Composite Foam Supported By Polysaccharide Nanofibrils And Its Application In Water Pollutant Treatment

The porous foam has broad application prospects in tissue engineering, adsorption, catalyst, biomedical and many other fields because of its many advantages such as relatively low density, high specific surface area, light weight, sound insulation, heat insulation and good permeability. Poly vinyl alcohol (PVA) foam prepared by freeze-drying method is easily to shrink after moisture adsorption due to its abundant hydroxyl. Graphene oxide (GO) is a kind of excellent adsorbent material. However, GO foam could collapse and disperse in aqueous quickly and it’s tough for separation. Cellulose and chitin are two of the most abundant polysaccharide in nature and they have the advantages of extensive sources, low cost, non-toxic, non-pollution, biocompatibility, biodegradability. They are favorable reinforcing materials because their nanofibrils have high elastic modulus and rigidity.In this thesis, cellulose and chitin nanofibrils with diameter of 20-50 nm were defibrillated through wet-grinding and homogenizing process. The GO was prepared according to the modified Hummers method. The PVA/cellulose nanofibrils (PC) and GO/ chitin nannofibrils (GO-CNF) composite foams were fabricated by freeze-drying method. The morphology, structure and mechanical property of composite foams were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrogram (FTIR) and compression testing. Moreover, water uptake and biodegradability tests of PVA composite foams were studied and the application of GO composite foams in batch adsorption and column adsorption were investigated.The porous sizes of PVA composite foams increased with the increase of nanofibril contents, but dropped with the decrease of freezing temperature and improvement of solid contents. The PC30 foam had the highest compressive stress of 328.5 kPa. Comparing with PVA foam, the ultimate moisture contents of PC60 foam decreased from 14.70% to 11.38% and the volume shrinkage changed from 70.7% to 2.4% at equilibrium of water uptake test. After 30 days’ biodegradation in compost environment, the PC60 foam was almost degraded completely.The introduction of chitin nanofibrils improved the mechanical strength of GO composite foams from 10.5 to 24.3 kPa. The equilibrium adsorption of methylene blue (MB) on GO-CNF40 was well-fitted to Langmuir isotherm model and the Qm was 173.3 mg/g. The composite foams reinforced by CNF were dimensionally stable during the column adsorption process and could be reused after elution. The removal efficiency of MB on GO-CNF40 was still nearly 90% after 3 cycles. Furthermore, methyl orange (MO), Pb(Ⅱ) and p-chloroaniline adsorbed by GO-CNF40 were also explored. The results indicated that GO composite foams reinforced by chitin nanofibrils were effective adsorbents to heavy metal ions and cationic pollutants.