100 Nano-Stories: Carbon Aerogels!

Episode #98: (1,3)-Dihydroxybenzene + Methanal + Pyrolysis!

Carlos Manuel Jarquín Sánchez
8 min readMay 20, 2021

Preface! ✨

It’s your favorite material science & nanotechnology enthusiast! Today, we will cover the chemistry of carbon aerogels (with a smidge of graphene aerogels)!

There is no article to prepare you today, reader! Let’s begin today’s topic! 😃

Carbon Aerogels! 💡

Definitions! 🔑

Carbon aerogel is. . . well, an aerogel made out of carbon atoms only.

Why Should I Care, Carlos?

Carbon aerogels will be part of your cell phone, batteries, and hydrogen storage because of their electrical conductivity! Without carbon aerogel in the future, you’ll have a crappy phone. 🙃

But how do we produce carbon aerogels?

You first have to create an aerogel that has carbon in it but is not pure carbon. This is called an organic aerogel.

Creating a carbon aerogel is the most common form of creating a resorcinol-formaldehyde Aerogel (RF Aerogel). Then you would heat it to extreme temperatures in a non-reactive atmosphere to remove all the atoms in the aerogel except for carbon to get a carbon aerogel.

Time to reintroduce the sol-gel process to create the RF Aerogel! 😮

The Sol-Gel Process → RF Aerogels! 🔑

If you have been reading “100 Nano-Stories: Bookmarked!” for a while, you know that the sol-gel process requires a precursor to make the solution, the nanometer-sized particles inside the solution, and a catalyst to speed up the reactions to create the large network of interconnected nanoparticles, aka a gel.

Sol-Gel ChemistryA solution of either a metal or carbon-based precursor with ethers to form a polymer. This polymer will create a vast network of polymers bonded to each other, creating a gel!

PolymersA chain of many repeating/identical large molecules that make up a material.

However, the main precursors to make RF Aerogels are 1,3-dihydroxybenzene & Methanal.

  • Another name for 1,3-dihydroxybenzene is Resorcinol.
  • Another name for Methanal is Formaldehyde.

Author's Note #1:

I will use the chemical/official name for the majority of the article, but every once in a while, I will use the unofficial/easier name. 😃

Author’s Note #2:

If you want to know more about creating the aerogel, skip the next part to “Let’s Make RF Aerogels!”.

I will be discussing the properties and the naming/nomenclature of the precursors in the next section “Chemistry Course Nomenclature”. 👍🏽

Chemistry Course Nomenclature! 🔑

The reason why the chemical name has the numbers (1,3) is that the position of the hydroxyl (OH) groups. The first OH Group is on Carbon #1, and the second Carbon #3.

The OH Groups have these numbers because we want to find the shortest distance between the two hydroxyl groups. So we count from one OH Group to the other hydroxyl group, and that gives us (1,3) as their positioning on the hexagon ring made out of carbons.

This hexagon is called a benzene ring, and it is made of pure carbons.

Author's Note:

Each number stands for 1 carbon atom since the hexagon/benzene ring is made out of pure carbon atoms.

Finally, let’s dissect the rest of the name “1,3-dihydroxybenzene” (Resorcinol).

  • (1,3) → The Carbon Number of where the Hydroxyl (OH) Groups are attached/located.
  • Di-(hydro)-(oxy) → 2 Hydrogen and 2 Oxygen Atoms are in The Benzene Ring.
  • Benzene → A hexagonal-shaped ring made of pure carbon atoms with a hydrogen atom attached to each carbon atom.
1,3-dihydroxybenzene (Resorcinol)

The reason why we call it methanal is because it's an aldehyde. An aldehyde means that it contains a carbon atom that is double-bonded to an oxygen atom (carbonyl). Additionally, the carbon atom must be bonded to a hydrogen atom or a methyl group (CH₃).

In our case, we have a carbon atom that is double-bonded to oxygen AND the carbon atom is chemically bonding with a hydrogen atom (or two in this case lol).

Finally, let’s dissect the rest of the name “Methanal” (Formaldehyde).

  • Methan → contains Carbon and Hydrogen.
  • al → Aldehyde/Contains a double bond between carbon and oxygen, along with a bond between carbon and hydrogen.
Methanal (Formaldehyde)

Let’s Make RF Aerogels! 🔑

Resorcinol-Formaldehyde Aerogel (RF Aerogel) is the final product, and we have defined the two chemicals responsible for the next steps of the process.

Resorcinol and Formaldehyde will be thrown into the water to polycondensate.

