Development and Performance Characterization of a Polyimine Covalent Organic Framework Thin-Film Composite Nanofiltration Membrane

Two-dimensional covalent organic frameworks (COFs) were used to create the first asymmetric, thin-film composite (TFC) nanofiltration (NF) membrane with a COF active layer. NF membrane active layers of polyimine COF were synthesized via the interfacial polymerization (IP) of terephthalaldehyde and tris­(4-aminophenyl)­benzene monomers on top of a poly­(ether sulfone) (PES) ultrafiltration membrane support. Rutherford backscattering spectrometry and Fourier transform infrared spectroscopy analyses confirmed the presence of an imine-linked film with a thickness of ∼10 nm that was formed reproducibly. The rejection efficiencies of the COF NF membrane for a model organic compound, Rhodamine-WT, and a background electrolyte, NaCl, were higher than those of the PES support without the COF film. This enhanced solute rejection is the first successful demonstration of a TFC membrane with a thin COF active layer. However, this work also demonstrates the need for COF NF membranes with smaller active layer pores and alternative support materials. The former should result in greater solute rejection, and the latter is key because the PES used for support in the COF membranes is incompatible with the organic solvents used for the COF IP process

System-Wide Emissions Implications of Increased Wind Power Penetration

This paper discusses the environmental effects of incorporating wind energy into the electric power system. We present a detailed emissions analysis based on comprehensive modeling of power system operations with unit commitment and economic dispatch for different wind penetration levels. First, by minimizing cost, the unit commitment model decides which thermal power plants will be utilized based on a wind power forecast, and then, the economic dispatch model dictates the level of production for each unit as a function of the realized wind power generation. Finally, knowing the power production from each power plant, the emissions are calculated. The emissions model incorporates the effects of both cycling and start-ups of thermal power plants in analyzing emissions from an electric power system with increasing levels of wind power. Our results for the power system in the state of Illinois show significant emissions effects from increased cycling and particularly start-ups of thermal power plants. However, we conclude that as the wind power penetration increases, pollutant emissions decrease overall due to the replacement of fossil fuels

Changes in Physicochemical and Transport Properties of a Reverse Osmosis Membrane Exposed to Chloraminated Seawater

This study contributed to improving our understanding of how disinfectants, applied to control biofouling of reverse osmosis (RO) membranes, result in membrane performance degradation. We investigated changes in physicochemical properties and permeation performance of a RO membrane with fully aromatic polyamide (PA) active layer. Membrane samples were exposed to varying concentrations of monochloramine, bromide, and iodide in both synthetic and natural seawater. Elemental analysis of the membrane active layer by Rutherford backscattering spectrometry (RBS) revealed the incorporation of bromine and iodine into the polyamide. The kinetics of polyamide bromination were first order with respect to the concentration of the secondary oxidizing agent Br₂ for the conditions investigated. Halogenated membranes were characterized after treatment with a reducing agent and heavy ion probes to reveal the occurrence of irreversible ring halogenation and an increase in carboxylic groups, the latter produced as a result of amide bond cleavage. Finally, permeation experiments revealed increases in both water permeability and salt passage as a result of oxidative damage

Reconciling DLVO and non-DLVO Forces and Their Implications for Ion Rejection by a Polyamide Membrane

Recognizing the significance of surface interactions for ion rejection and membrane fouling in nanofiltration, we revise the theories of DLVO (named after Derjaguin, Landau, Verwey, and Overbeek) and non-DLVO forces in the context of polyamide active layers. Using an atomic force microscope, surface forces between polyamide active layers and a micrometer-large and smooth silica colloid were measured in electrolyte solutions of representative monovalent and divalent ions. While the analysis of DLVO forces, accounting for surface roughness, provides how surface charge of the active layer changes with electrolyte concentration, scrutiny of non-DLVO hydration forces gives molecular insight into the composition of the membrane-solution interface. Importantly, we report an expansion of the diffuse layer at high ionic strength, consistent with the recent development of the electrical double layer theory, but in contrast to the widely accepted phenomenon of aggregation in the secondary minimum. Further, the enhanced repulsion acting on modified membranes via polyelectrolyte adsorption can be quantitatively predicted by DLVO and non-DLVO forces. This work serves to solve past misunderstandings about the interaction forces acting on nanofiltration membranes, and it provides guidance for future work on the relation between surface properties and rejection mechanisms and fouling

Supplementary Tables from Enhanced macroboring and depressed calcification drive net dissolution at high-CO₂ coral reefs

Tables S1,S

Supplementary Figures from Enhanced macroboring and depressed calcification drive net dissolution at high-CO₂ coral reefs

Figures S1-S

Video S1 from Enhanced macroboring and depressed calcification drive net dissolution at high-CO₂ coral reefs

Three-dimensional volume rendering of bioerosion accretion replicate (BAR), showing original carbonate block in grey, new accretion in green, and annelid boreholes in red

Map of Maug showing the locations of the High-pCO₂, Mid-pCO₂ and Control sites.

<p>CNMI, Commonwealth of the Northern Mariana Islands.</p

Mean rates of calcite erosion (mass loss) by microborers in each block and between sites.

<p>Blocks within sites or sites that share a letter (Roman or Greek, respectively) are not significantly different (P>0.05). Error bars are standard error of the mean, calculated among individual estimates within each block (30 estimates per block, 6–7 blocks per site) and among all estimates within each site (180–210) in the left and right panels, respectively.</p

Mean percent surface area colonized by microborers in each block and between sites.

<p>Blocks within sites or sites that share a letter (Roman or Greek, respectively) are not significantly different (P>0.05). Error bars are standard error of the mean, calculated among individual measurements within each block (5 measurements per blocks, 6–7 blocks per site) and among all measurements within each site (30–35) in the left and right panels, respectively.</p