Tiny Sheets, Big Impact: How Size and Charge Shape Ion Separation
Mon Feb 17 2025
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Tiny sheets, so small you can't even see them, stacked together to create a super thin membrane. These sheets, called nanosheets, are made from a type of clay called montmorillonite. Scientists have found a way to use these nanosheets to separate lithium (Li+) and magnesium (Mg2+) ions from salt-lake brines. This is a big deal because these ions are important for making batteries and other tech.
The challenge? Figuring out how the size and charge of these nanosheets affect how well they separate the ions. When making nanosheets, defects and changes in surface properties can occur, making it hard to pinpoint the exact effects. So, researchers used nanosheets that were free of defects and had a permanent charge.
Smaller nanosheets created membranes with tiny channels, which helped to separate the ions more effectively. This is because the smaller channels made it harder for the larger magnesium ions to pass through, a concept known as steric hindrance.
The charge of the nanosheets also played a role. The researchers found that the difference in energy barriers for ion transport was key to the separation process. This means that the charge of the nanosheets created an energy barrier that the ions had to overcome to pass through, and this barrier was different for lithium and magnesium ions.
The result? A membrane that could separate lithium and magnesium ions efficiently and stably, even under tough conditions. This membrane had an optimal selectivity ratio (S_Li/Mg) of 38. 9, which is better than most other membranes out there.
This discovery is important because it shows how the properties of nanosheets can be tuned to control ion transport and separation. This could lead to the development of advanced membranes for sustainable and environmentally friendly energy use.
But here's a question to think about: How can we make these membranes even better? What other properties of nanosheets could we tweak to improve ion separation? And how can we make these membranes more durable and efficient for real-world applications?
