A biocidal coating was developed in order to reduce biofouling on a reverse osmosis (RO) membrane using a quaternary ammonium (QA) functionalized polymer. The synthesis of a series of polysulfone (PS) ionomers with QA groups is described, and a method for spraying these QA ionomers as an alcoholic solution, which dried into water insoluble coatings. Contact angle and streaming potential were used to analyze the coating's hydrophilicity and surface charge. Both PS-QA1 and the commercial RO membrane had an apparent contact angle of 68° that increased to 126° for PS-QA12 corresponding to alkyl chain length. A negatively charged particle-probe was used to measure coated and uncoated RO membrane interaction forces. Measured interaction forces correlated strongly with the length of alkyl chains or hydrophobicity of the coated surfaces. Uncoated RO membranes and ones coated with PS-QA were exposed to suspensions of Escherichia coli cells. All four PS-QA coatings showed significant biotoxicity and killed 100% of the E. coli cells, but uncoated RO membranes had metabolically active biofilms. However, coatings tested in a RO crossflow system showed a flux reduction that is attributed to mass transfer resistance due to excessively thick films.
The goal of this SAND report is to provide guidance for other groups hosting workshops and peerto-peer learning events at Sandia. Thus this SAND report provides detail about our team structure, how we brainstormed workshop topics and developed the workshop structure. A Workshop “Nuts and Bolts” section provides our timeline and check-list for workshop activities. The survey section provides examples of the questions we asked and how we adapted the workshop in response to the feedback.
Janarthanan, Rajeswari; Serov, Alexey; Pilli, Satyananda K.; Gamarra, Daniel A.; Atanassov, Plamen; Hibbs, Michael R.; Herring, Andrew M.
The objective of the current report is to compare the performance of poly(phenylene) based anion exchange membranes in an alkaline direct methanol fuel cell when platinum cathode catalysts are replaced with non-platinum cathode catalysts. In a KOH-free methanol fuel, we show that a less expensive non-Pt cathode catalyst (derived from Fe-Aminoantipyrine, Fe-AAPyr using Generations 1 and 2 sacrificial silica supports) provide better or comparable performance to commercial Pt cathode catalysts. The peak power density, current density and open circuit voltage of Fe-AAPyr-G-1 in 1 M methanol at 80°C are 2.78 mW cm-2, 19.1 mA cm-2 and 0.7 V respectively. In a direct methanol fuel cell utilizing KOH in the fuel feed, the non-Pt catalyst shows promising peak power density of 52 mW cm-2 with the Fe-AAPyr-G-2 cathode catalyst, comparable to a commercial Pt catalyst.
A series of polysulfone and polyacrylate-based zwitterionic coatings were prepared on epoxy-primed aluminum substrata and characterized for their antifouling (AF) and fouling-release (FR) properties towards marine bacteria, microalgae and barnacles. The zwitterionic polymer coatings provided minimal resistance against bacterial biofilm retention and microalgal cell attachment, but facilitated good removal of attached microbial biomass by exposure to water-jet apparatus generated hydrodynamic shearing forces. Increasing the ion content of the coatings improved the AF properties, but required a stronger adhesive bond to the epoxy-primed aluminum substratum to prevent coating swelling and dissolution. Grafted poly(sulfobetaine) (gpSBMA), the most promising zwitterionic coating identified from microfouling evaluations, enabled the removal of four out of five barnacles reattached to its surface without incurring damage to their baseplates. This significant result indicated that gpSBMA relied predominately on its surface chemistry for its FR properties since it was very thin (~1–2 µm) relative to commercial coating standards (>200 µm).
The ability of three aryldiazonium salts to spontaneously assemble onto the surface of type 440C stainless steel is investigated in acetonitrile (ACN) and the model hydraulic fluids tributyl phosphate (TBP) and hexamethyldisiloxane (HMDS). Competition between native oxide formation and organic film growth at different diazonium salt concentrations is monitored by electrochemical impedance spectroscopy. At 1 mM diazonium salt, 70% of total assembly is complete within 10 min, though total surface coverage by organics is limited to ≈0.15 monolayers. Adding HCl to the electrolyte renders native oxide formation unfavorable, yet the diazonium molecules are still unable to the increase surface coverage over 1 M-10 μM HCl in solution. X-ray photoelectron spectroscopy confirms preferential bonding of organic molecules to iron over chromium, while secondary ion mass spectroscopy reveals the ability of these films to self-heal when mechanically removed or damaged. Aging the diazonium salts in these nonaqueous environments demonstrates that up to 90% of the original diazonium salt concentration remains after 21 days at room temperature, while increasing the temperature beyond 50 °C results in complete decomposition within 24 h, regardless of solvent-salt combination. It is concluded that the investigated diazonium molecules will not spontaneously form a continuous monolayer on 440C stainless steel immersed in ACN, TBP, or HMDS.
