Adsorption of Congo red from solution by iron doped PVA-chitosan composite film

Chitosan-polyvinyl alcohol-iron (CS-PVA-Fe) composite films with acid resistance and large adsorption capacity were prepared by doping trivalent iron, chitosan, and polyvinyl alcohol. The adsorption mechanism of Congo red (CR) on the composite films was investigated by changing the adsorption conditions (temperature, pH, salt) and characterization (isoelectric point, infrared spectroscopy, photoelectric spectroscopy, scanning electron microscopy). The results showed that the adsorption capacity of the composite film was 450 mg g –1 at pH 5.0, and the adsorption of CR by high concentration salt had only a slight negative effect. The adsorption was following Langmuir, pseudo-first-order kinetics and pseudo-second-order kinetics model, which showed that the adsorption process was based on the single-layer heterogeneous adsorption, and there were both physical and chemical adsorption processes. Thermodynamic analysis shows that adsorption was spontaneous, endothermic and entropy increasing process. According to the characterization analysis, the adsorption mechanism of CR was mainly hydrogen bonding, ion exchange, and complexation. Also, the desorption of CR-loaded film can be performed using 75% alcohol at pH 12. The results showed that CS-PVA-Fe composite films are promising as a suitable candidate for the efficient removal of CR from solution.