Simultaneous oleophobic hydrophilic chitosan silica halloysite nanocomposite coating membrane for separation of oily wastewater
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Date
2022
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Universiti Teknologi Malaysia
Abstract
The treatment of oily wastewater has been a difficult endeavour as oil in water emulsion is one of the most difficult pollutant to remove. Extensive numbers of studies were conducted by many researchers that use nanocomposite to separate oil in water emulsion in a facile way with minimal use of energy while being environmentally friendly. In the case of oily wastewater treatment, the most desired materials are ones with oil-removing properties which are hydrophilic and oleophobic. Therefore, this study focused on the development of nanocomposite coating which is made of silica hybridized with chitosan and halloysite nanotube (HNT). Both chitosan (CTS) and HNT are chosen as the adsorbent in the nanocomposite coating for its excellent water adsorption and can be easily modified to achieve different wettabilities. Chitosan-silica (CTS-Si) hybrid was functionalized onto the external side of HNT and has exhibited simultaneously oleophobic-hydrophilic properties where the coated polysulfone (PSf) membrane had shown improved performance. The nanocomposite coating was characterized for its morphological properties via field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM) and physicochemical properties via Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), colloidal stability and zeta potential analysis. The performance of the nanocomposite as coating on PSf membrane was evaluated in terms of pure water flux, oil rejection rate and oil antifouling properties using crude oil as foulant. Finally, the optimization of the nanocomposite coating formulation was done in terms of pH and loading, and the optimization of coated membrane was done in terms of dipping time and feed concentration. The XPS results revealed that there is a wide band between 102.6–103.7 eV at Si2p denoted the successful grafting of organosilanes (Si-O-Si) groups of HNT onto the CTS-Si. The FTIR spectrum presented significant peaks at 3621 cm-1 attributed to chitosan, 1013 cm-1 attributed to the characteristics of C-N stretching on chitosan and 787 cm-1 signifying the stretching of Si-O-Si on HNT. 29Si, 27Al and 13H NMR spectroscopy confirmed the extensive modification of the particles’ shells with chitosan-silica hybrid covalently linked to the HNT domains. The morphological analysis via FESEM resulted in the surface morphology that indicated improved wettability of the nanocomposite. The resultant colloids have high colloid stability of 19.3mV and electrophoretic mobility of 0.1904μmcm/Vs. The nanocomposite was coated on PSf membrane and compared with its precursor in which PSf coated with CTS-Si/HNT at 60s coating retention time recorded the best wettability of 28.1° water contact angle and 171.3° oil contact angle. In terms of performance, the CTS-Si/HNT coated PSf showed the highest water flux of 680 Lm-2h-1 and oil rejection of 99%. The optimization study has shown that the optimum condition for the coating synthesis was found to be at pH7.5 and CTS-Si/HNT loading of 1.33wt%. The optimum water contact angle of the coating was found to be 45° and oil contact angle of 183.6°. The confirmatory test has revealed that the optimum performance was acceptable with average error of 1.78% and 1.91% for water contact angle and oil contact angle, respectively. Therefore, the application of CTS-Si/HNT as coating for polymer membrane has shown great potential to be applied in treating oily wastewater due to its excellent oil rejection capability and surface wettability.
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Thesis (PhD.)
Keywords
Sewage—Purification—Oil removal, Nanocomposites (Materials), Polymeric membranes