Small materials have big potential
When it comes to maintaining quality water resources, it turns out that even the smallest solution can have a major impact. Researchers from both the Chemical and Civil and Environmental Engineering departments in the University of Missouri College of Engineering have discovered that some very tiny materials can effectively treat water.
Baolin Deng, department chairman of chemical engineering, and two student research assistants have been working to explore the application of carbon nanotubes (CNT) research.
Deng, who also serves as the C.W. LaPierre Professor of civil and environmental engineering, worked with Jun Yin, a doctoral civil engineering student, and visiting scholar Guocheng Zhu to develop a system to create hollow fiber membranes that utilize CNTs, as well as an application for the product in water treatment.
“Carbon nanotubes are very special nanomaterials,” Yin said.
CNTs are carbon allotropes — variations of an element based on how the atoms are bonded together— structured in a cylindrical form, with their length hundreds of times longer than their width. Previous researchers have examined the use of CNTs for water filtration, Yin said, and those earlier investigations served as the catalyst for the MU researchers.
Deng’s team explored the use of CNTs in hollow fiber polymer membranes. During the first year of the project, Yin said the team worked almost exclusively on creating the polymer and designing the system to make the membrane structures, which are approximately one millimeter in diameter, in lengths that can be customized. The membranes are hollow in the center, and have porous walls, similar to the pores in a sponge. The CNTs are introduced into the polymeric membrane structures.
“We can control, with the polymer and chemistry, the structure and size of the membrane pores,” Deng said.
In an article published by the Journal of Membrane Science, Deng and his graduate researchers found using membrane structures with CNTs could more effectively filter contaminants from water. In their study, membranes are contained in narrow glass tubes through which pressurized water flows. The membrane is able to reject any contaminant larger than its pores. The CNTs found within the membrane structures create properties that significantly increase the efficiency of water flow. The CNTs also help prevent a build up of contaminants on the membrane surface that would otherwise obstruct water flow and allows water to more easily flow through.
“Because the used carbon nanotube has a negative charge to its surface, the resulting membrane can more easily reject negatively-charged particles,” Yin said.
As for potential applications of the research, Deng said the methods used in the project could be used for treating different types of water — wastewater, greywater or drinking water — from a myriad of sources. He speculated the methods also could be used to treat brackish groundwater.
“This could be one way to solve water treatment problems or a fresh water shortage,” Deng said.
He said the task now lies in finding the right balance between great potential applications and potential risks of CNTs.
Deng’s previous research examined the effects of carbon nanotube exposure in aquatic environments and risks to aquatic organisms.
He found largely the risks to be the result of “uncleaned” carbon nanotubes — untreated and therefore still retaining trace amounts of metals leftover from the manufacturing process. CNTs used in the research team’s membrane structures, are pre-treated with mixed acid solutions to remove these metals.
“If we find that the benefits outweigh the risks, we know this is something that we can take to a commercial level, but if we find the risks are too high, we may have to restrict how this technology is used or who can use it.”
Water treatment is an ever-evolving topic, Deng said. Modern research looks to improve upon approaches that were groundbreaking 100 years ago.
“What we’re doing could be the same approach researchers will be using 100 years from now.”