An in situ deposition procedure was developed for the nanopeapod (NPP) formation of NiAu nanoparticles inside preformed acid-exchanged hexaniobate nanoscrolls (HNB). Metal salt precursors of Ni(acac)2 and HAuCl4∙3H2O were reduced in solution under mild synthetic conditions in the presence of the preformed acid-exchanged hexaniobate nanoscrolls. Two of the surfactants used for the formation of the nanoparticles were oleylamine and triphenylphosphine oxide (TTPO). Reaction conditions were studied and modified to produce well-defined NiAu@HNB NPP systems, with monodispersed particles evenly filling and orienting within the nanoscrolls. The synthetic parameters studied were both time and temperature, with the most well-defined peapod systems being those produced from lower temperatures (100°C) and longer reaction times (60 minutes). NiAu@HNB NPPs synthesized under these conditions yielded a narrow size distribution of NiAu nanoparticles, ranging ~ 4 – 10 nm in diameter, evenly filled and oriented within the inner diameter of hexaniobate nanoscrolls (ranging ~2 μm in length).

The ability to encapsulate/insert different kinds of nanoparticles (NPs) in scrolled nanosheets (NSs) may lead to the formation of new nanocomposite materials that yield novel properties. These nanostructures resemble “peapods” that consist of NPs chains (“peas”) located in a hollow space of desired nanoscrolls (“pods”). Depending on different combinations of “peas” and “pods” diverse families of nanopeapods (NPPs) can be synthesized which may exhibit interesting properties not accessible from the individual components. Though there exist various synthetic methods for the formation of NPPs, more development in terms of simplicity, flexibility, and productivity of synthetic approaches are needed so that different classes of NPPs with unique combinations/characteristics of “peas” and “pods” can be synthesized. A simple solvothermal synthesis method for the encapsulation of spherical Fe3O4 NPs by the capture of preformed NPs in scrolled hexaniobate has previously been developed in our group. In the first part of this research, efforts were made to extend the “pod” materials to other inorganic NScs. Vanadate nanoscrolls (NScs) could rapidly (2h) be produced using a simple solvothermal treatment in the presence of V2O5 as vanadium source, and either dodecylamine (DDA) or octadecylamine (ODA) as the structure-directing agent. The synthesis parameters were successfully adjusted to obtain high yields vanadate NScs (~ 20 g of NScs per synthesis) with different average lengths as 383 nm, 816 nm to 3.3 µm. The effects of reaction time on the formation of NScs were also investigated. Further efforts focused on the development of methods for making vanadate NPPs. Here, two novel approaches for the formation of these NPPs have been successfully developed. In the first, solvothermal methods utilizing preformed Ag NPs and vanadate NSs lead to the formation of Ag@vanadate NPPs where NPs could be encapsulated during the scrolling of NSs. High NP loadings were acquired with this approach. In the second method, an insertion strategy was developed where Ag NPs were drawn into the lumen of preformed vanadate NScs upon controlled solvent evaporation. This method was also quite effective, though much lower loadings of NPs were achieved with larger average NP-NP distances. Also noteworthy in the study of vanadate NScs and NPPs is the observation of an uncommon asymmetric scrolling behavior; this was realized for both vanadate NScs and solvothermally synthesized Ag@vanadate NPPs. Novel solvothermal approaches for the effective construction of organic-MoOx hybrid structures and MoOx nanosheets (NSs) have also been developed. These NSs can be controlled so as to exist in different oxidation states as well as in different crystal structures. Layer spacing as a function of organic molecule lengths could also be controlled by changing the type of surfactants located between the NSs. Individual NSs or a few layers of stacked NSs, up to four micrometers in lateral size were successfully prepared upon sonication. The effect of time, temperature, as well as the type of structure-directing agents on the formation and crystal structure of MoOx intercalated compound/NSs were also explored. Lastly, a modified solvothermal method previously used for the encapsulation of spherical Fe3O4 NPs inside hexaniobate NScs was applied for the construction of cubic-CeO2 NPPs. High yield encapsulations of preformed cubic ~5 nm ceria NPs within the lumen of hexaniobate NScs were readily accomplished. Size selective encapsulation and the formation mechanism of cubic-CeO2 NPPs were also studied. Pre-organization and attachment of ceria NPs to the surface/edges of hexaniobate crystals prior to the scrolling process were observed, which is in a good agreement with our previous studies on the formation mechanism of NPPs. Partially filled CeO2@hexaniobate NPPs were further used in the in-situ growth of gold NPs within the empty/hollow space of hexaniobate NScs. This led to the formation of high-quality Au-CeO2@hexaniobate NPPs. We believe that smart combinations of the methods for the formation of NPPs, encapsulation, in-situ growth and insertion, will allow one to acquire other classes of nanocomposite materials composed of different types, shapes, and arrangements of NPs in the hollow spaces of distinct NTs/NScs.

