Study On Preparation And Application Of Titanium Dioxide/Poly (Acrylic Acid) Hybrid Photocatalytic Membrane

Three kinds of titania/poly(acrylic acid).photocatalysis ultrafiltration were prepared by lending, crosslinking and in-situ polymerization method. The membrane material is poly (vinylidene fluoride) (PVDF) and polyethersulfon (PES). Humic acid was selected as natural representative pollutants, methyl orange was selected as dye industry representative pollutants. In lending the membrane porosity increased from 50% to 59%, and the average pore size reduced from 128nm to 125nm, contact angle reduced from 79.3 degrees to 51.3 degrees and the membrane flux increased from 1022L/m2/h 1246L/m2/h; the solid residual value in thermal gravimetric analysis increased from 18.51% to 29.25%, the roughness of membrane surface and cross-sectional was increased. Membrane has a certain photocatalytic effect under the conditions of ultraviolet (UV) irradiation after TiO2/PAA added to the casting solution. In crosslinking method the performance of surface crosslinking membrane was best with the preparation condition that reaction time of 2 hours, the reaction temperature of 90℃, polyacrylic acid (PAA) content of 20%, titanium dioxide (TiO2) content of 5%. more compact and smooth skin was obtained because the PAA cross-linking skin on membrane surface was formed, part of the membrane pores covered and flux decreased. Better filtration performance was got because more effective TiO2/PAA were coated on the membrane surface by crosslinking method compared to blending method and membrane pore was smaller than blending membrane. The normalized flux of the membrane was increased from 0.41% to 2 under UV irradiation. In-situ polymerization AA molecular weight is smaller than the PAA, radical combination and cross-linking occur simultaneously that can form a denser crosslinked network resulting in further reduced flux.The operation characteristics of the photocatalytic membrane separation process were studied. When the photocatalytic membrane separated coagulation waste water the photocatalytic action was weakened because coagulant hindered part of the UV to reach the catalytic active site of the membrane surface. But more hydroxyl groups was produced on the membrane surface at larger radiation intensity (1.5mW/cm2) and the flux increased. Which was quite different from experimental phenomenon of treatment of humic acids (photocatalytic degradation resulting in some small molecules through the membrane so that the retention rate decreased but membrane flux improved). Water flow induced larger fluid shear force on the surface of the membrane and less membrane fouling but excessive flow will cause serious irreversible pollution; pH affected the process by impacting on on contaminant morphology and changing the charge of pollutants and membrane surface; the influent flow rate and pH had little influence on the photocatalytic process. In cleaning process, chemical cleaning can achieve good cleaning effect. TiO2/PAA modified membrane had photocatalytic self-cleaning ability that can avoid secondary pollution.