Titanium dioxide for upconversion markers @ INCM

• Autor(a) principal: Sousa, Bernardo Daniel Fevereiro e
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/129163
• topic: Upconversion; TiO2; Ytterbium; Europium; Nanoparticles; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias; Domínio/Área Científica::Engenharia e Tecnologia::Nanotecnologia

The work achieved with this thesis consisted of the production and characterization of new low-cost upconversion nanoparticles based on a titanium dioxide (TiO2) host matrix. These nanoparticles were produced by solvothermal synthesis assisted by microwave irradiation. Two elements (europium and ytterbium) were used as dopant in the matrix to allow the upconversion process. Different parameters of synthesis were considered, to achieve an ideal process of synthesis. Also, different acids and solvents were considered and studied to achieve the most successful conditions. Three acids were tested: ( hydro-chloric acid (HCl), nitric acid (HNO3,), and oxalic acid (C2H2O4)). Besides acids, also 2 solvents were tested: ethanol (C2H6O) and water (H2O). The nanoparticles produced are going to be an essential part of a security marker ink to be used by INCM (Imprensa Nacional – Casa da Moeda). The goal of this thesis is to achieve the synthesis of nanoparticles to be mixed in an ink to be used as a low-cost security marker ink to replace the current ink used by INCM. According to studies realized on the different reagents, it was concluded that oxalic acid and ethanol produced particles with desired properties (good size uniformity, spherical particles, and small size) for the TiO2 matrix. The concentration of dopant was also considered and studied, in an initial test, 4 molar concentrations were considered: 2.5%; 5%; 7.5%; and 10%. The 7.5% concentration was decided due to particles size, shape, and uniformity. The upscaling of the process was successful, when converting 50ml solutions to 600 ml. The nanoparticles produced in both solutions presented similar properties when analyzed. The ink formulation was achieved with good results, the nanoparticles were easily mixed without the need to add dispersants. The detection of the dopant in the nanoparticles was successful in both powder and when mixed as ink.