Study On The Polyacrylonitrile/silica Hybrid Membranes Fabricated Through A Novel Approach Of Non-solvent Induced Phase Separation Followed By In-situ Sol-gel

Fouling is the major obstacle for the extensive application of porous polymeric membranes,which results in reduced lifetime and increased costs. The introduction of inorganic nanoparticles with the characteristics of high specific surface area and good hydrophilicity into the polymeric membrane matrix has been illustrated as an effective approach to improve the anti-fouling property of the polymeric membranes. However, the agglomeration of inorganic nanoparticle and the poor miscibility between the inorganic nanoparticle and the organic polymer are the two major problems for the preparation of organic-inorganic hybrid membranes.Therefore, it is still of great importance to develop new approaches for the preparation organic-inorganic hybrid membranes with good pore size controllability and narrow pore size distribution.Accordingly, in this work, a novel approach of non-solvent induced phase separation（NIPS）followed by hydrolysis and in-situ sol-gel was adopted to prepare PAN/SiO₂ hybrid membrane with good pore size controllability, narrow pore size distribution and improved anti-fouling property, by investigating the influences of hydrolysis modification and preparation conditions.Surface properties including chemical structure, morphology, roughness, charge and hydrophilicity were measured through FE-SEM, ATR-FTIR, contact angle measurement, AFM and Zeta potential analyzer, respectively. The permeation properties including molecular weight cut-off（MWCO）, pure water permeability and rejections to different solutes were estimated by cross-flow filtration experiments. The anti-fouling properties were evaluated through static protein adsorption experiments and dynamic anti-fouling experiments. In addition, the stability of the hybrid membranes were investigated. The following conclusions are obtained from the experiments:（1） The results of ATR-FTIR and XPS analyses showed the formation of SiO₂ nanoparticles on membrane surface through hydrolysis and polycondensation reactions of TEOS and the cross-linking reaction between the silanols of the generated SiO₂ nanoparticles and the carboxyl groups of the hydrolyzed PAN membrane. SEM image and Si-Mapping illustrate that there was no obvious agglomeration of SiO₂ nanoparticles on both the top and inner surfaces of the porous membrane. The flux recovery ratio（FRR） of the PAN/SiO₂-25 hybrid membrane during the 3-cycle anti-fouling experiments maintained the same value of around 90.3%, indicating the good stability of the prepared hybrid membrane.（2） SEM and EDS analyses showed that the size of generated SiO₂ nanoparticle increased with the increase of TEOS concentration. The depositions of SiO₂ nanoparticles on the top andinner surfaces resulted in a slight increase of surface roughness and a more compact skin layer,respectively. Both membrane pore size and porosity decreased with increasing TEOS concentration. The pore size decreased from 0.073 μm of membrane PAN to 0.006 μm of the PAN/SiO₂-25 hydrid membrane, the water flux decreased from 605.4 to 58.7 L/m2·h, and the porosity decreased from 78.6 to 72.3%, respectively.（3） The properties of PAN/SiO₂ hybrid membranes were affected by the polymer concentration, degree of hydrolysis, cross-linking time, cross-linking temperature and so on.With increasing polymer concentration, degree of hydrolysis, cross-linking time and/or temperature, the permeate flux decreased and the retention of PEG increased. he hybrid membrane prepared under the conditions of PAN concentration=15.0 wt.%, TEOS concentration=25%v/v（TEOS/C2H5OH）, degree of hydrolysis=44.69%, cross-linking temperature=105 ℃, and the cross-linking time=8 min exhibited a water flux of 58.7 L/m2·h and PEG6000 rejection of 90.18%.（4） The results of static fouling experiments using BSA indicated that the anti-protein adsorption capacity of the studied membranes followed the order of PAN/SiO₂-100>PAN/SiO₂-50>PAN/SiO₂-25 >PAN-COOH >PAN. The cross-flow filtration tests with BSA also demonstrated that the generated SiO₂ nanoparticles endow the hybrid membranes with improved anti-fouling performance, showing lower relative flux reduction（RFR） and higher flux recovery ratio（FRR） when compared with membrane PAN.