This project focuses on the development and demonstration of anion exchange membrane (AEM) fuel cells for portable power applications. Novel polymeric anion exchange membranes and ionomers with high chemical stabilities were prepared characterized by researchers at Sandia National Laboratories. Durable, non-precious metal catalysts were prepared by Dr. Plamen Atanassovs research group at the University of New Mexico by utilizing an aerosol-based process to prepare templated nano-structures. Dr. Andy Herrings group at the Colorado School of Mines combined all of these materials to fabricate and test membrane electrode assemblies for single cell testing in a methanol-fueled alkaline system. The highest power density achieved in this study was 54 mW/cm2 which was 90% of the project target and the highest reported power density for a direct methanol alkaline fuel cell.
Ceragenins were used to create biofouling resistant water-treatment membranes. Ceragenins are synthetically produced antimicrobial peptide mimics that display broad-spectrum bactericidal activity. While ceragenins have been used on bio-medical devices, use of ceragenins on water-treatment membranes is novel. Biofouling impacts membrane separation processes for many industrial applications such as desalination, waste-water treatment, oil and gas extraction, and power generation. Biofouling results in a loss of permeate flux and increase in energy use. Creation of biofouling resistant membranes will assist in creation of clean water with lower energy usage and energy with lower water usage. Five methods of attaching three different ceragenin molecules were conducted and tested. Biofouling reduction was observed in the majority of the tests, indicating the ceragenins are a viable solution to biofouling on water treatment membranes. Silane direct attachment appears to be the most promising attachment method if a high concentration of CSA-121a is used. Additional refinement of the attachment methods are needed in order to achieve our goal of several log-reduction in biofilm cell density without impacting the membrane flux. Concurrently, biofilm forming bacteria were isolated from source waters relevant for water treatment: wastewater, agricultural drainage, river water, seawater, and brackish groundwater. These isolates can be used for future testing of methods to control biofouling. Once isolated, the ability of the isolates to grow biofilms was tested with high-throughput multiwell methods. Based on these tests, the following species were selected for further testing in tube reactors and CDC reactors: Pseudomonas ssp. (wastewater, agricultural drainage, and Colorado River water), Nocardia coeliaca or Rhodococcus spp. (wastewater), Pseudomonas fluorescens and Hydrogenophaga palleronii (agricultural drainage), Sulfitobacter donghicola, Rhodococcus fascians, Rhodobacter katedanii, and Paracoccus marcusii (seawater), and Sphingopyxis spp. (groundwater). The testing demonstrated the ability of these isolates to be used for biofouling control testing under laboratory conditions. Biofilm forming bacteria were obtained from all the source water samples.
Biofouling, the unwanted growth of biofilms on a surface, of water-treatment membranes negatively impacts in desalination and water treatment. With biofouling there is a decrease in permeate production, degradation of permeate water quality, and an increase in energy expenditure due to increased cross-flow pressure needed. To date, a universal successful and cost-effect method for controlling biofouling has not been implemented. The overall goal of the work described in this report was to use high-performance computing to direct polymer, material, and biological research to create the next generation of water-treatment membranes. Both physical (micromixers - UV-curable epoxy traces printed on the surface of a water-treatment membrane that promote chaotic mixing) and chemical (quaternary ammonium groups) modifications of the membranes for the purpose of increasing resistance to biofouling were evaluated. Creation of low-cost, efficient water-treatment membranes helps assure the availability of fresh water for human use, a growing need in both the U. S. and the world.
A series of poly(sulfone)s with quaternary ammonium groups and another series with aldehyde groups are synthesized and tested for biocidal activity against vegetative bacteria and spores, respectively. The polymers are sprayed onto substrates as coatings which are then exposed to aqueous suspensions of organisms. The coatings are inherently biocidal and do not release any agents into the environment. The coatings adhere well to both glass and CARC-coated coupons and they exhibit significant biotoxicity. The most effective quaternary ammonium polymers kills 99.9% of both gram negative and gram positive bacteria and the best aldehyde coating kills 81% of the spores on its surface.