Orientador: André Luiz Barboza Formiga / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-21T22:34:48Z (GMT). No. of bitstreams: 1 Ferreira_RicardoBarroso_M.pdf: 14699923 bytes, checksum: 14c38ecd37cab3267087c49c4b168a4e (MD5) Previous issue date: 2013 / Resumo: O trabalho apresentado explora a modificaçãoo do processo de síntese de uma rede metalorgânica conhecida como MIL-101(Cr), um material formado por clusters trinucleares de crômio(III) unidos por ligantes tereftalato em ponte. A partir do uso de meios reacionais contendo uma mistura de componentes (ligantes ou metais), visou-se a incorporação de diferentes componentes em materiais contendo a mesma estrutura do MIL-101(Cr). Os produtos formados por esta estratégia foram analisados por difração de raios X pelo método de pó, onde se observou que, dependendo da composição do meio reacional, materiais contendo a mesma estrutura do MIL-101(Cr) foram formados. Evidências da incorporação dos diferentes componentes na estrutura dos materiais foram conseguidas pelo uso das espectroscopias nas regiões do infravermelho e ultravioleta e visível. Para os materiais contendo diferentes ligantes, observou-se um grau de incorporação de um dos ligantes substituídos de até aproximadamente 20%, apresentando áreas superficiais da ordem de 2300 mg. Já, para os materiais contendo diferentes metais, obteve-se uma incorporação de Fe(III) de até 17%. Além do mais, neste caso, alguns resultados mostram que há uma homogeneidade da distribuição de ferro nestes materiais. Desta forma, a partir do desenvolvimento deste trabalho, mostrou-se que o método de síntese utilizado foi bastante simples e eficiente para a produção de novos materiais que apresentam a estrutura do MIL-101, mas com superfícies com características e reatividade diferenciadas. / Abstract: This study explores modifications in the process of synthesis of a metal-organic framework known as MIL-101(Cr), formed by chromium(III) trinuclear clusters linked by terephthalate bridges. Through the use of reaction media containing a mixture of components (linkers or metals), we aimed the incorporation of different components in materials presenting MIL-101(Cr) structure. The products obtained from this approach were characterized by powder X-ray diffraction, where we could observe that materials isoreticular to MIL-101(Cr) were formed, depending on the composition of reaction medium. From infrared and ultraviolet and visible spectroscopies, the incorporation of the different components in the structures was confirmed. For the materials containing different linkers, we observed incorporation degrees up to 20% for one of the substituted linkers and these materials presented specific surface areas in the order of 2300 mg. For the systems containing different metals, we obtained incorporation degrees up to 17%. Moreover, some results show that iron centers are homogeneously distributed over the structures. In conclusion, we could show that this synthetic approach was very simple and efficient for the formation of novel materials that are isoreticular to MIL-101(Cr), but presenting surfaces with diverse characteristics and reactivity. / Mestrado / Quimica Inorganica / Mestre em Química

Depuis une quinzaine d’années, les matériaux poreux de type Metal Organic Frameworks (MOFs) offrent de nouvelles perspectives dans le cadre du stockage d’hydrogène par adsorption. Ces matériaux possèdent une structure et un réseau de pores particulièrement bien adaptés à l’adsorption des gaz. Ainsi, le téréphtalate de Chrome (III) (MIL-101(Cr)), composé chimiquement très stable, possède une grande capacité de stockage de l’hydrogène, du dioxyde de carbone et du méthane. Afin de renforcer sa capacité de stockage d’hydrogène, un dopage au charbon actif (AC) du matériau a été envisagé. Les synthèses des matériaux dopés et non-dopés ont été réalisées et, pour cela, différents agents minéralisants (acide fluorhydrique, acide acétique et acétate de sodium) ont été testés. Les matériaux synthétisés furent caractérisés par diffraction des rayons X (DRX), par microscopie électronique à balayage (MEB), par analyses thermogravimétriques (ATG) et par adsorption d’azote à 77K. Les capacités de stockage d’hydrogène de ces matériaux à 77 K et 100 bar ont été évaluées par mesures des isothermes d’adsorption d’hydrogène, réalisées par méthodes volumétrique et gravimétrique. Les résultats obtenus par ces deux méthodes sont en parfait accord et le matériau composite affiche une capacité d’adsorption de 13.5 wt%, qui est supérieure à celle du matériau non dopé (8.2 wt% dans les même conditions expérimentales). Les cinétiques d’adsorption ont été mesurées à 77 K par méthode volumétrique. Les résultats obtenus ont été comparés au modèle de la force motrice linéaire, Linear Driving Force (LDF). Un modèle de diffusion dépendant de la température a été développé afin de tenir compte des variations de températures qui se produisent durant le processus d’adsorption. / Since the last 15 years, the porous solids such as Metal-Organic Frameworks (MOFs) have opened new perspectives for the development of adsorbents for hydrogen storage. The structure and the pore networks of these materials are especially adapted