Graphene oxide (GO) is a promising material for the development of antimicrobial surfaces due to its contact-based antimicrobial activity. However, the relationship between GO physicochemical properties and its antimicrobial activity has yet to be elucidated. In this study, we investigated the size-dependency of GO antimicrobial activity using the Gram-negative bacteria Escherichia coli. GO suspensions of average sheet area ranging from 0.01 to 0.65 μm(2) were produced and their antimicrobial activity evaluated in cell suspensions or as a model GO surface coating. The antimicrobial activity of GO surface coatings increased 4-fold when GO sheet area decreased from 0.65 to 0.01 μm(2). The higher antimicrobial effect of smaller GO sheets is attributed to oxidative mechanisms associated with the higher defect density of smaller sheets. In contrast, in suspension assays, GO interacted with bacteria in a cell entrapment mechanism; in this case, the antimicrobial effect of GO increased with increasing sheet area, with apparent complete inactivation observed for the 0.65 μm(2) sheets after a 3 h exposure. However, cell inactivation by GO entrapment was reversible and all initially viable cells could be recovered when separated from GO sheets by sonication. These findings provide useful guidelines for future development of graphene-based antimicrobial surface coatings, where smaller sheet sizes can increase the antimicrobial activity of the material. Our study further emphasizes the importance of an accurate assessment of the antimicrobial effect of nanomaterials when used for antimicrobial surface design.
There is long-standing interest in developing membranes possessing uniform pores with dimensions in the range of 1 nm and physical continuity in the macroscopic transport direction to meet the needs of challenging small molecule and ionic separations. Here we report facile, scalabe fabrication of polymer membranes with vertically (i.e., along the through-plane direction) aligned 1 nm pores by magnetic-field alignment and subsequent cross-linking of a liquid crystalline mesophase. We utilize a wedge-shaped amphiphilic species as the building block of a thermotropic columnar mesophase with 1 nm ionic nanochannels, and leverage the magnetic anisotropy of the amphiphile to control the alignment of these pores with a magnetic field. In situ X-ray scattering and subsequent optical microscopy reveal the formation of highly ordered nanostructured mesophases and cross-linked polymer films with orientational order parameters of ca. 0.95. High-resolution transmission electron microscopy (TEM) imaging provides direct visualization of long-range persistence of vertically aligned, hexagonally packed nanopores in unprecedented detail, demonstrating high-fidelity retention of structure and alignment after photo-cross-linking. Ionic conductivity measurements on the aligned membranes show a remarkable 85-fold enhancement of conductivity over nonaligned samples. These results provide a path to achieving the large area control of morphology and related enhancement of properties required for high-performance membranes and other applications.
In this work, we fabricate an omniphobic microporous membrane for membrane distillation (MD) by modifying a hydrophilic glass fiber membrane with silica nanoparticles followed by surface fluorination and polymer coating. The modified glass fiber membrane exhibits an antiwetting property not only against water but also against low surface tension organic solvents that easily wet a hydrophobic polytetrafluoroethylene (PTFE) membrane that is commonly used in MD applications. By comparing the performance of the PTFE and omniphobic membranes in direct contact MD experiments in the presence of a surfactant (sodium dodecyl sulfate, SDS), we show that SDS wets the hydrophobic PTFE membrane but not the omniphobic membrane. Our results suggest that omniphobic membranes are critical for MD applications with feed waters containing surface active species, such as oil and gas produced water, to prevent membrane pore wetting. ■ INTRODUCTIONMembrane distillation (MD) is a thermal separation process using a microporous hydrophobic membrane. 1−3 MD can operate at relatively low temperatures and is thus able to tap into the vast amount of low-grade waste heat. 4−6 MD is also advantageous over pressure-driven membrane processes, such as reverse osmosis (RO) or nanofiltration, as its low operating pressure reduces the capital cost due to the absence of expensive components, such as high pressure pumps and vessels, as well as pressure exchangers. Recently, MD has been proposed as a low-temperature thermal separation component for hybrid membrane processes coupled with forward osmosis for simultaneous wastewater reuse and mineral recovery 7,8 and with pressure retarded osmosis for harvesting low-grade waste heat. 9 Although MD, as any thermal separation process, is inherently less energy efficient than RO, 10,11 there exist scenarios in which MD may be preferred. For example, if an abundant amount of waste heat or solar thermal energy is readily available, MD can be employed to utilize such low-grade heat to considerably reduce the energy cost and carbon footprint for desalination compared to RO powered by conventional energy sources. 12−14 MD can also be used to desalinate high salinity brines, such as shale gas wastewater, as the osmotic pressure of such brines is far beyond the allowable pressure in RO operations. 15 In addition, MD can be employed for small-scale desalination in remote regions for which RO is not an option due to its dependence on grid power and costly high-pressure components that are not readily adaptable for small-scale systems.In MD desalination, a hydrophobic membrane is employed to create a vapor gap that separates a salty feed solution and the desalted permeate solution. 16 It is critically important that the membrane pores are not wetted by the feed solution as liquid flooding of the pores destroys the vapor gap and undermines the function of the membrane as a selective barrier for salt passage. 1,17,18 Preventing pore wetting is particularly challenging in desalinating shale gas wastewater or ot...
The dye sensitized solar cell (DSSC) operation depends on a liquid electrolyte. To achieve better performance, the liquid should be replaced with a solid or gel electrolyte, e.g., polymers. Here, we demonstrate initiated chemical vapor deposition as an effective liquid-free means for in situ polymerization and pore filling. We achieve complete pore filling of 12 μm thick titania resulting in enhanced cell performance that is attributed to reduced charge recombination at the electrolyte-electrode interface.
Membrane separations are critically important in areas ranging from health care and analytical chemistry to bioprocessing and water purification. An ideal nanoporous membrane would consist of a thin film with physically continuous and vertically aligned nanopores and would display a narrow distribution of pore sizes. However, the current state of the art departs considerably from this ideal and is beset by intrinsic trade-offs between permeability and selectivity. We demonstrate an effective and scalable method to fabricate polymer films with ideal membrane morphologies consisting of submicron thickness films with physically continuous and vertically aligned 1 nm pores. The approach is based on soft confinement to control the orientation of a cross-linkable mesophase in which the pores are produced by self-assembly. The scalability, exceptional ease of fabrication, and potential to create a new class of nanofiltration membranes stand out as compelling aspects.
Common methods for fabrication of polyelectrolyte microcapsules rely on a multi-step process. We propose a single-step approach to generate polyelectrolyte microcapsules with 1-2 μm shells based on polyelectrolyte complexation across a water/oil droplet interface and study the effect of parameters controlling the polyelectrolyte complexation on shell thickness.
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