Characterization of zero-valent iron nanoparticles

https://doi.org/10.1016/j.cis.2006.03.001Get rights and content

Abstract

The iron nanoparticle technology has received considerable attention for its potential applications in groundwater treatment and site remediation. Recent studies have demonstrated the efficacy of zero-valent iron nanoparticles for the transformation of halogenated organic contaminants and heavy metals. In this work, we present a systematic characterization of the iron nanoparticles prepared with the method of ferric iron reduction by sodium borohydride. Particle size, size distribution and surface composition were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), high-resolution X-ray photoelectron spectroscopy (HR-XPS), X-ray absorption near edge structure (XANES) and acoustic/electroacoustic spectrometry. BET surface area, zeta (ζ) potential, iso-electric point (IEP), solution Eh and pH were also measured. Methods and results presented may foster better understanding, facilitate information exchange, and contribute to further research and development of iron nanoparticles for environmental and other applications.

Introduction

Nanotechnology is the engineering and art of manipulating matter at the nanoscale (1–100 nm) [1], [2], [3]. For environmental applications, nanotechnology offers the potential of novel functional materials, processes and devices with unique activity toward recalcitrant contaminants, enhanced mobility in environmental media and desired application flexibility [3], [4], [5], [6], [7], [8], [9], [10]. Many nano-based environmental technologies (e.g., sensors, sorbents, reactants) are under very active research and development, and are expected to emerge as the next generation environmental technologies to improve or replace various conventional environmental technologies in the near future [3], [4], [5], [6], [7], [8], [9], [10].

Iron nanoparticle technology represents perhaps one of the first generation nanoscale environmental technologies [4]. Over the last few years, various synthetic methods have been developed to produce iron nanoparticles [3], [4], [11], [12], [13], [14], modify the nanoparticle surface properties [15], [16], [17], [18], [19], and enhance the efficiency for field delivery and reactions [17], [18], [19], [20]. Extensive laboratory studies have demonstrated that nanoscale iron particles are effective for the transformation of a wide array of common environmental contaminants such as chlorinated organic solvents [3], [4], [17], [19], [21], [22], organochlorine pesticides [23], PCBs [3], [24], organic dyes [25], various inorganic compounds [26], [27] and metal ions such as As(III), Pb(II), Cu(II), Ni(II) and Cr(VI) [16], [26], [28]. Several field tests have demonstrated the promising prospective for in situ remediation [19], [29], [30].

Many research papers on applications of iron nanoparticles have been published over the last few years. While several types of iron nanoparticles are available on the market, information on the nanoparticle synthesis and properties is still limited in peer-reviewed journals. Fundamental information on characterization methods has not been well documented. Quality control and insurance is rapidly becoming a major issue as nanoparticles are being used in more and more projects. Objective of this work is to provide an in-depth report on the characterization of zero-valent iron nanoparticles. The synthetic methods described in this work have been used in many laboratories. We believe that such information is valuable for the comparison and quality control of iron nanoparticles produced with different methods and experimental conditions.

Section snippets

Synthesis of iron nanoparticles

Nanoscale zero-valent iron particles can be prepared in aqueous solutions via the reduction of ferric iron (Fe(III)) or ferrous iron(II) with sodium borohydride [3], [4], or via decomposition of iron pentacarbonyl (Fe(CO)5) in organic solvents or in argon [11], [12], [13]. Zero-valent iron particles can also be prepared from hydrogen reduction of iron oxides. In this work, synthesis of nanoscale iron particles with the sodium borohydride method was used. A key advantage of this method is its

Results and discussion

Fig. 3 presents TEM images of the iron nanoparticles. The laboratory prepared iron particles were largely spherical, characteristic of particles formed in solution. A representative single particle size is around 60–70 nm as shown in Fig. 3a. A few particles had size as large as 200–250 nm, whereas most (> 92%) particles were less than 100 nm. TEM images (Fig. 3b–d) also show that most particles formed chain-like aggregates.

A size distribution (Fig. 4a) was calculated after more than 420

Conclusions

Iron nanoparticles synthesized with the borohydride method have been characterized with the techniques of TEM, XRD, HR-XPS, XANES, acoustic spectrometer and BET nitrogen adsorption isotherm. Average particle size of the particles is approximately 60 nm with majority (> 90%) in the nano-domain (1–100). Iso-electric point (IEP) is in the range of pH 8.1–8.3. The nanoparticles have strong tendency to form microscale aggregates likely due to the weak surface charges. In water, 2–3 mg/L iron loading

Acknowledgements

This research is partially supported by USEPA STAR grants (R829624 and GR832225).

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