Tag Archives: Andrew Barron

Safe nanomaterial handling on a tiny budget

A June 3, 2019 news item on Nanowerk describes an inexpensive way to safely handle carbon nanotubes (CNTs), Note: A link has been removed,

With a little practice, it doesn’t take much more than 10 minutes, a couple of bags and a big bucket to keep nanomaterials in their place.

The Rice University lab of chemist Andrew Barron works with bulk carbon nanotubes on a variety of projects. Years ago, members of the lab became concerned that nanotubes could escape into the air, and developed a cheap and clean method to keep them contained as they were transferred from large containers into jars for experimental use.

More recently Barron himself became concerned that too few labs around the world were employing best practices to handle nanomaterials. He decided to share what his Rice team had learned.

“There was a series of studies that said if you’re going to handle nanotubes, you really need to use safety protocols,” Barron said. “Then I saw a study that said many labs didn’t use any form of hood or containment system. In the U.S., it was really bad, and in Asia it was even worse. But there are a significant number of labs scaling up to use these materials at the kilogram scale without taking the proper precautions.”

The lab’s inexpensive method is detailed in an open-access paper in the Springer Nature journal SN Applied Sciences (“The safe handling of bulk low-density nanomaterials”).

Here’s a bag and a bucket,

Caption: A plastic bucket and a plastic bag contain a 5-gallon supply of carbon nanotubes in a lab at Rice University, the beginning of the process to safely transfer the nanotubes for experimental use. The Rice lab published its technique in SN Applied Sciences. Credit: Barron Research Group/Rice University

A June 3, 2019 Rice University news release (also on EurekAlert and received separately by email), which originated the news item, provides more detail,

In bulk form, carbon nanotubes are fluffy and disperse easily if disturbed. The Rice lab typically stores the tubes in 5-gallon plastic buckets, and simply opening the lid is enough to send them flying because of their low density.

Varun Shenoy Gangoli, a research scientist in Barron’s lab, and Pavan Raja, a scientist with Rice’s Nanotechnology-Enabled Water Treatment center, developed for their own use a method that involves protecting the worker and sequestering loose tubes when removing smaller amounts of the material for use in experiments.

Full details are available in the paper, but the precautions include making sure workers are properly attired with long pants, long sleeves, lab coats, full goggles and face masks, along with two pairs of gloves duct-taped to the lab coat sleeves. The improvised glove bag involves a 25-gallon trash bin with a plastic bag taped to the rim. The unopened storage container is placed inside, and then the bin is covered with another transparent trash bag, with small holes cut in the top for access.

After transferring the nanotubes, acetone wipes are used to clean the gloves and more acetone is sprayed inside the barrel so settling nanotubes would stick to the surfaces. These can be recovered and returned to the storage container.

Barron said it took lab members time to learn to use the protocol efficiently, “but now they can get their samples in 5 to 10 minutes.” He’s sure other labs can and will enhance the technique for their own circumstances. He noted a poster presented at the Ninth Guadalupe Workshop on the proper handling of carbon nanotubes earned recognition and discussion among the world’s premier researchers in the field, noting the importance of the work for agencies in general.

“When we decided to write about this, we were originally just going to put it on the web and hope somebody would read it occasionally,” Barron said. “We couldn’t imagine who would publish it, but we heard that an editor at Springer Nature was really keen to have published articles like this.

“I think this is something people will use,” he said. “There’s nothing outrageous but it helps everybody, from high schools and colleges that are starting to use nanoparticles for experiments to small companies. That was the goal: Let’s provide a process that doesn’t cost thousands of dollars to install and allows you to transfer nanomaterials safely and on a large scale. Finally, publish said work in an open-access journal to maximize the reach across the globe.”

Here’s a link to and a citation for the paper,

The safe handling of bulk low-density nanomaterials by Varun Shenoy Gangoli, Pavan M. V. Raja, Gibran Liezer Esquenazi, Andrew R. Barron. SN Applied Sciences June 2019, 1:644 DOI: https://doi.org/10.1007/s42452-019-0647-5 First Online 25 May 2019

This paper is open access.

How small can a carbon nanotube get before it stops being ‘electrical’?

