A non-isothermal thermokinetic degradation study of the mesoporous Ni–Co layered double hydroxide using isoconversional approaches

Abstract

The present study describes the phenomenological thermokinetic behavior of the mesoporous Ni–Co layered double hydroxide (LDH) and determines three basic parameters called ‘kinetic triplets’. The non-isothermal kinetic heating program was carried out at four different heating rates, viz. 5,10,15, and 20oC.min−1, respectively, in the temperature range of 50−800oC. Various isoconversional or model-free kinetics involving integral and differentials like Kissinger–Akahira–Sunose, Flynn-Wall-Ozawa, Friedman, and non-linear Vyazovkin methods were utilized. Due to the presence of physisorbed gas or moisture phases, the temperature integral from 50−198oC was excluded from the present study. The experimental and simulation results described the consistency in depicting the effective activation energies by either Friedman or non-linear Vyazovkin isoconversional methods. Also, it was observed that the variation in activation energies was found to differ by 9–10%, which confirms the Ni–Co LDH degradation undergoes a kinetically complex process. The evaluation of the preexponential factor and master plot determination of reaction models f(α) showed that the mesoporous Ni–Co LDH degradation pathway strongly depends on kinetic compensation effect and undergoes a reaction process governed by nucleation models. Furthermore, the kinetics of pseudo-components of Ni–Co LDH (mathematical deconvolution analysis) showed that the second (three subtransitions) and third stage (two subtransitions) degradation process are controlled by a number of individual peak components in the thermodynamic temperature range 536–727 K (second) and 727–803 K (third).