Reducing ion exchange particles to nano-size shows big potential

Jan 30, 2012

Sometimes bigger isn't better. Researchers at the U.S. Department of Energy's Savannah River National Laboratory have successfully shown that they can replace useful little particles of monosodium titanate (MST) with even tinier nano-sized particles, making them even more useful for a variety of applications.

MST is an material used to decontaminate radioactive and industrial wastewater solutions, and has been shown to be an effective way to deliver metals into living cells for some types of medical treatment. Typically, MST, and a modified form known as mMST developed by SRNL and Sandia National Laboratories, are in the form of fine powders, spherically-shaped about 1 to 10 microns in diameter.

"By making each particle smaller," says Dr. David Hobbs of SRNL, lead of the research project, "you increase the amount of surface area, compared to the overall volume of the particle. Since the particle surface is where reactions take place, you've increased the MST's working area." For example, a 10-nanometer particle has a surface area-to-volume ratio that is 1000 times that of a 10-micron particle. Thus, this project sought to synthesize materials that feature nano-scale particle sizes (1 – 200 nm). After successfully synthesizing nanosize titanates, the team investigated and found that the smaller particles do indeed exhibit good ion exchange characteristics. They also serve as photocatalysts for the decomposition of organic contaminants and are effective platforms for the delivery of therapeutic metals.

Dr. Hobbs and his partners in the project examined three methods of producing nano-sized particles, resulting in three different shapes. One is a sol-gel method, similar to the process used to produce "normal" micron-sized MST particles, but using surfactants and dilute concentrations of reactive chemicals to control particle size. This method resulted in spherical particles about 100 – 150 nm in diameter.

A second method started with typical micron-sized particles, then delaminated and "unzipped" them to produce fibrous particles about 10 nm in diameter and 100 – 150 nm long. The third method, which had been previously reported in the scientific literature, was a hydrothermal technique that produced nanotubes with a diameter of about 10 nm and lengths of about 100 -500 nm.

The team had considerable expertise in working with MST, having previously modified it with peroxide to form mMST, which exhibits enhanced performance in removing certain contaminants from radioactive waste and delivering metals for . Nanosize MST produced by all three methods was successfully converted to the peroxide-modified form. As with micron-sized titanates, the peroxide-modified nanosize titanates exhibit a yellow color. The intensity of the yellow color appeared less intense with the hydrothermally produced nanotubes, suggesting the chemically resistant surface of the nanotubes may limit conversion to mMST.

Testing confirmed that the materials function as effective ion exchangers. For example, the spherical nanoMST and nanotube samples and their respective peroxide-modified forms remove strontium and actinides from alkaline high-level waste radioactive waste. Under weakly acidic conditions, the nanosize titanates and peroxotitanates removed more than 90% of 17 different ions.

The "unzipped" titanates and their peroxide-modified forms proved to be particularly good photocatalysts for the decomposition of organic contaminants.

Screening in-vitro tests showed that both nano-size and micron-size metal-exchanged titanates inhibit the growth of a number of oral cancer and bacterial cell lines. The mechanism of inhibition is not known, but preliminary scanning electron microscopy results suggest that the titanates may be interacting directly with the wall of the nucleus to deliver sufficient metal ion concentration to the cell nucleus to inhibit cell replication.

Explore further: Improving printed electronics process and device characterization

Provided by Savannah River National Laboratory

5 /5 (2 votes)
add to favorites email to friend print save as pdf

Related Stories

When Nano May Not Be Nano

Sep 13, 2009

(PhysOrg.com) -- The same properties of nanoparticles that make them so appealing to manufacturers may also have negative effects on the environment and human health. However, little is known which particles ...

Recommended for you

Tiny graphene drum could form future quantum memory

Aug 28, 2014

Scientists from TU Delft's Kavli Institute of Nanoscience have demonstrated that they can detect extremely small changes in position and forces on very small drums of graphene. Graphene drums have great potential ...

Graphene reinvents the future

Aug 27, 2014

For many scientists, the discovery of one-atom-thick sheets of graphene is hugely significant, something with the potential to affect just about every aspect of human activity and endeavour.

User comments : 0