Research, which began as an attempt to get reproducible electronics (?) measurements, yielded some unexpected results according ta January 3, 2018 news item on phys.org,

Carbon nanotubes bound for electronics not only need to be as clean as possible to maximize their utility in next-generation nanoscale devices, but contact effects may limit how small a nano device can be, according to researchers at the Energy Safety Research Institute (ESRI) at Swansea University [UK] in collaboration with researchers at Rice University [US].

ESRI Director Andrew Barron, also a professor at Rice University in the USA, and his team have figured out how to get nanotubes clean enough to obtain reproducible electronic measurements and in the process not only explained why the electrical properties of nanotubes have historically been so difficult to measure consistently, but have shown that there may be a limit to how “nano” future electronic devices can be using carbon nanotubes.

Swansea University Issued a January 3, 2018 press release (also on EurekAlert), which originated the news item, explains the work in more detail,

Like any normal wire, semiconducting nanotubes are progressively more resistant to current along their length. But conductivity measurements of nanotubes over the years have been anything but consistent. The ESRI team wanted to know why.

“We are interested in the creation of nanotube based conductors, and while people have been able to make wires their conduction has not met expectations. We were interested in determining the basic sconce behind the variability observed by other researchers.”

They discovered that hard-to-remove contaminants — leftover iron catalyst, carbon and water — could easily skew the results of conductivity tests. Burning them away, Barron said, creates new possibilities for carbon nanotubes in nanoscale electronics.

The new study appears in the American Chemical Society journal Nano Letters.

The researchers first made multiwalled carbon nanotubes between 40 and 200 nanometers in diameter and up to 30 microns long. They then either heated the nanotubes in a vacuum or bombarded them with argon ions to clean their surfaces.

They tested individual nanotubes the same way one would test any electrical conductor: By touching them with two probes to see how much current passes through the material from one tip to the other. In this case, their tungsten probes were attached to a scanning tunneling microscope.

In clean nanotubes, resistance got progressively stronger as the distance increased, as it should. But the results were skewed when the probes encountered surface contaminants, which increased the electric field strength at the tip. And when measurements were taken within 4 microns of each other, regions of depleted conductivity caused by contaminants overlapped, further scrambling the results.

“We think this is why there’s such inconsistency in the literature,” Barron said.

“If nanotubes are to be the next generation lightweight conductor, then consistent results, batch-to-batch, and sample-to-sample, is needed for devices such as motors and generators as well as power systems.”

Annealing the nanotubes in a vacuum above 200 degrees Celsius (392 degrees Fahrenheit) reduced surface contamination, but not enough to eliminate inconsistent results, they found. Argon ion bombardment also cleaned the tubes, but led to an increase in defects that degrade conductivity.

Ultimately they discovered vacuum annealing nanotubes at 500 degrees Celsius (932 Fahrenheit) reduced contamination enough to accurately measure resistance, they reported.

To now, Barron said, engineers who use nanotube fibers or films in devices modify the material through doping or other means to get the conductive properties they require. But if the source nanotubes are sufficiently decontaminated, they should be able to get the right conductivity by simply putting their contacts in the right spot.

“A key result of our work was that if contacts on a nanotube are less than 1 micron apart, the electronic properties of the nanotube changes from conductor to semiconductor, due to the presence of overlapping depletion zones” said Barron, “this has a potential limiting factor on the size of nanotube based electronic devices – this would limit the application of Moore’s law to nanotube devices.”

Chris Barnett of Swansea is lead author of the paper. Co-authors are Cathren Gowenlock and Kathryn Welsby, and Rice alumnus Alvin Orbaek White of Swansea. Barron is the Sêr Cymru Chair of Low Carbon Energy and Environment at Swansea and the Charles W. Duncan Jr.–Welch Professor of Chemistry and a professor of materials science and nanoengineering at Rice.

The Welsh Government Sêr Cymru National Research Network in Advanced Engineering and Materials, the Sêr Cymru Chair Program, the Office of Naval Research and the Robert A. Welch Foundation supported the research.

Rice University has published a January 4, 2018 Rice University news release (also on EurekAlert), which is almost (95%) identical to the press release from Swansea. That’s a bit unusual as collaborating institutions usually like to focus on their unique contributions to the research, hence, multiple news/press releases.

Dexter Johnson, in a January 11, 2018 post on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website,  adds a detail or two while writing in an accessible style.