to the adsorption of gases. The chromium (III) terephthalate-based MIL-101(Cr) is a very stable material which exhibits good adsorption uptakes for hydrogen (H2), carbon dioxide (CO2) and methane (CH4).In this study, syntheses were carried out by different ways and several mineralizing agents such as hydrofluoric acid (HF), acetic acid (CH3COOH) and sodium acetate (CH3COONa) have been tested. Moreover, Activated Carbon (AC) has been introduced in the framework to create an AC incorporated composite material with an enhanced specific surface area. Conventional techniques such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and nitrogen (N2) adsorption isotherms at 77 K were used for materials characterizations.In the aim to evaluate hydrogen storage capacities of these materials, hydrogen adsorption isotherms were measured at 77 K via both volumetric and gravimetric methods, and the obtained results are in good agreement. A hydrogen uptake value of 13.5 wt% has been measured at 77 K and 100 bar for the composite material which shows a great improvement of hydrogen capacity compared to the pristine MIL-101(Cr) (8.2 wt%).Finally, hydrogen adsorption kinetics has been measured at 77 K using volumetric method. The obtained results were compared to the Linear Driving Force (LDF) and a temperature dependent diffusion model was also considered to take into account the temperature variations which occur during the adsorption process.

A supply of clean, carbon neutral and sustainable energy is the most scientific and technical challenge that humanity is facing in the 21st century. Though there is enough fossil fuels available for a few centuries, their use would increase the level of CO2 in the atmosphere. This would lead to global warming and may pose serious threats such as rising of sea level, change in hydrological cycle, etc. Hence there is a need for an alternative source of fuel that is clean and sustainable. Among the many resources considered as an alternative power source, hydrogen is considered one of the most promising candidates. To use hydrogen commercially, appropriate hydrogen storage system is required. Various options to store hydrogen for onboard use include gaseous form in high-pressure tanks, liquid form in cryogenic conditions, solid form in chemical or metal hydrides, or by physisorption of hydrogen on porous materials. One of the emerging porous materials are metal-organic frameworks (MOFs) which provide several advantages over zeolites and carbon materials because the MOFs can be designed to possess variable pore size, dimensions, and metrics. In general, MOFs adsorb hydrogen through weak interactions such as London dispersion and electrostatic potential which lead to low binding enthalpies in the range of 4 to 10 kJ/mol. As a result, cryogenic conditions are required to store sufficient amounts of hydrogen inside MOFs. Up to date several MOFs have been designed and tested for hydrogen storage at variable temperature and pressure levels. The overall results thus far suggest that the use of MOFs for hydrogen storage without chemical and electronic modifications such as doping with electropositive metals or incorporating low density elements such as boron in the MOFs backbone will not yield practical storage media. Such modifications are required to meet gravimetric and volumetric constraints. With these considerations in mind, we have selected a Cr-based MOF (MIL-101; Cr(F,OH)-(H2O)2O[(O2C)-C6H4-(CO2)]3•nH2O (n ≈ 25)) to investigate the impact of nickel inclusion inside the pores of MIL-101 on its performance in hydrogen storage. MIL-101 has a very high Langmuir surface area (5900 m2/g) and two types of mesoporous cavities (2.7 and 3.4 nm) and exhibits exceptional chemical and thermal stabilities. Without any modifications, MIL-101 can store hydrogen reversibly with adsorption enthalpy of 10 kJ/mol which is the highest ever reported among MOFs. At 298 K and 86 bar, MIL-101 can store only 0.36 wt% of hydrogen. Further improvement of hydrogen storage to 5.5 wt% at 40 bar was achieved only at low temperatures (77.3 K). As reported in the literature, hydrogen storage could be improved by doping metals such as Pt. Doping is known to improve hydrogen storage by spillover mechanism and Kubas interaction. Hence we proposed that doping MIL-101 with a relatively light metal possessing large electron density could improve hydrogen adsorption. Preferential Ni doping of the MIL-101’s large cavities which usually do not contribute to hydrogen uptake is believed to improve hydrogen uptake by increasing the potential surface in those cavities. We have used incipient wetness impregnation method to dope MIL-101 with Ni nanoparticles (NPs) and investigated their effect on hydrogen uptake at 77.3 K and 298 K, at 1 bar. In addition, the impact of metal doping on the surface area and pore size distribution of the parent MIL-101 was addressed. Metal content and NPs size was investigated by ICP and TEM, respectively. Furthermore, crystallinity of the resulting doped samples was confirmed by Powder X-ray Diffraction (PXRD) technique. The results of our studies on the successful doping with Ni NPs and their impact on hydrogen adsorption are discussed.

