Influence of structure of iron nanoparticles in aggregates on their magnetic properties
© Rosická and Šembera; licensee Springer. 2011
Received: 19 May 2011
Accepted: 14 September 2011
Published: 14 September 2011
Zero-valent iron nanoparticles rapidly aggregate. One of the reasons is magnetic forces among the nanoparticles. Magnetic field around particles is caused by composition of the particles. Their core is formed from zero-valent iron, and shell is a layer of magnetite. The magnetic forces contribute to attractive forces among the nanoparticles and that leads to increasing of aggregation of the nanoparticles. This effect is undesirable for decreasing of remediation properties of iron particles and limited transport possibilities. The aggregation of iron nanoparticles was established for consequent processes: Brownian motion, sedimentation, velocity gradient of fluid around particles and electrostatic forces. In our previous work, an introduction of influence of magnetic forces among particles on the aggregation was presented. These forces have significant impact on the rate of aggregation. In this article, a numerical computation of magnetic forces between an aggregate and a nanoparticle and between two aggregates is shown. It is done for random position of nanoparticles in an aggregate and random or arranged directions of magnetic polarizations and for structured aggregates with arranged vectors of polarizations. Statistical computation by Monte Carlo is done, and range of dominant area of magnetic forces around particles is assessed.
Zero-valent iron nanoparticles (nZVI) composed of iron Fe0 and its oxides are spherical particles with diameter approximately 40 nm and with a large specific surface. These particles are used for decontamination of groundwater and soil and especially for decontamination of organic pollutants such as halogenated hydrocarbons . Nanoparticles migrate through the soil and can reach the contamination in situ. Properties of the nZVI and remediation possibilities depend on methods of production . At the Technical University of Liberec, experiments with iron nanoparticles TODA, produced by the company Toda Kogyo Corp. , and with the nanoparticles NANOFER, produced by the company NANO IRON s.r.o. , are made. During a remedial intervention, transport of the iron nanoparticles is slowed down due to rapid aggregation of them. The rate of aggregation increases with growing concentration of particles in solution and with growing ionic strength of the solution . With the word particle we mean both nanoparticles and aggregates. For preservation of the transport properties, it is advisable to stabilize the particles. A lot of methods of stabilization were published [6–10]. We simulate the transport of the iron nanoparticles and that is why we examine the interactions among them causing the aggregation. Models of aggregation of small particles were published in many articles (e.g., [11–13]). They are mostly based on the publications  and . However, this generally used model is insufficient for our case. A surface charge established on the surface of particles causes repulsive electrostatic forces between them. The influence on the aggregation into the known aggregation model was implemented in submitted article [Rosicka and Sembera (2009)]. The iron particles corrode in the water, and this process causes change of the surface charge as well as the change of the rate of aggregation . Because the particles are made from iron, they also have magnetic properties, which significantly affects the rate of aggregation [2, 17–20]. In the previous work, the influence of magnetic forces on rate of aggregation of iron particles was assessed . The magnetic forces have significant effect on aggregation. Size of this effect is dependent on the magnitude of polarization of nanoparticles, their directions and distances among nanoparticles or aggregates. We suppose same magnitude of vectors of polarization of all nanoparticles. Hence, there is presented evaluation of magnetic forces among particles depending only on the structure of aggregates, respectively, on directions of the vectors of polarization and distances between particles in this paper. In the future, the extended model of the aggregation of iron nanoparticles will be included into a solver of particle transport in groundwater. It would allow to simulate the transport of iron nanoparticles and to predict effciency of the remedial intervention. That could be useful for proposal of optimal remedial intervention which would enable to decontaminate an affected area effciently and economically.
2 Methods and models
2.1 Magnetic properties of nanoparticles
where M is the vector of magnetic polarization at the point dV , the vector R is the difference between the source of magnetic field dV and the point r, R is the length of R.
where a is the radius of the nanoparticle, and [x 1, x 2, x 3] are the coordinates of the point r. Here, the direction of the vector of polarization M is set to the direction x 3, M is the magnitude of the vector M.
