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.