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

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-QD) and polyvinyl alcohol, using the same temperature but employing two different heating-assisted (conventional oven- and microwave oven-assisted heating) hydrothermal syntheses. The microwave oven-assisted heating allows the formation of the C-QD 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.