Review on the utilisation of sensing materials for intrinsic optical NH3 gas sensors

TiO2 Hollow Nanofiber/Polyaniline Nanocomposites for Ammonia Detection at Room Temperature

“…Their mixing generates a hybrid structure that presents characteristic of p-n heterojunction, where the creation of an electric field facilitates the charge transfer within the structure, which in turn allows sensor operation at room temperature [51] . With the adsorption of NH 3 in the structure, the polymer will lose some H + , creating vacancies (holes) during the formation of NH 4 + (Figure 9 (a)) [52,53] . In this step, the electron recombination process will occur with an increase of charge carriers mainly in the LUMO band of TiO 2 to the LUMO band of PANI (creating electron-hole pairs) [54] , resulting in the observed increase of electrical resistance.…”

Poly(3,4-ethylenedioxythiophene) Electrosynthesis in the Presence of Mixtures of Flexible-Chain and Rigid-Chain Polyelectrolytes

“…Conductive polymers (CPs) such as poly (3,4-ethylenedioxythiophene) (PEDOT), polyaniline (PANI) and polypyrrole reveal a unique combination of physicochemical, electrochemical, optical and magnetic characteristics that make them promising for use as antistatic or conductive coatings, components of electrochromic, electroluminescent and organic photovoltaic devices, supercapacitors, chemical and biological sensors [1]. This is the main reason for the intensive research and development of such materials.…”

“…Besides the change in conductivity, the doping of a CP leads to a change in the electronic structure of the CP that is accompanied by a change in the optical properties in the UV, visible and near-IR (UV-Vis-NIR) regions. This allows them to be used in electrochromic displays and optical sensors for gaseous or liquid substances [2,3].…”

“…In the majority of ammonia sensors based on CP films, two popular sensing techniques are used: chemiresistive and optical methods [3,[17][18][19][20]. The use of the optical detection method has a number of significant advantages, such as reduced influence of humidity on the operation of the detector, insensitivity to electromagnetic and radiation fields and remote control-the ability to transmit an analytical signal without distortion over long distances [3,18,19,21]. In comparison to most sensors based on metal oxides, sensors based on CPs have good mechanical properties and stability in air, as well as sensitivity at room temperature [3,[17][18][19].…”

“…The use of the optical detection method has a number of significant advantages, such as reduced influence of humidity on the operation of the detector, insensitivity to electromagnetic and radiation fields and remote control-the ability to transmit an analytical signal without distortion over long distances [3,18,19,21]. In comparison to most sensors based on metal oxides, sensors based on CPs have good mechanical properties and stability in air, as well as sensitivity at room temperature [3,[17][18][19].…”