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1. Improving anti-fouling properties of alumina tubular microfiltration membranes through the use of hydrophilic silica nanoparticles for oil/water separation

   https://doi.org/10.1080/01496395.2023.2259605  

   Ghosh, Anirban; Mahmodi, Ghader; Miranda, Michael; Xie, Songpei; Shaw, Madelyn; Krzmarzick, Mark; Lampert, David J.; Kim, Seok-Jhin; Aichele, Clint P. (September 2023, Separation Science and Technology)

   In this study, hydrophilic silica nanoparticles (Si NPs) were used to modify α-alumina tubular membranes to improve their performance in terms of flux, oil rejection, and anti-fouling properties. Our work focuses on enhancing membrane performance, particularly for difficult applications such as produced water treatment. The prepared membranes were applied for oil-in-water emulsion treatment. After coating hydrophilic Si NPs, the oil contact angle improved from 133.8° to 171.4°. To prevent Si NPs from leaching off the surface of α-alumina tubular membranes, polyvinyl alcohol was used to coat the membranes as a pre-treatment step before Si NP modification. After coating the membrane with Si NPs, the roughness of the membrane surface decreased, likely leading to less fouling. After coating Si NPs, Total Organic Carbon rejection increased from 93.1% for pristine α-alumina tubular membranes to 97.7% for silica-modified membranes because of hydrophilic improvements of the modified membranes. The Si NP coating improved the anti-fouling property of membranes with the flux recovery ratio increasing from 71.3% for pristine α-alumina tubular membranes to 85.9% for silica-modified membranes. Scanning Electron Microscopy, Energy- dispersive X-ray spectroscopy, oil contact angle, and Atomic Force Microscopy characterization tests were done. The tests showed successful Si NPs impregnation and altered wettability. 

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2. Flexible percolation fibrous thermal insulating composite membranes for thermal management

   An, Lu; Di_Luigi, Massimigliano; Tan, Jingye; Faghihi, Danial; Ren, Shenqiang (November 2022, Materials advances)

   Flexible thermal insulating membranes are ubiquitous in thermal management. Nevertheless, difficulties arise for composite membranes to combine a resilient, robust structural framework with uniform percolation networks purposefully conceived for thermal insulation. Herein, by controlling the microstructure homogeneity, we report flexible, hydrophobic thermal insulating membranes consisting of ceramic fiber and porous silica materials. The resulting nanofibrous membrane composites exhibit a low thermal insulation of 11.4 mW m−1 K−1, a low density of 0.245 g cm−3, mechanical flexibility with a bending rigidity of 1.25 cN mm−1, and hydrophobicity with a water contact angle of 144°. These nanofibrous-reinforced, silica-aerogel-based nanocomposite membranes are potential candidates for advanced thermal management applications. 

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3. Ultrathin polyorganosilica membranes synthesized by oxygen-plasma treatment of polysiloxanes for H2/CO2 separation

   https://doi.org/10.1016/j.memsci.2023.122099  

   Bui, Vinh; Satti, Varun R.; Haddad, Elizabeth; Hu, Leiqing; Deng, Erda; Zhu, Lingxiang; Lee, Won-Il; Yin, Yifan; Kisslinger, Kim; Zhang, Yugang; et al (December 2023, Journal of Membrane Science)

   Oxygen plasma treatment of polydimethylsiloxane (PDMS) induces an ultrathin polyorganosilica (POSi) layer (< 10 nm) on top of a PDMS membrane, leading to excellent H2/gas separation properties and providing a rapid and scalable way to fabricate robust silica membranes compared with conventional high-temperature and time-consuming sol-gel methods. Here, we thoroughly investigate POSi membranes derived from poly(dimethylsiloxane-co-methylhydroxidesiloxane) (poly(DMS-co-MHOS)) containing -SiOH groups that can be more easily converted to silica networks than the -SiCH3 in PDMS. The effect of the polysiloxane structure and plasma treatment conditions (including plasma generating powers, oxygen flowrate, chamber pressure, and treatment time) on the silica chemistry, structure, and H2/CO2 separation properties are systematically determined to derive structure/property relationships. An optimized membrane exhibits H2 permeance of 880 GPU and H2/CO2 selectivity of 67 at 150 ℃, superior to state-of-the-art polymeric membranes. The membrane retains H2/CO2 selectivity as high as 46 when challenged with simulated syngas containing 2.8 mol% water vapor at 150 ℃, demonstrating the potential of these POSi membranes for practical applications. 

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4. Role of nanoparticle size and surface chemistry on ion transport and nanostructure of perfluorosulfonic acid ionomer nanocomposites

   https://doi.org/10.1039/d1sm01573g  

   Domhoff, Allison; Wang, Xueting; Silva, Mayura S.; Creager, Stephen; Martin, Tyler B.; Davis, Eric M. (May 2022, Soft Matter)

   Herein, we present a systematic investigation of the impact of silica nanoparticle (SiNP) size and surface chemistry on the nanoparticle dispersion state and the resulting morphology and vanadium ion permeability of the composite ionomer membranes. Specifically, Nafion containing a mass fraction of 5% silica particles, ranging in nominal diameters from 10 nm to >1 μm and with both sulfonic acid- and amine-functionalized surfaces, was fabricated. Most notably, an 80% reduction in vanadium ion permeability was observed for ionomer membranes containing amine-functionalized SiNPs at a nominal diameter of 200 nm. Further, these membranes exhibited an almost 400% increase in proton selectivity when compared to pristine Nafion. Trends in vanadium ion permeability within a particular nominal diameter were seen to be a function of the surface chemistry, where, for example, vanadyl ion permeability was observed to increase with increasing particle size for membranes containing unfunctionalized SiNPs, while it was seen to remain relatively constant for membranes containing amine-functionalized SiNPs. In general, the silica particles tended to exhibit a higher extent of aggregation as the size of the particles was increased. From small-angle neutron scattering experiments, an increase in the spacing of the hydrophobic domains was observed for all composite membranes, though particle size and surface chemistry were seen to have varying impacts on the spacing of the ionic domains of the ionomer. 

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5. Low Fouling Nanostructured Cellulose Membranes for Ultrafiltration in Wastewater Treatment

   https://doi.org/10.3390/membranes13020147  

   Joshi, Ritika; Sebat, Nilay; Chi, Kai; Khan, Madani; Johnson, Ken I.; Alhamzani, Abdulrahman G.; Habib, M. A.; Lindstrom, Tom; Hsiao, Benjamin S. (February 2023, Membranes)

   Ultrafiltration (UF) is a common technique used in wastewater treatments. However, the issue of membrane fouling in UF can greatly hinder the effectiveness of the treatments. This study demonstrated a low-fouling composite cellulose membrane system based on microfibrillated cellulose (MFC) and silica nanoparticle additives. The incorporation of ‘non-spherical’ silica nanoparticles was found to exhibit better structural integration in the membrane (i.e., minimal aggregation of silica nanoparticles in the membrane scaffold) as compared to spherical silica. The resulting composite membranes were tested for UF using local wastewater, where the best-performing membrane exhibited higher permeation flux than commercial polyvinylidene difluoride (PVDF) and polyether sulfone (PES) membranes while maintaining a high separation efficiency (~99.6%) and good flux recovery ratio (>90%). The analysis of the fouling behavior using different models suggested that the processes of cake layer formation and pore-constriction were probably two dominant fouling mechanisms, likely due to the presence of humic substances in wastewater. The demonstrated cellulose composite membrane system showed low-fouling and high restoration capability by a simple hydraulic cleaning method due to the super hydrophilic nature of the cellulose scaffold containing silica nanoparticles. 

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