Separation performance and mechanism of the novel modified polyether sulfone composite nanofiltration membrane for the detection on dissolved organic nitrogen

The most effective pretreatment method for the detection of dissolved organic nitrogen (DON) is the nanofiltration (NF) by effectively intercepting DON into the concentrated solution, thus increasing the proportion of DON in solution so that achieving accurate detection of DON. The existing NF pretreatment technology for detection of DON has the problem of low accuracy and unclear separation mechanism of mass transfer upon the NF membranes. Based on the problems of NF membrane, the polyether sulfone (PES) composite NF membrane was modified by mesoporous carbon and the basic performance parameters of the modified PES composite NF membrane were characterized by Static contact angle (SCA), Zeta potential, and X-ray photoelectron spectroscopy (XPS). The results show that the optimum doping amount of mesoporous carbon is in the range of 0.5%-1.0%. Furthermore, the pore size of NF membrane could be controlled effectively by changing doping amount of mesoporous carbon, so as to guide the improvement of membrane pore structure. After the pretreatment of mesoporous material modified PES composite NF membrane, the ratio of dissolved inorganic nitrogen (DIN)/total dissolved nitrogen (TDN) could be reduced to 0.55-0.65 and the pretreatment effect was also affected by screening effect and electrostatic effect. The best retention performance of amino acids is the 1.0%C modified membrane which retention rate of the amino acid is between 32.3% and 94.7%, and the membrane loss of the four amino acids is much smaller than other membranes. The mass transfer process of NF membrane was simulated by steric-hindrance pore (SHP) model, Teorell-Meyer-Sievers (TMS) model, and Electrostatic Steric-hindrance (ES) model respectively. According to the simulation software designed by ourselves, the dominant effects of screening and electrostatic effects are simultaneously affected by the pore structure of membranes and the size of the contaminant molecules. Practitioner points The feasibility of mesoporous carbon with modified PES composite nanofiltration membrane pretreatment for DON measurement in comparison to pure NF membranes was investigated. The ability of modified PES composite NF membrane with different molecular weight of DON and the relationship between pore radius of membrane and interception pollutant molecular size was discussed. The influence of screening effect and electrostatic effect on the retention of pollutants was discussed by the SHP model, TMS model and ES model; the simulation software interface is designed and the calculation process of the model is simulated by computer.