Advanced polymers help streamline water purification, environmental remediation

January 21, 2020

CHAMPAIGN, Ill. -- It takes a lot of energy to collect, clean and dispose of contaminated water. Some contaminants, like arsenic, occur in low concentrations, calling for even more energy-intensive selective removal processes.

In a new paper, researchers address this water-energy relationship by introducing a device that can purify and remediate arsenic-contaminated water in a single step. Using specialized polymer electrodes, the device can reduce arsenic in water by over 90% while using roughly 10 times less energy than other methods.

The findings of the new study are published in the journal Advanced Materials. Arsenic is a naturally occurring element that enters aquifers, streams and lakes when water reacts with arsenic-containing rocks and is considered highly toxic, the researchers said. This is a global issue affecting more than 200 million people in 70 countries.

Not all arsenic is the same, said Xiao Su, a chemical and biomolecular engineering professor at the University of Illinois who directed the study. The most dangerous form of arsenic, known as arsenite, is highly reactive with biological tissues, but converts to a less toxic form, called arsenate, through a simple oxidation reaction.

"We can remove arsenite from water using absorbents, specialized membranes or evaporation, but these are all very energy-intensive processes that ultimately leave behind a lot of toxic waste," Su said. "By having a device that can capture arsenite with a high selectivity and convert it to a less toxic form, we can reduce the toxicity of the waste while purifying the water."

The proof-of-concept device works by integrating the contaminant separation and reaction steps within a single unit with an electrocatalytic cell - similar to a battery -using redox-active polymers. When the contaminated water enters the device, the first polymer electrode selectively captures the arsenite and sends it to the other polymer electrode, where it is stripped of two of its electrons - or oxidized - to form arsenate. Pure water then leaves the device, and the arsenate waste is concentrated for further disposal, Su said.

"The process is powered by electrochemical reactions, so the device does not require a lot of electricity to run and allows for the reuse of the electrodes based only on electrochemical potential," Su said. "Combining the separation and reaction steps into one device is an example of what we call processes intensification, which we believe is an important approach for addressing environmental concerns related to energy and water - in particular, the amount of energy it takes to purify and remediate contaminated water."

In addition to improved sustainability and energy efficiency, this elctrochemical approach has advantages for field deployment, the researchers said. Users can run the device using solar panels in areas where electricity is scarce - like in parts of rural Bangladesh, a country where over 60% of the population is affected by arsenic-contaminated water, the researchers said.

There are challenges to address before the device is ready for real-world implementation. "We need to increase the stability of the electrodes because this process will need to be cycled many times while running," Su said. "We're using very specialized, highly advanced polymer materials for the electrodes. However, we need to make sure we design them to be not only highly selective for arsenic, but also very stable and robust so that they do not need to be replaced constantly. This will require further chemical development to overcome."
-end-
Su also is affliated with the Beckman Institute for Advanced Science and Technology at the U. of. I.

Postdoctoral researcher Kwiyong Kim and graduate student Stephen Cotty, both from the Su group, are the lead authors of the study. Professor Chia-Hung Hou, from the Graduate Institute of Environmental Engineering at the National University of Taiwan, collborated with the U. of I. on this research.

The National Science Foundation and the U. of I. supported this research.

Editor's notes:

To reach Xiao Su, call 217-300-0134; email x2su@illinois.edu.

The paper "Asymmetric redox-polymer interfaces for electrochemical reactive separations: Synergistic capture and conversion of arsenic" is available online and from the U. of I. News Bureau. DOI: 10.1002/adma.201906877

University of Illinois at Urbana-Champaign, News Bureau

Related Arsenic Articles from Brightsurf:

New map reveals global scope of groundwater arsenic risk
Up to 220 million people worldwide, with approximately 94% of them in Asia, could be at risk of drinking well water containing harmful levels of arsenic, a tasteless, odorless and naturally occurring poison.

River-groundwater hot spot for arsenic
Naturally occurring groundwater arsenic contamination is a problem of global significance, particularly in South and Southeast Asian aquifers.

Natural organic matter influences arsenic release into groundwater
Millions of people worldwide consume water contaminated with levels of arsenic that exceed those recommended by the World Health Organization.

New study finds inaccuracies in arsenic test kits in Bangladesh
Researchers at the University of Michigan have raised serious concerns with the performance of some arsenic test kits commonly used in Bangladesh to monitor water contamination.

Bayreuth researchers discover new arsenic compounds in rice fields
University of Bayreuth researchers, together with scientists from Italy and China, have for the first time sys-tematically investigated under which conditions, and to what extent, sulphur-containing arsenic com-pounds are formed in rice-growing soils.

Kids rice snacks in Australia contain arsenic above EU guidelines: Study
Three out of four rice-based products tested have concentrations of arsenic that exceed the EU guideline for safe rice consumption for babies and toddlers.

Arsenic in drinking water may change heart structure
Among young adults, drinking water contaminated with arsenic may lead to structural changes in the heart that raise their risk of heart disease.

Arsenic-breathing life discovered in the tropical Pacific Ocean
In low-oxygen parts of the ocean, some microbes are surviving by getting energy from arsenic.

Parboiling method reduces inorganic arsenic in rice
Contamination of rice with arsenic is a major problem in some regions of the world with high rice consumption.

UN University compares technologies that remove arsenic from groundwater
A UN University study compares for the first time the effectiveness and costs of many different technologies designed to remove arsenic from groundwater -- a health threat to at least 140 million people in 50 countries.

Read More: Arsenic News and Arsenic Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.