This study aimed to improve the known microwave method to produce carbon dot nanoparticles from ethylenediamine and citric acid. Carbon dots have recently gained much attention as they have diverse applications, such as bioimaging and drug delivery reagents as cancer theranostics. Research was focused on establishing the ideal time for the synthetic reaction to produce carbon dot nanoparticles with the microwave method. After several trials, the 16-minute trial provided the best results based on Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, and ultraviolet exposure.

Made available in DSpace on 2015-05-14T13:21:32Z (GMT). No. of bitstreams: 1 parte1.pdf: 2899615 bytes, checksum: 75e6cc1845e4dc8219f3bc05e1249db6 (MD5) Previous issue date: 2009-03-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The motivation of this work was to obtain zinc oxide (ZnO), which is a semiconductor of large technological application, by a new chemical method, the Hydrothermal Method coupled to the use of a domestic microwave oven. Such method favors the obtainment of materials at lower temperature and short time period, besides favoring the formation of particles with controlled size and morphology, and also allowing a good control of the particle properties. The ZnO samples were synthesized at low temperature (100 °C) and at a short time period, using different reaction media: water, ethanol and water/ethanol (1:1); and alkalized with NaOH and NH4OH. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Field Emission Gun (FEG), Infrared Spectroscopy (IR), Raman Spectroscopy, UV-vis Spectroscopy and Photoluminescence techniques were carried out to characterize the material. All the samples obtained crystallized in a hexagonal structure of the wurtzite type whose unit cell volumes do not significantly vary with the time. Moreover, the samples alkalized with NH4OH were more organized, both in the short and in the long ranges, than the samples alkalized with NaOH. This was due to the formation of two different ions with opposite charges, − 24 ) (OH Zn and + 24 3 Zn(NH ) , that are attracted to each other during the process and then lead to the material organization. Several structures, such as spherical nanoparticles, nanoarrays, nanorods and flower-like clusters were obtained according to the reaction medium, alkali and synthesis time. The size of these structures increases with the increase of the synthesis time and varies from 20 to 570 nm, when they are synthesized in a lower time and from 500 nm to 1,5 μm in a higher synthesis time, showing that the particle sizes can be controlled easily. / A motivação deste trabalho foi a obtenção do Óxido de Zinco (ZnO), que é um semicondutor de grande emprego tecnológico, através de um novo método químico, o método hidrotermal acoplado a um forno de microondas doméstico. Tal método possibilita a obtenção de materiais em temperaturas baixas e em baixo tempo, alem de facilitar a formação de partículas com tamanho e morfologia controlados, e favorecer um bom controle de suas propriedades. As amostras de ZnO foram sintetizadas em baixa temperatura (100 °C) e em baixo tempo, utilizando diferentes meios reacionais: água, etanol e água/etanol (1:1); e alcalinizadas com NaOH e NH4OH. Foram realizadas as técnicas de difração de raios X (DRX), microscopia eletrônica de varredura (MEV), Field Emission Gun (FEG), espectroscopia de absorção na região do infravermelho (IV), Raman, UV-vis e Fotoluminescência (FL) para caracterizar o material. Todas as amostras obtidas se cristalizaram numa estrutura hexagonal do tipo Wurtzita cujo volume da célula unitária não varia muito com o tempo. Além disso, as amostras alcalinizadas com NH4OH são mais ordenadas tanto a curto quanto a longo alcance quando comparadas com as amostras alcalinizadas com NaOH, devido a formação de dois íons de cargas opostas, − 24 Zn(OH) e o + 24 3 Zn(NH ) , que se atraem durante o processo e facilitam a organização do material. Estruturas diferenciadas como nanopartículas esféricas, nanoplacas, nanobastões e clusters na forma de flores foram obtidas segundo o meio reacional, base e o tempo de síntese. Os tamanhos destas estruturas aumentam com o aumento do tempo de síntese, elas variam de 20 e 570 nm quando sintetizadas em menor tempo e de 500 nm a 1.5 μm em um tempo de síntese mais elevado, indicando que o tamanho das partículas pode ser facilmente controlado.

The diploma thesis is focused on the issue of measuring the moisture content in building materials using indirect methods that allow its long-term measurement. The theoretical part of the thesis provides an overview of the forms of moisture in porous building materials and provide an overview of the principles of measuring moisture content. In the experimental part of the thesis, the aim is to verify the available methods for long-term monitoring of moisture in building materials built into building structures. Proven methods of measuring humidity include resistance, capacitive and microwave methods and their comparison with the results of gravimetric measurements. At the end of the work is an evaluation of knowledge and recommendations for further research in this area.