Doped Polyaniline for Gas Sensors for the Detection of Formaldehyde
Stewart, Katherine Mariann Elizabeth
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Formaldehyde is one of the main gases that contribute to poor indoor air quality since it is so widely used in the manufacturing of goods. Over time, formaldehyde leaches out of various materials and reduces the quality of air. Formaldehyde, even at very low concentrations, can cause respiratory problems and a general feeling of unwellness. The World Health Organization (WHO) states that formaldehyde exposure should not exceed 0.08 ppm over a 30 minute period. Therefore, formaldehyde sensors are needed to ensure optimal indoor air quality. Polyaniline (PANI), as well as PANI doped with NiO or NiO and Al2O3, were tested to determine their suitability as sensing materials for formaldehyde. It was found that at higher concentrations of formaldehyde (above 1 ppm), PANI doped with 5% NiO and 15% Al2O3 was the most suitable sensing material with respect to both sensitivity and selectivity. At lower concentrations (below 1 ppm), however, PANI doped with 5% NiO and 15% Al2O3 did not detect formaldehyde. PANI doped with 15% NiO only was a much better option since it was able to detect the highest concentration of formaldehyde at very low concentrations (0.09 ppm) and still have moderate selectivity. A special test system was designed that could test single or multiple gases at various concentrations. Ethanol, acetaldehyde and benzene were chosen as interferents for formaldehyde and nitrogen was used to dilute the gases to achieve lower concentrations. A specialized gas chromatograph (GC) was used to determine the amount of gas or analyte that interacted with the sensing material being tested. Replicate polymer samples of varying dopant concentrations were tested with different gases at different concentrations and statistically analyzed. Both sensitivity and selectivity towards formaldehyde was taken into consideration. Among all tests conducted with single and multiple gases, it was concluded that PANI doped with 5% NiO and 15% Al2O3 was the best sensing material at high concentrations of formaldehyde (above 1 ppm), whereas PANI doped with 15% NiO was the best sensing material at low concentrations (below 1 ppm).