Tin dioxide is a widely used sensitive material for gas sensors. Many research and development groups in academia and industry are contributing to the increase of (basic) knowledge/(applied) know-how. However, from a systematic point of view the knowledge gaining process seems not to be coherent. One reason is the lack of a general applicable model which combines the basic principles with measurable sensor parameters. The approach in the presented work is to provide a frame model that deals with all contributions involved in conduction within a real world sensor. For doing so, one starts with identifying the different building blocks of a sensor. Afterwards their main inputs are analyzed in combination with the gas reaction involved in sensing. At the end, the contributions are summarized together with their interactions. The work presented here is one step towards a general applicable model for real world gas sensors.

Conduction Model of Metal Oxide Gas Sensors

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 (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

Xin Zhou,†,‡ Songyi Lee,† Zhaochao Xu,* and Juyoung Yoon*,† †Department of Chemistry and Nanoscience, Ewha Womans University, Seoul 120-750, Republic of Korea ‡Research Center for Chemical Biology, Department of Chemistry, Yanbian University, Yanjii 133002, People’s Republic of China Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Shahekou, Dalian, Liaoning, People’s Republic of China

Recent Progress on the Development of Chemosensors for Gases.

https://research.sabanciuniv.edu/11523/1/HE4440.pdf

Storage of hydrogen in nanostructured carbon materials

This article presents an XPS study of Ce 3d emission spectra dominated by atomic multiplet effects in core level spectroscopy of rare earth compounds (Ce oxides). Core level spectroscopy has been used to study the electronic states of Ce 3d5/2 and Ce 3d3/2 levels in Ce4+ and Ce3+ states. The well-resolved components of Ce 3d5/2 and Ce 3d3/2 spin-orbit components, due to various final states (4f0, 4f1, 4f2 configurations), were determined on 3d XPS spectra from commercial powders (CeO2, CePO4).

These results were used to study the 3d spin-orbit component of mixed cerium-titanium oxide.

This compound was prepared by co-melting commercial powders of CeO2 and TiO2 at 1800 K under air using a solar furnace with a flux density of 16 MW.m−2 at the focal point of the parabolic concentrator. The mixed oxide Ce2Ti2O7 was produced and contained Ce(III) species which may be reactive with water to give back the initial metal oxides and generate hydrogen, a valuable product considered as a promising energy carrier in the future in replacement of oil.

The 3d photoemission spectra revealed the presence of mixed components attributed to mainly Ce(III) and Ce(IV) species. Copyright © 2008 John Wiley & Sons, Ltd.

Ce 3d XPS investigation of cerium oxides and mixed cerium oxide (CexTiyOz)

This study addresses the synthesis, characterization, and thermochemical redox performance evaluation of perovskites and parent structures (Ruddlesden–Popper phases) as a class of oxygen-exchange m...

Investigation of Perovskite Structures as Oxygen-Exchange Redox Materials for Hydrogen Production from Thermochemical Two-Step Water-Splitting Cycles

https://hal.archives-ouvertes.fr/hal-01634399/document

Removal of Lead (Pb) by Hydroxyapatite Sorbent

Thick amorphous SiCxNy coatings have been deposited by chemical vapor deposition at 1000–1200 °C from the TMS–NH3–H2 system. Hardness (H) and stiffness (E) were measured by nanoindentation with a Berkovich indenter. The relative influence on H and E have been investigated using an experimental design by varying: deposition temperature; pressure; and ammonia flow rate. The deposits exhibit a high chemical complexity in a large domain of composition (0.04≤x/x+y)≤0.67) with Si(C4−nNn) units connected by sp3–sp2 carbon configurations. Correlations between the mechanical features and the chemical bonding and local order around the different atoms have been established. Two groups of samples have been distinguished depending on the x/(x+y) ratio. Below x/(x+y)=0.1, the N-rich coatings were obtained in which the main bond was Si–N and H and E tended to decrease from 27 to 31 GPa and 224 to 289 GPa, respectively, with increasing numbers of Si–C, C–N and C–C bonds. For 0.38≤x/(x+y)≤0.67, the C-rich coatings were obtained for which the increases of H and E from 29 to 38 GPa and 240 to 360 GPa, respectively, have been correlated to the increasing proportion of SiC4 units.

Hardness and stiffness of amorphous SiCxNy chemical vapor deposited coatings

In the frame of the Generation IV International Forum, Gas-cooled Fast Reactor (GFR) is one system studied by CEA (France). Helium pressurized at 7 MPa is the coolant and the nominal temperature of use is about 1300 K. The cladding materials currently considered is a SiC/SiC composite with a β-SiC coating. In case of accident, reactor temperatures can reach 1900–2300 K. A previous study was carried out to determine the physico-chemical behavior of another polytype, α-SiC, for comparison on the position of the active to passive transition and of the mass loss rates under active conditions to simulate a typical accident. Experimental oxidation tests at high temperature (1400–2300 K) on massive β-SiC samples processed by Chemical Vapor Deposition (CVD) coupled to mass variation, SEM, XPS, AFM and roughness analyses enabled to determine the transition between passive and active oxidation regimes, and to study the resistance to oxidation of such material in some conditions that might be encountered in case of accident (high temperature increase up to 2300 K). Finally, the experimental results have shown that the transition from passive to active regime occurs at higher temperature for β-SiC than for α-SiC and that the mass loss rate of β-SiC is lower than the one measured for α-SiC on the common temperature range investigated (up to 2100 K).

Eric Bêche

Papers

Ce 3d XPS investigation of cerium oxides and mixed cerium oxide (CexTiyOz)

Investigation of Perovskite Structures as Oxygen-Exchange Redox Materials for Hydrogen Production from Thermochemical Two-Step Water-Splitting Cycles

Removal of Lead (Pb) by Hydroxyapatite Sorbent

Hardness and stiffness of amorphous SiCxNy chemical vapor deposited coatings

High temperature oxidation of SiC under helium with low-pressure oxygen—Part 1: Sintered α-SiC