Synergistic effects of cupric and fluoride ions on photocatalytic degradation of phenol

Synergistic effects of cupric ions and fluoride ions were investigated on the photocatalytic degradation of phenol in TiO2 (Degussa P25) suspensions at pH 3 under UV irradiation. Under all tested conditions, the phenol photodegradation was observed to follow a pseudo-first-order reaction in kinetics. The rate constant k of the phenol photodegradation was evaluated as 0.010 min−1 in the absence of Cu2+ and F− ions, and was increased up to 0.014 min−1 by adding 0.4 mmol L−1 Cu2+, and to 0.022 min−1 by adding 5 mmol L−1 F− ions. The coexistence of both Cu2+ and F− ions increased the k value further to 0.041 min−1, being 410% of that without any addition of Cu2+ and F− ions. The much increased rate of phenol degradation induced by the coexistence of Cu2+ and F− ions were also confirmed by the monitoring of degradation intermediates. With the aid of the determination of OH radicals and H2O2 generated during the photodegradation, the observed significant synergistic effects were attributed to the shielding effect of fluoride on the charge separation efficiency and the efficient trapping of the photogenerated electron by the Cu2+ adsorbed on TiO2 surface.