**Voltammetric Analysis of Platinum Group Metals Using a Bismuth-Silver Bimetallic Nanoparticles Sensor**

Charlton van der Horst, Bongiwe Silwana, Emmanuel Iwuoha and Vernon S. Somerset

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/68132

#### **Abstract**

This study dealt with the development of a bismuth-silver bimetallic nanosensor for differential pulse adsorptive stripping voltammetry of platinum group metals (PGMs) in environmental samples. The nanosensor was fabricated by drop coating a thin bismuth-silver bimetallic film onto the active area of the screen-printed carbon electrodes. Optimization parameters such as pH, dimethylglyoxime (DMG) concentration, deposition potential and deposition time, stability test and interferences were also studied. In 0.2 M acetate buffer (pH = 4.7) solution and DMG as the chelating agent, the reduction signal for PGMs ranged from 0.2 to 1.0 ng L−1. In the study of possible interferences, the results have shown that Ni(II), Co(II), Fe(III), Na<sup>+</sup> , SO<sup>4</sup> 2−, and PO4 3− do not interfere with Pd(II), Pt(II), and Rh(III) in the presence of DMG with sodium acetate buffer as the supporting electrolyte solution. The limit of detection for Pd(II), Pt(II), and Rh(III) was found to be 0.07, 0.06 and 0.2 ng L−1, respectively. Good precision for the sensor application was obtained with a reproducibility of 7.58% for Pd(II), 6.31% for Pt(II), and 5.37% for Rh(III) (*n* = 10).

**Keywords:** adsorptive stripping voltammetry, bismuth-silver bimetallic, platinum group metals, dimethylglyoxime, screen-printed electrode

## **1. Introduction**

Nowadays, the pollution of surface waters with chemical contaminants is one of the most crucial environmental problems. These chemical contaminants enter rivers and streams resulting in tremendous amount of destruction to the aquatic ecosystem [1]. Heavy and platinum group metal (PGM) contaminations at trace levels in water resources present a major current environmental threat, so the detection and monitoring of these metal contaminants

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result in an ever-increasing demand [2, 3]. According to El Mhammedi et al. [4], heavy metal analysis has been carried out in laboratories with time-consuming sampling, transportation and storage steps. Spectroscopy instrumentation was used for the simultaneous analysis of metal ions in water and, sediment biota samples. For the detection of trace metals, electrochemical analysis has always been recognized as a powerful tool [5–7].

In electroanalysis, much attention has been dedicated to the development of mercury-free sensors the last decade [8, 9]. Various materials have been used as working electrodes for heavy metal analysis [10, 11]. One of these working electrodes is bismuth film electrodes (BiFEs) and has been widely explored as a replacement for the toxic hanging drop mercury electrodes and films [12]. In differential pulse adsorptive stripping voltammetry (DPAdSV), nanoparticles play also a very important role. Due to their unique electronic, chemical, mechanical and thermal properties of nanoparticles make them extremely attractive for heavy metal electrochemical sensors in comparison with conventional materials [13]. In comparison with traditional macro-electrodes, nanoparticle electrodes show a decreased influence of the solution resistance, an increased mass-transport rate, and a higher signalto-noise ratio [14].

Rahman et al. [15] use gold-silver bimetallic nanoparticles for the sensing of an environmental toxin, pyrene. These bimetallic nanoparticles were prepared by chemical reduction method involving the reduction of AgNO<sup>3</sup> and HAuCl4 in aqueous solution of 2% hydrazine as reducing agent, cetryl trimethyl ammonium bromide as the capping agent, deionized water as the solvent and iso-octane as a co-precipitator. In another study, Mailu et al. [16] used overoxidized-polypyrrole/Ag-Au bimetallic nanoparticles for the determination of anthracene, using square wave voltammetry as technique. Bimetallic nanoparticles have been mainly used for the construction of biosensors and electrochemical sensors for determination of PGMs [17], arsenic [18], glucose and ascorbic acid [19], nitrite [20], carcinogenic organic compounds [21] and antidepressant drug [22].

This study focuses on the development of a new working electrode, such as bismuth-silver bimetallic nanoparticles for heavy metal analysis. The work done by Van der Horst et al. [23] describes the development of a DPAdSV procedure for the determination of platinum in environmental samples. In this procedure, a glassy carbon electrode modified with a bismuth film (GCE/Bi-AgF) was constructed. The optimization of several stripping voltammetric parameters such as dimethylglyoxime (DMG) concentration, composition of supporting electrolyte, pH, deposition potential and deposition time was performed. In this study, the results obtained showed low detection limits of 0.2 ng L−1 for Pt(II). These bismuth-silver bimetallic nanoparticles have been utilized for the determination of Pd(II), Pt(III), and Rh(III) [17] and Pt-Rh and Pd-Rh complexes [24] and the improved detection of ascorbic acid [25].

The main aim of the work described in this chapter was to investigate the construction and application of a disposable screen-printed carbon electrode (SPCE) that utilizes bismuthsilver bimetallic nanomaterials for PGMs determination. The electrochemical behavior of PGMs in road dust and roadside soil samples was investigated by voltammetry, and the optimum instrumental conditions were defined by DPAdSV measurements. The bismuth-silver bimetallic screen-printed nanosensor was further successfully applied for the analysis of PGMs in environmental samples.
