Rohit Karnik

Ceramic Membranes This image illustrates a palladium “plug” composite membrane separating hydrogen (red) from helium (blue). The isolated plug architecture resists solid-state de-wetting and maintains stable performance even after exposure to 1000 K. This design expands the operating temperature range of palladium-based membranes and opens pathways for achieving stable high-temperature hydrogen separation. More information can be found in the Research Article by Rohit Karnik and co-workers (10.1002/adfm.202516184).

Biological systems rely on ions and molecules as information carriers rather than electrons, motivating the development of devices that interface with biochemical systems for sensing, information processing, and actuation via spatiotemporal control of ions and molecules. Iontronics aims to achieve this vision by constructing devices composed of ion-conducting materials such as polyelectrolyte hydrogels, but advancing beyond simple single-stage circuit configurations that operate under steady-state conditions is a challenge. Here, we propose and model more complex ionic circuits, namely bistable flip-flop and ring oscillators, consisting of multiple ionic bipolar junction transistors (IBJTs). We begin by modeling and characterizing single IBJTs using both a simplified one-dimensional Nernst-Planck model and a more-detailed two-dimensional Poisson-Nernst-Planck model, elucidating the effects of geometry, size, and fixed charge on the IBJT performance and response time. The one- and two-dimensional models exhibit good agreement, indicating negligible transverse inhomogeneities. In addition, these models show that reducing the base width improves current amplification, a behavior analogous to electronic bipolar junction transistors. Building on this understanding, by using the IBJTs as voltage inverters and buffers, we design and model more complex ionic circuits that dynamically change their states in response to ionic signals. Specifically, we demonstrate that the ionic flip-flop retains one-bit memory and that the ring oscillator achieves autonomous periodic self-oscillation without an external clock. Our work provides a foundation for designing dynamic iontronic circuitry using ionic conductors, enabling biochemical signal processing and logic operations based on ionic transport.

Abstract The thermal instability of conventional palladium (Pd) membranes at high temperatures due to solid‐state dewetting or interdiffusion‐induced alloying limits hydrogen (H 2 ) separations in applications such as small‐scale steam methane reforming, ammonia cracking, and nuclear fusion. Here, to mitigate these key degradation mechanisms in Pd membranes, a nanostructured Pd “plug” composite membrane is developed comprising discretized, thermally stable plug structures embedded in nanopores of a silicon‐based membrane. The membrane is fabricated via directional electroless plating, achieving practically 100% filling of the nanopores with Pd plugs. Gas permeation tests compared well with transport model predictions and demonstrated H 2 permeance of ≈10 −7 mol m −2 ·s −1 ·Pa −1 at 800 K, with no detectable helium or nitrogen leakage, indicating high H 2 selectivity. Structural analysis revealed some morphological transitions of the Pd plugs at high temperatures, but without degrading the performance. The membrane remained leakage‐free after 114 h of operation at 800 K and after 100 h at 1000 K, demonstrating exceptional thermal robustness over conventional Pd membranes. These findings establish the Pd plug membrane as a strong candidate for high‐temperature H 2 separations and illustrate the design of membranes with thermally stable metal nanostructures as a general strategy to realize high‐temperature H 2 separations.

Biological systems rely on ions and molecules as information carriers rather than electrons, motivating the development of devices that interface with biochemical systems for sensing, information processing, and actuation via spatiotemporal control of ions and molecules. Iontronics aims to achieve this vision by constructing devices composed of ion-conducting materials such as polyelectrolyte hydrogels, but advancing beyond simple single-stage circuit configurations that operate under steady-state conditions is a challenge. Here, we propose and model more complex ionic circuits, namely bistable flip-flop and ring oscillators, consisting of multiple ionic bipolar junction transistors (IBJTs). We begin by modeling and characterizing single IBJTs using both a simplified one-dimensional Nernst-Planck model and a more-detailed two-dimensional Poisson-Nernst-Planck model, elucidating the effects of geometry, size, and fixed charge on the IBJT performance and response time. The one- and two-dimensional models exhibit good agreement, indicating negligible transverse inhomogeneities. Additionally, these models show that reducing the base width improves current amplification, a behavior analogous to electronic BJTs. Building on this understanding, by using the IBJTs as voltage inverters and buffers, we design and model more complex ionic circuits that dynamically change their states in response to ionic signals. Specifically, we demonstrate that the ionic flip-flop retains one-bit memory and that the ring oscillator achieves autonomous periodic self-oscillation without an external clock. Our work provides a foundation for designing dynamic iontronic circuitry using ionic conductors, enabling biochemical signal processing and logic operations based on ionic transport.

