Superhydrophobic fluorescent carbon quantum dots for AI-enabled anti-counterfeiting and textile coating applications

Nature has engineered superhydrophobic materials and applied them as coatings of micro- and nano-scale structures, such as the lotus leaf, facilitating the self-cleaning of dirt, dust, and bacteria. Inspired by nature, a series of superhydrophobic solid-state fluorescent carbon quantum dots (CQDs) was synthesized using a solvothermal method with dithiosalicylic acid (DTSA) and aminopyridine-3-carboxylic acid (2-APC)/4-amino-4H-1,2,4-triazole (AHT)/2-aminobenzenethiol (ABT)/2-hydrazinebenzothiazole (HBT) in acetic acid. Furthermore, emission tuning was achieved by alteration of nitrogen, oxygen, and sulfur contents from 2-APC, AHT, ABT, and HBT, leading to the successful synthesis of APC (red), YR (orange), YG (green), and CR (yellow) CQDs, respectively. All four CQDs exhibited superhydrophobic behaviour, while the CR CQDs demonstrated an exceptionally high water-contact angle (CA) of 172° with extraordinary surface water repellence. TEM analysis revealed clear lattice fringes with a lattice spacing of 0.21 nm, indicating the graphite-like 2D planar structure of the CQDs. The superhydrophobic and fluorescent CQDs were further utilized as an anti-counterfeiting agent to create luminous fingerprints. These fluorescent latent fingerprints (LFPs) were resolved to Level 3 detail and examined using an automated Python-based image-processing program developed as a proof-of-concept. The performance surpasses that of conventional methods, validating the suitability of superhydrophobic CQDs powders and the digital processing program for practical applications. Further, the promising superhydrophobic effects of these multi-coloured CQDs have also been demonstrated in coatings on various substrates, including textiles and mild steel.