Monday 5 September 2022

Carbon Conference 2022

The 2022 World Conference on Carbon was held at Imperial College London in early July. Given the tumultuous time, it felt remarkable to be sitting in the introductory lecture and welcomed by Prof. Geoff Fowler. It was especially remarkable for me as I had travelled on one of the longest flights in the world from Perth to London (17 hours) to be there. Here are some of my thoughts from my great week in London.

Carbon for a Clea​​​​ner Future 

The theme for this year's conference was "Carbon for a Cleaner Future", which is an apt theme for a world in need of carbon to rapidly decarbonise. We heard from excellent plenary speakers including Prof. Novoselov on graphene, Prof. Bandosz on the chemical effects within porous carbon, Prof. Conchi Ania on lighting up nanoporous carbons for catalysts, Prof. Marc Monthioux on carbons mimicking water droplets on a spider's web and Prof. Milo Shaffer on assembling scalable nanocarbons! I filled many more pages of notes from other excellent speakers and presenters throughout the conference. 

Industry at the cutting edge

Another highlight was meeting and hearing talks from industrial scientists at the cutting edge of carbon science. It was remarkable to see the work on reducing the power and degradation of graphite furnaces from Dr Timm Ohnweiler at Carbolite furnaces. 

LinkedIn post from Carbolite

Brian Kelly award

I was very grateful to receive the Brian Kelly Award from Prof. Fowler at the beginning of the conference. The work for which I was awarded the prize is close to that of Prof. Kelly's. In 1981, he wrote, 
"The material presented shows that graphitisation is not a simple process, and it is not well understood." Brian Kelly, Physics of Graphite, 1981

Here is the personal story of the discussions and collaborations from past Carbon conferences that led to the work I presented in London. 

In 2017, at the Melbourne Carbon Conference, I met Dr Nigel Marks, Dr Irene Suarez-Martinez and Dr Carla de Tomas from the Carbon Group at Curtin University in Perth, Australia. I was in the middle of my PhD on soot/carbon black formation at the University of Cambridge but became fascinated by the disordered carbon structures the Carbon Group had prepared using molecular dynamics simulations that were able to capture all of the features in glassy and porous carbons. I visited Perth briefly and started to work on these structures with the group, employing some novel visualisation approaches of 3D printing and analysing the structures using a mesh. We managed to find a common nanostructure between the glassy and porous carbons. These disordered carbons also contained an excess of saddle-shaped (net-negative Gaussian) curvature [Martin, Jacob W., et al. "Topology of disordered 3D graphene networks." Physical Review Letters 123.11 (2019): 116105.]. The stacking order in the glassy carbon could then be explained by the sheets winding up to form screw-like defects that enabled a fullerene-like structure to be stacked in particular regions. This provided a potential explanation for the transition from porous carbon to impervious glassy carbon as well as the isotropic properties of the material. 

Model of disordered carbons

I presented this work at the 2019 Carbon Conference in Lexington, USA and was very happy to receive the student prize for the talk. It was the SFEC French Carbon Award talk that drew my attention to graphite. Dr Philippe Ouzilleau spoke about the formation of graphite through a thermodynamic model that was done with Prof. Marc Monthioux and others [Ouzilleau, Philippe, et al. "Why some carbons may or may not graphitize? The point of view of thermodynamics." Carbon 149 (2019): 419-435.]. They firstly showed that graphitisation is a second-order phase transition with a critical temperature around Tc=2550 K. Secondly, they suggested the presence of annealable topological defects in graphite that give rise to the phase transition while in non-graphitising carbons other non-annealable topological defects are present that are unable to be removed. 

In 2020 I was able to join the Carbon Group at Curtin University through a Forrest Fellowship. I began working with Jason Fogg and Kate Putman, both PhD students in the Carbon Group. They had been developing a novel, low-cost approach to heat up carbon to 3000 °C using the furnace in an atomic absorption spectrometer (AAS) [Putman, K. J., et al. "Pulsed thermal treatment of carbon up to 3000° C using an atomic absorption spectrometer." Carbon 135 (2018): 157-163.]. This approach had been discovered by Dr Peter Harris, who had previously asked a colleague in chemistry to use these furnaces to prepare samples for electron microscopy.

