A dirhodium(II,II) molecular species as a candidate material for resistive carbon monoxide gas sensors
Introduction
The detection of toxic and combustible gases by simple and cost-effective chemical sensors has gained a tremendous attention in recent years and many efforts, in this field, are today devoted to the synthesis of novel sensing materials with enhanced performance. Currently, the majority of chemical sensors for monitoring of harmful and toxic gases are based on thick/thin films of semiconducting metal oxides (MOS), for example SnO2. These materials exhibit a large variation of their electrical properties under gas exposures and a good thermal stability at relatively high temperatures, coupled with very low processing costs [1], [2], [3], [4].
Carbon monoxide represents one of the most harmful pollutants because of its interference with the mechanism of oxygen transport and storage in living systems [5]. Moreover, due to its strong coordination ability, CO acts as a poison for noble metals (i.e. supported Pt particles in reforming and fuel cells catalysts), decreasing their performance and lifetime [6], [7].
For the above applications, the CO concentration to be analyzed varies from a few ppm up to 15% in volume in an air, inert or hydrogen ambience. MOS CO gas sensors, which are well-established and available from commercial suppliers, have successfully employed for monitoring low CO concentrations, but, due to saturation effects, they fail to detect high CO concentrations [8], [9]. Further, they are characterized by a very poor selectivity, being sensitive to a large number of substances in addition to CO [1]. Then, the development of a CO gas sensor, combining linearity in a wide range of concentrations with high selectivity, is of prominent interest.
As a part of our ongoing research on gas resistive sensors, we turned our attention on the capability of transition metal complexes (TMCs) to act as novel sensing materials for CO-detection. Despite of the much current interest in transition metal complexes as promising candidates for applications in the context of gas sensing [10], [11], [12], [13], to our knowledge, the only example of transition metal complex-based CO resistive sensors is represented by a ferrocenyl dendrimer described by Koo et al. [14].
Here, we report a preliminary investigation on the CO sensing performance of a dirhodium(II,II) molecular species. Dirhodium(II,II) with a lantern structure represents a versatile class of redox metal complexes characterized by a rich chemistry spanning from axial and/or equatorial reactivity [15], [16], [17], [18] and catalytic and biological activity [19] to the formation of supramolecular assemblies and coordination polymers [20]. Covalent incorporation into polymer backbones to produce functional materials represents a further recent development of their chemistry [21].
A peculiar property of dirhodium(II,II) species is their axial reactivity, which allows the introduction, at the axial sites, of a large number of Lewis bases, including gaseous species. Lippard and coworkers have recently demonstrated the potential utility of these complexes in the fabrication of fluorescence-based NO sensors [22]. Nevertheless, their potential as sensing materials for resistive gas sensors has never been explored yet.
For our purposes, the reversible binding capability of carbon monoxide displayed by dirhodium(II,II), even in the solid state [16], is of particular interest. Of course, it is essential for practical applications in resistive gas sensors that, dirhodium(II,II) materials, as a consequence of reversible CO coordination, display a reversible and measurable change of the solid state conductance (resistance).
In the present communication we report, for the first time, on the development of a CO-resistive sensor based on the dirhodium(II,II) square molecular box [Rh2(form)2(ox)(H2O)2]4 (1) (form = N,N′-di-p-tolyl-formamidinate, ox = oxalate), focusing our attention on the thermal stability, film processability, electrical properties and CO sensitivity and selectivity.
Section snippets
Synthesis
[Rh2(form)2(ox)]4 was synthesized as follows: to an aqueous solution (40 mL) of disodium oxalate (0.300 g) was added a chloroform/acetone solution (1:3, 20 mL) of [Rh2(form)2(CF3COO)2(H2O)2] (form = N,N-di-p-tolylformamidinate) (0.200 mg), and the resulting mixture was left to stir for ca. 24 h. After this the organic volatiles were removed on a rotary evaporator and the green solid was collected by filtration, washed several times with warm water and methanol, and dried. The crude green solid was
Powders characterization
Powdered samples of [Rh2(form)2(ox)]4 (1) were prepared by following the already published procedure [18]. A detailed description of its chemical structure (see Fig. 1), formulated by means of 1H NMR, FT-IR spectroscopy and liquid secondary ionization mass spectrometry (LSI-MS) was reported elsewhere [18]. Here, the morphological and microstructural features of 1, both as a powder and a film, are described.
