Preparation And Properties Of Carboxylated Chitosan Composite Nanofiltration Membrane

Nanofiltration membrane technology plays an important role in many areas including water treatment,traditional industries and other fields.Nanofiltration membranes with high separation performance and stability are needed for treatment of systems containing complex substances.It is one of the research hotspots in the field of membrane science to prepare high-performance composite nanofiltration membranes through the selection of membrane-forming materials and optimization of membrane-forming technique.In this study,single-layer and multi-layer composite membranes were prepared through interfacial polymerization of carboxylated chitosan(C-CS)and trimesyl chloride(TMC)on polysulfone(PS)ultrafiltration membrane.The effects of process parameters such as phase transfer catalyst,aqueous phase pH,heat treatment temperature and heat treatment time on the nanofiltration performance of C-CS/TMC composite membrane were systematically studied.The microstructure of the composite nanofiltration membrane was characterized using ATR-FTIR,FE-SEM,AFM,and zeta potential analyzer.Cross-flow filtration tests were conducted to evaluate molecular weight cut-off,inorganic salt separation performance and dye retention performance of the ontained membranes.Finally,the anti-fouling performance of C-CS/TMC composite membrane was studied using bovine serum protein(BSA)and humic acid(HA)as model pollutants.The conclusions obtained from experiental results are as follows:(1)ATR-FTIR analysis showed that the interfacial polymerization of C-CS and TMC could form a smooth active separation layer on porous support.With increasing C-CS concentration,the salt rejection of single-layer PS-[(C-CS)n/TMC]composite membrane increased,while the permeate flux decreased.As the C-CS concentration increased from 1.0 to 2 wt%,Na2SO4 rejection single-layer membrane increased from 56.33 to 68.70%,while permeate flux decreased from 23.22 to 14.55 L/(m2.h).With increasing number of polyesteramide layer,the salt rejection of mult-ilayer PS-[(C-CS)/TMC]n composite membrane ascended and the permeate flux declined.When the number of polyesteramide layer increases from one to two,The multilayer Na2SO4 rejection of multi-layer membrane increased from 57.94 to 71.61%,while the permeate flux decreased from 20.50 to 8.37 L/(m2.h).Modulation of C-CS content is more effective in enhancing membrane performance than change the number of polyester-amide layer.The hydrophilicity of single-layer membrane was better than that of the multi-layer membrane(surface contact angles of PS-[(C-CS)2/TMC]and PS-[(C-CS)/TMC]2 are 56° and 61°,respectively).30-hour long-term test results showed that both single-layer and multi-layer composite membranes possessed good performance stability.(2)The results of performance optimization indictaed that the performance of the composite membrane was largely determined by the phase polymerization catalyst,aqueous phase pH,heat treatment temperature,heat treatment time and other interface polymerization parameters.The optimal preparation conditions for single-layer PS-[(C-CS)/TMC]composite membranes were as follows:C-CS=2.0wt%,TMC=0.4wt%,pH=10,reaction time=5min,phase transfer catalysis content=0.04,heat treatment time=15 min and heat treatment temperature=55℃.The obtained PS-[(C-CS)2/TMC]composite membrane had a pure water permeability coefficient of 31.25 L/(m2·h·MPa)and a molecular weight cut-off of 983 Da.(3)Dye separation test results showed that the PS-[(C-CS)2/TMC]composite membrane had a good dye removal performance.The dye removals followed the order of reactive black 5(89.74%)>Indigo Carmine(81.33%)>Rhodamine B(51.19%).The dye removal decreased with increasing dye concentration.With increasing applied pressure,removals of reactive black 5 and Indigo Carmine ascended,while removal of Rhodamine B declined.The anti-flouing experiment results showed that the PS-[(C-CS)2/TMC]membrane possessed better fouling resistance to HA than BSA,the flux reduction ratio to HA aqueous solution was 16%,while to BSA aqueous was relatively high of 20.4%.