Nav: Home

NewcCompetition for MOFs: Scientists make stronger COFs

August 01, 2018

Hollow molecular structures known as COFs (covalent organic frameworks), which could serve as selective filters or containers for other substances and have many other potential uses, also tend to suffer from an inherent problem: It's difficult to keep a network of COFs connected in harsh chemical environments.

The conventional chemistry for linking building blocks into 2D COF sheets or 3D COF frameworks is reversible. This reversibility makes the connections within COFs weak and unstable in some chemical environments, limiting the practical applications of these COF materials.

Now, a team at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has used a chemical process discovered decades ago to make the linkages between COFs much more sturdy, and to give the COFs new characteristics that could expand their applications.

"It's like a 'weaving' and welding approach," said Yi Liu, a staff scientist at Berkeley Lab's Molecular Foundry. Liu led a team that found out how to strengthen the weakest links binding COFs.

This one simple chemical approach targets a chemical reaction to the area of these weak links, forming resilient bonds that were shown to hold up - like a strong weld - to harsh chemical environments during experiments.

The team's findings are detailed in a study, reported Tuesday in the journal Nature Communications, that details how the technique works.

"Here we show that these bonds are exceptionally stable to a variety of chemicals. We've tried harsh conditions and it still sustains these bonds," Liu said. "This beats everything reported in the literature."

The chemical transformation, he noted, makes the bonds between COFs more useful by changing their electronic and optical (light-based) properties, for example. "They can transfer electrons more easily after the reaction," he said, so that 2D layers of these strongly bound COFs behave more like graphene, another exotic 2D material that exhibits special electronic and optical properties.

Xinle Li, a postdoctoral fellow at the Molecular Foundry and the study's lead author, said, "We gave that reaction process, first reported in the 1960s, a new life. We applied it to COFs for the first time."

COFs have been heavily studied because they are highly tunable and can be composed entirely of light elements like carbon, hydrogen, nitrogen, and oxygen - unlike structures known as MOFs (metal-organic frameworks) that contain heavier elements. Scientists can make COFs with different pore sizes that can impact their function, changing what can pass through them or what can be contained within these pores.

This could make the COF-based materials useful in systems that filter unwanted chemicals from water, for example, reduce carbon dioxide into other value-added chemical forms, or serve as highly efficient facilitators for other types of chemical processes.

An important aspect of the study was the use of advanced imaging techniques, such as high-resolution transmission electron microscopy (HRTEM) at the Molecular Foundry to see the structure of the bound COFs, Liu and Li said.

The researchers said the images obtained, which clearly show the honeycomb-like lattice of 2D COFs, are among the best images yet of COFs, confirming the chemical changes in the COFs down to a fraction of a nanometer (a nanometer is 1 billionth of a meter).

"Before and after the reaction, the pore size changes by about 0.3 nanometer, Liu said. "You can see these differences before and after the reaction."

To carry out the chemical modification reaction, the researchers placed the COFs in a liquid solution that was heated to about 230 degrees Fahrenheit, and then stirred it up.

Researchers said it should be possible to scale up the amount of the COF-based materials, and the team has already experimented with using COF sheets with other material layers to customize the function of the combined material.

The team plans to test how to better automate the production of these COF materials, and will also pursue ways to make the reaction process more efficient. The team will explore theories to help understand and improve upon the COF-altering chemistry.

"We want to make this chemical modification process even faster and better," Li said. "We hope we can make the reaction conditions milder, and further increase the chemical stability and functionality of COFs."

The team's work is one of the first published efforts of a new program at the Molecular Foundry aiming to advance "combinatorial nanoscience" that is focused on using high throughput processes, in combination with theory and imaging technology, to create and study nanostructures that are components in new materials with enhanced properties.
-end-
The Molecular Foundry is a DOE Office of Science User Facility.

The study is co-authored by other Molecular Foundry researchers, and also had participation from Molecular Foundry users from South China Normal University and Zhejiang University in China. This work was supported by the U.S. Department of Energy's Office of Basic Energy Sciences and the National Nature Science Foundation of China.

Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel Prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit http://www.lbl.gov.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov.

DOE/Lawrence Berkeley National Laboratory

Related Molecular Foundry Articles:

How to code a functional molecular machine?
An international team has developed a model that simulates protein evolution.
Visualization of molecular soccer balls
Researchers led by the University of Tsukuba imaged lithium ion-doped fullerene, which resembles a molecular soccer ball, by scanning tunneling microscopy.
A molecular dance of phospholipid synthesis
The most abundant molecule in cell membranes is the lipid phosphatidylcholine (PC, commonly known as lecithin); accordingly, the enzymes responsible for synthesizing it are essential.
Molecular motor: Four states of rotation
With the help of ultrafast spectroscopy and quantum mechanical calculations, Ludwig-Maximilians-Universitaet (LMU) in Munich researchers have characterized the complete rotational cycle of the light-driven, chemical motor molecule hemithioindigo.
What else can molecular perovskite do?
Combining good detonation performance, high stability and low cost is the major hindrance on high-performance explosives.
Molecular cuisine for gut bacteria
Scientific recipes to successfully grow and study gut bacteria in the lab: that's what EMBL scientists are publishing in Nature Microbiology on March 19.
News from Molecular & Cellular Proteomics
These are research highlights from Molecular & Cellular Proteomics: proteostasis and cancer in a collagen-deficient skin disease; chemical tools for probing protein glycosylation in T-cell activation
Study suggests molecular imaging strategy for determining molecular classifications of NSCLC
Recent findings suggest a novel positron emission tomography (PET) imaging approach determining epidermal growth factor receptor (EGFR) mutation status for improved lung cancer patient management.
Measuring molecular interactions
ETH researchers have used a new approach to discover previously unknown interactions between proteins and small metabolic molecules in bacterial cells.
Understanding the molecular mechanisms of ALS
Scientists have revealed more details of the molecular mechanism behind neuronal cell death in amyotrophic lateral sclerosis (ALS), a step forward to find ways to control progression of the disease.

Related Molecular Foundry Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...