Carbon Group at Curtin University (Ms Kate Putman, Mr Jason Fogg, Dr Irene Suarez-Martinez, Dr Jacob Martin, Dr Nigel Marks)

The Atomic Absorption Spectrometer (AAS) was invented in Australia by Alan Walsh at CSIRO in the 1950s. It works by vaporising metals that then absorb light and it is often used for environmental metal tests such as detecting lead contamination. Vaporisation was originally achieved in a flame, however, a small graphite tube furnace has mainly replaced the flame. This small joule heated graphite furnace has been extensively developed since the 1960s to ramp up extremely rapidly (~3000 °C/s) and have power control to reproducibly control the temperature. Both time and temperature are critical to control for reproducible measurements. These ramp rates far exceed those for conventional graphite furnaces, which require at least an hour to reach >2500 °C. Given the precise control over the time and temperature, it was the perfect instrument to study graphitisation kinetics and so the Carbon Group worked with GBC Scientific, one of the original Australian companies to commercialise the AAS, to have a custom tube furnace provided. 

Dr Irene Suarez-Martinez and Mr Jason Fogg operating the GBC graphite tube furnace.

This new furnace provided a means to address the problem posed by Prof. Brian Kelly in 1981 for studying graphite. 
"The proper study of the variation of a property (of graphite) with time at temperature is difficult because of the necessity to raise the specimen temperature rapidly to very high levels, and the difficulties associated with very high temperature measurements." 
Brian Kelly, Physics of Graphite, 1981
When I arrived in Perth, I suggested we look at a graphitising carbon and search for an annealable topological defect. Jason prepared samples across the graphitisation transition with varying residence times by applying multiple thermal pulses. I then took the samples to the transmission electron microscope for imaging. This new microscope had a cold field emission gun that provided atomic resolution of the graphite and clearly resolved the interplanar defects as screw dislocations that were removed with heat treatment. To find out how the screws form and are removed we performed molecular dynamics simulations to find the mechanism for their removal. There was a nice connection with the screw dislocations, as Dr Suarez-Martinez studied these in her PhD with the late Malcolm Heggie. 

Electron microscopy and model of a screw dislocation.

We could then probe the kinetics of graphitisation by tracking the crystallites using X-ray diffraction of the pulse heated samples. This revealed that the graphitisation kinetics were more rapid than first thought, occurring on the seconds timescale. The speed at which graphitisation occurs was the aspect that most interested those in the graphite industry at the conference. At 2500 °C, graphitisation takes a few minutes, however, above 2800 °C it takes less than 10 seconds. These insights could have significant cost savings when it comes to industrial production of graphite. Additionally, the removal of screw defects could be targeted to catalyse graphitisation. The preprint for the work is currently online if you would like to read more. A recording of the lecture I gave is also available online

Nanocarbon in virtual reality and 3D printing

Alongside the presentation on graphite, I gave two other talks on the formation of soot/carbon black (recording available online) and also on the visualisations of carbon nanostructures using VR and 3D printing (recording available online). 

During the lunch breaks I was able to demonstrate the virtual reality headset and show people carbon in 3D. It was a lot of fun to see people explore these computational models. We also had the opportunity to view other groups' atomistic structures that were emailed as xyz coordinates, providing a new way to engage with other peoples work. 

Not yet back to normal

Many people were absent from the conference and were sadly missed. Colleagues from China and Japan could not attend due to travel restrictions in their home countries. There were also instances of scientists unable to attend due to global conflict. Dr Yuriy A. Olkhovyk from Ukraine gave an excellent recorded talk on containment of nuclear graphite at Chernobyl. I hope that these barriers will soon be removed within the Carbon community and we can all freely meet at future conferences. 

However, given the situation it was remarkable what the British Carbon Society achieved in spite of terrible uncertainty. I wanted to personally thank them for bringing together an excellent conference programme, expertly planned and executed. 

Molly the anthropomorphic Molymod

Another attendee sorely missed was the late Malcolm Heggie. In memory of Malcolm and to bring his humour back to the Carbon community, Molly was reconstructed out of a Molymod molecular modelling kit.

