Platinum-based nanostructured materials: synthesis, properties, and applications.

Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

Nanostructured Materials for Room-Temperature Gas Sensors

Carbon nanotubes have aroused great interest since their discovery in 1991. Because of the vast potential of these materials, researchers from diverse disciplines have come together to further develop our understanding of the fundamental properties governing their electronic structure and susceptibility towards chemical reaction. Carbon nanotubes show extreme sensitivity towards changes in their local chemical environment that stems from the susceptibility of their electronic structure to interacting molecules. This chemical sensitivity has made them ideal candidates for incorporation into the design of chemical sensors. Towards this end, carbon nanotubes have made impressive strides in sensitivity and chemical selectivity to a diverse array of chemical species. Despite the lengthy list of accomplishments, several key challenges must be addressed before carbon nanotubes are capable of competing with state-of-the-art solid-state sensor materials. The development of carbon nanotube based sensors is still in its infancy, but continued progress may lead to their integration into commercially viable sensors of unrivalled sensitivity and vanishingly small dimensions.

Carbon nanotube gas and vapor sensors.

Carbon nanotubes (CNTs) promise to advance a number of real-world technologies. Of these applications, they are particularly attractive for uses in chemical sensors for environmental and health monitoring. However, chemical sensors based on CNTs are often lacking in selectivity, and the elucidation of their sensing mechanisms remains challenging. This review is a comprehensive description of the parameters that give rise to the sensing capabilities of CNT-based sensors and the application of CNT-based devices in chemical sensing. This review begins with the discussion of the sensing mechanisms in CNT-based devices, the chemical methods of CNT functionalization, architectures of sensors, performance parameters, and theoretical models used to describe CNT sensors. It then discusses the expansive applications of CNT-based sensors to multiple areas including environmental monitoring, food and agriculture applications, biological sensors, and national security. The discussion of each analyte focuses on the strategies used to impart selectivity and the molecular interactions between the selector and the analyte. Finally, the review concludes with a brief outlook over future developments in the field of chemical sensors and their prospects for commercialization.

Carbon Nanotube Chemical Sensors

The development of carbon nanotube-(CNTs-)based gas sensors and sensor arrays has attracted intensive research interest in the last several years because of their potential for the selective and rapid detection of various gaseous species by novel nanostructures integrated in miniature and low-power consuming electronics. Chemiresistors and chemical field effect transistors are probably the most promising types of gas nanosensors. In these sensors, the electrical properties of nanostructures are dramatically changed when exposed to the target gas analytes. In this review, recent progress on the development of different types of CNT-based nanosensors is summarized. The focus was placed on the means used by various researchers to improve the sensing performance (sensitivity, selectivity and response time) through the rational functionalization of CNTs with different methods (covalent and non-covalent) and with different materials (polymers and metals).

https://iopscience.iop.org/article/10.1088/0957-4484/19/33/332001/pdf

Recent progress in carbon nanotube-based gas sensors.

Multiwalled carbon nanotube (MWCNT) films have been fabricated by using plasma-enhanced chemical vapor deposition system onto Cr–Au patterned alumina substrates, provided with 3nm thick Fe growth catalyst, for NO2 and NH3 gas sensing applications, at sensor temperature in the range of 100–250°C. Nanoclusters of noble metal surface catalysts (Au and Pt) have been sputtered on the surface of MWCNTs to enhance the gas sensitivity with respect to unfunctionalized carbon nanotube films. It was found that the gas sensitivity of Pt- and Au-functionalized MWCNT gas sensors significantly improved by a factor up to an order of magnitude through a spillover effect for NH3 and NO2 gas detections, respectively. The metal-functionalized MWCNT sensors exhibit very high gas sensitivity, fast response, reversibility, good repeatability, and sub-ppm range detection limit with the sensing properties of the MWCNT films tailored by surface catalyst used to functionalize the MWCNT sensors.

Enhancement of sensitivity in gas chemiresistors based on carbon nanotube surface functionalized with noble metal (Au, Pt) nanoclusters

Sputter deposition was investigated as a tool for manufacturing proton-exchange membrane fuel cell (PEMFC) electrodes with improved performance and better catalyst utilization vs. commercial electrode. Nanosized (diameter 2–5 nm) platinum clusters were deposited on gas diffusion electrodes (carbon paper + PTFE/C diffusive layer). The activity for methanol oxidation was increased about 14 times compared to commercial catalyst, with loading − 2 . SEM–FEG characterization and cyclic voltammetry were carried out to study the morphology, and the behavior of the Pt clusters as cathodic electrocatalyst of a polymer electrolyte fuel cell.

Sputter deposition of Pt nanoclusters and thin films on PEM fuel cell electrodes

In this paper the effect of the surface functionalization of the carbon nanotubes (CNT) networked films with a metalloporphyrins layer is investigated for gas sensing. Modified film exhibits an increased sensitivity of the electrical resistance towards the concentrations of common volatile compounds (alcohols, amines, aromatic and ketones), at room temperature. Furthermore, a part of the adsorption properties of the functional units is transferred to the sensor signal and, as a consequence, the selectivity of the sensor is also modified. Principal Component Analysis (PCA) demonstrates that the functionalization provides enough selectivity change to turn a triplicate of the same CNT film into an effective sensor array capable of the compounds recognition. These findings are then promising for the development of arrays of CNT-based gas nanosensors with broad selectivities for fingerprinting analysis of complex samples.

Metalloporphyrins-modified carbon nanotubes networked films-based chemical sensors for enhanced gas sensitivity

Characterization of metal-modified and vertically-aligned carbon nanotube films for functionally enhanced gas sensor applications

Multiwalled carbon nanotube (MWCNT) films have been deposited by using plasma enhanced chemical vapor deposition (PECVD) system onto Cr–Au patterned alumina substrates for NO2 and NH3 gas sensing applications, at operating temperature of 200°C. Nanoclusters of different MWCNT-growth catalysts (Fe and Co) have been predeposited onto substrates to promote the growth of the carbon nanotube films with different structural properties. It is demonstrated that the gas sensitivity of the MWCNT films depends on catalyst used for their growth with highest gas sensitivity achieved for Co-grown MWCNT films. The chemiresistor gas response is attributed to the p-type conductivity in semiconducting MWCNTs and the electrical charge transfer is found to be the major sensing mechanism. The results obtained demonstrate that the MWCNT-based sensors exhibit high gas sensitivity, fast response and reversibility, good repeatability and reproducibility, and sub-ppm range detection limit with the gas sensing properties of the MWCNT films tailored by catalyst employed in the PECVD growth process.

M.A. Signore

Papers

Enhancement of sensitivity in gas chemiresistors based on carbon nanotube surface functionalized with noble metal (Au, Pt) nanoclusters

Sputter deposition of Pt nanoclusters and thin films on PEM fuel cell electrodes

Metalloporphyrins-modified carbon nanotubes networked films-based chemical sensors for enhanced gas sensitivity

Characterization of metal-modified and vertically-aligned carbon nanotube films for functionally enhanced gas sensor applications

Effect of growth catalysts on gas sensitivity in carbon nanotube film based chemiresistive sensors