| Nowadays the PVDF untrafiltration has been widely used in the water treatmentfield. However, it has been limited in the application due to its strong hydrophobicity.But it is the admirable additive material because the inorganic nanometer SiO2haslarge surface area, strong chemical stability and good compatibility with solvents.Meanwhile, more and more attention are caused by Poly (Vinyl alcohol)(PVA) with itscharacteristics of good solubility, membrane-forming and hydrophility, especiallyhydrophility. Therefore, the nanometer SiO2and Poly (Vinyl alcohol)(PVA) wereadopted respectively in the present study to make the PVDF/SiO2modified membranesand PVDF/PVA modified membranes by immersion precipitation process, in order toimprove the hydrophility and anti-fouling properties of PVDF UF membrane. Themain conclusions are presented as follows:(1) The modified membranes were prepared by blending SiO2and PVA with purePVDF respectively. The effects of SiO2concentration from1%to3%and PVAcontents on the permeability, tensile strength, average pore size and contact angle ofmembranes were investigated. The surface and cross-sectional structure and pore sizeof membranes were observed by SEM and AFM. Results showed that, to PVDF/SiO2modified membranes, the structure and properties of membranes were optimum andpure water flux was highest when the adding amount of SiO2was1%, ensuring thatcertain tensile strength and reject rate were obstained. To PVDF/PVA modifiedmembranes, the structure and properties of membranes were optimal when thePVDF/PVA mass ratio was8/2. Compared with PVDF membrane, the contact angle ofPVDF/PVA modified membranes was decreased significantly, indicating that the hydrophility of PVDF/PVA modified membranes was increased. Meanwhile, purewater flux, tensile strength and pore size were enhanced.(2) The anti-fouling behavior of PVDF/SiO2modified membranes andPVDF/PVA modified membranes was evaluated by macro filtration experiment withfour typical foulants, such as bovine serum albumin (BSA), Humic acid (HA), sodiumalginate (SA) and the secondary effluent of municipal sewage (EfOM). In addition, theadhesive forces between hydrophilic modified membranesn (PVDF/SiO2andPVDF/PVA modified membranes) and four different typical foulants or the adhesiveforces of membrane-organic matters in the fouling process were investigated by atomicforce microscope (AFM) in conjunction with self-made foulant-coated colloidal probe.The mechanism of anti-fouling properties of modified membranes was preliminarilyanalyzed by the micro forces combined with the flux decline rate and the flux recoveryrate that were carried out by macro fouling experiment. It was found from macro filterexperimental data that the flux decline rate and the flux recovery rate of modifiedmembranes were improved, indicating that the anti-fouling property of modifiedmembranes was improved by adding the nano-SiO2and PVA respectively. It wasreported from adhesive forces data that the adhesive force of modified membraneswere weaker than that of PVDF membrane. The adhesive force between modifiedmembranes and foulants were decreased with the hydrophilic of the surface ofmembranes increased.(3) Combined the results of macro filtration experiment with that of adhesiveforces between modified membranes and four typical foulants. It was analyzed that thedata of adhesive forces and the corresponding macro filtration experiment maintainedgood consistency. Also, there was a great correlation between adhesive forces ofmembrane-organic matters and the hydrophilic of the surface membranes. That is, nomatter which kind of foulants, the membrane was more hydrophilic, the adhesive forceof membrane-foulant was smaller.(4) The optimal UF membranes of the modified membrane (P1membrane and8/2membrane) were chosen to measure the adhesive forces of membrane-organic mattersin the fouling process. Results showed that, no matter which kind of foulant andmembrane, the adhesive forces were decreased with the increase of filtration time, thatis, the adhesive forces of membrane-foulant in the initial stage were stronger than that in the later stage, illustrating that the membrane interaction of membranes andpollutants in the initial stage was the main cause of membrane fouling. Therefore, themembrane interaction between membranes and pollutants was reduced by improvingthe hydrophilicity of the membrane interface, which improved effectively theanti-fouling properties of PVDF ultrafiltration membrane. |
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