Eco-Friendly Chitosan (CTS) Films for Indigo Carmine Removal and Wastewater Treatment

The discharge of synthetic dyes such as indigo carmine (IC) into industrial effluents poses serious environmental risks due to their persistence, toxicity, and resistance to conventional treatment. This study developed chitosan (CTS)-based films as biodegradable, eco-friendly adsorbents for IC removal and wastewater reuse. CTS was dissolved in acetic acid (AA) solutions (0.05%, 1.5%, and 3%), and homogenized hydrogels were prepared by stirring in sealed vials at ambient temperature for 3 h. In our trials, casting on glass and watch glass at 73 °C for 35 min caused irreversible adhesion, whereas polyethylene (PE) at ambient temperature produced homogeneous, transparent, and detachable films. The optimized formulation (1% CTS in 1.5% AA) on PE plates yielded stable, transparent films used for further experiments. Fourier-transform infrared (FTIR) spectroscopy of CTS, AA, the homogenized hydrogel, and dried CTS–1.5%AA/PE films confirmed structural interactions. Adsorption tests were carried out with IC solutions (16 mg/mL) prepared in ultrapure water and secondary treated wastewater supplied by Aquasoil Company (Italy). Full decolorization of the solutions occurred within the first hour, accompanied by a visible change as the initially transparent CTS films turned blue, confirming rapid dye uptake. Subsequent irradiation with a UV lamp (365 nm, UV-A range) promoted photodegradation; after 2 hours, the films lost their blue coloration and exhibited a light yellow tone. The films remained structurally stable and could be readily removed. These findings confirm a dual adsorption–photodegradation mechanism, demonstrating the promise of CTS–1.5%AA/PE films as low-cost, biodegradable, and scalable materials for sustainable wastewater treatment. Further studies on biodegradation, reusability, and large-scale application are recommended to validate their industrial potential. Acknowledgment: This project was supported by S.D. through a Doctoral Fellowship funded by the National Operational Programme Research and Innovation 2014–2020 (grant CCI2014IT16M2OP005).