| In this dissertation,a modified polyethersulfone nanofiltration membrane was prepared by UV light grafting method with DMC as monomer.The effects of irradiation time and concentration of the monomer on separation performances of the membrane were studied.The membrane was applied to separating dye solutions.Effects of operating conditions,such as concentrations of dye and salt,and pressure on the separation performances of the membrane were studied by measuring flux and rejection to dye and salt,and measuring other parameters.In addition,water contact angle,zeta potential,scanning electron microscopy and ATR-FTIR were used to characterize the two membranes before and after modification.The experimental results showed that the membrane reached the best separation performances when the irradiation time was 7 min and the grafting monomer concentration was 50 wt%.The rejection order to seven dyes was:Congo red>Acid chrome blue K>Acid fuchsin>Crystal violet>Safranine O>Basic green 4>Acid orange 7.The separation performance of the modified membrane was better than that of the unmodified membrane.The rejection to salt decreased in the order of MgCl2>Na2SO4>MgSO4>NaCl.Since the contact angle of the unmodified membrane was 68.5°,larger than that of the modified membrane,61.5°,it meant the hydrophilicity of the modified membrane was better than that of the unmodified membrane.Due to the surface zeta potential of the unmodified membrane was-70.76 mV,it meant that the membrane was negatively charged.After modifing,the surface zeta potential of the modified membrane was 61.12 mV.Therefore,the membrane was positively charged.In addition,the change of operating conditions affected the separation performances of the modified membrane.With the increase of operating pressure,the flux of dye/salt mixed solution increased.The rejection to salt increased and the rejection to dye decreased slightly.With the increase of dye concentration,the flux decreased.However,the rejection to dye and salt did not change greatly.With the increase of the salt concentration,the flux of dye/salt mixed solution increased,but the rejection to dye and salt decreased.The grafted groups at the surface of the modified membrane were affected at acid and alkali conditions.Consequently,the stability of the modified membrane was not good.It needed to be used under suitable conditions.In addition,MWCNT/PES composite nanofiltration membrane was prepared by phase transformation method with carboxylated MWCNT as additives.The prepared membrane was used for treating dye solutions and concentrating anthocyanin solution.The effects of operating pressure,concentration and pH of dye solutions on the separation performances of the membrane were investigated.The most suitable concentration conditions were decided after researching the effect of temperature and pH of anthocyanin solution on the separation performances.The experimental results showed that the membrane blended with 0.04wt%carbon nanotubes had the best performances.The separation performances of the MWCNT/PES membrane to dye and anthocyanin solutions was higher than that of the PES nanofiltration membrane.The hydrophilicity and anti-pollution of the membrane were also higher than that of the PES nanofiltration membrane.In neutral condition,the surface zeta potential of the MWCNT/PES membrane was the smallest and the negative charge at the surface of the membrane reached the most density.In addition,the operating conditions had a great influence on the separation performance for treating dye solutions.The increased operating pressure led to an increase of flux,but led to decreasing rejection to cation dye.The increase of feed concentration led to decreasing dye flux and rejection to cation dye.The increase of pH led to increasing flux of anion dye solution,but decreasing the flux of cation dye solution.The MWCNT/PES membrane had a good effect on concentrating anthocyanin when the pH was 3 and the temperature was 20?. |
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