Chitosan–ZnO nanocomposite from a circular economy perspective: in situ cotton-used fabric recycling and the nanocomposite recovering.

End-of-life textile recycling presents a real economic and environmental challenge. From a circular economy perspective, we attempt to evaluate the chitosan–ZnO nanocomposite efficiency in the recycling of cotton-used fabric, accompanied by the electroanalytic and the optoelectronic investigation of the resulting nanocomposites. For comparison, the precipitation and the sonochemical pathways were used as in situ treatment methods. The effect of chitosan characteristics on the antibacterial sustainability of the treated fabrics and the properties of the resulting nanocomposites were studied. The chemical bonding, crystal structure, morphology, optical and optoelectronic properties, intermolecular interactions and antibacterial properties of the resulting free nanocomposites were investigated. The treated used fabrics were characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy before and after 20 washes. Density functional theory study and atoms in molecules analysis of cellulose–nanocomposite interaction were carried out. The results indicate an effective dose of 2 mg against tested bacteria for all the nanocomposites. The nanocomposites have an orange-red emission with no Zn defects and large oscillator strength (ƒ) values. Medium molecular weight chitosan-based nanocomposites showed more intense orange-red emission and higher ƒ values. Sustainable antibacterial properties of treated fabrics are generated with high molecular weight chitosan-based nanocomposites. More than 83% of the antibacterial activity is retained after 20 washes. The theoretical study confirms the stability of the free nanocomposite (chitosan–ZnO) and its destabilization by contacting the fabric when ZnO is a rod shaped, which generates its growth-promoting. [ABSTRACT FROM AUTHOR]