The Research On Preparation Of Polyvinylamine Modified Polypropylene Membrane And Removal Of Ionic Pollutants From Water

For decades,ionic pollutants in water have attracted worldwide attention due to their toxic and carcinogenic effects on organisms.Ionic pollutants are widely present in industrial wastewater and drinking water.Therefore,the removal of ionic pollutants has always been the focus of research in the field of water treatment.The current methods for removing ionic pollutants still have certain limitations,such as the high cost,complex post-processing,secondary pollution to the environment,etc.As a commonly used method for removing ionic pollutants in water,adsorption has the advantage of low cost,high efficiency,none by-product,and friendliness to the environment.As an adsorbent,adsorption membrane has good performance in both static adsorption and dynamic adsorption,featuring the properties such as large flux and low operating pressure,high efficiency,low energy consumption,good compatibility with industry,etc.In this study,N-vinylformamide was grafted on a commercial polypropylene fiber membrane,and the PPM-PVAm modified membrane with adsorption effect on ionic pollutants had successfully prepared through a hydrolysis reaction.The details are as follows:(1)Based on a two-step method,N-vinylformamide was successfully grafted on polypropylene fiber membrane,and PPM-PVAm modified membrane was obtained through hydrolysis reaction.The surface morphology and element composition of PPM-PVAm were characterized by SEM,EDS,FT-IR,XPS,dynamic water contact angle test,Zeta potential test,etc.,and the method to control the grafting rate and the hydrolysis degree of PPM-PVAm was explored according to controlling the reaction time.(2)Two typical ionic pollutants in water,chromium ion Cr(VI)and phosphate ion P(V),were selected as adsorption objects to explore the adsorption of ionic pollutants in water medium on PPM-PVAm adsorption membrane.The results showed that the graft ratio of PPM-PVAm modified adsorption membrane was 55wt%,the degree of hydrolysis was 80%,and the solution p H was 2(Cr(VI))and 3(P(V))and the temperature at 40 °C was the most ideal adsorption effect,and the equilibrium adsorption capacities for Cr(VI)and P(V)were 109.8 mg/g and 107.7 mg/g,respectively.(3)The adsorption kinetics and adsorption isotherm studies showed that the adsorption of Cr(VI)and P(V)by PPM-PVAm conforms to the pseudosecond-order model and the Langmuir model,both of which are monolayer chemisorption,and the maximum adsorption capacity is 208.8 mg/g and 263.2mg/g,respectively.The adsorption thermodynamics revealed that the adsorption process of the PPM-PVAm was an entropy-driven spontaneous endothermic process,and the increase of temperature was beneficial to the progress of the adsorption reaction.(4)PPM-PVAm can achieve adsorption of Cr(VI)and P(V)when the solution is acidic,and desorption can occur when the solution is alkaline because of the p H responsiveness.After 10 adsorption-desorption cycles for Cr(VI)and 15 adsorption-desorption cycles for P(V)by PPM-PVAm,the adsorption efficiency retention rates were 94.3% and 92.4%,respectively,indicating that PPM-PVAm has excellent regeneration cycle.(5)The adsorption properties of PPM-PVAm in simulated polluted water samples prepared from natural river water were investigated.The results showed that the removal rate of Cr(VI)and P(V)at low and high concentrations was both maintained above 97%,and after 5 regeneration cycles in large volumes of Cr(VI)and P(V)solutions,There is still good performance retention,showing excellent anti-interference performance and cycle stability performance against potential adsorption interferers in water.(6)The adsorption mechanism of Cr(VI)and P(V)ions by PPM-PVAm was explored.Conductometric titration and other experimental results show that the driving force for the adsorption of Cr(VI)and P(V)on the PPMPVAm is mainly the electrostatic interaction between the protonated amine group and the oxyanion group.In addition,there is a small amount of redox reaction between Cr(VI)and amine groups.Compared with the adsorption membranes in the literature,the adsorption membranes in this study have higher equilibrium adsorption capacity,higher maximum adsorption capacity and better cycling stability for Cr(VI)and P(V)ions,which may be due to the electrostatic synergy between polyvinylamine units and reversible protonation of amine groups.