Mechanochemical Activation of Synthetic Nanosized 2-d Layered Materials: Preparation and Characterization

Fahami, Abbas
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The clay materials provide a 2-D lamellar structure with a myriad of applications in medicine, water treatment, catalysis, and biochemistry. They are utilized for the development of organic and/or inorganic-clay nanocomposites due to high cation exchange capacity, swelling behaviour, adsorption and large surface area. The surface can be chemically and physically modified to suit technological needs. Various ionic clay minerals such as Hydrotalcite (HT: Mg1-xAlx(OH)2Clx), Hydrocalumite (HC: Ca1-xAlx(OH)2Clx), Talc (Mg3Si4O10(OH)2), Pyrophyllite (PP: Al2Si4O10(OH)2), Haloysite (HS: Al2Si2O5(OH)4), Montmorillonite (MMT: Al2-xMgxSi4O10(OH)2Nax), and Hectorite (HEC: Mg3-xLixSi4O10(OH)2Nax) can be synthesized utilizing hydrothermal procedures. This synthesis method is tedious, time consuming, expensive, energy-intensive, and dangerous due to the high temperatures and pressures required. In the synthesis of clay minerals precursor compounds are dissolved in water and precipitated as amorphous gels. Subsequent hydrothermal treatment produces the desired clay mineral. This process involves bond breaking by the solvent and then reformation through hydrothermal treatment. The hypothesis in this project is based on breaking the bonding of reagents and reforming a new clay material through a facile solid state method rather than through solvents. The ultimate objective of this research is synthesis of these materials via mechanochemical means, study structural features, morphological characterization, and thermal behavior of products as a function of synthesis conditions (e.g. the effect of ion substitution and synthesis parameters on the porosity and textural characteristics of synthetic clays). Mechanochemistry is the combination of mechanical and chemical phenomena which is complex and different from thermal or photochemical mechanisms. In this project, we successfully prepared anionic clays (e.g. HT, and HC), non-ionic (e.g. Talc and PP), and cationic clays (e.g. MMT, and HEC) through the mechanochemistry method. The subsequent autoclaving process on the non-ionic and cationic samples were studied. The structural features and morphological characteristics of milled samples were analyzed and characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), elemental mapping analysis, transmission electron microscopy (TEM), X-ray fluorescence (XRF), and differential thermogravimetric analysis (DTGA). The results presented in this dissertation provided a plethora of new information that challenge old dogmas. One of the main contributions of this study was to demonstrate, for the first time, that many smectite clays can be synthesized via a one step, wet mechanochemistry process.
Mechanochemistry, Hydrotalcite, Haydrocalumite, Talc, Kaolinite, Halloysite, Montmorillonite, Hectorite
Fahami, A. (2017). <i>Mechanochemical activation of synthetic nanosized 2-d layered materials: Preparation and characterization</i> (Unpublished dissertation). Texas State University, San Marcos, Texas.