Halloysite nanotube-based melamine sponge composite material prepared under supercritical carbon dioxide atmosphere: Characterization studies and evaluation of its performance as sorbent for the selective removal of petroleum derivatives, oily substances and organic solvents from water

In this thesis; some studies related with the characterization, the determination of sorption capacity values for various petroleum derivatives, oily substances and organic solvents, the sorption kinetics and the determination of separation and selective removal performance for oil-water or organic solvent-water mixtures were performed for a new MS-based sorbent material (MS/METES) prepared by the coating of sponge with purified- and activated-halloysite nanotube (HNT) and methyltriethoxysilane (METES) in supercritical carbon dioxide atmosphere. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques were used to determine the surface morphology and elemental composition of MS sorbent material coated with HNT and METES, respectively. It was proved from SEM analysis that there was a smooth surface on uncoated MS material and a rough surface structure was formed on the coated MS material by performing the coating process on the MS surface. Moreover, it was also verified by XPS analysis that the coating was successfully applied to the MS material. Water and oil contact angle measurements were carried out to prove the superhydrophobic and superoleophilic surface properties of MS/METES, respectively. Water contact angle of 153.0° and oil contact angle of 0° were measured for MS/METES sorbent material. Water contact angle measurements of new sorbent material maintained at different temperatures for 24 h were performed and it was observed that the thermal stability of the material was quite good. For the determination of chemical stability of MS/METES sorbent material, water contact angle measurements were carried out on the sorbent material after exposure of the sorbent material to HCl, NaOH and NaCl solutions. Water contact angle value of the sorbent material kept in 0.01 M HCl solution, 0.01 M NaOH solution and 5% NaCl solution was found to be 152.0°, 151.9° and 151.2°, respectively. The sorption-squeezing process was applied to the MS/METES sorbent material with the selected pollutants (diesel, machine oil and chloroform) for 15 times and then the water contact angle value of each sorbent material was measured to determine whether there is any serious deformation in the coating of sorbent material after 15 uses. For the sorbent materials used in the 15 sorption-squeezing processes of diesel, machine oil and chloroform pollutants, water contact angle measurement results obtained in the range of 148.2°-150.8° exhibited that the coating on the MS/METES sorbent material did not undergo a serious deformation even after 15 uses. Kinetic studies were performed for diesel, chloroform and machine oil pollutants and it was found that the fitting of pseudo second order kinetic model with experimental sorption kinetics data was better than that of the pseudo first order kinetic model. Furthermore, the sorption capacity values of MS/METES for various pollutants were determined. Among the various pollutants including gasoline, diesel, kerosene, machine oil, olive oil, toluene, n-hexane, N,N-dimethylformamide, dimethyl sulfoxide, chloroform, petroleum ether, ethyl alcohol and crude oil, it was observed that MS/METES reached the highest sorption capacity value in chloroform with a sorption capacity value of 122.4 g/g and the lowest sorption capacity value in petroleum ether with a sorption capacity value of 46.9 g/g. In this study, the usability of sorbent material in different separation methods was investigated. Using the spontaneous separation method, the selective separation of chloroform from water was achieved by the MS/METES sorbent material with the separation efficiency of 99.9% and the flux of 2780 L/(m2.h) in the chloroform-water mixture.