of the formation of a solid solution in nanoparticles with carbon. X-ray analysis and magnetic properties convincingly demonstrate that a disordered supersaturated solid solution of carbon in FeNi@C and FeCo@C nanoparticles is formed.

In this work, we developed and optimized conjugates of carbon-coated iron nanoparticles (Fe@C) with streptavidin and monoclonal antibodies. The conjugation procedure included two stages. First, amino groups were grafted onto the carbon shell to facilitate noncovalent sorption of bovine serum albumin (BSA). Further, the covalent attachment of proteins to the BSA layer via glutaraldehyde coupling was performed. It was established and confirmed that the synthesis procedure is reproducible and allows preparation of stable conjugates. The resulting nanoparticles are clusters of Fe@C particles coated by proteins. The size of the clusters is in the range of 100–190 nm and can be controlled via the tuning of conjugation conditions, including pH, BSA-to-Fe@C ratio, etc. Conjugates of Fe@C with streptavidin and monoclonal antibodies (sizes of approximately 140–150 nm) were synthesized. Proton T2 relaxometry was used to detect these conjugates with very high sensitivity due to the magnetic markers, Fe@C. The relaxivity (r2) of different conjugates varied within the range of 290–450 1/s*mM. Conjugate applicability for relaxometry-based assay was confirmed by direct detection of streptococcal protein G and biotinylated BSA in a dot immunoassay.

Nanopowders Ni@C synthesized by gas condensation have a core-shell structure. The size of the core is 2–10 nm and the thickness of the shell is 1–3 nm. The changes in the magnetic properties and the structure of these particles upon annealing in the 100–1100°C temperature range are investigated in this work. Analysis of changes in the magnetic properties, the structure, and the chemical stability shows that the core of the particles in the initial state after synthesis is a supersaturated solid solution of carbon in nickel, which decomposes into nickel and carbon upon high-temperature annealing. Rather slow cooling of nickel particles causes the carbon shell to form. The shell ensures their chemical stability.

Core–shell CoFe@C and NiFe@C nanocomposites were prepared by gas-condensation synthesis. CoFe@C and NiFe@C particles had bcc and fcc cores, respectively. The treatment of these nanocomposites with hydrochloric acid revealed that they are more chemically stable than Fe@C composites. The maximum specific magnetization of CoFe@C and NiFe@C nanocomposites at room temperature in the field with a strength of 27 kOe was 125 and 58 G cm3/g, respectively. The processes of longitudinal and transverse relaxation of nuclear proton spins of aqueous suspensions of nanocomposites in various magnetic fields (0.5, 1, and 2 kOe) were studied. NiFe@C and CoFe@C nanocomposites have high transverse relaxivity values and can be used as magnetic markers for detection of low concentrations of bioobjects by NMR relaxometry.

The dependence of the transverse relaxation time T2 on the liquid, flow velocity in a porous medium (for the water and water suspension of magnetic nanoparticles (MNPs)) is studied. The T2 value allows measuring the filtration velocity of a liquid on the order of 0.05 mm/s. MNPs in a small concentration decrease T2 but at the same time the dependence of T2 on the liquid’s velocity becomes more pronounced.

This paper reports about excitons in strongly correlated oxide nanocrystals NicMg1-cO (c = 0.008 and c = 1). At 8 K two weak peaks were firstly observed in the optical density spectrum of NiO nanocrystals at the energies of 3.510 eV and 3.543 eV. The intensity of the peaks subsides with an increase of temperature and a decrease of nanoparticle sizes from 25 nm to 10 nm. The peaks were attributed to the formation of p-d charge transfer excitons {d9h}. A tunneling annihilation for {d9h} excitons diminishes their lifetime drastically, even at low temperatures. This fact is considered as an inherent feature in the p-d charge transfer excitons {d9h}, which makes them significantly different from the Wannier-Mott excitons for semiconductors with direct allowed transitions. We believe that energy shift between two peaks originates due to the spin-orbit splitting of the top of the valence band, equals 33 meV. In p-d charge transfer photoluminescence excitation spectrum of NicMg1-cO (c = 0.008), we have revealed two [d9h] exciton lines near the charge transfer band edge. Energy shift of these lines (equals 25 meV) is due to the spin-orbit splitting of MgO valence band top.

