关键词: 醋酸纤维素, 纳米纤维膜, 戊二醛, 交联, 缩醛反应, 离子吸附

Abstract: Heavy metal ions are widely present in the aquatic environment, not only damaging the aquatic ecosystem, but also accumulating in the human body, and posing a serious threat to health. Therefore, it is necessary to remove heavy metal ions from water. Compared to traditional methods, the membrane separation method has the characteristics of low energy consumption, high accuracy, simple equipment, simple operation, and wide application range, making it one of the most promising separation technologies at present. Among numerous separation membranes, nanofiber membranes have become one of the most widely used separation membrane materials due to their high specific surface area, easy modification, and high adsorption efficiency. Nanofiber membranes can be prepared through various methods, and electrospinning is currently one of the most commonly used preparation techniques. The preparation process is fast, efficient, and the equipment is simple and easy to operate. At present, the use of natural, environmentally friendly, economical, and efficient raw materials to develop water treatment membrane materials has become a research trend. Cellulose acetate (CA) is a derivative of cellulose, which has advantages such as wide source, low price, and biodegradability. Its molecules contain a large number of hydroxyl groups, making it a good natural adsorption material. However, there are also a large number of hydrogen bonds between and within CA molecules, which can cause tight intermolecular connections and make it difficult for molecular chains to move. There are also shortcomings in the mechanical properties of CA nanofiber membranes, such as low strength and poor toughness. Polyvinyl alcohol (PVA), as a good degradable material, not only has good fiber forming properties and excellent mechanical properties, but also has a large number of negatively charged hydroxyl groups on the molecular chain, which can adsorb a large number of heavy metal cations. Therefore, co-spinning CA and PVA can not only improve the performance of CA nanofiber membranes, but also avoid the problem of poor separation ability of nanofiber membranes prepared from a single polymer. However, PVA itself also has some shortcomings. The presence of a large number of hydroxyl groups in PVA molecules gives it good hydrophilicity, which leads to poor water resistance of the prepared nanofiber membrane. However, the water resistance of CA/PVA nanofiber membranes can be effectively improved through glutaraldehyde (GA) steam crosslinking method. Therefore, to prepare a naturally degradable and highly efficient adsorption membrane material, this article uses electrospinning technology to prepare CA/PVA composite nanofiber membranes, and uses the glutaraldehyde vapor crosslinking method to cross-link and modify the membranes. The water resistance and heavy metal ion adsorption performance of the modified membranes under different conditions are explored. The research in this article can provide a fast and efficient method for preparing adsorption membrane materials, and promote the application of CA in the field of heavy metal adsorption.
The results show that CA and PVA still have good spinnability after blending. Due to the acetal reaction between glutaraldehyde and a large amount of hydroxyl groups in the raw material, the surface of the nanofiber membrane gradually densifies. After 24 h in water, the mass loss rate of the modified membrane decreases from 70.76% before modification to 7.28%, effectively improving the water resistance of the CA/PVA nanofiber membrane. The mechanical properties of the modified CA/PVA nanofiber membrane have also been improved to a certain extent, with a fracture strength increased from 0.76 MPa to 1.51 MPa and a maximum elongation at break of 9.30%. It was found by exploring the ion adsorption performance of the membrane that the modified CA/PVA nanofiber membrane reached an adsorption equilibrium for Cu2+ at 2 h, with a maximum adsorption capacity of 89.52 mg/g. Exploration has shown that the modified CA/PVA nanofiber membrane has good water resistance and mechanical properties, and has good adsorption effect on heavy metal ions, providing an effective method for the treatment of heavy metal wastewater.

Key words: cellulose acetate, nanofiber membrane, glutaraldehyde, crosslinking, acetal reaction, ion adsorption