Ultrasonic-assisted synthesis of highly effective visible light Fe3O4/ZnO/PANI nanocomposite: Thoroughly kinetics and thermodynamic investigations on the Congo red dye decomposition

Abstract

A visible-light active Fe3O4/ZnO/PANI photocatalysts prepared using ultrasonic-mediated optimization with a core-shell structure. Characterization was carried out by FT-IR, XRD, SEM, EDX, BET, VGSM, TGA, and TEM micrography. Photocatalytic degradation revealed a preference for visible light versus UV light. The effects of nanocomposite dosage and pH on the Congo red (CR) visible light decomposition revealed the optimum condition, including dosage of 2 gL−1 and pH = 3. Different isotherm models were applied to analyze the thermodynamic and kinetics of the adsorption & decomposition process through the linear and non-linear regression methods. Three error functions, including Chi-square statistic (χ2), root mean square error (RMSE), and average percentage error (APE) utilized for the comparison of experimental data with the predicted ones. The determination coefficient was (R2) also applied for choosing the best-fit optimization of the kinetic and thermodynamic models.The Temkin and Freundlich isotherm showed the best fits (R2>0.999) and low standard errors. The kinetic studies data showed that the pseudo-second-order model was the best model (R2>0.99). The equilibrium constant of CR adsorption & decomposition was studied at various temperatures of 298, 308, 318, 328, and 338 K. The values of thermodynamic parameters, including standard free energy changes (ΔG°), standard enthalpy (ΔH°), and entropy changes (ΔS°), were explored to be -4.73, 4.0 kJmol−1, and 29.22 Jmol−1K−1, respectively, which showed the process would be endothermic and spontaneous. The prepared nanocomposite separated quickly from the reaction mixture by a magnetic rod. Besides, it almost maintained its photocatalytic activity after five cycles of the process.