Polycondensation The contraction/compression of smaller molecules that get closer to each other (condense) to form a compound with high molecular weight (aka increased fluid friction/viscosity). Water is released from the condensation of these smaller molecules.

However, this process of smaller molecules getting closer to each other takes a while, so we introduce a catalyst, which is a chemical that can speed up a reaction without the catalyst affecting the overall reaction. To produce the RF Aerogel, the catalyst will be sodium carbonate.

The sodium carbonate/catalyst will speed up the compression of resorcinol and formaldehyde to create the long strands of interconnected nanoparticles of resorcinol-formaldehyde (RF), creating a wet RF Gel.

RF Wet Gel Polymer Strands

To remove impurities/clean the gel, the wet RF Gel is soaked in a polar molecule like ethanol (hydrocarbons with a hydroxyl group (OH group).

Once the gel has been soaked in the water for polycondensation and in ethanol, it will undergo supercritical drying with Supercritical Carbon Dioxide. We have our RF Aerogel!

Authors Note:

For those wondering, the Critical Temperature is about 31°C or about 300 Kelvin, and Critical Temperature is about 74 bar (Pascals) for Carbon Dioxide, specifically. 👍🏽

Beautiful! 😄

RF Aerogels → Carbon Aerogels! 💡

OK, Carlitos, you showed us how to go get a Resorcinol-Formaldehyde (RF) Aerogel. But how do we get a Pure Carbon Aerogel?

Simple! Just light that sh*t on fire!. . . Or you can heat it to a certain temperature, and all the atoms in the RF Aerogel that aren’t carbon atoms will leave the RF Aerogel, leaving behind a Carbon Aerogel! This process is known as Pyrolysis!

Pyrolysis → Dehydration of material by raising the temperature to very high temperatures in an inert/non-reactive atmosphere like nitrogen.

The ideal temperature to heat an RF Aerogel is 1323 K/1049.85°C/1921.73°F. However, it can be heated higher than 1323 Kelvin, all depending on the RF/Organic Aerogel chemistry. But if you are going to heat the RF Aerogel to such a temperature, you cannot do it in the open air.

If you do, the RF Aerogel and the fire will react with Oxygen, and the material will combust/go on fire. OOPS!😅

So you must undergo pyrolysis in a non-reactive/inert gas like nitrogen. That way, the aerogel won’t go up in flames!

Once these steps are complete, you leave the RF Aerogel in such high temperatures from 90 minutes to about 10 hours. During this time, all the atoms that aren’t carbon (hydroxyl (OH) groups, the inert nitrogen gas) will leave the aerogel, and you end up with this:

Carbon Aerogels!

Closing Thoughts! 💭

Look, reader, I know this was a longer article than usual, but listen. This is Episode #98 of “100 Nano-Stories: Bookmarked!”.

You gotta celebrate when you can! :) Shoutout to all my readers and followers for supporting me in writing this digital book on nanotechnology, material science, and nanomaterials! I will make this a physical copy soon, I promise!

Some applications of Carbon Aerogel range from electrical conductors with high surface areas to the production of supercapacitors.

See you soon to finalize the knowledge in carbon/graphene aerogels! 🌠

Vocabulary! 📓

Sol“Solution.”

Gel“Gel.”

Sol-Gel ChemistryA solution of either a metal or carbon-based precursor with ethers to form a polymer. this polymer will create a vast network of polymers bonded to each other, creating a gel!

Condensation → A reaction in which two molecules combine to form a larger molecule, producing a small molecule such as H2O as a byproduct.

Polycondensation The contraction/compression of smaller molecules that get closer to each other (condense) to form a compound with high molecular weight (aka increased fluid friction/viscosity). Water is released from the condensation of these smaller molecules.

MesoporousMaterial that has pores/openings between 2–50 nanometers in size/diameter. Aerogel is a mesoporous material.

Pyrolysis → Dehydration of material by raising the temperature to very high temperatures in an inert/non-reactive atmosphere like nitrogen.

PolymersA chain of many repeating/identical large molecules that make up a material.

Precursors Chemical compounds that participate in a chemical reaction to produce a new compound/molecule.

Colloid (Colloidal) A particle that is in the range of 1 nanometer to 100 nanometers in diameter/size.

SuspensionA mixture where the composition isn’t the same in every single place of the mixture (heterogeneous).

Catalyst → A chemical that speeds up a chemical reaction without being affected; and it lowers the activation energy of the reactants so the reaction between two compounds can occur and form the new compound.

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© 2021 by Carlos Manuel Jarquin Sanchez. All Rights Reserved.

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