Another carbon great passed away when the conference was just beginning - Prof. Robert Curl, from Rice University. The winner of the 1996 novel Prize for Chemistry discovered the C60 buckminsterfullerene, the molecule that started my love of carbon. I recommend the well written article from Rice University on Prof. Curl's life

I recall emailing Prof. Curl as an undergraduate to ask for help with a paper. I was working on whether giant fullerenes could be synthesised. He not only responded to my email but organised for someone at Rice to perform an experiment I proposed, however, it was not initially successful. I tried a different approach to heating the fullerenes to size them into giant fullerenes, which ended up working. I sent him the manuscript that was subsequently published in Carbon. He wrote, 

"Thank you for sending me your manuscript on the heat driven solid state coalescence of giant fullerenes in toluene-extracted fullerene soots. I think this paper makes significant progress in understanding this interesting and challenging subject. I am flattered by your offer to join you as an author to this paper, but have to decline. I believe that any contributions I might have made to this work are trivial."
This was followed by extensive feedback on the manuscript. He continued to help me in another projects too. I was fascinated by the lack of fullerenes in fullerene-like carbons such as charcoal. Prof. Curl emailed the late Prof. Sir Harry Kroto and Prof. Alan Marshall to organise some high resolution mass spectrometry to be done at Florida State University. These experiments demonstrated similar oxygen-containing giant fullerene-like fragments, as seen in the giant fullerene paper. This suggested that the heat treated fullerene arc-carbon and charcoal share a common nanostructure. We published this work in Environmental Science & Technology with Prof. Curl again refusing to be on the authorship. 

He also kindly wrote a letter of support for one of my fellowship applications in 2020. I hadn't even met him in person but he agree to support the science present in my application. As a young person exploring carbon science this was extraordinarily encouraging with all of my interactions with Prof. Curl demonstrated his kindness, humility and generosity to a student he had never met.

Conference dinner on the Thames

A significant highlight was having a sit-down dinner on board a river boat and having the tower bridge open for us. The cloudless sky was also a nice touch from the organising committee! 

On board the boat with friends.

I spent the following week in Cambridge with a Covid-induced fever, enhanced by the heat wave, but with no regrets. I can only reiterate words from Prof. Kelly that ring true also for me: 

"The study of these materials has brought me considerable pleasure and the good fellowship of the 'carbon' community." Brian Kelly Physics of Graphite, 1981

Monday 22 November 2021

What’s in a flame? How soot forms from molecule to particle

Andrew Breeson and I put together this press release that was picked up by PhysOrg on a review paper Maurin Salamanca, Markus Kraft and I recently wrote.

Soot is one of the world's worst contributors to climate change. Its impact is similar to global methane emissions and is second only to carbon dioxide in its destructive potential. This is because soot particles absorb solar radiation, which heats the surrounding atmosphere, resulting in warmer global temperatures. Soot also causes several other environmental and health problems including making us more susceptible to respiratory viruses.

Soot only persists in the atmosphere for a few weeks, suggesting that if these emissions could be stopped then the air could rapidly clear. This has recently been demonstrated during recent lockdowns, with some major cities reporting clear skies after industrial emissions stopped.

But soot is also part of our future. Soot can be converted into the useful carbon black product through thermal treatment to remove any harmful components. Carbon blacks are critical ingredients in batteries, tires and paint. If these carbons are made small enough they can even be made to fluoresce and have been used for tagging biological molecules, in catalysts and even in solar cells.

Given the importance of soot and how long humankind has been producing it, you would think its formation was completely understood. However, this is not the case. In particular, the critical transition when the molecules cluster to form the very first nanoparticles of soot is unknown.

If the origins of soot were to be entirely understood, we could potentially eliminate its formation and therefore drastically reduce its environmental impact as well as make better carbon materials. With this in mind, researchers from the University of Cambridge and Cambridge CARES have recently published a comprehensive review on the birth of soot—where molecules become particles.

In the review, titled: "Soot inception: Carbonaceous nanoparticle formation in flames" published in Progress in Energy and Combustion Science, the authors Dr. Jacob Martin, Dr. Maurin Salamanca and CARES Director Professor Markus Kraft begin by noting that;

"It has only been in the last decade, however, that experimental and computational techniques in combustion science have been able to peek behind the door to reveal insights into the earliest formation mechanisms of carbonaceous particulates in the flame."

