Knowledge · Materials
What is a photocatalyst.
A photocatalyst is a material that absorbs light and uses that energy to accelerate a chemical reaction at its surface — without being consumed in the process.
Almost every practical photocatalyst is a semiconductor. Light with enough energy lifts an electron out of the valence band and leaves a positively charged hole behind. That pair is the working currency of the material: the electron reduces whatever it meets on the surface, the hole oxidises it. When both carriers have reacted, the catalyst is back in its starting state and ready for the next photon.
The distinction worth holding on to is between the material and the process. The photocatalyst is the substance. The reaction it enables is photocatalysis.
If you want the mechanism first, start with what photocatalysis is and how it works — then come back here for the materials.
Properties
What makes a material a good photocatalyst?
Which light it can use
Band gap
The band gap is the energy step an electron must clear. Anatase TiO₂ sits near 3.2 eV, so it only responds to UV below ~390 nm. Narrower gaps (ZnO ~3.2 eV, carbon nitride ~2.7 eV, WO₃ ~2.6 eV) reach into visible light and therefore into ordinary daylight or LED spectra.
Whether the energy survives
Charge separation
Most excited pairs recombine within nanoseconds and release the energy as heat. Doping, heterojunctions and co-catalysts (Pt, Au, NiO) pull electrons and holes apart so more of them reach the surface where they can react.
How much chemistry fits
Surface area
Reactions only happen on adsorbed species, so accessible surface — nanoparticles, mesoporous films, coated fibres — sets throughput. A high-surface catalyst with a mediocre band gap often outperforms a perfect crystal with none.
Whether it lasts
Stability
A useful photocatalyst is not consumed. TiO₂ is the reference because it resists photocorrosion, is cheap and non-toxic. ZnO absorbs more light but dissolves at low pH; sulfides oxidise themselves under the very conditions they create.
These four properties trade against each other. Absorbing more light usually costs stability; separating charges better usually costs simplicity and price. Which compromise is right depends entirely on the job — and on whether the reaction you want is a clean oxidation, a reduction, or a synthesis step.
Examples
Photocatalyst examples you will actually meet
Titanium dioxide (TiO₂)
The benchmark. Anatase-phase TiO₂ powders and coatings drive self-cleaning glass, antibacterial tiles and most water-treatment reactors. UV-limited, but unmatched on stability per unit cost.
Zinc oxide (ZnO)
Similar band gap, higher electron mobility, cheaper to deposit as films. Used in air-purification media, but it photocorrodes in acidic water, which limits reactor lifetime.
Graphitic carbon nitride (g-C₃N₄)
A metal-free, visible-light polymer photocatalyst. Popular for hydrogen evolution and dye degradation research; lower activity per gram, so it is usually paired with a co-catalyst.
Bismuth vanadate and tungsten oxide
Visible-light oxides used mainly for water oxidation in solar fuel work, often as the oxidising half of a two-material (Z-scheme) system.
Molecular and homogeneous photocatalysts
Ruthenium and iridium complexes, plus organic dyes such as eosin Y, dissolve in the reaction mixture and power photoredox synthesis rather than surface cleaning.
In practice
Where photocatalysts show up in cultivation
In controlled-environment growing, photocatalysts appear on the water side rather than in the feed itself: TiO₂-coated reactors used to oxidise organic residues and pathogens in irrigation water before the nutrient solution is mixed. They deliberately destroy organic molecules, which is exactly why they belong upstream of dosing and never in the tank.
The relevant lesson for nutrition is about surfaces. Mineral availability depends on the same variables — purity, particle surface, chemical stability under light and pH — which is why our base chemistry is chelated and filler-free rather than simply concentrated.
The oxidising reaction those reactors run is covered in detail in photocatalytic oxidation explained
FAQ
Photocatalyst questions we get asked
What is a photocatalyst in simple terms?
A photocatalyst is a material that absorbs light and uses that energy to speed up a chemical reaction without being used up itself. Light goes in, the reaction runs faster, and the material is still there afterwards.
Is a photocatalyst the same as a catalyst?
It is a subset. Every catalyst lowers the barrier to a reaction without being consumed; a photocatalyst is one that needs photons to become active, so it switches off in the dark.
What is the most common photocatalyst?
Titanium dioxide in its anatase crystal phase. It is stable, inexpensive, non-toxic and well characterised, which is why it appears in coatings, air filters and water reactors far more often than any alternative.
Do photocatalysts wear out?
Not chemically, in principle. In practice activity drops because the surface fouls with reaction residues, particles agglomerate, or less stable materials photocorrode — so real systems are rated by service life, not by consumption.
Can a photocatalyst work with visible light?
Yes, if its band gap is narrow enough or it is doped or coupled to a sensitiser. Pure TiO₂ needs UV; nitrogen-doped TiO₂, carbon nitride and tungsten oxide all work under visible light with lower quantum efficiency.
Cluster
Back to the photocatalysis pillar
Knowledge
What is photocatalysis and how it works
The mechanism behind light-driven catalysis, the photocatalysts involved, and why it matters for nutrient chemistry.
Read more →
Process
Photocatalytic oxidation explained
How light-activated surfaces generate reactive oxygen species that break down contaminants in air and water.
Read more →
Product
VitaBase — the foundational nutrient matrix
The chelated, filler-free base feed the photocatalytic and signaling inputs are built on top of.
Read more →
Foundation feed