Introduction
Drinking water quality is a crucial indicator of public safety and living standards. However, over 10% of the world’s population still has minimal access to clean water, leading to millions of people dying yearly due to this global issue, resulting in pressing demand for the development of novel, easy-to-use, and economically attractive technology enabling reasonable water use.
Limitations on current water treatment method
There are various water treatment methods, such as filtration, activated carbon adsorption, and chlorination. Why don't we use what we have used until now? In truth, those current methods cannot altogether remove microorganisms and toxic compounds from drinking water sources. For instance, chlorination, the most commonly used disinfection method, could lead to the formation of mutagenic and carcinogenic by-products, disclaiming it as a safe method. Furthermore, the high energy and chemical consumption of chlorination limits its applications in rural areas.
Introduction to photocatalysis
A newly proposed water treatment technology, known as ‘photocatalysis’, is a method that will allow the treatment and disinfection of water without producing any harmful by-products.
The term photocatalyst is a combination of two words: photo and catalyst. Photo is related to the photon, a particle representing a quantum of light or other electromagnetic radiation; a catalyst is a substance altering the reaction rate while remaining unchanged. Therefore, photocatalysis is a phenomenon in which semiconducting material changes the chemical reaction rate upon light exposure.
Mechanism of photocatalysis
During photocatalysis, solid, semiconductive catalysts generate active oxygen forms on their surface with the radiation from light. These oxygen forms are responsible for oxidising and reducing compounds adsorbed on the catalyst surface. Titanium dioxide ( TiO2 ) is usually used as a semiconductive catalyst, performing a series of redox reactions on the surface of the catalyst.
How could photocatalysis be used to treat water?
Water should be treated before being given out to people as it contains various microorganisms. However, all microorganisms, such as bacteria cells, consist of 70-90% water and cell compounds such as polysaccharides, lipids, lipopolysaccharides, proteins, and nucleic acids. Thus, oxygen-containing radicals produced during photocatalysis can attack and destroy their cell.
Advantages of photocatalysis on water treatment
The photocatalytic reaction is among the developing future technologies that are currently under the spotlight. The most significant advantage of photocatalysis is that it does not require high temperatures for a reaction. With photocatalysis, it is possible for reactions that only occur at very high temperatures to occur at room temperature, allowing it to be used in rural areas as well. The possibility of using sunlight as the radiation source expands its possibilities. Furthermore, it can neutralise viruses and bacteria in water without adding contaminants, such as antibiotics or disinfection byproducts, to the environment.
Why is it yet to be commercialised?
The main factor that limits the commercialisation of photocatalysis on a global scale is the final separation of the semiconductive catalyst TiO2 from the treated water. The small size of TiO2 particles and high specific surface energy cause catalysts to assemble during the reaction. This results in the reduction of particular surfaces and limits the multiple application of TiO2.
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