Undoped and Mn-doped Co3O4 nanorods for ethanol sensing

Undoped and Mn-doped (1 at.%) Co3O4 were synthesized by simple precipitation method. The morphology of the material was investigated by scanning electron microscopy which confirmed the formation of nanorods (NRs). The NRs were formed from interconnected nanoparticles. X-ray diffraction analysis confirmed the presence and crystalline nature of the Co3O4 NRs. FTIR studies revealed that the defects are present in undoped Co3O4. Raman spectra confirmed the presence of five Raman active modes and the doping of Mn shifts the Raman peaks to higher wave number. Spectral responses of clad modified fiber optic gas sensor are studied for various concentrations (0-500 ppm) of ethanol at room temperature, where the clad portion is replaced with undoped and Mn-doped Co3O4 and used as gas sensing material. Since the refractive index of the samples calculated from UV-Vis absorption spectra is greater than that of core, the fiber optic sensor works under leaky mode condition. The sensor showed linear variation in the spectral peak intensity with ethanol concentration. Undoped Co3O4 exhibits higher sensitivity compared to Mn-doped Co3O4 due to defects present in the undoped sample which offers more reactive sites for ethanol adsorption.