Antifouling properties of TiO2: Photocatalytic decomposition and adhesion of fatty and rosin acids, sterols and lipophilic wood extractives

Titanium dioxide has the well-known property to catalyze the decomposition of organic substances and also becomes strongly hydrophilic under UV illumination, rendering TiO2 interesting as an antifouling material. The kinetics of decomposition and removal of Langmuir–Blodgett or spin-coated films of stearic, dehydroabietic, capric and linoleic acid, β-sitosterol, wood resin components and colloidal wood resin particles from a TiO2 surface was measured with a quartz crystal microbalance with dissipation monitoring (QCM-D). In the beginning of the degradation measurements, a 0–3 min long initation period, with hindered or prevented degradation was often detected. After the initiation period the degradation continued with relatively constant rate, until it decelerated again near the end of experiment. The primary mechanism of removal of the films was photocatalytic degradation, but it was shown that the penetration or formation of water at the TiO2/film interface and the flow of oxygen to the interface also are of importance. Correlation of the flow of oxygen to the rate of photocatalytic degradation was observed. Adhesion of wood resin components to TiO2 in aqueous solutions was determined by contact angle measurement. UV illumination reduced the adhesion of liquid wood extractives on TiO2. A model focused on photocatalytic cleaning mechanisms in solution is presented. Possible applications in papermaking are discussed.