2D MATERIAL NANOFLUIDICS AND CRYOGENICS LAB

Room-Temperature Deuterium Separation in van Der Waals Gap Engineered Vermiculite Quantum Sieves

DOI: 10.1002/smll.202412229

As the demand for nuclear energy grows, enriching deuterium from hydrogen mixtures has become more important. However, traditional methods are either very energy-intensive because they require extremely cold temperatures, or they don't separate deuterium (D2) from regular hydrogen (H2) very well, with a D2/H2 selectivity of ≈0.71. To achieve efficient deuterium separation at room temperature, materials with very tiny spaces, on an atomic scale are needed. For the first time, a material with spaces just ≈2.1 Å (angstroms) wide is successfully created, which is similar in size to the wavelength of hydrogen isotopes at room temperature. This allows for efficient deuterium separation, with a much higher D2/H2 selectivity of ≈2.20, meaning the material can separate deuterium from hydrogen much more effectively at room temperature. The smaller deuterium molecules are more likely to pass through these tiny spaces, showing that quantum effects play a key role in this process. In contrast, a material like graphene oxide, with larger spaces (≈4.0 Å), only shows a lower D2/H2 selectivity of ≈1.17, indicating weaker quantum effects. This discovery suggests that materials with very small, atomic-scale spaces can be key to efficient separation of hydrogen isotopes at room temperature.

Can structure influence hydrovoltaic energy generation? Insights from the metallic 1T′ and semiconducting 2H phases of MoS2

DOI: 10.1039/D4NR02416H

Hydrovoltaic power generation from liquid water and ambient moisture has attracted considerable research efforts. However, there is still limited consensus on the optimal material properties required to maximize the power output. Here, we used laminates of two different phases of layered MoS2 – metallic 1T′ and semiconducting 2H – as representative systems to investigate the critical influence of specific characteristics, such as hydrophilicity, interlayer channels, and structure, on the hydrovoltaic performance. The metallic 1T′ phase was synthesized via a chemical exfoliation process and assembled into laminates, which can then be converted to the semiconducting 2H phase by thermal annealing. Under liquid water conditions, the 1T′ laminates (having a channel size of ∼6 Å) achieved a peak power density of 2.0 mW m−2, significantly outperforming the 2H phase (lacking defined channels) that produced a power of 2.4 μW m−2. Our theoretical analysis suggests that energy generation in these hydrophilic materials primarily arises from electro-kinetic and surface diffusion mechanisms. These findings highlight the crucial role of phase-engineered MoS2 and underscore the potential of 2D material laminates in advancing hydrovoltaic energy technologies. 

Angstrom Scale Ionic Memristors’ Engineering with van der WaalsMaterials: A Route to Highly Tunable Memory States

DOI: 10.1021/acsami.4c14521

Memristors that mimic brain functions are crucial for energy-efficient neuromorphic devices. Ion channels that emulate biological synapses are still in the early stages of development, especially the tunability of memory states. Here, we demonstrate that cations such as K+, Na+, Ca2+, and Al3+ intercalated in the interlayer spaces of vermiculite result in highly confined channels of size 3–5 Å. They host exotic memristor properties through ion exchange dynamics, even at high salt concentrations of 1 M. The bipolar memristor characteristics observed are tunable with frequency, geometric asymmetry, ion concentration, and intercalants. Notably, we observe polarization-flipping memristor behavior in two cases: one with Al3+ ions and another with devices having a geometric asymmetry ratio greater than 15. This inversion is attributed to the overscreening of counterions due to their accumulation at the channel entrance. Our results suggest that ion exchange dynamics, ion–ion interactions, and ion accumulation/depletion mechanisms, particularly with multivalent ions, can be harnessed to develop advanced memristor devices. 

Ion-hydration-controlled large osmotic power with arrays of angstrom scale capillaries of vermiculite

DOI: 10.1016/j.xcrp.2023.101717.

The significant difference in salt concentration at the seawater and river water interface is a clean source of enormous osmotic power of ∼ 2.4 TW. This power is much larger than that solar and wind power produced together as of 2021. However, in the osmotic power generation field, reaching the industrial benchmark has been challenging because of the need for capillaries close to the sizes of ions and molecules. Here, we fabricated well-controlled ‘along-the-capillary’ membranes of Na-vermiculite with a capillary size of ∼ 5 Å. They exhibit 1600 times enhanced conductivity compared to commonly studied ‘across-the-capillary’ membranes. Interestingly, they show a very high cation selectivity of 0.83 for NaCl solutions, which resulted in large power densities of 9.6 W/m2 and 12.2 W/m2 at concentration gradients of 50 and 1000, respectively, at 296 K, for an unusually large membrane length of 100 μm. The power density shows an exponential increase with temperature, reaching 65.1 W/m2 for a concentration gradient of 50 at 333 K. This markedly differs from the classical behavior and indicates the role of ion (de)hydration in enhancing power density, opening new possibilities for exploiting such membranes for energy harvesting applications.

Membranes for desalination and dye separation: Are 2D materials better

than polymers? A critical comparison 

DOI: 10.1016/j.seppur.2023.124693

2D materials-based membranes have emerged as a promising alternative to polymer-based membranes in desalination and dye separation applications. With their exceptional permeation properties, 2D membranes outperform traditional polymers, offering higher water flux rates and improved efficiency. These membranes exhibit tunable properties, allowing customization for specific separation needs, and their atomic smoothness minimizes fouling, ensuring prolonged operational life. To enhance ion rejection and water flux, researchers propose using 2D membranes with high surface charge and sterically excluded sub-nm fluidic structures. These advancements in membrane technology hold great potential for addressing water scarcity and improving industrial separation processes. However, further research is needed to ensure their practical implementation on a larger scale.