We measured the first order rate constant at different catalyst
loadings, as shown on Fig. 4. It increases first linearly when
increasing the catalyst loading to reach a maximum at about2.5gL−1. Since this optimum value is identical to that observed
in other liquid phase reactions, either inwater or in liquid organic
phases [20], it seems to depend only on the design of the photoreactor
(geometry, texture of the catalyst, optical pathway).
The existence of a threshold is attributed to a screening effect of
TiO2 particles as their concentration increases. The supplementary
number of adsorption sites cannot then compensate the loss
of photon flux by reflexion and diffusion.