A High-Temperature Electrochemical Carbon Monoxide Sensor with Nanostructured Metal Oxide Electrode

Carbon monoxide (CO) is one of the major air pollutants which are emitted due to the incomplete combustion of hydrocarbon fuels. It is a colorless, odorless and tasteless gas that is highly toxic to humans and animals. Hence, a CO sensor not only serves as an alarm system for threat of CO, but also be used for monitoring the combustion process to improve the combustion efficiency. The currently existing technologies to detect CO such as gas chromatography and optical absorption spectrometry are cumbersome, costly, and lack the capability of on-line monitoring. Thus there is a critical need for developing CO sensors that can give accurate and fast response to change in the concentrations of CO as low as 20 ppm at high temperature (\u3e 500 °C).;In the present work, La0.8Sr0.2MnO3 (LSM) nanofibers were prepared by electrospinning method and utilized as a mixed potential sensor electrode for sensing CO at high temperature. The nanofibers show good thermal stability even after heat treatment at 1050 °C. This nano-fibrous structure possesses several advantages such as high porosity, high surface to volume ratio and high activity towards CO electrochemical oxidation. The nanofibers bring improved sensitivity and lower the limit of detection as compared with bulk LSM powders. Electrochemical impedance (EIS) analysis indicated that the nano-fibrous electrode shows better charge transfer capability, leading to improved catalytic activity for CO oxidation and sensor performance. The developed sensor can be used for monitoring emissions from coal-fired power plants and vehicle exhausts

Novel Enhancements and Analytical Applications of Amperometric Nitric Oxide (NO) Sensors

Improvements to the selectivity of the Shibuki-design and solid-polymer electrolyte (SPE) based amperometric NO sensors are described in this dissertation. Novel applications of SPE-based NO sensors are also demonstrated with results compared with those obtained using chemiluminescence as a reference method. The selectivity with respect to aqueous-phase interfering species of Shibuki-type sensors is substantial; however, certain gas-phase species such as CO are major interferences. By increasing the pH of the internal electrolyte solution, the selectivity of Shibuki-design sensors vs. CO can be improved by up to 100-fold (Chapter 2). This improvement is the result of more extensive Pt-oxides formed on the electrode surface that inhibits CO adsorption. Gas-phase detection of NO requires a high surface area electrode, which can be deposited into the surface of a solid-polymer electrolyte (SPE) such as Nafion (Chapter 3). Pt-Nafion sensors exhibited excellent performance with a limit of detection (LOD) of 4.3 ± 1.1 ppb and response time under 5 s. Detection of NO released from NO-donor doped biomedical polymer films and electrochemically reduced nitrite solutions was performed using Pt-Nafion sensors and repeated using chemiluminescence. Strong agreement was found for both the NO-releasing films and the electrochemically reduced nitrite solution. In Chapter 4, several strategies were explored to enhance the selectivity of the Pt-Nafion sensors. Filtration of the sample gas was shown to be promising for the removal of CO (using an activated carbon fiber filter) and NH3 (using various acid traps) although further optimization of conditions is needed. Sampled current/sensitivity voltammetry of NO, CO and NH3 did not reveal a potential range with substantially improved selectivity and applying the principles developed in Chapter 2 (elevated internal electrolyte) also proved ineffective because Nafion cannot transport anions such as OH- or NO2-. Despite the current selectivity limitations, Pt-Nafion sensors have other useful applications (Chapter 5). The determination of nitrite and GSNO was examined with LOD of 26±5 nM and 17±10 nM, respectively. NO delivered by a cost-effective inhaled nitric oxide therapy (INO) system was monitored with no adverse effects from altering O2 concentration. NO2 sensing and scrubbing were also developed as potential safety measures.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133344/1/zzhen_1.pd

Development of gas sensors for binary mixtures and solvent-free sample preparation techniques based on polymeric membranes

Tese de doutoramento. Engenharia Química. 2005. Faculdade de Engenharia. Universidade do Port