Temperature-dependent, selective molecular diffusion through porous materials is crucial for membrane separations and is typically modeled as an Arrhenius-type activated process. Although this dependence can be described phenomenologically by an activation energy, tracing its molecular origins is often difficult, hindering robust membrane design for practical applications. Here, we investigate gas transport across monolayer nanoporous graphene membranes and observe significant, reversible, temperature-robust, and gas species-selective activated transport, with increased selectivity at rising temperatures, unlike many conventional membranes. Combined experiment and modelling trace this behavior to graphene nanopore edge functional groups, whose thermal fluctuations modulate effective pore size. This activated transport remains stable with aging over 1 year and shows selectivity exceeding 70 for hydrogen/hydrocarbon mixture separation at 220 °C, representative of dehydrogenation reactor temperatures. Our results demonstrate the thermal and long-term robustness of nanoporous graphene membranes, suggesting potential for precise engineering of nanopore surface chemistries in membranes for challenging molecular separations.

Abstract The growing importance of hydrogen in clean energy highlights the need for advanced technologies for efficient hydrogen flow control and separation. Stimuli‐responsive membranes, regulating flow in response to external stimuli, could present new approaches to enhance hydrogen management. However, hydrogen gas‐responsive membranes have yet to be realized, and palladium‐based membranes, known for their high affinity and selectivity for hydrogen, suffer from irreversible structural damage during the palladium hydride phase transition. Here, a palladium composite membrane is developed, consisting of a single nanoporous graphene layer supporting an ultrathin (≈100 nm) palladium film. Gas permeation tests under varying hydrogen pressures and temperatures and with gas mixtures, demonstrate approximately 10‐fold reversible modulation in permeation in response to the partial pressure of hydrogen, corresponding to the palladium phase transition. Control experiments and modeling suggest that reversible adhesion at the graphene/palladium interface and the graphene porosity are key to this switching. Further reduction of the palladium layer thickness leads to discrete palladium islands, tuning the pore size in graphene and producing a hydrogen‐selective molecular sieving membrane with high permeance. These findings illustrate the potential of palladium–graphene synergy to create new functional materials for applications in hydrogen sensing, flow control, and related fields.

Abstract Inadequate clearance of protein-bound uremic toxins (PBUTs) during dialysis is associated with morbidities in chronic kidney disease patients. The development of high-permeance membranes made from materials such as graphene raises the question whether they could enable the design of dialyzers with improved PBUT clearance. Here, we develop device-level and multi-compartment (body) system-level models that account for PBUT-albumin binding (specifically indoxyl sulfate and p -cresyl sulfate) and diffusive and convective transport of toxins to investigate how the overall membrane permeance (or area) and system parameters including flow rates and ultrafiltration affect PBUT clearance in hemodialysis. Our simulation results indicate that, in contrast to urea clearance, PBUT clearance in current dialyzers is mass-transfer limited: Assuming that the membrane resistance is dominant, raising PBUT permeance from 3 × 10 −6 to 10 −5 m s −1 (or equivalently, 3.3 × increase in membrane area from ~ 2 to ~ 6 m 2 ) increases PBUT removal by 48% (from 22 to 33%, i.e., ~ 0.15 to ~ 0.22 g per session), whereas increasing dialysate flow rates or adding adsorptive species have no substantial impact on PBUT removal unless permeance is above ~ 10 −5 m s −1 . Our results guide the future development of membranes, dialyzers, and operational parameters that could enhance PBUT clearance and improve patient outcomes.

