Adsorption of copper ions and alizarin red S from aqueous solutions onto a polymeric nanocomposite in single and binary systems

Adsorption of Cu(II) ions and alizarin red S (ARS) has been studied using beads of chitosan (CS) and a chitosan/ZnO nanorod composite (CS-ZnO) in single and binary systems. The beads were synthesized and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray analysis. Factors affecting adsorption of Cu(II) ions and ARS such as pH and initial concentrations as well as adsorption kinetics, isotherms, thermodynamics, reusability, and competitive adsorption in binary systems were studied. The results showed that the adsorption kinetics and isotherm data for both adsorbates followed a pseudo -second-order model and the Freundlich model, respectively. Studies of intraparticle diffusion and Dumwald-Wagner models indicated that the adsorption occurred in a complex mechanism where the intraparticle diffusion stage was not the only rate-determining step for both adsorbates. Thermodynamic studies showed that the adsorption process was favorable, endothermic, and physisorptive in nature. In both single and binary systems, CS-ZnO beads showed better adsorption efficiency than CS beads. For the binary system, Cu(II) ions did not affect the adsorption of ARS; however, ARS reduced the Cu(II) adsorption.