Aerogel: Building The Filter
My intentions for writing these articles are:
- Explain technical information about aerogels in simple terms (to the public)
- Store information and habits for my future self and others (in <7 minutes)
Coolio? Sweet. Enjoy the series :-)
TL;DR Of Selected Cross-Linking Chemicals 🆒
Note: This week’s article will be a short one. Why? We will be analyzing the selection of the desired cross-linkers for the filter.
The necessary criteria for an effective cross-linker are:
- Have five or more “bonding atoms” to attach to the heavy metal ion
- Contain functional groups (metal-adsorbing molecules)
- Adsorb heavy metal ions via ion exchange and/or chelation
- Anionic (negatively charged) & a pH lower than 7
It’s a combination of EN (Ethylenediamine) & DETA (Diethylenetriamine) as the cross-linkers. These functional groups are:
- Amines (Contain -NH And/Or NH2, Most Effective Functional Groups)
- Prefer To Adsorb Lead, Mercury, & Cadmium
- Abundant & Environmentally-Friendly
- Anionic By Nature With Stable Properties At A pH Below 7
- Contain Six Open “Bonding Atoms” (Dots On Nitrogen)
- Able To Be Freeze-Dried & Make Proper Aerogels
One More Modification… 💻
This article’s interested in adsorbing and removing heavy metal ions from water. But the filter is not yet hydrophobic.
Hydrophobic → Repels Water.
The filter will perform terribly if it fails to ensure the selective absorption of the heavy metal ions instead of both the ions and the water. One solution is to add a hydrophobic functional group during the mixing stage of the wet hydrogel. The most effective and environmentally friendly are methyl groups.
Methyl Groups → A molecule containing one carbon atom & three hydrogen atoms.
Use Methyltriethoxysilane (MTES) or Sodium Carboxymethyl Cellulose (SCC) as the hydrophobic functional group. Why? It can be biodegradable.
It’s best to live in a world of responsible consumption & production.
Why It Works 🔨
The hydrophobization of the filter is effective in water-induced environments because of the hydrophobe’s electronegativity.
Electronegativity → The chance that a pair of electrons will be closer to a certain atom in a molecule.
The molecule is non-polar (hydrophobic) if the difference in electronegativity in the molecule is less than 0.5.
Methyl groups contain carbon and hydrogen.
The electronegativity of a carbon atom is 2.5, while the electronegativity of a hydrogen atom is 2.1.
One must subtract the higher value from the lower value (of electronegativity) to find out if a molecule is hydrophobic or not.
2.5 - 2.1 = 0.4 | It Is Hydrophobic!
Any molecule that is composed of only carbon or hydrogen will have non-polar bonds and still have covalent bonds.
The electrical charges are evenly distributed throughout the molecule/functional group and the electrons within the molecule are “being shared”.
The Basics Of The Filter Are Complete.
© 2023 by Carlos Manuel Jarquín Sánchez. All Rights Reserved.