Nanoparticles with surface-modified shells are used for selective sorption of different impurities from water. Subsequent removal of nanoparticles from water can be strongly enhanced by using particles with magnetic core, providing their separation by sedimentation or filtration in magnetic field. The velocity of the magnetic sedimentation is strongly controlled by the particles aggregation which can be efficiently changed by interparticles interaction, in particular, by mixing the positively charged particles with negatively charged particles. The aggregation and sedimentation dynamics of the mixtures of the complex nanoparticles having the magnetite or the iron core, e.g., Fe 3 O 4 /SiO 2 , Fe 3 O 4 /SiO 2 NH 2 and Fe/C NH 2 in water were studied in a vertical gradient magnetic field B ≤ 0.3 T, dB/dz ≤ 0.13 T/cm. The sedimentation time t s was measured using two independent methods: by optically registered turbidity and from residual particle concentration in water by Nuclear Magnetic Resonance Relaxometry (NMRR) method. The t s reaches a minimum (7–10 min) for the (1:1) mixtures of the target Fe 3 O 4 /SiO 2 and the seed Fe 3 O 4 /SiO 2 NH 2 nanoparticles. Adding of the seed Fe/C NH 2 nanoparticles to the target Fe 3 O 4 /SiO 2 water suspension is more effective due to smaller sizes and to larger magnetic moments of the Fe-based particles. The sedimentation time of about (6−10) minutes is observed for rather small fraction (6, 15 mass%) of the added Fe/C NH 2 particles, which is important for application to reduce the residual sediment volume significantly. Preliminary exposure of the mixtures in the absence of magnetic field favors to more complete nanoparticles aggregation and, as a result, more rapid sedimentation of the nanoparticles in a vertical gradient magnetic field. The data obtained are useful for development of the methods aimed at magnetic separation of magnetic and nonmagnetic nanoparticles in water purification technologies.

Radiative recombination with charge transfer was observed in NicMg1−cO (c = 0.008) oxides over the 8–300 K temperature range. This recombination occurs as a result of strong hybridization of the Ni2+ ion 3d-states and the band states. The charge transfer radiation excitation spectrum shows vibrational LO repeats of two exciton lines having charge transfer energy intervals of about 35 meV. The NiO nanocrystal absorption spectrum shows two weak peaks with energies of 3.510 and 3.543 eV, which are highly dependent on temperature. They are interpreted as charge transfer excitons at the edge of NiO fundamental absorption. The distance between the charge transfer exciton lines in the NicMg1−cO oxide spectra are caused by spin-orbit splitting of the valence band peak that was formed by the p-states of the oxygen ion.

The magnetic properties of an oxygen-deficient nanocrystalline undoped titanium dioxide synthesized by the gas-phase, electric-explosion, and chemical method have been studied. The defect state was controlled using reduction treatments in vacuum or in a hydrogen atmosphere. It is shown that the defect state of the surface of nanocrystalline oxides (for example, the existence of vacancies in the anion sublattice and other defects) has a dominant influence on the formation of the magnetic properties of the samples under study. The main contributions to the magnetism of TiO2 nanoparticles after the reduction treatments are the paramagnetic contribution of the matrix, the paramagnetic Curie–Weiss contribution, and the contribution of the spontaneous magnetic moment provided by the existence of regions with different spin ordering. A heterogeneous magnetic state is found to exist in the TiO2 nanopowders; for example, at low temperatures, shifted hysteresis loops are observed as a result of a possible set of magnetic states with different spin orders. It is shown that a soft compaction or grinding of nanopowders in an agate mortar lead to substantial increase in the magnetization, sometimes, by a factor of more than two, regardless of the nanopowder synthesis method and the initial phase state of TiO2 (anatase or rutile structures). This experimental fact proves the key role of the surface defects and the magnetic moment carriers with different spin configurations localized mainly on the nanoparticle surface. The compaction changes the magnetization only in the case when the initial magnetic state has a nonlinear “quasi-superparamagnetic” character of the magnetization curve. As a result of predominant exchange interaction between the nanoparticles with a frustrated character of spin ordering on the nanoparticles surface, the ferromagnetic contribution increases as nanoparticles contact.

