Structural, optical, elastic and humidity sensing properties of magnesium ferrite - polyaniline nanocomposites

Abstract

Polyaniline (PANI) is most suited material for humidity sensing, but has its own limitations. Nanocomposites of magnesium ferrite (MgF) and Polyaniline have been synthesized using sol gel auto combustion method; to improve the overall properties and stability. Samples were characterized using the standard XRD, FTIR, UV-Vis spectroscopy, SEM, EDS, BET and BJH techniques to explore their structural, optical, elastic and humidity sensing properties. XRD revealed cubic spinel structure of magnesium ferrite without much variation in lattice parameter and a semicrystalline nature of PANI. Crystallite size showed a variation from 12 nm to 17 nm obtained using XRD data by various methods including Scherrer, Williamson-Hall (W-H), Size-strain plot and Halder-Wagner methods. Intrinsic strain, stress, energy density of prepared samples were calculated using different models of W-H method. FTIR spectra shows shift in band position for specific ferrite content indicating interaction between ferrite and PANI. SEM micrographs exhibit pronounced effect on microstructure due to change in composition. EDS data confirms the phase purity as revealed by XRD earlier. Energy band gap obtained using UV-Vis spectroscopy shows decrement from 1.75 eV to 1.41 eV. Elastic and anisotropic properties of the nanocomposites including elastic moduli, acoustic wave velocities, directional dependency of Young’s modulus, elastic anisotropy indices, etc. have been discussed at length correlating the XRD and FTIR data. Humidity sensing properties have been investigated by measuring humidity dependent change in impedance. The sensing mechanism considering synthesis process, change in intrinsic conductivity of PANI, Grotthuss mechanism have been discussed at length. Results of humidity sensing parameters like hysteresis, sensitivity, stability, response and recovery time, etc. have reveal that change in composition has a momentous effect giving maximum sensitivity of 98.2%, applicability over a large humidity range, lowest response and recovery times of 3 and 12 seconds respectively.