Electrical Impedance of V 2 O 5 /POMA Hybrid Film Deposited by Casting for Application in Ammonia Gas Sensor
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https://doi.org/10.1007/s11664-020-08587-9 2020 The Minerals, Metals & Materials Society
ORIGINAL RESEARCH ARTICLE
Electrical Impedance of V2O5/POMA Hybrid Film Deposited by Casting for Application in Ammonia Gas Sensor M.O. DINIZ,1 R.S. COELHO,2 R.F. BIANCHI,2 and E.M. GUERRA
1,3
1.—Universidade Federal de Sa˜o Joa˜o Del-Rei - UFSJ, Ouro Branco, Minas Gerais CEP 36420-000, Brazil. 2.—Universidade Federal de Ouro Preto - UFOP, Ouro Preto, Minas Gerais 35400-000, Brazil. 3.—e-mail: [email protected]
The sensitivity evaluation of a vanadium pentoxide/poly-o-methoxyaniline hybrid material (V2O5/POMA) using casting deposition for the preparation of an ammonia gas sensor was investigated herein. V2O5/POMA was produced by the intercalation of V2O5 via sol–gel and o-methoxyaniline monomers. V2O5/ POMA thin film deposition onto electrodes was performed by casting. The electrical studies confirmed that V2O5/POMA exhibited increased complex impedance as a function of increasing ammonia concentration. The conductivity of the film decreased with increasing ammonia concentration due to the de-doping process. According to theoretical adjustment, a significant increase in the bulk and interfacial electrical resistance in the presence of ammonia was observed. The combination of these effects contributed to the high sensitivity of the prepared film in both the real and imaginary components of the complex impedance for ammonia gas in a range of 0 to 100 ppm, which indicated that the film is a good candidate for use as an ammonia sensing material. Key words: V2O5/POMA, casting deposition, sensitivity, ammonia gas sensor
INTRODUCTION Several gases, including NH3, NOx, CO, and CO2, are released from industrial processes, poultry sheds, and vehicles, causing hazardous health risks.1–3 Ammonia gas is a toxic pollutant that causes respiratory problems as well as skin and eye irritation at concentrations of > 25 ppm.2 According to the Occupational Safety and Health Administration, the exposure limit for ammonia is 50 ppm (8 h per day), and the maximum exposure tolerance is 500 ppm.4–7 Owada et al.8 showed that ammonia concentrations of > 5 ppm in poultry sheds caused losses at the production stage and high mortality. Therefore, the development of novel disposables for gas sensors with high sensitivity, selectivity, and facility-wide operation9 is needed. Several materials are available for the detection of ammonia gas, such
(Received May 27, 2020; accepted October 22, 2020)
as POMA polymer, and can be used since this gas promotes POMA deprotonation and consequently causes a reduction in its conductivity. The polymer doping and de-doping process is reversible, and in contact with air, the ammonia gas is evaporated and the POMA returns to the protonated state.10 The protonation/deprotonation process in the presence of POMA ammonia is shown in Scheme 1. Vanadium pentoxide/polyaniline (V2O5/PANI) and vanadium pentoxide/poly-o-methoxyaniline (V2O5/POMA) hybrid materials11,12 can also be used to improve the performance of an amm
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