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.

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Gas Sensors Based on Conducting Polymers

This article gives an overview of the application of nanomaterials in environmental remediation. In the area of environmental remediation, nanomaterials offer the potential for the efficient removal of pollutants and biological contaminants. Nanomaterials in various shapes/morphologies, such as nanoparticles, tubes, wires, fibres etc., function as adsorbents and catalysts and their composites with polymers are used for the detection and removal of gases (SO2, CO, NOx, etc.), contaminated chemicals (arsenic, iron, manganese, nitrate, heavy metals, etc.), organic pollutants (aliphatic and aromatic hydrocarbons) and biological substances, such as viruses, bacteria, parasites and antibiotics. Nanomaterials show a better performance in environmental remediation than other conventional techniques because of their high surface area (surface-to-volume ratio) and their associated high reactivity. Recent advances in the fabrication of novel nanoscale materials and processes for the treatment of drinking water and industrial waste water contaminated by toxic metal ions, radionuclides, organic and inorganic solutes, bacteria and viruses and the treatment of air are highlighted. In addition, recent advances in the application of polymer nanocomposite materials for the treatment of contaminants and the monitoring of pollutants are also discussed. Furthermore, the research trends and future prospects are briefly discussed.

A review on nanomaterials for environmental remediation

As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with:  (a) increased suppression of the known spiral spin structure (period length of ∼62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.

Size-Dependent Magnetic Properties of Single-Crystalline Multiferroic BiFeO3 Nanoparticles

Polymers in sensor applications

(1976). Nuclear Tracks in Solids (Principles and Applications) Nuclear Technology: Vol. 30, No. 1, pp. 91-92.

Nuclear Tracks in Solids (Principles and Applications)

Nanocomposites of iron oxide and polypyrrole were prepared by simultaneous gelation and polymerization process. This resulted in the formation of mixed iron oxide phase for lower polypyrrole concentration, stabilizing to a single cubic iron oxide phase at higher polypyrrole concentration. The composites in the pellet form were used for humidity and gas sensing investigations. Their sensitivity to humidity was found to increase with increasing concentration of polypyrrole. Gas sensing was performed for CO2, N2 and CH4 gases at varying pressures. The sensors showed a linear relationship between sensitivity and pressures for all the gases studied. The sensors showed highest sensitivity to CO2 gas.

Gas and humidity sensors based on iron oxide–polypyrrole nanocomposites

Here we present, a useful ammonia (NH3) gas sensor based on polyaniline (PANI) film as an active sensing layer. The PANI films were successfully deposited on a polyethylene terephthalate (PET) flexible substrate by a simple in-situ polymerization technique. Ammonia (NH3) gas-sensing properties of the films prepared at optimum conditions were examined at room temperature in the range of 5–1000 ppm. The room temperature functioning of the sensor is critical, which facilitates low-power operation and also enhances the life time of a sensor. The observed variation in resistance of PANI film corresponding to 1000 ppm and 200 ppm of NH3 exposure, is approximately 520 and 110 times of that observed for ∼5 ppm of NH3. Furthermore, good reproducibility and long-term stability were also observed over a concentration range from 5 to 1000 ppm. Moreover the sensor is mechanically robust and can be bent sharply without damage, demonstrating excellent mechanical stability and exhibiting no lack in performance even after several bending cycles. These results indicate that the PANI films on flexible substrates are promising for portable on-site detection.

Flexible room temperature ammonia sensor based on polyaniline

An attempt has been made toward the chemical synthesis of poly(aniline-co-o-anisidine). It has been found that this conducting polymer is soluble in common organic solvents such as acetone, DMF, THF, and NMP at room temperature. The characterization of poly(aniline-co-o-anisidine) has been carried out using FTIR, UV-visible, DSC, and electrical conductivity measurements

S. Annapoorni

Papers

Gas and humidity sensors based on iron oxide–polypyrrole nanocomposites

Flexible room temperature ammonia sensor based on polyaniline

Synthesis and characterization of poly(aniline-co-o-anisidine) : a processable conducting copolymer

Humidity-sensing properties of nanocrystalline haematite thin films prepared by sol-gel processing

Immobilization of urease on poly(N-vinyl carbazole)/stearic acid Langmuir-Blodgett films for application to urea biosensor.