Interactions of bimodal (fluorescent and magnetic) nanoparticles with HeLa cells were studied. The nanoparticles, characterized by high magnetic moment and relaxing capacity, exhibited fluorescence sufficient for their use as labels in confocal microscopy and flow cytometry. Penetration of these nanoparticles into the cell depended on their surface charge: positively charged nanoparticles of this structure penetrated inside, while negatively charged particles were not found in the cells.

The surface functionalization of magnetic nanoparticles improves their physicochemical properties and applicability in biomedicine. Natural polymers, including proteins, are prospective coatings capable of increasing the stability, biocompatibility, and transverse relaxivity (r2) of magnetic nanoparticles. In this work, we functionalized the nanoclusters of carbon-coated iron nanoparticles with four proteins: bovine serum albumin, casein, and gelatins A and B, and we conducted a comprehensive comparative study of their properties essential to applications in biosensing. First, we examined the influence of environmental parameters on the size of prepared nanoclusters and synthesized protein-coated nanoclusters with a tunable size. Second, we showed that protein coating does not significantly influence the r2 relaxivity of clustered nanoparticles, however, the uniform distribution of individual nanoparticles inside the protein coating facilitates increased relaxivity. Third, we demonstrated the applicability of the obtained nanoclusters in biosensing by the development of a nuclear-magnetic-resonance-based immunoassay for the quantification of antibodies against tetanus toxoid. Fourth, the protein coronas of nanoclusters were studied using SDS-PAGE and Bradford protein assay. Finally, we compared the colloidal stability at various pH values and ionic strengths and in relevant complex media (i.e., blood serum, plasma, milk, juice, beer, and red wine), as well as the heat stability, resistance to proteolytic digestion, and shelf-life of protein-coated nanoclusters.

The sedimentation dynamics of Fe3O4@SiO2 nanoparticles (20/30 nm) in water with additions of Na2SO4, CaCl2, NaH2PO4 salts with concentration of (5–100) mM were studied in a vertical gradient magnetic field (B1 ⩽ 0.3 T, dB/dz ⩽ 0.13 T/cm). The presence of magnetic field leads to nanoparticle sedimentation time decreasing from 103 h to 101 h and to 10−2 h when the salts are added. The results are interpreted on the basis of aggregate formation caused by electrostatic, steric and magnetic inter-particle interactions in water medium. While the stability of Fe3O4@SiO2 nanoparticles in pure water is dependent on steric inter-particle interactions involving polymeric Si–O groups on the surface of the composite particles, the presence of Na+ and Ca2+ cations in water leads to a decrease of electrostatic repulsion because the charge on the nanoparticle surfaces decreases. Magnetic moments, induced in the magnetic field, contribute to the enlargement of the aggregates and, in interacting with the magnetic field gradient, facilitates a quicker sedimentation of the suspension. The data obtained are useful for the development of methods aimed at the magnetic separation of magnetic nanosorbents in water purification technology.

In this work photoluminescence spectra for Ni c Mg 1− c O and Ni x Zn 1− x O solid solutions with the rock-salt crystal structure were obtained under synchrotron radiation excitation. Periodical peaks in the photoluminescence excitation spectrum of Ni c Mg 1− c O ( c =0.008) have been discovered for a wide-gap oxide doped with 3d impurities for the first time. They can be considered as LO phonon repetitions of the narrow zero phonon line resulted from the optical transitions into the p–d charge transfer exciton [d 9 h] state. A close coincidence in energy of different peculiarities in the optical absorption and photoluminescence excitation spectra for the Ni c Mg 1− c O and Ni x Zn 1− x O solid solutions is due to the practically equal interatomic distances Ni–O in the investigated materials. The bulk of new experimental results is the trustworthy evidence that only the p–d charge transfer transitions manifest themselves in the spectral region of 3.5–6.5 eV.