Orientadores: Munir Salomão Skaf, Vitor Rafael Coluci / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T20:42:42Z (GMT). No. of bitstreams: 1 Faro_TatianaMellodaCosta_D.pdf: 8054394 bytes, checksum: ce0d79df42ce453ffc39b51bf0ad1094 (MD5) Previous issue date: 2015 / Resumo: Atualmente, a economia mundial depende do uso de combustíveis fósseis para a geração de energia. Esse modelo apresenta problemas ambientais graves, uma vez que o petróleo é um material não-renovável e muito poluente. O gás hidrogênio apresenta-se como uma alternativa promissora para substituir os combustíveis utilizados atualmente devido a um conjunto de características positivas: ele é atóxico, tem uma alta densidade energética gravimétrica e gera apenas água como produto de sua combustão. Apesar de tais vantagens, ele ainda não é utilizado comercialmente em larga escala. O maior empecilho tecnológico para que o hidrogênio possa substituir os combustíveis fósseis está no seu armazenamento. Existem diversas propostas para armazenar o hidrogênio, como tanques contendo o hidrogênio nas formas de gás pressurizado ou de líquido, além de sistemas sólidos que permitam a sua adsorção. Todavia, nenhum sistema construído até então foi capaz de armazenar o hidrogênio de forma tão barata, segura e eficaz quanto seria necessário. Nanoestruturas de carbono são vistas como uma boa alternativa para construir dispositivos de armazenamento de hidrogênio baseados na fisissorção. Os nanopapiros de carbono, formados por folhas de grafeno enroladas no formato de um papiro, são considerados particularmente promissores para armazenar o hidrogênio, uma vez que possuem uma alta área superficial, extremidades abertas e distâncias intercamadas facilmente controláveis. Na primeira etapa deste trabalho, realizamos simulações de Dinâmica Molecular (MD) para estudar a dinâmica e a estabilidade de diversos nanopapiros em função de alguns dos seus parâmetros estruturais. Posteriormente, aplicamos o método de Monte Carlo Grand-Canônico (GCMC) para estudar o processo de adsorção de hidrogênio em nanopapiros selecionados, de forma a caracterizar quantitativamente e qualitativamente as fases adsorvidas / Abstract: Presently, the world economy depends on the use of fossil fuels to generate energy. This model presents serious environmental problems, since petroleum is a non-renewable and very pollutant material. Hydrogen gas presents itself as a promising alternative to substitute the fuels currently used due to a few positive characteristics: it is non-toxic, possesses a high gravimetric energetic density and only generates water as a combustion byproduct. In spite of all these advantages, hydrogen still isn't used commercially in a large scale. The biggest technological drawback for hydrogen to substitute fossil fuels is in its storage. There are many proposed ways to store hydrogen, such as tanks containing highly pressurized or liquid hydrogen, or solid systems that allow its adsorption. However, no system built up to the date had been able to store hydrogen as cheap, safe and efficiently as necessary. Carbon nanostructures are seen as a good alternative to build hydrogen storage devices based on physisorption. Carbon nanoscrolls, formed by graphene sheets scrolled in a papirus-like shape, are considered as particularly promising adsorption materials, since they possess a high surface area, open edges and easily controllable interlayer distances. In the first step of this work, we made Molecular Dynamics (MD) simulations to study the dynamics and the stability of several nanoscrolls as a function of their structural parameters. Subsequently, we used the Grand-Canonical Monte Carlo (GCMC) method to study the hydrogen adsorption process in selected nanoscrolls, as to characterize the adsorbed phases quantitatively and qualitatively / Doutorado / Físico-Química / Doutora em Ciências