One-Step Catalyst Turns Toxic Nitrates into Water and Air

Achievement date: 
2018
Outcome/accomplishment: 

Engineers at the National Science Foundation (NSF)-funded Nanotechnology Enabled Water Treatment (NEWT) Engineering Research Center (ERC) at Rice University have developed indium-palladium nanoparticle catalysts that clean toxic nitrates from drinking water by converting them into air and water. The discovery was published in the American Chemical Society’s journal, ACS Catalysis, as well as in Science Daily.

Impact/benefits: 

With the prevalent use of fertilizers in agriculture, harmful nitrates increasingly pollute runoff water, negatively impacting the health and environments of nearby communities. While ion-exchange filters can be used to remove the resulting toxins, these require repeat flushing and tend to return more concentrated toxins back to the water supply. As carcinogens, nitrates are dangerous to pregnant women and children, particularly in the U.S. Corn Belt and California’s Central Valley. But because more than 75 percent of the Earth's atmosphere is gaseous nitrogen, the use of NEWT’s catalyst to convert nitrates into air and water could prove beneficial for numerous applications impacting global drinking water supplies.

Explanation/Background: 

In order to keep drinking water safe, the Environmental Protection Agency advises the filtering of nitrate-polluted wells and lakes with ion-exchange resins that trap and remove nitrates and nitrites without destroying them. Michael Wong, lead scientist for NEWT, previously demonstrated the use of gold-spheres dotted with specks of palladium in breaking apart nitrites—even more toxic molecules that evolve from nitrates when they lose oxygen. However, Wong’s gold-palladium approach was not a good catalyst for breaking apart nitrates.

In response, Wong’s co-researcher, Kim Heck, found that covering about 40 percent of a palladium sphere's surface with indium created an even more active catalyst. Indium quickly splits the nitrates; palladium prevents permanent oxidation. By further adding hydrogen-saturated water, palladium allows some bonding of oxygen with hydrogen to form water. The remaining indium can then be used to break apart more nitrates. Because of its speed, NEWT’s one-step indium-palladium catalyst offers gains of 50 percent more efficiency over prior methods.

The team’s next step is to create a flow system for use in the field; NEWT is also exploring commercial applications for water treatment with its industrial partners. Collaborators on the project included Jeffrey Miller of Purdue University and Lars Grabow of the University of Houston, TX.