Gd2O3, SiO2-Gd2O3 and SiO2-MnO2 nanoparticles were produced by the method of pulsed electron evaporation of oxide targets with condensation of the vapors in a vacuum. These materials are considered as probable contrast agents for magnetic resonance imaging (MRI). The Gd2O3 nanoparticles exhibit a rather high r1 and r2 relaxivities. These results point to the potential of using nanocrystals for MRI diagnosis. The mesoporous nanostructures SiO2-Gd2O3 and SiO2-MnO2 could be considered as multimodal theranostic agents.

The distribution of iron-carbon nanoparticles in FeC-DSPE-PEG-2000 modification (micellar particles with structure (Fe) core-carbon shell; PEG-based coating) is studied. The greater part of the nanoparticles accumulated in the spleen and liver, a small amount in the lungs, and the minimum amount in the thymus. The structural changes in the lymphoid organs were minor and involved only the microcirculatory bed. Analysis of the peripheral blood showed manifest anemia, thrombocytopenia, and leukocytosis.

We studied new magnetic nanocomposites consisting of a core(Fe) and carbon-shell inert to biological media. Iron-carbon nanoparticles circulate in the bloodstream for several minutes and are primarily accumulated in the liver; less intensive accumulation was found in the spleen and minimum in the lungs, kidneys, and heart. Accumulation of nanoparticles in the liver leads to the development of destructive processes and is accompanied by activation of compensatory-adaptive mechanisms. In the liver and spleen, structural changes are mild and mainly relate to changes in the microvasculature. In 6 months, the total content of nanoparticles in all tissues decreased due to their elimination from the body and the structure of the organs returned to normal.

This paper presents the results of investigations of the structural state and magnetic properties of nanocrystalline cupric oxide samples with average particle sizes of approximately 40 and 13 nm, which were synthesized by the electric explosion and gas phase methods, respectively. The samples have been studied using X-ray diffraction, neutron diffraction, magnetic measurements, high-resolution transmission electron microscopy, and copper nuclear magnetic resonance. It has been shown that, in the initial state, regardless of the synthesis method, CuO nanoparticles are characterized by a heterogeneous magnetic state, i.e., by the existence of long-range antiferromagnetic order, spontaneous magnetization, especially at low temperatures, and paramagnetic centers in the material. The ferromagnetic contribution is probably caused by the formation of magnetic polaron states due to the phase separation induced in the system by excess charge carriers as a result of the existence of point defects (vacancies in the anion sublattice) in the nanocrystalline state. In this state, there is an inhomogeneously broadened nuclear magnetic resonance spectrum, which is a superposition of the spectrum of the initial antiferromagnetic matrix and the spectrum of ferromagnetically ordered regions. At high concentrations of ferromagnetically ordered regions, the antiferromagnetic matrix exhibits a nuclear magnetic resonance spectrum of CuO nanoparticles, predominantly from regions with the ferromagnetic phase. The appearance of magnetization can also be partly due to the frustration of spins in CuO, and this state is presumably localized near the most imperfect surface of the nanoparticles. The magnetic susceptibility of nanoparticles in the initial state in strong magnetic fields is significantly higher than that for the annealed samples, which, most likely, is associated with the influence of the high concentration of magnetic polarons. No correlation between the ferromagnetic contribution and the size of particles is found. In the CuO samples annealed at 400°C in air, when the average size of CuO nanoparticles remains unchanged, the ferromagnetic contribution completely disappears, and the magnetic behavior of the nanoparticles becomes qualitatively similar to the magnetic behavior of bulk CuO.