Abstract Dynabeads are superparamagnetic particles used for the immunomagnetic purification of cells and biomolecules. Post‐capture, however, target identification relies on tedious culturing, fluorescence staining, and/or target amplification. Raman spectroscopy presents a rapid detection alternative, but current implementations target cells themselves with weak Raman signals. We present antibody‐coated Dynabeads as strong Raman reporter labels whose effect can be considered a Raman parallel of immunofluorescent probes. Recent developments in techniques for separating target‐bound Dynabeads from unbound Dynabeads make such an implementation feasible with high specificity. We deploy Dynabeads anti ‐Salmonella to bind and identify Salmonella enterica , a major foodborne pathogen. Dynabeads present major peaks around 1000 and 1600 cm −1 from aliphatic and aromatic C‐C stretching of the polystyrene coating and near 1350 cm −1 from the ɣ‐Fe 2 O 3 and Fe 3 O 4 core, confirmed with electron dispersive X‐ray (EDX) imaging. Minor to no contributions are made from the surface antibodies themselves as confirmed by Raman analysis of surface‐activated, antibody‐free beads. Dynabeads' Raman signature can be measured in dry and liquid samples even at single shot ~30 × 30 μm area imaging using 0.5 s, 7‐mW laser acquisition with single and clustered beads providing a 44‐ and 68‐fold larger Raman intensity compared with the signature from cells. Higher polystyrene and iron oxide content in clusters yields larger signal intensity, and conjugation to bacteria strengthens clustering as a bacterium can bind to more than one bead as observed via transmission electron microscopy (TEM). Our findings shed light on the intrinsic Raman reporter nature of Dynabeads. When combined with emerging techniques for the separation of target‐bound Dynabeads from unbound Dynabeads such as using centrifugation through a density media bilayer, they have the potential to demonstrate their dual function for target isolation and detection without tedious staining steps or unique plasmonic substrate engineering, advancing their applications in heterogeneous samples like food, water, and blood.

m area imaging using 0.5 s, 7 mW laser acquisition with single and clustered beads providing a 44- and 68-fold larger Raman intensity compared to signature from cells. Higher polystyrene and iron oxide content in clusters yields larger signal intensity and conjugation to bacteria strengthens clustering as a bacterium can bind to more than one bead as observed via transmission electron microscopy (TEM). Our findings shed light on the intrinsic Raman reporter nature of Dynabeads. When combined with emerging techniques for the separation of target-bound Dynabeads from unbound Dynabeads such as using centrifugation through a density media bi-layer, they have potential to demonstrate their dual function for target isolation and detection without tedious staining steps or unique plasmonic substrate engineering, advancing their applications in heterogeneous samples like food, water, and blood.

Dynabeads are superparamagnetic particles used for immunomagnetic purification of cells and biomolecules. Post-capture, however, target identification relies on tedious culturing, fluorescence staining and/or target amplification. Raman spectroscopy presents a rapid detection alternative, but current implementations target cells themselves with weak Raman signals. We present antibody-coated Dynabeads as strong Raman reporter labels whose effect can be considered a Raman parallel of immunofluorescent probes. Recent developments in techniques for separating target-bound Dynabeads from unbound Dynabeads makes such an implementation feasible. We deploy Dynabeads anti-Salmonella to bind and identify Salmonella enterica, a major foodborne pathogen. Dynabeads present signature peaks at 1000 and 1600 1/cm from aliphatic and aromatic C-C stretching of polystyrene, and 1350 1/cm and 1600 1/cm from amide, alpha-helix and beta-sheet of antibody coatings of the Fe2O3 core, confirmed with electron dispersive X-ray (EDX) imaging. Their Raman signature can be measured in dry and liquid samples even at single shot ~30 x 30-micrometer area imaging using 0.5 s, 7 mW laser acquisition with single and clustered beads providing a 44- and 68-fold larger Raman intensity compared to signature from cells. Higher polystyrene and antibody content in clusters yields to the larger signal intensity and conjugation to bacteria strengthens clustering as a bacterium can bind to more than one bead as observed via transmission electron microscopy (TEM). Our findings shed light on the intrinsic Raman reporter nature of Dynabeads, demonstrating their dual function for target isolation and detection without additional sample preparation, staining, or unique plasmonic substrate engineering, advancing their applications in heterogeneous samples like food, water, and blood.

Two-dimensional material based filters, their method of manufacture, and their use are disclosed. In one embodiment, a membrane may include an active layer including a plurality of defects and a deposited material associated with the plurality of defects may reduce flow therethrough. Additionally, a majority of the active layer may be free from the material. In another embodiment, a membrane may include a porous substrate and an atomic layer deposited material disposed on a surface of the porous substrate. The atomic layer deposited material may be less hydrophilic than the porous substrate and an atomically thin active layer may be disposed on the atomic layer deposited material.