Effect Of Typical Cations On Ultrafiltration Membrane Fouling Of Protein

This thesis used BSA as the organic membrane fouling of protein.Typical hydrated monovalent and divalent cations which respectively take lithium chloride,sodium chloride,potassium chloride and calcium chloride four chlorides as representatives.A quartz crystal microbalance with dissipation monitoring?QCM-D?combined with a self-made PVDF-coated sensor crystal,was used to investigate the deposition and adsorption behavior of BSA on the PVDF surface and the structure of the BSA adsorption the layers at a high ionic strengths.These results were combined with those of fouling experiments and the flux recovery rate?at corresponding ionic strengths?to further proved the effect mechanism of the cationic hydration characteristics influence on membrane fouling mechanism.The main results are as follows:?1?Compared with ionic strength 0 m M,the hydration repulsive forces between PVDF membrane and BSA or between BSA and BSA could produce effectively by hydrated cations,which leading to a decrease in the adsorption amount and rate of BSA on PVDF surface,a more nonrigid and soft BSA layer was formed,accompanied by a decrease in membrane fouling.According to the results,Li⁺?Na⁺?K⁺ and Ca²⁺ are typical of hydrated cations,which will adsorption on the negatively charged BSA with electrostatic interaction.In BSA molecular and PVDF membrane surface form the specific structure of water molecules layer,thus triggering the hydration repulsion between PVDF-BSA and BSA-BSA,the adsorption rate and adsorption amount of BSA on the surface of the PVDF is reduced,and form the BSA adsorption layer of loose and soft,membrane fouling significantly reduced in the end.?2?For monovalent cations Li⁺,Na⁺,K⁺ with the same electrified capacity under the condition of the same ionic strength?100 m M?,the corresponding BSA pollution membrane flux decline rate of Li⁺,Na⁺,K⁺ is respectively 52%,58% and 62%,when no ion adding,the membrane flux decline rate is 85%.Obviously,this three ions can reduced the membrane fouling after reaching a certain concentration,but the extent of the slowdown is different.Run at the same time,because of its hydration radius,the strongest slow ability of Li⁺ and the weakest of K⁺.Relatively,Li⁺ with the minimum radius,the greatest surface charge density,the largest combining ability of water molecules,it triggered the biggest hydration repulsion,in which the BSA adsorption rate is slower,the pollution layer is relatively loose,and the amplitude of the membrane fouling is minimal.On the other hand,K⁺ ion radius is the largest,with the smallest surface charge density,the ability combined with the water molecules most weak.So it triggered the smallest hydration repulsion,relative ability to cope with BSA membrane pollution weaken is the smallest.In conclusion,cations take the same electrified capacity,the smaller radius,the more easy to trigger the hydration reaction.?3?The hydrated cation K⁺ and Ca²⁺ with the same ionic radius are investigated further and found that,when the ionic strength is 100 m M,run in the same time,K⁺ and Ca²⁺ ions in the corresponding BSA pollution flux attenuation rate were 62% and 48% respectively.Obviously,bivalent Ca²⁺ ions ability to slow BSA membrane pollution significantly greater than monovalent ion of K⁺.Although the same radius of K⁺ and Ca²⁺ ions,its electric charge are different.Compared with K⁺ ions,Ca²⁺ has high surface charge density and strong ability to combine with water molecules,trigger of the stronger the hydration repulsion.Cause the BSA slower adsorption cumulative rate,forming loose BSA pollution layer at the membrane surface and the minimal membrane irreversible pollution under the condition of Ca²⁺.In conclusion,hydrated ions of the same size,charge high easier to trigger the hydration reaction.