Faculty Publications
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Item Eco-friendly ink formulation of column purified carbon dots from GABA for anticounterfeiting applications(Elsevier B.V., 2023) Ullal, N.; Dhanya, D.; Kulkarni, S.D.; Sinha, R.K.; Anand, P.J.; Bhat K, U.K.Forgery of valuable products causes a negative impact on the society as well as the economy of the country. There is a growing demand to not only differentiate or authenticate genuine documents/products but also to protect their integrity. Carbon dots (CDs) are a class of fluorescent nanomaterials that are well-known for their facile synthesis, good photostability and less toxicity profile. The current research work focuses on the preparation of CDs via hydrothermal method using γ-aminobutyric acid (GABA) that contains amino and carboxylic groups. Column chromatography technique is adopted to purify the GABA-derived CDs from the reactants and by-products. The fourth fraction obtained after column purification containing CDs with fluorescence emission in the visible region is chosen for further studies. The presence of spherical CDs confirmed through TEM imaging are chemically characterised using SAED, EDS, DLS, FTIR, XPS, Raman and XRD spectroscopy. The blue (λem = 490 nm) and green (λem = 538 nm) emitting CDs present in the fourth fraction displayed a fluorescence lifetime of 1.90 ns and 2.02 ns. Theoretical studies are performed using B3LYP/6-31G(d,p) theory level on different plausible structures. The HOMO-LUMO band gap of 2.3 eV deduced using DFT calculation is in close agreement with the optical band gap of 2.6 eV derived from Tauc plot. A complex forming mechanism is proposed for the fluorescence quenching of CDs upon examining the EDS data of the precipitate obtained upon addition of cupric ions. Further, the CDs are used as pigments to formulate a water-based ink for flexographic printing on UV-dull paper substrate. The printed samples exhibited good colorimetric values, lightfastness, and rub resistance. The security features of the ink film include an UV-induced yellow fluorescence, which will be known to the forger and a secondary quenching of fluorescence when exposed to cupric ions, which can be used by the user to validate document/product authenticity. This stimulus responsive optical property is also explored in the design of ionochromic security paper based on cupric ion induced fluorescence quenching of CDs for data storage and decryption. Moreover, the lesser surface roughness and electrical parameter values obtained for the print proofs could be further explored for the potential application of CD-derived ink in electronic anticounterfeiting. © 2023 Elsevier B.V.Item Pistachio shell-derived carbon dots and their screen-printing formulation for anticounterfeiting applications(Springer, 2024) Chinmayi, H.D.; Ullal, N.; Dhanya, D.; Kulkarni, S.D.; Anand, P.J.; Udaya Bhat, K.In synergy with constructing a sustainable environment, facile reuse of carbon-rich biowastes as inexpensive precursors for the synthesis of value-added functional carbon dots (CDs) has garnered fruitful outcomes. Pistachio shells comprising cellulose, hemicellulose, and lignin were successfully utilized as a carbon source for the synthesis of CDs through carbonization and subsequent hydrothermal method. The methanolic fraction with desirable fluorescence in the visible region obtained after column purification of CDs was further characterized using TEM, EDS, SAED, FTIR, XPS, RS, XRD, and TCSPC techniques. The blue and green emitting CDs were used as colorants to prepare a water-based ink for screen printing. The screen prints on UV dull paper substrate exhibited good colorimetric and density values. The UV-induced yellow fluorescence of the ink film can be used as a security feature to authenticate genuine document/products and data storage. Graphical abstract: (Figure presented.). © American Coatings Association 2024.