Polyurethane nanocomposite film embedded with carbon quantum dots from spent Coffea arabica grounds for the UV and blue light shielding

The development of anti-blue-light coatings simultaneously possessing high optical transparency and blue-light protective functions derived from renewable and biodegradable biomass represents a promising strategy for eye protection. In the present study, we introduce a sustainable protecting film by embedding carbon quantum dots derived from Coffea arabica grounds (CAG-CQDs) into a polyurethane (PU) matrix via solvent casting. The CAG-CQDs were synthesized using a carbonization at 300 °C for 2 h followed by ultrasonication for 20 min, and microwave irradiation at 800 W power for 10 min. The PU films were prepared in toluene at 60 °C under continuous stirring, and the CAG-CQDs at different concentrations were incorporated into the hot solution of PU prior to solvent casting at ambient temperature. The CQDs obtained in this study exhibit nanoparticles with an average size of 6.34 ± 0.51 nm, absorb the UV light at λex = 265 nm and capable of emitting a visible light at λem = 445 nm with quantum yield of 16.7%, and a band gap of 4.86 eV. The nanocomposite films show the capability in blocking up to 95% of UV-A, 91% of UV-B and 81% of HEBL radiations, were found to hydrophobic with contact angle of 97.3–107.7 o and low water absorption capacity (2.243–3.242%). The results confirm the potential of polyurethane-CQDs nanocomposite films as protective coatings for electronic displays, including smartphones and tablets.