Development of carbon quantum dots-based transparent coatings for enhanced UV shielding

[Display omitted] •C-QD were created using microwave or hydrothermal methods.•Microwave-generated coatings show the highest uniformity.•The best withdrawal rate for uniform UV protection is 10 mm/min.•Optimal coatings were achieved with the 300 min hydrothermal treatment.•Carbon quantum dots (C-QD) provide over 90% UV protection for coatings. The development of easy, translucent, and scalable UV-protection coatings for transparent containers is of utmost importance to ensure the safety of several food and medical products. Here it is studied the preparation of coatings based on carbon quantum dots (C-QDs) with very high absolute emission quantum yields (above 55%) for an excitation wavelenght of 360 nm, and polyvinyl alcohol, using the same temperature but employing two different heating-assisted (conventional and microwave oven-assisted heating) hydrothermal syntheses. The microwave oven-assisted heating allows the formation of the C-QDs in only 1 min, while 180 min are needed to produce them in a conventional oven. The impact of dip-coating withdrawal rates on the coatings properties, such as thickness, UV protective ability and colour is extensively studied. The coatings made under microwave oven-assisted heating achieved superior UV absorbance and colour gain. The best coatings were either the ones prepared under conventional oven for 300 min or the ones synthetised by microwave oven over 15 min, displaying 85% or 92% of UV protection capacity, respectively. The selection of the best conditions strongly depends on the level of colour deemed acceptable, with the microwave oven coatings showing more intense colour gain.