Ammonia sensors based on sensitive polyaniline films
TL;DR: In this paper, a new type of ammonia sensor with polyaniline (electroconducting polymer) as the sensitive element is proposed, which is characterized by high sensitivity, wide range of measured concentrations and high stability of electrical parameters.
Abstract: We propose a new type of ammonia sensor with polyaniline (electroconducting polymer) as the sensitive element. Such sensors are characterized by high sensitivity, wide range of measured concentrations (1–2000 ppm) and high stability of electrical parameters. The use of polyaniline ensures high chemical stability of the sensors in oxidizing ambients. A sensor design based on a silicon chip custom-packed into a linear plastic case is presented. The chip is provided with a system of heaters and thermometers to check the temperature regime of sensor operation. We have studied I – V curves, temperature, concentration and kinetic characteristics of the sensors, as well as their ageing. The possibility for thermoregeneration of the sensor parameters after long-term functioning in an ammonia ambient is emphasized.
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TL;DR: In this article, a survey of sensors and sensor systems for gaseous ammonia is presented, where the authors present different application areas for ammonia sensors or measurement systems and different techniques available for making selective ammonia sensing devices.
Abstract: Many scientific papers have been written concerning gas sensors for different sensor applications using several sensing principles. This review focuses on sensors and sensor systems for gaseous ammonia. Apart from its natural origin, there are many sources of ammonia, like the chemical industry or intensive life-stock. The survey that we present here treats different application areas for ammonia sensors or measurement systems and different techniques available for making selective ammonia sensing devices. When very low concentrations are to be measured, e.g. less than 2 ppb for environmental monitoring and 50 ppb for diagnostic breath analysis, solid-state ammonia sensors are not sensitive enough. In addition, they lack the required selectivity to other gasses that are often available in much higher concentrations. Optical methods that make use of lasers are often expensive and large. Indirect measurement principles have been described in literature that seems very suited as ammonia sensing devices. Such systems are suited for miniaturization and integration to make them suitable for measuring in the small gas volumes that are normally available in medical applications like diagnostic breath analysis equipment.
1,351 citations
TL;DR: In this article, a review of gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers has been reviewed.
Abstract: The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.
1,333 citations
Cites background from "Ammonia sensors based on sensitive ..."
...When adsorption/desorption is the preponderant step, sensitivity will dwindle down as temperature increases [16, 18, 75, 204, 210, 233]....
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TL;DR: In this article, a new interfacial polymerization method for the synthesis of polyaniline nanofibers was used and compared with conventional polyanile sensors, and five different response mechanisms were explored: acid doping (HCl), base dedoping (NH3), reduction (with N2H4), swelling (with CHCl3), and polymer chain conformational changes (induced by CH3OH).
Abstract: Using a new interfacial polymerization method for the synthesis of polyaniline nanofibers, we have developed nanofiber sensors and compared them to conventional polyaniline sensors. Five different response mechanisms are explored: acid doping (HCl), base dedoping (NH3), reduction (with N2H4), swelling (with CHCl3), and polymer chain conformational changes (induced by CH3OH). In all cases, the polyaniline nanofibers perform better than conventional thin films. Their high surface area, porosity and small diameters enhance diffusion of molecules and dopants into the nanofibers.
1,041 citations
TL;DR: In this article, different synthesis routes and deposition methods of polyaniline (PANi) as sensitive layer, as well as the various techniques to monitor the gas adsorption on polyanoiline are reviewed.
460 citations
TL;DR: In this article, a novel approach toward development of advanced chemical sensors based on chemically functionalized single-walled carbon nanotubes (SWNTs) was demonstrated for detection of NH3.
Abstract: This study demonstrates a novel approach toward development of advanced chemical sensors based on chemically functionalized single-walled carbon nanotubes (SWNTs). SWNTs with covalently attached poly(m-aminobenzene sulfonic acid), SWNT-PABS, have shown improved sensor performance for detection of NH3. Compared to purified SWNTs, devices fabricated with SWNT-PABS have shown more than 2 times higher change of resistance upon exposure to NH3. Importantly, the SWNT-PABS sensors rapidly recover their resistance when NH3 is replaced with nitrogen. Exposure to NH3 induces significant changes in the electronic structure of SWNT-PABS, which allow detection of NH3 at concentrations as low as 5 ppm. Thin film deposited between interdigitated electrodes was explored as a device configuration for development of gas sensors.
