| Chitosan (CS) is a type of natural renewable resource with many attractive properties such as non-toxic, pollution-free, biocompatible and biodegradable etc. More importantly, it is quite easy to prepare films or fibers from it. Meanwhile, the chitosan contains a large amount of -NH2 groups, which can chelate with heavy metal ions. So it is a great natural-made water treatment material. In order to overcome the disadvantage of secondary pollution caused by the chitosan adsorbents in the shape of powder, microsphere, solution and gel, in this study, a series of chitosan porous films with nanofibers inside were fabricated by a particular method which combines the thermally induced phase separation with the phase inversion. The main results are listed below:(1) The physicochemical properties of the chitosan raw material were determined. Through the molecular viscosity method and titration method, the molecular weight and degree of deacetylation of chitosan were determined. They were 8.99×105 and 93.3%, respectively.(2) By thermally induced phase separation combined with phase inversion method, CS porous films (P-CSNF) and CS/PVA porous blend films (P-CS/PVANF) were successfully prepared. When the quenching temperature was -20℃, the quenching time was 12 hours and the concentration of NaOH coagulation solution was 1%, P-CSNF with a moderate thickness dense layer, low density (0.040g.cm-3), high porosity (95%) and high specific surface (15.07m2/g) was prepared; Extending the quenching time and decreasing the quenching temperature were both beneficial to the growth of the internal nanofibers; The chitosan films prepared from 1% chitosan solution showed the best properties. However, those films are fragile without free-standing ability. So we chose the films prepared from 2% chitosan solution to continue our subsequent experiments. For P-CS/PVANF, instrumental analysis including FITR, thermogravimetric analysis and mechanical performance showed that when the blending ratio of CS and PVA was 6:4, they have the best compatibility, and the best performance. The initial thermal decomposition temperature of the blend film is 234℃, the tensile strength and elongation at break are 0.16MPa and 14%, the film density, porosity and specific surface area are 0.032g/cm3,96% and 18.87m2/g, respectively.The P-CSNF and P-CS/PVANF were used for adsorption of Cu2+ and Pb2+ and the adsorption kinetics, isothermal adsorption, the influence of pH and film desorption performance were studied. The adsorption kinetics of the four kinds of film samples complys with the quasi-dynamic equation. The adsorption rate was determined by the chemical adsorption, and the adsorption rates of four samples is ranked in the order of P-CSNF>P-CS/PVANF>CL-CS>FC-CS; The adsorption isotherm study indicates that the isothermal adsorption behavior of four kinds of film samples on Cu2+ and Pb2+ is consistent with the Langmuir model. So the adsorption process belongs to the Langmuir single molecular layer adsorption, which may be owing to the coordination between -NH2 groups and metal ions. The date of saturation adsorption capacity of Cu2+ and Pb2+ are 131.83 mg/L(2.08 mmol/g),74.58 mg/L(0.36 mmol/g) and 98.06 mg/L(1.54 mmol/g),46.55 mg/L(0.23 mmol/g). In the pH value influence factor experiment, with the increase of the pH value, the adsorption capacity of the film increases until the adsorption saturation. This phenomenon is caused by the electrostatic interaction of functional groups and the chelation of -NH2 groups; When the disodium EDTA acted as the desorption agent, desorption rate of the films can reach 90%. In the second adsorption cycle of CS film, the adsorption capacity of Cu2+ and Pb2+ can reach more than 95% of the original adsorption capacity. With increasing recycle times, the adsorption efficiency of Cu2+ and Pb2+ decreased. In the 6th cycle of the adsorption, the adsorption capacity of Cu2+ and Pb2+ can reach more than 88% of the original adsorption capacity. |
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