A team led by UC Riverside engineers has developed a catalyst to remove a
dangerous chemical from water on Earth that could also make Martian soil safer
for agriculture and help produce oxygen for human Mars explorers.
Perchlorate, a negative ion consisting of one chlorine atom bonded to four
oxygen atoms, occurs naturally in some soils on Earth, and is especially
abundant in Martian soil. As a powerful oxidizer, perchlorate is also
manufactured and used in solid rocket fuel, fireworks, munitions, airbag
initiators for vehicles, matches and signal flares. It is a byproduct in
some disinfectants and herbicides.
Because of its ubiquity in both soil and industrial goods, perchlorate is a
common water contaminant that causes certain thyroid disorders. Perchlorate
bioaccumulates in plant tissues and a large amount of perchlorate found in
Martian soil could make food grown there unsafe to eat, limiting the
potential for human settlements on Mars. Perchlorate in Martian dust could
also be hazardous to explorers. Current methods of removing perchlorate from
water require either harsh conditions or a multistep enzymatic process to
lower the oxidation state of the chlorine element into the harmless chloride
ion.
Doctoral student Changxu Ren and Jinyong Liu, an assistant professor of
chemical and environmental engineering at UC Riverside's Marlan and Rosemary
Bourns College of Engineering, took inspiration from nature to reduce
perchlorate in water at ambient pressure and temperature in one simple step.
Ren and Liu noted anaerobic microbes use molybdenum in their enzymes to
reduce perchlorate and harvest energy in oxygen-starved environments.
"Previous efforts in constructing a chemical molybdenum catalyst for
perchlorate reduction have not been successful," Liu said. "Many other metal
catalysts either require harsh conditions or are not compatible with water."
The researchers tried to emulate the complicated microbial perchlorate
reduction process with a simplified approach. They found by simply mixing a
common fertilizer called sodium molybdate, a common organic ligand called
bipyridine to bind the molybdenum, and a common hydrogen-activating catalyst
called palladium on carbon, they produced a powerful catalyst that quickly
and efficiently broke down the perchlorate in water using hydrogen gas at
room temperature with no combustion involved.
"This catalyst is much more active than any other chemical catalyst reported
to date and reduces more than 99.99% of the perchlorate into chloride
regardless of the initial perchlorate concentration," Ren said.
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 various scenarios, including remediating contaminated
groundwater, treating heavily contaminated wastewater from explosives
manufacturing, and making Mars habitable.
"A convenient catalytic reduction system may help harvest oxygen gas from
perchlorate washed from the Martian soil when the catalyst is coupled with
other processes," Liu said.
Reference:
Changxu Ren, Peng Yang, Jiaonan Sun, Eric Y. Bi, Jinyu Gao, Jacob Palmer,
Mengqiang Zhu, Yiying Wu, Jinyong Liu. A Bioinspired Molybdenum Catalyst for
Aqueous Perchlorate Reduction. Journal of the American Chemical Society,
2021; 143 (21): 7891 DOI:
10.1021/jacs.1c00595