Interview: New filtering technique removes toxic metals from water

July 27, 2017

A chemist from Rice University and a high school student have developed a filter that can remove toxic heavy metals — including cadmium, cobalt, copper, mercury, nickel, and lead — from the water. The researchers calculated that one gram of the material could purify 83,000 liters of water to World Health Organization standards. The filter can be washed with household vinegar and reused.

We spoke to one of the authors of the study, Andrew R. Barron from Rice University.

ResearchGate: What motivated this study?

Andrew Barron: The initial idea came from two different directions. First, was the desire to be able to remove toxic metals from drinking water in remote locations that didn’t have power. The second was the Fukushima disaster, where there was a need to remove complex radioactive metal waste.

Plain quartz fiber, top, gains the ability to remove toxic metals from water when carbon nanotubes are added, bottom. The filters absorbed more than 99 percent of metals from test samples laden with cadmium, cobalt, copper, mercury, nickel and lead. Once saturated, the filters can be washed and reused. Barron Research Group/Rice University.

RG: Can you tell us what you developed?

Barron: Simply put, we realized that there are issues with most nano carbon based absorbents such as graphene. Once they adsorb the metals, you usually have to then dispose of the “contaminated” graphene. We rationalized that if we grew the carbon nanotubes on a substrate that could be manipulated then we could re-generate them.

RG: How did you develop this?

Barron: We grew carbon nanotubes onto quartz wool, then epoxidized them to make them active to adsorb metal ions. We then discovered that vinegar reacts with the metal in solution to adsorb it from solution in a very efficient manner.

RG: Did you experience any particularly difficult challenges in the development process?

Barron: Not really, for once research actually went ahead in a straight-forward manner.

RG: What are some of the filter’s practical applications that excite you the most?

Barron: The first is a test we have performed in Guatemala City demonstrated that highly polluted water could be pre-treated by a membrane and then flowed through the activated nanotubes to remove hazardous metals such as mercury and cadmium. We are also interested in developing the technology to remove metals from waste water from abandoned coal mines, which is part of an EU program called DE-MINE.

An electron microscope image shows quartz fibers with carbon nanotubes grown in place. Credit: Barron Research Group/Rice University

RG: Can you tell us how you came to collaborate with the then high school student Perry Alagappan?

Barron: Perry approached me to get some experience in research before applying to college. I had an undergraduate, Jessica Heimann, who had started the project and was spending a year abroad, so this became a perfect project for a high school student. This is the culmination of several pieces of research from my group over the years that came together with a group of excellent researchers, including graduate student Lauren Morrow. It is also an example of multi-national collaboration.

Featured image: An electron microscope image shows quartz fibers with carbon nanotubes after epoxidation. Experiments showed epoxidation appears to give the filters their absorptive quality. Credit: Barron Research Group/Rice University.

Read more stories