| Dyes in waste water are difficult to degrade and are harmful to human body and environment.Membrane separation,biodegradation,electrochemical and adsorption methods have been widely used in the removal of dyes in wastewater.Adsorption method has the advantages of low cost,easy regeneration and high efficiency.Many kinds of materials such as activated carbon,clay,natural polymer can be used as adsorption materials.The natural macromolecule sodium alginate has the advantages of low cost,easy degradation,non-toxic,reusable and so on and can be prepared into various adsorption materials such as microspheres,fibers,gels and nanofiber membranes by its unique gel properties.Among them,sodium alginate nanofiber membrane has the advantages of high porosity,large specific surface and easy modification,so it has a broad application prospect in the field of dye wastewater treatment.From the structural point of view,sodium alginate has a large number of carboxyl groups on its molecular chain,which can produce strong Coulomb attraction between cationic dyes,resulting in a large number of fast adsorption of cationic dyes on its surface,which is difficult to control,and poor uniformity of adsorption and deposition.Sodium alginate and anionic dyes have strong same charge repulsion,so the adsorption capacity of anionic dyes is weak,which limits its application.In this paper,the sodium alginate nanofiber membrane was modified by electrospinning with different polymers?gelatin and chitosan?with different electrochemical properties to effectively solve the above problems.Firstly,gelatin modified sodium alginate nanofiber membrane was prepared by electrospinning.Gelatin is an amphoteric polyelectrolyte,which contains carboxy and amino groups on the molecular chain and is weak in electricity,so it can be directly mixed with sodium alginate solution for electrospinning.A modified sodium alginate membrane adsorption material containing both positive amino group and negative carboxy group was obtained,which can be used to regulate the adsorption properties of dyes.Secondly,chitosan modified sodium alginate nanofiber membrane was prepared by coaxial electrospinning technology.Chitosan is a polycationic electrolyte with higher amino content and electricity than gelatin.It has a strong interaction with sodium alginate molecules.When directly mixed,it will be complexed into a gel,making it difficult to conduct electrostatic spinning.The chitosan modified sodium alginate nanofiber membrane with unique core-shell structure can be prepared by coaxial electrospinning technique,and its adsorption ability to dye can be improved to a certain extent.The adsorption properties of gelatin-modified sodium alginate nanofiber membrane on methylene blue and acid blue were studied.After gelatin modification,the adsorption mechanism of methylene blue on nanofiber membrane can be analyzed by Langmuir isotherm adsorption model and pseudo-second-order kinetic model.It is calculated that the saturated adsorption capacity decreases from 2046 mg/g to 1937 mg/g.The adsorption rate constant decreased from 1.689×10-4 g/mg·min decreased to 1.071×10-4g/mg·min,but the deposition uniformity of methylene blue was improved obviously.The standard deviation of methylene blue adsorbed by nanofiber membrane decreased from0.140 to 0.050 at 60 min.Gelatin modification can improve the reuse of sodium alginate nanofiber membrane,and the regeneration efficiency after four cycles of adsorption-desorption is increased from 69%to 88%.In addition,the adsorption rate constant of the nanofiber membrane to acid blue dye increased from 1 g/mg·min to 45g/mg·min,and the saturation adsorption increased from 15.4 mg/g to 212.8 mg/g.The adsorption properties of chitosan modified sodium alginate nanofiber membrane for methylene blue and acid blue were systematically studied.After chitosan modification,the adsorption mechanism of acid blue on nanofiber membrane can be analyzed by Langmuir isotherm adsorption model and pseudo-second-order kinetic model.It is calculated that the saturated adsorption capacity decreases from 2135 mg/g to1625 mg/g.The adsorption rate constant decreased from 2.489×10-4 g/mg·min to 1.821×10-4 g/mg·min.Chitosan modification could improve the reusability of sodium alginate nanofiber membrane.The regeneration efficiency increased from 67%to 92%after the fourth adsorption-desorption cycle.In addition,the adsorption rate constant of acid blue dye on nanofiber membrane increased from 1.1 g/mg·min to 56 g/mg·min,and the saturated adsorption capacity increased from 16.9 mg/g to 278.5 mg/g.Firstly,gelatin-modified sodium alginate nanofiber membrane is prepared by electrospinning technology.Gelatin is an amphoteric polyelectrolyte with carboxyl and amino groups on the molecular chain.It is weak in electrical properties and can be directly blended with sodium alginate solution.Electrospinning gives a modified sodium alginate adsorbent containing both a positive amino group and a negative carboxyl group,which can regulate the adsorption performance of the dye.Secondly,chitosan modified sodium alginate nanofiber membrane was prepared by coaxial electrospinning technology.Chitosan is a polycationic electrolyte.The amino content and electrical properties of chitosan are higher than gelatin,and there is a comparison between sodium alginate and sodium alginate.Strong interaction,direct solution blending will synthesize gel and it is difficult to directly electrospin,while coaxial electrospinning technology can be used to prepare chitosan modified sodium alginate nanometer with unique core-shell structure.The fiber membrane has a certain improvement in its ability to adsorb dyes.In this paper,based on the system's investigation of the effects of electrospinning process parameters such as voltage,receiving distance,solution flow rate and temperature on the morphology of nanofiber membranes,scanning electron microscopy,automatic specific surface area,Fourier transform infrared spectroscopy,thermogravimetric analysis,etc.Changes in morphology,pore size,chemical structure and thermal stability of nanofiber membranes before and after modification.The results show that as the voltage decreases,the solution flow rate and the receiving distance increase,the average diameter of the nanofibers decreases.The addition of gelatin and chitosan to the sodium alginate spinning solution can increase the specific surface area of the nanofiber membrane,enhance the mechanical properties of the membrane,and slightly reduce the thermal stability of the sodium alginate nanofiber membrane. |
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