In the present study, a commercial TiO 2 , several BiVO 4 photocatalysts, a WO 3 nanomaterial, and their composites were used to prepare photocatalytic polyvinylidene fluoride (PVDF) ultrafilter membranes. Their photocatalytic activities and the effects of coatings on the filtration of oil-in-water emulsion (crude oil; c oil = 100 mg L −1) were investigated. Fluxes, filtration resistances, purification efficiencies, and fouling resistance abilities-like flux decay ratios (FDRs) and flux recovery ratios (FRRs)-were compared. The solar light-induced photocatalytic decomposition of the foulants was also investigated. WO 3 was used as a composite component to suppress the electron-hole recombination with the goal of achieving higher photocatalytic activity, but the presence of WO 3 was not beneficial concerning the filtration properties. However, the application of TiO 2 , one of the investigated BiVO 4 photocatalysts, and their composites was also beneficial. In the case of the neat membrane, only 87 L m −2 h −1 flux was measured, whereas with the most beneficial BiVO 4 coating, 464 L m −2 h −1 flux was achieved. Pure BiVO 4 coating was more beneficial in terms of filtration properties, whereas pure TiO 2 coating proved to be more beneficial concerning the photocatalytic regeneration of the membrane. The TiO 2 (80%)/BiVO 4 (20%) composite was estimated to be the most beneficial combination taking into account both the aspects of photocatalytic activity and filtration properties.
Membrane filtration is an effective technique for separating micro- and nano-sized oil droplets from harmful oil-contaminated waters produced by numerous industrial activities. However, significant flux reduction discourages the extensive application of this technology; therefore, developing antifouling membranes is necessary. For this purpose, various titanium dioxide/carbon nanotube (TiO2/CNT) nanocomposites (containing 1, 2, and 5 wt.% multi-walled CNTs) were used for the modification of polyvinylidene fluoride (PVDF) ultrafilter (250 kDa) membrane surfaces. The effects of surface modifications were compared in relation to the flux, the filtration resistance, the flux recovery ratio, and the purification efficiency. TiO2/CNT2% composite modification reduced both irreversible and total filtration resistances the most during the filtration of 100 ppm oil emulsions. The fluxes were approximately 4–7 times higher compared to the unmodified PVDF membrane, depending on the used transmembrane pressure (510, 900, and 1340 L/m2h fluxes were measured at 0.1, 0.2, and 0.3 MPa pressures, respectively). Moreover, the flux recovery ratio (up to 68%) and the purification efficiency (95.1–99.8%) were also significantly higher because of the surface modification, and the beneficial effects were more dominant at higher transmembrane pressures. TiO2/CNT2% nanocomposites are promising to be applied to modify membranes used for oil–water separation and achieve outstanding flux, cleanability, and purification efficiency.
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