When Two Wastewater Treatment Methods Are Better Than One

Coupling two popular chemical processes leads to better organic pollutant removal than either method alone, say researchers from India and Saudi Arabia.

AsianScientist (Dec. 6, 2021) – Nearly every major river in Asia is polluted, according to a 2021 United Nations report on water quality. One group of organic pollutants known as phenols are particularly concerning because they are not easily biodegradable and accumulate over time in soil and groundwater. That may soon change, thanks to a new phenol removal method published in the Journal of Industrial and Engineering Chemistry.

Chemical techniques are traditionally used to remove phenol from water. The Fenton oxidation process uses a reaction between hydrogen peroxide (H2O2) and ferrous (Fe2+) ions to yield highly oxidizing hydroxyl ions (.OH) that can degrade phenols into carbon dioxide and water. However, this process is a slow one that requires a lot of H2O2.

Furthermore, the Fenton process has lower catalytic activity compared to semiconductor-assisted photocatalysts, which produce phenol-degrading .OH ions when exposed to light. But despite its better catalytic activity, this isn’t a perfect solution either: because of their dependence on light, photocatalytic reactions are bottlenecked by the strength of the light source.

Now, scientists from India’s Shoolini University and Saudi Arabia’s King Abdulaziz University seem to have found the perfect strategy for wastewater treatment — by coupling the Fenton reaction and photocatalysis to extract the best of both reactions while compensating for their limitations.

The researchers combined an Ag3PO4/CdS/Fe-g-C3N4 (AP/CdS/FeCN) photocatalyst with H2O2 to develop what they termed a photo-Fenton system.

“We opted for a dual Z-scheme approach since it is emerging as an effective way to enhance light absorption ability, photostability and separation of photogenerated electron-hole pair in the Ag3PO4 photocatalyst,” explained study corresponding author Professor Pardeep Singh from Shoolini University.

The new coupled system works by using the photocatalyst to mimic the natural process of photosynthesis, harvesting sufficient light to undergo the oxidation reactions required to degrade phenol.

When Singh and his team put the system to the test, they found that it showed higher phenol degradation rates than either approach alone. The researchers believe that coupling the reactions generated more Fe2+ ions and .OH radicals, thus enhancing the phenol degradation rate.

Furthermore, the photo-Fenton system proved to be highly photostable and reusable, maintaining its catalytic activity even after five successive cycles of usage.

According to the researchers, their discovery shows promise for practical applications in wastewater purification. In addition, their findings could provide insights on how to design a new generation of catalytic systems for large-scale water treatment.

“Apart from its practical implications, the novelty of this technique could invoke interest in researchers to explore and discover newer methods for environmental remediation and pave a path towards sustainable development,” concluded co-author Associate Professor Pankaj Raizada, also from Shoolini University.

The article can be found at: Khan et al. (2021) Converting Ag3PO4/CdS/Fe doped C3N4 based dual Z-scheme photocatalyst into photo- Fenton system for efficient photocatalytic phenol removal.


Source: Shoolini University; Photo: Shutterstock.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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