Soil and soil breathing remote monitoring: A short review

The efficiency of agricultural use of soils depends directly on their quality indicators, which include an extended set of characteristics: from data of the environmental situation to the component composition of the soil air. Therefore, for a more complete survey of agricultural land in order to determine their qualitative indicators and subsequent application, it is necessary to carry out comprehensive monitoring while simultaneously studying the characteristics of soils and their air composition. The article is devoted to the literature analysis on the remote monitoring of soils and soil air. Particular attention was paid to the relationship between soil type and soil air composition and it was found that the soil air composition (in the combination with pH and humidity parameters) can assess the type, quality and environmental condition of soils. Since when developing a remote monitoring system of soil air soil moisture and soil structure significantly affect the processes occurring in soils, and ultimately the quantitative composition of soil air, it is very important to know the dependence of the soil air composition on the type and quality of the soil itself, the influence of moisture, structure and other parameters on it. It was shown that the use of sensors is a promising direction for the development of the soils and soil air remote monitoring. It was indicated that soil and soil air remote monitoring in real time will provide reliable, timely information on the environmental status of soils and their quality. Commercial sensors that can be used to determine CO2, O2, NOx, CH4, CO, H2 and NH3 were considered and the technique for sensor signal processing was chosen. A remote monitoring system with the use of existing commercial sensors was proposed, the movement of which can be realized with the help of quadcopter, which will allow parallel scanning of the soils and the land terrain. Such a system will make it possible to correctly assess the readiness of soils for planting, determine their intended use, correctly apply fertilizers, and even predict the yield of certain crops. Thereby, this approach will create a modern on-line system for full monitoring of soil, land and rapid response in the case of its change for the agro-industrial sector

A new LED-LED portable CO2 gas sensor based on an interchangeable membrane system for industrial applications

A new system for CO2 measurement (0-100%) by based on a paired emitter-detector diode arrangement as a colorimetric detection system is described. Two different configurations were tested: configuration 1 (an opposite side configuration) where a secondary inner-filter effect accounts for CO2 sensitivity. This configuration involves the absorption of the phosphorescence emitted from a CO2-insensitive luminophore by an acid-base indicator and configuration 2 wherein the membrane containing the luminophore is removed, simplifying the sensing membrane that now only contains the acid-base indicator. In addition, two different instrumental configurations have been studied, using a paired emitter-detector diode system, consisting of two LEDs wherein one is used as the light source (emitter) and the other is used in reverse bias mode as the light detector. The first configuration uses a green LED as emitter and a red LED as detector, whereas in the second case two identical red LEDs are used as emitter and detector. The system was characterised in terms of sensitivity, dynamic response, reproducibility, stability and temperature influence. We found that configuration 2 presented a better CO2 response in terms of sensitivity

Application of a portable FTIR for measuring on-road emissions

The objective of this work was the development of an onroad in-vehicle emissions measurement technique utilizing a relatively new, commercial, portable Fourier Transform Infra-Red (FTIR) Spectrometer capable of identifying and measuring (at approximately 3 second intervals) up to 51 different compounds. The FTIR was installed in a medium class EURO1 spark ignition passenger vehicle in order to measure on-road emissions. The vehicle was also instrumented to allow the logging of engine speed, road speed, global position, throttle position, air-fuel ratio, air flow and fuel flow in addition to engine, exhaust and catalyst temperatures. This instrumentation allowed the calculation of massbased emissions from the volume-based concentrations measured by the FTIR. To validate the FTIR data, the instrument was used to measure emissions from an engine subjected to a real-world drive cycle using an AC dynamometer. Standard analyzers were operated simultaneously for comparison with the FTIR and the standard analyzer results showed that most pollutants (NOx, CO2, CO) were within ~10% of a standard analyzer during steady state conditions and within 20% during transients. The exception to this was total HC which was generally 50% or less than actual total HC, but this was due to the limited number of hydrocarbons measured by the FTIR. In addition to the regulated emissions, five toxic hydrocarbon species were analyzed and found to be sensitive to cold starts in varying proportions. Finally, FTIR data was compared to results from a commercially available on-road measurement system (Horiba OBS- 1000), and there was good agreement

Design and evaluation of the emissions measurement components for a heavy-duty diesel-powered vehicle mobile emissions measurement system (MEMS)

The objective of this study was the design, construction, and preliminary qualification of the Mobile Emissions Measurement System (MEMS) for in-use, on-road testing of heavy-duty diesel-powered vehicles. This included selection of emissions analyzers and sampling system components capable of producing emissions results of similar accuracy to those attained with laboratory-grade instruments. A thorough investigation of commercially available systems, and a literature review, identified no suitable designs. Therefore, a complete emissions measurement system, designed specifically for the testing of heavy-duty diesel powered vehicles, was developed using available components.;The candidate analyzers that performed successfully during bottled gas bench tests were then incorporated into a sampling system and tested with diesel engine exhaust. Emissions concentrations reported by the MEMS were compared to concentrations reported by laboratory-grade analyzers. Results indicated that the system is capable of reporting cycle-integrated, brake-specific CO2 within 3%, and NOx within 5% of laboratory data over an FTP cycle