Fig. 2 shows the two steps of preliminary adsorption and
photodegradation. In standard conditions given in Table 1, naph-
Table 2
Adsorption constants of naphthalene on TiO2 P-25
KL (L mol−1) 4100±100
Qmax (mol g−1) 24±3
Qmax (molecules nm−2) 0.29
Fig. 2. Evolution of naphthalene concentration in standard conditions of dark
adsorption and photocatalytic disappearance. The inset shows the logarithmic
representation of naphthalene conversion vs. irradiation time.
thalene half-life time is less than 30 min. Photodegradation was
carried on different initial naphthalene concentrations, with a
constant photon flux. When plotting the initial reaction rate
versus the initial equilibrium concentration (Fig. 3), it can be
observed that reaction rate increases linearly with concentration,
up to 40mol L−1. At higher concentrations, there is a
clear deviation from linearity and the reaction rate increases
more slowly with increasing initial concentration. Since solubility
of naphthalene is very low (200–250mol L−1), it was not
possible to investigate higher concentrations to clearly identify
a saturation behaviour. However, this saturation seems to occur
at much lower concentration than the adsorption saturation.