Climate change is a serious issue that is affecting the world, even in the present day (it is no longer a theory of what will happen in the future). Manifestations of the effects of climate change have been realised through a series of atmospheric and weather changes in the last couple of years, including the huge number of hurricanes that plagued the US in 2017, to the series of heatwaves that the UK, Europe and East Asia have been experiencing in 2018.
The main way to try and reverse the effects of climate change and global warming is by reducing the number of greenhouse gases that are released into the atmosphere. At present, there is too much of a reliance on fossil fuels and non-renewable energy production. Whilst there has been a shift towards renewables (in some countries more than others, with Costa Rica currently leading the way), more effort is needed, and this is one way where nanotechnology can help.
The second way is through improving the emissions of existing non-renewable process. Whilst the shift to renewable materials is the preferable approach, it is not going to possible to completely change to renewable energy in some countries, so there will also be a small need for non-renewable energy. So, if non-renewables are still going to be around for many years to come, removing some of the carbon dioxide gases from entering the atmosphere is a key way to help limit climate change. This can be done through carbon capture technologies using nano-sized membranes.
Carbon capture is the process of collecting the carbon dioxide produced when fossil fuels are burned. Carbon capture technologies rely on the principles of adhesion to bind the gaseous molecule to a membrane. To date, membranes created for this purpose can capture up to 90% of the carbon dioxide released in the fuel burning process, and this represents a significant reduction of greenhouse gases being released into the atmosphere.
So where does nanotechnology come in? The membrane needs to be small enough to adhere the carbon dioxide molecules to the sheet (so that they don’t pass straight through) and they must be selective enough to attract only the molecules of interest. They essentially act as highly selective filter systems.
Membranes that can do this are inherently porous in nature, such as zeolites and metal-organic frameworks (MOFs). These materials are small enough to capture gaseous molecules, but the internal pore structure can be tailored to only capture carbon-based gases, whilst leaving the rest of the air constituents to pass through unimpeded. A lot of these membranes are also reusable as the pores can be cleaned of the carbon deposits without damaging the membrane or its internal pore structure.
Even though there are many types of renewable energy, solar cells show the most promise for worldwide use (others are location limited, such as the need to be near water etc) and are currently the most widely invested and researched form of renewable energy.
Solar cells rely on semiconducting junctions to convert the solar energy into electricity. Many nanomaterials have been widely established as materials that can be used in these junctions. There are currently many different types of solar cell that employ nanomaterials because they provide a much greater conversion efficiency over traditional solar cells by minimising the energy loss at these junctions.
Traditional inorganic solar cells composed of silicon and indium tin oxide (ITO) are slowly being replaced by nanomaterials such as graphene, quantum dots, perovskite nanomaterials and 1D nanowires. Additionally, there has been a realisation of conductive nanomaterial inks (often made from conductive polymers) that can be used to create organic solar cells, and whilst these don’t currently have the highest efficiency, they can be used to create flexible solar cells (and potentially printed solar cells in the future). The inclusion of non-fullerene acceptor (NFA) materials in recent organic solar cells has also created a class of organic solar cells with a much higher efficiency (although they are not yet at the level of inorganic solar cells).
Written by Liam Critchley.