Development and characterization of expanded graphite for oil sorption application

Expanded graphite (EG) is a versatile material with various unique properties, making it useful in various industrial and commercial applications. As a carbon-based sorbent with high porosity, EG has recently been prepared using different methods, most of which focus on environmental and economic perspectives. In this thesis, EG is prepared using two methods: a one-step method, which focuses on economic aspects by minimizing energy use, and a two-step method, which avoids using strong acids and is considered more environmentally friendly. Due to its strong oleophilic properties towards various oils and its hydrophobic nature, EG is widely used as a sorbent to address oil spills in oceans resulting from fossil fuel transportation. EG was prepared by a sulfur-free EG preparation process that is believed to be eco-friendly because it limits the use of sulfur, which is considered a key component in EG preparation in traditional methods. Eco-friendly EG was prepared using natural flake graphite as a precursor in a two-step chemical oxidation method. In the first step “oxidation,” the chemical intercalation process was carried out at room temperature for 30 min with an optimum weight ratio of 1 g: 5.1 g: 0.2 g of natural flake graphite (NFG), hexadecanoic acid, and potassium permanganate. Then, in the second step “intercalation,” nitric acid, acetic acid, and potassium permanganate were employed as the intercalating agents to further increase the expanded volume of EG. Under the optimal conditions, a maximum expanded volume of 470 mL/g was obtained. An efficient and energy-conserving preparation process to obtain EG, in which flake graphite is intercalated and expanded at room temperature. The flake graphite was expanded using a simple and effective method in which graphite intercalation and expansion are accomplished using a binary system of concentrated sulfuric acid (H2SO4) and inorganic salts, specifically sodium peroxydisulfate (Na2S2O8). The optimal conditions were at room temperature, with mass ratios of graphite to Na2S2O8 of 1:7 and graphite to concentrated H2SO4 of 1:20. This gave a maximum expanded volume of 140 mL/g. XRD, SEM, and FT-IR were utilized to characterize the microstructures, morphologies, and functional groups of the expanded graphite. Following expansion, the flake graphite transformed into a worm-like structure, with minimal damage to the graphite sheets. Additionally, the findings revealed that the interlayers of natural flake graphite were fully opened and transformed into a structure resembling a fluffy, rope-like form, similar to a worm, upon expansion. Furthermore, the two types of fabricated expanded graphites were applied to oil sorption. Both types show promise as engineering materials for water purification sorbents and demonstrate significant oil sorption capacities. ATEG and EG-SF exhibited maximum oil sorption capacities of 27 g/g and 89 g/g, respectively. When compared to their expanded volumes, ATEG absorbed more oil than EG-SF. These results suggest that the preparation methods for EG have a significant impact on its oil adsorption capacity.

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