Elsevier

Applied Surface Science

Volumes 467–468, 15 February 2019, Pages 402-410
Applied Surface Science

Full Length Article
Comparative study of magnetite nanoparticles obtained by pulsed laser ablation in water and air

https://doi.org/10.1016/j.apsusc.2018.10.189Get rights and content

Highlights

  • Magnetic nanomaterials were formed by pulsed laser ablation of iron in water and air.

  • Material ablated in water contained spherical particles of Fe3O4, Fe2O3, FeO and Fe.

  • Material ablated in air contained more Fe3O4 and nitrogen (N-O, N-H or FeNx)

  • The surface composition and electrokinetic properties of the materials differed.

  • Material obtained in air is more stable in colloids due to its surface composition.

Abstract

Magnetic nanomaterials were synthesized using a method of pulsed laser ablation of an iron target in water (PLAL) and in air (PLAG). The microstructure and composition of the obtained materials differed. Spherical nanoparticles (NPs) of 2–80 nm containing Fe3O4, α-Fe2O3, γ-Fe2O3, FeO and Fe were obtained using PLAL. According to the XPS and FTIR data, the surfaces of these particles contained both Fe3O4 and Fe2O3. PLAG led to the formation of NPs of 2–120 nm and 2-D lamellar structures up to 1 μm. This material contained more magnetite and nitrogen species, presumably iron nitrides. This material’s surface contained FeOOH; the OH-group content was very high. It exhibited the greatest sedimentation stability and zeta potential value, while magnetic NPs (MNPs) obtained in water were less stable in colloids. The difference in the magnetic parameters of the two materials can be connected to not only the different composition (different magnetite content and nitrogen species presence) but also their structural features. Thus, PLAL and PLAG methods allowed for obtaining magnetic nanostructured materials with different characteristics suitable for application in different fields.

Introduction

Magnetic nanoparticles (MNPs) based on iron-containing compounds, primarily oxides, are of great interest for various applications, as well as for fundamental studies of the effect of their structure, size and morphology on magnetic properties [1], [2], [3]. In fields such as biomedicine, for example, magnetite Fe3O4 is preferable to hematite α-Fe2O3 because it exhibits higher residual magnetization [4], [5].

There are a number of chemical methods for obtaining MNPs consisting of various iron oxides [6], [7], [8]. However, the purity of the final nanomaterials, meaning the absence of the precursors’ traces and other contaminants, is important for a number of applications. That is why high-energy physical methods of obtaining MNPs have been intensively developed recently [9], [10], [11]. Pulsed laser ablation in a liquid (PLAL) is one of these methods. It has been effectively developing since the ‘90s [12], [13]. PLAL allows one to obtain particles directly in the form of colloids in pure solvents with a minimal amount of precursors, or without them. It also provides the possibility of varying the particles’ size and structure within certain limits [14], [15], [16], [17]. Recent achievements in understanding the ablation mechanisms and increasing productivity [18], [19], [20] have expanded the fields of its practical use, for example, for catalysis [21], [22], [23], [24].

The preparation of iron oxide nanoparticles by PLAL has been studied rather in depth. Varying the parameters of the radiation (wavelength, pulse duration, power), as well as changing the solvent composition, makes it possible to obtain iron oxide particles of different sizes and compositions [25], [26], [20]. For our group, the synthesis of MNPs by PLAL is the most interesting area [27], [28], [29], [30].

NPs with a given composition and structure obtaining under pulsed laser ablation in gas (PLAG) or a vacuum is a much less developed technology. Thus, according to the literature data, PLAG of the iron target was carried out under the conditions that predominantly led to hematite α-Fe2O3 nanoparticle formation [31], [32]. MNPs for the first time were obtained through nanosecond laser ablation in atmospheric air in our previous work [33].

In previous works, our group studied the composition, structure and morphology of iron oxide nanoparticles obtained by nanosecond pulsed laser ablation of a metallic iron target in air at atmospheric pressure [33] and in distilled water [34], [35] using the radiation of the fundamental harmonic of a Nd:YAG laser. These studies showed that NPs obtained through PLAL and PLAG are predominantly composed of magnetite and have similar dimensional characteristics. The main difference of the MNPs obtained in air is the presence of a small amount of nitrogen. Nitrogen, presumably, can present in different forms (iron nitrides, adsorbed nitro and amino groups [33], etc.). Moreover, in addition to spherical NPs, lamellar nanostructures were present in the sample obtained through PLAG.

The aim of this work is a detailed comparative study of the composition and properties of the surface of Fe3O4 MNPs, depending on the method of obtaining them (PLAL in water or PLAG in air with the same laser source). The surface, along with the size and magnetic and other properties, plays a decisive role in the practical use of MNPs in biology, medicine, catalysis and optoelectronics, which determines the relevance of this study.

Section snippets

Samples preparation

Iron oxide MNPs were obtained through the ablation of an Fe target (99.5%) by the pulsed focused radiation of an Nd:YAG laser TII LS-2131 M-20 (LOTIS, Belarus) at 1064 nm, 20 Hz, 7 ns and 150 mJ. PLAL and PLAG methods were performed.

  • (1)

    In the case of PLAL, a target with a size of 40 × 10 × 5 mm was immersed in a 100-ml glass cylindrical reactor filled with distilled water (see the scheme in Fig. 1a). The laser radiation was focused using a short-focus (F = 50 mm) collecting lens. The laser beam

Microstructure study

The materials obtained were studied through TEM. Fig. 2 presents the obtained images with the additional HRTEM insets. The samples contain different structural elements. The Fe/water sample consists of agglomerated spherical or near-spherical crystalline particles (Fig. 2a). The largest particles are up to 80 nm in size, but the main fraction is presented by the NPs of 1–10 nm in size, with the maximum of distribution at 2 nm [35]. The Fe/air sample is represented by three different structures.

Conclusions

Iron-based magnetic nanomaterials were synthesized using pulsed laser ablation in water and air. The samples obtained were studied and compared.

It was found that not only the microstructure but also the phase composition of the samples obtained in water and air media differed.

Iron ablated in water consisted of spherical and near-spherical NPs 2–80 nm in size (maximum of 2 nm) of magnetite (74%) with other oxide phases and metallic iron. The surface of these particles contained both Fe3O4 and Fe2

Acknowledgments

This work was supported by the Ministry of Education and Science of the Russian Federation, Project Number 3.9604.2017/8.9. The authors express their appreciation to A.E. Sokolov and D.A. Velikanov from Kirensky Institute of Physics (Krasnoyarsk, Russia) for the VSM measurements. Also, the authors thank the service Proof-Reading.com for the English text improvement.

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