Hierarchical MnO2 Nanoflowers based Efficient Room Temperature Alcohol Sensor

In the present work, hierarchical 3-D MnO2 nanoflowers (consisting of 2D nanosheets) were synthesized employing hydrothermal technique and subsequently alcohol sensing performance of the same was investigated. The morphological (FESEM, Transmission Electron Microscopy), and surface compositional (X-ray Photoelectron Spectroscopy) characterizations were carried out. Lattice fringe of TEM image confirmed that constituents of 3-D nanoflower to be birnessite (i.e. delta-MnO2) 2-D nanosheets. In addition, core level XPS spectra validated the presence of mixed valence state of Mn (i.e. Mn3+ and Mn(4+)states) in the MnO2 NFs. Further, Electrochemical Impedance Spectroscopy measurement (Mott Schottky analysis) revealed that the n-type conductivity of MnO2 NFs based sensing layer. It is clearly observed from the transient response characteristics that the device offered promising room temperature sensing performance towards alcohols (i.e. methanol, ethanol and 2-propanol). However, the device offered better sensing performance towards methanol than that of ethanol and 2-propanol. The response time and recovery time of the sensor also found to be moderately fast at room temperature. Interestingly, the device resistance was increased in presence of reducing vapor (although MnO2 NFs is a n-type material).