Photocatalytic

Photocatalytic refers to chemical reactions that are accelerated by a catalyst that becomes activated when exposed to light. In most cases, the catalyst is a semiconductor material that, upon absorbing photons, generates charge carriers that drive redox processes on the catalyst's surface.

In a typical semiconductor photocatalytic process, light with energy at least equal to the material’s band gap promotes electrons from the valence band to the conduction band, leaving holes behind. The photogenerated electrons and holes migrate to the surface and participate in oxidation and reduction reactions, such as converting water to hydroxyl radicals or reducing oxygen.

The most widely used photocatalyst is titanium dioxide (TiO2), valued for chemical stability, low cost, and strong oxidative power, though it primarily absorbs UV light. Strategies to harness visible light include element doping, forming heterojunctions, or coupling with other semiconductors. Other common materials include ZnO, CdS, WO3, and graphitic carbon nitride (g-C3N4), often engineered at the nanoscale.

Applications of photocatalysis include environmental remediation (degradation of organic pollutants in air and water), self-cleaning and antifouling coatings, antimicrobial surfaces, and energy-related processes such as water splitting to produce hydrogen and CO2 reduction to fuels.

Limitations include rapid recombination of charge carriers, limited light absorption, and catalyst stability or toxicity concerns for some materials. Ongoing research seeks improved quantum efficiency through dopants, engineered heterojunctions, Z-scheme systems, and better reactor designs to enable practical, scalable use.