Anatoly Ye. Yermakov

Removal of Cr(VI) from aqueous solutions by magnetite nanoparticles with different sizes and crystal structure

AbstractIn this work a few nanopowders of magnetite (Fe3O4) produced by different methods were used as a sorbents. Three techniques were applied to make the nanopowders: (1) gas-phase synthesis, (2) chemical precipitation from water solution, and (3) laser atomization. Using these methods, the particles with different sizes and crystal structure have been produced. The effects of the particles size and structure of nanopowders on the removal of toxic Cr(VI) from an aqueous solution imitating ground waters and wastewaters with pH = 7.4–7.8 were studied at different solution temperatures. It is shown that magnetite is effective sorbent for the removal of Cr(VI) from polluted natural waters and sewage. It is found that sorption of Cr(VI) by magnetite is irreversible and has chemisorption character, and even small rise in temperature of the solution during the sorption process sharply increases efficiency of the sorption.

Atomic, electronic and magnetic structure of graphene/iron and nickel interfaces: theory and experiment

First-principles calculations of the effect of carbon coverage on the atomic, electronic and magnetic structure of nickel and iron substrates demonstrate insignificant changes in the interatomic distances and magnetic moments on the atoms of the metallic substrates. The coverage of the iron surface by mono- and few-layer graphene induces significant changes in the orbital occupancies and exchange interactions between the layers in contrast to the case of a nickel substrate for which changes in the orbital ordering and exchange interactions are much smaller. Experimental measurements demonstrate the presence of ferromagnetic fcc-iron in Fe@C nanoparticles and the superparamagnetic behavior of Ni@C nanoparticles.

Magnetic field-enhanced sedimentation of nanopowder magnetite in water flow

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 V < 0.15 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.

Structure and Magnetic Properties of Hydrogenated Pr(Co1-xCux)5 Intermetallics and Mechanically Alloyed Cu-20%Co Systems

Quasi-binary Pr(Co 1-x Cu x ) 5 intermetallics with 0 ≤ x ≤ 1 were hydrogenated at elevated temperatures to precipitate Co and Cu and to study their mutual solubility. Low temperature hydrogenation was found to form a CaCu 5 -type hydride containing about 1.6 hydrogen atoms per formula unit. Above 500°C the sample decomposes into PrH 26 , Cu and h.c.p.-Co. In the temperature range 330 - 450°C the CaCu 5 -type hydride coexists with the decomposed phases. Structural and magnetic measurements indicate that no solid solution was formed in Co-Cu decomposed phases. Magnetic measurements indicate that no solid solution was formed in Co-Cu decomposed phases.

Chlorobenzene hydrodechlorination on bimetallic catalysts prepared by laser electrodispersion of NiPd alloy

Abstract NiPd bimetallic systems were for the first time synthesized by laser electrodispersion (LED) of the Ni77Pd23 alloy target followed by the deposition of produced bimetallic particles on a TEM copper grid and alumina granules. Selective area energy-dispersive analysis confirms the bimetallic nature of NiPd particles deposited on a TEM copper grid. Their mean size is 1.0 nm according to TEM. XPS data demonstrate that under deposition on alumina granules (total metal content of 0.005 wt.%), nickel in bimetallic particles nearly completely oxidizes to Ni2+ species predominantly in the form of aluminate. At the same time major part of palladium (84%) exists in Pd0 but oxidizes to Pd2+ (80%) during 6 months storage in air. Both metals are deposited on the external surface of alumina granules and localized in the same areas. In situ reduction of both metals by H2 in the catalytic cell of XPS spectrometer is hindered. Nickel is not reduced even at 450°C, confirming the formation of NiAlOx, whereas palladium is reduced at higher temperatures compared to a similar monometallic catalyst. Nevertheless, NiPd/Al2O3 catalyst is more efficient in gas-phase chlorobenzene hydrodechlorination at 150–350°C than Ni/Al2O3 and even Pd/Al2O3, and much more stable. The difference may be caused by the formation of new active sites due to the contact between Pd0 and NiAlOx-modified support, and the protective action of spinel reacting with HCl by-product.

Application Of Fe3O4 Nanoparticles For Metallic Cations Removal From Water Solution

Sedimentation of nanopowders of magnetite Fe3O4 in water solution was studied by optical method. Larger particles (50 nm) are sedimenting effectively during several minute, while for particles close to 20 nm more than 24 hours is required for full sedimentation in a solution of 5 g/l. Although the magnetization of nanopowders is noticeably less than that in a bulk material it provides a significant contribution to attractive interactions between particles, thus promoting the heavy aggregates formation. It has been shown that sedimentation rate can be strongly increased under the action of a gradient magnetic field dH/dz = 1.7 kOe/cm.