Engineers Develop a New Water Treatment Technology That Could Also Help Mars Explorers

Astronaut on Mars base

A catalyst that destroys perchlorate in water could clean the Martian soil.

A team led by engineers from the University of California Riverside has developed a catalyst to remove a dangerous chemical from the water on Earth that could also make the Martian soil safer for agriculture and help produce oxygen for human Martian explorers .

Perchlorate, a negative ion made up of one chlorine atom bonded to four oxygen atoms, occurs naturally in some soils on earth and is particularly common in the Martian soil. As a strong oxidizing agent, perchlorate is also manufactured and used in solid rocket fuel, fireworks, ammunition, airbag igniters for vehicles, matches and signal flares. It’s a by-product in some disinfectants and herbicides.

Because of its ubiquity in both soil and manufactured goods, perchlorate is a common water pollution that causes certain thyroid diseases. Perchlorate accumulates in plant tissues, and a large amount of perchlorate found in the Martian soil could unsafe the foods grown there and limit the potential for human settlement on Mars. Perchlorate in Martian dust could also be dangerous for explorers. Current methods of removing perchlorate from water require either harsh conditions or a multi-step enzymatic process to lower the oxidation state of the chlorine element into the harmless chloride ion.

PhD student Changxu Ren and Jinyong Liu, Assistant Professor of Chemical and Environmental Engineering at the Marlan and Rosemary Bourns College of Engineering at UC Riverside, took inspiration from nature to reduce perchlorate in water at ambient pressure and temperature in one simple step.

Ren and Liu found that anaerobic microbes use molybdenum in their enzymes to reduce perchlorate and generate energy in low-oxygen environments.

“Previous efforts to design a chemical molybdenum catalyst for perchlorate reduction have not been successful,” said Liu. “Many other metal catalysts either require harsh conditions or are not water-compatible.”

The researchers tried to recreate the intricate microbial perchlorate reduction process using a simplified approach. They found that by simply mixing a common fertilizer called sodium molybdate, a common organic ligand called bipyridine that binds the molybdenum, and a common hydrogen activating catalyst called palladium on carbon, they produced a powerful catalyst that quickly and efficiently breaks down the perchlorate in water using Hydrogen gas at room temperature without combustion.

“This catalyst is much more active than any other chemical catalyst known to date and reduces more than 99.99% of the perchlorate to chloride regardless of the initial perchlorate concentration,” said Ren.

The new catalyst reduces perchlorate in a wide concentration range from less than 1 milligram per liter to 10 grams per liter. This makes it suitable for use in a variety of scenarios including the remediation of contaminated groundwater, the treatment of heavily contaminated wastewater from explosives manufacture, and the habitability of Mars.

“A practical catalytic reduction system can help extract oxygen gas from perchlorate that is scrubbed from the Martian soil when the catalyst is coupled with other processes,” said Liu.

The article “A bioinspired molybdenum catalog for aqueous perchlorate reduction” was published in the Journal of the American Chemical Society. Ren and Liu were involved in the research by UC Riverside graduate student Jinyu Gao, undergraduate Jacob Palmer, and high school student Eric Y. Bi. Peng Yang and Mengqiang Zhu from the University of Wyoming characterized the catalyst using X-ray absorption spectroscopy, and Jiaonan Sun and Yiying Wu from Ohio State University performed the electrochemical tests. The research was funded by the National Science Foundation.

Reference: “A bio-inspired molybdenum catalyst for the reduction of aqueous perchlorate” by Changxu Ren, Peng Yang, Jiaonan Sun, Eric Y. Bi, Jinyu Gao, Jacob Palmer, Mengqiang Zhu, Yiying Wu and Jinyong Liu, May 18, 2021, Journal of the American Chemical Society.
DOI: 10.1021 / jacs.1c00595