The figure below shows some of these new experimental insights along the path from fuel to soot. In this diagram it is nanoparticle formation (soot inception) that is the birth of the soot particle.

The graphical abstract from "Soot inception: Carbonaceous nanoparticle formation in flames" Credit: Jacob Martin

Two main pathways have been suggested for soot inception—either physical condensation in which molecules form droplets or chemical polymerisation in which molecules react to form particles. But either pathway by itself is non-optimal, as "physical and electrical condensation of precursor molecules is rapid but too weak to hold soot together, while most chemical bonds are strong but the mechanisms proposed to date are too slow to account for rapid growth of soot as observed in experiments."

Schematic of various soot nanoparticles arranged as a function of their C/H ratio and molecular weight. Credit: Jacob Martin

Instead, the authors suggest a "middle way" involving mechanisms with both physical and chemical aspects. Promising options are highlighted involving π-radicals and diradicals, however, conclusive evidence for a specific mechanism as well as predictive models are still lacking.

Ultimately, the authors conclude that "the emission of carbonaceous nanoparticles needs to be a research and industrial priority for the future of combustion devices and new material applications."

"Soot inception: Carbonaceous nanoparticle formation in flames" is published in Progress in Energy and Combustion Science by researchers from Cambridge Centre for Advanced Research and Education in Singapore Ltd and University of Cambridge.

Thursday 5 August 2021

Molecular dance in sooting flames

Below is the press release that was picked up by PhysOrg 

A hidden, newly discovered molecular dance could hold the answer to the problem of soot pollution.

Soot pollution causes cancer and blood clots, as well as weakening immune systems to respiratory viruses. The atmosphere and glaciers are also blanketed by soot, leading to global heating and increased ice loss. Surprisingly, the way that soot particles form is still unknown, but is of pressing concern.

The reason for this long-running mystery is due to the extreme environment in which soot forms, the rapid speed of the reactions and the complex collection of molecules present in the flame. All of these obscure the pathway to soot formation.

An international team from the UK, Singapore, Switzerland and Italy has now used two microscopes to reveal the molecules and reactions taking place in a flame. The first microscope operates by touch, feeling for the arrangement of atoms in the molecules of soot. These tactile maps provide the first picture of soot's molecular chicken wire shape. Quantum chemistry was then used to show that one of the molecules was a reactive diradical. A diradical is a type of molecule with two reactive sites, allowing it to undergo a succession of chain reactions.

The first microscope operates by touch, feeling for the arrangement of atoms in the molecules of soot. These tactile maps provide the first picture of soot’s molecular chicken wire. Quantum chemistry was used to determine a new class of reactive molecules, diradicals.

Imaging of a soot precursor molecule and the reactive diradical revealed with quantum chemistry.

The second microscope is entirely virtual and shows the reaction between the diradicals. Quantum mechanics guided a supercomputer to virtually and realistically collide the molecules together and reveal the molecular dance in slow motion.

This simulation showed that the individual molecules are held together by intermolecular forces after they collide. This gives the reactive sites time to find each other and create a permanent chemical bond. Even after they have bonded they remain reactive, allowing more molecules to "stick" to what is now a rapidly growing soot particle.

This discovery could resolve the problems with previous attempts to explain soot formation via either a physical condensation or chemical reaction. In fact, both are required to adequately explain the rapid and high-temperature reactions.

One of the paper's lead authors, Jacob Martin, said, "If the concentration of these species is high enough in flames, this pathway could provide an explanation for the rapid formation of soot."

Co-author Markus Kraft, from the University of Cambridge's Department of Chemical Engineering and Biotechnology, said, "The project brought together cutting-edge computational modeling and experiments to reveal a completely new reaction pathway which potentially explains how soot is formed. Scientists and engineers have been working on solving this important problem for decades."

The researchers hope to target these reactive sites to see whether the soot formation process can be halted in its tracks. One promising option is the injection of ozone into a flame, which has already been found to effectively eliminate soot in some preliminary results in other work.

More information: Jacob W. Martin et al, π-Diradical Aromatic Soot Precursors in Flames, Journal of the American Chemical Society (2021). DOI: 10.1021/jacs.1c05030