2.2 Unstructured model of aggregates
2.3 Structured model of aggregates
3 Results and discussion
3.1 Unstructured model of aggregates
3.1.1 Random directions of polarization of nanoparticles in aggregates
Table of magnitudes of magnetic forces between interacting nanoparticle and aggregate
Averaged F mg
Summed F mg
Table of magnitudes of magnetic forces between interacting nanoparticle and aggregate
Averaged F mg
Summed F mg
On the basis of known concentration of particles, we are able to estimate the approximate distances among particles and to choose the right model of computation of magnetic forces and limit distances among the particles.
3.1.2 The same directions of polarization of all nanoparticles in aggregates
3.2 Structured model of aggregates
Table of magnetic forces between one nanoparticle and cubic aggregate
|F g |
Even though the distance between the particles is the smallest possible, the magnetic forces between the particles are negligible in comparison with gravitation forces. For structured aggregates with polarization of nanoparticles respecting the structure, the magnetic forces have insignificant influence on the rate of aggregation of the particles.
We examined the influence of structure of nanoparticles in aggregates on the resulting magnetic field around the aggregates. The comparing parameter was size of magnetic forces among particles and the limit distance. According to these two connected parameters, we are able to estimate the degree of influence of the magnetic forces on rate of aggregation of particles. We analyzed magnetic properties of unstructured aggregates with randomly distributed nanoparticles with random direction of polarization in the aggregates and of structured model of aggregates with orderly distributed nanoparticles and with arranged directions of polarization. In the case of structured model, resulting magnetic forces approach to zero. Since we suppose that magnetic field of iron particles has significant influence on the rate of aggregation , the structured model is not sufficient. Hence, we assume damaged structure of aggregates. In our future work, the unstructured model will be compared with experimental data of aggregation of iron particles.
This result was realized under the state subsidy of the Czech Republic within the research and development project "Advanced Remedial Technologies and Processes Centre" 1M0554--Programme of Research Centres supported by Ministry of Education and within the research project FR-TI1/456 "Development and implementation of the tools additively modulating soil and water bioremediation"--Programme MPO-TIP supported by Ministry of Industry and Trade.
- Zhang W-X: Nanoscale iron particles for environmental remediation: an overview. J Nanopart Res 2003, 5: 323–332. 10.1023/A:1025520116015View ArticleGoogle Scholar
- Li L, Fan M, Brown RC, Van Leeuwen J(H), Wang J, Wang W, Song Y, Zhang P: Synthesis, properties, and environmental applications of nanoscale iron-based materials. Rev Crit Rev Env Sci Technol 2006, 36: 405–431. 10.1080/10643380600620387View ArticleGoogle Scholar
- Nurmi JT, Tratnyek PG, Sarathy V, Baer DR, Amonette JE, Pecher K, Wang C, Linehan JC, Matson DW, Penn RL, Driessen MD: Characterization and properties of metallic iron nanoparticles: spectroscopy, electrochemistry and kinetics. Environ Sci Technol 2005, 39(5):1221–1230. 10.1021/es049190uView ArticleGoogle Scholar
- Filip J, Zboril R, Schneeweiss O, Zeman J, Cernik M, Kvapil P, Otyepka M: Environmental applications of chemically pure natural ferrihydrite. Environ Sci Technol 2007, 41: 4367–4374. 10.1021/es062312tView ArticleGoogle Scholar
