Electrochemical preparation of iron cuboid nanoparticles and their catalytic properties for nitrite reduction

doi:10.1016/j.electacta.2008.02.024

Electrochimica Acta

Volume 53, Issue 23, 1 October 2008, Pages 6938-6943

https://doi.org/10.1016/j.electacta.2008.02.024 Get rights and content

Abstract

Iron cuboid nanoparticles supported on glassy carbon (denoted nm-Fe/GC) were prepared by electrochemical deposition under cyclic voltammetric (CV) conditions. The structure and composition of the Fe nanomaterials were characterized by scanning electron microscopy (SEM), selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). The results demonstrated that the Fe cuboid nanoparticles are dispersed discretely on GC substrate with an average size ca. 171 nm, and confirmed that the electrochemical synthesized nanocubes are single crystals of pure Fe. The catalytic properties of the Fe cuboid nanoparticles towards nitrite electroreduction were investigated, and enhanced electrocatalytic activity of the Fe nanocubes has been determined. In comparison with the data obtained on a bulk-Fe electrode, the onset potential of nitrite reduction on nm-Fe/GC is positively sifted by 100 mV, and the steady reduction current density is enhanced about 2.4–3.2 times.

Introduction

As a result of small size effect, surface effect and other peculiar physicochemical effects, nanomaterials exhibit novel properties and have attracted considerable attentions in diverse fields such as optics, electronics, catalysis, and magnetic data storage [1], [2], [3], etc. The nanostructured materials have also played important roles in corrosion, fuel cells, and photochemistry due to their ease of preparation, high catalytic activity and low cost [4], [5], [6], [7].

Fe is an important member of the iron-triad elements and belongs to the body centered crystal (bcc) system. The Fe materials are important catalysts in ammonia synthesis [8], [9], [10], [11] and denitrification [12], [13], [14]. Somorjai et al. have demonstrated that the surface structure of Fe catalysts have a significant impact on their activity [8], [10]. For the iron-catalyzed ammonia synthesis reaction, the (1 1 1) plane of a Fe single crystal was found to be the most active, and the activity ratio was obtained to be 418:25:1 for the Fe(1 1 1), Fe(1 0 0) and Fe(1 1 0) [8]. Recently, extensive studies were carried out to synthesize Fe nanoparticles for different applications [15], [16], [17]. It is well known that the surface structure of nanoparticles can be tuned by shape control synthesis [18]. Song et al. [19] illustrated that Pt nanoparticles of cubes, cuboctahedra and octahedra can be obtained by chemical synthesis through well controlling the conditions. For these shapes of Pt nanoparticles, the corresponding surface structures are {1 0 0}, {1 0 0} + {1 1 1} and {1 1 1}, respectively. Recently, Tian et al. [20] have developed an electrochemical method to control the shape of Pt nanoparticles. In their work, tetrahexahedral Pt nanoparticles bounded with {7 3 0}, {5 2 0} and vicinity high-index facets were obtained, and exhibited high catalytic activity and stability. In concerning the shape control synthesis of Fe nanoparticles, the hollow Fe nanocubes and nanoframes [21], [22], α-Fe₂O₃ naocubes [23] and α-Fe₂O₃ rhombohedral nanoparticles [24] were obtained by chemical synthesis routes.

In today's society, the intensive use of fertilizers in agriculture and nitrates in some industrial sectors causes a severe nitrate pollution of water sources and industrial sites. Because nitrate becomes toxic once it is converted to nitrite by the reducing action of bacteria in the human body, the development of denitrification technology is therefore an important issue in environment and human being health. It exists a few technologies such as biological denitrification, ion-exchange, reverse osmosis, as well as chemical and catalytic reductions. In comparison, the electrochemical denitrification has received increasing attentions because it has superior advantages regarding environmental compatibility, versatility, energy efficiency, safety, selectivity, amenability and cost effectiveness [25]. The electroreduction of nitrate and nitrite has been conducted on different electrodes, such as Cu modified Au [26], brass (Cu₆₀Zn₄₀) screen [27], Rh-modified pyrolytic graphite [28], Sn-modified Pt [29], Pd/Sn/Au electrodes [30], copper thallium [31], Cu(1 0 0) [32], Pd-based bimetallic supported catalysts [33], polypyrrole nanowires modified graphite [34], and Fe catalysts [35], [36]. The electroreduction of nitrate and nitrite has contributed also in the nitrogen cycle that has attracted much attention in recent years because of its ecological importance concerning the widespread agricultural use of potentially polluting nitrate and nitrite.

In the current paper, Fe cuboid nanoparticles supported on glassy carbon were prepared by an electrochemical method. The study has illustrated that the Fe nanocubes exhibit enhanced electrocatalytic activity towards nitrite reduction, which is ascribed not only to the nanosize effect but also the surface structure effect of the nanocubes that are bounded by bcc {1 0 0} facets of open structure.

Section snippets

Preparation of Fe cuboid nanoparticles

Glassy carbon substrate (GC, 6.0 mm in diameter with a geometric area of 0.28 cm²) was sealed into a Teflon holder and polished mechanically using successively sand paper (6#) and alumina powder of size 5, 1, 0.3, and 0.05 μm before metal deposition. A polycrystalline Fe rod (99.995%, Alfa) of 5 mm in diameter sealed into a Teflon holder with a geometric area of 0.2 cm² was polished mechanically using the same procedure and served as a reference surface of bulk-Fe electrode in the study. The Fe

Preparation and electrochemical characterization of nm-Fe/GC electrode

Cyclic voltammograms recorded during Fe electrodeposition on GC in 0.02 mol L⁻¹ FeSO₄ solution is displayed in Fig. 1. In the first cycle, the reduction current (negative current) remains small till −1.23 V in the negative-going potential scan (NGPS), it is then increased quickly. The reduction current is continuously increasing in the reverse potential scan until −1.23 V then is decreased progressively. A fast increase in the cathodic current is observed in the second cycle, and the cathodic

Conclusions

The current paper has put emphasis upon shape control synthesis of Fe nanoparticles and their electrocatalytic properties. Fe cuboid nanoparticles supported on glassy carbon were prepared by electrochemical deposition under cyclic voltammetric conditions. The results of SEM, XRD, SAED and EDX analysis confirmed that the Fe nanoparticles are Fe single crystals of cube shape and distributed discretely on GC substrate with an average size of 171 nm. It has revealed by cyclic voltammetric studies

Acknowledgments

This work was supported by National Natural Science Foundation of China (Grant Nos. 20673091 and 20433060) and National Key Basic Research Program (“973” project, Grant No. 2002CB211804).

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Electrochemical preparation of iron cuboid nanoparticles and their catalytic properties for nitrite reduction

Abstract

Introduction

Section snippets

Preparation of Fe cuboid nanoparticles

Preparation and electrochemical characterization of nm-Fe/GC electrode

Conclusions

Acknowledgments

Thin Solid Films

Appl. Catal. A-Gen.

Solid. State Ionics

Electrochem. Commun.

J. Magn. Magn.

Prog. Solid State Chem.

Electrochim. Acta

Electrochim. Acta

J. Electroanal. Chem.

J. Electroanal. Chem.

J. Electroanal. Chem.

J. Mol. Catal A: Chem.

Synth. Met.

J. Electroanal. Chem.

J. Electroanal. Chem.

Electrochim. Acta

Phys. Rev. B

Adv. Mater.

Nature

J. Phys. Chem. B

Chem. Eur. J.