A photocatalyst molecule absorbs a photon and jumps to an excited
state that is both a stronger oxidant and reductant than its ground
state. In that brief window it transfers a single electron to (or
from) a nearby substrate, generating a reactive radical while
relaxing back to the ground state β ready to absorb another photon
and repeat the cycle.
PC + hΞ½ β PC*
PC* + Substrate β PCβΊ/β» + Substrateβ’
PCβΊ/β» + co-reductant β PC (cycle closes)
rate β Ξ¦_light Γ [PC] Γ (1 β e^(βΡ·[PC]Β·l))
- Light intensity β photon flux hitting the reactor; more photons excite more catalyst per second.
- Catalyst loading β concentration of photocatalyst; too little limits light absorption, too much just wastes catalyst.
- Substrate reactivity β how readily the excited catalyst can hand off its electron to substrate before decaying uselessly.
- Wavelength β must match the catalyst's absorption band; off-band light passes through unused.