Banca de QUALIFICAÇÃO: EDSON DA SILVA REIS

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : EDSON DA SILVA REIS
DATE: 10/07/2023
LOCAL: Programa de Pós-Graduação em Ciência de Materiais
TITLE:

USE OF HUMIDITY SENSITIVE CARBON DOTS AS A SAFETY DEVICE

KEY WORDS:

Carbon Nanodots; Phosphorescence; counterfeiting; data coding; impression.

PAGES: 91
BIG AREA: Outra
AREA: Multidisciplinar
SUMMARY:

Counterfeiting is a recurring problem that generates trillionaire losses for the world economy. In addition to the economic consequences due to the counterfeiting of consumer goods and luxury items, counterfeiting poses major risks to human health, such as the sale of counterfeit medicines and prescriptions, as well as products with levels of contaminants outside the standards allowed by the World Health Organization (WHO). Thus, photoluminescent nanomaterials with multiple emissions have been extensively investigated for coding information. The development of nanoparticles with multiple emissions based on carbon and free of metals, the Carbon Dots (CDs), has enabled their wide application in several areas, such as optoelectronic devices, bioimaging, document security, among others. In this work, carbon nanoparticles with semi-crystalline graphitic cores, Carbon Nanodots (CNDs), of low cost and fast synthesis method, doped with oxygen, nitrogen, and phosphorus, which fluoresce in blue and phosphorescence in blue and green with humidity sensitivity were developed, in addition to 11.83% absolute quantum yield. CNDs were obtained from ethanolamine and phosphoric acid, through microwave-assisted synthesis, varying the time from 1-3 min. The synthesized materials have an average particle size of 3.99 nm, with uniform distribution and low polydispersity. Using FTIR, evidence of surface functional groups -C–O, -C–N, -P–O, -P–N, -C=O, -C=N -P=O was observed, which are responsible for the multiple emissions. The CNDs showed π-π* and n-π* electronic transitions that lead to emission from the carbogenic nucleus, due to quantum confinement, and surface states caused by doping with heteroatoms, respectively. The emission spectrum (λEx=350 nm) in aqueous solution exhibits a broad band with maximum intensity at λEm=420 nm. Phosphorescence was also verified in aqueous medium at low temperature (77K), as well as in the solid state, at room temperature. The good water dispensability allowed the processing and deposition of the CNDs by printing, with a conventional inkjet printer. Printed in humid environmental conditions only fluoresced in blue. However, when removing moisture through heating or vacuum, the printed matter began to exhibit intense phosphorescence in green, visible to the
naked eye for at least 12 seconds, which is enough time to capture coded images. Thus, the material proved to be promising for encoding data based on the suppression of phosphorescence in the presence of humidity.

COMMITTEE MEMBERS:
Externa ao Programa - 1665775 - JANAINA VERSIANI DOS ANJOS - nullExterno à Instituição - LEONARDO TADEU BOAES MENDONÇA - UFMA
Externo à Instituição - MARCOS VINICIUS DA SILVA PAULA - UFPA