Kinetics Study of the Solid State Reaction of Iron(III)Citrate Leading to Hematite Nanoparticles

Abstract

Background: Thermal decomposition of iron-bearing organic complexes is a useful way to prepare iron oxides. Iron(III)citrate, FeC6H5O7, is a precursor for hematite (α-Fe2O3) synthesis by thermal decomposition technique. However, there is no information available on the nature of the mechanism of the reaction. Objective: Kinetic analysis of the solid-state thermal reaction of Iron(III)citrate, which decomposes to hematite under oxidative reaction atmosphere, has been studied in order to understand the reaction process. Method: Non-isothermal thermogravimetry under multiple heating rates has been employed. The obtained data are analyzed using model-free iso-conversional kinetic techniques in order to estimate the activation energy of reaction and reaction rate. Master plot method has been employed to determine the most-probable reaction mechanism. Reaction rate has been used to estimate the thermodynamic parameters (ΔS*, ΔH* and ΔG*). Decomposed material has been studied by XRD and TEM. Observations: Thermal decomposition of Iron(III)citrate is a three-step process and is completed by ~600 K. The decomposed product obtained is hematite nanomaterial. The estimated activation energy and reaction rate values are strongly dependent on the extent of conversion. The initial two steps of thermal decomposition reaction may involve ‘threedimensional diffusion’ and ‘random nucleation’, whereas the third step may be assigned again to ‘three-dimensional diffusion’. Simulated conversion curves justify the estimated kinetic parameters. A reaction pathway has also been predicted. Keywords: Iron(III)citrate, iso-conversional method, kinetics, thermal decomposition, thermogravimetry, thermal energy.