Sedimentation dynamics of magnetite (γ-Fe3O4) nanopowders (10 - 20 nm) in water in the presence of a gradient magnetic field was studied by optical and Nuclear Magnetic Resonance (NMR) relaxometry methods. The magnetic field B ≤ 0.3 T, dB/dz ≤ 0.13 T/cm was produced by the system of permanent strip magnets. The initial sedimentation rate of the nanoparticles in water and under magnetic fields is higher for less concentrated suspensions (c0 = 0.1 g/l) than for more concentrated ones (c0 = 1 g/l). This might be connected with the formation of gel structures due to strong magnetic attraction between ferromagnetic nanoparticles. In the gravitation field, the suspensions of the particles (10 - 20 nm) remain stable for over 20 hours. The sedimentation process can be greatly accelerated by the action of a vertical gradient magnetic field, reducing the sedimentation time down to several minutes. In a gradient magnetic field enhanced by a steel grid, sedimentation of the nanopowder (c0 = 0.1 g/l) for 180 minutes resulted in reduction of the iron concentration in water down to 0.4 mg/l. In flowing water regime, the residual iron concentration in water 0.3 mg/l is reached after 80 minutes.

The use of the effect of a decrease in the transverse relaxation time T 2 of the NMR signal of water protons in the presence of magnetic particles has been suggested for the quantitative estimation of the concentration of magnetite (Fe3O4) nanopowder in water. A calibration dependence of the relaxivity T 2 −1 on the iron concentration has been obtained for model suspensions of magnetite nanoparticles with sizes of approximately 20 nm in the concentration range of 0.15–70 mg/L. For comparison, the concentration dependences of T 2 −1 for aqueous solutions of Fe(NO3)3 · 9H2O and FeSO4 · 7H2O and paramagnetic salts Ni(NO3)2 · 9H2O, Cr(NO3)3 · 9H2O, and CuSO4 · 5H2O have been studied to show that they correlate with their paramagnetic susceptibilities.

H1 NMR relaxometry is a method that is extremely sensitive to the presence of magnetic nanoparticles, which significantly affect the transverse relaxation time of the water proton. Accordingly, the use of magnetic nanoparticles as labels allows detection of even extremely small amounts of the test substance. This paper analyzes the prospects for applying the method of solid-phase NMR-relaxometric determination of biologically active molecules. The nitrocellulose membranes are chosen as a solid phase and nanoparticles based on iron core with a carbon shell are used as magnetic labels. The possibility of detecting small concentrations of magnetic particles in porous medium is demonstrated. Finally, the ability to detect extremely low concentrations of an analyte, in this case, streptavidin protein (0.5 ng/ml to 100 ng/ml), which is actively used in various fields of biology and medicine, is demonstrated. © Published under licence by IOP Publishing Ltd. Russian Science Foundation, RSF: 17-15-01116 The work was carried out within the Russian Science Foundation project 17-15-01116. equipment of the Ural Center for Shared Use Modern nanotechnology UrFU was used.

A correlation between the morphology of the solid surface and electrochemical response was found in microscopic and electrochemical investigations. A shift of the oxidation potentials of metals to more negative values was observed on electrodes with microstructured surface with respect to similar processes on macrostructured electrodes. The formation of passivating films, causing reverse current and deteriorating the analytical signal, was not observed, and the performance characteristics of voltammetric procedures were improved. The experimental data indicated the increased electrochemical activity of modifying metal particles with a decrease in the particle size. As a result of the deliberate change of the surface composition and the formation of a micro- and nano-structured surface, a new generation of electrodes was developed with excellent electroanalytical characteristics.

The influence of heat treatment on the transmission of silicate thin films prepared by gelation from aqueous solutions of sodium silicate (water glass) is investigated. It is demonstrated that the initial films are characterized by a strong absorption in the IR range due to the presence of hydroxyl groups. The heat treatment of the films at temperatures in the range 150-250°C leads to the step-by-step removal of water from the films and, as a consequence, to an almost complete transmission in the high-frequency IR spectral range. An increase in the heat treatment temperature to 580°C is accompanied by the loss of transparency, most likely, as a result of the pore formation in the film. © 2008 MAIK Nauka.

