Jeffrey R. McCutcheon

Hydrophilic Nanofibers as New Supports for Thin Film Composite Membranes for Engineered Osmosis

Engineered osmosis (e.g., forward osmosis, pressure-retarded osmosis, direct osmosis) has emerged as a new platform for applications to water production, sustainable energy, and resource recovery. The lack of an adequately designed membrane has been the major challenge that hinders engineered osmosis (EO) development. In this study, nanotechnology has been integrated with membrane science to build a next generation membrane for engineered osmosis. Specifically, hydrophilic nanofiber, fabricated from different blends of polyacrylonitrile and cellulose acetate via electrospinning, was found to be an effective support for EO thin film composite membranes due to its intrinsically wetted open pore structure with superior interconnectivity. The resulting composite membrane exhibits excellent permselectivity while also showing a reduced resistance to mass transfer that commonly impacts EO processes due to its thin, highly porous nanofiber support layer. Our best membrane exhibited a two to three times enhanced water flux and 90% reduction in salt passage when compared to a standard commercial FO membrane. Furthermore, our membrane exhibited one of the lowest structural parameters reported in the open literature. These results indicate that hydrophilic nanofiber supported thin film composite membranes have the potential to be a next generation membrane for engineered osmosis.

Nanofiber Supported Thin-Film Composite Membrane for Pressure- Retarded Osmosis

Sustainable energy can be harnessed from fluids of differing salinity using a process known as pressure-retarded osmosis (PRO). We address one of the critical challenges of advance PRO by introducing a novel electrospun nanofiber-supported thin-film composite PRO membrane platform. The support was tiered with layers of nanofibers of different diameters to better withstand hydraulic pressure. The membranes successfully withstood an applied hydraulic pressure of 11.5 bar and exhibited performance that would produce an equivalent peak power density near 8.0 W/m(2) under real conditions (using 0.5 M NaCl and deionized water as the draw and feed solutions, respectively). This result shows the immense promise of nanofiber supported thin-film composite membranes for use in PRO.

Towards high power output of scaled-up benthic microbial fuel cells (BMFCs) using multiple electron collectors.

This study aimed at achieving high power output of benthic microbial fuel cells (BMFCs) with novel geometric anode setups (inverted tube granular activated charcoal (IT-GAC) and carbon cloth roll (CCR)) and multiple anodes/electron collectors. The lab-scale tests showed the power density of IT-GAC and CCR anodes achieved at 2.92 and 2.55 W m(-2), the highest value ever reported in BMFCs. The power density of BMFCs substantially increased with electron collector number (titanium rods) in anodes. The connection of multiple electron collectors with multiple cathodes had much higher total voltage/current output than that with single cathode. The possibility of maintaining high power density at scaled-up BMFCs was explored by arranging multiple anodes in sediment. The compact configuration of multiple CCR anodes contacting each other did not deteriorate the performance of individual anodes, showing the feasibility of maximizing anode numbers per sediment footprint and achieving high power output. Multiple IT-GAC and CCR anodes with multiple collectors effectively utilized sediment at both horizontal and vertical directions and enhanced electron collection efficiency. This study demonstrated that bacterial adhesion and electron collection should be optimized on small anodes in order to maintain high power density and achieve high power output in the scaled-up BMFCs.

Holographic characterization of contaminants in water: Differentiation of suspended particles in heterogeneous dispersions

Determining the size distribution and composition of particles suspended in water can be challenging in heterogeneous multicomponent samples. Light scattering techniques can measure the distribution of particle sizes, but provide no basis for distinguishing different types of particles. Direct imaging techniques can categorize particles by shape, but offer few insights into their composition. Holographic characterization meets this need by directly measuring the size, refractive index, and three-dimensional position of individual particles in a suspension. The ability to measure an individual colloidal particles refractive index is a unique capability of holographic characterization. Holographic characterization is fast enough, moreover, to build up population distribution data in real time, and to track time variations in the concentrations of different dispersed populations of particles. We demonstrate these capabilities using a model system consisting of polystyrene microbeads co-dispersed with bacteria in an oil-in-water emulsion. We also demonstrate how the holographic fingerprint of different contaminants can contribute to identifying their source.