Here’s a link to and a citation for the paper,

Spatial and Contamination-Dependent Electrical Properties of Carbon Nanotubes by Chris J. Barnett, Cathren E. Gowenlock, Kathryn Welsby, Alvin Orbaek White, and Andrew R. Barron. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.7b03390 Publication Date (Web): December 19, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Carbon nanotubes for enhanced wheat growth?

It’s been a long time (Oct. 22, 2009 posting; scroll down about 20% of the way) since I’ve written about carbon nanotubes and their possible use in agriculture but now a December 6, 2017 news item on ScienceDaily raises the topic again,

The introduction of purified carbon nanotubes appears to have a beneficial effect on the early growth of wheatgrass, according to Rice University scientists. But in the presence of contaminants, those same nanotubes could do great harm.

The Rice lab of chemist Andrew Barron grew wheatgrass in a hydroponic garden to test the potential toxicity of nanoparticles on the plant. To their surprise, they found one type of particle dispersed in water helped the plant grow bigger and faster.

They suspect the results spring from nanotubes’ natural hydrophobic (water-avoiding) nature that in one experiment apparently facilitated the plants’ enhanced uptake of water.

The research appears in the Royal Society of Chemistry journal Environmental Science: Nano.

A December 6, 2017 Rice University news release (also on EurekAlert), which originated the news item, expands on the theme,

The lab mounted the small-scale study with the knowledge that the industrial production of nanotubes will inevitably lead to their wider dispersal in the environment. The study cited rapid growth in the market for nanoparticles in drugs, cosmetic, fabrics, water filters and military weapons, with thousands of tons produced annually.

Despite their widespread use, Barron said few researchers have looked at the impact of environmental nanoparticles — whether natural or man-made — on plant growth.

The researchers planted wheatgrass seeds in multiple replicates in cotton wool and fed them with dispersions that contained raw single-walled or multi-walled nanotubes, purified single-walled nanotubes or iron oxide nanoparticles that mimicked leftover catalyst often attached to nanotubes. The solutions were either water or tetrahydrofuran (THF), an industrial solvent. Some of the seeds were fed pure water or THF as a control.

Rice University researchers tested the effects of carbon nanotubes on the growth of wheatgrass. While some showed no effect, purified single-walled nanotubes in water (5) enhanced the plants' growth, while the same nanotubes in a solvent (6) retarded their development. The photos at left show the plants after four days and at right after eight days, with odd-numbered plants growing in water and evens in a solvent. Numbers 1 and 2 are controls without nanotubes; 3-4 contain raw single-walled tubes; 5-6 purified single-walled tubes; 7-8 raw multi-walled tubes; 9-10 low-concentration iron-oxide nanoparticles and 11-12 high-concentration iron-oxide nanoparticles.

Rice University researchers tested the effects of carbon nanotubes on the growth of wheatgrass. While some showed no effect, purified single-walled nanotubes in water (5) enhanced the plants’ growth, while the same nanotubes in a solvent (6) retarded their development. The photos at left show the plants after four days and at right after eight days, with odd-numbered plants growing in water and evens in a solvent. Numbers 1 and 2 are controls without nanotubes; 3-4 contain raw single-walled tubes; 5-6 purified single-walled tubes; 7-8 raw multi-walled tubes; 9-10 low-concentration iron-oxide nanoparticles and 11-12 high-concentration iron-oxide nanoparticles. Click on the image for a larger version. Photos by Seung Mook Lee

After eight days, the plantings showed that purified single-walled nanotubes in water enhanced the germination rate and shoot growth of wheatgrass, which grew an average of 13 percent larger than plants in plain water. Raw single- and multi-walled nanotubes and particles in either solution had little effect on the plants’ growth, they found.

However, purified single-walled nanotubes in THF retarded plant development by 45 percent compared to single-walled nanotubes in water, suggesting the nanotubes act as a carrier for the toxic substance.

The concern, Barron said, is that if single-walled nanotubes combine with organic pollutants like pesticides, industrial chemicals or solvents in the environment, they may concentrate and immobilize the toxins and enhance their uptake by plants.

Nothing seen in the limited study indicated whether carbon nanotubes in the environment, and potentially in plants, will rise up the food chain and be harmful to humans, he said.

On the other hand, the researchers said it may be worth looking at whether hydrophobic substrates that mimic the positive effects observed in single-walled nanotubes could be used for high-efficiency channeling of water to seeds.

