Microwave-Assisted Synthesis of <i>trans</i>-Cinnamic Acid for Highly Efficient Removal of Copper from Aqueous Solution

Abstract

<i>trans</i>-Cinnamic acid was synthesized under microwave irradiation, and it was used for the removal of copper, a toxic metal found in industrial wastewater, from synthetic polluted aqueous solutions. Copper removal is more favorable at pH 5 and was enhanced by increasing the copper initial concentration, reaching a maximum uptake capacity of 389.5 mg/g, which is higher than those reported in the literature. Temperature exhibited a negligible effect on the removal of copper by <i>trans</i>-cinnamic acid. The isotherm equilibrium uptake data were found to be described by the Langmuir model. In addition, the study of the removal kinetics shows that the uptake of copper by <i>trans</i>-cinnamic acid follows pseudo-first order kinetics, and equilibrium is attained at approximately 30 min. Based on the X-ray photoelectron spectroscopy, X-ray diffraction, scanning transmission electron microscopy, and Fourier-transform infrared spectroscopy studies, a copper-cinnamic acid complex [Cu(CA)₂] is formed during the removal process. The reusability of this coordination compound was investigated using HCl, HNO₃, and NaOH 0.1 M as desorption eluents; HCl was capable of completely desorbing copper from [Cu(CA)₂], and <i>trans</i>-cinnamic acid was recovered as the <i>trans</i>-isomer. Alternatively, the [Cu(CA)₂] was used to remove octamethylcyclotetrasiloxane from gaseous streams for biogas purification, obtaining an adsorption capacity of 3.37 mg/g. These promising results demonstrate the feasibility of copper removal by <i>trans</i>-cinnamic acid because of its high uptake capacity and potential reusability.