UV-crosslinking of chitosan/spent coffee ground composites for enhanced durability and multifunctionality

Spent coffee grounds (SCGs) have numerous applications and are often blended with polymers to create composites. However, SCGs are physically trapped within the polymer matrix, lacking strong chemical bonding. Therefore, this study has developed a new method for UV crosslinking composites using phenyl azide to address the issue of SCG leakage and limited durability of the composites. The main approach involves grafting phenyl azide onto chitosan, which is then combined with SCGs. When exposed to UV light, the SCGs become covalently linked to the chitosan chains. This method not only resolves the problem of chitosan's porous material fragility but also prevents SCG detachment, surpassing the performance of glutaraldehyde-crosslinked composites. Regarding applications, CS/SCG composites exhibit rapid heating and photothermal stability, making them suitable for use as thermal pads in evaporative water purification, enabling for the collection of pure water from contaminated sources. Furthermore, SCGs have the ability to adsorb metal ions, significantly enhancing the Cu²⁺ adsorption capacity of CS/SCG composites compared to pure CS, with an increase of more than twofold. This research not only presents a practical solution for stabilizing fillers within polymer matrices but also demonstrates the reusability of SCGs.