Chemi-resistive sensing of methylamine species using twinned α-MoO3 nanorods: Role of grain features, activation energy and surface defects

Detection of methylamines is primarily associated with the quality assessment of seafood. In this context, we report chemi-resistive sensing of methylamine species using α-MoO3 nanorods synthesized via microwave technique. Investigations were carried out by varying the microwave irradiation power to 300, 450, and 800 W, respectively. Along with the effect of microwave power, the influence of the calcination process on the growth patterns has been emphasized. The un-calcined samples exhibited the formation of triclinic phased ammonium molybdenum oxide ((NH4)8 Mo10O34), whereas it gets transformed into orthorhombic phased α-MoO3 upon calcination. The surface morphology of the un-calcined samples showed the formation of aggregated nanogranular morphology, whereas the calcined samples disclosed the formation of densely populated nanorods. These nanorods were found to be grown with a controlled aspect ratio and twinning dislocations. The influence of twinning dislocations on the grain features and activation energy is reported. The calcined sample prepared at 450 W showed a maximum sensing response of S = 413 towards 200 ppm of trimethylamine (TMA, (CH3)3NH) at room temperature. The observed response towards TMA was 8 times and 5.5 times higher than that of the response observed for monomethylamine (MMA, (CH3) NH2)) and dimethylamine (DMA, (CH3)2NH)) respectively. Response/recovery times were found to be 23/12 s, 38/13 s, and 35/11 s towards 1 ppm of MMA, DMA, and TMA, respectively.