Experimental investigations on liquefied petroleum gas sensing of Cd(NO3)2·(AAm)4·2H2O and CdS/polyacrylamide synthesized via frontal polymerization

This paper reports an experimental investigations on comparative assessment of CdS/polyacrylamide and Cd(NO3)2·(AAm)4·2H2O thick films for LPG sensing at room temperature. For synthesis of nanoparticles of CdS in polymer matrix, we used frontal polymerization of cadmium nitrate acrylamide complex Cd(NO3)2 (CH2CHCONH2)4(H2O)2 (CdAAm). According to IR spectroscopy in the spectra of polymeric CdS/AAm, there are absorption bands corresponding to stretching vibrations of OH and NH groups. The absence of absorptions bands of the ν (CC) and δ (CH) at 1580 and 980 cm−1 confirms the assumption of the CC bonds during polymerization. The formation of CdS nanoparticles was proved by X-ray diffractometry. The diffuse diffraction maxima and line broadening indicate that the sample contains nanoparticles. The crystallite size of the CdS/polyacrylamide was found ∼30 nm. Thick films of these metallopolymers were made by screen printing technique on alumina substrate and these were stabilized for 6 h at 80 °C. Further the films were annealed at 450 °C for 2 h. Silver contacts were made on both sides of the films for signal registration, and these films were used as gas sensing elements. Each film was put inside a gas chamber having a gas inlet and an outlet for measurements of LPG sensing characteristics. Variations in electrical resistance of the films with time for different concentrations of LPG were recorded. More variations in resistance were found for Cd(NO3)2·(AAm)4·2H2O as comparison to CdS/polyacrylamide. The maximum values of the sensitivities was 1.3 and 3.7 GΩ/min respectively, for CdS/polyacrylamide and Cd(NO3)2·(AAm)4·2H2O for 5 vol.% of LPG. The reproducibility of the sensor made of Cd(NO3)2·(AAm)4·2H2O after 1 month for 5 vol.% of LPG was found to be 97%.