SEM and TEM images of the powdered samples are reported in Fig. 2a–c. The observed
Conclusion
In summary, a dirhodium(II,II) square molecular box has been proposed as a new semiconducting material for CO resistive sensors for the first time. Reversible CO-binding capability, good film processability, high thermal stability in air, accompanied by a semiconducting behaviour, have resulted in a successful combination of properties of this complex to act as a CO-resistive sensing material.
The sensor was fabricated by a simple film technology and resulted to have satisfactory good sensing
Acknowledgments
Financial support from the MIUR (Contract no. 2005039547) is gratefully acknowledged.
Sandra Lo Schiavo received her degree in chemistry in 1980 from the University of Messina. She is associated professor of chemistry at the Department of Inorganic Chemistry, Analytical Chemistry and Physical Chemistry of University of Messina. Her research activity is actually devoted to the synthesis and characterization of functional transition metal complexes (TMCs) based materials, even by incorporation of TMCs into polymer network.
References (25)
- et al.
CO-free production of hydrogen via stepwise steam reforming of methane
J. Catal.
(2000) - et al.
High sensitivity Pt-doped SnO2 gas sensors fabricated using sol–gel solution on micromachined (1 0 0) Si substrates
Sens. Actuators B
(2004) - et al.
Hemilabile coordination complexes for sensing applications
Coord. Chem. Rev.
(2006) - et al.
Humidity sensing behaviour of mono- and dinuclear osmium(IV) chloro complexes
Sens. Actuators B
(2001) - et al.
CO gas sensor based on a conducting dendrite
Sens. Actuators B
(2001) - et al.
Solid State Gas Sensors
(1991) - et al.
Solid-state gas sensors: a review
J. Electrochem. Soc.
(1992) Gas Sensors
(1992)The effect of carbon monoxide on humans
Ann. Rev. Pharmacol.
(1975)
Carbon monoxide poisoning of proton exchange membrane fuel cells
Int. J. Energy Res.
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Sandra Lo Schiavo received her degree in chemistry in 1980 from the University of Messina. She is associated professor of chemistry at the Department of Inorganic Chemistry, Analytical Chemistry and Physical Chemistry of University of Messina. Her research activity is actually devoted to the synthesis and characterization of functional transition metal complexes (TMCs) based materials, even by incorporation of TMCs into polymer network.
Pasquale Piraino received his degree in chemistry in 1969 from the University of Messina. He is a full professor of chemistry and Head of the Department of Inorganic Chemistry, Analytical Chemistry and Physical Chemistry of University of Messina. His actual research activity concerns the synthesis of hydrophobic ionic liquid based polymers.
Anna Bonavita received her degree in materials engineering from the University of Messina in 1997. Her research activity concerns with the preparation, characterization and development of semiconductor films for gas sensing applications. At present she is at the Department of Materials Science and Engineering, University of Florida.
Giuseppe Micali received his degree in electronic engineering from the University of Messina in 2003. At present he is at the Department of Industrial Chemistry and Materials Engineering of the University of Messina. His research activity concerns with the implementation of software procedures for automated instrumentation control and with the electrical characterization of gas sensing devices.
Giuseppe Rizzo received his degree in chemistry from the University of Messina in 1999. Actually he works at the Department of Industrial Chemistry and Materials Engineering of the University of Messina. His research activity is focused on the synthesis and characterization of materials by sol–gel method both for catalytic and optical applications.
Giovanni Neri received his degree in chemistry from the University of Messina in 1980. He is full professor of chemistry and director of the Department of Industrial Chemistry and Materials Engineering of the University of Messina. During his research activity, he has worked on many aspects of the synthesis, characterization and chemical-physics of solids with particular emphasis to catalytic and sensing properties. In the latter research area his work has been focused on the preparation of metal oxide thick and thin films and their application in gas sensors.