- Saleh N, Kim H-J, Phenrat T, Matyjaszewski K, Tilton RD, Lowry GV: Ionic strength and composition affect the mobility of surface-modified Fe 0 nanoparticles in water-saturated sand columns. Environ Sci Technol 2008, 42(9):3349–3355. 10.1021/es071936bView ArticleGoogle Scholar
- Johnson RL, Johnson GO, Nurmi JT, Tratnyek PG: Natural organic matter enhanced mobility of nano zerovalent Iron. Environ Sci Technol 2009, 43(14):5455–5460. 10.1021/es900474fView ArticleGoogle Scholar
- Kanel SR, Grenche J-M, Choi H: Arsenic(V) removal from ground-water using nanoScale zero-valent iron as a colloidal reactive barrier material. Environ Sci Technol 2006, 40(6):2045–2050. 10.1021/es0520924View ArticleGoogle Scholar
- Tiraferri A, Chen KL, Sethi R, Elimelech M: Reduced aggregation and sedimentation of zero-valent iron nanoparticles in the presence of guar gum. J Colloid Interface Sci 2008, 324: 71–79. 10.1016/j.jcis.2008.04.064View ArticleGoogle Scholar
- Kanel SR, Manning B, Charlet L, Choi H: Removal of Arsenic(III) from groundwater by nano scale zero-valent iron. Environ Sci Technol 2005, 39(5):1291–1298. 10.1021/es048991uView ArticleGoogle Scholar
- Song H, Carraway ER: Reduction of chlorinated methanes by nano-sized zero-valent iron. Kinetics, pathways, and effect of reaction conditions. Environ Eng Sci 2006, 23(2):272–284. 10.1089/ees.2006.23.272View ArticleGoogle Scholar
- Buffle J, Van Leeuwen H, Eds: Environmental Particles. Lewis Publishers 2, Boca Raton FL; 1993:353–360.Google Scholar
- Somasundaran P, Runkana V: Modeling flocculation of colloidal mineral suspensions using population balances. Int J Min Process 2003, 72: 33–55. 10.1016/S0301-7516(03)00086-3View ArticleGoogle Scholar
- Garrick S, Zachariah M, Lehtinen K: Modeling and simulation of nanoparticle coagulation in high reynolds number incompressible flows. Proceeding of the National Conference of the Combustion Institute 25–27 2001; Oakland Google Scholar
- Thomas B, Camp R: Velocity gradients and internal work in fluid motion. J Boston Soc Civ Engi 1943, 30: 4.Google Scholar
- Smoluchowski MV: Test of a mathematical theory of coagulation kinetics of colloid solutions [in German]. Zeitschrift F Physik Chemie 1916, XCII: 129–168.Google Scholar
- Reardon EJ, Fagan R, Vogan JL, Przepiora A: Anaerobic corrosion reaction kinetics of nanosized iron. Environ Sci Technol 2008, 42(7):2420–2425. 10.1021/es0712120View ArticleGoogle Scholar
- Horák D, Petrovský E, Kapička A, Frederichs T: Synthesis and characterization of magnetic poly(glycidyl methacrylate) microspheres. J Magn Magn Mater 2007, 311: 500–506. 10.1016/j.jmmm.2006.08.006View ArticleGoogle Scholar
- Masheva V, Grigorova M, Nihtianova D, Schmidt JE, Mikhov M: Magnetization processes of small γ-Fe 2 O 3 particles in non-magnetic matrix. Phys D Appl Phys 1999, 32: 1595–1599. 10.1088/0022-3727/32/14/308View ArticleGoogle Scholar
- Phenrat T, Saleh N, Sirk K, Tilton RD, Lowry GV: Aggregation and sedimentation of aqueous nanoscale zerovalent iron dispersions. Environ Sci Technol 2007, 41(1):284–290. 10.1021/es061349aView ArticleGoogle Scholar
- Zhang LY, Wang J, Wei LM, Liu P, Wei H, Zhang YF: Synthesis of Ni nanowires via a hydrazine reduction route in aqueous ethanol solutions assisted by external magnetic fields. Nano-Micro Lett 2009, 1: 49–52.View ArticleGoogle Scholar
- Rosická D, Šembera J: Assessment of influence of magnetic forces on aggregation of zero-valent iron nanoparticles. Nanoscale Res Lett 2010.Google Scholar
- Votrubík V: Theory of the Electromagnetic Field, [in Czech]. Praha: Czechoslovak Academy of Science Publication; 1958.Google Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.