| Forward osmosis?FO?membrane performance was improved using different organic acids?formic acid,acetic acid,lactic acid?for the addition of the casting solution of N-Methyl-2-pyrrolidon?NMP?,acetone and cellulose triacetate?CTA?.Scanning electron microscope?SEM?images of all the FO CTA membranes exhibited essentially the membranes composing of two dense skin layers and a sponge-like supporting layer.Additionally,based on the surface roughness values analysis of Atomic Force Microscope?AFM?,the membranes with lactic acid,with similar roughness to the membranes without any acid,have bigger roughness than the membranes with formic acid or acetic acid.Furthermore,the water flux of membranes with acids has been improved and the reverse salt flux decreased.The membranes with lactic acid,with an outstanding penetration performance,were utilized to test the performance when 1 mol/L sodium chloride?NaCl?,magnesium chloride?MgCl2?,magnesium sulfate?MgSO4?and sodium sulfate?Na2SO4?were respectively as the draw solutions.The experimental results revealed that when the driving solution was MgCl2,the flux was the highest,19.61 L/?m2·h?;when the driving solution was MgSO4,the flux was the lowest,specifically 13.72 L/?m2·h?,and according to the reverse salt flux,the membrane had a high rejection rate of MgSO4,and the reverse salt flux can reach 4.40 g/?m2·h?.In addition,in the process of separating the oil-water mixture,the sewage flux of the original membrane CTA0000 was 8.00 L/?m2·h?,the flux recovery rate is 78.69%,and the water fluxes of the membranes CTA00LA,CTA00FA,and CTA00AA were 17.20 L/?m2·h?,19.20 L/?m2·h?,14.60 L/?m2·h?respectively.And the flux recovery rates were 97.87%,99.15%,and 94.16%,respectively,indicating that the modified membrane had good anti-pollution performance.Metal-organic frameworks?MOFs?are widely used in many industries due to their superior surface area and adjustable pore structure.However,there has been little research that membranes were modified by MOFs for the development of water treatment.Here,CTA FO membranes containing poly?sodium 4-styrenesulfonate??PSS?modified ZIF-8?mZIF?were constructed via an immersion precipitation method.It was confirmed that the mZIF nanoparticles presenced on the membranes through FT-IR spectroscopy and EDX analyses.SEM images showed some large cavities appeared in the cross-section of modified membranes and AFM images displayed the modified membranes have rougher surface.The hydrophilicity of the modified membrane was improved,and as the amount of mZIF-8 was increased,the hydrophilicity of the membrane was gradually increased.The permeability of the modified membrane was improved,the flux is increased,and the water flux of the original membrane was 4.84 L/?m2·h?,and the fluxes of the modified membranes M1,M2,and M3rose to 11.74 L/?m2·h?,11.43 L/?m2·h?,and 11.79 L/?m2·h?,respectively.The reverse salt flux decreased,the reverse salt flux of M0 was 36.40 g/?m2·h?,and the reverse salt fluxes of M1,M2 and M3 decreased to 10.00 g/?m2·h?,12.71 g/?m2·h?,11.62 g/?m2·h?.The treatment efficiency of the modified membrane for sewage is greatly improved.The sewage flux of M0is 3.67 L/?m2·h?,the flux recovery rate is 86.98%,and the sewage fluxes of the modified membranes M1,M2 and M3 are 7.03 L/?m2·h?,6.08 L/?m2·h?and 6.45 L/?m2·h?.The flux recovery rates were increased to 93.78%,94.49%,and 96.44%,respectively.This facile,effective method will provide a guideline to modify FO membrane for water treatment. |
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