Abstract
In the presented paper, studies of magnetite nanoparticle stability in selected environmental solutions are reported. The durability tests were performed in four types of liquids: treated and untreated wastewater, river water, and commercial milk (0.5% fat). Nanoparticles before and after deposition in the testing conditions were measured by transmission electron microscopy, X-ray diffraction, infrared spectroscopy, and Mössbauer spectroscopy. The amount of Fe atoms transferred into the solutions was estimated on the basis of flame atomic absorption spectroscopy. The analysis of the obtained results shows good stability of the tested nanoparticles in all water solutions. They do not change their structure or magnetic properties significantly, which makes them a good candidate to be used as, for example, detectors of specific compounds or heavy metals. On the other hand, studies show that particles are stable in environmental conditions for a long period of time in an unchanged form, which can cause their accumulation; therefore, they may be hazardous to living organisms.
Highlights
The nanoparticles used for the stability tests in environmental solutions were made from the following chemicals, which were purchased from: (a) Sigma-Aldrich, Darmstad, Germany: Fe(acac)3, 1,2-hexadecanediol, phenyl ether, and tetrabutylammonium hydroxide (TBAOH); (b) Avantor (Gliwice, Poland): FeCl3 ·6H2 O, FeCl2 ·4H2 O, HCl, NaOH, citric acid, acetone, NH3, and oleic acid; and (c) Fluka (Sigma-Aldrich, Darmstad, Germany): 98% tetraethoxysilane (TEOS), tetramethylammonium hydroxide (TMAOH), 1octadecanol, and oleyl amine
Transmission electron microscopy (TEM) measurements were conducted with a FEI Tecnai G2 X-TWIN 200kV microscope (Thermo Fisher Scientific, Hilsboro, USA), where the nanoparticles were placed by means of drop-casting onto the carbon-covered 400 mesh
No significant changes to the cores of the particles that have been induced by the used solutions can be seen. These results show that each kind of nanoparticle, Fe3 O4, SiO2 @Fe3 O4, and Fe3 O4 @Fe3 O4, presents strong durability in the tested environmental solutions
Summary
One of the main reasons why magnetite nanoparticles have become a popular subject for so many studies is their universality, low toxicity to living organisms, and relatively high biodegradability [1,2,3,4]. The drawback is that the solubility of magnetite is rather low in most solvents [5,6], which provides new advantages and allows them to be used in medicine or environmental protection [7,8,9] To add to their primary functions new properties, simple single-phase nanoparticles can be modified layer-wise to obtain more advanced core–shell structures [10,11,12]. Knowledge of the extraordinary structural and magnetic properties of these materials permits the performance of modifications on the objects obtained by superficial functionalization with compounds containing free functional groups such as, for example, amine, carboxylic, phosphonic, or thiolated [23,24,25] The presence of such groups on the surface allows, for example, the capturing of specific compounds (heavy metals, derivatives of medicaments, pesticides, etc.) in a relatively well-controlled way [26,27,28]. The reason for these studies is based on the idea of developing a new class of filters in which purposely modified magnetite nanoparticles can be used as well as to show the potential of hazards related to the long-lasting migration of nanoobjects that have been introduced into the real environment
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