The environment around us is in a constant state of flux, influenced by myriad interwoven systems that adapt and recalibrate in response to diverse stimuli. This ever-changing landscape mirrors the dynamic functions of sustainable technologies, which are at the forefront of today’s innovations as the globe strives for net-zero emissions.
Just as fluctuating weather conditions can significantly affect an ecosystem, various parameters within a technological system—such as temperature, pressure, and humidity—need to be constantly and accurately monitored. This not only ensures its peak performance but also mitigates risks, preventing catastrophic outcomes such as the failure of lithium-ion batteries in electric vehicles that result in violent and deadly explosions.
In biology, membranes wear many important hats. “From separating organs and controlling the flow of chemicals, to transmitting signals and protecting cells from external threats such as viruses, membranes maintain the equilibrium and stability of cellular functions amidst environmental changes,” said Professor Konstantin Sergeevich Novoselov, Director of the National University of Singapore (NUS) Institute for Functional Intelligent Materials (I-FIM).
Although diverse in function, all membranes share a common feature: selective permeability. Depending on the specific function of a cell or organelle, the membrane can selectively permit certain chemicals to pass through. Its control encompasses a broad spectrum of chemicals, from the tiniest ions, including protons, to large protein molecules. Ion channels and pumps within these membranes exhibit high selectivity. For instance, they can distinguish even between sodium and potassium ions. Furthermore, their permeation can be activated by external voltage—a crucial function for processes such as the propagation of nerve signals in our nervous system.
Now, what if we could harness the useful properties of these biological membranes to catalyse the next big breakthrough in sustainable technologies?
In recent times, advancements in the sustainable technology sector have sought inspiration from these membranes. By tapping into their inherent ‘intelligence’, a wide array of applications—from water desalination to ion extraction and from hydrogen separation to carbon capture—could be made more efficient.
A research team from the NUS I-FIM has leveraged two-dimensional (2D) materials to craft smart membranes. Long tipped for their potential in sustainable membrane applications, 2D materials are one-atom thick and can be assembled into stacks with controllable separation between the layers, which enables them to perform different functions.
Published in the journal Nature, the team’s study exploits the unique attributes of molybdenum disulphide (MoS2) as smart membranes. A monolayer of MoS2 is composed of three atomic layers, with molybdenum atoms sandwiched between sulphur in a complex arrangement. Such structures can exist in multiple distinct phases, differentiated solely by the arrangement of atoms in relation to one another. These varying phases can exhibit profoundly different properties.
In their study, the researchers discovered that a specific phase of MoS2 could controllably adsorb and desorb protons, thereby changing the charge on the layers. By manipulating this charge, they can determine the interaction of these layers with various gases and liquids, leading to controlled permeation.
“Even more intriguingly, these membranes can be ‘programmed’ to remember specific functions, suggesting applications in areas like ion extraction and controlled ion permeation,” added Prof Novoselov. Such innovations are central to modern sustainable technologies, including lithium extraction for batteries and the crafting of ionic membranes for fuel cells.
But what are the broader implications of this?
For one, smart membranes hold the promise of enhanced energy efficiency. They can autonomously perform basic operations without relying on external computers or sensors, providing a more streamlined and self-contained solution. Safety, too, can be vastly improved, as these membranes can incorporate internal safety triggers, thus averting potential system failures.
Furthermore, these membranes offer the possibility of external control and monitoring. This would allow for more transparent and traceable production processes, which could, in turn, be integrated with systems like blockchain ledgers for record-keeping.