344 citations
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05 Oct 2014
TL;DR: In the last fifteen years, there has been a noticeable shift towards impure semiconductors -a shift which came about because it is precisely the impurities that are essential to a number of major semiconductor devices as discussed by the authors.
Abstract: First-generation semiconductors could not be properly termed "doped- they were simply very impure. Uncontrolled impurities hindered the discovery of physical laws, baffling researchers and evoking pessimism and derision in advocates of the burgeoning "pure" physical disciplines. The eventual banish ment of the "dirt" heralded a new era in semiconductor physics, an era that had "purity" as its motto. It was this era that yielded the successes of the 1950s and brought about a new technology of "semiconductor electronics." Experiments with pure crystals provided a powerful stimulus to the develop ment of semiconductor theory. New methods and theories were developed and tested: the effective-mass method for complex bands, the theory of impurity states, and the theory of kinetic phenomena. These developments constitute what is now known as semiconductor phys ics. In the last fifteen years, however, there has been a noticeable shift towards impure semiconductors - a shift which came about because it is precisely the impurities that are essential to a number of major semiconductor devices. Technology needs impure semiconductors, which unlike the first-generation items, are termed "doped" rather than "impure" to indicate that the impurity levels can now be controlled to a certain extent."
1,243 citations
TL;DR: The considerable progress which has been made in characterizing and understanding the properties of polyaniline derived from aniline is discussed and the progress towards technological applications is evaluated.
460 citations
TL;DR: In this paper, solid-state semiconductor gas sensors based on organic sensor elements are reviewed and compared to metal-oxide devices in their sensitivity to toxic gases and their ability to operate at or near room temperature.
Abstract: Recent results with solid-state semiconductor gas sensors based on organic sensor elements are reviewed. Devices based on metal phthalocyanines show useful responses to NO2. Lead phthalocyanine combines the highest conductivity with the maximum sensitivity to NO2. A thin-film lead phthalocyanine sensor has successfully been used to monitor NOx produced by shot-firing in coal mines. To obtain reasonable conductance and speed of response and recovery, phthalocyanine sensors have been operated at 170°C. Conducting polymer materials, and particularly chemically doped polypyrrole, show responses to toxic gases at ambient temperature. Initial work, using polypyrrole black impregnated filter paper, showed a response to ammonia. More recently, using polypyrrole films electrochemically deposited over electrode arrays, responses to nitrogen dioxide and hydrogen sulphide have also been obtained. Organic-semiconductor gas sensors may have advantages compared to metal-oxide devices in their sensitivity to toxic gases and in their ability to operate at or near room temperature. However, the mechanisms of device function are not yet well understood.
336 citations
TL;DR: In this article, a lifetime of 60 days has been reported for ECP-based biosensors, where the enzyme (glucose oxidase) was included with an anionic electron relay.
Abstract: Electroconducting conjugated polymers, ECPs, appear very attractive for use in sensors either as sensitive components or as a matrix for easy immobilization of specific substrates. This is due to their intrinsic properties: a one-step electrosynthesis in the form of an adherent film deposited at the surface of the electrode with anionic species being included by doping. This doping reaction makes it possible to modulate the conductivity reversibly over several orders of magnitude via redox interactions. ECP-based gas sensors are sensitive to gases (NO2, NH3, etc.) affecting the doping level, which results in a straightforward conductance monitoring. ECP-based ionic sensors amperometrically detect electroinactive ions, since the doping of the ECP results in a current flow. The ion-sieving effect allows some selectivity by cut-off size. SGFET microelectrochemical 'transistor' devices are sensitive to pH. Immobilization with a good 'electrical wiring' of enzymes in ECP films explains the increasing interest in research on ECP-based biosensors. An interesting approach is the simultaneous inclusion of the enzyme (glucose oxidase) with an anionic electron relay. A lifetime of 60 days has been reported. The versatile properties of ECP promise improvements in specificity, enzyme wiring and lifetime.
249 citations