| Chitosan,(1,4)-2-amino-2-deoxy-β-D-glucose,(C8H13NO5)n. Since the amino group,hydroxyl group and a small amount of N-acetyl group of amino group in the presence ofchitosan, is a heavy metal based adsorbent. However, the lower the specific surface area ofchitosan, resulting in less surface adsorption sites, the adsorption capacity remains to beimproved. Research shows that the adsorption capacity of chitosan membrane is best, chitosanmicrospheres is better than powder, However, chitosan membrane commonly prepared isfragility. Therefore, improving adsorption capacity by enlargeing the chitosan surface area, isone of the hot research. A novel material, chitosan/poly(vinyl alcohol) nanofibermembrane,was prepared by electrospining, one can greatly increase the surface area andporosity of the material, on the other hand,the addition of polyvinyl alcohol not onlyimproved the brittleness of chitosan membranes, improve the mechanical properties of thematerial, but also can better reduce material costs.To this end, this paper carried out optimization through electrostatic spinning CS/PVAnanofiber membrane process and successfully prepared continuous defect-free nano-materials,and the use of SEM, BET, FTIR, XRD, mechanical properties and other means to studycharacterization of the material, while the experimental study by adsorption of heavy metalions adsorption performance, the study obtained the following main results and conclusions:The applied voltage, tip-collector distance and solution flow rate of the electrospinningprocess were25kV,15.0cm and0.12mL h-1,respectively. and ultimately determine theoptimum spinning conditions: use of low viscosity (100-200mPa.s deacetylation degree of97.5) chitosan, CS/PVA weight ratio of20/80solution at7wt%, the concentration of aceticacid solvent is20wt%. Morphology of the fibers obtained by spinning under the bestconditions.The prepared nanofibers were characterized by Scanning Electron Microscope (SEM),Fourier Transform Infrared (FTIR), X-ray diffraction (XRD) and Brunauer–Emmert–Teller(BET). The results showed that: the obtained CS/PVA as continuous filaments withoutbreaking the beads without fiber, The average diameter of76.31nm, a surface area of219.42m2g-1, at the maximum load of the tensile stress51.98Mpa, tensile strain of4.967%,a modulus of elasticity3029.35Mpa, IR and XRD are shown in the CS and PVA, which arenot simply mixing, but a chemical reaction occurs.The CS/PVA nanofiber membranes used for the adsorption of heavy metal ions, results showed The adsorption equilibrium of CS/PVA on metal ions can be reached within2hours.Sorption capacities of CS/PVA onto metal ions increased with the increases of temperature,initial metal ion and pH and the optimum pH was determined as5.5. The adsorptioncapacities of Cu2+,Ni2+and Cd2+by the chitosan/poly(vinyl alcohol) nanofiber were98.65mg g-1,116.89mg g-1and124.23mg g-1,respectively at25℃, pH5.5and initial heavymetal concentration of100mg L-1.the adsorption of Cd2+, Ni2+, Cu2+by CS/PVA nanofiber membrane is no obviousdiffrent, the removal rate was above85%, and the effect of adsorption rate is still sort ofCd2+> Ni2+> Cu2+.The results of ionic strength surface shows that, the adsorption capacityof Cd2+, Ni2+and Cu2+by CS/PVA nanofiber membrane were rather slight decrease with increasing NaClconcentration.The sorption process was found to follow pseudo-first-order and pseudo-second-orderkinetic models and the adsorption isotherm was well described by Langmuir and Freundlichadsorption isotherm models. The calculated thermodynamic parameters (△G,△H and△S)showed that the adsorption of metal ions onto the PVA/Chitosan nanofiber membrane wasfeasible, spontaneous and endothermic. |
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