Study On The Properties Of Polyvinylidene Fluoride Membrane Doped With Ordered Mesoporous ZrO₂/void/tiO₂solid Superacid

Polyvinylidene fluoride (PVDF) is an ideal membrane material owing to its goodphysicochemical stability, resistance to abration, acid, alkali, oxidation and chlorine.PVDF membranes have been widely used in many areas, such as water desalination,water purification, wastewater treatment and bioreactor. However, when applied inwastewater treatment, PVDF membranes are easily contaminated due to theirhydrophobicity. This leads to flux declining sharply, frequently membrane washingand short lifespan of PVDF membranes, which limit the large scale applications ofPVDF membranes. Thus，it’s significant to prepare PVDF membranes with stronghydrophilic property by modification in order to reduce the times of membranewashing and prolong the lifespan of PVDF membranes.In this paper, TiO2with photocatalytic performance and SO42-/ZrO2solidsuperacid were integrated to prepare ordered mesoporous ZrO2/void/TiO2(ZVT)particles which were doped into PVDF uniformly. In the process of wastewatertreatment, a few micromolecular organics adsorbed on inner wall of PVDFmembranes’ pores and reached the photocatalytic active sites of TiO2through themesoporous channels distributing on the surface of ZrO2, organics were degraded toCO2and H2O under an ultraviolet spotlight, which reduced the membrane foulingcaused by organics; an acid environment with a low pH value was formed on thesurface of PVDF membranes due to SO42-/ZrO2solid superacid, this proton acid layercould degrade part of inorganic oxide particles, which alleviated the membranefouling caused by inorganic oxide particles. Moreover, lots of hydroxy generated inaccompany with the forming of the proton acid layer, which greatly improved thehydrophilic property of PVDF membranes, furthermore, the doping of ZVT particlesalso enhanced the mechanical properties of PVDF membranes.ZVT particles were dispersed uniformly into PVDF casting solution to prepareZVT/PVDF composite membranes, the preparation conditions were determined: thePVDF concentration,20wt%; the DMAc concentration,70wt%; the porogenPVP-K30concentration,5wt%; the mass ratio of ZVT: PVDF,15:100. ThenZVT/PVDF composite membranes were characterized by SEM, the contact angle andmechanical properties. SEM micrographs show that ZVT particles disperse uniformlyin the channels of ZVT/PVDF composite membranes, the contact angle ofZVT/PVDF-15composite membrane (the mass ratio of ZVT: PVDF,15:100) is 33.9°while the PVDF membrane is67.4°, which indicates that the hydrophilicproperty of ZVT/PVDF-15composite membrane is enhanced greatly. Besides, theanalysis of mechanical properties indicates that the tensile strength andanti-compaction capability of ZVT/PVDF composite membranes have beenimproved.ZVT/PVDF composite membranes were used to process wastewater containingoil, the oil concentration of the permeation is less than10mg/L, which meets thereinjection technology recommended norm of oilfield produced water. Thephotocatalytic test shows that ZVT/PVDF composite membranes possess excellentphotocatalytic properties, chemical washing of different PVDF membranes indicatesthat ZVT/PVDF composite membranes have part of pickling function. Therefore,ZVT/PVDF composite membranes have great potentials to be applied in the treatmentof wasterwater containing oil.Finally, the decontamination mechanism of ZVT/PVDF composite membranesand the interactions between ZVT particles and PVDF chains were studied.