Cleaning Water with Light
Titanium dioxide photocatalysis harnesses UV light to destroy organic pollutants in water and air. When TiO₂ nanoparticles absorb UV photons, they generate electron-hole pairs that produce hydroxyl radicals — one of the most powerful oxidizing agents known. These radicals attack organic molecules indiscriminately, breaking them down into harmless CO₂ and water. It is an advanced oxidation process (AOP) increasingly used for water purification and self-cleaning surfaces.
Langmuir-Hinshelwood Kinetics
Photocatalytic degradation follows the Langmuir-Hinshelwood (L-H) model, which accounts for both surface adsorption and reaction. At low pollutant concentrations, the rate is proportional to concentration (pseudo-first-order). At high concentrations, the surface becomes saturated and the rate plateaus. The apparent rate constant depends on UV intensity, catalyst loading, temperature, and the specific pollutant's adsorption affinity for the TiO₂ surface.
Optimizing the Reaction
Several factors control photocatalytic efficiency. UV intensity drives electron-hole pair generation — rate typically scales as I^0.5 at high intensities due to recombination. Catalyst loading increases available surface area but excessive loading creates shielding. pH affects surface charge and pollutant adsorption. Dissolved oxygen acts as an electron acceptor, reducing recombination. This simulator lets you explore these trade-offs and find optimal conditions.
From Lab to Application
TiO₂ photocatalysis has moved from laboratory curiosity to commercial technology. Self-cleaning glass coatings decompose organic grime under sunlight. Photocatalytic concrete reduces urban NOx pollution. Water treatment systems using UV-LED-activated TiO₂ remove pharmaceutical residues that conventional treatment misses. Research now focuses on visible-light-active catalysts — doping TiO₂ with nitrogen or coupling it with narrow-bandgap semiconductors to harness the full solar spectrum.