Aerogel: Sodium Hydroxide

Week #15: pH Adjustments (Alginate Aerogels)

Carlos Manuel Jarquín Sánchez
3 min readNov 4, 2022

Preface! ✨

Hello everyone!

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 :-)

pH Overload ⚛️

Note: This week’s article will be a short one. Why? We’re transitioning to potential collaborations for this.

pH can change in the material during manufacturing. Some scenarios where this could occur include:

  • The beads drop into the gel bath
  • Calcium Nitrate & other materials with acidity
  • Heavy Metals prefer a lower pH (i.e. pH 2–4)

We don’t have a solution to this potential problem… until now.

The solution?

Utilize Sodium Hydroxide to control the pH of the material & its final properties! (i.e. mechanical strength, adsorption rates, size, pore size, etc.)

TL;DR Of Sodium Hydroxide 🌡️

Sodium Hydroxide (NaOH) consists of a cationic Na+ Group and an anionic OH- group.

Na+ has an extra proton. OH- has an extra electron. This extra pair of protons & electrons make the ionic bond/compound “stick together”.


NaOH neutralizes extra anionic charge (acidic environments).

The first reason why it works is that NaOH is a very strong alkaline. Alkalines have OH- groups… and NaOH consists of an OH- group!

A low amount of NaOH (0.1M) has a pH of 13!

The OH- group needs one proton (H+) to become a water molecule.

Acidic environments always have extra protons that they want to give up. NaOH is perfect for environments like this!

For Visual Purposes ONLY | Source

But what about the Na+ ion? What happens to it? And where will the remaining proton for the OH- group come from?

It will bind with a chlorine ion (Cl-) from another chemical that will be added to the gelation bath: EDC.

1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride

EDC Raw Chemistry

EDC will act as a coupling agent in the material. It will bond the base material (MGDA-Na3) with Sodium Alginate & DETA (another cross-linker).

Notice that EDC contains an (HCl) group that can react with the leftover (Na+) group. This creates the famous NaCl group.

Final Reactions Of pH Neutralization!

TL;DR Of Hydrochloric Acid (HCl) ⌚️

Hydrochloric Acid (HCl) is an acidic compound (pH is 3.01) because the chlorine atom contains more electronegativity (negative charge) than the hydrogen atom (contains more positive charge).

This is known as a polar covalent bond. The electric charges are not evenly distributed within the molecule.

A low pH contains more H+ ions, and the hydrogen atom in HCl behaves similarly to an H+ ion.

Electron Cloud Is Bigger For The Cl- Atom & A More Negative Charge Occurs

When HCl reacts with NaOH, the hydrogen atom in HCl leaves the chlorine atom as a proton (H+) because the Cl atom stays with the negative charge (Cl-) group.

(H+) ion plus (OH-) group makes a water molecule (H2O).

(Na+) ion plus (Cl-) group makes table salt (NaCl).

The Filter Is Ready For A Wet-Lab Prototype. 🗸

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© 2023 by Carlos Manuel Jarquín Sánchez. All Rights Reserved.