Waste-not ideology improves toxin removal from contaminated waters

The production of plastic produces phenols, organic compounds known to destroy aquatic ecosystems when they seep into our water. To mitigate the dangers, a research team at Khalifa University has created a photocatalyst from organic byproducts, which could be used as a high-performing and stable photoanode in the electrochemical treatment of water.

Electrochemical oxidation is one exciting approach to remove phenols, alongside inorganic pollutants such lead, mercury and arsenic, from wastewater. Applying a voltage across two electrodes in a wastewater-electrolyte solution prompts phenol molecules to migrate towards one electrode, where they are oxidized,  creating phenol radicals. Further chemical reactions reduce these radicals to carbon dioxide or water.

“Photoelectrochemical processes offer a renewable and environmentally friendly alternative to conventional treatment methods.”

Fawzi Banat

This process can be enhanced with sunlight if the anode is made from a light-sensitive material, or photoelectrocatalyst. “Photoelectrochemical processes offer a renewable and environmentally friendly alternative to conventional treatment methods,” says Fawzi Banat, Chair of the Chemical Engineering Department at KU. “Notably, this method selectively oxidizes target pollutants, while minimizing the generation of harmful byproducts, ensuring cleaner water treatment.”

Banat and his colleagues from the Department of Chemistry and the Center for Catalysis and Separation, together with collaborators from India and the United Kingdom, have created chemically stable photo-electrocatalysts from the two-dimensional material tungsten sulfide. Moreover, they showed optimization could be achieved by incorporating gold nanoparticles.

Two-dimensional materials, substances just a few atoms thick, have several advantages for catalytic applications. First, their optoelectronic properties can be controlled, exhibiting a high electrical conductivity to ensure efficient transfer of electrons through the electrode. Second, they have a high surface-to-volume ratio that improves their catalytic activity.

Banat and the team engineered their tungsten sulfide photocatalyst using organic sulfur from decomposed garlic. Gold nanodots with an average size of 6nm were incorporated onto its surface following a lemon-juice-based reduction process. “Our two-dimensional tungsten sulfide photo-electrocatalysts are fabricated using organosulfur sources, giving high chemical stability and strong absorption of visible light,” explains Banat. “We then successfully incorporated citrate-stabilized gold nanodots into the nanosheets to reduce charge-carrier recombination, improving overall efficiency.”

Experiments proved the remarkable efficacy of the gold-tungsten sulfide photoanode in oxidizing the phenol in an electrolyte solution in 60 minutes under visible light. When arsenic was added to the mix, this was oxidized too. Reproducibility testing went on to indicate the stability of the photoanode for prolonged use.

“Our next step is to investigate using waste sulfur from the petroleum industry to synthesize the two-dimensional tungsten sulfide nanomaterials,” says Banat. “This is the waste-to-wealth concept.”

Reference

1. Bharath, G., Rambabu, K., Alqassem, B., Morajkar, P.P., Abu Haija, M., Nadda, A.K., Gupta, V.K., and Banat, F. Fabrication of gold nanodots decorated on 2D tungsten sulfide (Au-WS₂) photoanode for simultaneous oxidation of phenol and arsenic (III) from industrial wastewater. Chemical Engineering Journal 456, 141062 (2023). | Article