Síntese e caracterização de carbon dots e seus compósitos à base de resina melamínica aplicados como tinta antifalsificação e em pó revelador de impressões digitais latentes

Abstract

Carbon dots (CDs) have stood out on the scientific scene for their unique properties, such as high fluorescence intensity, biocompatibility; and versatility in different applications, revolutionizing areas such as document security, intellectual property and copyright, as well as forensics. The aim of this study was to synthesize CDs derived from the precursors citric acid and urea, with a view to using them as a fluorescent anti-counterfeiting ink, as well as incorporating them into the melamine-urea-formaldehyde (MUF) polymer base to obtain a fluorescent powder for revealing latent fingerprints (IDLs). To this end, the CDs obtained (CD UAC) were synthesized using a microwave method (720 W), while the MUF resin was obtained by precipitation. The nanocomposite (MUF_CD-UAC) was obtained by incorporating the CD UAC as a fluorescent powder for developing IDLs, while the fluorescent dye was obtained by adding P.A. glycerin to the CD-UAC solution. The materials obtained were characterized using TEM, SEM, XRD, FTIR, UV-Vis and PL techniques. The CD-UAC exhibited an average size of 2.19 nm ± 0.58 nm, with a lattice spacing of 1.31 Å, characteristic of the diffraction plane (100). The FTIR spectra revealed that the synthesized materials exhibited oxygenated and nitrogenated groups, and for the nanocomposite, regions that indicated the presence of vibrations and stretches characteristic of both precursors. In addition, CD-UAC exhibited a maximum emission wavelength (𝛌em max) at 440 nm (𝛌exc max = 350 nm), while MUF_CD UAC showed 𝛌em max at 500 nm, in addition to a band at 350 nm from MUF. The nanoparticle proved to be photostable, with only a percentage difference in intensity relative to 0.794% - in 60 minutes of exposure to UV light (𝛌=350 nm). Tests were carried out with CD-UAC-based anti-counterfeiting inks, which showed high fluorescence intensity and stability even after 1 year of printing. The fluorescent powder obtained was used to reveal IDLs on different surfaces, showing adequate contrast so that they could be validated using the Vucetich method and Verifinger SDK software, making it possible to identify characteristic points and examine the match. Finally, the IDLs also showed stability when exposed to air for 6 months, without affecting their contrast and FL intensity and helping to prove the validation of the carbon dots in both applications.