Modified sol–gel method for synthesis and structure characterisation of ternary and quaternary ferrite-based oxides for thermogravimetrically carbon dioxide adsorption.

Soft-NiFe₂O₄ (S-spinel), hard-BaFe₁₂O₁₉ (M-type) and BaNi₂Fe₁₆O₂₇ (W-type) were successfully prepared via a novel modified sol–gel method. The mechanism of modified sol–gel method is to utilise the esterification reaction between citric acid chelate and 2-propanol to spontaneously generate more homogeneous esterified-gel. This modified sol–gel method produced pure and highly crystalline ferrite-based oxides with more uniform morphology and effective carbon dioxide (CO₂) adsorption. It is a simpler and more efficient method than the traditional sol–gel method. XRD results proved the purity of the prepared ferrite-based oxides and exhibited smaller and comparable crystallite size when determined by the Debye–Scherrer equation. FTIR indicates the presence of metal–oxygen stretching bonds in the samples. Nitrogen sorption analysis confirmed the high surface area of ferrite-based oxides using this improvement method. EDX and XPS analyses verified the purity and chemical composition of the samples. The morphologies of the samples were investigated by SEM and HRTEM analysis. The CO₂ adsorption was evaluated by thermogravimetry method for all the samples, and BaNi₂Fe₁₆O₂₇ (W-type) shows the maximum CO₂ uptake with 20.43 mg/g_ads compared to hard-BaFe₁₂O₁₉ (M-type) and soft-NiFe₂O₄ (S-spinel) with 17.33 and 11.31 mg/g_ads, respectively. All the samples are best fitted with the pseudo-second order in kinetic analysis with high R² values (> 0.98). Therefore, this improvement modified sol–gel method proved better and promising option and at the same time beneficial for CO₂ adsorption. [ABSTRACT FROM AUTHOR]