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  • Graphene foam membranes with tunable pore size for next-generation reverse osmosis water desalination.

    Ho, Duc Tam; Nguyen, Thi Phuong Nga; Jangir, Arun; Schwingenschlögl, Udo (Nanoscale horizons, 2023-05-31) [Article]
    The development of carbon-based reverse osmosis membranes for water desalination is hindered by challenges in achieving a high pore density and controlling the pore size. We use molecular dynamics simulations to demonstrate that graphene foam membranes with a high pore density provide the possibility to tune the pore size by applying mechanical strain. As the pore size is found to be effectively reduced by a structural transformation under strain, graphene foam membranes are able to combine perfect salt rejection with unprecedented water permeability.
  • Compositional Reservoir Simulation of Underground Hydrogen Storage in Depleted Gas Reservoirs

    Huang, Tianjia; Moridis, George J.; Blasingame, Thomas A.; Afifi, Abdulkader M.; Yan, Bicheng (Accepted by International Journal of Hydrogen Energy, 2023-05-31) [Article]
    The unstable supply of renewable energy due to seasonal dependency contradicts the periodic energy demand. As hydrogen presents high energy density and flow mobility, and low solubility and residual saturation, underground hydrogen storage (UHS) is a promising solution of scalable energy storage to rebalance energy demand and supply. Depleted gas reservoirs (DGR) are a suitable option for UHS due to their demonstrated integrity. In this study, we developed a numerical simulation model based on Tough + RealGasBrine (T+RGB) simulator to evaluate the feasibility of UHS in DGR. We calibrated different Equation-of-State (EOS) models for modeling the phase behavior of hydrogen-included mixtures with experimental data, and this further helps to examine the impact of various cushion gas pre-injection strategies on pressure maintenance and potential hydrogen leakage through cap-rock. After comparison among three EOS models, we adopted the Soave-Redlich-Kwong (SRK) EOS in our simulations as its high accuracy and computational efficiency. Afterward, we simulated one hydrogen injection-idle-withdrawal operation in a high-resolution mesh based on a synthetic heterogeneous anticline DGR. We observed that hydrogen displaces pre-existing methane and resides at the top of the storage zone due to gravity segregation. The average pressure and gas saturation of the whole simulation domain increase with the hydrogen injection. With regard to the hydrogen leakage, when the cap-rock permeability ranges from 10−510−5 to 10−310−3mD, 0.05% of the injected hydrogen at maximum leaks into the cap-rock while about 1% of injected hydrogen is dissolved into the aqueous phase. Those results demonstrate that DGR is a viable option for UHS. However, only about 73% of injected hydrogen can be recovered if the bottom-hole pressure of the production well is 2 MPa below the reservoir pressure. The cushion gas becomes necessary for the UHS project to increase hydrogen recovery. Injecting cushion gas of nitrogen and carbon dioxide increases hydrogen recovery from the initial 73% to 91% and 81%, respectively. The simulation results demonstrate that nitrogen exhibits better performance, in terms of higher hydrogen recovery factor and purity of producing gas, as the cushion gas. In this work, we quantitatively evaluated the hydrogen leakage problem, including leakage into cap-rock, dissolution in water, and mixing with other gas components, which is the first-of-its-kind analysis in literature to the author’s best knowledge. The simulation results support the feasibility of UHS in the DGR.
  • Polycage membranes for precise molecular separation and catalysis.

    Li, Xiang; Lin, Weibin; Sharma, Vivekanand; Gorecki, Radoslaw; Ghosh, Munmun; Moosa, Basem; Aristizábal, Sandra L; Hong, Shanshan; Khashab, Niveen M.; Nunes, Suzana Pereira (Nature communications, 2023-05-30) [Article]
    The evolution of the chemical and pharmaceutical industry requires effective and less energy-intensive separation technologies. Engineering smart materials at a large scale with tunable properties for molecular separation is a challenging step to materialize this goal. Herein, we report thin film composite membranes prepared by the interfacial polymerization of porous organic cages (POCs) (RCC3 and tren cages). Ultrathin crosslinked polycage selective layers (thickness as low as 9.5 nm) are obtained with high permeance and strict molecular sieving for nanofiltration. A dual function is achieved by combining molecular separation and catalysis. This is demonstrated by impregnating the cages with highly catalytically active Pd nanoclusters ( ~ 0.7 nm). While the membrane promotes a precise molecular separation, its catalytic activity enables surface self-cleaning, by reacting with any potentially adsorbed dye and recovering the original performance. This strategy opens opportunities for the development of other smart membranes combining different functions and well-tailored abilities.
  • Interfacial Reconstructed Layer Controls the Orientation of Monolayer Transition-Metal Dichalcogenides.

    Aljarb, Areej; Min, Jiacheng; Hakami, Marim A.; Fu, Jui-Han; Albaridy, Rehab; Wan, Yi; Lopatin, Sergei; Kaltsas, Dimitrios; Naphade, Dipti; Yengel, Emre; Hedhili, Mohamed N.; Sait, Roaa; Emwas, Abdul-Hamid M.; Kutbee, Arwa; Alsabban, Merfat; Huang, Kuo-Wei; Shih, Kaimin; Tsetseris, Leonidas; Anthopoulos, Thomas D.; Tung, Vincent; Li, Lain-Jong (ACS nano, 2023-05-30) [Article]
    Growing continuous monolayer films of transition-metal dichalcogenides (TMDs) without the disruption of grain boundaries is essential to realize the full potential of these materials for future electronics and optoelectronics, but it remains a formidable challenge. It is generally believed that controlling the TMDs orientations on epitaxial substrates stems from matching the atomic registry, symmetry, and penetrable van der Waals forces. Interfacial reconstruction within the exceedingly narrow substrate-epilayer gap has been anticipated. However, its role in the growth mechanism has not been intensively investigated. Here, we report the experimental conformation of an interfacial reconstructed (IR) layer within the substrate-epilayer gap. Such an IR layer profoundly impacts the orientations of nucleating TMDs domains and, thus, affects the materials' properties. These findings provide deeper insights into the buried interface that could have profound implications for the development of TMD-based electronics and optoelectronics.
  • Two-Photon Excitation Photoredox Catalysis Enabled Atom Transfer Radical Polymerization.

    Yang, Yu-Ying; Zhang, Pengfei; Hadjichristidis, Nikos (Journal of the American Chemical Society, 2023-05-30) [Article]
    In recent years, metal-free photoredox-catalyzed atom transfer radical polymerization (O-ATRP) has gained wide attention because of its advantages (e.g., no metal contamination and mild reaction conditions). However, this traditional one-photon excitation catalysis has thermodynamic limits. Most photocatalysts cannot effectively reduce the initiators and drive the polymerization under visible light. Herein, we investigate the two-photon excitation-catalyzed O-ATRP, in which the catalyst can absorb two photons to accumulate energy. Compared to one-photon excitation catalysis, this method not only has distinct advantages in the controllability, reaction rate, and catalyst loading but also can chemically reduce the various initiators (e.g., aryl halides) to initiate the polymerization. Density functional theory (DFT) calculation reveals that the two-photon excitation process reached a higher energy end state with stronger reduced ability via a thermodynamically more stable intermediate. We believe that this work will provide a new strategy for photoredox-catalyzed O-ATRP.

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