<div> <p>Metal-organic frameworks (MOFs) are a class of compounds consisting of metal ions or clusters coordinated to organic ligands in porous structure forms. MOFs have been proposed in use for gas adsorption, purification, and separation applications. This work combines MOFs with 3D printing technologies, in which 3D printed plastics serve as a mechanical structural support for MOFs powder, in order to realize a component design for gas adsorption. The objective of the thesis is to understand the gas adsorption behavior of MIL-101 (Cr) MOF coated on 3D printed PETG, a glycol modified version of polyethylene terephthalate, through a combined experimental and modeling study. The specific goals are: (1) synthesis of MIL-101 (Cr) MOFs; (2) nitrogen gas adsorption measurements and microstructure and phase characterization of the MOFs; (3) design and 3D printing of porous PETG substrate structures; (4) deposition of MOFs coating on the PETG substrates; and (5) Monte Carlo (MC) modeling of sorption isotherms of nitrogen and carbon dioxide in the MOFs.</p><p>The results show that pure MIL-101 (Cr) MOFs were successfully synthesized, as confirmed by the scanning electron microscopy (SEM) images and X-ray diffrac- tion (XRD), which are consistent with literature data. The Brunauer-Emmett-Teller (BET) surface area measurement shows that the MOFs samples have a high cover- age of nitrogen. The specific surface area of a typical MIL-101 (Cr) MOFs sample is 2716.83 m2/g. MIL-101 (Cr) also shows good uptake at low pressures in experimental tests for nitrogen adsorption. For the PETG substrate, disk-shape plastic samples with a controlled pore morphology were designed and fabricated using the fused de-</p><p> </p><p>position modeling (FDM) process. MOFs were coated on the PETG substrates using a layer-by-layer (LbL) assembly approach, up to 30 layers. The MOFs coating layer thicknesses increase with the number of deposition layers. The computational model illustrates that the MOFs show increased outputs in adsorption of nitrogen as pres- sure increases, similar to the trend observed in the adsorption experiment. The model also shows promising results for carbon dioxide uptake at low pressures, and hence the developed MOFs based components would serve as a viable candidate in gas adsorption applications.</p><div><br></div></div>

Indiana University-Purdue University Indianapolis (IUPUI) / Metal-organic frameworks (MOFs) are a class of compounds consisting of metal ions or clusters coordinated to organic ligands in porous structure forms. MOFs have been proposed in use for gas adsorption, purification, and separation applications. This work combines MOFs with 3D printing technologies, in which 3D printed plastics serve as a mechanical structural support for MOFs powder, in order to realize a component design for gas adsorption. The objective of the thesis is to understand the gas adsorption behavior of MIL-101 (Cr) MOF coated on 3D printed PETG, a glycol modified version of polyethylene terephthalate, through a combined experimental and modeling study. The specific goals are: (1) synthesis of MIL-101 (Cr) MOFs; (2) nitrogen gas adsorption measurements and microstructure and phase characterization of the MOFs; (3) design and 3D printing of porous PETG substrate structures; (4) deposition of MOFs coating on the PETG substrates; and (5) Monte Carlo (MC) modeling of sorption isotherms of nitrogen and carbon dioxide in the MOFs. The results show that pure MIL-101 (Cr) MOFs were successfully synthesized, as confirmed by the scanning electron microscopy (SEM) images and X-ray diffraction (XRD), which are consistent with literature data. The Brunauer-Emmett-Teller (BET) surface area measurement shows that the MOFs samples have a high cover- age of nitrogen. The specific surface area of a typical MIL-101 (Cr) MOFs sample is 2716.83 m2/g. MIL-101 (Cr) also shows good uptake at low pressures in experimental tests for nitrogen adsorption. For the PETG substrate, disk-shape plastic samples with a controlled pore morphology were designed and fabricated using the fused deposition modeling (FDM) process. MOFs were coated on the PETG substrates using a layer-by-layer (LbL) assembly approach, up to 30 layers. The MOFs coating layer thicknesses increase with the number of deposition layers. The computational model illustrates that the MOFs show increased outputs in adsorption of nitrogen as pressure increases, similar to the trend observed in the adsorption experiment. The model also shows promising results for carbon dioxide uptake at low pressures, and hence the developed MOFs based components would serve as a viable candidate in gas adsorption applications.