Using sunlight to clean water

Though in its early stages of development, titanium dioxide can be used to speed up the process of purifying water, potentially saving billions of lives

 
Three out of ten people worldwide – 2.1 billion people – do not have access to safe and clean drinking water in their homes, according to recent report by the World Health Organisation.

Supplying people with access to clean water when there is a lack of infrastructure can be difficult, but developments in chemistry are helping to pave the way.
 

Purifying water

It’s incredible to consider, but sunlight actually cleans water naturally. When water is left in sunlight for a certain duration – around 24 hours – the radiation from the sun kills the microorganisms contaminating the water.

Unfortunately, this process is slow, and it only works if the water is clear and not clouded by dirt, so that the light can reach all the microorganisms.

However, there is now an emerging solution to speed this process up significantly – photocatalysts, such as titanium dioxide (TiO2).

 

Due to its incredible photocatalytic properties, titanium dioxide can be used to accelerate the process of killing microorganisms in sunlight. This means that clean water can be produced in a fraction of the time it takes naturally.

If the inside of a clear water container is coated in a layer of very fine TiO2, this can enhance the sun’s disinfection process. Organic molecules and microorganisms are destroyed because the TiO2 creates very reactive hydroxyl free radicals in the water, which attack the impurities. The free radicals dissipate rapidly, making the water safe to consume.

While the technology is still being tested, a paper in 2012 looked into the different properties of titanium dioxide for purifying water. The research team from Tomsk Polytechnic University in Russia found that titanium dioxide in a powder form works best for purifying water when it has been created in an alkaline solution.
 

Disinfecting surfaces

It goes without saying that the effect of being able to create safe drinking water quickly on a large scale would be world-changing, but titanium dioxide’s photocatalytic properties can also be used to tackle another global scourge – poor sanitation and the spread of diseases.

A paper published in 2016 found that when titanium dioxide powder is combined with sunlight, it can be used to destroy harmful bacteria including E. coli and staphylococcus aureus, both of which commonly infect humans and cause potentially fatal sickness.

“These antibacterial surfaces may be applied to hospital, food ceramic, and building industries or to environmental remediation where bacteria inactivation is required to ensure the safety of human health and the environment,” says Changseok Han, from the US Environmental Protection Agency, and part of the team that wrote the paper.

The relatively low energy needed for the process and the non-toxicity of titanium dioxide make it a safe and economic way of disinfecting surfaces, which is particularly important in the poorest and most at-risk communities.

 


 

The future

Though a relatively young technology, photocatalysis by titanium dioxide continues to be tested to explore its potential as a water purifier and disinfectant, and there’s no telling what an incredible, life-changing effect this could have on those who need it most.

As Dr Tedros Adhanom Ghebreyesus, WHO Director-General, says: “Safe water, sanitation and hygiene at home should not be a privilege of only those who are rich or live in urban centres. These are some of the most basic requirements for human health, and all countries have a responsibility to ensure that everyone can access them.”

If TiO2’s photocatalytic properties are put to good use, safer drinking water for everyone doesn’t look so far out of reach.