February 15, 2010, 9:27 pm
Safe water using sunshine!
Making water safe to drink using sunlight and nanotechnology!
What was discovered?
A 'photocatalyst' could kill bacteria in water, making it safe to drink.
Catalysts speed up chemical reactions, and a photocatalyst is activated using light - in this case using visible light from sunlight. The photocatalyst used was made from a grid of titanium oxide fibres with nanoparticles made from the metal palladium, and the fibres had nitrogen in them. As photons from sunlight hit the grid a positive charge was created which splits water molecules, producing a substance deadly to microbes.
And the photocatalyst just kept on working, even when night time came!
Experiments showed how bacteria called Eschericia coli, which can make us very ill, could be killed using sunlight and the new photocatalyst.
Better still, the new technology killed bacterial spores which are usually unharmed with other water purification techniques.
Why is it important?
This new technology was more effective than the current methods which use chlorine or ultra-violet light to purify the water and make it safe to drink.
Now we need to see if it can be scaled up and used in developing countries.
The fact that it keeps on working, even in the dark, is important in remote places where electricity blackouts make other systems unreliable.
How are the bacteria killed?
Ha! This is the really cool bit! This is the first time that it has been demonstrated that in sunlight electrons flowing to the palladium oxide nanoparticles from the fibres of titanium oxide and nitrogen (yes, the nitrogen must be there for the system to work!) can actually kill bacteria.
Most likely the biological molecules in the bacteria are themselves oxidised, changing their properties and killing the bacteria.
How does the effect continue in the dark?
It is as if the photocatalyst "remebers" that it can kill bacteria with its flow of electrons, and carries on doing so even when the light is turned off - for up to 10 hours!
The explanation is most likely that the electrons now flow back from the palladium, triggering the production of highly reactive OH radicals that kill the bacteria.
What techniques were used ?
The flow of electrons to and from the palladium oxide nanoparticles when visible light was shone on the titanium oxide and nitrogen fibres was measured using an Atomic Force Microscope (AFM).
This gave amazing details of the charge distribution on the surface of the nanomaterials.
An X-ray Photoelectron Spectrometer (XPS) was used to analyse the surface chemistry of the nanomaterials, to find out the electronic state of each element.
Full details can be read in the Journal of Materials Chemistry
What can this study tell us about how we do science?
Scientific data can show us in amazing detail what is going on in the world of molecules!
This is only possible with lots of patience and dedication to make and test the delicate materials.
As well as increasing our understanding, scientific discoveries can have very important practical applications, such as purifying water to make it safe to drink.
But even if we can use highly sophisticated technology, sometimes the older traditional methods may have other advantages, which need to be considered before going ahead with large scale production.
And yet, even if the research is not used for its original purpose, the techniques and knowledge gained can have wider applications, sometimes far more important than the reasons that they were developed in the first place.
So, perhaps most importantly of all, we cannot plan where our great discoveries will come from - but we must be ready to catch them as they flutter before our very eyes (or experimental instruments!!!)