“Our work confirms the importance of thinking of nanomaterials as part of a system rather in isolation,” Barron said. “It is the combination with other compounds that is important to understand.”

Seung Mook Lee, a former visiting student research assistant from Memorial High School in Houston and now an undergraduate student at the University of California, Berkeley, is lead author of the paper. Co-authors are Rice research scientist Pavan Raja and graduate student Gibran Esquenazi. Barron is the Charles W. Duncan Jr.–Welch Professor of Chemistry and a professor of materials science and nanoengineering at Rice and the Sêr Cymru Chair of Low Carbon Energy and Environment at Swansea University, Wales (UK).

The Welsh Government Sêr Cymru Program and the Robert A. Welch Foundation supported the research.

Here’s a link to and a citation for the paper,

Effect of raw and purified carbon nanotubes and iron oxide nanoparticles on the growth of wheatgrass prepared from the cotyledons of common wheat (triticum aestivum) by Seung Mook Lee, Pavan M. V. Raja, Gibran L. Esquenazi, and Andrew R. Barron. Environ. Sci.: Nano, 2018, Advance Article DOI: 10.1039/C7EN00680B First published on 09 Nov 2017

This paper appears to be behind a paywall.

Decontamination of carbon nanotubes by microwave ovens

The lowly microwave oven plays a starring role in this tale of carbon nanotube purification. From a Jan. 22, 2016 news item on phys.org,

Amid all the fancy equipment found in a typical nanomaterials lab, one of the most useful may turn out to be the humble microwave oven.

A standard kitchen microwave proved effective as part of a two-step process invented at Rice [US] and Swansea [UK] universities to clean carbon nanotubes.

Basic [carbon] nanotubes are good for many things, like forming into microelectronic components or electrically conductive fibers and composites; for more sensitive uses like drug delivery and solar panels, they need to be as pristine as possible.

A Jan. 22, 2016 Rice University news release (also on EurekAlert), which originated the news item, describes the problem the researchers were solving and how they did it,

[Carbon] Nanotubes form from metal catalysts in the presence of heated gas, but residues of those catalysts (usually iron) sometimes remain stuck on and inside the tubes. The catalyst remnants can be difficult to remove by physical or chemical means because the same carbon-laden gas used to make the tubes lets carbon atoms form encapsulating layers around the remaining iron, reducing the ability to remove it during purification.

In the new process, treating the tubes in open air in a microwave burns off the amorphous carbon. The nanotubes can then be treated with high-temperature chlorine to eliminate almost all of the extraneous particles.

The labs of chemists Robert Hauge, Andrew Barron and Charles Dunnill led the study. Barron is a professor at Rice in Houston and at Swansea University in the United Kingdom. Rice’s Hauge is a pioneer in nanotube growth techniques. Dunnill is a senior lecturer at the Energy Safety Research Institute at Swansea.

There are many ways to purify nanotubes, but at a cost, Barron said. “The chlorine method developed by Hauge has the advantage of not damaging the nanotubes, unlike other methods,” he said. “Unfortunately, many of the residual catalyst particles are surrounded by a carbon layer that stops the chlorine from reacting, and this is a problem for making high-purity carbon nanotubes.”

The researchers gathered microscope images and spectroscopy data on batches of single-walled and multiwalled nanotubes before and after microwaving them in a 1,000-watt oven, and again after bathing them in an oxidizing bath of chlorine gas under high heat and pressure. They found that once the iron particles were exposed to the microwave, it was much easier to get them to react with chlorine. The resulting volatile iron chloride was then removed.

Eliminating iron particles lodged inside large multiwalled nanotubes proved to be harder, but transmission electron microscope images showed their numbers, especially in single-walled tubes, to be greatly diminished.

“We would like to remove all the iron, but for many applications, residue within these tubes is less of an issue than if it were on the surface,” Barron said. “The presence of residual catalyst on the surface of carbon nanotubes can limit their use in biological or medical applications.”

Here’s a link to and a citation for the paper,

Enhanced purification of carbon nanotubes by microwave and chlorine cleaning procedures by Virginia Gomez,   Silvia Irusta, Wade Adams, Robert H Hauge, Charles W Dunnill, and Andrew Ross Barron.  RSC Adv., 2016, DOI: 10.1039/C5RA24854J First published online 22 Jan 2016

I believe this paper is behind a paywall.