Fig. 15. (a) Reaction of citric acid and ethylenediamine, resulting in e-CQDs and the fluorophore IPCA. (b) Reaction of citric acid with hexamethylenetetramine, producing h-CQDs and citrazinic acid and/or 3,5 derivatives (marked by –X) due to the decomposition of hexamethylenetetramine to ammonia and formaldehyde at temperatures exceeding 96 °C. (c) Reaction of citric acid and triethanolamine, resulting in t-CQDs and no derivatives of citrazinic acid since the tertiary amine prohibits their formation. (a–c) Images of the purified reaction products under ambient light and the corresponding diluted solutions under UV light excitation (this figure has been adapted/reproduced from ref. 104 with permission from the American Chemical Society, Copyright 2016).