Sedimentation dynamics of magnetite (γ-Fe3O4) nanopowder (10-20 nm) in water in a gradient magnetic field Bmax=0.3 T, (dB/dz)max=0.13 T/cm was studied for different water flow speeds and starting particle concentrations (0.1 and 1.0 g/l). The aggregates formation in water was monitored under the same conditions. In cyclical water flow, the velocity of particle sedimentation increases significantly in comparison to its rate in still water, which corresponds to the intensified aggregate formation. However, at a water flow speed more than 0.1 cm/s sedimentation velocity slows down, which might be connected to aggregate destruction in a faster water flow. Correlation between sedimentation time and the nanoparticle concentration in water does not follow the trend expected for spherical superparamagnetic particles. In our case sedimentation time is shorter for c=0.1 g/l in comparison with that for c=1 g/l. We submit that such a feature is caused by particle self-organization in water into complex structures of fractal type. This effect is unexplained in the framework of existing theoretical models of colloids systems, so far. Provisional recommendations are suggested for the design of a magnetic separator on the permanent magnets base. The main device parameters are magnetic field intensity B≥0.1 T, magnetic field gradient (dB/dz)max≈(0.1-0.2) T/cm, and water flow speed V0.15 cm/s. For particle concentration c=1 g/l, purification of water from magnetite down to ecological and hygienic standards is reached in 80 min, for c=0.1 g/l the time is reduced down to 50 min.

Magnetite (γ-Fe3O4) nanoparticles are promising effective sorbents for water cleaning of heavy metal, radionuclides, organic and biological materials. A good sorption capacity can be achieved due to their high specific surface area. Application of gradient magnetic fields helps to separate the magnetic nanoparticles from the water suspension, which is rather hard to do using the conventional mechanical filtration and sedimentation methods without coagulants. The sedimentation dynamics of magnetite nanoparticles with sizes of 10–20 nm in aqueous media in the presence of a gradient magnetic field was studied by optical and NMR relaxometry methods. The gradient magnetic field was produced by a series of strip permanent magnets with B ≤ 0.5 T, dB/dz ≤ 0.13 T/cm and in some cases enhanced by a steel grid with sharp edges (dB/dz ≤ 5 T/cm). Dynamic Light Scattering in the water suspension with different nanoparticle concentrations (c 0 = 0.1–1 g/l) revealed the characteristic features in the aggregate formation, which is reflected in the sedimentation behavior. The sedimentation rate of the nanoparticles in water and in magnetic fields is higher for less concentrated suspensions (c 0 = 0.1 g/l) than for more concentrated ones (c 0 = 1 g/l), which might be connected with the formation of a gel structures due to a strong magnetic attraction between ferromagnetic nanoparticles. In 180 min this resulted in the reduction of the iron concentration in water down to 0.4 mg/l, which is close to hygienic and environmental norms for drinking water and fishery.

The sedimentation dynamic of magnetite (Fe3O4) nanoparticles in water was investigated, both in the presence of a vertical gradient magnetic field and in the gravitational field only. The nanopowders (four samples with average particle diameter ranging from 16 to 84 nm) were prepared by a gas-condensation synthesis method. The sedimentation was monitored by measuring the light transmission coefficient k of the suspension as a function of time. The sedimentation process is of rather complex character for both the large and the small particles. Specifically, the light transmission reflects the different stages of the particle aggregation. Magnetite nanoparticles tend to aggregate into micron-sized aggregates which sediment rather rapidly in high concentrated suspensions (for example 5 g/L), even in the absence of a magnetic field. Gradient magnetic fields (for example H = 6 kOe, dH/dz = 1.6 kOe/cm) help to increase the sedimentation rate tremendously and reduce the total sedimentation time from several days up to several minutes—here for an average particle size of 16 nm. An effective removal of heavy metal pollutants (Cr, Cu, etc.) from water can be achieved using the optimal combination of the magnetite particle size, particle concentration in water suspension, and magnetic field strength and gradient.