Preparation Of Silica-poly (Ionic Liquid) Composite Nanofiltration Membranes With Enhanced Removal Efficiencies For Heavy Metals

As a common water treatment technology,nanofiltration membrane is widely used in various wastewater treatment fields.In recent years,a large number of technologies have been applied to improve the performance of nanofiltration membranes due to the limitation of trade off effect,which is the mutual restriction between permeation flux and separation performance.For example,some nanoparticles or porous materials are added in the preparation of nanofiltration membrane to meet the personalized needs of different industries for membrane performance.As a common inorganic additive,silica?SiO₂?has many advantages,such as convenient preparation,low cost,low toxicity and good hydrophilicity.It has been widely used in nanofiltration membrane modification.However,the dispersion of the additive materials,including silica,is limited,and the compatibility with organic membrane materials is poor,which leads to the degradation of separation performance.In this paper,ionic liquid was grafted onto the surface of silica by atom transfer radical polymerization.Results shows that the pore size of modified silica nanoparticles decreased from 0.84 nm to 0.62 nm.The zeta potential on the surface of the modified particles was measured,and it was suggested that the negative charge of the particles was partly neutralized,and the sedimentation experiment results showed that the grafting of ionic liquid improved the dispersion of silica particles in the water phase.At the interface polymerization stage,the modified silica particles?SiO₂-PIL?were mixed into the nanofiltration membrane to prepare the thin film nanocomposite?TFN?nanofiltration membrane.The results showed that the hydrophilicity of nanofiltration membrane was improved to some extent after adding different silica particles,but the pore size distribution changed little.Due to the improvement of particle dispersion and particle charge,the filtration performance of nanofiltration membrane has been improved to varying degrees.Moreover,compared with the pristine silica,the performance of hybrid membrane prepared by modified silica particles is more stable,which is due to the higher compatibility between modified particles and TFN nanofiltration membrane.Combined with the permeability and separation performance,the flux of the TFN nanofiltration membrane was 46.98 L·m^-2·h^-1,which was 34% higher than that of the blank nanofiltration membrane,and the rejection of MgCl₂ was increased from 62.04% to 87.83%.The removal effect of heavy metal ions by TFN nanofiltration membrane in water and the influencing factors were studied.Compared with the blank nanofiltration membrane,the rejection of different heavy metals by TFN nanofiltration membrane was increased to some extent.A lower p H value is helpful to improve the retention rate of heavy metal salts in a certain range,.For other inorganic salts in water,taking sodium chloride as an example,a high concentration of sodium chloride may inhibit the rejection.In addition,it was also found that the type of anions,the concentration of heavy metal ions and the coexisting state of ions had some influence on the rejection performance.In this project,silica was modified by ionic liquid,which provided a new method to improve the dispersion of inorganic nanoparticles in water.Finally,the treatment effect of nanofiltration membrane on heavy metal ions in water was studied.The composite hybrid membrane showed better separation performance than the blank nanofiltration membrane.