Fouling of TiO2 induced by natural organic matters during photocatalytic water treatment: Mechanisms and regeneration strategy

Photocatalysis has been intensively investigated for the removal of pollutants but little attention was paid to the deactivation of photocatalysts during the long-term operation. Herein we used TiO2 as the model photocatalyst to investigate its durability in the presence of humic acid (HA), a ubiquitous constituent of real water. No sign of TiO2 deactivation was observed without HA, whereas significant deactivation occurred with HA. Interestingly, the adsorption of intact HA had only a minor contribution to the deactivation, and the major contributing factor was the adsorption of in-situ oxidized HA, which formed surface complexes with TiO2, blocked the active sites, and decreased the efficiency of photogenerated charge transfer. The regeneration of the deactivated TiO2 was also systematically investigated. The present study provides basic information that is required to understand and hinder the complex fouling phenomenon that can be serious in photocatalytic treatment of water containing natural organic matters.