Photocatalysis

"Exploration is what you do when you don't know what you're doing. That's what scientists do every day.

If a scientist already knew what they were doing, they wouldn't be discovering anything."

Neil deGrasse Tyson

May 10, 2023

Hi, it's Gabriella!

Today I'm going to talk you about a special type of catalysts: photocatalysts.

Photocatalysts are semiconductors whose electrons, originally in the valence band (VB), can be transferred in the conduction band (CB) by a photon having the correct energy.

This transfer causes a charge separation: the negative charge can be used in a reduction and the positive one in an oxidation.

Maybe you have already seen a mechanism like this. In fact, this is a process very similar to natural photosynthesis: plants absorb light thanks to chlorophyll, electrons are excited causing a charge separation, water is oxidised and CO₂ is reduced to produce sugar.

Metallic oxides are traditionally used in photocatalysis, but scientists are finding better alternatives, such as open architecture metal sulfides. One of the advantages of these materials is a lower band gap than oxides. "Open architecture" means that they have a porous structure. This type of structure permits:

• higher active site accessibility
• more efficient light harvesting
• lower charge recombination

Applications of photocatalysis

Reactions that become possible thanks to photocatalysis are H₂ photogeneration by water splitting and CO₂ photoreduction.

These reactions would help us face some of the main challenges of these days: produce green fuel and remove CO₂ from atmosphere. In fact, CO₂ emitted by human activities is reaching intolerable levels and is one of the main causes of climate change. We have the possibility to capture and store CO₂, but the best solution is to reduce it, transforming it into useful compounds. 

Lab

Now I'm going to tell you what we did in the laboratories of ITQ.

For this experience we didn't work personally, but Beatriz showed us how to synthesize her photocatalyst. 

First you have to mix all the reagents. You need organic, inorganic and metallic chemicals to create the reaction mixture.

Then she took us to the Black room, where she tests the performance of her catalysts. As you can imagine, it's a very dark room with the walls totally black. This is because in photocatalysis it's very important to control the light.

She uses a solar simulator with a lens to focus the light and another lens to filter radiation in order to avoid overheating. She showed us also the instrument that allows to remove oxygen from the reaction environment: this is important because oxygen would catch electrons produced by the reaction.

That's all for now!

G.M.