Solid-State Reaction of Ferrocene Controlled by Co-Precursor and Reaction Atmosphere Leading to Hematite and Cohenite Nanomaterials: A Reaction Kinetic Study

Abstract

The present article investigates the thermal decomposition of ferrocene in the presence of oxalic acid dihydrate in oxidative and inert atmospheres. A mixture of ferrocene and oxalic acid dihydrate on thermal decomposition in O 2 and N 2 atmospheres produces hematite and cohenite nanomaterials, respectively. These decompositions are complex and reflected through multiple overlapped reaction steps in the thermogravimetry profiles, and peak deconvolution method is adopted to separate the reaction steps involved. It is found that the synthesis of hematite is a two-step process, while that of cohenite is a one-step process. Model-free integral isoconversional methods are adopted to estimate the values of activation energy for these thermal reactions. The most probable reaction mechanism and the reaction rate of thermal decomposition are determined by an intercept-based model fitting method. The reaction mechanism is found to be different for different steps. To verify the suitability of the adopted kinetic models, the experimental conversion curves are compared with the reversely constructed ones and the agreement is quite reasonable. The conversion dependence of thermodynamic parameters is obtained using the estimated kinetic parameters. Comparing the estimated values of the kinetic and thermodynamic parameters, the effect of the reaction atmosphere on the thermal decomposition process of ferrocene is realized. Utilizing the kinetic and thermodynamic parameters conversion-dependent nucleation rates of the reaction steps have been estimated. The present study describes how different nanomaterials of iron can be synthesized starting with the same precursor material, how the reaction (solid and gaseous) atmosphere affects the reaction profile and the residual material, and finally, how kinetic calculations help in understanding the solid state reaction process involved. This study suggests the use suitable combination of precursor, co-precursor, and gaseous reaction atmosphere for the solid-state thermal synthesis of iron-based nanoparticles using organo-iron compounds. The study also highlights the successful application of the peak-deconvolution method.

Insights into a co-precursor driven solid-state thermal reaction of ferrocene carboxaldehyde leading to hematite nanomaterial: a reaction kinetic study

“…The peak deconvolution method shows that thermal decomposition of FO 11 takes place in six different steps, where the steps are quite overlapped, while OxA and FcCHO decompose in three and six different steps, respectively, in agreement with earlier reports. 23,25 Table 1 compares the temperature corresponding to the maximum decomposition ( T p ) for each reaction step and the temperature range of steps (Δ T ) for the decomposition of FO 11 , FcCHO and OxA in an O 2 atmosphere. From Fig.…”

“…, they follow multiple consecutive overlapping reaction steps. 21,23,25,52 For a multistep complex process, the overall rate equation is the combination of multiple single-step reactions. 53 To separate the individual steps, the peak deconvolution method is a suitable process.…”

“…S1†). Thus, using the Fraser Suzuki function, 21,23,25 eqn (11) is written aswhere is the conversion rate of the overall process, and h i , p i , s i and w i are the parameters corresponding to the peak amplitude, position, asymmetry and half-width of the i th peak, respectively. After setting the initial values of the fit parameters , an optimization operation is done to minimize F defined aswhere M is the total number of data points under a constant heating rate.…”

“…24 This technique has a number of merits such as synthesis at comparatively low temperature, control by reaction time, temperature and environment, faster reaction, and use of a variety of iron-bearing compounds as precursors and organic compounds as co-precursors. 20–23…”

“…37 Apart from the reaction environment, additional presence of a co-precursor inuences the decomposition process of ferrocene materials, affecting the reaction kinetics. 23,39,40 For a co-precursor driven thermal decomposition, the co-precursor is chosen in such a way that it decomposes prior to the decomposition of the precursor, so that the decomposed products may react with the intermediate decomposed products from the precursor. In a previous article, 25 the kinetics of thermal decomposition of ferrocene carboxaldehyde in an oxidative atmosphere was reported.…”