Anion Exchange Kinetics of Nanodimensional Layered Metal Hydroxides: Use of Isoconversional Analysis

Abstract

Anion exchange reactions of nanodimensional layered metal hydroxide compounds are utilized to create materials with targeted physical and chemical properties and also as a means for controlled release of intercalated anions. The kinetics of this important class of reaction are generally characterized by model-based approaches. In this work, a different approach based on isothermal, isoconversional analysis was utilized to determine effective activation energies with respect to extent of reaction. Two different layered metal hydroxide materials were chosen for reaction with chloride anions, using a temperature range of 30−60 °C. The concentrations of anions released into solution and the changes in polycrystalline solid phases were evaluated using model-based (Avrami-Erofe'ev nucleation−growth model) and model-free (integral isoconversional) methods. The results demonstrate the utility of the isoconversional approach for identifying when fitting to a single model is not appropriate, particularly for characterizing the temperature dependence of the reaction kinetics.

Controlled Release Kinetics in Hydroxy Double Salts: Effect of Host Anion Structure

“…ZC-Ac used here exhibits a spacing between the planes ( -spacing) of 9.43 ± 0.03Å [21] which is comparable to the literature value of 9.46Å [19]. The PXRD patterns for ZC-Ac and exchange products are shown in Figure 2(a).…”

“…A summary of elemental analysis for the nanohybrids is shown in Table 1. From the formulae obtained from elemental analyses, the ratio of copper to zinc in the metal hydroxide layers of ZC-m-HCn (2.8) and ZC-p-HCn (2.5) is comparable to that of the precursor ZC-Ac (2.8) nanohybrid [21]. This may indicate that the exchange reaction in the formation of these compounds was topotactic.…”

Nanostructured biocompatible thermal/electrical stimuli-responsive biopolymer-doped polypyrrole for controlled release of chlorpromazine: Kinetics studies

“…Avrami's equation is another mathematic model originally used to describe the crystallization mechanism (Avrami, 1940;Lorenzo et al, 2007). It has also been used extensively for description kinetic of encapsulation, and ion exchange release recently (Gao et al, 2013;Machingauta and Hossenlopp 2013;Majoni and Hossenlopp, 2010;Shamaeli and Alizadeh, 2013;Stojakovic et al, 2012). A simple expression of Avrami's equation is described in Eq.…”

Understanding the Ion Exchange Process in LDH Nanomaterials by Fast In Situ XRPD and PCA-Assisted Kinetic Analysis

“…Peak Fitting Analysis of Raw XRPD Data. In situ XRPD data were then analyzed with a traditional, well-established method of analysis of peak fitting [32,33] (referred to as peakfit from now on) to check and compare the results of the PCA-based approach. A phase quantification by Pawley fit was performed on the patterns, and the area of the basal peaks of the two phases (reported in Figure 4) was used to calculate the reaction extent for the decay of the host phase (α host ) as a function of time (t) by…”

“…The exchange of carbonate with nitrate ions into LDH is hence studied by in situ XRPD, allowing kinetic, reaction mechanism, and microstructural information to be extracted. The reaction kinetics were analyzed by the Avrami-Erofe'ev approach to obtain the reaction order by the traditional refinement approach [27,28,32,33] and by the recently proposed PCA-based approach [24,[34][35][36]].…”