Engenharia de Materiais e Nanotecnologia - Teses - EE Higienópolis

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    Tese
    Desenvolvimento de uma ferramenta analítica para purificação de dispersões de materiais bidimensionais (2D)
    Santos, Marcos Alves dos (2020-06-08)

    Escola de Engenharia Mackenzie (EE)

    With the advent of graphene, in 2004 by Geim and Novoselov, this new twodimensional (2D) material and its derivatives such as graphene oxide (GO) and reduced graphene oxide (rGO), have been widely studied and used in the development of several technologies, such as energy conversion and storage devices, optoelectronics, (bio) sensors, composite materials, among others. The main way to obtain GO is through the oxidation of graphite, using the Hummers method, by strong oxidizing agents. However, the GO purification process is a key parameter in the production of this 2D material. This step demands a large volume of water, energy and time. The inefficient removal of the contaminants (residual species from the synthesis process, such as ions and metal oxides) present in GO may affect GO properties and turn unfeasible some applications, as in the biological field. In this sense, this thesis demonstrates the development of a new purification device, which involves a continuous flow system, coupled to a diffusion cell, with a microporous nitrocellulose membrane. The contaminant removal process is led by a concentration gradient. The purification system developed in this work had its efficiency compared to traditional purification methods, such as dialysis and centrifugation. It was also evaluated how the contaminants impurities and the purification processes can impact the structural, morphological and electrochemical behavior of the GO. In addition, the contaminants impurities were quantified by pH and conductivity measurements of the GO dispersions and analyzed by ion chromatography and graphite furnace atomic absorption spectrometry. The purification device developed by this work, achieves the best performance in the removal of the major contaminants (K+(aq.), Na+(aq.), Cl-(aq.), SO42-(aq.), Mn2+(aq.) and MnO2(s)), demanding ~95% less water than dialysis and in a shorter time (~23 h). The system operates in flow, with a minimum handling of the operator and allows to preserve and select the GO sheets by the pore size of the membrane used. This work represents a simple and fast alternative to purification of GO dispersion that can be easily scaled-up and applied in the purification of other dispersions of 2D materials.