Characterization of Thin Film Composite Membranes Using Porosimetry and X-Ray Microscopy

Engineered osmosis is a membrane-based technology employing osmotic pressure gradients to desalinate water (forward osmosis, FO) and produce power (pressure retarded osmosis, PRO). Internal concentration polarization (ICP) is one of the most important phenomena limiting commercialization of EO. Structural characteristics of the membrane greatly influence the ICP phenomena and are expressed using the structural parameter, S as

Large-scale polymeric carbon nanotube membranes with sub–1.27-nm pores

We report the first study of large-scale polymer membranes with <1.27-nm-diameter aligned carbon nanotubes. We report the first characterization study of commercial prototype carbon nanotube (CNT) membranes consisting of sub–1.27-nm-diameter CNTs traversing a large-area nonporous polysulfone film. The membranes show rejection of NaCl and MgSO4 at higher ionic strengths than have previously been reported in CNT membranes, and specific size selectivity for analytes with diameters below 1.24 nm. The CNTs used in the membranes were arc discharge nanotubes with inner diameters of 0.67 to 1.27 nm. Water flow through the membranes was 1000 times higher than predicted by Hagen-Poiseuille flow, in agreement with previous CNT membrane studies. Ideal gas selectivity was found to deviate significantly from that predicted by both viscous and Knudsen flow, suggesting that surface diffusion effects may begin to dominate gas selectivity at this size scale.

3D printed polyamide membranes for desalination

Spraying makes it smoother Commercial reverse osmosis processes for water desalination use membranes made by the polymerization of polyamide at the oil/water interface. Chowdhury et al. show that thinner, smoother membranes can be made with an electrospray technique. Using high voltage, the two precursors are finely sprayed onto a substrate and polymerize on contact. The composition of the resulting membrane can be tuned on the basis of the proportion of the two components. At optimum conditions, the membranes appear to be better at desalination than current commercial reverse osmosis membranes. Science, this issue p. 682 Electrospraying precursors leads to a smoother, more efficient polyamide water purification membrane. Polyamide thickness and roughness have been identified as critical properties that affect thin-film composite membrane performance for reverse osmosis. Conventional formation methodologies lack the ability to control these properties independently with high resolution or precision. An additive approach is presented that uses electrospraying to deposit monomers directly onto a substrate, where they react to form polyamide. The small droplet size coupled with low monomer concentrations result in polyamide films that are smoother and thinner than conventional polyamides, while the additive nature of the approach allows for control of thickness and roughness. Polyamide films are formed with a thickness that is controllable down to 4-nanometer increments and a roughness as low as 2 nanometers while still exhibiting good permselectivity relative to a commercial benchmarking membrane.

Method for direct observation of biofilm formation during operation on forward osmosis membranes

The purpose of this study is to describe a method for direct visual observation of biofilm formation on membranes used in a forward osmosis flow cell. Until recently biofouling research has focused on biofouling during reverse osmosis, and generally examined biofilms after, not during, operation. Direct observation allows for more sensitive measurements of fouling than flux data and membrane autopsies alone. The flow cell proposed here can be used to examine the mechanism of membrane fouling and to systematically examine the effects of surface coatings, membrane materials, and cleaning methods on biofouling using a broad range of process conditions.

Visualizing Hydrated Polymeric Membranes Using X-Ray Microscopy

Membrane separations are used in a variety of applications with water treatment technologies being one of the most notable ones. For a number of these technologies, like nanofiltration, reverse osmosis, forward osmosis, membrane bioreactors and electrodialysis, the membranes used are polymeric materials. In all of these applications the pore structure of the membrane influences its performance, and especially in forward osmosis, the influence is significant. Different types of polymers, both hydrophilic and hydrophobic, are used to make these membranes and the membrane structure can vary based on the polymer’s interaction with water and other ionic solutions in contact with it. Thus there have been several studies on characterizing the structures of polymeric membranes in an effort to correlate it to their performance. A majority of these studies characterized the membranes in their dry state. The working state of the membranes, however, is in the hydrated state and there can be significant differences in the structure of the membrane in the wet vs. dry state [1]. In this study, we have characterized polymeric membranes in their hydrated state to see how effectively the pore structure is wetted out with water and to ultimately determine water connectivity in the pores to see how the membrane pore structure contributes to water transport. The technique used in this study was x-ray microscopy (XRM) and we have previously used it extensively to characterize polymeric materials in their dry state [2, 3]. The images have been used, in addition to calculate % water saturation (to determine % wetted porosity) and water connectivity, to also see if there are any changes to the polymeric structure as a result of swelling/de-swelling behaviors. This study is, according to the best of our knowledge of the literature in this field, the only work where hydrated polymeric membranes have been characterized for the metrics listed above. The findings from this work can benefit researchers in membrane separations to better understand the behavior and performance of polymeric membranes.

Effect of Atmosphere on Heat-Treated Electro-Spun TiO 2 Fibers

1 Depto. de Materiales Metálicos y Cerámicos, IIM. UNAM. Mexico City, 04510, Mexico 2 Dept. of Chemical & Biomolecular Engng, U. of Connecticut, 191 Auditorium Rd, Storrs, CT 06269 3 Sandia National Laboratory, Materials Characterization Dept., MS 0886, Albuquerque, NM 87185 4 Dept. of Materials Science & Engineering, U. of Connecticut, 191 Auditorium Rd, Storrs, CT 06269 5 Institute of Materials Science, U. of Connecticut, 97 North Eagleville Road, Storrs, CT 06269