Superwetting TiO2-decorated single-walled carbon nanotube composite membrane for highly efficient oil-in-water emulsion separation

RUO2 nanoparticle-decorated MWCNTS synthesized using a sonochemical method as reinforcing agents for PEI composite membranes

This work presents a new and facile synthesis approach for multiwalled carbon nanotubes (MWCNTs) decorated with ruthenium oxide (RuO2) nanoparticles using a simple and efficient sonochemical method. The strong interaction and homogenous distribution of RuO2 nanoparticles on the surface of MWCNTs were revealed by Raman spectroscopy and transmission electron microscopy. The presence of metal oxide nanoparticles anchored onto the surface of MWCNTs was further confirmed by X-ray diffraction and energy-dispersive X-ray analysis. Furthermore, the chemical state of the MWCNTs before and after decoration with RuO2 was revealed by X-ray photoelectron spectroscopy. Scanning electron microscopy illustrated that the decoration process did not induce any modification on the morphology of the surface of MWCNTs. The percentage of RuO2 nanoparticles anchored onto the MWCNT surface was determined by thermogravimetric analysis, where 15% could be calculated considering the weight loss. Furthermore, both MWCNTs and decorated MWCNTs with RuO2 nanoparticles were used as nanofillers to develop some composite membranes using polyetherimine as polymer matrices. The morphological and structural properties of the membranes were characterized by SEM and XRD. The mechanical properties of the composite membranes, contact angle and antimicrobial properties using Escherichia coli and Staphylococcus aureus were also studied.

Effects of Different TiO2/CNT Coatings of PVDF Membranes on the Filtration of Oil-Contaminated Wastewaters

Six different TiO2/CNT nanocomposite-coated polyvinylidene-fluoride (PVDF) microfilter membranes (including -OH or/and -COOH functionalized CNTs) were evaluated in terms of their performance in filtering oil-in-water emulsions. In the early stages of filtration, until reaching a volume reduction ratio (VRR) of ~1.5, the membranes coated with functionalized CNT-containing composites provided significantly higher fluxes than the non-functionalized ones, proving the beneficial effect of the surface modifications of the CNTs. Additionally, until the end of the filtration experiments (VRR = 5), notable flux enhancements were achieved with both TiO2 (~50%) and TiO2/CNT-coated membranes (up to ~300%), compared to the uncoated membrane. The irreversible filtration resistances of the membranes indicated that both the hydrophilicity and surface charge (zeta potential) played a crucial role in membrane fouling. However, a sharp and significant flux decrease (~90% flux reduction ratio) was observed for all membranes until reaching a VRR of 1.1-1.8, which could be attributed to the chemical composition of the oil. Gas chromatography measurements revealed a lack of hydrocarbon derivatives with polar molecular fractions (which can act as natural emulsifiers), resulting in significant coalescent ability (and less stable emulsion). Therefore, this led to a more compact cake layer formation on the surface of the membranes (compared to a previous study). It was also demonstrated that all membranes had excellent purification efficiency (97-99.8%) regarding the turbidity, but the effectiveness of the chemical oxygen demand reduction was slightly lower, ranging from 93.7% to 98%.

Outstanding Separation Performance of Oil-in-Water Emulsions with TiO2/CNT Nanocomposite-Modified PVDF Membranes

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/CNT_2% 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/CNT_2% nanocomposites are promising to be applied to modify membranes used for oil-water separation and achieve outstanding flux, cleanability, and purification efficiency.

Substrate-independent three-dimensional polymer nanosheets induced by solution casting

Nanosheets are important structures usually composed of inorganic materials, such as metals, metal oxides, and carbon. Their creation typically involves hydrothermal, electrochemical or microwave processes. In this study, we report a novel formation mechanism of 3D polymer nanosheets via facile solution casting using a comb copolymer consisting of poly(ethylene glycol) behenyl ether methacrylate and poly(oxyethylene) methacrylate (PEGBEM–POEM). Controlling the composition of comb copolymer yielded nanosheets with different packing density and surface coverage. Interestingly, the structure exhibits substrate independence as confirmed by glass, inorganic wafer, organic filter paper, and porous membrane. The formation of 3D nanosheets was investigated in detail using coarse-grained molecular dynamics simulations. The obtained polymer nanosheets were further utilized as templates for inorganic nanosheets, which exhibit high conductivity owing to interconnectivity, and hence have promising electronic and electrochemical applications.

Unprecedented substrate-independent polymeric 3D nanosheets were induced via simple solution casting using PEGBEM–POEM comb copolymer. A possible mechanism is the change in the polymer–solvent interactions on the surface.