Microwave-enhanced electro-deposition and stripping of palladium at boron-doped diamond electrodes
Introduction
Over the recent years several methods have been proposed to introduce in situ thermal activation into electrochemical experiments. These methods have been based on (i) laser pulse heating [1], (ii) rf-heating of microelectrodes [2] or macroelectrodes [3], (iii) “hot wire” electrodes [4], and thin film heating [5], [6]. They have in common that only the electrode or a very small solution volume in the vicinity of the electrode is heated in order to minimize sample degradation and handling while improving sensitivity and speed. The benefits of thermal activation in electroanalytical processes have been exploited for example in analytical stripping voltammetry [7].
The activation of electrochemical processes by focused microwave radiation has been proposed to achieve both a high rate of mass transport and highly localized heating in a small solution phase region within the diffusion layer at electrode–solution interface. Both, dielectric heating of the solution phase (for metal electrodes) and direct heating of the electrode (for non-metallic electrodes) has been observed and models have been developed to account for the temperature effects and the electrochemical current enhancements [8], [9], [10]. It has been demonstrated that in the high temperature zone at the electrode surface, mass transport is enhanced in approximately equal amounts by (i) the temperature effect on rate of diffusion and (ii) by additional convection in the presence of temperature and viscosity gradients. Microwave activation of electrochemical processes has been studied in aqueous solutions [11], [12], in organic solvents [13], in ionic liquids [14], and in micellar solutions [15]. Various types of electrodes such as platinum, gold, glassy carbon, or boron-doped diamond have been employed [16] as well as array electrode systems [17]. One particular benefit of microwave activation in electroanalysis is that only highly localized effects occur and that conventional equipment, electrodes, and procedures are employed which are readily interfaced to a microwave source.
Palladium is a catalytically active component released from automotive catalytic converters [18], [19] or potentially introduced into synthetic products such as drugs via synthetic catalysts. Palladium has the ability to undergo bioaccumulation [20]. The release of palladium for example from diesel engines has been estimated as 250 ng palladium per kilometer [21] for new engines. Anodic stripping methods can be very sensitive and have been developed to determine palladium in the presence of gold [22] or in the presence of other platinum group metals [23]. Usually, several metals such as palladium, rhodium, and platinum are found together and determined individually. In this study we only consider palladium as a model system for this group of analytes and we explore the effects introduced by microwave heating. The stripping voltammetry method is employed based on a pre-concentration step (by electro-depositing the metal) followed by a detection step (quantitative anodic stripping). Low detection limits as well as relatively inexpensive instrumentation makes electrochemical stripping analysis an important and commonly used tool for the trace metal determination [24] and it is demonstrated here that the application of focused microwave heating can further improve this methodology.
In this report we explore the effects of microwave activation on the electro-deposition and stripping of palladium on boron-doped diamond electrodes which are relatively inert towards cavitation erosion [25]. Due to their inert surface characteristics and wide potential window, boron-doped diamond electrodes have been increasingly used for metal pre-concentration and anodic stripping processes. They offer advantages over other type of carbon-based electrode materials due to their mechanical strength and extreme hardness which can resist any damage caused by boiling liquid and cavitation in the presence of microwave radiation [26].
The effect of microwave activation has been previously investigated for cadmium accumulation in mercury [27], for copper electro-deposition onto platinum [28], and for the stripping voltammetry of Pb and PbO2 using boron-doped diamond electrodes [29], [30]. In this paper we report the effect of microwaves on the pre-concentration and stripping of Pd metal using cyclic voltammetry. Both, the electro-deposition and stripping processes are shown to be enhanced at boron-doped diamond of 500 μm × 500 μm size. The nucleation and growth of palladium on boron-doped diamond is strongly affected and detrimental effects of hydrogen evolution are shown to ultimately limit the efficiency of the process under microwave conditions. Without further optimization, detection of palladium down to concentrations of 0.1 μM were readily achieved using linear sweep voltammetry in the presence of microwave activation and accumulation times of 5 min.
Section snippets
Chemical reagents
PdCl2, KCl, HCl, potassium ferrocyanide, and potassium ferricyanide were obtained from Aldrich and used without further purification. Demineralised and filtered water of resistivity not less than 18 MΩ cm was taken from an Elga water purification system. Argon (Pure shield, BOC) was employed for de-aeration of electrolyte solutions.
Instrumentation
Scanning electron microscopy images were obtained on a JEOL JSM6310 system. A conventional three-electrode micro-Autolab III potentiostat system (Eco Chemie, NL) was
Temperature and mass transport calibration for boron-doped diamond electrodes in the presence of microwaves
Microwave radiation induces primarily localized temperature effects which then lead to convection and mass transport phenomena. These effects can be investigated and “calibrated” for each type of electrode with a suitable reversible redox system [24]. The calibration of the boron-doped diamond electrode surface temperature, Telectrode, was achieved here by monitoring the equilibrium potential of the Fe(CN)63−/4− redox system. Fig. 1A shows that the application of microwave radiation to a
Conclusions
It has been shown that microwave radiation applied to boron-doped diamond electrodes strongly affects the deposition and stripping processes for palladium. Both temperature and mass transport effects are observed and exploited. The relatively simple introduction of localized thermal activation via microwave radiation into electrochemical systems and sensors provides a general future platform for the improvement of electroanalytical procedures and it is suggested that in particular with low
Acknowledgements
This work was funded by the EPSRC (GR/S06349/01) and undertaken as part of the EU sponsored COST Programme (Action D32, working group D32/005/04, “Microwave and Ultrasound Activation in Chemical Analysis”). W.L. Gore & Associates (UK) Ltd. are gratefully acknowledged for the generous supply of porous PTFE degassing tubing.
References (34)
- et al.
J. Electroanal. Chem.
(2001) - et al.
J. Electroanal. Chem.
(2001) - et al.
J. Electroanal. Chem.
(2001) - et al.
Sci. Total Environ.
(2000) Anal. Chim. Acta
(2006)- et al.
J. Electroanal. Chem.
(2001) - et al.
Electrochim. Acta
(2006) - et al.
Anal. Chem.
(2000) Anal. Chem.
(2002)- et al.
Electroanalysis
(2002)
Electroanalysis
New J. Chem.
Chem. Commun.
Electroanalysis
J. Electroanal. Chem.
New J. Chem.
J. Am. Chem. Soc.
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Photoelectrocatalytic interface of boron-doped diamond: Modification, functionalization and environmental applications
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Microwave-Electrochemical Deposition of a Fe-Co Alloy with Catalytic Ability in Hydrogen Evolution
2017, Electrochimica ActaCitation Excerpt :The fabrication of electrodes to study these materials has not been reported. Although electrodeposition processes under microwave-electrochemical conditions have been studied before [36,37,42,43], there has been no investigation of the products that are formed via microwave-electrochemical co-deposition. The massively enhanced electrodeposition rate in the presence of microwaves (up to three orders of magnitude) has been shown to lead to new morphologies by exploiting the focused stationary high temperatures and of the forced convection at the electrode-electrolyte interface [44].
Microwaves and Electrochemistry
2013, Microwaves in Organic Synthesis: Third Edition
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